Cascaded active EMI filter based on element multiplexing and converter system

Abstract

The invention discloses a cascaded active EMI filter and converter system based on element multiplexing. The cascaded active EMI filter comprises a feedforward current compensation EMI filter and a feedback current compensation EMI filter, the two filters share one power supply circuit and one current induction circuit and each comprise a voltage amplification circuit, a power amplification circuit and an output impedance circuit which are the same in structure. The input end of the current induction circuit is connected with positive and negative buses of the power electronic converter, and the output end is connected with the input end of the voltage amplification circuit; the output end of the voltage amplification circuit is connected with the input end of the power amplification circuit, and the output end of the power amplification circuit is connected with the output impedance; the output end of the output impedor is connected with the direct-current negative bus; the current sensing circuit is used for sensing common-mode current and outputting the same voltage signal to the voltage amplifying circuit; the voltage amplification circuit is used for amplifying the voltage signal and outputting the voltage signal to the power amplification circuit; the power amplification circuit outputs an amplified voltage signal to the output impedance circuit; the output impedance circuit is used for converting the amplified voltage signal into a current signal and offsetting the current signal with a system common-mode current; the EMI filter with the feedforward current compensation and the EMI filter with the feedback current compensation share the current induction circuit, the power supply circuit and the operational amplifier, low-frequency common-mode EMI of a converter system can be well restrained, the size of the cascaded active EMI filter is reduced, and the cost of the EMI filter is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of conducted EMI suppression of power electronic devices, and in particular to a cascaded active EMI filter and converter system based on component reuse. Background Art

[0002] Power electronic converters are widely used due to their superior performance. However, due to the high-speed switching of power electronic converters, serious electromagnetic interference will occur. Electromagnetic interference will seriously affect the reliable operation of the converter system, and with the development of wide bandgap semiconductor devices, EMI problems are becoming more and more serious. In order to ensure the reliable operation of the system, the electromagnetic interference generated by it must be suppressed and the electromagnetic interference value must be limited to the range specified by the standard.

[0003] Common-mode electromagnetic interference is usually suppressed by common-mode EMI filters in engineering, but passive EMI filters are large in size. Therefore, in order to reduce the size of EMI filters, active EMI filters are used. However, the suppression effect of a single active EMI filter is limited. To improve the suppression effect, the existing method uses a cascade method for active EMI, but the existing cascade active EMI filters are usually large in size, which increases the design cost. Summary of the invention

[0004] The present invention provides a cascaded active EMI filter and a converter system based on component reuse, so as to overcome the technical problems of large volume and high design cost of the existing cascaded active EMI filter.

[0005] In order to achieve the above object, the technical solution of the present invention is:

[0006] A cascade active EMI filter based on component reuse is connected to a power electronic converter and a line impedance stabilization network, comprising: a power supply circuit, a feedforward current compensated EMI filter and a feedback current compensated EMI filter;

[0007] The feedforward current-compensated EMI filter comprises a first voltage amplifier circuit, a first power amplifier circuit Q1, and a first output impedance circuit; the feedback current-compensated EMI filter comprises a second voltage amplifier circuit, a second power amplifier circuit Q2, a second output impedance circuit, and shares a current sensing circuit and a power supply circuit with the feedforward current-compensated EMI filter;

[0008] The power supply circuit is connected to both the feedforward current compensated EMI filter and the feedback current compensated EMI filter;

[0009] The input end of the current sensing circuit is connected to the positive and negative busbars of the power electronic converter, and the output end is respectively connected to the input ends of the first voltage amplifier circuit and the second voltage amplifier circuit; the output end of the first voltage amplifier circuit is connected to the input end of the first power amplifier circuit Q1, and the output end of the first power amplifier circuit Q1 is connected to the first output impedance; the output end of the first output impedance is connected to the DC negative busbar; the output end of the second voltage amplifier circuit is connected to the input end of the second power amplifier circuit Q2, and the output end of the second power amplifier circuit Q2 is connected to the second output impedance; the output end of the second output impedance is connected to the DC negative busbar;

[0010] The current sensing circuit is used to sense the common-mode current of the line impedance stabilization network and output the same voltage signal to two voltage amplification circuits; the two voltage amplification circuits are used to amplify the voltage signal output by the current sensing circuit and output the amplified voltage signal to two power amplification circuits respectively; the two power amplification circuits are used to output the amplified voltage signal to two output impedance circuits respectively; the two output impedance circuits are used to convert the amplified voltage signal into a current signal to offset the common-mode current in the converter system.

