RELATED APPLICATION

[0001] The present disclosure claims benefit of priority to Australian Provisional Patent Application Number: 2021901242 filed 27 April, 2022, the contents of which are incorporated herein by reference. In jurisdictions where incorporation by reference is not permitted, the applicant reserves the right to add any or the whole of the contents of said Application Number: 2021901242 as an Appendix hereto, forming part of the specification.

FIELD OF THE INVENTION

[0002] The present invention is directed to the area of control of electric brushless DC (BLDC) motors, and, in particular discloses a system and a method of electronic commutation of a sensorless BLDC motor in applications such as electric power tools.

References

[0003] [1] Midwest Research Institute, BRUSHLESS DC MOTORS, National Aeronautics and

Space Administration, Washington, D.C., 1975

[0004] [2] Wikipedia, Brushless DC electric motor, http://en.wikipedia.org/wiki/Brushless_DC_electric_motor

[0005] [3] Muhammad Mubeen, Brushless DC Motors Primer, Radford, VA, 2008

[0006] [4] Hendershot J.R. Jr and Miller Tje, Design of Brushless Permanent-Magnet Motors,

Magna Physics Publishing, New York, 1994

[0007] [5] Gamazo-Real J., Vazquez-Sanchez E., Gomez-Gil J., Position and Speed Control of

Brushless DC Motors Using Sensorless Techniques and Application Trends, Open Access, Sensors, 2010

[0008] [6] Bhim Singh and Sanjeev Singh, State of the Art on Permanent Magnet Brushless DC

Motor Drives, Journal of Power Electronics, Vol. 9, No. 1, January 2009 [0009] [7] Lee S., Lemley T., A Comparison Study of the Commutation Methods for the Three-

Phase Permanent Magnet Brushless DC Motor, Electrical Manufacturing Technical Conference 2009: Electrical Manufacturing and Coil Winding Expo, EMCWA 2009 - Nashville, TN, United States

[0010] [8] Hu B., Sathia Kumar S., A Novel 180-Degree Sensorless System Of Permanent Magnet

Brushless DC Motor, Journal of Circuits, Systems, and Computers Vol. 21, No. 7, 2012

[0011] [9] Saha S., et al, A Novel Sensorless Control Drive for an Interior Permanent Magnet Motor,

The 27th Annual Conference of the IEEE Industrial Electronics Society, 2001

[0012] [10] Wang C., et al., A Novel Twelve-Step Sensorless Drive Scheme for a Brushless DC

Motor, IEEE Transactions on Magnetics, Vol. 43, No. 6, June 2007

[0013] [11] STMicroelectronics, An Introduction to Sensorless Brushless DC Motor Drive

Applications with the ST72141, Application Note AN1130, 2000

[0014] [12] Schmidt P., Gasperi, M., Ray, G. and Wijenayake A., Initial rotor angle detection of a non-salient pole permanent magnet synchronous machine, IEEE Industry Applications Society Annual Meeting, New Orleans, 1997

BACKGROUND OF THE INVENTION

[0015] Any discussion of the background art throughout the specification should in no way be considered as an admission that such art is widely known or forms part of common general knowledge in the field.

[0016] BLDC Motors: Brushless DC motors are used in a wide variety of market applications, such electric power tools, because they can offer increased energy efficiency and density, power output, compactness, operational reliability and life expectancy. BLDC motors, also known as permanent magnet synchronous motors (PMSM), are classified according to their phase winding configuration, such as wye or delta, and the number of magnetic poles [1], [2], [3], [4]

[0017] Sensored BLDC Motor Control: In today’s global markets, brushless motor applications are dominated by sensored BLDC motor control technologies [5], which utilize rotor position sensors inside the motors, such as Hall effect sensors or encoders. These sensors make it easy to electronically commutate and operate BLDC motors from start to high speeds. However, they increase the size and weight of the motors, and manufacturing costs due to additional components, circuitry and inter-wiring connections that are required. The rotor position sensors can also be subjected to operation at very high temperatures, electric and magnetic interference, and assembly placement errors that can lead to losses in energy efficiency and motor torque. Sensored BLDC motors are also prone to more electrical and mechanical failures which reduce system reliability and increase operating costs compared to alternate brushless motor control technologies that do not employ rotor position sensors.

[0018] Sensorless BLDC Motor Control: Instead of using rotor position sensors, sensorless BLDC motor control techniques use only electrical measurements, such as motor phase voltages and currents, obtained directly from the motor in order to ascertain the rotor position during operation. Those skilled in the art of sensorless BLDC motor controller design are familiar with the inherent challenges of operating such motors at and near zero speeds [5], particularly in the presence of demanding dynamic loads, for example such as encountered in power tool fastening and drilling applications with cordless drill drivers. These issues often arise because of the technical difficulties associated with determining accurate rotor position information at zero and low speeds, which is important for robust electronic commutation of sensorless BLDC motors. There exists a significant amount of prior art related to the design of sensorless BLDC motor controllers [5], [6] However, it is evident that no single controller solution, alone, can reliably operate motors from start to high speed under all load conditions. Thus, in practice, sensorless BLDC motor controller designs may use a hybrid approach, such as described in PCT Publication W02019/056072, entitled “System and Method for Controlling a Motor”, to the present applicant, incorporated here by cross reference, which can encompass one or more of the following key areas of controller operation: Initial rotor position detection (IRPD); Sensorless operation at zero and low motor speeds; Sensorless operation at high motor speeds. When designed successfully, sensorless BLDC motor control systems can offer increased energy efficiency, reliability and cost effectiveness compared to sensored BLDC motor control systems.

[0019] 6-Step Electronic Commutation: The BLDC motor control systems described in previous sections generally employ the 6-step trapezoidal electronic commutation method because of its simplicity and effectiveness in controlling the torque and speed of a motor [7] In this commutation technique only two of the three BLDC motor phases conduct current at any time, while the third phase winding is left open. In sensorless BLDC motors the open phase windings are used to detect six consecutive commutation timing points separated by an angle of 60°, for example, as described in the “Low to High Speed Sensorless BLDCM Operation” embodiment of the aforementioned PCT Publication W02019/056072. The resultant 120° phase conduction angle motor driving scheme, however, does not generate the maximum possible torque in a motor. Compared to other electronic commutation techniques, such as sinusoidal and FOC [7], the 6-step commutation also produces higher motor temperatures and increased motor torque ripple during operation, which can reduce the dynamic response when controlling the speed and torque of a motor in demanding applications, such as electric power tools.

[0020] 12-Step Electronic Commutation: To increase the output motor torque and reduce the motor temperatures generated by a trapezoidal commutated motor, a 12-step commutation method is often used to extend the motor’s phase conduction angle beyond 120° as described in [8], [9], [10] In cordless power tools, increased commutation conduction angles can offer users faster applications speeds and extended operation times before a battery must be recharged or a motor thermal overload occurs. In a sensorless BLDC motor, a 12-step commutation scheme with increased phase conduction angle is implemented by activating the power transistors in a three-phase inverter so that current also flows through the third motor phase winding, which is normally left open in the 6-step trapezoidal commutation scheme, for an additional number of degrees during a commutation step. When a new commutation step is taken and this third phase winding is switched back to the open phase state, it is important to ensure that the current flowing in this winding from a previous commutation step is decayed to zero, that is, the winding is fully de-energized or demagnetized as described in [11] This must be performed before a zero-crossing point can be detected, for example, when the open phase BEMF voltage crosses half of the power supply voltage during commutation of a sensorless BLDC motor.

