Dual-stator twelve-phase compound permanent magnet motor system and multi-inverter cooperative modulation method

Abstract

This invention discloses a dual-stator twelve-phase composite permanent magnet motor system and a multi-inverter collaborative modulation method, belonging to the field of motors. The motor system adopts an axial dual-stator structure, with each stator employing two sets of dual three-phase windings with a 30° phase shift electrical angle, staggered by 15° electrical angles along the circumferential direction. It is driven by four sets of inverters, each set of inverters supplying power to a set of three-phase symmetrical windings with a 120° phase difference. The inverter collaborative modulation method includes: calculating the duty cycle of each bridge arm according to the conventional SVPWM five-segment vector modulation method, and calculating the bus current waveform of each inverter in the next switching cycle based on the instantaneous current of each phase; calculating the peak-to-peak value of the bus current of each inverter, and dividing the four inverters into two groups according to the magnitude; reconstructing the bus current of the two groups of inverters, assigning different bus current waveform patterns; and redistributing the switching waveforms of each bridge arm switching device according to the correspondence between the bus current pattern and the switching waveform pattern of each bridge arm.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of electric machines, and particularly relates to a dual-stator twelve-phase compound permanent magnet motor system and a multi-inverter coordinated modulation method. BACKGROUND

[0002] As a direct tool for electric energy production and conversion, the performance of an electric machine directly determines the efficiency of electric energy production and utilization. With the great improvement in the performance of rare earth permanent magnet materials, among numerous types of electric machines, rare earth permanent magnet electric machines are gradually becoming the focus of more and more scholars due to their high power density, high power factor, simple control circuit and other characteristics. The idea of compound permanent magnet electric machines originates from the memory machine scheme proposed by German scholars, which introduces low-coercivity AlNiCo magnetic poles into permanent magnet electric machines to make the flux linkage of the permanent magnet electric machines adjustable, and thus balances the advantages of torque density and magnetic adjustment range, providing a selectable space for the flux-weakening speed expansion and efficiency optimization of the permanent magnet electric machines. Generally, the instantaneous pulse amplitude required for the magnetic adjustment pulse is large, and the capacity requirement of the inverter is large. However, the multi-phase electric machine itself has the advantages of strong fault tolerance and high reliability, and in the low-voltage high-power application scenario, multiple sets of windings can share the current pulse required for magnetic adjustment. In addition, in the low-voltage high-power scenario, the fractional-slot concentrated winding electric machine has the advantages of improved power density, short winding end, high reliability and the like.

[0003] However, in the existing multi-phase compound permanent magnet motor system, the number of inverters increases, and in the inverter modulation process, different switch states of the inverter reflect the inverter alternating current side phase current to the direct current bus. Due to the discrete behavior of the switch state, the inverter direct current bus current pulsation is large. SUMMARY

[0004] In view of the deficiencies of the prior art, the purpose of the present application is to provide a dual-stator twelve-phase compound permanent magnet motor system and a multi-inverter coordinated modulation method.

[0005] The purpose of the present application can be achieved by the following technical solutions:

[0006] A dual-stator twelve-phase compound permanent magnet motor system adopts an axial dual-stator structure, both of the two stators adopt two sets of double three-phase windings with a phase shift of 30° electric angle, and the two stators are staggered by 15° electric angle along the circumferential direction; the twelve phases are driven by four sets of inverters, and each set of inverter supplies power to a group of three-phase symmetrical windings with a phase difference of 120°.

[0007] Further, the motor system further comprises a permanent magnet rotor, and the permanent magnet flux linkage is provided by the NdFeB magnetic pole and the AlNiCo magnetic pole.

[0008] Further, in the permanent magnet rotor, the magnetic fluxes of NdFeB and AlNiCo are connected in series in the same magnetic circuit by adopting a series magnetic circuit connection mode.