[0011] Further, the current sensing circuit includes: a current transformer and a first resistor R1;

[0012] The primary winding L1 of the current transformer is connected to the power electronic converter, and the secondary winding L2 of the current transformer is connected to both ends of the first resistor R1; one end of the first resistor R1 is connected to the ground.

[0013] Furthermore, the first voltage amplifier circuit and the second voltage amplifier circuit have the same structure and share a dual-channel operational amplifier U1, wherein the operational amplifier U1 includes a first channel operational amplifier U 1.1 and the second channel operational amplifier U 1.2 ; The first voltage amplifying circuit includes a second resistor R2 and a third resistor R3, and the second voltage amplifying circuit includes a fourth resistor R4 and a fifth resistor R5;

[0014] One end of the second resistor R2, one end of the third resistor R3 and the first channel operational amplifier U 1.1 The other end of the second resistor R2 is grounded;

[0015] One end of the fourth resistor R4, one end of the fifth resistor R5 and the second channel operational amplifier U 1.2 The other end of the fourth resistor R4 is grounded;

[0016] The two in-phase input terminals of the operational amplifier U1 are connected to the other end of the first resistor R1; the positive voltage input terminal of the operational amplifier U1 is connected to the +V CC The negative voltage input terminal of the operational amplifier U1 and the -V CC connected.

[0017] Furthermore, the first power amplifier circuit Q1 and the second power amplifier circuit Q2 have the same structure. The first power amplifier circuit Q1 includes a sixth resistor R6, a seventh resistor R7, an eighth resistor R8, a ninth resistor R9, a first transistor T1, a second transistor T2, a first diode D1 and a second diode D2; the second power amplifier circuit Q2 includes an eleventh resistor R 11 , the twelfth resistor R 12 、Thirteenth resistor R 13 , the fourteenth resistor R 14 , a third transistor T3, a fourth transistor T4, a third diode D3 and a fourth diode D4;

[0018] One end of the sixth resistor R6 is connected to the collector of the first transistor T1 and the +V CC The other end of the sixth resistor R6, the base of the first transistor T1 and the anode of the first diode D1 are connected; the cathode of the first diode D1 is respectively connected to the first channel operational amplifier U 1.1 The output end of is connected to the anode of the second diode D2; the cathode of the second diode D2, one end of the seventh resistor R7 and the base of the second transistor T2 are connected; the other end of the seventh resistor R7, the collector of the second transistor T2 and -V CC The emitter of the first transistor T1 is connected to one end of the eighth resistor R8; the emitter of the second transistor T2 is connected to one end of the ninth resistor R9; the other end of the eighth resistor R8, the other end of the ninth resistor R9 and the other end of the third resistor R3 are connected;

[0019] The eleventh resistor R 11 One end is connected to the collector of the third transistor T3 and the +V CC connected; the eleventh resistor R 11 The other end of the third transistor T3, the base of the third transistor T3 and the anode of the third diode D3 are connected; the cathode of the third diode D3 is connected to the second channel operational amplifier U 1.2 The output end of the twelfth resistor R 12One end of the twelfth resistor R is connected to the base of the fourth transistor T4; 12 The other end of the fourth transistor T4, the collector and the -V CC The emitter of the third transistor T3 and the thirteenth resistor R 13 The emitter of the fourth transistor T4 and the fourteenth resistor R 14 The thirteenth resistor R 13 The other end of the fourteenth resistor R 14 The other end of is connected to the other end of the fifth resistor R5.

