High-efficiency low-cost open-winding permanent magnet flat wire motor driving system and control method

Abstract

The invention discloses a high-efficiency low-cost open-winding permanent magnet flat wire motor driving system and a control method. The invention comprises an open-winding permanent magnet synchronous motor with a square wave reverse electric function, a driving topological structure of a hybrid power device composed of a front-stage DC / DC and a rear-stage DC / AC, and a driving control method provided for the special counter electromotive force and the special driving topology of the motor. According to the invention, the usage amount of the motor stator winding copper material can be effectively reduced, and the usage amount of the copper winding material can be reduced by 50% under the same output power. Meanwhile, the cost of power electronic power devices is reduced through the hybrid drive topology of the high-speed power devices and the low-speed power devices, the use number of the high-speed SiC power devices can be reduced by 91.6%, and the cost of the electric drive system is effectively reduced. The construction cost of the open winding electric drive system can be reduced, and the energy efficiency of the open winding electric drive system is improved. The invention is applied to the electric driving system in the new energy automobile.

Description

Technical Field

[0001] The present invention relates to an electric drive system in new energy vehicles, and particularly to a high-efficiency and low-cost open-winding permanent magnet flat wire motor drive system and control method. Background Art

[0002] In order to save energy and reduce consumption and improve 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. At present, 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:

[0003] 1. Easy to control, with better response characteristics, enabling precise control of vehicle movement;

[0004] 2. Can be combined with a braking energy recovery system to reduce energy loss;

[0005] 3. Has multiple drive forms, can realize multiple vehicle dynamics control functions, and truly realizes the electronic and active control of vehicle dynamics.

[0006] Currently, new energy vehicles are gradually changing from centralized drive to distributed drive. In distributed drive, each vehicle is equipped with a motor, and the motors in each vehicle can be controlled separately. Therefore, the number of drive motors and motor controllers in new energy vehicles has increased significantly, making the impact of the cost and performance of the electric drive system on the cost and performance of new energy vehicles more significant.

[0007] Currently, the main motor used in the electric drive system of new energy vehicles is a three-phase sine wave permanent magnet synchronous flat wire motor. Compared with traditional round wire motors, flat wire motors have many advantages in the field of new energy vehicles, including high slot fill factor, high power density and efficiency, excellent heat dissipation performance, excellent electromagnetic noise and NVH performance, and are easier to achieve miniaturization and automated processing. The high energy efficiency, high power density, and low noise characteristics of permanent magnet flat wire motors make them more suitable for the high-speed electric drive system of new energy vehicles. Currently, for new high-performance new energy vehicles, basically 70% of the models choose permanent magnet flat wire motors as the main drive motors. However, as the motor speed in the electric drive system of new energy vehicles increases and the motor current frequency increases, the skin effect of the flat wire winding in the flat wire motor becomes more and more significant, resulting in an increase in the AC loss of the motor stator, affecting the operating efficiency of the flat wire permanent magnet motor at high speeds, and restricting the further improvement of the efficiency and power density of the electric drive system.

[0008] In the current rapid development of distributed drive methods, in order to further improve the power density, efficiency, and reliability of the electric drive system, the winding structure of the motor in the electric drive system has gradually been upgraded from a three-phase star-connected topology to a three-phase open-winding topology, as Figure 1 shown.

[0009] After the winding structure of the motor is changed from the traditional three-phase star connection to the open-winding topology, the open-winding permanent magnet synchronous motor drive system with a common bus power supply three-phase full-bridge drive has a higher bus voltage utilization rate, stronger fault tolerance ability, and multilevel modulation ability, improving the operating performance and system reliability of the open-winding permanent magnet synchronous motor. However, compared with the traditional three-phase star-connected permanent magnet synchronous open-winding motor drive system, the open-winding three-phase permanent magnet synchronous open-winding motor drive system requires twice as many power electronic power devices, which results in a significant increase in the cost of the electric drive device. And as the motor speed increases and the motor phase current frequency increases, in order to meet the demand for the carrier ratio for the stable operation of the electric drive system, the electric drive system has to choose SiC devices with a higher switching speed to meet the requirement of the increased switching frequency, which makes the cost of the open-winding electric drive system even higher. This affects the use and popularization of the open-winding electric drive system. Summary of the Invention

[0010] The present invention aims to solve the problems of increased system losses, reduced efficiency, and rising cost of power devices after the high-speed operation of the electric drive system, and further proposes a high-efficiency and low-cost open-winding permanent magnet flat wire motor drive system and control method.

