High performance brushless motor and drive for an electrical vehicle motorization

[0001] This application is a continuation-in-part of U.S. application Ser. No. 09/937,936 filed Feb. 1, 2002 by Applicant now U.S. Pat. No. 6,630,764, which is a 371 of PCT/CA99/00290 filed Apr. 1, 1999.

[0002] The present invention relates to a low cost electric system composed of a new DC brushless permanent magnet motor and its electronic drive which provides high efficiency operation and low torque ripple for the motorization of electric vehicles like, bicycles, rolling chairs, scooters, tricycles, golf cars, trolleys and small utility vehicles.

[0003] The motor and its electronic system are supplied by one or several batteries. The vehicle wheel drive can be direct to maximize efficiency or equipped with a speed reducer to minimize the motor size. The proposed solution uses a permanent magnet three-phase motor which can reach four times the nominal torque. This motor structure includes an outer rotor which can be fitted into a vehicle wheel. It can be used as motor or generator with energy recuperation in the battery during braking periods or to create electricity to recharge battery, or power other devices by changing the motor. This motor structure is supplied by a PWM (Pulse Width Modulation) current controlled inverter. The operator can impose the machine torque level in motor or generator operation by setting a current reference. The shape of the alternative phase current waveform is rectangular with a width of 120 electrical degrees. This kind of motor supply is the simplest to realize and it reduces the cost of the control system and the number of sensors.

[0004] The brushless motor includes a cylindrical outer rotor wherein permanent magnets are mounted on the surface and an internal stator with coils of insulated wire wound around the teeth. There are twenty-two magnet poles on the rotor alternatively magnetized north and south and twenty-four slots on the stator. This combination of slots and poles for a three-phase motor structure allows the realization of a special concentrated winding around the teeth with only one coil per slot. In this case, there are only twelve coils to realize. The winding coefficient and the copper filling factor are higher than in the other known solutions described by Konecny U.S. Pat. No. 4,774,428, Huang and al. U.S. Pat. No. 5,675,196 and Katsuma and al. U.S. Pat. No. 4,719,378 which are using winding with two coils per slot.

[0005] This kind of winding with one coil per slot simplifies the assembling of the rotor position sensors (i.e. hall detectors) near the air gap. The hall detector are fixed on the side of several teeth which have no winding and they are using the leakage flux of the permanent magnets to detect the rotor position.

[0006] The proposed structure maximizes the energy efficiency and the motor starting torque per unit volume of winding. The advantages of a concentrated winding around the teeth in comparison with a classical distributed winding are described in Konecny U.S. Pat. No. 4,774,428 and Permanent magnet brushless DC motor with soft metal powder for automotive application by J. Cros and P. Viarouge published in the IEEE Industry applications Society in October 1998. The volume of copper is reduced and subsequently the Joule losses are minimized.

[0007] The amount of vibrations and the cogging torque ripple are reduced drastically like in the other structure combinations described by Konecny U.S. Pat. No. 4,774,428, Huang and al. U.S. Pat. No. 5,675,196 and Katsuma and al. U.S. Pat. No. 4,719,378. The least common multiple (LCM) of the motor's poles and slots describes how many peaks of cogging torque will be present over a single revolution of the motor. In this case, there are 264 torque pulses per revolution and consequently, the cogging torque amplitude is very low (less than 3% of the rated torque).

[0008] The proposed motor structure also minimizes the net radial force like another structure described by Huang and al. U.S. Pat. No. 5,675,196.

[0009] Reference is made to British Patent GB 2 289 991 which discloses a winding sequence for a motor having twelve slots and ten poles. It is described in that Patent the use of a structure and a specific winding sequence wherein one winding per slot is provided to obtain independent magnetic flux flow for each phase.

[0010] Japanese Patent A-400 4703 relates to an electric bicycle most specifically to a system capable of detecting the direction of rotation of the rotor as well as its speed by the use of an optical sensor whereby to control the amplitude of the current in the motor.

[0011] The electronic supply includes a power electronics supply and a current control electronics circuit. Both systems can be inserted inside the motor housing, in the center of the stator yoke. The power electronics system is composed of an inverter with six MOSFETs or multiple MOSFETs which operate like six MOSFETs. The structure diodes of the MOSFETs are used to ensure the current reversibility. At each sequence of conduction defined by the rotor position detector, two transistors are switched on to supply two motor phases. In the classical mode of operation, a modulation signal is applied on the gate of these two transistors. This method simplifies the control realization and only one current sensor can be inserted in the DC bus for the current measurement.

