A Hybrid EMI Filter for Permanent Magnet Synchronous Motor Drives

Abstract

The present invention discloses a hybrid EMI filter for a permanent magnet synchronous motor drive, belonging to the field of suppressing conducted EMI in a drive system. The hybrid EMI filter mentioned in the present invention includes a passive filter and an active compensation circuit; the passive filter consists of a filtering inductor L f and a filtering capacitor C f . The active compensation circuit includes: an operational amplifier OPAM, a push-pull amplifier Push-Pull, and a voltage converter; the passive filter is installed on the AC line of the drive system, and a branch is led out from the star node of the filtering capacitor C f and connected to the neutral point of the DC bus through a voltage converter; the active compensation circuit is connected across the neutral point of the DC bus and the star node of the filtering capacitor. Based on the original passive filter, the present invention can greatly suppress the common-mode EMI in the drive system by introducing an active compensation circuit, effectively reduce the volume of the filter, and further reduce the overall volume of the drive system.

Description

Technical Field

[0001] The present invention relates to the field of electromagnetic interference suppression of motor drive systems, and in particular to a design method for a hybrid EMI filter for a permanent magnet synchronous motor driver. The scheme is suitable for fields with high requirements for electromagnetic interference suppression, such as vehicles, aerospace, and industrial control. Background Art

[0002] In recent years, with the development of power electronics technology and power semiconductor switching devices, the switching frequency of voltage pulse width modulation (PWM) inverters has been continuously increased, and the rise and fall time of voltage pulses has been continuously reduced. In the permanent magnet synchronous motor (PMSM) drive system, high switching frequency helps to optimize controllability, but it also causes electromagnetic interference (EMI) problems. This not only reduces the reliability of the inverter itself, but also seriously affects the working performance of surrounding electronic products and power supply systems. Therefore, the electromagnetic compatibility (EMC) problem of inverters has received widespread attention from researchers at home and abroad.

[0003] The traditional method of suppressing EMI in motor drives is to use passive filters, including common mode (CM) and differential mode (DM) filters. Although the method of using passive filters to suppress EMI is simple, the effect of common mode EMI filters is limited by the safety leakage current of Y capacitors. Therefore, in order to obtain good common mode EMI suppression effect, the inductance value must be increased, which not only increases the power loss of the system but also increases the weight and volume of the system. In addition, with the introduction of a new generation of wide bandgap semiconductor power devices, the EMI problem of the drive has become more serious.

[0004] In high-power driver modules, the EMI filter will occupy more than 30% of the driver volume, or even up to 50%, which greatly reduces the power density of the driver. Therefore, designing a new EMI filter that can effectively reduce the EMI problem of power devices and reduce the filter volume is a technical problem that needs to be solved in this field. Summary of the invention

[0005] In view of the current development status of passive EMI filters and the currently common technical difficulties, the present invention proposes a hybrid EMI filter for a PMSM driver, the purpose of which is to obtain better EMI filtering performance with a smaller filter volume.

[0006] In order to achieve the above functions, the present invention provides a hybrid electromagnetic interference EMI filter for a permanent magnet synchronous motor PMSM drive, which is used to suppress common mode electromagnetic interference EMI in a PMSM drive system, including a passive LC filter and an active compensation circuit; the passive LC filter is composed of a filter inductor L f And filter capacitor C f The filter inductor Lf It is composed of three filter inductors. One end of each of the three filter inductors is respectively connected to the three-phase cables of the permanent magnet synchronous motor (PMSM), and the other end of each of the three filter inductors is respectively connected to the three-phase output terminals of the PMSM driver. The filter capacitor C f It is composed of three filter capacitors. One end of each of the three filter capacitors is connected in a star connection and a branch is led out and connected to the midpoint of the DC bus through a voltage converter. The other end of each of the three filter capacitors is respectively connected to the three-phase cables between the filter inductor and the PMSM; The active compensation circuit is composed of detection resistors R1 and R2, feedback resistors R3 and R4, output resistor R0, operational amplifier OPAM, push-pull amplifier Push-Pull and voltage converter;