[0020] Furthermore, the first output impedance circuit and the second output impedance circuit have the same structure, and the first output impedance circuit includes a tenth resistor R 10 and a first capacitor C1; the second output impedance circuit includes a fifteenth resistor R 15 and a second capacitor C2;

[0021] The tenth resistor R 10 One end of the tenth resistor R is connected to the other end of the eighth resistor R8 and the other end of the ninth resistor R9 respectively; 10 The other end of is connected to one end of the first capacitor C1; the other end of the first capacitor C1 is connected to the negative bus;

[0022] The fifteenth resistor R 15 One end of each resistor R 13 The other end and the fourteenth resistor R 14 The other end of the fifteenth resistor R 15 The other end of is connected to one end of the second capacitor C2; the other end of the second capacitor C2 is connected to the negative bus.

[0023] Furthermore, the first transistor T1 and the third transistor T3 are of NPN structure; the second transistor T2 and the fourth transistor T4 are of PNP structure.

[0024] Furthermore, it also includes a power electronic converter system, which includes the cascaded active EMI filter based on component reuse.

[0025] Beneficial effect: The present invention provides a cascaded active EMI filter based on component reuse. By designing a feedforward current compensated EMI filter and a feedback current compensated EMI filter, and sharing a current sensing circuit and a power supply circuit, the low-frequency common-mode EMI of the converter system can be well suppressed, while reducing the volume of the cascaded active EMI filter and the cost of the EMI filter. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0027] Figure 1 is a schematic diagram of a general power electronic converter system;

[0028] Figure 2 A schematic diagram of a cascaded active EMI filter based on component reuse in the present invention;

[0029] Figure 3 is a schematic diagram of a first power amplifier circuit in the present invention;

[0030] Figure 4 is a schematic diagram of a second power amplifier circuit in the present invention;

[0031] Figure 5 The equivalent circuit diagram of the cascaded active EMI filter based on component reuse;

[0032] In the figure, Q1 is the first power amplifier circuit; Q2 is the second power amplifier circuit. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] This embodiment provides a cascade active EMI filter based on component reuse, such as Figure 2 As shown, it is connected to a power electronic converter and a line impedance stabilization network, and includes: a power supply circuit, an EMI filter of feedforward current compensation and an EMI filter of feedback current compensation;

[0035] The feedforward current-compensated EMI filter comprises a first voltage amplifier circuit, a first power amplifier circuit Q1, and a first output impedance circuit; the feedback current-compensated EMI filter comprises a second voltage amplifier circuit, a second power amplifier circuit Q2, a second output impedance circuit, and shares a current sensing circuit and a power supply circuit with the feedforward current-compensated EMI filter;

[0036] The power supply circuit is connected to both the feedforward current compensated EMI filter and the feedback current compensated EMI filter;

[0037] The input end of the current sensing circuit is connected to the positive and negative busbars of the power electronic converter, and the output end is respectively connected to the input ends of the first voltage amplifier circuit and the second voltage amplifier circuit; the output end of the first voltage amplifier circuit is connected to the input end of the first power amplifier circuit Q1, and the output end of the first power amplifier circuit Q1 is connected to the first output impedance; the output end of the first output impedance is connected to the DC negative busbar; the output end of the second voltage amplifier circuit is connected to the input end of the second power amplifier circuit Q2, and the output end of the second power amplifier circuit Q2 is connected to the second output impedance; the output end of the second output impedance is connected to the DC negative busbar;

[0038] The current sensing circuit is used to sense the common-mode current of the line impedance stabilization network and output the same voltage signal to two voltage amplification circuits; the two voltage amplification circuits are used to amplify the voltage signal output by the current sensing circuit and output the amplified voltage signal to two power amplification circuits respectively; the two power amplification circuits are used to output the amplified voltage signal to two output impedance circuits respectively, and provide additional current at the same time to improve the current output capacity; the two output impedance circuits are used to convert the amplified voltage signal into a current signal to offset the common-mode current in the converter system.