[0009] Further, the dual-stator twelve-phase compound permanent magnet motor adopts a fractional slot concentrated winding, and a 20-pole / 24-slot pole-slot matching is selected, and two periodic winding distributions are correspondingly distributed in one 360° mechanical circumference.

[0010] Further, the number of the inverters is greater than four.

[0011] The multi-inverter cooperative modulation method in the motor system comprises the following steps:

[0012] S1, according to the conventional SVPWM five-segment vector modulation method, the duty cycles of the bridge arms are calculated in advance, and the bus current waveforms of the inverters in the next switching period are calculated according to the instantaneous currents of the phases;

[0013] S2, the peak-to-peak values of the bus currents of the inverters are calculated, and the four inverters are divided into two groups according to the sizes of the peak-to-peak values of the bus currents of the inverters;

[0014] S3, the bus currents of the two groups of inverters are reconstructed, and different bus current waveform patterns are distributed;

[0015] S4, according to the corresponding relationship between the bus current patterns and the switching waveform patterns of the bridge arms, the switching waveforms of the bridge switching devices are redistributed.

[0016] Further, in S2, the grouping method of the inverters is that the two inverters with the maximum and minimum peak-to-peak values of the bus currents are divided into a group, which is called the first group, and the remaining two inverters are another group, which is called the second group.

[0017] Further, the switching waveforms of the inverters are redesigned without changing the duty cycles, so that the switching state sequence is reordered according to the order of the bus current from small to large in a half switching period, which is recorded as a "+" arrangement mode, and the switching state sequence is reordered according to the order of the bus current from large to small in a half switching period, which is recorded as a "-" arrangement mode.

[0018] The switching waveforms of the first group of inverters are respectively redesigned according to the "+" arrangement mode, and the switching waveforms of the second group of inverters are respectively redesigned according to the "-" arrangement mode.

[0019] A multi-inverter cooperative modulation system in a motor system comprises:

[0020] The bus current waveform calculation module calculates the duty cycles of the bridge arms according to the conventional SVPWM five-segment vector modulation method, and calculates the bus current waveforms of the inverters in the next switching period according to the instantaneous currents of the phases;

[0021] Inverter grouping module: Calculates the peak-to-peak value of the bus current of each inverter and divides the four inverters into two groups according to the magnitude of the peak-to-peak value of the bus current of each inverter.

[0022] Bus current reconfiguration module: Reconfigures the bus current of the two inverters and assigns different bus current waveform styles;

[0023] Additionally, the waveform allocation module: based on the correspondence between the bus current pattern and the waveform patterns of each bridge arm switch, it reallocates the switching waveforms for each bridge arm switch device.

[0024] The beneficial effects of this invention are:

[0025] 1. In this invention, the motor adopts an axial double stator structure, with the two stators staggered by 15° electrical angle along the circumferential direction. Since the frequency of torque pulsation is 12 times the electrical frequency, one torque cycle corresponds to 30° electrical angle. Therefore, the torque peaks and troughs of the two stators of the motor overlap and cancel each other out, further reducing torque pulsation. At the same time, the two stators in the axial double stator structure have no electromagnetic coupling, strong independence, and simplify the order of coordinate transformation and the complexity of system control strategy.

[0026] 2. This invention adds low coercivity AlNiCo magnetic poles to the permanent magnet rotor. The permanent magnet flux is provided by NdFeB magnetic poles and AlNiCo magnetic poles. By utilizing the adjustable remanence of AlNiCo magnetic poles, the permanent magnet magnetic field of the motor becomes a variable. The adjustment of the permanent magnet magnetic field is achieved through instantaneous d-axis pulses, providing adjustment space for motor efficiency optimization.

[0027] 3. This invention adopts a composite method of series magnetic circuit, with the magnetic poles arranged in an ABAB form. The magnetic fluxes of NdFeB and AlNiCo are connected in series in the same magnetic circuit. Since the magnetic field of the NdFeB magnetic pole will increase the operating point of the AlNiCo magnetic pole, the permanent magnet flux linkage after series connection will increase. Therefore, the torque output capability of the motor is improved under the same amount of permanent magnet.