[0007] The resistors R1 and R4 are connected to the non-inverting input terminal of the OPAM, and the resistors R2 and R3 are connected to the inverting input terminal of the OPAM; The inverting input terminal is connected to the star node of the filter capacitor C in the passive LC filter through R2 f The non-inverting input terminal is connected to the two support capacitors C of the neutral point of the DC bus through R1 d The input terminal of Push-Pull is directly connected to the output terminal of the OPAM. The output terminal of Push-Pull is connected to the resistors R3 and R0, and is connected to the input terminal of the voltage converter through the resistor R0. The pin 1 of the voltage converter is connected to the output terminal of Push-Pull through the resistor R0, the pin 2 is connected to the non-inverting input terminal of the OPAM through the resistor R4, the pin 3 is connected to the star node of the filter capacitor, and the pin 4 is connected to the two support capacitors C of the bus midpoint d connected.

[0008] Furthermore, the passive filter is a first-order LC filter. The filter inductor L f is at the μH level, and the filter capacitor C f is at the μF level and is larger than the support capacitor C d .

[0009] Furthermore, the output terminal of the OPAM is connected to the input terminal of the Push-Pull to obtain sufficient driving power so that the voltage converter can output a higher-power compensation voltage.

[0010] Furthermore, the OPAM and Push-Pull in the active compensation circuit are powered by independent power supply circuits.

[0011] Furthermore, the output terminals of the primary side and the secondary side of the voltage converter are of the same name, and the compensation voltage output by the voltage converter has the opposite polarity to the electromagnetic interference voltage.

[0012] Furthermore, in the active compensation circuit, the gain of the compensation voltage is changed by adjusting the feedback resistor, the detection resistor and the turns ratio of the voltage converter winding.

[0013] Furthermore, when the frequency of the common-mode interference voltage generated by the drive system (the drive system is attached Figure 1 , mainly composed of a PMSM driver, a permanent magnet synchronous motor (PMSM), and a power supply. Additionally, the LISN installed in the attachment Figure 1 is designed to detect electromagnetic interference in the drive system.) reaches the corner frequency of the passive filter, the active compensation circuit will provide a compensation voltage with the opposite polarity to the common-mode interference voltage to the passive filter as the frequency changes, reducing the equivalent impedance of the filter capacitor branch, thereby reducing the common-mode interference voltage.

[0014] Furthermore, the passive part of the passive LC filter is directly connected to the three-phase AC cable of the PMSM, and the filtered capacitor branch led out is connected to the neutral point of the DC bus through a voltage converter. The active part is connected across the star node of the filter capacitor and the midpoint of the DC bus, and there is no leakage current injected into the ground loop, which can greatly improve the safety of the PMSM drive system.

[0015] The hybrid EMI filter of the PMSM driver proposed by the present invention is mainly used for common-mode EMI suppression in the drive system loop, and improves the common-mode EMI suppression performance of the passive filter through the active compensation circuit. Therefore, the present invention can effectively reduce the volume of the passive EMI filter and further reduce the overall volume of the drive system while suppressing the common-mode EMI of the drive system.

[0016] Furthermore, the filtering inductor L f used in the passive filter part is at the μH level, and the filtering capacitor C f is at the μF level, and the volume is reduced by about 50% compared with the traditional passive LC filter.

[0017] Furthermore, in order to isolate the DC component on the power supply side, the support capacitor C d is at the μF level, and at the same time, the support capacitor C d should be smaller than the filtering capacitor C f

[0018] Furthermore, due to the gain-bandwidth product problem, a high-bandwidth and high-gain OPAM is used in the active compensation circuit.

[0019] Furthermore, the detection resistors R1 and R2 are equal, and the feedback resistors R3 and R4 are equal.

[0020] Furthermore, the magnetic circuit inductance of the voltage converter should be less than the threshold.