[0011] The technical solution adopted by the present invention to solve the above problems is:

[0012] A high-efficiency and low-cost open-winding permanent magnet flat wire motor drive system described in the present invention includes:

[0013] An open-winding permanent magnet flat wire motor with a square-wave back electromotive force, including a rotating shaft, a rotor core, a Halbach permanent magnet array, a stator winding, and a stator core. The Halbach permanent magnet array is composed of five independent permanent magnets under a single magnetic pole. The permanent magnet in the middle is radially magnetized; the inner permanent magnet and the outer permanent magnet are symmetrically distributed on both sides of the middle permanent magnet from the inside to the outside. The inner permanent magnet close to the middle permanent magnet is radially magnetized, and its remanence density is higher than that of the middle permanent magnet. The outer permanent magnet is parallel magnetized, and the magnetization direction points to the adjacent magnetic pole and has a magnetic focusing effect;

[0014] Hybrid power device drive topology, including a front-stage DC-DC conversion circuit and a rear-stage DC-AC conversion circuit. The front-stage DC-DC conversion circuit and the rear-stage DC-AC conversion circuit share a DC bus voltage to form a common DC bus power supply structure. The front-stage DC-DC conversion circuit uses SiC MOSFET power devices. The rear-stage DC-AC conversion circuit includes two-stage inverter circuits based on Si IGBT power devices.

[0015] Further, the stator winding uses a flat wire winding to form an 8-pole 48-slot topology.

[0016] Further, the front-stage DC-DC conversion circuit includes a SiC MOSFET power device S1, a SiC fast recovery diode D1, a filter inductor L, and a voltage stabilizing capacitor C. The positive pole of the DC 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 D1 and one end of the filter inductor L. The other end of the SiC fast recovery diode D1 is connected to one end of the voltage stabilizing capacitor C. The other end of the voltage stabilizing capacitor C is connected to the other end of the filter inductor L.

[0017] Further, the rear-stage DC-AC conversion circuit includes 12 IGBT power elements Q1 to Q12 and 12 fast recovery freewheeling diodes D1 to D12. Each IGBT power element is connected in parallel with a fast recovery freewheeling diode. The IGBT power elements are connected in series in pairs to form a three-phase full-bridge drive circuit. Each phase full-bridge circuit is connected to one phase of the permanent magnet motor. By controlling the duty cycle of the high-speed switch S1 and the switching states of the slow-speed switches Q1 to Q12, the motor speed control is realized.

[0018] The control method of an energy-efficient and low-cost open-winding permanent magnet flat wire motor drive system according to the present invention includes the following steps:

[0019] Step 1: Control the duty cycle of the SiC MOSFET power device S1 in the front-stage DC-DC conversion circuit, and convert the DC voltage into a DC bus voltage through S1.

[0020] Step 2: Control the switching logic of the IGBT power elements Q1 to Q12 in the rear-stage DC-AC conversion circuit, and convert the DC bus voltage into a target AC voltage to drive the open-winding permanent magnet flat wire motor.

[0021] Step 3: Control an appropriate advance commutation angle so that when the back electromotive force of the motor commutes, the phase current of the motor has completed commutation, realizing the in-phase of the current and voltage, and making the motor drive more stable and fast.