[0028] 4. This invention adopts a fractional slot concentrated winding, selecting a 20-pole / 24-slot pole-slot combination, with two corresponding periodic windings distributed within a 360° mechanical circumference. The radial tension of the two unit motors differs by 180° along the circumferential direction and cancels each other out. Under the condition of not considering winding error, the combined radial unbalanced force is zero, which is beneficial to improving the stability of motor operation.

[0029] 5. In this invention, each stator of the motor adopts two sets of double three-phase windings with a phase shift of 30° electrical angle, which improves the harmonics of the motor's magnetomotive force. At the same time, the two sets of double three-phase windings are driven by four sets of three-phase inverters. Each inverter supplies power to a set of three-phase symmetrical windings with a phase difference of 120°. The multi-winding power supply method can also give full play to the advantages of the strong fault tolerance of multi-phase motors.

[0030] 6. This invention addresses the problem of high-frequency ripple in the bus current when a multi-phase permanent magnet motor is powered by multiple inverters in parallel. It redesigns the switching waveforms of each bridge arm using the principle of area equivalence and recombines the switching waveforms of each inverter by sorting and grouping the peak-to-peak values ​​of the bus currents among the multiple inverters. This effectively reduces the peak value of bus current pulsation when multiple inverters are in parallel. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 This is the phase relationship diagram of the twelve-phase motor of the present invention;

[0033] Figure 2 This is a structural diagram of the axial dual-stator motor of the present invention;

[0034] Figure 3 This is the cogging torque waveform of the dual-stator twelve-phase motor of the present invention;

[0035] Figure 4 These are schematic diagrams of different magnetic pole arrangements;

[0036] Figure 5 This is a comparison diagram of torques with different magnetic pole arrangements;

[0037] Figure 6 This is a wiring diagram for a 20-pole / 24-slot winding.

[0038] Figure 7 This is a Fourier decomposition diagram of the air gap magnetic flux density of the three-phase winding and the double three-phase winding of the present invention;

[0039] Figure 8 This is a block diagram of the control structure of the dual-stator twelve-phase motor of the present invention;

[0040] Figure 9 This is a block diagram of the stator six-phase current closed-loop control of the present invention;

[0041] Figure 10 This is a structural diagram of the dual-stator twelve-phase permanent magnet motor power drive system of the present invention;

[0042] Figure 11 This is a comparison of the coordinated modulation of inverter three and inverter four before and after the present invention;

[0043] Figure 12 This is a flowchart of the cooperative modulation strategy of the present invention;

[0044] Figure 13 These are the total bus current waveforms corresponding to different inverter grouping methods of this invention.

