Voltage resonance suppression method for direct-current busbar film capacitor of permanent magnet synchronous motor

Abstract

A voltage resonance suppression method for a direct-current busbar film capacitor of a permanent magnet synchronous motor. The permanent magnet synchronous motor uses field-oriented control (FOC), and the method comprises: S1, collecting busbar voltage data Udc on an inverter by means of a busbar voltage collection circuit; S2, performing low-pass filtering processing on the collected busbar voltage data Udc, so as to obtain a direct-current component Udc0 of a busbar voltage; S3, subtracting the direct-current component Udc0 of the busbar voltage from the collected busbar voltage data Udc, so as to acquire a fluctuating component of the busbar voltage: (I)=Udc-Udc0; S4, subtracting the fluctuating component of the busbar voltage from the direct-current component Udc0 of the busbar voltage, so as to obtain busbar voltage reference voltage data: u* dc=Udc0-(I), which is finally output to an SVPWM module; and S5, the SVPWM module using the inputted busbar voltage reference voltage data u* dc as a parameter to perform SVPWM waveform generation modulation calculation.

Description

Voltage resonance suppression method of DC bus film capacitor of permanent magnet synchronous motor Technical field:

[0001] The invention relates to a voltage resonance suppression method of a DC bus film capacitor of a permanent magnet synchronous motor. Background technology:

[0002] Permanent magnet synchronous motors (PMSMs) generally utilize the Field-Oriented Control (FOC) control strategy. FOC, which stands for Field-Oriented Control and is also known as Vector Control (VC), is currently one of the most efficient methods for controlling permanent magnet synchronous motors (PMSMs). The FOC control strategy aims to achieve smooth torque, low noise, high efficiency, and fast dynamic response by precisely controlling the magnitude and direction of the magnetic field.

[0003] The specific structure of the PMSM motor is shown in Figures 1, 2, and 3. The PMSM motor consists of a motor monomer 1 and a motor controller 2. The motor monomer 1 includes a stator assembly 12, a rotor assembly 13, and a housing assembly 11, including a stator core and a coil winding wound on the stator core. The stator assembly 13 is mounted on the housing assembly 11, and the rotor assembly 13 is sleeved on the inner side of the stator assembly 12. The motor controller 2 includes a control box 22 and a control circuit board 21 installed in the control box 22. Several electrolytic capacitors are installed on the control circuit board 21 as DC bus capacitors 23 (that is, the DC bus electrolytic capacitors in Figure 2).

[0004] Traditional motor controllers use electrolytic capacitors as DC bus capacitors with a capacitance of more than a few hundred microfarads. They can stabilize the bus voltage and absorb energy during motor deceleration. However, electrolytic capacitors have problems such as short life, large size, and high cost. Thin-film capacitors are used instead of electrolytic capacitors as DC bus capacitors to solve the inherent defects of electrolytic capacitors. However, due to the very small capacitance of thin-film capacitors, which are about tens of microhenries, they are prone to overvoltage failures and even burn out power devices. Therefore, overvoltage suppression must be performed. The patent number is CN202210694048, and the patent name is "Overvoltage suppression method of thin-film capacitors for DC bus of permanent magnet synchronous motors." It effectively solves the above problems.

[0005] However, since there is also an LC harmonic circuit in the circuit structure, that is, the inductor L of the DC filter circuit and the DC bus film capacitor B5 form an LC harmonic circuit, as shown in Figure 4, the existence of the LC harmonic circuit is bound to form harmonic vibration of the voltage on the DC bus film capacitor B5, which of course has a substantial impact on the precise control and efficiency control of the motor. In FIG4 , the permanent magnet synchronous motor includes a motor unit B7 and a motor controller. The motor unit B7 includes a stator assembly and a permanent magnet rotor assembly. The stator assembly includes a stator core and coil windings wound on the stator core. The motor controller includes an AC filter circuit B2, a rectifier circuit B3, a DC filter circuit B4, a DC bus film capacitor B5, an inverter circuit B6, a microprocessor MCU, and a phase current detection circuit. A three-phase power supply B1 (an AC power supply) sequentially charges the DC bus film capacitor B5 through the AC filter circuit B2, the rectifier circuit B3, and the DC filter circuit B4. The DC bus film capacitor B5 provides high-voltage DC power to the inverter circuit B6. The phase current detection circuit detects the phase current flowing through the coil winding and sends it to the microprocessor MCU. The microprocessor MCU controls the operation of the inverter circuit, which controls the power on and off of each phase coil winding of the stator assembly. The permanent magnet synchronous motor adopts a field-oriented control (FOC) field. The method of FOC field-oriented control can be found in textbooks or on the Internet and will not be described in detail here.

