A feed-forward current compensation-based active common-mode EMI filter and an application system

Abstract

The application discloses a kind of active common-mode EMI filter and application system based on feedforward current compensation, wherein, the port of several common-mode current sampling circuits is respectively connected with one end of emitter follower and power supply ground, and the port of several current amplification circuits is respectively connected with the other end of emitter follower and power supply circuit;Common-mode current sampling circuit is used for sampling common-mode current and outputting voltage signal;Emitter follower is used as the isolation buffer circuit of common-mode current sampling circuit and current amplification circuit to make output voltage signal remain unchanged;Current amplification circuit is used for converting the voltage signal output by emitter follower into current signal, and providing additional current, so that the final output current is equal to the size of common-mode current.The application designs active EMI filter based on triode, which can effectively suppress common-mode interference of power electronic converter, and has the characteristics of simple structure, small occupied volume and low production cost.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electromagnetic interference suppression devices, and particularly relates to an active common-mode EMI filter based on feedforward current compensation and an application system. BACKGROUND

[0002] Due to the increasingly wide application of various power electronic devices in industry and daily life, high di / dt and dv / dt in the switching process can generate strong electromagnetic interference (EMI), which not only affects the operation reliability of the device itself, but also affects the normal operation of other devices. In order to ensure the reliable operation of the system, the electromagnetic interference generated by the power electronic device must be suppressed to limit the electromagnetic interference value within the range specified in the standard.

[0003] According to the propagation path of electromagnetic interference, the electromagnetic interference is divided into differential mode interference and common mode interference. The common mode interference propagates in the entire system and is relatively complex. In engineering, a passive common-mode EMI filter is usually used to achieve the suppression of common-mode interference. However, the conventional passive common-mode EMI filter is usually large in size and weight, and in practice, an active EMI filter can also be considered to achieve the suppression of common-mode interference. However, the existing active EMI filter usually adopts a structure with an operational amplifier, resulting in high cost. SUMMARY

[0004] The present application provides an active common-mode EMI filter based on feedforward current compensation and an application system to overcome the technical problem of high cost caused by the structure with an operational amplifier when using an active EMI filter to achieve the suppression of common-mode interference.

[0005] In order to achieve the above-mentioned purpose, the technical scheme of the present application is as follows:

[0006] An active common-mode EMI filter based on feedforward current compensation, comprising a common-mode current sampling circuit B, an emitter follower C, a current amplification circuit D and a power supply circuit E;

[0007] A plurality of ports of the common-mode current sampling circuit B are respectively connected with one end of the emitter follower C and a power supply ground, and a plurality of ports of the current amplification circuit D are respectively connected with the other end of the emitter follower C and the power supply circuit E;

[0008] The power supply circuit E is used to supply power to the emitter follower C and the current amplification circuit D;

[0009] The common-mode current sampling circuit B is used to sample the common-mode current and output a voltage signal;

[0010] The emitter follower C is used as an isolation buffer circuit of the common-mode current sampling circuit B and the current amplification circuit D so that the output voltage signal remains unchanged.

[0011] The current amplification circuit D is used to convert the voltage signal output by the emitter follower C into a current signal and provide additional current so that the final output current is equal to the common-mode current size.

[0012] Further, the emitter follower C includes a first capacitor C1, a second resistor R2, a third resistor R3, a fourth resistor R4, a first transistor T1, and a second capacitor C2; the power supply circuit E includes a first power supply V1 and a second power supply V2;

[0013] One end of the first capacitor C1 is connected to the common-mode current sampling circuit B, the base of the first transistor T1 is connected to the other end of the first capacitor C1, one end of the second resistor R2, and one end of the third resistor R3, respectively, the collector of the first transistor T1 is connected to the other end of the second resistor R2 and the first power supply V1, respectively, the emitter of the first transistor T1 is connected to one end of the fourth resistor R4 and one end of the second capacitor C2, and the other end of the third resistor R3 is connected to the other end of the fourth resistor R4.

