A method for suppressing third harmonics in a nine-phase open-wound PMSM

Abstract

This invention discloses a method for suppressing third harmonics in a nine-phase open-winding permanent magnet synchronous motor. The method includes: acquiring signals such as motor terminal voltage and current, and calculating the third harmonic back electromotive force; calculating the third harmonic voltage in each group of three phases based on the characteristics of the third harmonic current between the three phases; symmetricizing the obtained three groups of three-phase signals and inputting them into a three-phase phase-locked loop (PLL); processing the voltage signals using the PLL, and reconstructing the third harmonic voltage based on its voltage amplitude, phase, and other information; and changing the modulation voltage using the obtained third harmonic voltage and third harmonic back electromotive force, thereby achieving the effect of suppressing the third harmonic current. This invention is simple and easy to implement, has a significant effect on eliminating third harmonics, and can effectively improve the motor current waveform.

Description

Technical Field

[0001] This invention belongs to the field of multiphase motor drive control, specifically relating to a third harmonic suppression method for a nine-phase open-winding permanent magnet synchronous motor, which is suitable for optimizing motor control. Background Technology

[0002] Multiphase open-winding permanent magnet motors, building upon the high performance of ordinary permanent magnet synchronous motors, leverage the advantages of multiphase operation to enable low-voltage, high-power operation. Furthermore, the full-bridge inverter structure of the open-winding system allows for higher output power than common half-bridge inverters, thus increasing system capacity. Simultaneously, the full-bridge inverter can generate more and more flexible inverter levels, resulting in more voltage vectors and enhanced system controllability. Therefore, multiphase open-winding motor drive systems have broad research and application prospects. However, for common DC bus type open-winding systems, the presence of low-order harmonic paths makes the motor system significantly affected by low-order harmonics, with the third harmonic having the most pronounced impact. Large third harmonic currents severely affect the motor's operating state under rated conditions, necessitating the elimination of third harmonic currents in the system.

[0003] Currently, there are two main methods for harmonic suppression in multiphase open-winding motor systems: the first is to utilize the coordinate transformation characteristics of the multiphase motor to decouple the harmonic current and suppress it through a current controller. The second method addresses the dead-time problem of the inverter; however, there are few current dead-time suppression methods for multiphase motor SPWM, and applying SVPWM modulation to multiphase open-winding systems would significantly increase the control difficulty.

[0004] Therefore, it is necessary to propose a simple and effective solution for low-order harmonic suppression in multiphase open-winding permanent magnet synchronous motors (SMPWM). Summary of the Invention

[0005] The purpose of this invention is to provide a method for suppressing third harmonics in a nine-phase open-winding permanent magnet synchronous motor (PMSM). This method can solve the problem of high low-order harmonic content during normal operation of a nine-phase open-winding PMSM, which affects the fundamental electromagnetic torque output of the motor.

[0006] To solve the above-mentioned technical problems, the technical solution designed in this invention is as follows:

[0007] A method for suppressing third harmonics applied to a nine-phase open-wound PMSM includes the following steps:

[0008] Step 1: Collect signals of terminal voltage, terminal current and motor speed of the nine-phase open-winding permanent magnet synchronous motor, and calculate the third harmonic back EMF of the motor by combining the speed and motor flux linkage information.

[0009] Step 2: Divide the voltage signal into three groups, each group being a symmetrical three-phase signal. After subtracting the third back EMF from each phase voltage signal, add the signals from each group together and divide by three to obtain the third harmonic voltage signal in each group.

[0010] Step 3: In a semi-symmetrical nine-phase open-winding permanent magnet synchronous motor, reverse the phase difference π / 3 between one of the three obtained signals and the other two sets, so that the three signals become three-phase symmetrical signals, and input them into the three-phase phase-locked loop; if the winding structure is fully symmetrical, it is not necessary to reverse the signals, and they can be directly input into the three-phase phase-locked loop.

[0011] Step 4: Obtain the amplitude and phase signals of the third harmonic voltage using a three-phase phase-locked loop, and recalculate the processed non-pulse third harmonic voltage signal based on the information of the third harmonic voltage.

[0012] Step 5: Invert the pulse signal obtained in the previous step and add it together with the calculated third harmonic back EMF of the motor to the modulation voltage of the current closed-loop output.

