High-efficiency material-saving low-cost permanent magnet motor rotor and driving system

Abstract

The invention relates to a high-efficiency material-saving low-cost permanent magnet motor and a driving system, and belongs to the technical field of driving systems. In order to solve the problems that after the new energy electric driving system is high in speed, the loss of the electric driving system is increased, and the cost is increased, rotor permanent magnets are arranged on the outer surface of a rotor iron core, the rotor permanent magnets are of a block Halbach array structure, each block comprises more than two permanent magnets, second permanent magnets and first permanent magnets are sequentially arranged on the two sides of each block, and the second permanent magnets and the first permanent magnets are arranged on the outer surface of the rotor iron core. The permanent magnet is radially magnetized, the driving system comprises a DC / DC converter and a DC / AC converter, and a power supply, a DC / DC conversion circuit, a DC / AC conversion circuit and the motor are electrically connected in sequence. The stator alternating current loss of the permanent magnet motor at a high speed is effectively reduced, the operation efficiency of an electric drive system is improved, the use of copper wire materials and expensive SiC power devices is reduced, and the cost of the electric drive system is reduced.

Description

Technical Field

[0001] The present invention relates to a motor rotor and a drive system, belonging to the technical field of drive systems. Background Art

[0002] In order to save energy and reduce consumption and improve the energy utilization efficiency, the core technologies of the electric drive system of new energy electric vehicles are battery energy storage technology, motor design technology and motor drive control technology. And the main power output of new energy vehicles depends on the motor drive control system. Therefore, the cost, power density and operating efficiency of the motor drive control system seriously affect the cost and cruising range of new energy vehicles. The drive mode of new energy vehicles is gradually changing from centralized drive to distributed drive. The distributed drive electric drive system has the following advantages for new energy vehicles: ① It is easy to control, has better response characteristics, and realizes precise control of vehicle movement; ② It can be combined with a braking energy recovery system to reduce energy loss; ③ It has a variety of drive forms, can realize a variety of vehicle dynamics control functions, and truly realizes the electronic and active control of vehicle dynamics.

[0003] New energy vehicles are gradually changing from centralized drive to distributed drive. A motor is installed in each wheel of the distributed drive. Each motor in each wheel can be controlled independently. Therefore, the number of drive motors and motor controllers in new energy vehicles has increased significantly, and the impact of the cost and performance of the electric drive system on the cost and performance of new energy vehicles is more significant.

[0004] At present, the main motor used in the electric drive system of new energy vehicles is a three-phase sinusoidal permanent magnet synchronous flat wire motor. The flat wire motor has a small volume, high efficiency and low noise. Compared with the round wire winding, at the same power, the flat wire winding has a higher slot fill factor, lower material cost, slower temperature rise, lighter weight, greater power density, etc., and has now become the main actuator of new energy vehicles. Since the volume size of the motor is directly related to the output torque of the motor, in order to further improve the power density of the drive motor, the typical speed of the drive motor in the current electric drive system of new energy vehicles has been increased from 12000 rpm to 22000 rpm or even higher. High speed can improve the motor power density, improve the motor working efficiency, and reduce the motor volume, but it will cause an increase in the motor current frequency. Although the flat wire motor has great improvements in terms of slot fill factor, material cost, temperature rise, weight, power density, etc. compared with the round wire winding, it has a relatively large AC resistance. Therefore, the disadvantage of large AC loss of the flat wire is becoming more and more prominent when the motor speed is continuously increased.

[0005] Currently, the structure of the sine wave flat wire motor drive system widely used in new energy vehicles is shown in Figure Figure 10As shown in the figure. For a sine-wave permanent magnet synchronous motor, the high-speed operation of the motor will increase the back electromotive force of the motor. According to the working principle of the sine-wave permanent magnet motor, the corresponding stator current frequency also increases accordingly. In order to meet the current control performance of the motor and suppress the harmonic loss of the motor, the switching frequency of the power components of the motor driver is often required to be more than 30 times the current frequency, that is, the carrier is required to be greater than 30. Therefore, as the motor speed increases, the switching frequency of the power devices also increases. On the one hand, this causes an increase in the switching loss of the power components in the motor driver. In order to reduce the driver loss, relatively expensive SiC power components are often forced to be used in current industrial products, resulting in an increase in the cost of the motor driver. In the circuit topology diagram of the technical solution of the invention with the publication number CN114567213B and the invention creation name of "Four-switch buck-boost motor PAM modulation method and control method based on fuel cell", it can be seen that the DC-DC part (buck-boost) adopts a hybrid topology of Si power devices and SiC power devices, and the DC-AC part (inverter bridge) uses SiC power devices. It is applicable to BLDCM brushless DC motors, and the three-phase back electromotive force waveform is a 120° trapezoidal wave. Only two-phase bridge arms are energized at any time during driving, which is used to boost the voltage of the hydrogen fuel cell and improve the efficiency of the drive system. However, it does not propose leading commutation and the cost is also relatively high.