[0039] Specifically, the current sensing circuit in the cascade active EMI filter of the present invention detects the common mode current in the line impedance stabilization network, the offset current output by the EMI filter of the feedforward current compensation in the cascade active EMI filter is in front of the position where the common mode current is detected by the current sensing circuit, and the offset current output by the EMI filter of the feedback current compensation is behind the position where the common mode current is detected by the current sensing circuit; it is connected to the power electronic converter and the line impedance stabilization network, and the power supply circuit is connected to both the two voltage amplifier circuits and the two power amplifier circuits; the current sensing circuit is used to detect the common mode current signal and convert it into a voltage signal, and is respectively connected to the input end of the first voltage amplifier circuit and the second voltage amplifier circuit; the two voltage amplifier circuits are composed of a common-phase amplifier, and its input impedance is large, which can Reduce the attenuation of the voltage signal; the output end of the first voltage amplifier circuit is connected to the input end of the first power amplifier circuit Q1, and the output end of the second voltage amplifier circuit is connected to the input end of the second power amplifier circuit Q2. The power amplifier circuit is used to transmit the voltage signal output by the voltage amplifier circuit to the output impedance, and improve the output current capacity of the converter system to better offset the common mode current; the output end of the first power amplifier circuit Q1 is connected to the first output impedance, and the output end of the second power amplifier circuit Q2 is connected to the second output impedance. The output impedance converts the amplified voltage signal into a current signal, offsets the common mode current in the converter system, thereby suppressing EMI on the DC side and playing an isolation role. The output ends of the two output impedance circuits are connected to the DC negative bus.

[0040] In a specific embodiment, a fifth capacitor C5 is further included, wherein two ends of the fifth capacitor C5 are respectively connected to two ends of the line impedance stabilization network and are arranged between the current sensing circuit and the line impedance stabilization network;

[0041] The fifth capacitor C5 is provided in front of the position where the current sensing circuit detects the common mode current in order to ensure that the offset current output by the first power amplifier circuit in the feedforward current compensation EMI filter flows freely in the system.

[0042] In a specific embodiment, Figure 2 As shown, the current sensing circuit includes: a current transformer and a first resistor R1;

[0043] The primary winding L1 of the current transformer is connected to the power electronic converter, and the secondary winding L2 of the current transformer is connected to both ends of the first resistor R1; one end of the first resistor R1 is connected to the ground.

[0044] In the current sensing circuit designed in this embodiment, the first resistor R1 is 10 ohms, and the turns ratio of the current transformer is 1:10; in this embodiment, the number of gates on the positive and negative busbars of the primary winding L1 of the current transformer is equal; the primary winding L1 of the current transformer and the secondary winding L2 of the current transformer share a magnetic core and are tightly coupled.

[0045] The current sensing circuit can detect the common mode current on the line impedance stabilization network side and output a voltage signal; in the current sensing circuit, the cascaded active EMI filter only needs one current transformer, and the obtained voltage signal is transmitted to the voltage amplification circuits of the feedforward current compensated EMI filter and the feedback current compensated EMI filter of the cascaded active EMI filter respectively, so the number of transformers of the cascaded active EMI filter is reduced, and the volume of the cascaded active EMI filter can be reduced.

[0046] In a specific embodiment, Figure 2 As shown, the first voltage amplifier circuit and the second voltage amplifier circuit have the same structure and share a dual-channel operational amplifier U1, wherein the operational amplifier U1 includes a first channel operational amplifier U 1.1 and the second channel operational amplifier U 1.2 ; The first voltage amplifying circuit includes a second resistor R2 and a third resistor R3, and the second voltage amplifying circuit includes a fourth resistor R4 and a fifth resistor R5;

[0047] One end of the second resistor R2, one end of the third resistor R3 and the first channel operational amplifier U 1.1 The other end of the second resistor R2 is grounded;

[0048] One end of the fourth resistor R4, one end of the fifth resistor R5 and the second channel operational amplifier U 1.2 The other end of the fourth resistor R4 is grounded;

[0049] The two in-phase input terminals of the operational amplifier U1 are connected to the other end of the first resistor R1; the positive voltage input terminal of the operational amplifier U1 is connected to the +V CC The negative voltage input terminal of the operational amplifier U1 and the -V CC connected.