[0014] Further, the current amplification circuit D includes a fifth resistor R5, a sixth resistor R6, a seventh resistor R7, an eighth resistor R8, a first diode D1, a second diode D2, a second transistor T2, a third transistor T3, a ninth resistor R9, and a plurality of injection capacitors;

[0015] One end of the first diode D1 and one end of the second diode D2 are respectively connected to the other end of the second capacitor C2, the base of the second transistor T2 is connected to the other end of the first diode D1 and one end of the fifth resistor R5, the collector of the second transistor T2 is connected to the other end of the fifth resistor R5 and the first power supply V1, respectively, and the emitter of the second transistor T2 is connected to one end of the seventh resistor R7.

[0016] The base of the third transistor T3 is connected to the other end of the second diode D2 and one end of the sixth resistor R6, the collector of the third transistor T3 is connected to the other end of the sixth resistor R6 and the second power supply V2, respectively, and the emitter of the third transistor T3 is connected to one end of the eighth resistor R8.

[0017] The other end of the seventh resistor R7 and the other end of the eighth resistor R8 are respectively connected to one end of the ninth resistor R9, and the other end of the ninth resistor R9 is respectively connected to one end of a plurality of injection capacitors.

[0018] Further, the common-mode current sampling circuit B comprises a current transformer and a first resistor R1, one end of the first resistor R1 is connected with one end of a secondary winding L2 of the current transformer, and is connected with a power supply ground of the active EMI filter, the other end of the first resistor R1 and the other end of the secondary winding L2 of the current transformer are both connected with the other end of the first capacitor C1.

[0019] Further, the first and second triodes T1 and T2 are NPN type triodes, and the third triode T3 is a PNP type triode.

[0020] An application system comprises an active common-mode EMI filter and a power electronic converter, the active common-mode EMI filter is connected with the power electronic converter, wherein:

[0021] The several injection capacitors are respectively a third capacitor C3 and a fourth capacitor C4, the other end of the ninth resistor R9 is connected with one end of the third capacitor C3 and one end of the fourth capacitor C4, the other end of the third capacitor C3 and the other end of the fourth capacitor C4 are respectively connected with L line and N line in the DC bus A of the power electronic converter.

[0022] The primary winding of the current transformer comprises a first primary winding L1 and a second primary winding L1', and the two ends of the first primary winding L1 are respectively connected with L line in the DC bus A of the power electronic converter, and the two ends of the second primary winding L1' are respectively connected with N line in the DC bus A of the power electronic converter.

[0023] Beneficial effects: the active EMI filter is designed based on the emitter follower with triodes, can effectively suppress the common-mode interference of the power electronic converter, meanwhile, the active EMI filter has the characteristics of simple structure and small occupied volume, and compared with other existing active EMI filters, the production cost of the active EMI filter is lower. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiment or prior art description. Obviously, the drawings in the following description are some embodiments of the present application, and those skilled in the art can also obtain other drawings according to these drawings without creative labor.

[0025] Figure 1 It is a structure schematic diagram of an active common-mode EMI filter based on feedforward current compensation in the present application;

[0026] Figure 2A schematic diagram of connection between the LISN and the power electronic converter in the embodiment of the present application;

[0027] Figure 3 A structural schematic diagram of the test device in the embodiment of the present application;

[0028] Figure 4 An equivalent circuit diagram of the test device in the embodiment of the present application;

[0029] In the figure: A, DC bus of the power electronic converter; B, common-mode current sampling circuit; C, emitter follower; D, current amplification circuit; E, power supply circuit. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0031] The embodiment provides an active common-mode EMI filter based on feedforward current compensation, as shown in the figure, comprising a common-mode current sampling circuit B, an emitter follower C, a current amplification circuit D and a power supply circuit E, and the injection current connection point of the current amplification circuit D is located in front of the detection current connection point of the common-mode current sampling circuit B, so as to realize feedforward current compensation. Figure 1

[0032] The plurality of ports of the common-mode current sampling circuit B are respectively connected with one end of the emitter follower C and a power supply ground, and the plurality of ports of the current amplification circuit D are respectively connected with the other end of the emitter follower C and the power supply circuit E.