[0021] US Patent US5463300, US Patent US4758768 and US Patent US9154062 disclose 12-step trapezoidal commutation methods for BLDC motors employing rotor position sensors, such as Hall effect sensors. However, these sensors increase manufacturing cost, equipment size, weight and reduce system efficiency and reliability of such BLDC motor control systems. US Patent US6570353B2 discloses a 12-step BEMF voltage sensing commutation method of a sensorless BLDC motor with a fixed phase conduction angle of 150°. Examples of 12-step sensorless BLDC motor commutation schemes with a phase conduction angle greater than 150° are proposed in [9], [10] However, in applications such as electric power tools that use interior permanent magnet (IPM) BLDC motors with high saliency and large electrical time constants (TE), the known prior art commutation methods were in practise found to have stability issues when operating with high and dynamic motor loads and conduction angles greater than about 140°. This is due to the large open phase winding demagnetization currents in such motors and the ensuing inductive voltages spikes, which clamp the open phase winding voltage to the positive power supply voltage rail and the ground voltage rail after a commutation state is changed, for example as described in [11] As a consequence of this, the window of opportunity to measure the open phase BEMF zero-crossing points is reduced. It is apparent that known prior art commutation methods do not address the effects of these open phase winding demagnetization currents in their solutions. For example, during testing with power tools at high motor loads, as shown in Fig. 5, the time required to decay the open phase winding currents to zero (CDE) was measured to be greater than 1/3 of the available time between consecutive commutation points. This reduces the BEMF zero crossing point detection window (to) and limits the available time to extend the phase conduction angle (a) beyond 120° when the third motor phase winding is energized. In the same exemplary Fig. 5, the maximum possible conduction angle is limited to approximately 140°. If this problem is not addressed, instabilities during zero-crossing point detection can occur with very high phase conduction angles, which can lead to delayed and missed zero-crossing points and commutation errors, for example, as measured during testing with a power tool in Fig. 6. US Patent Application US2020/0343840A1 discloses a 12-step commutation of a sensorless BLDC motor for power tools that can generate higher output motor torque with phase conduction angles greater than 120°, however, this method does not consider the problematic phase winding commutation demagnetization currents when determining the conduction angle. US Patent US 8212504B2 discloses a method to improve stability of a 12-step commutation of a sensorless BLDC motor by reducing the conduction angle when the power supply voltage fluctuates. However this method also neglects the problematic open phase winding demagnetization currents that are present in the motor at the beginning of a new commutation step.

[0022] It is also apparent that the known prior art methods lack safety measures to address stability and robustness of operation when commutating a sensorless BLDC motor with high conduction angles (eg. >140°). For example, in power tool applications, it was discovered that it is also important to detect and prevent potential motor commutation errors in order to operate successfully with very high conduction angles and thus maximize the output motor torque under different types of motor loading and operating conditions, such as, high and low motor loads, high open phase winding demagnetization currents and long phase winding demagnetization times (eg. >1/3 of the commutation interval), high and low motor speeds, and rapid motor accelerations and decelerations. Therefore, it would be desirable if an electronic commutation method with improved stability and performance would be provided for the more cost effective, efficient and reliable sensorless BLDC motors in applications such as electric power tools.

SUMMARY OF THE INVENTION

[0023] It is an object of the invention, in its preferred form to provide for an improved form of electronic commutation of a sensorless brushless DC motor in applications such as electric power tools.

[0024] In accordance with a first aspect of the present invention there is provided an electronic commutation of a sensorless brushless DC motor, where the open phase voltages are used to measure the phase winding demagnetizing voltage of a BLDC motor so as to detect when the phase winding current is decaying to zero.

[0025] In some embodiments the open phase voltages are used to measure the rotor inherent and magnetic saturation (RIMS) saliency voltage of a BLDC motor.

[0026] In some embodiments the open phase voltages are used to measure the back electro-motive force (BEMF) voltage of a BLDC motor.

[0027] In accordance with another aspect of the present invention there is provided an electronic commutation of a sensorless brushless DC motor, which monitors the open phase winding demagnetization currents after a commutation state is changed in order to measure the corresponding open phase winding demagnetization time required to decay the open phase winding currents to zero.

[0028] In some embodiments, the open phase winding demagnetization currents are measured using the open phase voltages, which are clipped by the internal power transistor diodes to the positive power supply voltage rail and the ground voltage rail after a commutation state is changed.

[0029] In accordance with another aspect of the present invention there is provided an electronic commutation of a sensorless brushless DC motor, which measures the open phase voltages in order to detect the low to high and high to low zero-crossing points and to determine the time between consecutive zero-crossing points.

[0030] In accordance with another aspect of the present invention there is provided an electronic commutation of a sensorless brushless DC motor, which determines the low to high and high to low open phase zero-crossing point detection voltage thresholds using CPFmaxR values that take into account the effects of rotor inherent and magnetic saliency of a BFDC motor present in open phase voltages, in order to control and improve the timing accuracy of the detected zero-crossing points.

[0031] In some embodiments, the low to high and high to low open phase zero-crossing point detection voltage thresholds adjusted with CPFmaxR values are used to shift the detected zero-crossing points to the left. In some embodiments, the low to high and high to low open phase zero-crossing point detection voltage thresholds adjusted with CPFmaxR values are used to shift the detected zero-crossing points to the right. [0032] In accordance with another aspect of the present invention there is provided an electronic commutation of a sensorless brushless DC motor, which determines the open phase zero-crossing point detection window time using the measured open phase winding commutation demagnetization event time and the measured open phase zero-crossing point detection time, in order to obtain the corresponding open phase zero-crossing point detection window angle.

[0033] In some embodiments, the measured open phase zero-crossing point detection window angle is maintained above a minimum reference open phase zero-crossing point detection window angle, by determining the open phase zero-crossing point detection window angle difference and using it as the input to a feedback controller in order to regulate the phase conduction angle so that the low to high and high to low open phase zero-crossing points are always detectable.

[0034] In some embodiments, the open phase zero-crossing point detection window angle difference is used as the input to a feedback controller in order to stabilize the electronic commutation of a sensorless BLDC motor and to control the phase conduction angle between a set minimum and maximum phase conduction angle values so as to maximize the output phase conduction angle and the generated motor torque under all motor loading and operating conditions.

[0035] In accordance with another aspect of the present invention there is provided an electronic commutation of a sensorless brushless DC motor, which monitors the behaviour of the measured open phase zero-crossing voltages during zero-crossing point detection, by comparing the said open phase voltages during the low to high and high to low zero-crossing point detection intervals against a set of voltage references calculated from the power supply voltage, in order to prevent zero-crossing point run aways and commutation timing errors.

[0036] In some embodiments, zero-crossing point run-away limiters are used to limit the maximum phase conduction angle in order to prevent commutation timing errors and improve the stability of commutation of a sensorless brushless DC motor.

[0037] In some embodiments, a soft zero-crossing point run-away limiter is used, which decreases the phase conduction angle to a minimum conduction angle value at a controlled rate when the open phase BEMF voltage exceeds a set of voltage references during zero-crossing point detection.

[0038] In some embodiments, a hard zero-crossing point run-away limiter is used, which decreases the phase conduction angle to a minimum conduction angle value immediately when the open phase BEMF voltage exceeds a set of voltage references during zero-crossing point detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

[0040] Fig. 1 illustrates a system block diagram of a disclosed method of electronic commutation of a sensorless BLDC motor.

[0041] Fig. 2 illustrates a sensorless BFDC motor controller circuitry (prior art).

[0042] Fig. 3 illustrates an operation flow diagram of a sensorless BFDC motor controller (prior art).

[0043] Fig. 4 illustrates a low to high (F H) and a high to low (H F) commutation point detection employing voltage thresholds calculated with CPFmax measurements that account for effects of rotor inherent and magnetic saturation (RIMS) saliency in a sensorless BFDC motor (prior art).

[0044] Fig. 5 illustrates a practical example of measured motor phase voltages during operation of disclosed electronic commutation of a sensorless BFDC motor in a power tool at high load, showing commutation timing intervals consisting of a zero-crossing point interval (TZCP), an open phase winding commutation demagnetization event (CDE), an open phase zero-crossing point detection window angle (to) and a resultant phase conduction angle (a).

[0045] Fig. 6 illustrates a practical example of measured motor phase voltages during operation of disclosed electronic commutation of a sensorless BFDC motor in a power tool operating at a high speed (-50KRPM electrical cycle) and a high phase conduction angle (-162°), with disclosed zero-crossing point “run-away” limiter functionality disabled, showing an increasing voltage difference (dV) between consecutive open phase BEMF voltage and half of the supply voltage (Vs/2) measurements, leading to a missed zero-crossing point detection and ultimately a motor commutation error.

[0046] Fig. 7 illustrates a practical example of measured motor phase voltages during an initialization operation of disclosed electronic commutation of a sensorless BFDC motor in a power tool, showing three zero-crossing point detection initialization cycles when commutation operation changes from 6-step to 12-step with conduction angle (a) initialized to a minimum value (a _mm ). [0047] Fig. 8 illustrates a waveform and timing diagram of disclosed 12-step electronic commutation of a sensorless BLDC motor, showing motor phase voltages, phase currents, three-phase PWM transistor gate driver outputs and important commutation logic signals.