[0045] In the diagram, 1.1 is phase A1, the first three-phase winding A of stator 1; 1.2 is phase A2, the first three-phase winding A of stator 2; 1.3 is phase A3, the second three-phase winding A of stator 1; 1.4 is phase A4, the second three-phase winding A of stator 2; 2.1 is stator 2; 2.2 is stator 1; 2.3 is the rotor; 2.4 is the S pole; 2.5 is the N pole; 2.6 is the spatial angle between the two stators; 3.1 is the cogging torque waveform of stator 1; 3.2 is the cogging torque waveform of stator 2; 3.3 is the total cogging torque waveform of both stators; 4.1 is the composite method of parallel magnetic circuit, with the magnetic pole arrangement in AABB form; 4. 2 represents the N pole of the AlNiCo permanent magnet, 4.3 represents the S pole of the NdFeB permanent magnet, 4.4 represents a composite magnetic circuit with series connection and an ABAB pole arrangement, 4.5 represents the N pole of the AlNiCo permanent magnet, 4.6 represents the S pole of the NdFeB permanent magnet, 5.1 represents the average torque of the motor with the ABAB pole arrangement, and 5.2 represents the average torque of the motor with the AABB pole arrangement; 8.1 represents the dual-stator shared speed-changing PI controller, 8.2 represents the stator-1 six-phase current closed-loop control section, 8.3 represents the stator-2 six-phase current closed-loop control section, 8.4 represents the dual-stator torque distribution coefficient r, and 8.5 represents the stator-1 six-phase current... The current closed-loop controller includes: 8.6 a voltage space vector modulation module; 8.7 inverter one; 8.8 a dual-stator twelve-phase motor; 8.9 a speed encoder; and 8.10 a speed calculation module. 9.1 a fundamental plane d-axis and q-axis current loop PI controller; 9.2 a harmonic plane z1-axis and z2-axis current loop PI controller; 9.3 a polar coordinate transformation module; and 9.4 a decoupling inverse transformation module. 11.1 shows the A3 phase switching waveform in a "+" arrangement; 11.2 shows the B3 phase switching waveform in a "+" arrangement; 11.3 shows the C3 phase switching waveform in a "+" arrangement; and 11.4 shows the inverter's three busbars in a "+" arrangement. The current waveforms are as follows: 11.5 is the A4 phase switch waveform under the "-" arrangement; 11.6 is the B4 phase switch waveform under the "-" arrangement; 11.7 is the C4 phase switch waveform under the "-" arrangement; 11.8 is the inverter four bus current waveform under the "-" arrangement; 11.9 is the superimposed waveform of the inverter three and inverter four bus currents before co-modulation; 11.10 is the superimposed waveform of the inverter three and inverter four bus currents after co-modulation; 13.1 is the total bus current waveform under the "1100" grouping mode; 13.2 is the total bus current waveform under the "1010" grouping mode; and 13.3 is the total bus current waveform under the "1001" grouping mode. Detailed Implementation

[0046] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0047] like Figure 1 and Figure 2 As shown, the dual-stator twelve-phase composite permanent magnet motor system includes stator 1 (2.2), stator 2 (2.1), and rotor 2.3. Phase A1 (1.1) and phase A3 (1.3) are located on stator 1 (2.2), and phase A2 (1.2) and phase A4 (1.4) are located on stator 2 (2.1). The phase difference between stator 1 (2.2) and stator 2 (2.1) is 15° electrical angle. Both stator 1 (2.2) and stator 2 (2.1) use two sets of double three-phase windings with a phase shift of 30° electrical angle. The number of pole pairs of the motor is 10, so the spatial angle between the two stators (2.6) is 1.5°.

[0048] Figure 3 It is the cogging torque waveform of a dual-stator twelve-phase motor, from Figure 3 It can be seen that the peak value of the motor cogging torque occurs 12 times in one electrical cycle, that is, the frequency of cogging torque pulsation is 12 times that of the electrical cycle. In the axial double stator structure adopted in this invention, the two stators are staggered by 15° electrical angle along the circumferential direction, so that the peaks and troughs of the cogging torque of the two stators of the motor overlap and cancel each other out, further reducing the total torque pulsation.

[0049] In this embodiment, low-coercivity AlNiCo magnetic poles are added to the rotor 2.3. The permanent magnet flux linkage is provided by both NdFeB and AlNiCo magnetic poles. Utilizing the adjustable remanence of the AlNiCo magnetic poles, the permanent magnet field of the motor becomes variable. The adjustment of the permanent magnet field is achieved through instantaneous d-axis pulses. During the operation of the composite permanent magnet, the magnetic poles of this invention are arranged in a series magnetic circuit, i.e., an ABAB configuration. Figure 4 indivual Figure 5 These are schematic diagrams and torque comparison diagrams for different magnetic pole arrangements. From Figure 4 As can be seen, the magnetic fluxes of NdFeB and AlNiCo are connected in series in the same magnetic circuit. Because the magnetic field of the NdFeB poles raises the operating point of the AlNiCo poles, the permanent magnet flux linkage after series connection increases, thus increasing the motor's torque output capability with the same amount of permanent magnets. From... Figure 5 As can be seen from the data, when using the same size parameters, the average torque of the motor using the series magnetic circuit (ABAB magnetic pole arrangement) in this invention is about 20% higher than that using the parallel magnetic circuit (AABB arrangement).

