BRUSHLESS DC ELECTRIC MOTOR OR GENERATOR

STATE OF THE ART

In the past years there have been a considerable development of high performances BrushLess Direct Current (BLDC) machines, motors and generators, thanks to improved permanent magnets and sensor, or sensorless, control system. Most of them have external rotor and magnetic flux in the radial direction but axial flux motors are also becoming more and more common and there are oblique flux machines as well. There are also types of machines which use electromagnets, instead of permanent magnets, even on the rotor.

Many of these are 3-phase machines. The control and power electronics is usually not integrated in the machine. Often the manufacturer offers only the engine and the electronics must be purchased from a different supplier. It often happens that the electronic system is not optimally matched to the engine. It also requires the customer to have a good technical knowledge to use the engine and to connect and configure the control electronic. ^¾

OBJECTS AND SUMMARY OF THE INVENTION

Aim of the present invention is to provide a BLDC rotation machine, motor or generator, which overcomes some drawbacks of the prior art.

In particular, aim of the present invention is to provide an innovative electrical configuration and integrated control system for BLDC machines in order to achieve high power to weight ratio, compactness and simplicity. The presented configuration is explained in relation to an axial- flux BLDC motor, but it is not limited to it. This configuration can be also applied to other machines like radial-flux BLDC machines or oblique-flux BLDC machines.

These and other aims are reached by means of a machine which is provided with the features of the appended claims, which are integral part of the present description. The basic idea of the present invention is to provide a BLDC machine, motor or generator, which includes one or more rotor elements mounted on bearings and that can rotate around a rotation axis, each of them with a number of magnets and with ferromagnetic support material which may also include halbach array, a stator with a different number of electromagnets whose winding terminations are electrically connected, with proper electrical junctions, one to the other in series to form a closed loop electrical circuit. The number of magnets, in each rotor element, and the number of electromagnets in the stator can differ by one, two or more to provide the shift of the magnets-electromagnets positions, but shall not be same number. In the axial flux motors or generators the electromagnets are circularly positioned, with core axes parallel to the motor rotating axis.

In this invention the stator is provided with two closed loop electrical buses, one connected to the positive (+) dc power supply (positive bus) and the other to the negative (-) dc power supply (negative bus) . These two electrical buses are also electrically connected, through controllable switching transistors integrated into the stator, to all the junctions between any two electromagnets windings. The machine comprises a sensor system to provide the angular position of the rotor with respect to the stator. The flow and versus of the current in the winding of each electromagnet depends on the status of these switching transistors. According to the control principle chosen, some of these switching transistors may be enabled to change from off to on and viceversa at certain angular positions of the rotor with respect to the stator. Different control principles may be chosen to provide the wanted torque and rotation speed. Some of these control principles will be described in the following detailed description of the invention. With some type of control all electromagnets may be switched on at the same time for higher torque density. This will allow a high degree of flexibility.

By using these configurations of electromagnets and switching transistors the frequency of electromagnets polarity inversion is reduced leading to better efficiency.

The electrical connections of all windings in closed loop circuit within the stator provides very short electrical connections between two adjacent electromagnets and reduce losses. Moreover by integrating the switching transistors into the stator, close to the electromagnets, the electrical losses are reduced and the elec ^¬ trical machine configuration is more compact and easy to accommodate. With the electrical machine configuration including a stator and the related electromagnets (windings with ferromagnetic rods) between two disc rotors comprising magnets the magnetic circuits are short and the magnetic losses minimized.

A further advantage of the proposed configuration is the simplicity to connect back up motors or generators in redundant systems. This because there is a very low resistance torque when the rotor (s) turns and the coils are off with all switches off (open) . Also the torque ripple is less than in other machines and this reduces the losses and improve the efficiency .

Our innovative configuration apply to machines which includes electromagnets, instead of permanent magnets, even on the rotor.