[0012] Another solution consists in applying the modulation signal on one transistor only at each sequence of operation: this method is the single switch modulation technique. The other transistor is switched “on” during all the duration of this sequence of conduction. This mode of operation is described in E.M.I. tests on a brushless actuator: Comparison by M. Lajoie-Mazene and J. P. Berry published in European Power Electronics in September 1993, in the case of monitoring operation only, compared to the classical mode of operation where the modulation signal is applied on the gate of the two transistors. It is shown that the single switch modulation provides lower electromagnetic interferences (EMI) and reduces the commutation losses, the conduction losses in low voltage applications, the current ripple and the size of the input filtering capacitor. The proposed electronic system is using the single switch modulation and it can be used for motor as well as generator operation. Consequently, the current regulation is realized without any external current sensor.

[0013] Another article of interest is the Synthesis of high performance PM motors with concentrated windings by J. Cros and P. Viarouge published in the IEEE Transactions on Energy Conversion in June 2002. It explains a method for determining a winding for a concentrated winding motor.

[0014] It is a feature of the present invention to provide a high performance brushless DC permanent magnet motor and a pulse width modulation electronic inverter for the motorization of electric vehicles supplied with electrical batteries. The motor structure includes an outer rotor which can be fitted to a vehicle wheel. It can be used as a motor or as a generator with recuperation of kinetic energy in the batteries during braking periods.

[0015] Another feature of the invention is to provide a special design and the design of its three-phase winding maximize the energy efficiency and the motor starting torque per unit volume of winding. A concentrated winding is wound around the teeth with only one coil per slot. This solution simplifies the winding realization and maximizes the winding coefficient and the copper filling factor.

[0016] Another feature of the invention is that the assembling of the rotor position sensor (i.e. hall detectors) near the air gap is simplified by the winding configuration. The hall detector are fixed on the side of several teeth which have no winding and they are using the leakage flux of the permanent magnets to detect the rotor position. The amount of vibrations, the cogging torque ripple and the radial force are greatly reduced.

[0017] Another feature of the invention is to provide specific inverter control system which reduces the commutation losses, the diode conduction losses in low voltage applications, the current ripple, the size of the input filtering capacitor and electromagnetic interference. A specific single switch modulation technique is used: The modulation signal is applied only on one transistor at each sequence of operation defined by the rotor position detector. The other transistor is switched on during all the duration of this sequence of conduction. This single switch modulation method maximizes the efficiency of the electronic supply and the current regulation is realized without any external current sensor.

[0018] According to the above features, from a broad aspect, the present invention provides a brushless DC motor for electrical vehicle motorization. The motor comprises a cylindrical rotor with 22 poles constructed with segments of permanent magnet material alternatively magnetized north and south. A stator core of ferromagnetic material is spaced inwardly of the rotor and defines a magnetic clearance gap therebetween. The stator core has twenty four slots and define teeth between the slots. A three-phase winding with coils of insulated wire is wound around the teeth. There is provided two coils per slot having predetermined connection patterns C, C′, C, C′, B′, B, B′, A′, A, A′, A, A′, C′, C, C′, B′, B, B′, B, B′, A′, A, A′, C′.

[0019] According to a still further broad aspect of the present invention there is provided a brushless DC motor electronic pulse with modulation driver and control system. It includes a power electronic three phase inverter having six power of MOSFETs. A current control system is coupled to the inverter for generating a 120 electrical degrees rectangular phase current pulses. An electronic control system is provided for both motor and a generator operation mode of the motor and uses a single switch modulation technique.

[0020] According to a still further broad aspect of the present invention there is provided a brushless DC motor for breaking a wheel of devices on which people are displaced by self-motorization or electric motor motorization. The motor comprises a cylindrical rotor with twenty two poles constructed with segments of permanent magnet material alternatively magnetized north and south, a stator core of ferromagnetic material spaced inwardly of said rotor and defining a magnetic clearance gap, therebetween said stator core having twenty-four slots and defining teeth between said slots, a three phase winding with coils of insulated wire being wound around the teeth. The rotor is connected to a hub of the wheel. Control circuit means is provided to control the torque of the motor and therefore its arresting force.

[0037] In electrical vehicle applications, it is necessary to produce high starting torque and to ensure variable speed in both motor and generator modes of operation. The use of a brushless DC motor is particularly well adapted to this kind of applications. To reduce the cost of the electronic system and the number of sensors, it is better to supply the motor winding phases with a rectangular waveform current. The motor torque is controlled by a simple current regulation and the phase voltage is chopped with a pulse width modulation technique (PWM). The schematic diagram of this kind of brushless DC motor is presented on FIG. 1. It includes a permanent magnet motor 10, a power electronic supply 11, a rotor position detector 12, a current measurement system 13 and a current regulation system which is comprised of a current control circuit 14 fed by the current measuring circuit 13 and a torque reference or current reference circuit 16. The current control circuit 14 is connected to the power electric supply circuit 11 to control the torque of the motor 10. The system can be used for motor or generator operation with energy recuperation on the battery 15 during braking periods.