[0006] Therefore, there is an urgent need to propose a low-cost permanent magnet motor rotor and drive system with high efficiency and material saving to solve the above technical problems. Summary of the Invention

[0007] To solve the problems of increased losses and rising costs of the new energy electric drive system after high-speed operation, a low-cost permanent magnet motor rotor and drive system with high efficiency and material saving are provided, which can effectively reduce the stator AC loss of the permanent magnet motor at high speed, improve the operating efficiency of the electric drive system, reduce the use of copper wire materials and expensive SiC power devices, and reduce the cost of the electric drive system. A brief overview of the present invention is given below to provide a basic understanding of certain aspects of the present invention. It should be understood that this overview is not an exhaustive overview of the present invention. It is not intended to identify the key or important parts of the present invention, nor is it intended to limit the scope of the present invention.

[0008] The technical solution of the present invention:

[0009] A low-cost permanent magnet motor with high efficiency and material saving, including a rotor. The outer surface of the rotor core is provided with rotor permanent magnets. The rotor permanent magnets adopt a segmented Halbach array structure. Each segment contains more than two permanent magnets. The second permanent magnet and the first permanent magnet are sequentially arranged on both sides of the segment, and the permanent magnets are magnetized radially.

[0010] Preferably: The first permanent magnet is used for magnetic focusing, and the second permanent magnet has a remanence density higher than that of the permanent magnet and is used to suppress the decrease in the air-gap magnetic density at the flat top edge.

[0011] Preferably: It further includes a stator winding, a stator core, and a rotating shaft. The rotating shaft, the rotor core, the rotor permanent magnet, and the stator core are coaxially arranged in sequence from the inside to the outside. The stator winding is arranged in the slots of the stator core.

[0012] Preferably: The number of blocks of the Halbach array structure is the same as the number of poles of the motor and is correspondingly arranged.

[0013] Preferably: The motor is applied to a motor configuration of 8 poles and 48 slots. The blocks of the rotor permanent magnet include five independent permanent magnets.

[0014] An efficient, material-saving, and low-cost permanent magnet motor drive system uses the described motor. The drive system includes a DC / DC converter and a DC / AC converter. The power supply, the DC / DC conversion circuit, the DC / AC conversion circuit, and the motor are electrically connected in sequence.

[0015] Preferably: The front-stage DC / DC conversion circuit includes a SiC MOSFET power device S1, a SiC fast recovery diode D, a filter inductor L, and a voltage stabilizing capacitor C. One end of the power supply is connected to one end of the SiC MOSFET power device S1. The other end of the SiC MOSFET power device S1 is respectively connected to one end of the SiC fast recovery diode D and the filter inductor L. The other end of the filter inductor L is connected to one end of the voltage stabilizing capacitor C and the DC / AC conversion circuit. The other ends of the SiC fast recovery diode D, the voltage stabilizing capacitor C, and the DC / AC conversion circuit are all connected to the other end of the power supply.

[0016] Preferably: The rear-stage DC / AC conversion circuit includes six IGBT power devices Q1-Q6 and fast recovery freewheeling diodes D1-D6. Each IGBT power device is connected in parallel with a fast recovery freewheeling diode, and each half-bridge circuit is connected to one phase of the motor.

[0017] Preferably: In order to achieve the stable operation of the motor, the duty cycle D of the SiC MOSFET power device S1 S1 needs to be controlled as:

[0018]

[0019] where, I s is the phase current of the permanent magnet motor, R s is the phase resistance of the permanent magnet motor, n p is the number of pole pairs of the motor, ω r is the angular velocity of the motor rotation, ψ f is the magnetic flux of the rotor permanent magnet of the motor, V dcis the input bus voltage, which needs to satisfy:

[0020]

[0021] where ω r_max is the angular velocity corresponding to the maximum motor speed;

[0022] The switching frequency of S1 needs to satisfy:

[0023]

[0024] The SiC device adopts PWM control, and Q1 - Q6 adopt the form of slow switches. Their switching logic is directly related to the phase angle electrical angle of the back electromotive force on the motor rotor. The switching logic of the IGBT device is as shown in Table 1, which is determined according to the position of the motor; the switching logic is affected by the position of the motor rotor. In one electrical angle cycle, the slow power tube (IGBT power device) is only turned on and off once;

[0025] And by the method of advanced commutation, the voltage required for the rapid current response is reduced. By setting an appropriate advanced commutation angle, when the back electromotive force of the motor commutes, the phase current of the motor completes commutation. The magnitude of the advanced commutation angle θ can be calculated by the following formula:

[0026]

[0027] where L s is the stator inductance of the permanent magnet motor.