[0021] Furthermore, the same-name terminals of the voltage converter should be set at the output ends of the primary side and the secondary side.

[0022] A hybrid EMI filter for the output side of a PMSM inverter designed by the present invention introduces an active compensation circuit on the basis of a traditional passive LC filter, which can improve the common-mode EMI filtering performance of the filter, reduce the volume of the filter, and increase the power density of the inverter, thus reducing the overall volume.

[0023] Through the proposed inventive concept, the following beneficial effects can be obtained:

[0024] 1. The present invention adds an active compensation circuit on the basis of the original passive LC filter, which can not only greatly reduce the common-mode interference current flowing through the three-phase AC line, but also suppress the influence of the driver on the DC power supply. Compared with the case of only using a passive filter, a better filtering effect can be obtained while reducing the volume of the filter.

[0025] 2. In the hybrid EMI filter mentioned in the present invention, by connecting a Push-Pull at the output end of the OPAM, the output power of the active compensation circuit can be increased, thereby further improving the suppression effect on common-mode EMI.

[0026] 3. In the hybrid EMI filter mentioned in the present invention, the output end of the filtering capacitor is connected to the midpoint of the DC bus through a voltage converter, and no leakage current flows into the ground loop. Compared with the traditional common-mode EMI filter, the risk of electric shock is reduced, and it can be used in occasions with strict safety standards.

[0027] 4. The present invention does not need to consider the influence of the impedance of the main circuit on the active part, which makes the scheme have strong transplantability and expandability, and the filter parameters can be flexibly set according to the needs of suppressing EMI.

[0028] 5. The hybrid EMI filter proposed by the present invention reduces the inductance and capacitance parameters of the passive LC filter, and greatly reduces the influence of the filtering delay on the operating performance of the PMSM. Description of the Drawings

[0029] Figure 1 Is the conduction path of the common-mode EMI of the PMSM drive system;

[0030] Figure 2 Is the structure diagram of the hybrid EMI filter installed on the output side of the driver;

[0031] Figure 3 Is the structure diagram of the push-pull amplifier;

[0032] Figure 4 Is the equivalent impedance diagram of the filtering capacitor branch;

[0033] Figure 5Waveform diagram of the A-phase current of the driver: (a) A-phase current without the filter installed, (b) A-phase current with the proposed hybrid EMI filter installed;

[0034] Figure 6 Spectrum values detected by LISN: (a) Spectrum values without the filter installed, (b) Spectrum values with the proposed hybrid EMI filter installed. Detailed implementation manners

[0035] For a clearer description of the objectives, technical solutions, and advantages of the present invention, the following drawings are incorporated for detailed illustration. It should be understood that the specific implementation manners described herein are only for the purpose of explaining the present invention and are not intended to limit the present invention.

[0036] The structure of the PMSM drive system is as Figure 1 shown. The system includes a direct current (DC) power supply, a three-phase inverter, and a PMSM. To detect the EMI generated by the switching of power devices in the system, the present invention connects a line impedance stabilization network (LISN) for detecting EMI at the DC power supply end.

[0037] Since the radiator of the three-phase inverter and the PMSM housing are grounded, when the power devices in the inverter switch, the common-mode EMI generated flows into the ground wire through parasitic capacitance, parasitic inductance, and line impedance, generating an interference loop, which seriously affects the performance of the drive system.

[0038] In order to enable the filter to have a more obvious filtering effect and a smaller volume in a wider frequency band, a hybrid EMI filter for a PMSM driver is proposed.

[0039] The following are the embodiments of the present invention.

[0040] A hybrid EMI filter for a PMSM drive system is used to suppress the common-mode EMI generated by the switching of power devices in the three-phase inverter of the PMSM drive system. As Figure 2 shown, it includes a passive filter and an active compensation circuit.