[0038] As shown in FIG. 2, the proposed solution in the present invention is to use a motor 10 structure having a twenty-two poles and twenty-four slots 18 with a cylindrical outer rotor 19. Permanent magnets 20 are mounted on the rotor inner surface 21 and alternatively magnetized north and south. The high number of poles reduces the iron volume and provides acceptable iron losses when the speed is less than 1,000 rpm.

[0039] As shown in FIG. 3, a concentrated winding 22 is wound around the teeth 23. The advantages of a concentrated winding around the teeth in comparison with a classical distributed winding are described in Konecny U.S. Pat. No. 4,774,428 and the article reference E.M.I. tests on a brushless actuator: Comparison of different operation modes by J. Cros, S. Astier, J. M. Vinassa, M. Lajoie-Mazenc and J. P Berry published in European Power Electronics in September 1993. The volume of copper is reduced and subsequently the Joule losses are minimized. The energy efficiency and the motor starting torque per unit volume of winding are maximized.

[0040] In the embodiment shown in FIG. 2 and FIG. 3, an additional two coils (7) per slot (18) are shown with predetermined connection patterns as follows: C, C′, C, C′, B′, B, B′, A′, A, A′, A, A′, C′, C, C′, B′, B, B′, B, B′, A′, A, A′, C′, wherein an apostrophe after a letter represents a counterclockwise winding direction and a letter without an apostrophe represents a clockwise winding direction and wherein each letter represents one phase of the motor. This results in reduced torque ripple without any slot or magnet skewing. This connection pattern is referred to as a “5-3 pattern”. A mutual inductance between the phases of the stator has a value which corresponds to roughly one half of the value of the inductance of each phase.

[0041] A winding configuration with two coils per slots is presented on FIG. 3 and it can be used for the proposed motor structure (winding coefficient: 0.941). As shown in FIG. 4, Hall sensors or detectors 24 are placed to position the phase current and the phase electromagnetic force (back emf) waveforms like in FIGS. 7 & 8. The maximum value of the torque to current ratio is then obtained with this configuration.

[0042] The cogging torque ripple are greatly reduced without any slot skewing, as in the other structure combinations described by Konecny U.S. Pat. No. 4,774,428, Huang and al. U.S. Pat. No. 5,675,196 and Katsuma and al. U.S. Pat. No. 4,719,378. The least common multiple (LCM) of the motor's poles and slots describes how many peaks of cogging torque will be present over a single revolution of the motor. In this case, there are 264 torque pulses per revolution and consequently, the cogging torque amplitude is very low (less than 3% of the rated torque). The proposed motor structure also minimizes the net radial force like another structure described by Huang and al. U.S. Pat. No. 5,675,196.

[0043] Referring now to FIG. 5 there is shown the electronic supply which includes a power electronics system and a low power control electronics system. Both systems can be inserted in the cavity 26 inside the motor housing, in the center if the stator yoke 27. The power electronics system is a six switches, PWM (pulse width modulation) inverter 26. Six type N MOSFETs 28 (T1, T2, T3, T′1, T′2, T′3) are used and the structure diodes of the MOSFETs 29 are used to ensure the current reversibility. The electronic system also includes a push-pull driver 30 for each MOSFET, three boostrap supplies 31 feed the driver stages of the three transistors T′1, T′2, T′3 of the upper side of the inverter 28 and three level-shift control signals are applied to the driver stages of transistor T′1, T′2, T′3.

[0044] A current regulation circuit 32 generates a PWM signal at each transistor control signal. The voltages of the power MOSFETs 29′ T1, T2, T3 on the lower side 28′ of the inverter 28 are used to measure the motor currents. The rotor position sensors 24 define the conduction sequence order and are also used to select the voltage of the power MOSFET 29 in conduction to be sensed by means of a multiplexer 33 with 3 inputs 33′ and 1 output 33″. The multiplexer 33 is used to generate a signal equivalent to the motor current, which can be used in the current regulation loop. The operator can select the operation mode of the system (motor or generator operation mode) and the current reference level to impose the torque of the machine.

[0045] FIG. 6 presents the chronogram 37 of the conduction sequences of the power MOSFETs 29. At each time, there are only tow MOSFETs switched on. There are six sequences of operation in an electric period . During each sequence two phases of the machine are supplied. There are six current commutations when the rotor rotates with an angle of 32.7 degrees. The commutation process is controlled by the rotor position detectors 24 (i.e. Hall sensors).