[0022] Furthermore, the duty cycle D of the SiC MOSFET power device S1 S1 needs to be controlled as:

[0023]

[0024] where Is is the phase current of the permanent magnet motor, Rs is the phase resistance of the permanent magnet motor, np is the number of pole pairs of the motor, ωr is the angular velocity of the motor rotation, ψf is the rotor permanent magnet flux of the motor, and Vdc is the input bus voltage, which needs to satisfy:

[0025] V dc ≥I s R s +n p ω r_max ψ f (2)

[0026] where ωr_max is the angular velocity corresponding to the maximum speed of the motor;

[0027] The switching frequency of S1 needs to satisfy:

[0028]

[0029] The SiC device adopts a high-speed PWM drive form, and Q1 to Q12 adopt a slow switching drive form. Its switching logic is directly related to the phase angle of the back electromotive force on the motor rotor. The switching logic of the IGBT device is determined according to the position of the motor, as shown in Table 1; the switching logic is affected by the position of the motor rotor. In one electrical angle cycle, the slow power transistor (IGBT power device) is only turned on and off once.

[0030] Compared with the switching frequency of the traditional drive scheme, the system described in the present invention significantly reduces the switching times of the power transistors, reduces the switching losses of the power transistors and the overall energy consumption; under the switching logic control of the present system, the method of advanced commutation is adopted 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 completes commutation. The magnitude of the advanced commutation angle θ can be calculated by the following formula:

[0031]

[0032] where L s is the stator inductance of the permanent magnet motor.

[0033] The beneficial effects of the present invention are:

[0034] 1. In the present invention, the post-stage DC-AC circuit only functions as a commutator and can employ relatively inexpensive Si-based power devices with low switching speeds, including fully-controlled devices such as JFETs, GTOs, or IGBTs (used in the examples of the present invention). Only expensive SiC power devices need to be used in the pre-stage DC-DC converter. Theoretically, at least only one fully-controlled SiC MOSFET power device and one uncontrollable SiC diode are required. Thus, compared with the traditional sine-wave permanent magnet synchronous open-winding motor drive controller that requires 12 SiC MOSFET power devices and 12 SiC diodes, the present invention significantly reduces the number of expensive SiC power devices used, and can reduce the number of SiC devices used by up to 91.6%, reducing the cost of the driver.

[0035] 2. During the operation of the motor drive system of the present patent invention, the current in each phase winding is DC within the duration of each sector, thus basically eliminating the increase in AC copper loss of the motor stator winding caused by the high-frequencyization of the current during the high-speed rotation of the motor. Compared with the traditional permanent magnet synchronous open-winding motor, the stator loss of the motor is reduced and the operating efficiency of the motor is improved.

[0036] 3. Save the use of ferromagnetic materials and winding copper materials. The back electromotive force and drive current of the flat wire motor drive system of the present patent invention are square waves with the same phase. Compared with the traditional sine-wave permanent magnet synchronous open-winding motor, under the same back electromotive force peak and current peak, the electromagnetic output power of the permanent magnet motor of the electric drive system proposed in the present patent can be increased to twice the original. Thus, at 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.

[0037] 4. Under the conditions of the same motor rotor back electromotive force peak and the same output power limit, the phase current amplitude of the electric drive system of the present invention is only 50% of the phase current amplitude of the traditional sine-wave permanent magnet synchronous open-winding motor. Thus, without changing the use of ferromagnetic materials and copper winding materials of the motor, the phase current of the motor is reduced, the heating of the motor copper winding is reduced, and the operating efficiency of the motor is improved. Description of the Drawings

[0038] Figure 1 is the drive topology of a typical three-phase full-bridge open-winding permanent magnet synchronous open-winding motor;

[0039] Figure 2 is a schematic diagram of the topology structure of the electric drive system of the present invention;

[0040] Figure 3 is the drive topology diagram of the open-winding permanent magnet flat wire motor drive system of the present invention;

[0041] Figure 4aIt is a schematic structural diagram of the open-winding permanent magnet flat wire motor of the present invention;

[0042] Figure 4b It is a schematic diagram of the Halbach permanent magnet array of the present invention;

[0043] Figure 5 It is a waveform diagram of the air-gap magnetic flux density of the square-wave motor of the present invention;

[0044] Figure 6 It is a waveform diagram of the back electromotive force of the square-wave motor of the present invention;

[0045] Figure 7 It is a schematic diagram of the simulation model of the drive system of the present invention;

[0046] Figure 8 It is a diagram of the speed servo tracking result of the drive system of the present invention;

[0047] Figure 9 Simulation result diagram of the counter electromotive force and phase current during the speed servo process of the electric drive system of the present invention. Detailed implementation manners

[0048] Detailed implementation manner 1: The high-efficiency and low-cost open-winding permanent magnet flat wire motor drive system described in this implementation manner, wherein the open-winding permanent magnet flat wire motor is a permanent magnet motor with a square-wave back electromotive force, and a 1 / 8 schematic diagram of a typical structural form of an 8-pole 48-slot square-wave motor is shown in Figure 4.

