MAGNET SYNCHRONOUS MACHINES

[0001] This relates generally to electronic circuitry, and more particularly to a method and circuitry for detecting faults in field oriented controlled (FOC) permanent magnet synchronous machines (PMSM) and drives.

BACKGROUND

[0002] Electric machines are used in a range of applications, including industrial applications, household appliances, automotive traction, pumps and fans, and aerospace applications. Most of those applications require safe and reliable operation of the machine and any associated drive system. Faults in an electric machine can occur for numerous reasons, including mechanical vibration, thermal cycling, thermal shock, manufacturing defects and improper maintenance. Detection of electric machine faults can prevent damage to the machine, the drive electronics, personnel, and other equipment.

SUMMARY

[0003] In a first example, a system includes a proportional-integral-derivative (PID) regulator. The system also includes a fault detection unit. The fault detection unit is for receiving at least two outputs from the PID regulator. The at least two outputs include at least two rotor reference frame currents (D-Q currents). The fault detection unit is also for determining a magnitude of an amplitude for each of the at least two rotor reference frame currents. The fault detection unit is further for generating a detection signal based on the at least two rotor reference frame currents. The detection signal identifies a single amplitude magnitude value based on the magnitudes of the amplitudes for each of the at least two rotor reference frame currents. The fault detection unit is for identifying an existence of a permanent magnet motor/drive fault based on a comparison between the fault detection signal magnitude value and a pre-defined threshold value.

[0004] In a second example, a fault detection unit includes a threshold detector for receiving at least two outputs from a proportional-integral-derivative (PID) regulator and for determining a magnitude of an amplitude for each of the at least two rotor reference frame currents. The at least two outputs include at least two rotor reference frame currents. The fault detection unit also includes a detection signal generation unit for generating a detection signal based on the at least two rotor reference frame currents. The detection signal identifies a single amplitude magnitude value based on the magnitudes of the amplitudes for each of the at least two rotor reference frame currents. The fault detection unit further includes a comparator for comparing the signal magnitude value with a preset threshold value to identify an existence of a permanent magnet motor fault.

[0005] In a third example, a method includes receiving at least two outputs from a proportional-integral-derivative (PID) regulator, and determining a magnitude of an amplitude for each of the at least two rotor reference frame currents. The at least two outputs include at least two rotor reference frame currents. The method also includes determining a magnitude of an amplitude for each of the at least two rotor reference frame currents. The method further includes generating a detection signal based on the at least two rotor reference frame currents. The detection signal identifies a fault based on the magnitude value of the signal for each of the at least two rotor reference frame currents. The method includes identifying an existence of a permanent magnet motor/drive fault based on a comparison between the signal amplitude value and the preset threshold value.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] FIG. 1 is an example block diagram of a system with a field oriented controlled (FOC) permanent magnet synchronous machine (PMSM) according to this disclosure.

[0007] FIG. 2 is an example block diagram of a system for detecting faults in FOC PMSM machines and drives according to this disclosure.

[0008] FIG. 3A is an example diagram of a D-Q current signature (rotor reference frame current signature) according to this disclosure.

[0009] FIG. 3B is an example diagram of a phase current signature according to this disclosure.

[0010] FIG. 4 is an example block diagram of a fault detection unit according to this disclosure.

[0011] FIG. 5 is a flow diagram of an example fault detection method according to this disclosure. DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0012] Applications of permanent magnet synchronous machines (PMSMs) are proliferating due to power density, efficiency gains, and simplicity in control algorithms. Field oriented control (FOC) is one control algorithm applied towards the control of PMSMs, due to simplicity. Some typical faults that can occur in a PMSM drive system are listed below.

Table 1: PMSM Machine Drive System Failure Modes

magnetic field. The conductor loop is induced with a voltage generating a current flow in a low resistance path. Currents beyond the rated current for the winding can circulate in the loop of the conductor, even at low speeds due to low resistance. Exceeding the rated current of the winding can cause overheating of the machine and can lead to potentially harmful circumstances. The immediate detection of a winding fault will prevent damage to the machine, the drive electronics, personnel, and other equipment.

[0014] FIG. 1 is an example block diagram of a system 100 with a field oriented controlled (FOC) permanent magnet synchronous machine (PMSM) according to this disclosure. As shown in FIG. 1, the system 100 includes a rotor reference frame current regulation scheme and I _dq to V _dq converter unit 102 (hereinafter the RC unit 102), a rotor reference frame voltage form (V _dq ) to phase voltage form (V _abcs ) transformation unit 101 (hereinafter line voltage to phase voltage transformation unit 101), a pulse-width-modulation (PWM) generation unit 108, an inverter 104, a permanent magnet motor 106, DC machine or any mechanism for loading 107 (hereinafter machine 107), and a proportional-integral-derivative (PID) regulator 103. The PID regulator 103 includes an error calculation unit 110. The system also includes a Clark and Park (CP) transformation unit 112.