[0050] In this embodiment, a fractional-slot concentrated winding is selected for the motor winding. For a single-stator, three-phase permanent magnet synchronous motor with a 30° phase shift, when using a fractional-slot concentrated winding, it is necessary to ensure that the motor can achieve a uniform distribution of the six-phase windings, and also to ensure the realization of a 30° electrical phase shift between the two sets of windings. The number of slots Z and the number of pole pairs p need to satisfy the following relationship:

[0051] Z = 6k, k ∈ N (1)

[0052]

[0053] According to the theory of magnetomotive force (MOMF) synthesis, different winding combinations affect the winding factor of the synthesized MOMF. The larger the winding factor, the larger the fundamental amplitude of the synthesized MOMF, and the higher the winding utilization rate. The unit cycle number t is introduced to characterize the periodicity of the winding distribution, specifically referring to the number of cycles of the winding distribution within a mechanical circumference. In this embodiment, a 20-pole, 24-slot pole-slot combination is selected, with a unit cycle number of 2, indicating that there are two cycles of winding distribution within a 360° mechanical circumference, i.e., 180° of mechanical circumference constitutes one winding cycle. Figure 6 This is the winding distribution for one cycle of a 20-pole, 24-slot motor. The winding distribution for another cycle is the same, with a mechanical angle difference of 180 degrees. In composite permanent magnet motors, the imbalance of the permanent magnet field distribution on the rotor circumference is an objective reality due to the adjustment of the low-coercivity AlNiCo magnetization state. In this embodiment, when the number of cycles t=2 for the 20-pole, 24-slot motor unit, the motor windings have good periodic symmetry, and the radial tensions of the two unit motors, differing by 180° along the circumferential direction, cancel each other out. Without considering winding errors, the combined radial imbalance force is zero, which is beneficial for improving the stability of motor operation.

[0054] Figure 7 This involves a comparison of the Fourier decomposition results of the armature magnetic field in the air gap when the motor is configured as a three-phase winding and a double three-phase winding with a phase shift of 30°, respectively, and a q-axis current of 5A is injected into both configurations. Figure 7 It can be seen that after adopting the double three-phase winding, the spatial harmonics such as 2th, 22nd, and 26th in the air gap magnetic field are suppressed, which fully demonstrates the improvement effect of the double three-phase winding on the magnetomotive force harmonics of the fractional slot concentrated winding motor.

[0055] The control block diagram of a dual-stator twelve-phase permanent magnet motor is as follows: Figure 8As shown; since there is no magnetic coupling between stator 1 (2.2) and stator 2 (2.1), two six-phase current closed-loop modules are used to perform closed-loop control of the current signals in the two stators respectively. First, the twelve-phase current is sampled from the motor and fed back to the stator 1 six-phase current closed-loop control section 8.2 and stator 2 six-phase current closed-loop control section 8.3 according to their stator positions. The actual motor speed is obtained by the signal obtained by the speed encoder 8.9 and then processed by the speed calculation module 8.10. The speed error signal is input to the dual-stator shared speed loop PI controller 8.1 to obtain the total q-axis current reference value. The distribution of the total q-axis current reference value in stator 1 (2.2) and stator 2 (2.1) can be changed by adjusting the dual-stator torque distribution coefficient r 8.4, thereby adjusting the torque distribution of the two stators. The value of r can vary from 0 to 100%, corresponding to the torque proportion borne by stator 1 (2.2) changing from small to large. Taking stator one as an example, the reference value and feedback value of each phase current are input to the six-phase current closed-loop controller 8.5 of stator one to obtain the voltage reference signal. Then, it is modulated into a control signal in the voltage space vector modulation module 8.6. The power of the control signal is amplified by the inverter 8.7, and finally the control of the dual-stator twelve-phase motor 8.8 is realized.