[0013] Furthermore, step one specifically includes:

[0014] The motor terminal voltage signal in pulse form is obtained through a voltage sensor, the current signal is output from a Hall sensor, and the motor speed signal is obtained through a rotary transformer. Combining the motor's voltage equation with the amplitude of the corresponding permanent magnet flux linkage and the motor's angular velocity, the corresponding harmonic back EMF can be calculated.

[0015] Furthermore, step two specifically includes:

[0016] Just as with the Park transform, a typical phase voltage waveform can be considered as the result of the superposition of harmonics. Therefore, the stator voltage of a semi-symmetrical nine-phase PMSM motor can be expressed by the following formula:

[0017]

[0018] In the formula, n = 1, 2, 3 represents three sets of three phases; ν = 1, 3, 5, 7 represents the 1st, 3rd, 5th, and 7th harmonics; A ν This represents the amplitude of the νth harmonic. And U... an U bn U cn These represent the motor terminal voltages in the three groups, respectively. This represents the phase deviation of the νth harmonic voltage relative to the fundamental voltage. For a normal, symmetrical motor terminal voltage, after adding each group of three phases, the value obtained by adding the three phases is not zero only at the third harmonic, as shown in the following formula.

[0019]

[0020] In the formula, u sn This is the sum of the voltages of the nth group of three phases. Where, u sn The amplitude is three times the amplitude of the third harmonic voltage in a single phase. Therefore, dividing the above value by three will give the amplitude of the third harmonic voltage in a single phase.

[0021] Furthermore, step three specifically includes:

[0022] As can be seen from the above formula, the three sets of third harmonics in a semi-symmetrical nine-phase PMSM winding have a phase difference of π / 3. Inverting the middle term yields a symmetrical three-phase signal. For a fully symmetrical nine-phase PMSM system with an open winding on a common DC bus, which is also affected by third harmonics, its three sets of third harmonics will be a symmetrical signal with a phase difference of 2π / 3. Therefore, this third harmonic voltage suppression method can be applied to both semi-symmetrical and fully symmetrical nine-phase PMSM systems.

[0023] Furthermore, step four specifically includes:

[0024] Analysis of the inverter's dead-time characteristics reveals that the dead-time voltage of the motor system is a steadily changing quantity. Therefore, after excluding the back EMF component in the motor voltage, which fluctuates with speed, a relatively stable third harmonic voltage in the dead-time can be tracked using a phase-locked loop (PLL). Since the detected voltage signal contains high-frequency components, a low-pass filter is introduced within the PLL. Introducing a low-pass filter on the dq-axis signal avoids phase and amplitude distortion caused by the filter. Although the expected signal after filtering is a DC component, the DC component change caused by sudden input signal abrupt changes must be considered. Therefore, the order of the low-pass filter should not be too high, and the cutoff frequency should not be too low to prevent poor dynamic response performance of the PLL. Analysis shows that with a sampling frequency of 6000Hz and the inverter output frequency, a second-order filter with a cutoff frequency of 1000Hz is sufficient to meet the requirements. Relevant literature on the performance analysis of three-phase PLLs indicates that three-phase PLLs based on a synchronous coordinate system are suitable for frequency variations, have good anti-interference capabilities against harmonic distortion, and possess the characteristics of a low-pass filter. Therefore, it is suitable for tracking the third harmonic voltage deviation caused by dead zone voltage, and a low-order low-pass filter can achieve a good filtering effect. In summary, the purpose of using a three-phase phase-locked loop in this step is to achieve accurate tracking of the third harmonic voltage and filtering of high-frequency signals.

[0025] Furthermore, step five specifically includes:

[0026] After obtaining a third harmonic sinusoidal signal free from higher harmonic interference, it is important to correlate the phase information of the original third harmonic signal with that of the obtained third harmonic signal to prevent phase errors caused by the previous reverse direction. The observed harmonic voltage, harmonic back EMF, and harmonic voltage generated by the harmonic current closed-loop control are superimposed and output to the modulation wave side of the inverter along with the fundamental component generated by vector control, thus outputting an equivalent voltage signal through the inverter.

[0027] Compared with the prior art, the beneficial effects of this invention are:

[0028] 1. Utilizing the characteristics of a nine-phase permanent magnet synchronous motor, the third harmonic voltage is tracked using a three-phase phase-locked loop, and then compensated to the modulation wave side of the inverter through closed-loop proportional control. Combined with the aforementioned harmonic current closed-loop control, rapid and error-free regulation of low-order harmonics can be achieved, thereby improving the motor's operating performance. Compared with control using only harmonic current closed-loop control, it has a faster response speed, and the control effect is not weakened.