[0015] The RC unit 102 receives two line current forms (I _dq ) and converts the two line current forms to two rotor reference frame voltage forms (Vd _q ). The RC unit 102 transmits the two rotor reference frame voltage forms to the unit 101. The unit 101 converts the two rotor reference frame voltage forms to a phase voltage form (V _a b _cs ). The phase voltage form is supplied to the PWM generation unit 108. The PWM generation unit 108 controls the width of the pulse, formally the pulse duration, based on modulator signal information.

[0016] The inverter 104 receives the phase voltage form from the PMW generation unit 108 and converts the direct current (DC) power into alternating current (AC) power. In this example, the inverter 104 represents a three-phase inverter that converts DC power into three-phase AC power, which is provided to the motor 106. The inverter 104 includes any suitable structure for converting power from DC form to AC form. For example, the inverter 104 could include one or more transistor switches driven using pulse width modulation (PWM) signals.

[0017] The motor 106 represents a permanent magnet motor that operates using the voltages provided by the inverter 104. The motor 106 includes a rotor with magnets embedded in or connected to the rotor. The motor 106 also includes a stator with multiple teeth around which conductive windings are wound. The windings are selectively energized and de-energized based on the signals from the inverter 104, which creates a rotating magnetic field that causes the rotor to rotate. The motor 106 drives a machine 107. The motor can drive the machine 107 with, for example, a drive shaft and one or more gears.

[0018] The system 100 further includes a proportional-integral-derivative (PID) regulator 103. In an embodiment, the PID regulator 103 is a proportional-integral (PI) regulator. The controller includes a PID regulator 103 with an error calculation unit 110 and a Clark and Park (CP) transformation unit 112. The CP transformation unit 112 receives balanced three-phase AC currents from the inverter 104 in the stator reference frame and converts the balanced three-phase AC currents in the stator frame into two currents in the rotor reference frame (I _q and Id, Q and D axis currents). The CP transformation unit 112 transmits the two line currents to the error calculation unit 110. The error calculation unit 110 adjusts the two line currents, which are subsequently fed to the RC unit 102.

[0019] The RC unit 102, the unit 101, and the PWM generation unit 108 together control the operation of the inverter 104 to thereby control the operation of the motor 106. For example, the PWM generation unit 108 generates PWM signals that drive the transistor switches in the inverter 104. By controlling the duty cycles of the PWM signals, the PWM generation unit 108 controls the three-phase voltages provided by the inverter 104 to the motor 106.

[0020] In this example, the RC unit 102 receives as input a commanded speed signal ω*, which identifies a desired speed of the motor 106. The RC unit 102 also receives as input feedback from the PID regulator 103, where the feedback identifies the estimated motor speed, rotor position, or other characteristic(s) of the motor 106. The PWM generator 108 uses the inputs to generate PWM signals for driving the transistor switches in the inverter 104.

[0021] Various components in FIG. 1 can be combined or further subdivided. For example, one or more of the components 101, 102, 104 and 108 could be incorporated into the motor 106 itself.

[0022] FIG. 2 is an example block diagram of a system 200 for detecting faults in field oriented controlled (FOC) permanent magnet synchronous machines (PMSMs) according to this disclosure. As shown in FIG. 2, the system 200 includes an RC unit 202, a rotor reference frame voltage to phase voltage transformation unit 201, a PWM generation unit 208, an inverter 204, a permanent magnet motor 206, a machine 207, and a PID regulator 203. The PID regulator 203 includes an error calculation unit 210 and a Clark and Park (CP) transformation unit 212. Each of these components of system 200 is the same as or are similar to the corresponding RC unit 102, line voltage to phase voltage transformation unit 101, PWM generation unit 108, inverter 104, permanent magnet motor 106, machine 107, and PID regulator 103 including the error calculation unit 110 and the CP transformation unit 112 of FIG. 1.

[0023] The system 200 also includes a fault detection unit 214. The fault detection unit 214 detects an existence of a fault in the permanent magnet motor 206 by executing a detection algorithm based on a rotor reference frame current signature (D-Q current signature), due to machine imbalance caused by the fault. For example, for control purposes, an electric machine is considered a balanced three phase machine. An FOC algorithm relies on a balanced machine that is controlled with a balanced set of three phase currents. When the CP transformation unit 212 is activated, balanced three phase currents in the stator reference frame transform into two DC like signals (non- sinusoidal) in the rotor reference frame. Each of the two DC signals is in a steady state after the transient period.