[0006] In view of this, it is necessary to suppress the voltage fluctuation caused by the LC harmonic circuit in the circuit structure. As shown in Figure 5, it is a voltage resonance suppression scheme for DC bus film capacitors that is currently commonly used: LC resonance suppression is achieved by injecting dq axis voltage. The specific implementation process is: sampling the bus voltage to obtain the inverter bus voltage data U dc , and then perform low-pass filtering to obtain the bus voltage DC component U dc0 , then use U dc Subtract U dc0 Get the AC component of the bus voltage Finally, the AC component of the bus voltage Multiply by two coefficients kd and kq and superimpose them on the dq axis voltage respectively to change the system stability and achieve the effect of suppressing LC resonance.

[0007] The technical solution of using dq axis voltage injection to achieve LC resonance suppression has the following shortcomings: (1) The kd and kq parameters need to be re-adjusted and matched for different motor power levels or when the motor is running at different power levels. Therefore, this solution is not universal and parameter adjustment is difficult. (2) Using dq axis voltage injection will introduce high-frequency ripple current into the motor control, thereby affecting motor performance and introducing high-frequency electromagnetic noise.

[0008] As shown in Figures 5 and 6, the existing technology solution uses a dq-axis voltage injection scheme to achieve LC resonance suppression. For electrolytic capacitor-free motor drive systems, small-capacitance film capacitors are used instead of large-capacitance electrolytic capacitors, reducing the capacitance to approximately 1 / 50 of the original value. As the DC-side capacitance decreases, the bus voltage fluctuates significantly. Bus voltage fluctuations primarily stem from two factors. First, due to the small bus capacitance, its energy storage function is essentially lost. Therefore, after the three-phase power is rectified by the rectifier bridge, six times the power frequency oscillations are generated on the bus voltage. Second, LC resonant oscillations are superimposed on the bus voltage. To prevent high-frequency harmonics from being fed into the power grid, motor drive systems typically require a certain number of DC reactors. The LC resonance generated by the DC reactor and the bus film capacitors superimposes LC resonant frequency oscillations on the bus voltage, and the amplitude of these oscillations increases with increasing motor operating power.

[0009] Figure 6 shows a simplified model. The state equation of the drive system can be expressed as:

[0010] The inverter and motor system presents a constant power load characteristic. Ignoring the switching loss, the average power output of the inverter is equal to the average power of the motor. The average power output current of the inverter can be expressed as:

[0011] Since the bus voltage fluctuation component accounts for a very small proportion, the inverter output current can be linearized as:

[0012] According to Routh's stability criterion, if the coefficients of the characteristic equation are positive, the system is stable. The third coefficient of the characteristic equation is generally positive, so the second coefficient determines the stability of the system. The system stability condition is:

[0013] In electrolytic capacitor-free motor drive systems, due to the extremely small capacitance, when the motor is running at high power, the system will face instability, as can be seen from the system stability conditions. Improving drive system stability is one of the core issues facing electrolytic capacitor-free motor drive systems.

[0014] Summary of the invention:

[0015] The purpose of the present invention is to provide a method for suppressing the voltage resonance of the DC bus film capacitor of a permanent magnet synchronous motor, mainly to solve the technical problems in the prior art of using a dq axis voltage injection scheme to achieve LC resonance suppression, resulting in poor versatility, difficult parameter debugging and generation of high-frequency ripple current.

[0016] The purpose of the present invention is achieved through the following technical solutions:

[0017] A method for suppressing voltage resonance of a DC bus film capacitor of a permanent magnet synchronous motor, wherein the permanent magnet synchronous motor adopts FOC magnetic field oriented control, and is characterized in that:

[0018] S1: Collect the bus voltage data U on the inverter through the bus voltage acquisition circuit dc ;

[0019] S2: Sampled bus voltage data U dc Perform low-pass filtering to obtain the DC component U of the bus voltage dc0 ;

[0020] S3: Use the collected bus voltage data U dc Subtract the DC component of the bus voltage U dc0 , and obtain the bus voltage fluctuation component:

[0021] S4: Use the DC component of the bus voltage U dc0 Subtract the bus voltage fluctuation component to obtain the bus voltage reference voltage data that is finally output to the SVPWM module:

[0022] S5: SVPWM module uses the input bus voltage reference voltage data u * dc Use it as a parameter to calculate SVPWM wave modulation.