It is also possible to further expand the proposed configuration by adding switching transistors between any electromagnet winding termination and the junction. This would add further flexibility but will impact on high torque control strategies because these added switching transistors will be on most of the time and will increase heating.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in the following with reference to not limiting examples provided as explanatory purpose and not limitative of the appended drawings. These drawings show few aspects and embodiments of the present invention and, where appropriate, reference numbers showing structures, components, materials and/or elements similar throughout the different figures are indicated with the same reference number.

Fig.l is ^' a perspective exploded view of the stator and 2 rotors of an axial flux BLDC machine constructed and arranged in accordance with the principle of the invention Fig.2 is a front view of the stator of an axial flux BLDC machine constructed and arranged in accordance with the principle of the invention

Fig.3 shows a particular of the electromagnet basic configuration constructed and arranged in accordance with the principle of the invention

Fig.4 is an electrical configuration scheme of the stator electromagnets showing power buses and switching transistors electrical connections constructed and arranged in accordance with the principle of the invention

Fig.5 shows a possible electromagnets switching activation sequence for motor control based on "control principle 1" scheme in accordance with the principle of the invention

Fig.6 shows a possible electromagnets switching activation sequence for motor control based on "control principle 2" scheme in accordance with the principle of the invention

Fig.7 shows a possible electromagnets switching activation sequence for motor control based on "control principle 3" scheme in accordance with the principle of the invention

Fig.8 shows a possible electromagnets switching activation sequence for motor control based on "control principle 4" scheme in accordance with the principle of the invention

DETAILED DESCRIPTION OF THE INVENTION

While the invention is susceptible of many modifications and alternative constructions, some preferred embodiments thereof are shown in the drawings and will be described in detail in the following. However, it is to be intended that the present invention is not limited to the shown embodiment, but on the contrary, the invention is intended to cover all the modifications, alternative constructions and equivalents in the scope of the invention as claimed. The word or phrase "for example", "etc.", "or" indicates not exclusive alternatives without limitation, unless otherwise stated. The word "comprises" means "comprises but not limited to", unless otherwise stated and the word "includes" means "includes but not limited to", unless oth ^¬ erwise stated.

The word "machine" is intended to comprise both motor and generator.

The word "magnet" when used without "permanent" or "electro" is intended to comprise either permanent magnets or electromagnets.

The words "motor" or "generator" are intended to comprise any electrical motor or generator.

The word "brushless DC rotation machine" is intended to refer to sub ^¬ stantially to any electrical machine working with DC power supply and with electrical circuit electronic switching which includes BLDC motors and generators.

In general, disclosed herein is a machine, motor or generator, which in ^¬ cludes a rotor, a stator with a number of electromagnets, a sensor sys ^¬ tem to provide the angular position of the rotor with respect to the stator and a control system to activate/deactivate the electromagnets at certain angular position of the rotor. The electromagnets are disposed circularly around the rotation axis and their electrical winding termi ^¬ nations are electrically connected within the stator, with proper junc ^¬ tions, one to the other in series, to form a closed loop circuit. The stator includes two closed loop electrical buses, one connected to the positive ( + ) DC power supply connection (positive bus) and one to the negative (-) DC power supply connection (negative bus) . These two elec ^¬ trical buses are also connected, via controllable switching transistors integrated into the stator, to the electromagnets junctions.

The following discussion is in respect of an axial flux machine but this should not be understood to be limiting in any sense and the invention applies to radial flux or oblique flux machines as well.

Like reference characters indicate corresponding elements throughout several figures.

Fig.l is a perspective exploded view of an axial flux brushless DC ro ^¬ tation machine 1 (motor/generator) constructed and arranged in accordance with the principle of the invention, which, in this case, includes a stator 3 with a number of electromagnets 30 and two mechanical connected rotor elements 2A and 2B with a rotation axis parallel to Z axis, each of them with a number of magnets 21. The figure shows also the components of each rotor element, i.e. the back iron 22, the magnets 21 and the support structure 23. The magnets 21 of the rotor may either be permanent magnets or electromagnets or a combination of them. In the example figure shown there is a difference of two between the number of mag ^¬ nets 21 in each of the rotor element and the number of electromagnets 30 of the stator, but in general this difference might be one, two, three or more. The number of electromagnets 30 of the stator may be higher than the number of magnets 21 of each rotor element and viceversa.