[0028] Preferably: The drive system is a drive system applicable to the in - wheel motor of new energy vehicles.

[0029] The present invention has the following beneficial effects:

[0030] 1. Save the use of ferromagnetic materials and winding copper materials; The back electromotive force and drive current of the high - efficiency material - saving and low - cost permanent magnet motor drive system of the present invention are square waves with the same phase. Compared with the traditional sinusoidal permanent magnet synchronous motor, under the same back electromotive force peak value and current peak value, the electromagnetic output power of the permanent magnet motor of the electric drive system proposed in this patent can be increased to 1.33 times the original. Thus, under the same power, the use of ferromagnetic materials and winding copper materials of the permanent magnet motor is significantly reduced, achieving cost reduction and efficiency improvement;

[0031] 2. During the operation of the high - efficiency material - saving and low - cost permanent magnet motor drive system of the patented invention, the current in each phase winding is direct current during the duration of each sector, thus basically eliminating the increase in the AC copper loss of the motor stator winding caused by the high - frequency of the current during the high - speed rotation of the motor. Compared with the traditional permanent magnet synchronous motor, the stator loss of the motor is reduced, and the operation efficiency of the motor is improved;

[0032] 3. In the present invention, the subsequent DC-AC circuit only functions as a commutator, and relatively inexpensive Si-based power devices with low switching speeds can be used, including fully-controlled devices such as JFET, GTO, or IGBT (used as an example in this patent). Only expensive SiC power devices need to be used in the previous DC-DC converter. Theoretically, at least only 1 fully-controlled SiC MOSFET power device and 1 uncontrollable SiC diode are required. Thus, compared with the traditional sine-wave permanent magnet synchronous motor drive controller that requires 6 SiC MOSFET power devices and 6 SiC diodes, this patent significantly reduces the number of expensive SiC power devices used, and can reduce the usage quantity of SiC devices by up to 83%, reducing the cost of the driver.

[0033] 4. Similarly, under the same motor rotor back electromotive force and the same output power, the phase current amplitude of the electric drive system of the present invention is only 75% of the phase current amplitude of the traditional sine-wave permanent magnet synchronous motor. Thus, without changing the use of motor ferromagnetic materials and copper winding materials, the phase current of the motor is reduced, the heating of the motor copper winding is decreased, and the operating efficiency of the motor is improved. Description of the Drawings

[0034] Figure 1 Schematic diagram of a high-efficiency material-saving and low-cost permanent magnet motor;

[0035] Figure 2 Schematic diagram of a Halbach permanent magnet array;

[0036] Figure 3 Schematic diagram of the topology structure of the electric drive system;

[0037] Figure 4 Schematic diagram of the topology structure of an inverter with a mixture of SiC power devices and Si power devices;

[0038] Figure 5 Waveform diagram of the air-gap magnetic flux density of a square-wave motor;

[0039] Figure 6 Waveform diagram of the back electromotive force of a square-wave motor;

[0040] Figure 7 Schematic diagram of the simulation model of a high-efficiency material-saving and low-cost permanent magnet motor drive system;

[0041] Figure 8 Diagram of the speed servo tracking result of the electric drive system;

[0042] Figure 9 Diagram of the simulation results of the back electromotive force and phase current during the speed servo process of the electric drive system;

[0043] Figure 10 It is a schematic structural diagram of a sine-wave flat wire motor drive system currently widely used in new energy vehicles.

[0044] In the figure, 1 - rotor core, 2 - rotor permanent magnet, 3 - stator winding, 4 - stator core, 5 - rotating shaft, 6 - DC / DC converter, 7 - DC / AC converter, 21 - first permanent magnet, 22 - second permanent magnet, 23 - permanent magnet. Detailed implementation manners

[0045] To make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be described below through specific embodiments shown in the accompanying drawings. However, it should be understood that these descriptions are merely exemplary and are not intended to limit the scope of the present invention. In addition, in the following description, the descriptions of well-known structures and technologies are omitted to avoid unnecessarily confusing the concepts of the present invention.