[0029] 2. Compared with other dead-time compensation methods, it does not rely on the detection of current direction and has more reliable harmonic compensation accuracy. Compared with dead-time compensation methods that change the pulse, the control method is simpler and requires less computation.

[0030] 3. Unlike general dead zone compensation methods, although this invention is based on a semi-symmetrical nine-phase open-winding permanent magnet synchronous motor, it can also be applied to a fully symmetrical nine-phase open-winding motor, and has wide applicability.

[0031] 4. For multi-phase open-winding permanent magnet synchronous motor systems, the method proposed in this invention is simple and easy to implement, easy to implement in DSP programming, and takes up little processing time for the controller. Attached Figure Description

[0032] Figure 1 This is a system topology diagram of the nine-phase open-winding permanent magnet synchronous motor involved in the present invention;

[0033] Figure 2 This invention relates to a block diagram of a three-phase phase-locked loop control system with a low-pass filter.

[0034] Figure 3 This is a block diagram of the vector control system for a nine-phase open-winding permanent magnet synchronous motor, which relates to the present invention.

[0035] Figure 4 This is a flowchart of the third harmonic voltage compensation method involved in the present invention;

[0036] Figure 5 This invention relates to a simplified block diagram of the third harmonic voltage and current closed-loop control.

[0037] Figure 6a The current waveform before the addition of the third harmonic current suppression algorithm involved in this invention;

[0038] Figure 6b The current waveform after incorporating the third harmonic current suppression algorithm, as described in this invention;

[0039] Figure 7a The current waveform involved in this invention is when only the third harmonic current is added to the closed loop.

[0040] Figure 7b The current waveform of the present invention when the third harmonic voltage and current are added in a dual closed-loop control is described.

[0041] Figure 8a The present invention relates to a comparison between the motor output torque and the fundamental torque before eliminating the third harmonic;

[0042] Figure 8b This invention relates to a comparison between the motor output torque and the fundamental torque after eliminating the third harmonic. Detailed Implementation

[0043] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The embodiments described below are only for explaining the present invention and are not intended to limit the present invention.

[0044] The third harmonic suppression method proposed in this invention for a nine-phase open-wound PMSM (permanent-magnet synchronous motor) includes:

[0045] Step 1: Collect signals of the terminal voltage, terminal current and motor speed of the nine-phase open-winding permanent magnet synchronous motor, and calculate the third harmonic back EMF of the motor by combining the speed and motor flux linkage information.

[0046] In one embodiment, step one specifically includes:

[0047] The system topology is as follows Figure 1 As shown, the acquisition of both voltage and current signals relies on voltage sensors. Voltage signals are self-explanatory, and the Hall element used in the current sensor also outputs a voltage component. Therefore, voltage sensors are needed to process both signals. The third harmonic back EMF generated by the permanent magnet can be obtained from the following equation:

[0048]

[0049] In the formula, r s L is the stator resistance. d3 L q3 It is the stator inductance in the dq coordinate system, u d3 u q3 id3 i q3 These are the voltage and current of the stator in the dq coordinate system, respectively, where ω is the electric angular velocity and ψ is the electric current. f3 Let be the amplitude of the third harmonic flux linkage of the permanent magnet. Under normal control, the q-axis voltage in the third harmonic plane can be obtained using the above formula. The third harmonic voltage values ​​generated by the third harmonic flux linkage in each phase can be obtained through coordinate transformation.

[0050] Step 2: Divide the voltage signal into three groups, each group being a symmetrical three-phase signal. Subtract the third back EMF from each phase voltage signal, add the signals of each group together and divide by three to obtain the third harmonic voltage signal in each group.

[0051] In one embodiment, step two specifically includes: As shown in Formula 1 below, the third harmonic has the same amplitude and phase in each of the three phase groups. Therefore, in a nine-phase motor, the phase difference between the three groups of third harmonic voltages is three times the phase difference between the three groups of three phases. The third harmonic signal can be extracted by direct calculation. The third harmonic voltage shown in Formula 2 below can be obtained by summing the three phases within each group. However, the voltage amplitude obtained at this time is three times the original third harmonic voltage, so it is necessary to divide by three to obtain the actual harmonic voltage amplitude.