[0041] The passive filter part adopts an LC filter, which consists of a filtering inductor L f and a filtering capacitor C f . The filtering inductor L f is connected in series with the PMSM. The input end of the filtering capacitor C f is connected to the three-phase cable between the filtering inductor L f and the PMSM. The output end is connected by a star connection and leads out a branch to be connected to the midpoint of the two support capacitors C d on the DC bus through a voltage source converter.

[0042] Since the present invention is directed to common-mode EMI above 150 kHz, the filter inductor L f is at the μH level, and the filter capacitor C f is at the μF level, which is much smaller than the traditional passive filter. It can suppress common-mode EMI without affecting the normal operation of the drive system. In addition, it should be noted that the support capacitor C d should be smaller than the filter capacitor C f .

[0043] The active compensation circuit includes: detection resistors R1 and R2, feedback resistors R3 and R4, output resistor R0, operational amplifier OPAM, push-pull amplifier Pull-Push, and voltage converter. Its main functions include: sampling, amplifying, and compensating and canceling the common-mode EMI signal.

[0044] Resistors R1 and R4 are connected to the non-inverting input terminal of OPAM, and resistors R2 and R3 are connected to the inverting input terminal of OPAM.

[0045] The inverting input terminal is connected to the star node of the filter capacitor C f in the passive LC filter through R2, and the non-inverting input terminal is connected to the two support capacitors C d at the midpoint of the DC bus through R1.

[0046] The input terminal of Pull-Push is directly connected to the output terminal of OPAM, the output terminal is connected to resistors R3 and R0, and is connected to the input terminal of the voltage converter through resistor R0.

[0047] Pin 1 of the voltage converter is connected to the output terminal of Push-Pull through resistor R0, pin 2 of the voltage converter is connected to the non-inverting input terminal of OPAM through resistor R4; pin 3 of the voltage converter is connected to the star node of the filter capacitor; pin 4 of the voltage converter is connected to the two support capacitors at the midpoint of the bus. OPAM and Push-Pull are powered by an independent power supply circuit. This active circuit samples the interference voltage generated by the power devices in the PMSM driver through OPAM and amplifies it in reverse, and compensates the generated interference voltage to the filter capacitor branch through the voltage converter. The compensation voltage can be expressed as

[0048] V A =-A V NV in

[0049] where: V A is the compensation voltage of the voltage converter; A V is the gain multiple of OPAM, N is the winding turn ratio of the voltage converter, and V in is the interference voltage sampled by the active compensation circuit.

[0050] Adjusting the ratio of the detection resistor R2 and the feedback resistor R3 can change the gain multiple A of the OPAM. V The detection resistors R1 and R2 should be equal, and the feedback resistors R3 and R4 should be equal.

[0051] To fully increase the gain of the active circuit and avoid the influence of bandwidth reduction on the filtering performance, the gain A of the operational amplifier V should not be too large. In this embodiment, A V is set to 3.

[0052] To increase the output power of the OPAM, Pull-Push is introduced at the output end of the OPAM and the input end of the primary side of the voltage converter, as Figure 3 shown. The circuit includes: pull-up resistors R up1 and R up2 , bias diodes D1 and D2, PNP transistor Q1, NPN transistor Q2, emitter resistors R Q1 and R Q2 .

[0053] The output ends of the primary side and the secondary side of the voltage converter are the same-named terminals. The polarity of the compensation voltage V A output from the secondary side of the voltage converter should be opposite to the polarity of the interference voltage V in sampled by the active compensation circuit.

[0054] In this embodiment, to ensure that the filter capacitor branch maintains a low impedance in the high-frequency operating state, the magnetic circuit inductance of the voltage converter should not exceed the threshold; this threshold can be set according to the actual impedance characteristics of the filter capacitor branch. To prevent problems such as excessive volume of the voltage converter and bandwidth reduction caused by parasitic parameters, the number of winding turns should not be too large, and the maximum turns ratio should be less than 10.