[0046] Detailed implementation manner one: Combining Figure 1-2 To illustrate this implementation manner, a high-efficiency and material-saving low-cost permanent magnet motor rotor of this implementation manner adopts a surface-mounted structure. The outer surface of the rotor core 1 is provided with a rotor permanent magnet 2. The rotor permanent magnet 2 adopts a segmented Halbach array structure (Halbach permanent magnet array, with permanent magnets placed at 60-degree intervals). A stronger magnetic field is formed on one side of the rotor, and a weaker magnetic field is formed on the other side, thereby realizing a square-wave air-gap magnetic flux density distribution. Each segment contains more than two permanent magnets 23. The second permanent magnet 22 and the first permanent magnet 21 are sequentially arranged on both sides of the segment. The permanent magnet 23 is magnetized radially, and the rotor sheath is made of a non-magnetic material; as Figure 1-2 In the square-wave motor structure, by adjusting the position and structure of the permanent magnets in the motor rotor, a magnetic field with an almost 180° electrical angle square-wave back electromotive force is realized in the permanent magnet motor rotor; the first permanent magnet 21 is magnetized in parallel, and the magnetization direction points to the adjacent magnetic poles to shorten the positive and negative transition regions of the square-wave back electromotive force. The second permanent magnet 22 is magnetized radially, and its remanence density is slightly higher than that of the middle permanent magnet 23, having a magnetic concentration effect, suppressing the magnetic flux density attenuation at the magnetic pole edge, and increasing the proportion of the square-wave back electromotive force in the electrical cycle.

[0047] Detailed implementation manner two: Combining Figure 1-2To describe this embodiment, a high-efficiency material-saving and low-cost permanent magnet motor of this embodiment includes a rotor as described in Embodiment 1. The motor further includes a stator winding 3, a stator core 4, and a rotating shaft 5. The rotating shaft 5, the rotor core 1, the rotor permanent magnet 2, and the stator core 4 are coaxially arranged in sequence from the inside to the outside. The stator winding 3 is arranged in the slots of the stator core 4. The stator winding 3 is a flat wire winding and is arranged in a three-phase distribution. For the novel permanent magnet motor proposed by the present invention, its back electromotive force waveform is a 180° square wave. In a square wave PMSM, all three-phase bridge arms are working at any moment during driving, and there is always current in the three-phase windings of the motor. The driving current of the three-phase windings of the square wave PMSM has a value within a cycle and there is no time when it is not powered on.

[0048] The number of divided blocks of the Halbach array structure is the same as the number of poles of the motor and is correspondingly arranged.

[0049] The motor adopts a Halbach permanent magnet array to achieve a square wave air-gap magnetic density distribution. The air-gap magnetic density is close to a square wave. Taking the tooth-slot combination of 8 poles and 48 slots commonly used in a new energy vehicle in-wheel motor drive system as an example, the 1 / 8 model of the square wave motor proposed by the present invention is as Figure 1 shown; the Halbach permanent magnet array under one pole is composed of 5 independent permanent magnets. The characteristics and effects of this permanent magnet array are as follows: the middle permanent magnet is radially magnetized to ensure that the middle part of the air-gap magnetic density under this pole has a square wave waveform. In addition, in order to broaden the angular ratio of the square wave under one pole, Figure 2 two permanent magnets are arranged at the left and right edges respectively. The function of the first permanent magnet is to concentrate the magnetic field, and the remanence density of the second permanent magnet is slightly higher than that of the middle permanent magnet to suppress the decrease of the air-gap magnetic density at the flat top edge.

[0050] Embodiment 3: Combining Figure 1-4 To describe this embodiment, a high-efficiency material-saving and low-cost permanent magnet motor drive system of this embodiment. The drive topology of the present invention is an inverter topology structure mixed with SiC power devices and Si power devices, including a two-stage structure. Its topology structure is as Figure 3 shown. Using the motor described above, the drive system includes a DC / DC converter 6 and a DC / AC converter 7. The power supply, the DC / DC conversion circuit 6, the DC / AC conversion circuit 7, and the motor are electrically connected in sequence; as Figure 4As shown, the front stage is a DC-DC conversion circuit based on SiC MOSFET power devices, and the rear stage is a DC-AC conversion circuit based on Si IGBT power devices. In the drive topology proposed by the present invention, only one SiC MOSFET power device is used in the DC-DC part (buck), and all the originally expensive SiC power devices in the DC-AC part (inverter bridge) are replaced with Si IGBT power devices. Therefore, the hybrid topology of Si devices and SiC devices in the present invention is for the entire topology, not just a part of the circuit. At the same time, the topology proposed in this patent can achieve cost savings while meeting the high-speed operation of the motor.