[0049] In the square-wave motor shown in Figure 4, it includes a rotating shaft 1, a rotor core 2, a permanent magnet array 3, a stator winding 4, and a stator core 5. The Halbach permanent magnet array 3 under one pole is composed of 5 independent permanent magnets 3-1. The characteristics and effects of this permanent magnet array 3 are as follows: The middle permanent magnet 3-1 is radially magnetized to ensure that the middle part of the air-gap magnetic flux 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, two permanent magnets are arranged at the left and right edges of the middle permanent magnet 3-1 in Figure 4(b). The outer permanent magnet 3-2 is parallel magnetized, and the magnetization direction points to the adjacent magnetic pole, so as to shorten the positive and negative transition regions of the square-wave back electromotive force. The inner permanent magnet 3-3 is radially magnetized, and its remanence density is slightly higher than that of the middle permanent magnet 3-1, having a magnetic focusing effect, suppressing the magnetic flux density attenuation at the magnetic pole edge, and increasing the ratio of the square-wave back electromotive force in the electrical cycle.

[0050] The square-wave motor proposed by the present invention is simulated through simulation software, and the air-gap magnetic flux density waveform of this motor is as Figure 5 shown. Under one pole, the flat-top ratio of the square-wave magnetic flux density > 94.5% (42.5° / 45°), that is, the back electromotive force of this motor presents a square-wave waveform > 170° in a half electrical cycle (180°), as Figure 6 shown.

[0051] The back electromotive force and drive current of the motor in the high-efficiency and low-cost open-winding permanent magnet flat wire motor drive system of the present invention are square waves with the same phase. Compared with the traditional sine-wave permanent magnet synchronous open-winding motor, under the same back electromotive force peak and current peak, the electromagnetic output power of the permanent magnet motor in the electric drive system proposed by the present invention can be increased to 2 times the original. Therefore, under the same power, the use of ferromagnetic materials and winding copper materials of the permanent magnet motor can be significantly reduced, and the use of copper winding materials can be reduced by 50%, achieving cost reduction and efficiency improvement.

[0052] During the operation of the motor drive system, the current in each phase winding is a direct current within 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 open-winding motor, the stator loss of the motor is reduced, and the operating efficiency of the motor is improved.

[0053] Specific Embodiment 2: The high-efficiency and low-cost open-winding permanent magnet flat wire motor drive system described in this embodiment is an inverter topology structure of a common bus power supply mixed with high-speed power devices (SiC power devices) and slow-speed power devices (Si power devices), including a three-level structure, and its topology structure is as Figure 2 shown. The front stage is a DC-DC conversion circuit based on SiC MOSFET power devices, and the latter two stages are DC-AC conversion circuits based on Si IGBT power devices. The two inverters share a DC bus voltage, which is called a common DC bus power supply structure.

[0054] The DC-DC conversion circuit in the front stage is composed of a SiC MOSFET power device S1, a SiC fast-recovery diode D1, a filter inductor L, and a voltage-stabilizing capacitor C. The DC-AC conversion circuit in the latter stage includes 12 IGBT power devices Q1-Q12 and 12 fast-recovery freewheeling diodes D1-D12. Each IGBT power element is shunted by a fast-recovery freewheeling diode, and the power elements are connected in series in pairs to form a three-phase full-bridge drive circuit. Each phase full-bridge circuit is connected to one phase of the permanent magnet motor. Therefore, by controlling the duty cycle of the high-speed switch S1 and the switching states of the slow-speed switches Q1-Q12, the speed control of the motor of the present invention is realized.