[0056] Since there is no magnetic circuit coupling between the two stators of the dual-stator twelve-phase permanent magnet motor proposed in this embodiment, and there is a 30° phase shift between the two sets of windings of the same stator, decoupling can be achieved by using the coordinate transformation matrix of the dual three-phase windings for each stator. This transformation method simplifies the order of the spatial transformation equations, reducing the 12th-order matrix to two 6th-order transformation matrices, thus simplifying the program's calculation and storage space. During rotational transformation, compared to the angle θ between the rotor d-axis and the axis of stator one, the angle between the rotor d-axis and the axis of stator two is θ - π / 12 electrical degrees. Therefore, compared to the coordinate rotation angle θ of stator one, the required transformation angle for the coordinate system of stator two is θ - π / 12 electrical degrees. The specific transformation formula is as follows:

[0057]

[0058]

[0059]

[0060] In the formula, T 6s T is the decoupling coordinate transformation matrix between stator one and stator two. 6r1 Let T be the stator-rotation coordinate transformation matrix. 6r2 This is the coordinate transformation matrix for the stator.

[0061] The dual-stator twelve-phase permanent magnet motor proposed in this embodiment has the following six-phase current closed-loop control block diagram for stator 2.2: Figure 9As shown; Stator 2.2 is a double three-phase winding with a 30° electrical phase shift. After the six-phase winding current undergoes Clarke transformation, the components of the αβ and xy sub-planes are rotated by angles θ and -θ respectively, so that the fundamental and harmonic sub-planes can be mapped to a rotating coordinate system, becoming DC quantities. The current error signals of each axis are processed by the fundamental plane d and q-axis current loop PI controller 9.1 and the harmonic plane z1 and z2-axis current loop PI controller 9.2 to obtain the voltage reference signals of each axis. The voltage reference signals are then processed by the polar coordinate transformation module 9.3 to obtain the corresponding αβ and xy voltage reference quantities. Based on the relationship between the αβ and xy composite vectors of the double three-phase winding and the component vectors of the two three-phase windings, the decoupling inverse transformation module 9.4 can generate two spatial vectors with a 30° electrical phase shift. Then, the corresponding modulation pulses can be generated through the SVPWM modulation strategy, and the control method realizes the tracking of the reference current.

[0062] In this embodiment, the structure of the dual-stator twelve-phase permanent magnet motor power drive system is as follows: Figure 10 As shown, the DC bus supplies power to four inverters. Inverter 1 and Inverter 3 provide power to two sets of three-phase windings in stator 1, respectively, while Inverter 2 and Inverter 4 provide power to two sets of three-phase windings in stator 2, respectively. During inverter modulation, different switching states of the inverters reflect the AC side phase current onto the DC bus. Since the DC side shares a DC bus, the total DC bus current is the sum of the DC bus currents of the four three-phase inverters. Therefore, using conventional modulation methods will result in large ripples in the inverter DC bus current.

[0063] The following only considers the phase of phase A voltage as π / 4 and the time as t. π / 4 For example:

[0064] Figure 11 This is a comparison diagram of inverter 3 and inverter 4 before and after coordinated modulation; for example... Figure 11 As shown in (a), the switching waveforms are redesigned without changing the duty cycle, so that the three switching states of the inverter are rearranged according to the bus current in ascending order within half a switching cycle. The inverter's three bus current waveforms in the "+" arrangement are 10.4, denoted as the "+" arrangement. Figure 11 As shown in (b), the inverter's four-switch state sequence is reordered according to the bus current in descending order within half a switching cycle. The inverter's four-bus current waveforms under the "-" arrangement are denoted as the "-" arrangement. From Figure 11 As can be seen from (c), the ripple amplitude of the sum of the two inverter bus currents is reduced from 1.966Im to 0.741Im. Therefore, after adjusting the bus current waveforms of the two inverters using the bus current reconstruction method, the superposition of the peak values ​​of the two inverter bus currents can be effectively avoided, thereby reducing the amplitude of the total bus current ripple.