[0051] The DC / DC conversion circuit 6 in the front stage includes a SiC MOSFET power device S1, a SiC fast recovery diode D, a filter inductor L, and a voltage stabilizing capacitor C. One end of the power supply is connected to one end of the SiC MOSFET power device S1, the other end of the SiC MOSFET power device S1 is respectively connected to one end of the SiC fast recovery diode D and the filter inductor L, the other end of the filter inductor L is connected to one end of the voltage stabilizing capacitor C and the DC / AC conversion circuit 7, and the other ends of the SiC fast recovery diode D, the voltage stabilizing capacitor C, and the DC / AC conversion circuit 7 are all connected to the other end of the power supply.

[0052] The DC / AC conversion circuit 7 in the rear stage includes six IGBT power devices Q1 to Q6 and fast recovery freewheeling diodes D1 to D6. Each IGBT power device is connected in parallel with a fast recovery freewheeling diode, and each half-bridge circuit is connected to one phase of the motor. Thus, by controlling the duty cycle of the high-speed switch S1 and the switching states of the slow switches Q1 to Q6, the speed control of the motor in the present patent invention is realized. That is, every two IGBT power devices are connected in series to form a half-bridge, and three half-bridges are connected in parallel. One phase of the motor is connected between the two IGBT power devices of each half-bridge.

[0053] To achieve the stable operation of the motor, the duty cycle D of the SiC MOSFET power device S1 S1 needs to be controlled as:

[0054]

[0055] where, I s is the phase current of the permanent magnet motor, R s is the phase resistance of the permanent magnet motor, n p is the number of pole pairs of the motor, ω r is the angular velocity of the motor rotation, ψ f is the rotor permanent magnet flux linkage of the motor, V dc is the input bus voltage, which needs to satisfy:

[0056]

[0057] where ω r_max is the angular velocity corresponding to the maximum rotational speed of the motor;

[0058] The switching frequency of S1 needs to satisfy:

[0059]

[0060] For a traditional high-speed permanent magnet synchronous motor drive system, it is often required that Q1-Q6 adopt SPWM or SVPWM modulation methods, and a relatively high switching frequency is used to generate the sinusoidal voltage signal required to drive the motor by means of high-speed chopping through switching, so as to drive the motor to operate; due to the high-speed PWM drive method of Q1-Q6, its switching frequency often reaches 10 kHz or even higher, thus generating relatively high switching losses; and since the sinusoidal voltage for driving the motor is formed by high-speed PWM switching chopping, there must be other high-order harmonic voltages in the output voltage of Q1-Q6 in addition to the fundamental sinusoidal voltage. This part of the high-order harmonics will generate harmonic currents and harmonic losses in the motor, further affecting the stability and efficiency of the operation of the electric drive system; in the topological structure of the present patent invention, Q1-Q6 no longer adopt the high-speed PWM chopping drive form, but adopt a slow switching drive form, and its switching logic is directly related to the phase angle electrical angle of the back electromotive force on the motor rotor, and its switching logic is shown in Table 1;

[0061] Table 1 Switching logic table of slow switches Q1-Q6

[0062]

[0063]

[0064] where the phase angle when the back electromotive force of phase A changes from negative voltage to positive voltage is defined as 0 degrees;

[0065] It can be seen from Table 1 that the switching logic of the slow power tubes in the high-efficiency, material-saving and low-cost permanent magnet motor drive system of the present patent invention is mainly affected by the rotor position of the motor. In one electrical angle cycle, the slow power tubes Q1-Q6 are only turned on and off once. Compared with the 10 kHz switching frequency of the traditional drive scheme, the switching times of the power tubes are significantly reduced, and the switching losses of the power tubes are reduced; and under the switching logic control shown in Table 1, the motor phase current and the back electromotive force always remain in the same phase (motor state) or opposite phases (generator state), realizing the unity power factor control of the motor and reducing the energy loss in the process of motor electromechanical energy conversion;