[0023] The U in S2 dc0 This is how it is obtained: dc0 (n) = qu dc (n)+(1-q)u dc0 (n-1),

[0024] Where q is the low-pass filter coefficient, n is the number of times the bus voltage data Udc is sampled;

[0025] The above-mentioned bus voltage data U collected on the inverter dc The sampling frequency is the same as the carrier frequency of the SVPWM module.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] Effect 1: It suppresses LC resonant oscillations and reduces DC bus voltage fluctuations. Using film capacitors with capacitances of tens of microhenries instead of electrolytic capacitors of hundreds of microfarads results in bus voltage oscillations. These oscillations include 300Hz oscillations from the rectifier bridge and LC resonant oscillations between the DC bus film capacitors and the differential-mode inductor. The rectifier component's oscillations do not increase with increasing motor power, so their impact on motor control is limited. However, the LC resonant oscillations do increase with increasing motor power, and therefore must be suppressed.

[0028] Effect 2: Reduces motor phase current THD. The LC resonance suppression algorithm reduces bus voltage fluctuations, primarily due to the 300Hz rectifier component. For motor control systems, smaller bus voltage fluctuations result in more stable control performance.

[0029] Effect 3: It can reduce the THD of the grid-side incoming current. The THD of the grid-side incoming current is related to the motor control performance. The more stable the motor control performance, the smaller the impact on the grid-side incoming current.

[0030] Other advantages of the present invention will be further described in the embodiment section. Description of the drawings:

[0031] FIG1 is a perspective view of a PMSM motor in the prior art;

[0032] FIG2 is a perspective view of a motor controller for a PMSM motor in the prior art;

[0033] FIG3 is a cross-sectional view of the structure of a PMSM motor in the prior art;

[0034] FIG4 is a block diagram of an implementation circuit of a motor controller for a PMSM motor in the prior art;

[0035] FIG5 is a block diagram showing the principle of suppressing LC resonance using a dq-axis voltage injection scheme in a PMSM motor according to the prior art;

[0036] FIG6 is an equivalent circuit diagram of a PMSM motor in the prior art;

[0037] 7 is a block diagram of the principle of the LC resonance suppression scheme of the permanent magnet synchronous motor of the present invention;

[0038] FIG8 is a software flow chart of the LC resonance suppression solution for a permanent magnet synchronous motor according to the present invention;

[0039] FIG9 is a diagram showing simulation results of a motor drive system using a film capacitor as the DC bus capacitor without an LC resonance suppression solution;

[0040] FIG10 is an FFT analysis diagram of the bus voltage of a motor drive system using film capacitors as DC-side bus capacitors without an LC resonance suppression solution;

[0041] Figure 11 shows the simulation results of a motor drive system with an LC resonance suppression scheme using a film capacitor as the DC bus capacitor;

[0042] Figure 12 shows the FFT analysis of the bus voltage of a motor drive system with a film capacitor as the DC bus capacitor and an LC resonance suppression scheme;

[0043] FIG13 is a graph showing the experimental results of a motor drive system using a film capacitor as the DC bus capacitor without an LC resonance suppression scheme;

[0044] FIG14 is an FFT analysis diagram of the bus voltage, motor phase current, and grid-side incoming line current for a motor drive system using film capacitors as DC-side bus capacitors without an LC resonance suppression solution;

[0045] FIG15 is a diagram showing the experimental results of a motor drive system with an LC resonance suppression scheme using a film capacitor as the DC bus capacitor;

[0046] FIG16 is an FFT analysis diagram of the bus voltage, motor phase current, and grid-side incoming current of a motor drive system using a film capacitor as the bus capacitor on the DC side with an LC resonance suppression solution. Specific implementation method:

[0047] The present invention will be further described in detail below through specific embodiments in conjunction with the accompanying drawings.