[0048] Fig. 9 illustrates different modes of phase conduction angle regulation of disclosed electronic commutation of a sensorless BLDC motor, showing a zero-crossing point detection initialization mode, a zero-crossing point detection window feedback controller operation mode, and a soft and a hard zero crossing point run-away limiter operation mode, developed to improve performance and stability of electronic commutation operation with high conduction angles (a).

[0049] Fig. 10 illustrates a top-level operation flow diagram of a disclosed method of electronic commutation of a sensorless BLDC motor.

[0050] Fig. 11 illustrates a sub-level operation flow diagram of disclosed method of electronic commutation of a sensorless BLDC motor, showing a zero-crossing point detection unit operation.

[0051] Fig. 12 illustrates a sub-level operation flow diagram of disclosed method of electronic commutation of a sensorless BLDC motor, showing a commutation demagnetization event (CDE) detection unit operation.

[0052] Fig. 13 illustrates a sub-level operation flow diagram of disclosed method of electronic commutation of a sensorless BLDC motor, showing a zero -crossing point detection window feedback controller unit operation.

[0053] Fig. 14 illustrates a sub-level operation flow diagram of disclosed method of electronic commutation of a sensorless BLDC motor, showing a zero-crossing point run-away soft limiter unit operation.

[0054] Fig. 15 illustrates a sub-level operation flow diagram of disclosed method of electronic commutation of a sensorless BLDC motor, showing a zero-crossing point run-away hard limiter unit operation.

[0055] Fig. 16 illustrates a sub-level operation flow diagram of disclosed method of electronic commutation of a sensorless BLDC motor, showing a zero-crossing point detection initialization unit operation. DETAILED DESCRIPTION

[0056] The embodiments are directed to the area of electronic commutation of electric brushless DC (BLDC) motors, with a particular focus on the sensorless BLDC motors and control systems in applications, such as electric power tools. The application and technology relate generally to the challenges of creating an effective and a stable and robust electronic commutation of sensorless BLDC motors with increased motor torque. A set of challenges for electronic commutation of sensorless BLDC motors are apparent, which translate across a large set of applications and realizations, these are: Stability and robustness of electronic commutation of sensorless BLDC motors with high phase conduction angles; Stability and robustness of electronic commutation of sensorless BLDC motors in the presence of low motor speeds, high motor loads and high open phase winding demagnetization currents; Stability and robustness of electronic commutation of sensorless BLDC motors in the presence of high motor speeds and rapid accelerations and decelerations; Electronic commutation of sensorless BLDC motors in the presence of rotor inherent and magnetic saturation (RIMS) saliency effects in open phase voltages of a BLDC motor; Electronic commutation of a broad range of sensorless BLDC motors (IPM, salient and non-salient pole, wye and delta winding); Electronic commutation of sensorless BLDC motors without any rotor position sensors, such as Hall effect sensors or encoders.

[0057] The embodiments provide an electronic commutation of sensorless BLDC motors that have improved stability, performance, operational behaviour and greater flexibility across one or more of these areas of challenge. As such, the disclosure of the embodiments is applicable to a wide area, and more broadly applicable to the application of sensorless BLDC motors across applications, including and not limited to power tools, mobility, locomotion, robotics, automation and control, automotive, medical, consumer, hobby, etc. A general primer of the breadth and applicability of the areas of interest and application of BLDC motors can be found in [1], [2], [3], [4]

[0058] The embodiments provide an electronic commutation of a sensorless BLDC motor which uses a multiphase electric BLDC motor without any rotor position sensors.

[0059] The embodiments provide an electronic commutation of a sensorless BLDC motor where the open phase voltages are used to measure the phase winding demagnetizing voltage of a BLDC motor so as to detect when the phase winding current is decaying to zero.

[0060] The embodiments provide an electronic commutation of a sensorless BLDC motor where the open phase voltages are used to measure the rotor inherent and magnetic saturation (RIMS) saliency voltage of a BLDC motor. [0061] The embodiments provide an electronic commutation of a sensorless BLDC motor where the open phase voltages are used to measure the back electro -motive force (BEMF) voltage of a BLDC motor.

[0062] The embodiments provide an electronic commutation of a sensorless BLDC motor which monitors the open phase winding demagnetization currents after a commutation state is changed, ie. detects a commutation demagnetization event (CDE), in order to measure the corresponding open phase winding commutation demagnetization event time (TCDE) required to decay the phase winding currents to zero.

[0063] The embodiments provide an electronic commutation of a sensorless BLDC motor which measures the open phase winding demagnetization currents using the open phase voltages, which are clipped by the internal power transistor diodes to the power supply positive voltage rail and the ground voltage rail after a commutation state is changed.

[0064] The embodiments provide an electronic commutation of a sensorless BLDC motor which measures the open phase voltages in order to detect the low to high (L H) and high to low (H L) zero-crossing points and determine the time between consecutive zero-crossing points (TZCP).

[0065] The embodiments provide an electronic commutation of a sensorless BLDC motor which detects the zero-crossing point time (TZCP) using the low to high (L H) and high to low (H L) zero- crossing point detection voltage thresholds adjusted with CPFmaxR values that take into account the effects of rotor inherent and magnetic (RIMS) saliency of a BLDC motor present in the open phase voltages, which can shift the measured zero-crossing points away from the true zero-crossing points, in order to control and improve the timing accuracy of the detected zero-crossing points.

[0066] The embodiments provide an electronic commutation of a sensorless BLDC motor which adjusts the low to high and high to low open phase zero-crossing point detection voltage thresholds using CPFmaxR values in order to shift the detected zero-crossing points to the left.

[0067] The embodiments provide an electronic commutation of a sensorless BLDC motor which adjusts the low to high and high to low open phase zero-crossing point detection voltage thresholds using CPFmaxR values in order to shift the detected zero-crossing points to the right.

[0068] The embodiments provide an electronic commutation of a sensorless BLDC motor which determines the open phase zero-crossing point detection window time (Tco) using the measured open phase winding commutation demagnetization event time (TCDE) and the measured zero-crossing point detection time (TZCP), in order to obtain the corresponding open phase zero-crossing point detection window angle (to).

[0069] The embodiments provide an electronic commutation of a sensorless BLDC motor which ensures that the open phase zero-crossing point detection window angle (to) is always above a minimum reference zero-crossing point detection window angle (comin), by determining the zero-crossing point detection window angle difference (Dw) which is used as the input to a feedback controller in order to regulate the phase conduction angle (a) so that the low to high (L H) and high to low (H L) open phase zero-crossing points are always detectable during a commutation step.

[0070] The embodiments provide an electronic commutation of a sensorless BLDC motor which uses the open phase zero-crossing point detection window angle difference (Dw) as the input to a feedback controller, consisting of a PID controller and a magnitude saturator, in order to stabilize the electronic commutation of a sensorless BLDC motor and to control the phase conduction angle (a) in a range between a _min and oi _max so as to maximize the generated motor torque under all motor loading and operating conditions, for example, such as, high and low motor loads, high and low open phase winding demagnetization currents and corresponding long and short open phase winding demagnetization times, high and low motor speeds, and rapid motor accelerations and decelerations, as commonly encountered in applications such as electric power tools.

[0071] The embodiments provide an electronic commutation of a sensorless BLDC motor which monitors the behaviour of the measured open phase zero-crossing phase voltages during zero-crossing point detection, by comparing the open phase voltages during the low to high (L H) and high to low (H L) zero-crossing point detection intervals against a set of voltage references calculated from the power supply voltage (Vs), in order to prevent zero-crossing point run-away conditions and resultant 12- step commutation timing errors during high motor speeds and rapid motor accelerations and decelerations.

[0072] The embodiments provide an electronic commutation of a sensorless BLDC motor which uses zero-crossing point run-away limiters to limit the maximum phase conduction angle (a) in order to improve stability and prevent commutation timing errors by: Decreasing the phase conduction angle (a) to a minimum conduction angle (a _m in) at a controlled rate when the zero-crossing open phase voltage exceeds a set of voltage references, ie. a “soft” limiter; and, or Decreasing the phase conduction angle (a) to a minimum conduction angle (a _min ) immediately when the zero-crossing open phase voltage exceeds a set of voltage references, ie. a “hard” limiter. [0073] To proceed with the description of the embodiments, it is instructive to introduce some sensorless BLDC motor controller background information.