[0052] The stator voltage of a semi-symmetrical nine-phase PMSM motor is given by the following formula:

[0053]

[0054] In the formula, n = 1, 2, 3 represents three sets of three phases; ν = 1, 3, 5, 7 represents the 1st, 3rd, 5th, and 7th harmonics; A ν This represents the amplitude of the νth harmonic; while U an U bn U cn These represent the motor terminal voltages in the three groups, respectively; This represents the phase deviation of the νth harmonic voltage relative to the fundamental wave. For symmetrical motor terminal voltages, after adding each group of three phases, the value obtained by adding at the third harmonic is not zero, as shown in the following formula.

[0055]

[0056] In the formula, u sn Let u be the sum of the voltages of the nth group of three phases; where u sn The amplitude is three times the amplitude of the third harmonic voltage in a single phase; dividing the above value by three gives the amplitude of the third harmonic voltage in a single phase.

[0057] Step 3: In a semi-symmetrical nine-phase open-winding permanent magnet synchronous motor, reverse the phase difference π / 3 between one of the three obtained signals and the other two sets, so that the three signals become three-phase symmetrical signals, and input them into the three-phase phase-locked loop; if the winding structure is fully symmetrical, it is not necessary to reverse the signals, and they can be directly input into the three-phase phase-locked loop.

[0058] In one embodiment, step three specifically includes: For a fully symmetrical nine-phase motor, the phase difference between its three phases is 2π / 9, therefore the phase difference between the three sets of third harmonics is 2π / 3. For a semi-symmetrical nine-phase motor, the phase difference between the three phases used in this example is π / 9, therefore the phase difference between the three sets of third harmonics is π / 3. Thus, it can be seen that the third harmonic in a fully symmetrical motor is exactly a set of symmetrical sinusoidal signals, and the third harmonic signal in the semi-symmetrical motor used in this example can also be constructed as a set of symmetrical third harmonic signals by inverting the middle phase.

[0059] Furthermore, to avoid the impact of speed changes on the motor's back EMF, which in turn affects the acquisition of the third harmonic in the motor terminal voltage, it is necessary to remove the back EMF component from the calculated third harmonic voltage components. This results in three sets of symmetrical third harmonic dead-zone deviation voltage components, which are then output to the three-phase phase-locked loop. The analysis of the inverter's dead-zone voltage characteristics under different conditions will not be elaborated upon here.

[0060] Step 4: Process the voltage signal using a three-phase phase-locked loop to obtain the amplitude and phase signals of the third harmonic voltage, and recalculate the processed non-pulse third harmonic voltage signal based on the information of the third harmonic voltage.

[0061] The phase-locked loop used in this invention is a three-phase phase-locked loop based on a synchronous coordinate system, such as... Figure 2 As shown, this phase-locked loop (PLL) converts the three-phase signal into a DC signal in the dq coordinate system through coordinate transformation; the position angle signal used in the coordinate transformation is the signal position angle measured by the PLL itself. To solve the problem of high-frequency switching signal interference at the inverter end, a low-pass filter is added to the dq axis signal. Experiments and simulations show that a second-order low-pass filter is sufficient at a switching frequency of 6000Hz. The amplitude of the input three-phase signal composite vector can be calculated from the filtered PLL dq axis signal. By locking its q-axis component to 0 through the controller, the PLL can track the three-phase composite vector. Thus, the amplitude and phase of the processed third harmonic voltage are obtained, achieving third harmonic voltage tracking. Finally, using the measured signal amplitude and phase, the waveform of the third harmonic voltage without high-frequency signal interference is calculated.

[0062] Step 5: Invert the pulse signal obtained in the previous step and add it together with the calculated third harmonic back EMF of the motor to the modulation voltage of the current closed-loop output.

[0063] In one embodiment, step five specifically includes:

[0064] The above steps have yielded the third harmonic voltage component and the third harmonic back EMF component caused by the dead zone. These two components are then compensated together for the voltage generated by the current closed loop. By changing the third harmonic content in the modulation voltage, the third harmonic current content in the motor is controlled. Therefore, the overall control block diagram of the system is as follows: Figure 3 As shown, the voltage compensation flowchart is as follows. Figure 4 As shown. Through further simplification and abstraction, the entire compensation process is as follows: Figure 5 As shown.