[0055] When the system is running, the motor speed and speed command are sampled to the PWM generator to generate a high-frequency PWM wave to control the high-speed MOSFET switch in the front-stage BUCK circuit to adjust the magnitude of the inverter DC bus voltage. At the rear-stage inverter bridge, instead of performing high-frequency PWM chopping, a form of slow-switch driving is adopted. The on and off of Q1~Q12 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, by the method of advanced commutation, the voltage required for the rapid response of the current is reduced. 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.

[0056] According to a set of typical motor and driver parameters designed by the present invention, a simulation model of a high-efficiency and low-cost open-winding permanent magnet flat wire motor drive system is built, as Figure 7 shown.

[0057] The commanded speed of the motor is given as 2000 r / min. 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 to run, at 0.01 s, the motor speed has tracked the target speed, and the system has a high dynamic response. Since the motor is always running with a load, the speed remains basically stable after entering the steady state. After the motor speed enters the steady state, the actual speed is not much different from the given speed, and the error fluctuates around 0.5 r / min.

[0058] As can be seen from Figure 9 it, the back electromotive force of the motor designed by the present invention shows a square wave trend, its magnitude is directly related to the electrical speed, and its direction is directly related to the position of the motor. As shown in the figure, the main reason for the large fluctuation of the three-phase current before 0.01 s is that the motor speed is low at startup. In order to quickly increase the speed, the control system applies a relatively large current to the motor to generate a relatively large accelerating torque in the motor. When the motor speed rises to the commanded value, the three-phase current enters the steady state, and the waveform presents a square wave shape. And the phase current of the motor always remains basically in the same phase as the corresponding phase back electromotive force of the motor. When the back electromotive force of the motor commutes, the phase current of the motor has completed commutation in advance, thus improving the stability of the output torque of the electric drive system and the reliability of the operation of the electric drive system of the present invention.

[0059] At an operating speed of 2000 rpm and an output torque of 10 Nm, the current amplitude of the motor of the present invention is 10 A, while for a permanent magnet synchronous open-winding motor under the same output speed and output torque, the current amplitude of its sine wave is 20 A. Therefore, compared with the traditional sine wave permanent magnet synchronous open-winding 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, when ensuring that the back electromotive force peak and phase current peak of the motor remain unchanged, the electric drive system of the present invention can increase the power output by 100%, thereby significantly reducing the usage of ferromagnetic materials and copper winding materials in the electric drive system and achieving cost reduction and efficiency improvement.

[0060] The simulation results verify that the high-performance and low-cost open-winding permanent magnet flat wire motor drive system proposed by the present invention has stable performance, can achieve high-performance servo control through a hybrid drive method of high-speed switching devices and low-speed switching devices, and significantly reduces 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 process of motor design and manufacturing, as well as the use of expensive high-speed power switches in the manufacturing process of motor drivers, and reducing the cost of the electric drive system. And since the winding current is a direct current in each driving state of the electric drive system, the problem of increased AC copper loss of the stator flat wire winding of the motor caused by the high-frequencyization of the current during the high-speed rotation of the flat wire motor is basically eliminated. Compared with the traditional permanent magnet synchronous flat wire motor, the stator loss of the motor is further reduced, and the operating efficiency of the electric drive system is improved.

[0061] Specific Embodiment 3: A control method for a high-performance and low-cost open-winding permanent magnet flat wire motor drive system described in this embodiment, the control method includes the following steps:

[0062] Step 1: Control the duty cycle of the SiC MOSFET power device S1 in the front-stage DC-DC conversion circuit, and convert the DC voltage into a DC bus voltage through S1;

[0063] Step 2: Control the switching logic of the IGBT power elements Q1 to Q12 in the rear-stage DC-AC conversion circuit, and convert the DC bus voltage into a target AC voltage to drive the open-winding permanent magnet flat wire motor;

[0064] Step 3: Control an appropriate advance commutation angle so that when the back electromotive force of the motor commutes, the phase current of the motor has completed commutation, thereby achieving a steady-state in-phase of current and voltage through advance commutation control and making the motor drive more stable and fast.