[0074] A Sensorless BLDC Motor Controller Circuit

[0075] The basic equivalent circuit for the control of the sensorless BLDC motor, such as used by the disclosed electronic commutation, is illustrated 20 in Fig. 2. This sensorless BLDC motor control circuit is described in greater detail in the aforementioned PCT Publication W02019/056072. The sensorless BLDC motor control system includes:

[0076] A sensorless BLDC motor 21 with a stator consisting of plurality of coil phase windings, wye or delta phase winding configuration (Fig. 2 depicting a delta winding), a rotor 22 which includes a permanent magnet, arranged to rotate in or around the stator of the motor.

[0077] A sensorless BLDC motor switching control circuit 23, also commonly known as an inverter, consisting of plurality of semiconductor power transistor switches (A_L, A H, B_L, B_H, C L, C_H) 23 such as MOSFETs or IGBTs to control the pulse width modulated (PWM) phase winding currents in a synchronized manner with the rotor position, and includes freewheeling semiconductor diodes e.g. 24 to conduct PWM off-time switching inductive currents.

[0078] A power transistor gate control circuit 27 consisting of plurality of gate drivers (A_L, A_H, B_L, B_H, C L, C_H) to optimally control the power transistors during switching operation;

[0079] An analog to digital converter (ADC) circuit 26, converting at high speed, a plurality of analog voltage measurements (Va, Vb, Vc) 29, which can include voltage resistor divider networks to reduce the sampled analog voltages to an acceptable level for measurement with an ADC and capacitors to reduce measured analog voltage bandwidth and fdter out electrical noise .

[0080] A microcontroller 28 which provides various functionalities. The microcontroller may comprise peripherals such as an integrated high speed ADC circuit, volatile memory such as DRAM, and non-volatile memory such as PROM, EPROM, EEPROM, FLASH, MRAM, PCRAM, and other functionalities such as timers, user input and output interfaces, communication ports, comparator circuits, and operational amplifier circuits etc.

[0081] An electrical voltage source (Vs) such as a battery or a transformer or a switching power supply is also provided (not shown). The power supply voltage (Vs) can be measured: Indirectly via the analog voltage measurements (Va, Vb, Vc) 29 and an ADC circuit 26 when the corresponding high-side power transistors (A H, B_H, C_H) 23 are switched on to the power supply voltage rail (Vs); or Directly with an analog input voltage measurement connected directly to the voltage source rail (Vs) , which can include voltage resistor divider networks to reduce the sampled analog voltages to an acceptable level for measurement with an ADC and capacitors to reduce measured analog voltage bandwidth and fdter out electrical noise (not shown).

[0082] A Sensorless BLDC Motor Controller Operation Block Diagram

[0083] The sensorless BLDC motor controller operation block diagram 1, such as used by the disclosed electronic commutation method is illustrated in Fig. 3. This sensorless BLDC motor controller operation is described in greater detail in the aforementioned PCT publication WO2019/056072. The sensorless BLDC motor controller operation block diagram includes:

[0084] An initial rotor position detection (IRPD) operation which is used to detect the starting rotor position of a sensorless BLDC motor at standstill or in motion, including during reversed rotor momentum rotation, without using rotor position sensors such as Hall effect sensor or encoders.

[0085] A zero to high speed sensorless BLDC motor control operation, which may include a hybrid sensorless BLDC motor control approach as illustrated in Fig. 3, consisting of a zero to high speed sensorless BLDC motor operation, and a low to high speed sensorless BLDC motor operation, for example, during which the disclosed electronic commutation method is applied, designed to successfully drive a broader range of BLDC motors from zero speed to high speeds under all motor loading conditions, including during reversed rotor momentum motor operation conditions, without using rotor position sensors such as Hall effect sensor or encoders.

[0086] A sensorless BLDC motor brake operation designed to bring such motors to a standstill. [0087] Electronic Commutation of a Sensorless BLDC Motor

[0088] This section discloses the present embodiments of the system and method of electronic commutation of a sensorless BLDC motor developed for motor control applications, such as electric power tools.

[0089] (a) Electronic Commutation System Overview: The system block diagram 10 of the disclosed electronic commutation of a sensorless BLDC motor is illustrated in Fig. 1. The key system components of the developed 12-step commutation scheme include: A voltage sensing based sensorless BLDC motor controller, such as described in the “Low to High Speed Sensorless BLDCM Operation” embodiment of the aforementioned PCT Publication W02019/056072, consisting of a hardware circuitry 20, such as illustrated in Fig. 2, and an operational flow diagram 1, such as illustrated in Fig. 3, that integrates the disclosed electronic commutation of a sensorless BLDC motor with a method of operation as illustrated in the top-level operation flow diagram 30 in Fig. 10; A sensorless BLDC motor 21, such as illustrated in Fig. 2, which is, for example, integrated into a power tool; A motor phase voltage detection circuitry 100 which is used to measure the motor phase and BEMF voltages (Va, Vb, Vc) 29, and the power supply voltage (Vs) 16, for example using an ADC circuit 26 integrated inside a microcontroller 28 as illustrated in Fig. 2; An open phase voltage zero-crossing point detection unit 110; A motor commutation demagnetization event (CDE) detection unit 120; An open phase voltage zero crossing point detection window feedback controller 130 unit consisting of a PID controller 133 and a magnitude saturator 134; A BEMF voltage zero-crossing point run-away limiter 140 unit consisting of a soft 140a and a hard 140b phase conduction angle limiter; A three-phase PWM generator 170 implemented inside a microcontroller 28 that drives the power transistors using a gate driver 27, such as illustrated in Fig. 2, with phase conduction angles > 120°; A three-phase inverter 23 consisting of plurality of power transistors (A_L, A H, B_L, B_H, C L, C_H) that drive the three-phase BLDC motor 21, such as illustrated in Fig. 2.

[0090] (b) Electronic Commutation Method Advantages: In contrast to prior art methods, the present embodiments use information about the motor phase winding demagnetization currents and the behaviour of the BEMF voltage measurements during zero-crossing point detection, for example, a zero crossing point run-away event, such as shown in Fig. 6, to provide a distinct advantage and obtain improved stability, performance and operational behaviour with 12-step commutated sensorless BLDC motors, and to obtain greater possibility when operating these motors with high phase conduction angles (eg. a >140°) under different loading conditions, such as, high loads, low speeds, high speeds, rapid accelerations and decelerations, commonly encountered in electric power tool applications. The present embodiments take into account the effects of rotor inherent and magnetic (RIMS) saliency [12] of BLDC motors, which can shift the measured zero-crossing points away from the true zero-crossing points, to control and improve the timing accuracy of the detected zero-crossing points. The present embodiments offer improved performance with high saliency BLDC motors, such as interior permanent magnet (IPM) motors used in power tool applications, which exhibit high inductances and low resistances in the phase windings, and increased motor electrical time constants (TE = L/R), typically measured in the range between lOOOps to 1300ps. The present embodiments offer improved performance, operational behaviour and greater possibility in achieving a reliable and robust 12-step commutation of sensorless BLDC motors across a broader range of phase conduction angles (eg. 120° < a < 165°). In practical tests, the present embodiments can attain increased motor torque, faster applications speeds, longer operation run-times and lower motor temperatures when employing the disclosed 12-step trapezoidal commutation method with an increased conduction angle compared to the standard 6-step commutation, which is important in applications such as electric power tools.