[0065] Applying the aforementioned multi-inverter bus current reconfiguration principle to a four-inverter power drive system, a multi-inverter collaborative modulation method is proposed for a dual-stator twelve-phase permanent magnet motor system, such as... Figure 12 As shown, the multi-inverter cooperative modulation method includes the following steps:

[0066] S1, calculate the duty cycle of each bridge arm in advance according to the conventional SVPWM five-segment vector modulation method, and calculate the inverter bus current waveform for the next switching cycle based on the instantaneous current of each phase.

[0067] S2, Calculate the peak-to-peak bus current I of each inverter. pp The four inverters are divided into two groups according to the peak-to-peak value of the bus current of each inverter. The two inverters with the largest and smallest peak-to-peak values ​​of the bus current are grouped into one group, called Group 1, and the remaining two inverters are grouped into another group, called Group 2.

[0068] S3. Perform bus current reconstruction on the two sets of inverters and assign different bus current waveform patterns. The first set adopts the "+" arrangement, that is, the bus current is reordered from small to large within half a switching cycle. The second set adopts the "-" arrangement, that is, the bus current is reordered from large to small within half a switching cycle.

[0069] S4. Based on the correspondence between the bus current pattern and the waveform patterns of each bridge arm switch, the switching waveforms of each bridge arm switch device are redistributed.

[0070] The principle behind the grouping method in S3 is as follows:

[0071] In this embodiment, the peak-to-peak value of the bus current ripple of the four inverters in the designed four inverter power supply system is 0.966I. m 0.866I m 0.966I m I m Based on the combination principle, the four inverters are divided into two groups, with three grouping methods: inverter 1 and inverter 2 are in one group, and the remaining two are in another group, denoted as "1100" grouping method; inverter 1 and inverter 3 are in one group, and the remaining two are in another group, denoted as "1010" grouping method; inverter 1 and inverter 4 are in one group, and the remaining two are in another group, denoted as "1001" grouping method.

[0072] Figure 13 The total bus current waveforms corresponding to different inverter grouping methods of this invention are shown. When inverter 1 and inverter 2 are grouped together using a "+" arrangement, and inverter 3 and inverter 4 are grouped together using a "-" arrangement, the peak-to-peak value of the total bus current waveform under the "1100" grouping method is 1.966I. mWhen inverters 1 and 3 are grouped together in a "+" arrangement, and inverters 2 and 4 are grouped together in a "-" arrangement, the peak-to-peak value of the total bus current waveform for the "1010" group is 1.432 I. m When inverters 1 and 4 are grouped together in a "+" arrangement, and inverters 2 and 3 are grouped together in a "-" arrangement, the peak-to-peak value of the total bus current waveform under the "1001" group is 1.707I. m Therefore, grouping inverter I and inverter III together can minimize the peak-to-peak value of the bus current ripple after superposition.

[0073] The grouping method proposed in this invention is not fixed, but rather calculated and updated in real time for each switching cycle. Before each switching cycle, the peak-to-peak value of the bus current for each inverter is pre-calculated, and the four inverters are grouped in pairs accordingly. The PWM switching waveforms of the inverters are then selected for each pair using either a "+" or "-" arrangement. This method can be extended to motor control with a larger number of inverters. When the number of inverter groups is greater than four, grouping the inverters according to the peak-to-peak value of the bus current can minimize the overlap of the maximum bus current values, thus achieving bus current ripple suppression. Clearly, compared to a fixed grouping method, the flexible inverter grouping method proposed in this invention can better suppress bus current ripple.