[0055] In this embodiment, the DC side DC bus voltage is 220V, the switching frequency of the power device is 20kHz, and the three-phase common-mode interference voltage is

[0056]

[0057] where: V CM is the three-phase common-mode interference voltage, which is the interference source of the entire drive system; V dc is the DC bus voltage; S a , S b , S c are the switching states of the power devices on the upper bridge arm of the inverter, 1 indicates that the power device is conducting, and 0 indicates that the power device is off. When S a、b、c = 1 or 0, V CM = ±V dc / 2, otherwise it is ±V dc / 6; V ao , Vbo and V co is the three-phase input voltage of the PMSM.

[0058] In the hybrid EMI filter mentioned in the present invention, the passive LC filter is a first-order filter. The output three-phase voltage of this passive filter is

[0059]

[0060] where: I o is the leakage current of the filter capacitor branch; V f is the output three-phase voltage of the passive filter. It can be seen that the output three-phase voltage V f is equal to V CM . Therefore, reducing the impedance of the filter capacitor branch can reduce V CM in the drive system.

[0061] As Figure 4 shown, by introducing a compensation voltage V A through the active circuit, the equivalent impedance of the filter capacitor branch can be changed. This equivalent impedance is

[0062]

[0063] where: Z eq is the equivalent impedance of the filter capacitor branch; f is the frequency of V CM sampled by the active compensation circuit.

[0064] It can be seen that when the passive filter reaches the corner frequency f c , the active compensation circuit will provide V CM with the opposite polarity to V A to the passive filter as f changes, reducing the equivalent impedance of the filter capacitor branch, thereby reducing V CM .

[0065] Figure 5 is the comparison of the inverter output-side current waveforms when the motor speed reaches stability, without installing any filter and with installing the hybrid EMI filter, in accordance with the above design criteria. Under the same working conditions, installing the hybrid EMI filter significantly improves the common-mode EMI suppression effect on the three-phase inverter.

[0066] Figure 6 is to introduce LISN at the DC power supply terminal to detect the spectral values of V CM without installing any filter and with installing the hybrid EMI filter. The frequency sweep range in the figure is from 150 kHz to 30 MHz. It can be seen that the hybrid EMI filter mentioned in the present invention can achieve an attenuation of nearly 25 dB.

[0067] The hybrid EMI filter of the present invention adds a voltage source with opposite polarities on the basis of the original traditional passive filter, which can increase the capacitance value of the capacitor branch after reaching the corner frequency. According to the formula of insertion loss IL = 10lg[1+(ωCR / 2) 2 , it can be seen that when the capacitance value C is increased, the insertion loss of the filter will also be improved. And what is expressed in the figure here is the equivalent impedance Z = 1 / (jωC). It can be understood that after adding the active circuit, the impedance of the capacitor branch is reduced and the insertion loss is increased, making the filtering effect of the present invention better than that of the traditional passive filter.

[0068] As can be seen from the above, the hybrid EMI filter mentioned in the present invention combines the advantages of the passive filter and the active compensation circuit, which not only greatly improves the space utilization rate of the inverter, but also can improve the ability of the inverter to suppress the common-mode EMI on the output side and the input side, and improves the stability and reliability of the system. Since the leakage current flowing through the filter capacitor C f does not flow into the ground loop, this can also improve the safety of the inverter and has good application prospects in working environments with strict requirements for power density and safety standards.

[0069] The above embodiments are only described as examples and are not limitations. Those of ordinary skill in the art can understand that various changes, modifications, substitutions and deformations can be made to the example without departing from the principle and purpose of the present invention. The scope of the present invention is defined by the claims and their equivalents.