[0091] (c) Electronic Commutation Method Objectives: The key objectives of the disclosed 12-step commutation method developed for sensorless BLDC motors which can lead to improved operational stability and performance over the known prior art, are: To monitor the open phase winding demagnetization currents after a commutation state change, ie. detect a commutation demagnetization event (CDE) 120, and to measure the corresponding commutation demagnetization event time (TCDE) 121 required to decay the phase winding current to zero, for example, as illustrated in Fig. 1 and Fig. 5; To determine the zero-crossing point detection time (TZCP) 111 using low to high (L H) 51 and high to low (H L) 52 zero-crossing point detection voltage thresholds adjusted with CPFmaxR values that take into account the effects of rotor inherent and magnetic (RIMS) saliency of a BLDC motor, for example, as illustrated in Fig. 4 and described in greater detail in the aforementioned PCT Publication W02019/056072, in order to control and improve the timing accuracy of the zero-crossing points; To determine the open phase zero-crossing point detection window time (Tco) 139 using the measured commutation demagnetization event time (TCDE) 121 and the measured zero-crossing point detection time (TZCP) 111, in order to obtain the corresponding open phase zero-crossing point detection window angle (to) 131, as illustrated in Fig. 1, Fig. 5 and Fig. 8; To ensure that the open phase zero-crossing point detection window angle (to) 131 is always above a minimum reference zero-crossing point detection window angle (w,,, _ih ) 11, as set the by the application, by using the open phase zero-crossing point detection window angle difference (Dw) 132 as the input to a feedback controller 130, as illustrated in Fig. 1, which regulates the conduction angle (a) 14 so that the low to high (L H) 51 and high to low (H L) 52 open phase zero-crossing points are always detectable in a commutation step; To use the measured open phase zero-crossing point detection window angle difference (Dw) 132 as the input to a feedback controller 130 in order to stabilize the electronic commutation operation and to control the phase conduction angles (a) 14 in the range between a _min 12 and oi _max 13 (eg. 120° < a £ 165°) in order to maximize the generated motor torque under all motor loading and operating conditions, for example, such as, high and low motor loads, high and low open phase winding demagnetization currents and corresponding long and short open phase winding demagnetization times, high and low motor speeds, and rapid motor accelerations and decelerations, as commonly encountered in power tool applications; To monitor the behaviour of the measured open phase BEMF zero-crossing voltages during zero-crossing point detection, by comparing the open phase voltages 29 during the low to high (L H) 51 and high to low (H L) 52 zero-crossing point detection intervals against a set of voltage references 142, 143, 148, 149 calculated from the power supply voltage (Vs) 16; To prevent zero- crossing point run-away conditions and resultant 12-step commutation timing errors, for example, as shown in Fig. 6, during high motor speeds and rapid motor accelerations and decelerations, by: Decreasing the phase conduction angle (a) 15 to a minimum conduction angle (a _m in) 12 at a controlled rate when the open phase zero-crossing voltage exceeds the 142 or 143 voltage reference, for example, referred to as a “soft” limiter 140a; and, or Decreasing the phase conduction angle (a) 15 to a minimum conduction angle (a _min ) 12 in the fastest possible manner when the open phase zero-crossing phase voltage exceeds the 148 or 149 voltage reference, for example, referred to as a “hard” limiter 140b.

[0092] (d) Electronic Commutation Method of Operation: An overview of the preferred method of operation of the disclosed electronic commutation of a sensorless BLDC motor is now provided with reference to the system block diagram 10 illustrated Fig. 1, the waveform and timing diagram 50 illustrated Fig. 8, and the top-level the operation flow diagram 30 illustrated in Fig. 10. This is followed by a more detailed description of the embodiments in the proceeding sections.

[0093] The operation of the disclosed electronic commutation of a sensorless BLDC motor starts by measuring the motor phase voltages 100, which includes measuring the open phase voltage of the third phase winding when it is not activated. These open phase voltages can, for example, be used to measure: The back electro -motive force (BEMF) voltages of a BLDC motor; or the zero-crossing point detection voltages affected by rotor inherent and magnetic saturation (RIMS) saliency in a BLDC motor, for example, as illustrated in Fig. 4; or the open phase winding demagnetization voltages which are clipped by the internal power transistor diodes to the open phase voltages to the positive supply voltage rail 53 or the ground voltage rail 54 when the open phase winding current is decaying to zero, for example, as shown in Fig. 5 and Fig. 8. After performing a zero-crossing point detection initialization phase 150, the measured phase voltages (Va, Vb, Vc) 29 are used by the zero-crossing point detection unit 110 to obtain the zero-crossing points (TZCP) 111, and by the commutation demagnetization event (CDE) detection unit 120 to measure the time to decay the open phase winding demagnetization currents to zero (TCDE) 121. The measured TCDE 121 value varies with the motor speed and load, which in general results in a longer time with high motor loads and low speeds, and a shorter time with low motor loads and high speeds. The measured TZCP 111 and TCDE 121 are then used to calculate the open phase zero-crossing point detection window time (Tco) 139 and the corresponding zero-crossing point detection window angle (to) 131, which is used by a feedback controller 130 to calculate the optimal conduction angle (a) 14. This PID feedback controller 130 ensures that the zero-crossing point detection window angle (to) 131 is kept above the minimum window angle (comin) 11, set by the user, by reducing the conduction angle (a) 14 if w 131 < oj _mm 11. This stabilises the commutation operation at very high conduction angles (a) 14. At the same time the feedback controller 130 also maximizes the conduction angle (a) 14 value, which can, for example, be set in the range between a _min 12 and a _max 13 (eg. 120° < a < 165°) during operation, as required by the application. To further improve stability and reliability of operation when commutating sensorless BLDC motors with high conduction angles (eg. a >140°) at high speeds, and during rapid motor accelerations and deceleration, the open phase BEMF voltages are monitored to prevent missed zero-crossing point detections and commutation timing errors during operation, using the zero-crossing point run-away limiter 140. This is achieved by reducing the conduction angle (a) 15 to a minimum value (eg. a _min 12) when the open phase BEMF voltage 29 exceeds a set of voltage threshold values. Two phase conduction angle limiters are implemented: a soft conduction angle limiter 140a which reduces the conduction angle (a) 15 at a controlled rate when the open phase BEMF voltages exceed the set supply voltage thresholds 142 or 143; and a hard conduction angle limiter 140b, which limits the conduction angle (a) 15 to a _min 12 instantaneously when the open phase BEMF voltages exceed the set supply voltage thresholds 148 or 149. Fig. 9 illustrates the different zero-crossing point detection window feedback controller and run-away limiter modes of operation developed to regulate the conduction angle (a) 14 15 during commutation of a sensorless BLDC motor. The output conduction angle (a) 15 is then finally used to calculate the commutation timing point (TCP) 160, which in conjunction with the measured zero-crossing point detection time (TZCP) 111 is used by the three-phase PWM output generator 170 to drive the power transistors of the three-phase inverter 23 with conduction angles >120°.

[0094] The embodiments of the disclosed electronic commutation of a sensorless BLDC motor are now described in greater detail in the proceeding sections by way of example with reference to the disclosed diagrams in Fig. 1 to Fig. 16.

[0095] (i) Motor Phase Voltage Detection: The motor phase voltage detection 100 unit illustrated in

Fig. 1 is used to measure the motor phase voltages (Va, Vb, Vc) 29, and indirectly the power supply voltage (Vs) 16, for example, when the corresponding high-side power transistors (A H, B_H, C_H) 23 are switched-on to the power supply voltage rail (Vs) 16. The open phase voltages 29 measured when the third phase winding is not activated, can, for example, be used to measure: The back electro -motive force (BEMF) voltages of a BLDC motor; or the zero-crossing point detection voltages affected by rotor inherent and magnetic saturation (RIMS) saliency in a BLDC motor, for example, as illustrated in Fig. 4; or the open phase winding demagnetization voltages which are clipped, by the internal power transistor diodes, the open phase voltages to the positive supply voltage rail 53 or the ground voltage rail 54 when the open phase winding current is decaying to zero, for example, as shown in Fig. 5 and Fig. 8. These voltages are measured at a regular time interval (eg. every few microseconds), for example, using an ADC circuit 26 and a microcontroller 28, as shown in Fig. 2, which are integrated into a sensorless BLDC motor controller, such as described in the “Low to High Speed Sensorless BLDCM Operation” embodiment of the aforementioned PCT Publication W02019/056072. [0096] (ii) Zero-Crossing Point Detection: The zero-crossing point detection unit 110 illustrated in Fig. 1, detects when the open phase voltages 29 cross half of the power supply voltage rail (Vs/2), during a low to high (L H) 51 and a high to low (H L) 52 zero-crossing point detection, for example, as illustrated in the waveform and timing diagram in Fig. 8 and shown in the practical example in Fig. 5. The disclosed zero-crossing point detection 110 method extends on the commutation point detection method described in the “Low to High Speed Sensorless BLDCM Operation” embodiment of the aforementioned PCT Publication W02019/056072 by taking into account the rotor inherent and magnetic saturation (RIMS) saliency effects [12], for example, such as encountered in high saliency BLDC interior permanent magnet (IPM) motors used in power tools. It has been discovered that the measured open phase voltages affected by RIMS saliency can shift the detected zero-crossing points away from the true zero-crossing points (eg. at 30°, 90°, 150°, 210°, 270°, 330° electrical rotor positions) by a significant amount (eg. >10°), for example, as shown in Fig. 4. In this embodiment, the measured open phase winding voltages affected by RIMS saliency use the CPFmax value to correct the timing of the low to high (L H) 51 and high to low (H L) 52 zero-crossing point detection voltage thresholds during the 12-step commutation of sensorless BLDC motors, as illustrated in Fig. 4. Thus, more accurate zero-crossing-points can be obtained with this method, resulting in improved 12-step electronic commutation performance when extended phase conduction angles are used. A low to high zero-crossing point is detected when the phase voltage > Vs . ( ½+N . C P Fm ax R ) 113, and a high to low zero-crossing point is detected when the phase voltage < Vs. (½-N. CPFmaxR) 114, as illustrated in the operation flow diagram 110 in Fig. 11. The supply voltage independent ratio value CPFmaxR (ie. CPFmax/Vs), which is unique to a particular BLDC motor (eg. CPFmaxR = 0.1 - 1.0), is measured during the “Zero to Low Speed Sensorless BLDCM Operation” embodiment of the aforementioned PCT Publication WO2019/056072.