[0024] If a fault exists, the three phase currents will be unbalanced during steady state operation, and the CP transformation unit 212 does not produce two DC signals in the rotor reference frame that are in a steady state. In this case, an unbalanced motor has rotor reference frame currents with a sinusoidal component superimposed on the DC component. The fault detection unit 214 identifies the sinusoidal component superimposed on the DC component and determines that a fault exists, such as based on an amplitude value of the sinusoidal component.

[0025] FIG. 3A is an example diagram of a D-Q current according to this disclosure. An analogous variation is reflected on the PID controller error output and control signal output, which are being used for fault diagnostic and localization. The fault detection unit 214 detects the existence of faults. For example, as shown in FIG. 3 A, the fault detection unit 214 receives multiple D-Q current values over a period of time, producing a D-Q current signature. From the 0.48 second mark up to the 0.5 second mark, the fault detection unit 214 determines that the motor and the phase currents are balanced as the D-Q current signature is in a steady state. At the 0.5 second mark, the D-Q current signature changes from a steady state current to sinusoidal currents. The rotor reference frame PID regulator outputs are also affected by the sinusoidal currents. The fault detection unit 214 determines that the motor and the phase currents are out of balance as the D-Q current errors are not in a steady state, thus indicating the existence of a fault.

[0026] FIG. 3B is an example diagram of a phase current signature according to this disclosure. The fault detection unit 214 derives the D-Q current signature from the phase current signature, such as after the fault detection unit 214 determines the existence of a fault. The derived D-Q current signature has the same or similar phase current signature provided to the motor 206 from the inverter 204. By deriving the D-Q current signature from the phase signature, the fault detection unit 214 can identify the type of fault. For example, the derived D-Q current signature of FIG. 3A follows the phase current signature of FIG. 3B. As illustrated in Figure 3B, from the 0.48 second mark up to the 0.5 second mark, the derived phase current signature illustrates three sinusoidal current signatures (phases A, B, and C), with the same or similar amplitudes reflecting the steady state D-Q current signature within the same time frame. At the 0.5 second mark, the phase current signature changes, so that the phase B current signature has zero amplitude, while the phase A and phase C current signatures have increasing amplitudes reflecting the fault condition identified using the sinusoidal D-Q current signature of FIG. 3A.

[0027] D-Q currents and the rotor position together are used for locating fault occurrence. The rotor position can be estimated or acquired via a rotor position sensor. For example, a particular configuration or pattern of the phase current signature can identify switch failures, single leg failures, switch open failures, switch short to ground failures, and other failures. Based on the identifications of fault types, the fault detection unit 214 can determine a location of the fault. .

[0028] Also, the fault detection unit 214 uses an algorithm to detect the faulty phase. A faulty phase identification scheme is based on the phase shift induced in the function "f \ with respect to the actual rotor position due to the fault condition. The derivation is as follows assuming a fault on phase 'C.

[0029] If the actual electrical angle is known, the phase shift in the above signal 'y can be extracted. The phase shift will indicate the faulty winding/phase.

[0030] Various components in FIG. 2 can be combined or further subdivided. For example, one or more of the components 201, 202, 204 and 208 could be incorporated into the motor 206 itself.

[0031] FIG. 4 is an example block diagram of a fault detection unit 414 according to this disclosure. The design details of the fault detection unit 414 could be incorporated into the fault detection unit 214 in the system 200 of FIG. 2. Of course, these design details could be incorporated into other fault detection units operating in other systems. As shown in FIG. 4, the fault detection unit 414 includes a threshold detector 416, a detection signal generation unit 418, a comparator 420, a fault counter 422, and detection threshold storage unit 424.

[0032] The threshold detector 416 receives at least two outputs from a proportional-integral- derivative (PID) regulator (such as PID regulator 203 of FIG. 2). The at least two outputs include at least two rotor reference frame D-Q current signatures. The threshold detector 416 determines a magnitude of an amplitude for each of the at least two rotor reference frame D-Q currents to enable the fault detection circuit. For example, when the motor 206 is balanced, the threshold detector 416 will determine that the magnitude of the each of the at least two rotor reference frame D-Q currents is a value equal to zero or close to zero, as the rotor reference frame currents are in steady state. When the motor 206 is not balanced, the threshold detector 416 will determine that the magnitude of the amplitude for each of the at least two rotor reference frame D-Q currents is a value significantly greater than zero, as the rotor reference frame currents are not in a steady state. After the at least two rotor reference frame D-Q current signatures pass through the threshold detector 416, the at least two rotor reference frame D-Q current signatures are received by the detection signal generation unit 418.