The electromagnets 30 are circularly positioned as indicated in Fig.2 and their winding terminations are electrically connected, with proper junctions 31, one to the other in series to form a closed loop electrical circuit. In the example of axial flux machine, the electromagnets core axes 301 are parallel to the motor rotating axis 11. A s shown in Fig.3 electromagnets 30 include windings 302 and ferromagnetic core 303 and shoes 304 comprising laminated ferromagnetic material. The electrical conductors in the windings can be of circular, square or rectangular cross section and can also be tape conductors. These conductors may include copper or aluminum or other conductors.

As shown in Fig.4, which is the electrical scheme of the stator according to the invention, the stator is also provided with two closed loop electrical buses, one indicated with 41 electrically connected to the positive (+) dc power supply and the other, indicated with 42, electrically connected to the negative (-) DC power supply. As shown in the Fig.4 all the junctions 31 between any two electromagnets windings 302 terminations are electrically connected through controllable switching transistors 5 to the two electrical buses 41 and 42. In particular the switching transistors between the positive (+) bus 41 and the junctions 31 are indicated with TH (Transistor High) and the switching transistors between the negative (-) bus 42 and the junctions 31 are indicated with TL (Transistor Low) . Even if not indicated in the figures redundant transistors 5 may be used in the circuit for higher reliability. In the electrical configuration scheme of Fig.4, shown as example, there are twelve electromagnets 30 and twelve junctions 31.

The machine may be assembled with the winding of each electromagnet in the same versus (clockwise or counter clockwise) or it may be assembled with alternate versus of the windings in any adjacent electromagnet. This would allow, when the current flows in one versus, in the first case to have same polarity on the adjacent electromagnets and in the second case to have different polarities on the adjacent electromagnets. With the proposed invention, moreover, the current on each electromagnet may flow in one versus or the other depending on the status of the switching transistors.

The machine comprises a sensor system to provide the angular position of the rotor elements 2A and 2B with respect to the stator 3. For sensor system we intend a system which includes also the so called sensorless system where the system senses back EMF or make use of incremental position encoder or hall sensors. The flow and versus of the current in the windings 302 of each electromagnet 30 depends on the status of these switching transistors 5. According to the control principle chosen, some of these switching transistors 5 ^' may be enabled to change from off to on and viceversa at certain angular positions of the rotor 2 with respect to the stator 3. Different control principles may be chosen to provide the wanted ^■ torque and rotation speed and all electromagnets 30 may be switched on at the same time for higher torque density.

One control principle, which we will call Control Principle 1 is for a configuration in which the electromagnets windings are winded with opposite versus one from the adjacent two. In this control principle only two transistor switches 5 are switched on at any time and position: one transistor between the junction 31 and the positive bus 41 and one transistor between the diametrically opposed junction 31 and the negative bus 42.

To make the specific example of the Fig. 5 with a stator of twelve electromagnets and a two rotor elements of ten permanent magnets each, at a certain angular position of the rotor, indicated in the figure with Step 1, 0° of rotation, the TH1(+ ) switch is switched on (closed) and also the TL7(-) switch is switched on (closed). All the other switches are switched off (open). Looking also at the electrical scheme A of Fig.5, the current then flows through the windings L1,L2,L3,L4,L5 and L6 on the right side and through L12 , Lll , L10 , L9, L8 and L7 on the left side. Since the electromagnets are assembled with alternate winding versus and because of the current flows versus (clockwise on the right side and counterclockwise on the left side) then electromagnets L1,L3,L5 as well as L12,L10,L8 have one polarity while the remaining electromagnets have opposite polarity. In this way all the powered electromagnets interact with the facing permanent magnets of the two rotors giving rise to all counterclockwise rotation torques on the rotors.