[0065] To achieve the stable operation of the motor, the duty cycle D of the high-speed switch S1 S1 needs to be controlled as:

[0066]

[0067] Where Is is the phase current of the permanent magnet motor, Rs is the phase resistance of the permanent magnet motor, np is the number of pole pairs of the motor, ωr is the angular velocity of the motor rotation, ψf is the rotor permanent magnet flux linkage of the motor, and Vdc is the input bus voltage, which needs to satisfy

[0068] V dc ≥I s R s +n p ω r_max ψ f (2)

[0069] Where ωr_max is the angular velocity corresponding to the maximum speed of the motor.

[0070] The switching frequency of S1 needs to satisfy

[0071]

[0072] For a traditional high-speed permanent magnet synchronous open winding motor drive system, it is often required that Q1~Q12 adopt the SPWM or SVPWM modulation method, and a relatively high switching frequency is used to generate the sine voltage signal required to drive the motor through the PWM high-speed chopping method, so as to drive the motor to run. Since Q1~Q12 switch at a high speed, their switching frequency often reaches 10 kHz or even higher, thus generating relatively high switching losses. And because the sine voltage for driving the motor is formed by PWM high-speed switching chopping, there must be other high-order harmonic voltages in the output voltage of Q1~Q12 in addition to the fundamental sine 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 topology structure of the present invention, Q1~Q12 no longer adopt the form of high-speed PWM chopping, but adopt the form of slow-switching drive, and its switching logic is directly related to the phase angle (electrical angle) of the back electromotive force on the motor rotor. Its switching logic is as Figure 1 shown.

[0073] Table 1 Switching logic table of slow switches Q1~Q12

[0074]

[0075] Among them, the phase angle when the back electromotive force of phase A changes from negative voltage to positive voltage is defined as 0 degrees.

[0076] As can be seen from Table 1, the switching logic of the slow-speed power transistors in the high-efficiency and low-cost open-winding permanent magnet flat wire motor drive system of the present invention is mainly affected by the rotor position of the motor. In one electrical angle cycle, the slow-speed power transistors Q1 to Q12 are only turned on and off once, and their switching frequency is the same as the current frequency. Compared with the switching frequency of 10 kHz or even higher in the traditional drive scheme, the switching times of the power transistors are significantly reduced, and the switching losses of the power transistors are reduced. And under the switching logic control shown in Table 1, the phase current and back electromotive force of the motor 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 electromechanical energy conversion process of the motor.

[0077] Moreover, due to the existence of inductance in the motor, when the switching states of the slow switches Q1 to Q12 change according to the logic shown in Table 1, the current in the motor winding 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 bus drive voltage for the conventional control technology to make the current fast, it is easy to cause oscillation of the electric drive system and bring additional losses. In order to achieve the stable output of the torque of the electric drive system, the motor control method of the present invention proposes an advanced angle control technology for Q1 to Q12 on the basis of the PWM chopper control of the high-speed switch S1 and the phase switching control of the slow switches Q1 to Q12. According to the theoretical commutation position shown in Table 1, the method of advanced commutation is adopted 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 the advanced commutation control, and the stability of the operation of the electric drive system is improved. The magnitude of the advanced commutation angle θ can be calculated by Equation (4):

[0078]

[0079] where L s is the stator inductance of the permanent magnet motor.

[0080] The above-described embodiments are used to illustrate the technical solutions of the present invention, rather than to limit it. The front-stage DC-DC conversion circuit mentioned in the above embodiments 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.