[0065] The above method is now applied to the control of a nine-phase open-winding permanent magnet synchronous motor. Figure 6a and Figure 6b The display shows the motor current waveforms before and after the addition of a harmonic suppression algorithm. The comparison reveals that the third harmonic current severely interferes with the phase current waveform, and the harmonic suppression algorithm effectively suppresses the third harmonic current. Figure 7a and Figure 7b The invention demonstrates the current transient waveforms of a conventional closed-loop current control with only third harmonic current and the voltage-current dual-closed-loop harmonic control proposed in this invention. Figure 7a and Figure 7b It can be seen that the dual-closed-loop harmonic current control proposed in this invention can achieve a fast response in suppressing third harmonic current, and its response speed is significantly better than that of the case with only current closed-loop control. Through Figure 8a and Figure 8b It can be seen that the relationship between the total output torque and the fundamental torque of the motor is before and after adjusting the harmonic current. It can be seen that the direction of work done by the third harmonic current is opposite to that of the fundamental current. By suppressing the third harmonic current, the amplitude of the fundamental current and the effective value of the overall current can be reduced during rated operation, which can reduce the power loss and heat generation of the motor system.

[0066] In summary, this invention proposes a third harmonic suppression method for nine-phase open-wound PMSMs. The method includes extracting the third harmonic voltage caused by the inverter dead zone and implementing closed-loop control of the third harmonic voltage. Combined with closed-loop control of the third harmonic current as a supplement, it achieves rapid, zero-steady-state-error regulation of the third harmonic current. This invention effectively suppresses the third harmonic component in the control of nine-phase open-wound motors. The method is simple, easy to program, and highly versatile, applicable to various nine-phase open-wound structures.

Claims

1. A method for suppressing third harmonics applied to a nine-phase open-wound PMSM, characterized in that, Includes the following steps: Step 1: Collect the motor terminal voltage and terminal current signals, and calculate the third harmonic back EMF; Step 2: Calculate the third harmonic voltage in each group of three phases; Step 3: Symmetrically convert the three sets of three-phase third harmonic voltage signals obtained and subtract the third harmonic back EMF, then input them into the three-phase phase-locked loop; Step 4: Use a three-phase phase-locked loop to process the voltage signal and reconstruct the third harmonic voltage after removing the third harmonic back EMF based on its voltage amplitude and phase information; Step 5: Based on the reconstructed third harmonic voltage and the third harmonic back EMF, reverse the reconstructed third harmonic voltage obtained in Step 4, add it to the calculated motor third harmonic back EMF, and add it to the modulation voltage of the current closed-loop output to change the modulation voltage and suppress the third harmonic current.

2. The method for suppressing third harmonics applied to a nine-phase open-winding PMSM according to claim 1, characterized in that, Step one specifically includes: The motor terminal voltage signal, terminal current signal, and motor speed signal are obtained. Combined with the motor voltage equation, the corresponding harmonic back EMF is calculated using the amplitude of the permanent magnet flux linkage and the motor angular velocity.

3. The method for suppressing third harmonics applied to a nine-phase open-winding PMSM according to claim 2, characterized in that, Step two specifically includes: The stator voltage of a semi-symmetrical nine-phase open-winding PMSM motor is given by the following formula: In the formula, n = 1, 2, 3 represents three sets of three phases; ν = 1, 3, 5, 7 represents the 1st, 3rd, 5th, and 7th harmonics; A ν This represents the amplitude of the νth harmonic; while U an U bn U cn These represent the motor terminal voltages in the three groups, respectively; ω represents the phase deviation of the νth harmonic voltage relative to the fundamental wave; for symmetrical motor terminal voltages, after adding each group of three phases, the value obtained by adding at the third harmonic is not zero, as shown in the following formula; ω is the electric angular velocity. In the formula, u sn Let u be the sum of the voltages of the nth group of three phases; where u sn The amplitude is three times the amplitude of the third harmonic voltage in a single phase; dividing the above value by three gives the amplitude of the third harmonic voltage in a single phase.

4. The method for suppressing third harmonics applied to a nine-phase open-winding PMSM according to claim 3, characterized in that, Step 3 specifically includes: in a semi-symmetrical nine-phase open winding PMSM, one of the three obtained signals is reversed with the other two signals by a phase difference of π / 3, and the three signals become three-phase symmetrical signals, which are then input into the three-phase phase-locked loop; if the winding structure is fully symmetrical, it is not necessary to reverse the signals, and they are directly input into the three-phase phase-locked loop.

5. The method for third harmonic suppression applied to a nine-phase open-winding PMSM according to claim 4, characterized in that, Step four specifically includes: obtaining the amplitude and phase signals of the third harmonic voltage using a three-phase phase-locked loop, and recalculating the processed non-pulse third harmonic voltage signal based on the information of the third harmonic voltage.

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