Step 2 of Fig. 5 shows a 3° rotation of the rotor 2 as a consequence of the magnetic field generated by the switching selection. As can be seen at Step 2, 3° of rotation, there are still concurring counter clockwise torques contribute from the interaction of each stator electromagnets with rotor magnets and this contribution lasts until a rotation in counterclockwise direction of 6° is achieved i.e. Step 3 of Fig.5. At this point the TH1 and TL7 are switched off (open) . At the same time, as indicated in Step 4 and in the electrical scheme B of Fig.5, TH2( + ) and the opposite TL8 (-) are switched on (closed) . In this example the rotation angle of 6° comes from the number of electromagnets of the stator and the number of magnets in the rotor. This angle can be calculated as follows :

□ Stator segment angle: 360° / 12 electromagnets = 30°

□ Rotor segment angle: 360° / 10 Magnets = 36°

□ Difference: 36° - 30° = 6°

Step 5 of Fig.5 indicates a further rotation of 3°, overall 9° of rotor rotation from Step 1, where there are still concurring counter clockwise torques contribute from each rotor magnet as indicated in the figure and this contribution lasts until a total rotation in counterclockwise di ^¬ rection of 12° is achieved, i.e. Step 6 of the figure. At this point TH2( + ) and TL8(-) are switched off (open) and TH3(+ ) and the opposite TL9(-) would then switched on (closed) and so on every 6° the following couple of switch on (+ ) bus and the opposite switch on the (-) bus are on up to a whole revolution of the. magnetic field rotation is completed. The full turn of the magnetic field rotation is for this example: 12 coils x 6° =72° (for mechanical rotation) . That means that full mechanical rotation of the rotor (360°) will occur after 5 magnetic field rota ^¬ tions: (360°/72°= 5.

It must be pointed out with these sequence there is a change of current direction in any electromagnets when the electrical field has completed a rotation angle of 36° (72°/2 = 36°) . The required rotor rotation an- gle to determine the switches turn On and Off actually depends on the number of electromagnets and magnets.

In the Control Principle 1 one can notice that for a counter clockwise rotation versus of the rotor the switches on the stator are progressively activated or deactivated in clock wise versus. If the wanted rotation of the rotor is in clockwise versus, the switches on the stator should be activated and deactivated in counter clockwise versus and the same apply to all the other following control principles described hereafter.

A second control principle, which we will call Control Principle 2 is again for a configuration in which the electromagnets windings are winded with opposite versus one from the adjacent two. To make the specific example of the Fig.6 with a stator of twelve electromagnets and a two rotor elements of ten permanent magnets each, at a certain angular position of the rotor, indicated in the Fig.6 with Step 1, 0° of rotation, a couple of adjacent switches connected to the positive power bus-, i.e. TH1 and TH2, are switched on (closed) at the same time together with the diametrically opposed couple of switches connected to the negative bus, i.e. TL7 and TL8. All the other switches are switched off (open). Looking also at the electrical scheme A of Fig.6, the current then flows through the electromagnets L2,L3,L4,L5 and L6 on the right side and through electromagnets L12 , Ll 1 , L10, L9, and L8 on the left side.

After the rotor rotation in counterclockwise direction of 6°, shown as Step 3 and Step 4 of Fig.6, the TH1+ and TL7 are switched off (open) and TH3+ and the opposite TL9- are switched on while TH2+ and TL8- continue to remain on as it is also indicated in the electrical scheme B of Fig.6. After another 6° of rotation, indicated as Step 6 in Fig.6 (overall 12° of rotor rotation from Step 1), TH2+ and TL8- are switched off (open) and TH4+ and the opposite TL10- are switched on (closed) and so on every 6°the following couple of switch on (+ ) bus and the opposite switch on the (-) bus are on up to a whole revolution of the magnetic field is completed.