[0050] The voltage amplifier circuit of the feedforward current compensated EMI filter and the voltage amplifier circuit of the feedback current compensated EMI filter designed in this scheme, the second resistor R2 is 1K ohm, the third resistor R3 is 1K ohm, the fourth resistor R4 is 1K ohm, the fifth resistor R5 is 9K ohm, and the operational amplifier U1 is AD826.

[0051] In the voltage amplifier circuit of the feedforward current compensated EMI filter and the voltage amplifier circuit of the feedback current compensated EMI filter, a dual-channel operational amplifier can be shared to reduce the volume and cost of the cascade active EMI filter; the voltage amplifier circuit is composed of a common-phase amplifier, which has a large input impedance and can reduce the attenuation of the voltage signal.

[0052] In a specific embodiment, Figure 3 and Figure 4 As shown, the first power amplifier circuit Q1 and the second power amplifier circuit Q2 have the same structure. The first power amplifier circuit Q1 includes a sixth resistor R6, a seventh resistor R7, an eighth resistor R8, a ninth resistor R9, a first transistor T1, a second transistor T2, a first diode D1 and a second diode D2; the second power amplifier circuit Q2 includes an eleventh resistor R 11 , the twelfth resistor R 12 、Thirteenth resistor R 13 , the fourteenth resistor R 14 , a third transistor T3, a fourth transistor T4, a third diode D3 and a fourth diode D4;

[0053] One end of the sixth resistor R6 is connected to the collector of the first transistor T1 and the +V CC The other end of the sixth resistor R6, the base of the first transistor T1 and the anode of the first diode D1 are connected; the cathode of the first diode D1 is respectively connected to the first channel operational amplifier U 1.1 The output end of is connected to the anode of the second diode D2; the cathode of the second diode D2, one end of the seventh resistor R7 and the base of the second transistor T2 are connected; the other end of the seventh resistor R7, the collector of the second transistor T2 and -V CC The emitter of the first transistor T1 is connected to one end of the eighth resistor R8; the emitter of the second transistor T2 is connected to one end of the ninth resistor R9; the other end of the eighth resistor R8, the other end of the ninth resistor R9 and the other end of the third resistor R3 are connected;

[0054] The eleventh resistor R 11 One end is connected to the collector of the third transistor T3 and the +V CC connected; the eleventh resistor R 11 The other end of the third transistor T3, the base of the third transistor T3 and the anode of the third diode D3 are connected; the cathode of the third diode D3 is connected to the second channel operational amplifier U 1.2The output end of the twelfth resistor R 12 One end of the twelfth resistor R is connected to the base of the fourth transistor T4; 12 The other end of the fourth transistor T4, the collector and the -V CC The emitter of the third transistor T3 and the thirteenth resistor R 13 The emitter of the fourth transistor T4 and the fourteenth resistor R 14 The thirteenth resistor R 13 The other end of the fourteenth resistor R 14 The other end of is connected to the other end of the fifth resistor R5;

[0055] The first transistor T1 and the third transistor T3 are of NPN structure; the second transistor T2 and the fourth transistor T4 are of PNP structure.

[0056] In the power amplifier circuit designed in this scheme, the sixth resistor R6, the seventh resistor R7, and the eleventh resistor R 11 , the twelfth resistor R 12 All are 1K ohm, the eighth resistor R8, the ninth resistor R9, the thirteenth resistor R 13 , the fourteenth resistor R 14 All are 1 ohm, the first transistor T1 and the third transistor T3 are FZT692B, the second transistor T2 and the fourth transistor T4 are FZT792A, the first diode D1, the second diode D2, the third diode D3 and the fourth diode D4 are 1N4148.