[0066] Moreover, due to the existence of inductance in the motor, when the switching states of the slow switches Q1 to Q6 change according to the logic shown in Table 1, the current in the motor windings changes slowly to the final steady-state current under the limitation of the inductance, which will inevitably affect the output external characteristics of the electric drive system. In order to quickly adjust the current, conventional control technologies need to quickly adjust the bus drive voltage, which is likely to cause oscillations in the electric drive system and bring additional losses. In order to achieve stable output of the torque of the electric drive system, based on the PWM chopper control of the high-speed switch S1 and the phase-switching control of the slow switches Q1 to Q6, the motor control method of the present invention proposes an advanced commutation control technology for Q1 to Q6. According to the theoretical commutation position shown in Table 1, an advanced commutation method is adopted to reduce the voltage required for rapid current response. By setting an appropriate advanced commutation angle, when the back electromotive force of the motor commutes, the phase current of the motor has completed commutation, so that the steady-state in-phase of the current and voltage is achieved through advanced commutation control, improving the stability of the operation of the electric drive system. In order to meet the rapidity of the system under high-speed operating conditions of the motor, the present invention adopts advanced commutation during commutation, and the magnitude of the advanced commutation angle θ can be calculated by Equation (4):

[0067]

[0068] Wherein, L s is the stator inductance of the permanent magnet motor;

[0069] The above-described embodiments are used to illustrate the technical solutions of the present invention, rather than to limit the present invention. The above-described front-stage DC-DC conversion circuit adopts a topological structure capable of realizing DC voltage step-down or step-up control. As long as the required voltage regulation function can be realized, the control function of the electric drive system can be completed under the control method of the present invention;

[0070] An efficient material-saving and low-cost permanent magnet motor drive system of the present invention includes a permanent magnet synchronous motor with a special structure, a low-cost hybrid drive topology of a new type of wide-bandgap semiconductor power device and a conventional silicon semiconductor power device, and an electric drive system control technology; it can effectively reduce the amount of copper material used in the motor, reduce the use of copper winding materials by 30% under the same output power, and at the same time reduce the use of expensive SiC power devices, and can reduce the use quantity of SiC devices by up to 83% at most, effectively reducing the manufacturing cost of the electric drive system; and reduce the impact of the increase in AC resistance after high-speed operation on the energy consumption of the electric drive system, improving the system efficiency; this patent can achieve cost reduction and efficiency improvement of high-speed new energy electric drive systems, especially suitable for new energy vehicle distributed electric drive systems using multiple sets of motors and multiple sets of drivers, applicable to the electric drive systems in new energy vehicles, and the direct application field is the new energy vehicle distributed electric drive system and the permanent magnet hub motor drive control system. In the new energy distributed drive mode, adopting the present invention can drive the motor by adjusting the amplitude and phase of the output voltage, thereby reducing the cost of the electric drive system, increasing the output power of the motor, and reducing the motor loss.

[0071] Embodiment 1:

[0072] The efficient material-saving and low-cost permanent magnet motor drive system invented in this patent, where the motor is a permanent magnet motor with a square-wave back electromotive force. A 1 / 8 schematic diagram of a typical structure of an 8-pole 48-slot square-wave motor is as Figure 1-2 shown;

[0073] In Figure 1-2 the square-wave motor shown, the Halbach permanent magnet array under 1 pole is composed of 5 independent permanent magnets; the characteristics and effects of this permanent magnet array are: the middle permanent magnet is radially magnetized to ensure that the middle part of the air-gap magnetic density under this pole has a square-wave waveform; in addition, in order to broaden the angular ratio of the square wave under 1 pole, Figure 2 two permanent magnets are arranged at the left and right edges of [], the first permanent magnet is used for magnetic focusing, and the remanence density of the second permanent magnet is slightly higher than that of the middle permanent magnet to suppress the decrease of the flat-top edge air-gap magnetic density;

[0074] Through the finite element simulation software, a simulation experiment is carried out on the square-wave motor of the topology proposed in this patent. The air-gap magnetic density waveform of this motor is as Figure 5 shown; under 1 pole, the flat-top ratio of the square-wave magnetic density > 94.5% (42.5° / 45°), that is, the back electromotive force of this motor presents a square-wave waveform > 170° in half an electrical cycle (180°), as Figure 6 shown;