[0048] As shown in FIG7 and FIG8, the voltage resonance suppression method of the DC bus film capacitor of the permanent magnet synchronous motor adopts FOC magnetic field oriented control, which is characterized by:

[0049] S1: The microprocessor MCU collects the bus voltage data U on the inverter through the bus voltage acquisition circuit dc ;

[0050] S2: Sampled bus voltage data U dc Perform low-pass filtering to obtain the DC component U of the bus voltage dc0 ;

[0051] S3: Use the collected bus voltage data U dc Subtract the DC component of the bus voltage U dc0 , and obtain the bus voltage fluctuation component:

[0052] S4: Use the DC component of the bus voltage U dc0Subtract the bus voltage fluctuation component to obtain the bus voltage reference voltage data that is finally output to the SVPWM module:

[0053] S5: SVPWM module uses the input bus voltage reference voltage data u * dc Use it as a parameter to calculate SVPWM wave modulation.

[0054] U in S2 mentioned above dc0 This is how it is obtained: dc0 (n) = qu dc (n)+(1-q)u dc0 (n-1),

[0055] Where q is the low-pass filter coefficient, n is the number of times the bus voltage data Udc is sampled;

[0056] The above-mentioned bus voltage data U collected on the inverter dc The sampling frequency is the same as the carrier frequency of the SVPWM module.

[0057] The main idea of ​​the technical solution of the present invention is to modify the bus reference voltage u of the SVPWM wave module in software * dc , thereby changing the output voltage and thus enhancing system stability. This is specifically manifested in suppressing the LC oscillation component in the bus voltage oscillation, avoiding the instability problem caused by the increase in the operating power of the PMSM motor. The principle is as follows:

[0058] The motor output power expression is:

[0059] The general SVPWM module algorithm uses the actual sampled bus voltage as the reference voltage, that is:

[0060] The solution adopted in this paper is to reconstruct the sampled bus voltage and then input it into the SVPWM module as a reference voltage. The reconstructed bus reference voltage is:

[0061] The output voltage vector finally obtained by using the reconstructed reference voltage is

[0062] The actual operating power equation of the motor is derived as follows:

[0063] Then, the inverter output current after adopting the reconstructed reference voltage can be calculated as:

[0064] Substitute the inverter output current expression into the system state equation and perform Laplace transform to obtain the new system characteristic equation:

[0065] It can be seen from this that if the coefficients of the system characteristic equation are all positive, the system is in a stable state.

[0066] Figure 9 shows the simulated waveforms of a motor drive system using film capacitors as the DC bus capacitors without the LC resonance suppression algorithm. The bus voltage fluctuates between 200 V and 600 V. An FFT analysis of the bus voltage, shown in Figure 10, reveals that the bus voltage harmonics primarily consist of a rectifier component around 300 Hz and an LC resonance component around 200 Hz.

[0067] Using film capacitors as the DC bus capacitors, the motor drive system incorporates the LC resonance suppression algorithm. The simulation waveforms are shown in Figure 11. The bus voltage fluctuates between 390V and 430V. An FFT analysis of the bus voltage, shown in Figure 12, reveals that the bus voltage harmonics primarily consist of rectifier components around 300Hz, while the LC resonance component around 200Hz is significantly suppressed. This demonstrates the effectiveness of the algorithm in suppressing LC resonance and effectively reducing bus voltage fluctuations.

[0068] An LC resonance suppression algorithm was experimentally verified for a motor drive system using film capacitors as the DC bus capacitors. Figure 13 shows the experimental waveforms for a motor drive system using film capacitors as the DC bus capacitors without the LC resonance suppression algorithm. The bus voltage fluctuated between 401V and 618V. FFT analysis of the bus voltage, motor phase current, and grid-side incoming current was performed sequentially, as shown in Figure 14. The FFT results were 12.21%, 6.11%, and 42.92%, respectively.

[0069] Figure 15 shows the waveforms of an experiment in which a motor drive system, using film capacitors as the DC bus capacitors and incorporating an LC resonance suppression algorithm, exhibits bus voltage fluctuations between 438V and 549V. FFT analysis of the bus voltage, motor phase current, and grid-side incoming current is performed sequentially, as shown in Figure 16. The FFT results show 10.37%, 5.5%, and 37.15%, respectively.

[0070] Comparing the data before and after adding the LC resonance suppression algorithm shows that:

[0071] (1) The LC resonance suppression algorithm can suppress bus voltage fluctuations, reducing the fluctuation range from 401V-618V to 438V-549V.