[0074] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0075] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A multi-inverter coordinated modulation method in a dual-stator twelve-phase composite permanent magnet motor system, characterized in that, The motor system adopts an axial double stator structure. Both stators use two sets of double three-phase windings with a phase shift of 30° electrical angle. The two stators are staggered by 15° electrical angle along the circumferential direction. The twelve phases are driven by four sets of inverters. Each set of inverters supplies power to a set of three-phase symmetrical windings with a phase difference of 120°. The modulation method includes the following steps: S1, calculate the duty cycle of each bridge arm in advance according to the conventional SVPWM five-segment vector modulation method, and calculate the inverter bus current waveform for the next switching cycle based on the instantaneous current of each phase. S2, calculate the peak-to-peak value of the bus current of each inverter, and divide the four inverters into two groups according to the magnitude of the peak-to-peak value of the bus current of each inverter. S3 reconfigures the bus current for the two sets of inverters and assigns different bus current waveform styles. S4. Based on the correspondence between the bus current pattern and the waveform patterns of each bridge arm switch, the switching waveforms of each bridge arm switch device are redistributed.

2. The multi-inverter coordinated modulation method in a dual-stator twelve-phase composite permanent magnet motor system according to claim 1, characterized in that, The motor system includes a permanent magnet rotor, and the permanent magnet flux is provided by NdFeB and AlNiCo magnetic poles.

3. The multi-inverter coordinated modulation method in a dual-stator twelve-phase composite permanent magnet motor system according to claim 2, characterized in that, In the permanent magnet rotor, the magnetic fluxes of NdFeB and AlNiCo are connected in series in the same magnetic circuit.

4. The multi-inverter coordinated modulation method in a dual-stator twelve-phase composite permanent magnet motor system according to claim 1, characterized in that, The dual-stator twelve-phase composite permanent magnet motor adopts fractional slot concentrated winding, with a selected pole-slot combination of 20 poles / 24 slots, and two cycles of winding distribution within a 360° mechanical circumference.

5. The multi-inverter coordinated modulation method in a dual-stator twelve-phase composite permanent magnet motor system according to claim 1, characterized in that, The number of inverters is greater than four.

6. The multi-inverter coordinated modulation method in a dual-stator twelve-phase composite permanent magnet motor system according to claim 1, characterized in that, In S2, the inverters are grouped as follows: the two inverters with the largest and smallest peak-to-peak bus currents are grouped together, called Group 1, and the remaining two inverters are grouped together, called Group 2.

7. The multi-inverter coordinated modulation method in a dual-stator twelve-phase composite permanent magnet motor system according to claim 6, characterized in that, Without changing the duty cycle, the inverter switching waveforms are redesigned so that the switching state sequence is rearranged according to the bus current in ascending order within half a switching cycle, denoted as the "+" arrangement; and the switching state sequence is rearranged according to the bus current in descending order within half a switching cycle, denoted as the "-" arrangement. The switching waveforms of the first group of inverters are redesigned according to the "+" arrangement, and the switching waveforms of the second group of inverters are redesigned according to the "-" arrangement.

8. A multi-inverter coordinated modulation system for a motor system, comprising the multi-inverter coordinated modulation method for a dual-stator twelve-phase composite permanent magnet motor system as described in any one of claims 1-7, characterized in that, include: Bus current waveform calculation module: The duty cycle of each bridge arm is pre-calculated according to the conventional SVPWM five-segment vector modulation method, and the inverter bus current waveform of each phase is calculated according to the instantaneous current of each phase in the next switching cycle. Inverter grouping module: Calculates the peak-to-peak value of the bus current of each inverter and divides the four inverters into two groups according to the magnitude of the peak-to-peak value of the bus current of each inverter. Bus current reconfiguration module: Reconfigures the bus current of the two inverters and assigns different bus current waveform styles; Additionally, the waveform allocation module: based on the correspondence between the bus current pattern and the waveform patterns of each bridge arm switch, it reallocates the switching waveforms for each bridge arm switch device.

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