[0075] The drive topology of an efficient material-saving and low-cost permanent magnet motor drive system invented in this patent is as Figure 4As shown; when the system is running, by sampling the motor speed and speed command to the PWM generation controller, a high-frequency PWM wave is generated to control the on and off of the high-speed MOSFET in the BUCK circuit to adjust the magnitude of the inverter DC bus voltage; at the inverter bridge, instead of performing high-frequency PWM chopping, a slow-switching driving form is adopted. The on and off of Q1 - Q6 are related to the corresponding three-phase back electromotive force, and under the switch logic control shown in Table 1, the unity power factor control of the motor can be achieved. However, due to the presence of inductance, the time for the current to enter the steady state is slow. Therefore, this patent proposes a method of advanced commutation to reduce the voltage required for the rapid response of the current. By setting an appropriate advanced commutation angle, when the back electromotive force of the motor commutes, the phase current of the motor has completed commutation, so that the steady-state in-phase of the current and voltage is achieved through advanced commutation control, making the motor drive more stable and fast;

[0076] According to a set of typical motor and driver parameters designed in this patent invention, a simulation model of a low-cost permanent magnet motor drive system with high efficiency and material saving is built, as Figure 7 shown;

[0077] The orange curve is the speed target curve of 2000 r / min, and the blue curve is the actual speed curve; as Figure 8 shown, when the motor starts running, at 0.01 s, the motor speed has already exceeded the target speed. Due to the speed loop, the motor speed begins to gradually decrease and approach the target speed. At 0.05 s, due to the sudden application of a 10 N·m load, the motor speed also rapidly drops from 2005 rpm to 1990 rpm. Then, due to the regulation of the speed loop, the speed immediately starts to rise. At about 0.14 s, the motor speed is basically equal to the given speed, and the error is between 1 - 2 r / min; it can be seen that the square-wave motor proposed in this invention has high speed servo tracking performance;

[0078] The simulation results of the three-phase current and three-phase back electromotive force of the low-cost permanent magnet motor drive system of this patent invention are as Figure 9 shown; from Figure 9It can be seen from the figure that the back electromotive force of the motor designed by the present invention presents a square wave trend, and its size is directly related to the electrical speed, and its direction is directly related to the position of the motor; as shown in the figure, before 0.05s, the motor is in a no-load state, and the three-phase current is almost 0. The main reason for the large fluctuation of the three-phase current before 0.01s is that the motor has a low speed at startup and the back electromotive force amplitude is small. In order to quickly increase the speed, the control system increases the duty cycle of the high-speed switch S1 of the BUCK circuit, which increases the voltage at the DC bus, and finally increases the three-phase current to improve the output torque of the motor, so that the motor The speed responds to the command speed quickly; when the motor speed increases, the three-phase current is almost 0 but there will be some spikes, which is caused by the current ripple generated in the transient process of switching the 6 switch states; when a 10N.m load is applied to the motor at 0.05s, the three-phase current waveform presents a step-like waveform; and the phase current of the motor is always kept in the same phase with the opposite electromotive force of the corresponding phase of the motor. When the opposite electromotive force of the motor is switched, the phase current of the motor has started to switch phases in advance, so that the power factor of the electric drive system proposed in this patent is basically maintained at 1;

[0079] At an operating speed of 2000rpm and an output torque of 10Nm, the current amplitude of the motor of the present invention is 13A, while the current amplitude of the sine wave of the permanent magnet synchronous motor at the same output speed and output torque is 17A; thus, compared with the traditional sine wave permanent magnet synchronous motor, the present invention can significantly reduce the phase current amplitude of the motor, reduce the stator copper loss of the motor, and improve the operating efficiency of the electric drive system; similarly, while ensuring that the amplitude of the reverse electromotive force and the phase current amplitude of the motor remain unchanged, the electric drive system of the present invention can increase the power output by 33%, thereby significantly reducing the amount of ferromagnetic materials and copper winding materials used in the electric drive system, achieving cost reduction and efficiency improvement;

[0080] The simulation results verify that the high-efficiency, material-saving, low-cost permanent magnet motor drive system proposed in the present invention has stable performance, can achieve high-performance servo control through a hybrid drive mode of high-speed switching devices and low-speed switching devices, and significantly reduce the winding current value under the same output torque, thereby reducing the heat generation of the electric drive system, reducing the use of ferromagnetic materials and winding copper materials in the design and manufacturing process of the motor and the use of expensive high-speed power switches in the manufacturing process of the motor driver, thereby reducing the cost of the electric drive system; and because the winding current in each drive sector of the electric drive system is a DC quantity, the increase in AC copper loss of the motor stator winding caused by the high-frequency current during the high-speed rotation of the motor is basically eliminated. Compared with the traditional permanent magnet synchronous motor, the stator loss of the motor is further reduced, and the operating efficiency of the electric drive system is improved.