[0081] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Although the present invention has been disclosed above with the preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art, within the scope of the technical solution of the present invention, can make some changes or modifications to the above-disclosed technical content to obtain equivalent embodiments with equivalent changes. However, as long as it does not depart from the technical solution content of the present invention, and according to the technical essence of the present invention, any simple modifications, equivalent replacements, and improvements made to the above embodiments within the spirit and principles of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A high-efficiency and low-cost open-winding permanent magnet flat wire motor drive system, characterized in that, Comprising: An open-winding permanent magnet flat wire motor with square-wave back electromotive force, including a rotating shaft (1), a rotor core (2), a Halbach permanent magnet array (3), a stator winding (4) and a stator core (5). The Halbach permanent magnet array (3) is composed of five independent permanent magnets under a single magnetic pole. The middle permanent magnet (3-1) is radially magnetized. The outer permanent magnet (3-2) and the inner permanent magnet (3-3) are symmetrically distributed on both sides of the middle permanent magnet (3-1) from inside to outside. The inner permanent magnet (3-3) close to the middle permanent magnet (3-1) is radially magnetized, and its remanence density is higher than that of the middle permanent magnet (3-1). The outer permanent magnet (3-2) is parallel magnetized, and the magnetization direction points to the adjacent magnetic pole and has a magnetic focusing effect; A hybrid power device drive topology structure, including a front-stage DC-DC conversion circuit and a rear-stage DC-AC conversion circuit. The front-stage DC-DC conversion circuit and the rear-stage DC-AC conversion circuit share a DC bus voltage to form a common DC bus power supply structure. The front-stage DC-DC conversion circuit uses SiC MOSFET power devices. The rear-stage DC-AC conversion circuit includes two-stage inverter circuits based on Si IGBT power devices.

2. The high-efficiency and low-cost open-winding permanent magnet flat wire motor drive system according to claim 1, wherein, The stator winding (4) uses a flat wire winding to form an 8-pole 48-slot topology structure.

3. An efficient and low-cost open-winding permanent magnet flat wire motor drive system according to claim 1, wherein, The front-stage DC-DC conversion circuit includes a SiC MOSFET power device S1, a SiC fast recovery diode D1, a filter inductor L and a voltage stabilizing capacitor C. The positive pole of the DC 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 D1 and one end of the filter inductor L. The other end of the SiC fast recovery diode D1 is connected to one end of the voltage stabilizing capacitor C. The other end of the voltage stabilizing capacitor C is connected to the other end of the filter inductor L.

4. An efficient and low-cost open-winding permanent magnet flat wire motor drive system according to claim 1, characterized in that, The rear-stage DC-AC conversion circuit includes 12 IGBT power elements Q1-Q12 and 12 fast recovery freewheeling diodes D1-D12. Each IGBT power element is connected in parallel with a fast recovery freewheeling diode. The IGBT power elements are connected in series in pairs to form a three-phase full-bridge drive circuit. Each phase full-bridge circuit is connected to one phase of the permanent magnet motor. By controlling the duty cycle of the high-speed switch S1 and the switching states of the slow switches Q1-Q12, the motor speed regulation control is realized.

5. A control method for a high-efficiency and low-cost open-winding permanent magnet flat wire motor drive system according to any one of claims 1-4, characterized in that, The control method includes the following steps: Step 1: Control the duty cycle of the SiC MOSFET power device S1 in the front-stage DC-DC conversion circuit, and convert the DC voltage into a controllable DC bus voltage through S1; Step 2: Control the switching logic of the IGBT power elements Q1-Q12 in the rear-stage DC-AC conversion circuit, and convert the DC bus voltage into a target AC voltage to drive the open-winding permanent magnet flat wire motor; Step 3: Control an appropriate advance commutation angle, and realize the steady-state in-phase of current and voltage through advance commutation control.

6. The control method of a high-efficiency and low-cost open-winding permanent magnet flat wire motor drive system according to claim 5, characterized in that, The duty cycle D of the SiC MOSFET power device S1 S1 needs to be controlled as follows: Where Is is the phase current of the permanent magnet motor, Rs is the phase resistance of the permanent magnet motor, np is the number of pole pairs of the motor, ωr is the angular velocity of the motor rotation, ψf is the rotor permanent magnet flux linkage of the motor, and Vdc is the input bus voltage, which needs to satisfy: V dc ≥ I s R s + n p ω r_max ψ f (2) Where ωr_max is the angular velocity corresponding to the maximum speed of the motor; The switching frequency of S1 needs to satisfy: The SiC device uses PWM control, the IGBT device uses switching control, and the switching logic of the IGBT is determined according to the position of the motor; The magnitude of the advance commutation angle θ is controlled as: Among which L s is the stator inductance of the permanent magnet motor.

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