[0072] (2) The LC resonance suppression algorithm can effectively suppress the LC resonance component in the bus voltage. Without the algorithm, the bus voltage FFT results mainly contain the 300Hz rectification component and the LC resonance component near 400Hz. After adding the LC resonance suppression algorithm, the bus voltage FFT results mainly contain the 300Hz rectification component, and the LC resonance component is significantly suppressed.

[0073] (3) The LC resonance suppression algorithm can reduce the motor phase current and the grid-side line current THD, thereby improving the motor operating performance.

[0074] In the text, English in regular font represents English abbreviations, and italics represent variable variables in the software.

[0075] SVPWM: Space Vector Pulse Width Modulation, is a method of superimposing a high-frequency carrier frequency on the input signal and then outputting a high-frequency pulse signal to control the inverter power tube

[0076] d-axis: the axis in the same direction as the motor's N pole

[0077] q-axis: The axis that leads the N-pole of the motor by 90 degrees

[0078] PI: Proportional Integral Control

[0079] Clark transformation: transform the three-phase ABC coordinate system parameters to obtain the α-axis and β-axis

[0080] Park transformation: transform the α-axis and β-axis coordinate system parameters to obtain the d-axis and q-axis

[0081] U d : Target voltage in the d-axis direction output by the d-axis current loop PI regulation

[0082] U q : q-axis current loop PI regulation output q-axis target voltage

[0083] U α : α-axis voltage, obtained by ipark transformation of dq-axis voltage

[0084] U β : β-axis voltage, obtained by ipark transformation of dq-axis voltage

[0085] U a : A phase winding voltage, obtained by ipark transformation of dq axis voltage

[0086] U b : B phase winding voltage

[0087] U v : C phase winding voltage

[0088] i d: d-axis current feedback value

[0089] i q : q-axis current feedback value

[0090] R dc : Differential mode inductor equivalent resistance

[0091] L dc :Differential mode inductance

[0092] i g : Differential mode inductor current

[0093] u s : Equivalent simplified circuit power supply voltage

[0094] u dc : Actual bus voltage

[0095] C dc : Film capacitor capacitance

[0096] i inv : Average output current of the inverter

[0097] P L : Average output power of inverter

[0098] u dc0 : DC component of bus voltage

[0099] : AC component of bus voltage

[0100] s: Laplace operator

[0101] : Motor voltage vector

[0102] : Motor current vector

[0103] u * dc : Bus voltage reference voltage

[0104] q: low-pass filter coefficient

[0105] THD: Total harmonic distortion (THD) is the ratio of the RMS value of the harmonic current to the RMS value of the fundamental current. THD is the abbreviation of Total Harmonic Distortion.

[0106] FFT: Spectral analysis is an important tool in signal analysis and processing. FFT (Fast Fourier Transform) can convert time domain signals into frequency domain to obtain information such as the signal's frequency structure, amplitude, and phase.

[0107] The above embodiments are preferred implementations of the present invention, but the implementations of the present invention are not limited thereto. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention are equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A voltage resonance suppression method for a DC bus film capacitor of a permanent magnet synchronous motor, wherein the permanent magnet synchronous motor adopts FOC field oriented control, and is characterized in that: It includes S1: Collect the bus voltage data U on the inverter through the bus voltage acquisition circuit dc ; S2: Sampled bus voltage data U dc Perform low-pass filtering to obtain the DC component U of the bus voltage dc0 ; S3: Use the collected bus voltage data U dc Subtract the DC component of the bus voltage U dc0 , the bus voltage fluctuation component is obtained: S4: Use the DC component U of the bus voltage dc0 Subtract the bus voltage fluctuation component to obtain the bus voltage reference voltage data that is finally output to the SVPWM module: S5: SVPWM module uses the input bus voltage reference voltage data u * dc Use it as a parameter to calculate SVPWM wave modulation.

2. The voltage resonance suppression method of the DC bus film capacitor of the permanent magnet synchronous motor according to claim 1 is characterized in that: The U in S2 dc0 This is how we get it: dc0 (n) = qu dc (n)+(1-q)u dc0 (n-1), Where q is the low-pass filter coefficient, n is the number of times the bus voltage data Udc is sampled; 3. The voltage resonance suppression method of the DC bus film capacitor of the permanent magnet synchronous motor according to claim 2 is characterized in that: Collect bus voltage data U on the inverter dc The sampling frequency is the same as the carrier frequency of the SVPWM module.

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