The advantage of the principle 2 in comparison to principle 1 is that the current load for transistors switch is much smaller (i.e. the half).

The disadvantage of the principle 2 with respect to principle 1 is that it is less efficient for torque level provision because not all the coils are working at the same time and two coils are always switched off.

A third control principle, which we will call Control Principle 3 is for a configuration in which the electromagnets windings are winded all with the same. ersus. To make the specific example of the Fig. 7 with a sta- tor of twelve electromagnets and a two rotor elements of ten permanent magnets each, at a certain angular position of the rotor, indicated in the Fig.7 with Step 1, 0°of rotation, TH1, TH3, TH5, TH8 and TH10 are switched on (closed) at the same time together with TL2 , TL4, TL7, TL9 and TL11. All the other switches are switched off (open). As it is also indicated in the electrical scheme A of Fig.7, the current then flows through the electromagnets Ll, L3, L5, L6, L8 and L10 in clockwise versus and through electromagnets L12 , Lll , L9, L7 , L4 and L2 in counter clock versus. After the rotor rotation in counterclockwise direction of 6°, shown as Step 3 and Step 4 of Fig.7, the TH1, TH3, TH5, TH8 and TH10 and TL2, TL4, TL7, TL9 and TL11 are switched off (open) and TH2, TH4, TH6, TH9 and TH11 are switched on (closed) at the same time together with TL3, TL5, TL8, TL10 and TL12 and this is also indicated in the electrical scheme B of Fig.7. After another 6°of rotation, indicated as Step 6 in Fig.7 (overall 12°of rotor rotation from Step 1), the TH2, TH4, TH6, TH9 and TH11 and TL3, TL5, TL8 , TL10 and TL12 are switched off (open) and the following adjacent switching in clockwise direction are switched on (closed) and so on up to a whole revolution of the magnetic field is completed and then the switching sequence start again.

A fourth control principle, which we will call Control Principle 4 is for a configuration in which the electromagnets windings are winded all with the same versus. To make the specific example of the Fig. 8 with a stator of twelve electromagnets and a two rotor elements of ten permanent magnets each, at a certain angular position of the rotor, indicated in the Fig.8 with Step 1, 0° of rotation, TH1, TH3, TH5, TH8, TH10 and TH12 are switched on (closed) at the same time together with TL2, TL4, TL6, TL7, TL9 and TL11. All the other switches are switched off (open). As it is also indicated in the electrical scheme A of Fig.8, the current then flows through the electromagnets L1,L3,L5,L8 and L10 in clockwise versus and through electromagnets L11,L9,L7,L4 and L2 in counter clock versus. Electromagnets L12 and L6 do not work in this phase. After the rotor rotation in counterclockwise direction of 6°, shown as Step 3 and Step 4 of Fig.8, the TH3, TH5, TH8 , TH10 and TH12 and TL2, TL4, TL6, TL9 and TL11 are switched off (open) and TH2, TH4, TH6, TH9 and TH11 are switched on (closed) at the same time together with TL3 , TL5, TL8, TL10 and TL12 and this is also indicated in the electrical scheme B of Fig.8. In this page the electric current flows through the electromagnets L2 , L4 , L6, L9, Lll in clockwise versus and through the electromagnets L3,L5,L8, L10,L12 in counter clock versus while electromagnets LI and L7 do not work. After another 6° of rotation, indicated as Step 6 in Fig.7 (overall 12° of rotor rotation from Step 1) the switches which were on are switched off and the following adjacent switching, in clockwise versus, to these ones are switched on (closed) and so on up to a whole revolution of the magnetic field is completed and then the switching sequence start again.

The control principle 3 and 4 require higher on/off switching cycles with respect to control principles 1 and 2 but the electric current level flowing through the electromagnets is lower and this can be an advantage for the selection of the switching transistors and to limit ohm- ic dissipation and thermal load.