[0057] The sixth resistor R6, the seventh resistor R7, and the eleventh resistor R 11 , the twelfth resistor R 12 is a bias resistor, the eighth resistor R8, the ninth resistor R9, the thirteenth resistor R 13 , the fourteenth resistor R 14 It is a resistor set to prevent temperature drift. The first diode D1, the second diode D2, the third diode D3 and the fourth diode D4 are set to eliminate the dead zone effect. The power amplifier circuit works alternately through two complementary transistors. The two output stages can provide current for the cascaded active EMI filter to ensure the output of the offset current. At the same time, the two output stages can reduce the output impedance, enhance the output current capacity of the EMI filter, and ensure the common-mode EMI suppression effect of the active filter.

[0058] In a specific embodiment, the first output impedance circuit and the second output impedance circuit have the same structure, and the first output impedance circuit includes a tenth resistor R10 and a first capacitor C1; the second output impedance circuit includes a fifteenth resistor R 15 and a second capacitor C2;

[0059] The tenth resistor R 10 One end of the tenth resistor R is connected to the other end of the eighth resistor R8 and the other end of the ninth resistor R9 respectively; 10 The other end of is connected to one end of the first capacitor C1; the other end of the first capacitor C1 is connected to the negative bus;

[0060] The fifteenth resistor R 15 One end of each resistor R 13 The other end and the fourteenth resistor R 14 The other end of the fifteenth resistor R 15 The other end of is connected to one end of the second capacitor C2; the other end of the second capacitor C2 is connected to the negative bus.

[0061] In the output impedance circuit of the feedforward current compensated EMI filter and the output impedance circuit of the feedback current compensated EMI filter designed in this scheme, the tenth resistor R 10 is 2 ohms, the fifteenth resistor R 15 is 1 ohm, the first capacitor C1 and the second capacitor C2 are both 1 microfarad.

[0062] In this embodiment, the output impedance circuit of the feedforward current compensated EMI filter and the output impedance circuit of the feedback current compensated EMI filter convert the amplified voltage signal into a current signal, which offsets the common-mode current of the system, thereby suppressing EMI on the DC side. The first capacitor C1 and the second capacitor C2 play an isolation role.

[0063] In a specific embodiment, Figure 1 As shown, a power electronic converter system is also included, which includes the line impedance stabilization network.

[0064] The schematic diagram of the power electronic converter system is as follows: Figure 1 As shown, the figure includes a DC power supply, a line impedance stabilization network LISNs for testing the cascaded active EMI filter based on component reuse, a power electronic converter and a parasitic capacitor C p .

[0065] Figure 2The present invention is a circuit diagram of a power electronic converter connected to a cascaded active EMI filter based on component reuse, wherein the active EMI filter is composed of a feedforward current-compensated EMI filter and a feedback current-compensated EMI filter, and the two EMI filters share three parts: a current sensing circuit, a power supply circuit, and an operational amplifier, thereby reducing the volume and cost of the cascaded active EMI filter; the cascaded active EMI filter improves the suppression effect of low-frequency EMI by cascading two EMI active filters, thereby further reducing the volume of the required passive filter.

[0066] Figure 5 The equivalent circuit diagram of the power electronic converter after connecting to the cascade active EMI filter designed by the present invention. CM is the common-mode voltage source of the entire system, I LISN is the common mode current flowing through the LISN, I CM Is flowing through Z CM The common mode current, I s is the common mode current flowing through the primary winding of the transformer, Z outFF is the output impedance of the feedforward current compensated EMI filter, Z outFB is the output impedance of the feedback current compensated EMI filter, Z injFF is the impedance of the injection branch of the feedforward current compensated EMI filter, Z injFB is the impedance of the injection branch of the feedback current compensated EMI filter, Z LISN is the equivalent common-mode impedance of the parallel LISN, V outFF is the output voltage of the feedforward current compensated EMI filter, V outFB is the output voltage of the feedback current compensated EMI filter, I injFF is the output current of the feedforward current compensated EMI filter, I injFB is the output current of the feedback current compensated EMI filter. VFF is the gain from the inductive current to the output voltage of the feedforward current compensated EMI filter, A VFB It is the gain of the induced current to the output voltage of the feedback current compensated EMI filter. Ideally, it is mainly related to the turns ratio of the current transformer, the resistor R1 and the first channel operational amplifier U 1.1 , the second channel operational amplifier U 1.2 The amplification factor is related to