[0097] The disclosed method also extends the zero-crossing point detection tuning factor N values into the negative region (eg. N = -1.0 to 1.0), which can be varied during operation, for example, with motor load, or motor speed, or command throttle position, in order to shift the timing of the detected zero-crossing points to the left (eg. N < 0) or to the right (eg. N > 0), for example, to correct for the aforementioned distortions in the open phase voltages due to the effects of RIMS saliency in BLDC motors and thus improve the timing accuracy of the zero-crossing points. This method can also be used to increase (eg. N < 0) or decrease (eg. N > 0) the phase conduction angle (a) 15, for example, by shifting to the left (ie. advancing) or shifting to the right (ie. delaying) the start of the time interval when all three motor phases are actively driven by the three-phase PWM generator 170. Values N < 0, for example, can also be used to shift the timing of the zero-crossing points to the left to compensate for microcontroller 28 program execution delays that can lead to delayed zero-crossing point measurements. Value N = 0 sets the zero-crossing point timing instants equal to the standard half way point of the power supply voltage rail (Vs/2) that is commonly used in practise. Once a zero-crossing point is detected, the time between two consecutive zero-crossing points (TZCP) 111 is read from a timer 55, for example implemented inside a microcontroller 28. The zero-crossing point time TZCP 111 and the commutation demagnetization event time (TCDE) 121, which is measured by the CDE unit 120, are used to calculate the zero-crossing point detection window time (Tco) 139 and the next commutation point time (TCP) 160. The zero-crossing point detection 110 operation is performed during the top-level electronic commutation operation 30 illustrated in the flow diagram in Fig. 10, and during the zero crossing point detection initialization 150 illustrated in the operation flow diagram in Fig. 16.

[0098] (iii) Zero-Crossing Point Detection Initialization: At startup, the motor is normally driven using the 6-step commutation scheme, such as described in the “Fow to High Speed Sensorless BFDCM Operation” embodiment of the aforementioned PCT Publication W02019/056072. When a changeover from a 6-step to a 12-step commutation is demanded by the application, for example, at a set motor speed, or motor load or command throttle position, the disclosed electronic commutation of a sensorless BFDC motor performs a zero-crossing point detection initialization phase 150 before a changeover to the 12-step commutation can occur. This initialization operation step 150 is illustrated in the top-level the operation flow diagram 30 in Fig. 10 and the corresponding sub-level operation flow diagram 150 in Fig. 16.

[0099] The initialization operation 150 begins by setting the phase conduction angle (a) 15 to the minimum possible value a _mm 12, as set by the application, and then performing a number of initialization cycles (N) 153 during which consecutive zero-crossing points 110 are detected using the 6-step commutation method, as shown in the exemplary Fig. 7. This ensures that the reference commutation time between two consecutive zero-crossing points (TZCP) 111 has been measured and is valid as soon as the 12-step commutation method is enabled. The commutation point (TCP) 160, which sets the duration when the power transistors 23 are driven with conduction angles >120°, is also initialized during this phase:

TCP — a · TZCP ( 1)

[00100] After N (153) initialization cycles (eg. 2 - 3) have been performed, the ZCP initialized flag is set 154 and then checked 31 after every open phase voltage detection 100 during the execution of the top-level operation flow diagram 30, which asserts that the 12-step electronic commutation operation is enabled. [00101] (iv) Motor Commutation Demagnetization Event (CDE): An embodiment of the disclosed electronic commutation of a sensorless BLDC motor, which the known prior art methods do not appear to have addressed, for example, in dynamic motor control applications such as electric power tools, is the detection of the open phase winding demagnetization currents (CDE) 120 after a commutation state change has taken place, as shown in Fig. 5. This is important because this ensures that the open phase winding currents have decayed to zero, before the open phase voltages are measured and used to detect a zero-crossing point (ZCP) 110. This method results in more stable and reliable commutation of sensorless BLDC motors. In the disclosed commutation scheme, this operation is performed by the commutation demagnetization event (CDE) detection unit 120, illustrated in the system block diagram in Fig. 1 and in the operation flow diagram in Fig. 12. These open phase winding demagnetization currents can take a finite amount of time to decay to zero and this depends largely on the motor speed and load. In general, a longer demagnetization time (TCDE) 121 results when a motor is operated at high loads and slow speeds, and a shorter demagnetization time results when a motor is operated at low loads and high speeds. For example, as shown in Fig. 5 during testing with a power tool at high motor loads, a commutation demagnetization event (CDE) 120 can occupy >1/3 of the total time interval between two consecutive commutation points (TZCP) 111. This reduces the open phase zero-crossing point detection window time (Tco) 139 and the corresponding zero-crossing point detection window angle (to) 131, and for example, as shown in Fig. 5, this can leave only about 1/3 of the commutation interval to detect the zero-crossing points 51, 52, and another 1/3 of the interval to extend the conduction angle (a) 15 beyond 120° when current flow is enabled through the third motor phase winding. In high saliency interior permanent magnet (IPM) BLDC motors, which are commonly used in power tools, this problem is further exacerbated by the high inductance and very low resistance of the phase windings, which increases the motor electrical time constant (TE = L/R) of such motors, typically measured between lOOOps to 1300ps, and thus the required phase winding demagnetization time (TCDE) 121. In practise, when operating power tools at high motor loads, the known prior art 12-step commutation methods have been found to have difficulties operating reliably with conduction angles greater than approximately 140°, because of these large phase winding demagnetization currents. Therefore, to maximize the conduction angle (a) in a voltage sensing based 12-step trapezoidal commutation of sensorless BLDC motors, a proper phase winding demagnetization management is required, such as addressed in the disclosed method.

[00102] During commutation of a sensorless BLDC motor, the aforementioned phase winding demagnetization currents generate open phase inductive voltage spikes, which are clipped by the internal power transistor diodes 24 to the positive power supply voltage 53 and the ground voltage 54 rails after a commutation state is changed, as shown in exemplary Fig. 5, and illustrated in the waveform and timing diagram in Fig. 8. The commutation demagnetization event (CDE) unit 120 detects these open phase winding demagnetization voltage spikes 53, 54 using the open phase voltages (Va, Vb, Vc) 29 measured by the phase voltage detection unit 100. This operation is illustrated in the operation flow diagram in Fig. 12. During the CDE low to high (L H) zero-crossing point detection interval, the falling open phase voltage is compared to a supply voltage reference VS ^» NCDE_LH 123 (eg. where NCDELH = 0.5 - 0.9) and during the high to low (H L) zero-crossing point detection interval, the rising open phase voltage is compared to a supply voltage reference VSVNCDEHL 124 (eg. where NCDEHL = 0.1 - 0.5). When these conditions are met, the phase winding current has decayed to zero, as detected by CDE

120 unit. The corresponding phase winding demagnetization time (TC _DE ) 121 is read from a timer 55, for example implemented inside a microcontroller 28 such as illustrated in Fig. 2.