Claims

1. A hybrid electromagnetic interference (EMI) filter for a permanent magnet synchronous motor (PMSM) drive, which is used to suppress common-mode electromagnetic interference (EMI) in the PMSM drive system, is characterized in that, It includes a passive LC filter and an active compensation circuit; the passive LC filter consists of a filtering inductor L f and a filtering capacitor C f The filtering inductor L f is composed of three filtering inductors. One ends of the three filtering inductors are respectively connected to the three-phase cables of the permanent magnet synchronous motor PMSM, and the other ends of the three filtering inductors are respectively connected to the three-phase output terminals of the PMSM driver. The filtering capacitor C f is composed of three filtering capacitors. One ends of the three filtering capacitors are connected in a star connection and a branch is led out to be connected to the midpoint of the DC bus through a voltage converter, and the other ends of the three filtering capacitors are respectively connected to the three-phase cables between the filtering inductor and the PMSM; the active compensation circuit consists of detection resistors R1 and R2, feedback resistors R3 and R4, an output resistor R0, an operational amplifier OPAM, a push-pull amplifier Push-Pull and a voltage converter; The resistor R1 and R4 are connected to the non-inverting input terminal of the OPAM, and the resistors R2 and R3 are connected to the inverting input terminal of the OPAM; the inverting input terminal is connected to the star node of the filtering capacitor C in the passive LC filter through R2 f and the non-inverting input terminal is connected to the two support capacitors C at the neutral point of the DC bus through R1 d ; the Push-Pull input terminal is directly connected to the output terminal of the OPAM, the Push-Pull output terminal is connected to the resistors R3 and R0, and is connected to the input terminal of the voltage converter through the resistor R0. The pin 1 of the voltage converter is connected to the Push-Pull output terminal through the resistor R0, the pin 2 is connected to the non-inverting input terminal of the OPAM through the resistor R4, the pin 3 is connected to the star node of the filtering capacitor, and the pin 4 is connected to the two support capacitors C d at the midpoint of the bus.

2. The hybrid electromagnetic interference (EMI) filter for a permanent magnet synchronous motor (PMSM) driver according to claim 1, wherein The passive filter is a first-order LC filter, and the filtering inductor L f is at the μH level, and the filtering capacitor C f is at the μF level and is greater than the support capacitor C d .

3. A hybrid electromagnetic interference (EMI) filter for a permanent magnet synchronous motor (PMSM) driver according to claim 1, characterized in that, The OPAM output terminal is connected to the Push-Pull input terminal to obtain sufficient driving power so that the voltage converter has the ability to output a higher-power compensation voltage.

4. A hybrid electromagnetic interference (EMI) filter for a permanent magnet synchronous motor (PMSM) driver according to claim 1, wherein, The OPAM and Push-Pull in the active compensation circuit are powered by independent power supply circuits.

5. A hybrid electromagnetic interference (EMI) filter for a permanent magnet synchronous motor (PMSM) driver according to claim 1, characterized in that, The output terminals of the primary and secondary sides of the voltage converter are of the same name, and the compensation voltage output by the voltage converter has the opposite polarity to the electromagnetic interference voltage.

6. A hybrid electromagnetic interference (EMI) filter for a permanent magnet synchronous motor (PMSM) driver according to claim 1, characterized in that, In the active compensation circuit, the gain of the compensation voltage is changed by adjusting the feedback resistor, the detection resistor, and the winding turns ratio of the voltage converter.

7. A hybrid electromagnetic interference (EMI) filter for a permanent magnet synchronous motor (PMSM) driver according to claim 1, characterized in that, When the frequency of the common-mode interference voltage generated by the drive system reaches the corner frequency of the passive filter, the active compensation circuit will provide a compensation voltage with the opposite polarity to the common-mode interference voltage to the passive filter as the frequency changes, reducing the equivalent impedance of the filter capacitor branch, thereby reducing the common-mode interference voltage.

8. A hybrid electromagnetic interference (EMI) filter for a permanent magnet synchronous motor (PMSM) driver according to claim 1, characterized in that, The passive part of the passive LC filter is directly connected to the three-phase AC cable of the PMSM, and the led filter capacitor branch is connected to the neutral point of the DC bus through a voltage converter. The active part is connected across the star node of the filter capacitor and the midpoint of the DC bus, and there is no leakage current injected into the ground loop, which can greatly improve the safety of the PMSM drive system.

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