[0067] In order to reduce the volume of the transformer, the number of turns on the primary side of the transformer is 1, and the number of turns on the secondary side is n. According to the equivalent circuit diagram, the formula (1) of the output current of the active EMI filter can be obtained:

[0068]

[0069] Through the common mode current I flowing through the primary winding of the transformer s Compared with the above, we get the following formula (2):

[0070]

[0071] Based on the principle of active EMI filter with feedforward structure, I injFF Yinghe I s Equal, so that I LISN can be equal to 0. According to formula (2), A VFF / (Z outFF +Z injFF ) should be equal to 1; Based on the principle of active EMI filter with feedback structure, I injFB Should be much larger than I s , then the DC common mode noise can be well suppressed. According to formula (2), when A VFF / (Z outFF +Z injFF ) is equal to 1, A VFB / (Z outFB +Z injFB )>>1.

[0072] According to the equivalent circuit diagram, the ratio of the common mode noise on the DC side with and without the active EMI filter can be obtained, that is, the insertion loss IL, as shown in formula (3).

[0073]

[0074] It can be seen that when A VFF / (Z outFF +Z injFF ) is equal to 1, A VFB / (Z outFB +Z injFB )>>1, the smaller the insertion loss, the better the effect of the cascaded active EMI filter, and the common-mode noise on the DC side will be well suppressed. According to formula (3), when the active EMI filter with a feedforward structure and the active EMI filter with a feedback structure work together, the insertion loss can be greatly reduced. Compared with a single active EMI filter, the cascaded active EMI filter can further suppress the common-mode noise.

[0075] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A cascaded active EMI filter based on component reuse, connected to a power electronic converter and a line impedance stabilization network, characterized in that: include: Feedforward current compensated EMI filter and feedback current compensated EMI filter; The feedforward current-compensated EMI filter comprises a first voltage amplifier circuit, a first power amplifier circuit Q1, and a first output impedance circuit; the feedback current-compensated EMI filter comprises a second voltage amplifier circuit, a second power amplifier circuit Q2, a second output impedance circuit, and shares a current sensing circuit and a power supply circuit with the feedforward current-compensated EMI filter; The power supply circuit is connected to both the feedforward current compensated EMI filter and the feedback current compensated EMI filter; The input end of the current sensing circuit is connected to the positive and negative busbars of the power electronic converter, and the output end is respectively connected to the input ends of the first voltage amplifier circuit and the second voltage amplifier circuit; the output end of the first voltage amplifier circuit is connected to the input end of the first power amplifier circuit Q1, and the output end of the first power amplifier circuit Q1 is connected to the first output impedance; the output end of the first output impedance is connected to the DC negative busbar; the output end of the second voltage amplifier circuit is connected to the input end of the second power amplifier circuit Q2, and the output end of the second power amplifier circuit Q2 is connected to the second output impedance; the output end of the second output impedance is connected to the DC negative busbar; The current sensing circuit is used to sense the common-mode current of the line impedance stabilization network and output the same voltage signal to two voltage amplification circuits; the two voltage amplification circuits are used to amplify the voltage signal output by the current sensing circuit and output the amplified voltage signal to two power amplification circuits respectively; the two power amplification circuits are used to output the amplified voltage signal to two output impedance circuits respectively; the two output impedance circuits are used to convert the amplified voltage signal into a current signal to offset the common-mode current in the converter system.

2. The cascaded active EMI filter based on component reuse according to claim 1, characterized in that: The current sensing circuit comprises: a current transformer and a first resistor R1; The primary winding L1 of the current transformer is connected to the power electronic converter, and the secondary winding L2 of the current transformer is connected to both ends of the first resistor R1; one end of the first resistor R1 is connected to the ground.