[0033] The detection signal generation unit 418 receives the at least two rotor reference frame D-Q current signatures and generates a detection signal based on the at least two rotor reference frame D-Q current signatures. Accordingly, the detection signal is a single signal that is a combination of the D current signature and the Q current signature. The detection signal identifies a single amplitude magnitude value from a single signal, based on the magnitudes of the amplitudes for each of the at least two rotor reference frame D-Q current signatures. The detection signal generation unit 418 calculates the single amplitude magnitude value to provide an accurate amplitude magnitude value. The detection signal generation unit 418 can generate a detection signal using the following equation:

[0034] After the detection signal generation unit 418 generates the detection signal, the detection signal generation unit 418 transmits the detection signal to the comparator 420.

[0035] The comparator 420 receives the detection signal and compares the single amplitude magnitude value of the detection signal with an amplitude threshold value to identify an existence of a permanent magnet motor fault. For example, if the single amplitude magnitude value is greater than the amplitude threshold, then a fault exists. The detection threshold storage unit 424 stores the amplitude threshold value and provides the amplitude threshold value to the comparator 420 for signal comparisons.

[0036] The fault detection unit 414 also includes a fault counter 422. The fault counter 422 verifies that a fault exists. For example, after determining that a first fault exists, the fault counter 422 counts the number of subsequent fault signal threshold crossings that are detected at the comparator 420. When the fault counter 422 detects a predetermined quantity of subsequent faults, the fault counter 422 verifies that the fault exists. The fault counter 422 can verify that a fault exists after detecting at least one subsequent fault. The fault counter 422 can verify that a fault exists after a predetermined quantity of faults is detected within a predetermined period of time. The fault counter 422 can verify that a fault exists when a predetermined quantity of consecutive faults signal threshold crossings are detected within a predetermined period of time. The fault counter 422 can verify that a fault exists when a percentage of faults versus non-faults are detected within a predetermined period of time.

[0037] FIG. 5 is a flow diagram of an example fault detection method 500 according to this disclosure. At step 502, a fault detection unit 414 receives at least two outputs or output streams from a proportional-integral-derivative (PID) regulator. The at least two outputs include at least two rotor reference frame currents or current signatures. At step 504, the fault detection unit 414 determines a magnitude of an amplitude of each of the at least two rotor reference frame currents. At step 506, the fault detection unit 414 generates a detection signal based on the at least two rotor reference frame currents. The detection signal identifies a single amplitude magnitude value based on the magnitudes of the amplitudes for each of the at least two rotor reference frame currents. At step 508, the fault detection unit 414 identifies the existence of a fault, based on a comparison between the single amplitude magnitude value and an amplitude threshold value. For example, the fault detection unit 414 can compare the single amplitude magnitude value with an amplitude threshold value and determine if a fault exists based on the comparison. At step 510, the fault detection unit 414 verifies the existence of the permanent magnet motor fault by comparing a predetermined quantity of subsequent single amplitude magnitude values with the amplitude threshold value.

[0038] Although FIG. 5 illustrates a series of steps, various steps in each figure could overlap, occur in parallel, occur in a different order, or occur any number of times. Also, one or more of the steps of the method 500 could be removed, or other steps could be added to the method 500. The method 500 is described as being performed by the fault detection unit 414, but the method 500 could be performed by any other suitable unit, device, or system.

[0039] In some embodiments, various functions described above are implemented or supported by a computer program that is formed from computer readable program code and that is embodied in a computer readable medium. The phrase "computer readable program code" includes any type of computer code, including source code, object code, and executable code. The phrase "computer readable medium" includes any type of medium capable of being accessed by a computer, such as read only memory (ROM), random access memory (RAM), a hard disk drive, a compact disc (CD), a digital video disc (DVD), or any other type of memory. A "non-transitory" computer readable medium excludes wired, wireless, optical, or other communication links that transport transitory electrical or other signals. A non-transitory computer readable medium includes media where data can be permanently stored and media where data can be stored and later overwritten, such as a rewritable optical disc or an erasable memory device.

[0040] The terms "application" and "program" herein refer to one or more computer programs, software components, sets of instructions, procedures, functions, objects, classes, instances, related data, or a portion thereof adapted for implementation in a suitable computer code (including source code, object code, or executable code).

[0041] Modifications are possible in the described embodiments, and other embodiments are possible, within the scope of the claims.