[0046] FIG. 7 shows the rectangular waveform 38 of the phase current which is in phase with the waveform 39 of the back electromotive force (back emf) of the same phase.

[0047] Referring now to FIGS. 8 to 11, there is shown a single switch modulation technique used for both motor and generator operation. The modulation signal is only applied on the gate of the transistors of the inverter upper side (T′1, T′2, T′3) in the case of motor operation mode (see FIGS. 8 & 9). The transistors T1, T2, T3 remain switched “on” during all the duration of the conduction sequence. In comparison to the classical modulation technique where the modulation signal is applied to switches of both lower and upper sides. This specific single switch modulation technique provides lower commutation losses and lower conduction losses in the case of low voltage applications (the voltage drop of a power MOSFET is lower than the voltage drop of a diode) see the E.M.I. tests article referred herein. The efficiency of the inverter 28 is higher. This single switch modulation technique simplifies the measurement of the phase currents and it eliminates the need of an external current sensor. The voltage of the MOSFETs (T1, T2, T3) of the inverter lower side 28′ can be used to measure the motor phase currents during all the sequences. In the case of the sequence T′1-T2, the voltage of transistor T2 is used to measure the motor phase current.

[0048] FIG. 8 shows the control signals which are applied to the transistor gates in the case of the single switch modulation technique.

[0049] FIG. 9 shows the current flow during one sequence in the motor operation mode. When transistors T′1 and T2 are switched “on” (FIG. 9a), the battery supplies two phases 40 and 41 of the motor. When the transistor T′1 is switched “off”, the structure diode of MOSFET T1 is switched “on” and a free wheeling operation is occurring (FIG. 9b). The current ripple is reduced by half in comparison with the classical two-switch modulation technique. There is no current inversion in the DC bus and so the size of the filtering capacitor (not shown but well known in the art) can be reduced (lower RMS current on the DC bus). Consequently, the electromagnetic interferences are also lower than in the case of the classical modulation mode see E.M.I. article referred herein.

[0050] FIGS. 10 & 11 present the case of the generator operation mode. The upper side inverter transistors 29 T′1, T′2, T′3 are all switched “off” during the generator operation mode. Only the structure diodes of these transistors are used in this mode. A modulation signal is applied on the gate 42 of transistors T1, T2, T3 (see FIG. 5) in the lower side 28′ of the inverter 28. There are some intervals where permanent conduction is occurring. They are used to measure the MOSFET voltage for the current control (see FIG. 11). FIG. 11 shows the current flow during one sequence of operation. The machine or motor current increases when the transistors 30 T1, T2 are switched “on” (FIG. 11b). When transistor T1 is switched “off”, the structure diode of transistor T′1 is switched “on” and the machine supplies the battery 43 (FIG. 11a).

[0051] FIGS. 12 and 13 show block diagram views of a classical current regulation with a PI regulator 44 which can be applied in the case of the single switch modulation mode. The proposed electronic system for both motor and generator operation modes with the single switch modulation technique is presented on FIG. 14. This system includes two signal multiplexers and several AND/OR gates used to control the signals applied to the transistor driver stages and the signals of measurements of the machine current. The system is also realizable by an integrated circuit or a programmable circuit obvious to a person skilled in the art.

[0052] Referring now to FIG. 15 there is shown a brushless DC motor 50, constructed as above described, and wherein the rotor 51 is connected to a hub 52 of a wheel 53 herein a bicycle wheel. Alternatively, to reduce production cost, the motor cover housing may have connections to which the spokes of the wheel are connected to. A battery, not shown, is conveniently secured to the bicycle and power is fed to the control circuitry provided or mounted within the cavity inside the stator. A cable 54 is secured to a control device which is operated by the user of the bicycle to control the speed of the motor. This control device could be in the form of a rotating handle and grip, a hand lever device or any other convenient means. When the motor is used as a motorizing machine it drives the wheel 53. The motor can also be utilized as a brake when placed in its generating mode. As previously mentioned, this motor can be secured to all sorts of electrical vehicles such as wheel chairs, scooters, tricycles, golf trolleys, small utility vehicles etc.

[0053] It will be understood that numerous modifications thereto will appear to those skilled in the art. Accordingly, the above description and accompanying drawings should be taken as illustrative of the invention and not in a limiting sense. It will further be understood that it is intended to cover any variations, uses, or adaptations of the invention following, in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice within the art to which the invention pertains and as may be applied to the essential features herein before set forth, and as follows in the scope of the appended claims.