[00103] (v) Zero-Crossing Point Detection Window Feedback Controller: The disclosed 12-step trapezoidal commutation method uses a feedback control loop to improve stability and performance during commutation of a sensorless BLDC motor. The control objective of the disclosed feedback controller 130, illustrated in the system block diagram 10 in Fig. 1 and in the operation flow diagram in Fig. 13, is to ensure that the open phase zero-crossing point detection window angle (co) 131 is always kept above the minimum window angle (co _min ) 11. This is achieved by reducing the feedback controller’s output conduction angle (a) 14 when co 131 < oj _mm 11, for example, as illustrated in Fig. 9. This feedback action stabilises the commutation of a sensorless BLDC motor at very high conduction angles (a) 14, by ensuring that the open phase zero-crossing point detection window time (Tco) 139 is always sufficiently large to enable the zero-crossing points 51, 52 to be detected without errors. If the open phase zero crossing point detection window angle co 131 > co _max 11, then the feedback controller 130 increases the conduction angle (a) 14 to the maximum possible conduction angle (a _max ) 13, as set by the application, for example, as illustrated in Fig. 9. Thus, the feedback controller 130 optimizes the phase conduction angle (a) 14 value during operation in response to different motor load and speed conditions. In practise the conduction angle (a) 14 can vary between the set minimum oi _min 12 and maximum a _max 13 values (eg. 120° < a < 165°), for example, as illustrated in Fig. 9.

[00104] The zero-crossing point detection window feedback controller operation 130 is illustrated in the operation flow diagram in Fig. 13. It begins by calculating the open phase zero-crossing point detection window angle (co) 131, using the measured open phase winding demagnetization time (TCDE)

121 and the zero-crossing point time (T _Z C _P ) 111 :

Tw — TZCP - TCDE (2) co = Tco / T _Z C _P (3) [00105] The zero-crossing point detection window error difference (Dw) 132 which is applied at the input of the PID controller 133 is then calculated with:

Dqΐ CO - COmin (4)

[00106] The PID controller 133 sets the dynamic response of the feedback control loop, which ensures that phase conduction angle (a) 14 is adjusted sufficiently fast in response to a change in the input zero-crossing point detection window error (Dw) 132, thus increasing the stability during the 12- step commutation of a sensorless BLDC motor. The discrete time PID controller 133 can, for example, be implemented using a difference equation based on trapezoidal approximation of a continuous time PID controller, such as: a[n] = a[n-l] + Ki·Dw[h] + K ₂ ·Dw[h-1] + K ₃ ·Dw[h-2] (5) where the Ki, K _2, K ₃ coefficients are given by:

Ki = Kp + Ki · T / 2 + Kd / T (6)

K ₂ = -Kp + Ki * T/ 2 - 2 * Kd / T (7)

K ₃ = Kd / T (8)

[00107] and Kp is the proportional gain, Ki is the integral gain, Kd is the derivative gain, and T is the feedback controller update period. These controller gain settings can be used to obtain the desired dynamic response of the closed-loop feedback controller 130 in different motor control applications, such as in electric power tools. The PID controller 133 is not limited only to the implementation disclosed in equation (5). Other implementations can also be used to control the response of the feedback controller 130, for example, such as a computationally efficient algorithm that increments and decrements the conduction angle (a) 14 in response to the input zero-crossing point detection window error (Dw) 132: a[n] = a[n-l] + Aamc (if Dw > 0) (9) a[n] = a[n-l] - AOIDEC (if Dw < 0) (10) where AOIINC is the conduction angle increment rate and AOIDEC is the conduction angle decrement rate. These can be set to increment and decrement the conduction angle (a) 14 at different rates in order to achieve the required feedback controller 130 dynamic response, for example, a slower increment rate and a faster decrement rate can be used to increase the stability of operation. [00108] The magnitude saturator 134 implemented in the feedback controller 130 limits the output phase conduction angle (a) 14 value computed by the PID controller 133 between the minimum oimin 138 and maximum a _max 137 values set by the application, for example, as illustrated in Fig. 9.

[00109] (vi) Zero-Crossing Point Detection Window Feedback Controller Input Settings: The disclosed zero-crossing point detection window feedback controller 130 uses several inputs to set the desired phase conduction angle (a) 14 and the stability of operation during commutation of sensorless BLDC motors. These are: the minimum open phase zero-crossing point detection window angle (co _min ) 11; the minimum phase conduction angle a _min 12; and the maximum phase conduction angle a _max 13. The minimum zero-crossing point detection window angle (co _min ) 11 can, for example, use a fixed setting value. The maximum phase conduction angle a _max 13 value sets maximum possible value of the phase conduction angle (a) 14 during commutation of a sensorless BLDC motor, which is regulated by the feedback controller 130, for example, as illustrated in Fig. 9. The maximum phase conduction angle a _max 13 setting can use a fixed value or be varied in real-time during electronic commutation, for example, with motor load or speed or command throttle position to produce a desired motor torque output. In practise, the minimum phase conduction angle a _min 12 value, which is selected so that a stable and reliable operation can be achieved under all motor load and operating conditions, is set lower than the maximum phase conduction angle a _max 13, ie. a _min < a _mix . The actual angle (Q) in units of degrees is related to an input angle f setting via: q = f · 60° (11) where f equals to either the zero-crossing point detection window angle (to) or the phase conduction angle (a), and the 60° angle corresponds to the motor electrical revolution angle made by the rotor between consecutive zero-crossing point measurements (T _ZCP ) 111. For example, a value oj _mm = 0.25, sets the actual minimum zero-crossing point detection window angle to: 0.25 · 60° = 15°. Higher oj _mm 12 values increase the minimum zero-crossing point detection window time (Tco) 139 and thus make electronic commutation controller operation more stable and reliable, at the cost of a reduced maximum possible phase conduction angle (a) 14, since a total of 60° must be preserved between consecutive zero crossing point measurements (T _ZCP ) 111. The actual extended motor phase conduction angle (L) in units of degrees is calculated with:

A = 120° + a · 60° (12)

[00110] For example, a value a _max = 0.75, sets the actual maximum phase conduction angle to: 120° + 0.75 · 60° = 165°. In general, the minimum phase conduction angle a _min 12 is set lower than the maximum phase conduction angle a _max 13, ie. a _min < a _max . Table 1 shows a range of input angle setting values which have been applied successfully in motor control applications such as electric power tools.

[00111 ] Table 1 : Zero-crossing point detection window feedback controller input angle settings

[00112] (vii) Zero-crossing Point Run-Away Limiter: During 12-step commutation of sensorless BLDC motors with high conduction angle (a) 15 values, a further operation issue which can lead to instability was discovered when detecting open phase zero-crossing points at very high motor speeds and rapid motor accelerations and decelerations. It was found that with high phase conduction angles (a) 15 (eg. >140°) and high transient motor speeds, the low to high (L H) 51 and a high to low (H L) 52 zero-crossing points can become unmeasurable due to microcontroller 28 program execution delays and rotor position errors in the estimated commutation points when standard commutation time delay techniques are used, ie. TCP 160 calculation in equation (1), and for example, as described in [5] It is also apparent that the known prior art 12-step commutation methods may not have addressed such issues of instability during commutation of sensorless BLDC motors with high conduction angles (a) 15. In practise, this can lead to consecutive low to high (L H) 51 and high to low (H L) 52 open phase zero crossing points which become increasingly delayed from their true zero-crossing point (eg. Vs/2), resulting in a zero-crossing point detection “run-away” condition and a commutation error, for example, as shown in Fig. 6. In this practical example showing a power tool operating at a very high speed (eg. -50KRPM electrical cycle) and a very high phase conduction angle (a) 15 (eg. -160°), the voltage difference (dV[n]) between the measured low to high (L H) 51 and the high to low (H L) 52 open phase zero-crossing point voltages and half of the supply voltage rail (Vs/2) increases with each consecutive zero-crossing point. This condition can lead erroneous sensorless BLDC motor commutation point detections and ultimately a motor operation failure if left unaddressed.