[0081] It should be noted that in the above embodiments, as long as the technical solutions do not conflict, they can be arranged and combined. Those skilled in the art can exhaust all possibilities based on the mathematical knowledge of permutations and combinations. Therefore, the present invention will not describe the technical solutions after permutation and combination one by one, but it should be understood that the technical solutions after permutation and combination have been disclosed by the present invention.

[0082] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. An efficient material-saving and low-cost permanent magnet motor, characterized in that: It includes a rotor. The outer surface of the rotor core (1) of the rotor is provided with rotor permanent magnets (2). The rotor permanent magnets (2) adopt a segmented Halbach array structure. Each segment contains more than two permanent magnets (23). The second permanent magnets (22) and the first permanent magnets (21) are sequentially arranged on both sides of the segment. The permanent magnets (23) are magnetized radially.

2. An efficient material-saving and low-cost permanent magnet motor according to claim 1, characterized in that: The second permanent magnets (22) are magnetized radially, and their remanence density is higher than that of the permanent magnets (23). The first permanent magnets (21) are magnetized in parallel, and the magnetization direction points to the adjacent magnetic poles and has a magnetic focusing effect.

3. An efficient material-saving and low-cost permanent magnet motor according to claim 2, characterized in that: It further includes a stator winding (3), a stator core (4) and a rotating shaft (5). The rotating shaft (5), the rotor core (1), the rotor permanent magnets (2), and the stator core (4) are coaxially arranged in sequence from the inside to the outside. The stator winding (3) is arranged in the slots of the stator core (4).

4. An efficient material-saving and low-cost permanent magnet motor according to claim 3, characterized in that: The number of segments of the Halbach array structure is the same as the number of poles of the motor and is correspondingly arranged.

5. An efficient material-saving and low-cost permanent magnet motor according to claim 4, characterized in that: The motor is applied to an 8-pole 48-slot motor configuration. The segments of the rotor permanent magnets (2) include five independent permanent magnets (23).

6. An efficient material-saving and low-cost permanent magnet motor drive system, characterized in that: Adopting the motor according to any one of claims 1-5, the drive system includes a DC / DC converter (6) and a DC / AC converter (7). The power supply, the DC / DC conversion circuit (6), the DC / AC conversion circuit (7), and the motor are electrically connected in sequence.

7. An efficient material-saving and low-cost permanent magnet motor drive system according to claim 6, characterized in that: The front-stage DC / DC conversion circuit (6) includes a SiC MOSFET power device S1, a SiC fast recovery diode D, a filter inductor L, and a voltage stabilizing capacitor C. One end of the power supply is connected to one end of the SiC MOSFET power device S1. The other end of the SiC MOSFET power device S1 is respectively connected to one end of the SiC fast recovery diode D and the filter inductor L. The other end of the filter inductor L is connected to the voltage stabilizing capacitor C and one end of the DC / AC conversion circuit (7). The other ends of the SiC fast recovery diode D, the voltage stabilizing capacitor C, and the DC / AC conversion circuit (7) are all connected to the other end of the power supply.

8. An efficient material-saving and low-cost permanent magnet motor drive system according to claim 7, characterized in that: The rear-stage DC / AC conversion circuit (7) includes six IGBT power devices Q1-Q6 and fast recovery freewheeling diodes D1-D6. Each IGBT power device is connected in parallel with a fast recovery freewheeling diode. Each half-bridge circuit is connected to one phase of the motor.

9. An efficient material-saving and low-cost permanent magnet motor drive system according to claim 8, characterized in that: To achieve the stable operation of the motor, the duty cycle D of the SiC MOSFET power device S1 S1 needs to be controlled as follows: Among them, I s is the phase current of the permanent magnet motor, R s is the phase resistance of the permanent magnet motor, n p is the number of pole pairs of the motor, ω r is the angular velocity of the motor rotation, ψ f is the rotor permanent magnet flux linkage of the motor, V dc is the input bus voltage, which needs to satisfy: where ω r_max is the angular velocity corresponding to the maximum rotational speed of the motor; The switching frequency of S1 needs to meet: The SiC device adopts PWM control, and the IGBT device determines the switching logic of the IGBT according to the position of the motor; The magnitude of the advance commutation angle θ can be calculated by the following formula: where L s is the stator inductance of the permanent magnet motor.

10. An efficient material-saving and low-cost permanent magnet motor drive system according to claim 3, characterized in that: The drive system is a drive system applicable to a new energy vehicle in-wheel motor.

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