3. The cascaded active EMI filter based on component reuse according to claim 2, characterized in that: The first voltage amplifier circuit and the second voltage amplifier circuit have the same structure and share a dual-channel operational amplifier U1. The operational amplifier U1 includes a first channel operational amplifier U 1.1 and the second channel operational amplifier U 1.2 ; The first voltage amplifying circuit includes a second resistor R2 and a third resistor R3, and the second voltage amplifying circuit includes a fourth resistor R4 and a fifth resistor R5; One end of the second resistor R2, one end of the third resistor R3 and the first channel operational amplifier U 1.1 The other end of the second resistor R2 is grounded; One end of the fourth resistor R4, one end of the fifth resistor R5 and the second channel operational amplifier U 1.2 The other end of the fourth resistor R4 is grounded; The two in-phase input terminals of the operational amplifier U1 are connected to the other end of the first resistor R1; the positive voltage input terminal of the operational amplifier U1 is connected to the +V CC The negative voltage input terminal of the operational amplifier U1 and the -V CC connected.

4. The cascaded active EMI filter based on component reuse according to claim 3, characterized in that: The first power amplifier circuit Q1 and the second power amplifier circuit Q2 have the same structure. The first power amplifier circuit Q1 includes a sixth resistor R6, a seventh resistor R7, an eighth resistor R8, a ninth resistor R9, a first transistor T1, a second transistor T2, a first diode D1 and a second diode D2; the second power amplifier circuit Q2 includes an eleventh resistor R 11 , the twelfth resistor R 12 、Thirteenth resistor R 13 , the fourteenth resistor R 14 , a third transistor T3, a fourth transistor T4, a third diode D3 and a fourth diode D4; One end of the sixth resistor R6 is connected to the collector of the first transistor T1 and the +V CC The other end of the sixth resistor R6, the base of the first transistor T1 and the anode of the first diode D1 are connected; the cathode of the first diode D1 is respectively connected to the first channel operational amplifier U 1.1 The output end of is connected to the anode of the second diode D2; the cathode of the second diode D2, one end of the seventh resistor R7 and the base of the second transistor T2 are connected; the other end of the seventh resistor R7, the collector of the second transistor T2 and -V CC The emitter of the first transistor T1 is connected to one end of the eighth resistor R8; the emitter of the second transistor T2 is connected to one end of the ninth resistor R9; the other end of the eighth resistor R8, the other end of the ninth resistor R9 and the other end of the third resistor R3 are connected; The eleventh resistor R 11 One end is connected to the collector of the third transistor T3 and the +V CC connected; the eleventh resistor R 11 The other end of the third transistor T3, the base of the third transistor T3 and the anode of the third diode D3 are connected; the cathode of the third diode D3 is connected to the second channel operational amplifier U 1.2 The output end of the twelfth resistor R 12 One end of the twelfth resistor R is connected to the base of the fourth transistor T4; 12 The other end of the fourth transistor T4, the collector and the -V CC The emitter of the third transistor T3 and the thirteenth resistor R 13 The emitter of the fourth transistor T4 and the fourteenth resistor R 14 The thirteenth resistor R 13 The other end of the fourteenth resistor R 14 The other end of is connected to the other end of the fifth resistor R5.

5. The cascaded active EMI filter based on component reuse according to claim 4, characterized in that: The first output impedance circuit and the second output impedance circuit have the same structure. The first output impedance circuit includes a tenth resistor R 10 and a first capacitor C1; the second output impedance circuit includes a fifteenth resistor R 15 and a second capacitor C2; The tenth resistor R 10 One end of the tenth resistor R is connected to the other end of the eighth resistor R8 and the other end of the ninth resistor R9 respectively; 10 The other end of is connected to one end of the first capacitor C1; the other end of the first capacitor C1 is connected to the negative bus; The fifteenth resistor R 15 One end of each resistor R 13 The other end and the fourteenth resistor R 14 The other end of the fifteenth resistor R 15 The other end of is connected to one end of the second capacitor C2; the other end of the second capacitor C2 is connected to the negative bus.

6. The cascaded active EMI filter based on component reuse according to claim 4, characterized in that: The first transistor T1 and the third transistor T3 are of NPN structure; the second transistor T2 and the fourth transistor T4 are of PNP structure.

7. A power electronic converter system, comprising the cascaded active EMI filter based on component reuse according to claim 1.

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