[00113] The disclosed method of electronic commutation of a sensorless BLDC motor addresses these aforementioned instability issues with the developed zero-crossing point run-away limiter 140 unit, illustrated in the system block diagram in Fig. 1 and in the top-level operational flow diagram 30 in Fig. 10. A “soft” and a “hard” zero-crossing point run-away limiter have been implemented, as illustrated in the sub-level operation flow diagrams 140a and 140b in Fig. 14 and Fig. 15 respectively. The zero crossing point run-away limiter 140 monitors the behaviour of the measured open phase BEMF zero crossing voltages (eg. dV[n] illustrated in Fig. 6.) during zero-crossing point detection, by comparing the open phase BEMF voltages 29 during the low to high (F H) 51 and high to low (H F) 52 zero crossing point detection intervals against a set of voltage references VS ^» NZCP_LH_RA_SOFT 142, VS'NZCP in. RA soi l 143, VS*NZCP ui RA HARD 148, Vs*Nzci in. RA HARD 149 calculated from the power supply voltage (Vs) 16. The disclosed method prevents the zero-crossing point run-away instability conditions and ensuing 12-step commutation timing errors, for example, as shown in Fig. 6, when operating with high phase conduction angles (a) 15 (eg > 140°) and high motor speeds and rapid motor accelerations and decelerations. This is achieved by using two separate zero-crossing point run-away limiters operating in parallel to limit the phase conduction angle (a) 14 computed with the zero-crossing point detection window feedback controller 130, for example, as illustrated in Fig. 9. These are:

[00114] A zero-crossing point run-away soft limiter 140a illustrated in Fig. 14, which decreases the output phase conduction angle (a) 15 to a minimum conduction angle (a _m in) 12 at a controlled rate when the BEMF zero-crossing phase voltage exceeds the low to high (F H) 51 zero-crossing point detection voltage reference VS ^» NZCP_LH_RA_SOFT 142 (eg. where NZCP ui RA son = 0.5 - 0.9) or the high to low (H F) 52 zero-crossing point detection voltage reference VS*NZCP HI. RA SOFT 143 (eg. where NZCP HI. RA SOFT = 0.1 - 0.5). For example, this can be implemented with a computationally efficient algorithm that decrements the conduction angle (a) 15 when the measured open phase BEMF voltage exceeds the set voltage thresholds 142, 143, as calculated in the operation step 144 in Fig. 14 using the difference equation: a[h] = a[h-1] - AOIDEC (13) where AOIDEC is the phase conduction angle decrement rate. This AOIDEC value can be set to reduce the conduction angle (a) 15 at specific rate in order to achieve the required dynamic response of the zero crossing point run -away soft limiter 140a during commutation of a sensorless BLDC motor. The soft limiter 140a is not limited only to the implementation disclosed in equation (13).

[00115] Other implementations can also be used to control the response of the zero-crossing point run-away limiter 140a, for example, such as a PID controller 133 described in equation (5) by measuring the voltage difference between the open phase BEMF voltage and half of the supply voltage rail (Vs/2) (eg. dV[n] illustrated in Fig. 6.) and using it as the input to the PID controller. Operation steps 145 and 146 illustrated in the operation flow diagram in Fig. 14 restrict the minimum phase conduction angle (a) 15 value to the set minimum conduction angle (amin) 12 value;

[00116] A zero-crossing point run-away hard limiter 140b illustrated in Fig. 15, which decreases the output phase conduction angle (a) 15 to a minimum conduction angle (a _min ) 12 immediately when the open phase zero-crossing point detection voltage exceeds the low to high (L H) 51 zero-crossing point detection voltage reference VS-NZCP ui RA HARD 148 (eg. where N _Z CP I.II RA HARD = 0.5 - 0.9) or the high to low (H L) 52 zero-crossing point detection voltage reference Vs _* N _/ cp m. RA HARD 149 (eg. where NZCP in. RA HARD = 0.1 - 0.5). This hard limiter 140b has been implemented as an additional safety measure to prevent zero-crossing point run-away errors which may not have been corrected by the zero crossing point run-away soft limiter 140a, for example, in case the response of the soft limiter 140a was too slow to reduce the phase conduction angle (a) 15 sufficiently fast during commutation of a sensorless BLDC motor. In practise, the hard limiter 140b voltage references are set, such that NZCP_LH RA HARD > NZCP_LH RA SOFT and NZCP_HL RA HARD < NZCP_HL RA SOFT. When the hard limiter 140b detects the conditions 148, 149, the output phase conduction angle (a) 15 is set to the minimum conduction angle (a _min ) 12 immediately, as shown in operation step 146 of the flow diagram illustrated in Fig. 15.

[00117] (viii) Three-Phase PWM Output Generator: The three-phase PWM output generator 170, drives the three-phase inverter power transistors (A_L, A H, B_L, B_H, C L, C_H) 23 with a 12-step commutation motor phase driving sequence illustrated in the waveform and timing diagram in Fig. 8. The power transistors 23 activated during commutation steps 56 numbered 1 to 12 are shown in Table 2. During the odd numbered commutation steps only two motor phases are actively driven while the third phase is left open and used to detect the commutation demagnetization event (CDE) 120 and the zero- crossing point TZCP HO. During the even numbered commutation steps, all three motor phases are actively driven. After a zero-crossing point TZCP 111 is detected 34, the three-phase PWM output generator 170 commences the >120° conduction angle operation, as shown in the top-level operation flow diagram 30 in Fig. 10. The commutation point (TCP) 160 sets the duration when all three motor phases are conducting current during an even numbered commutation step. The TCP 160 duration is calculated with equation (1) and it depends on the value of the output phase conduction angle (a) 15, which is regulated with the zero-crossing point detection window feedback controller 130, and the measured zero-crossing point time TZCP 111· When the set TCP 160 value exceeds 33 the timer value 55, for example, implemented inside a microcontroller 28, the third phase is turned-off (ie. open phase) and the commutation step is incremented 35 (ie. odd step number). A commutation demagnetization event (CDE) 120 is detected next and the zero-crossing point detected flag is cleared 36. This is then followed by a new zero-crossing point T _ZCP 110 detection, as shown in the top-level operation flow diagram 30 in Fig. 10.

[00118] Table 2: 12-step commutation power transistor switching sequence

Interpretation

[00119] Reference throughout this specification to “one embodiment”, “some embodiments” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment”, “in some embodiments” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment, but may. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art from this disclosure, in one or more embodiments. [00120] As used herein, unless otherwise specified the use of the ordinal adjectives "first", "second", "third", etc., to describe a common object, merely indicate that different instances of like objects are being referred to, and are not intended to imply that the objects so described must be in a given sequence, either temporally, spatially, in ranking, or in any other manner.

[00121] In the claims below and the description herein, any one of the terms comprising, comprised of or which comprises is an open term that means including at least the elements/features that follow, but not excluding others. Thus, the term comprising, when used in the claims, should not be interpreted as being limitative to the means or elements or steps listed thereafter. For example, the scope of the expression a device comprising A and B should not be limited to devices consisting only of elements A and B. Any one of the terms including or which includes or that includes as used herein is also an open term that also means including at least the elements/features that follow the term, but not excluding others. Thus, including is synonymous with and means comprising.

[00122] As used herein, the term “exemplary” is used in the sense of providing examples, as opposed to indicating quality. That is, an “exemplary embodiment” is an embodiment provided as an example, as opposed to necessarily being an embodiment of exemplary quality.

[00123] It should be appreciated that in the above description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the Detailed Description are hereby expressly incorporated into this Detailed Description, with each claim standing on its own as a separate embodiment of this invention.

[00124] Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form different embodiments, as would be understood by those skilled in the art. For example, in the following claims, any of the claimed embodiments can be used in any combination.

[00125] Furthermore, some of the embodiments are described herein as a method or combination of elements of a method that can be implemented by a processor of a computer system or by other means of carrying out the function. Thus, a processor with the necessary instructions for carrying out such a method or element of a method forms a means for carrying out the method or element of a method. Furthermore, an element described herein of an apparatus embodiment is an example of a means for carrying out the function performed by the element for the purpose of carrying out the invention.

[00126] In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.

[00127] Similarly, it is to be noticed that the term coupled, when used in the claims, should not be interpreted as being limited to direct connections only. The terms "coupled" and "connected," along with their derivatives, may be used. It should be understood that these terms are not intended as synonyms for each other. Thus, the scope of the expression a device A coupled to a device B should not be limited to devices or systems wherein an output of device A is directly connected to an input of device B. It means that there exists a path between an output of A and an input of B which may be a path including other devices or means. "Coupled" may mean that two or more elements are either in direct physical or electrical contact, or that two or more elements are not in direct contact with each other but yet still co operate or interact with each other.

[00128] Thus, while there has been described what are believed to be the preferred embodiments of the invention, those skilled in the art will recognize that other and further modifications may be made thereto without departing from the spirit of the invention, and it is intended to claim all such changes and modifications as falling within the scope of the invention. For example, any formulas given above are merely representative of procedures that may be used. Functionality may be added or deleted from the block diagrams and operations may be interchanged among functional blocks. Steps may be added or deleted to methods described within the scope of the present invention.