[0033] The power supply circuit E is used for supplying power for the emitter follower C and the current amplification circuit D.

[0034] The common-mode current sampling circuit B is used for sampling common-mode current and outputting a voltage signal.

[0035] The emitter follower C is used as an isolation buffer circuit of the common-mode current sampling circuit B and the current amplification circuit D, so that the output voltage signal remains unchanged.

[0036] The current amplification circuit D is used for converting the voltage signal output by the emitter follower C into a current signal, and providing additional current, so that the finally output current is equal to the common-mode current.

[0037] In specific embodiments, as shown in the figure,​Figure 1 、 Figure 3 and Figure 4 As shown in the figure, the emitter follower C includes a first capacitor C1, a second resistor R2, a third resistor R3, a fourth resistor R4, a first transistor T1 and a second capacitor C2; the power supply circuit E includes a first power supply V1 and a second power supply V2;

[0038] One end of the first capacitor C1 is connected with the common-mode current sampling circuit B, the base of the first transistor T1 is connected with the other end of the first capacitor C1, one end of the second resistor R2 and one end of the third resistor R3 respectively, the collector of the first transistor T1 is connected with the other end of the second resistor R2 and the first power supply V1 respectively, the emitter of the first transistor T1 is connected with one end of the fourth resistor R4 and one end of the second capacitor C2, and the other end of the third resistor R3 is connected with the other end of the fourth resistor R4.

[0039] Specifically, in the embodiment, the main feature of the emitter follower C is that its output voltage is almost equal to the input voltage, and the input resistance of the emitter follower C is usually high, so it can well isolate the input signal source and the subsequent circuit, thereby preventing the input circuit from being affected by the load, enhancing the load capacity, and thus maintaining the stability of the input signal. Among them, for the emitter follower C, adjusting the resistance values of the second resistor R2, the third resistor R3 and the fourth resistor R4 can adjust its static working point, so as to ensure that the demand of the current amplification circuit D for the input current is met, and the first capacitor C1 and the second capacitor C2 play an isolation role, so that the static working points of the circuits at each stage do not affect each other.

[0040] In a specific embodiment, as shown in the figure, the current amplification circuit D includes a fifth resistor R5, a sixth resistor R6, a seventh resistor R7, an eighth resistor R8, a first diode D1, a second diode D2, a second transistor T2, a third transistor T3, a ninth resistor R9 and a plurality of injection capacitors; Figure 1 One end of the first diode D1 and one end of the second diode D2 are connected with the other end of the second capacitor C2 respectively, the base of the second transistor T2 is connected with the other end of the first diode D1 and one end of the fifth resistor R5, the collector of the second transistor T2 is connected with the other end of the fifth resistor R5 and the first power supply V1 respectively, and the emitter of the second transistor T2 is connected with one end of the seventh resistor R7.

[0041]

[0042] ​The base of the third triode T3 is connected with the other end of the second diode D2 and one end of the sixth resistor R6, the collector of the third triode T3 is connected with the other end of the sixth resistor R6 and the second power supply V2 respectively, and the emitter of the third triode T3 is connected with one end of the eighth resistor R8;

[0043] The other end of the seventh resistor R7 and the other end of the eighth resistor R8 are connected with one end of the ninth resistor R9 respectively, and the other end of the ninth resistor R9 is connected with one end of the injection capacitor.

[0044] Specifically, the current amplification circuit D, i.e. the push-pull circuit, has the following characteristics: 1) composed of two complementary output stages, including an NPN transistor and a PNP transistor, the two output stages can work simultaneously, but the current directions are opposite, which means that the two output stages can provide additional current during the positive half cycle and the negative half cycle of the output signal, thereby increasing the output current capacity of the entire circuit; 2) the two output stages in the push-pull circuit can effectively match the impedance of the load, when one output stage is in the on state, the other output stage is in the off state, which can reduce the output impedance of the entire circuit, therefore, the push-pull circuit can drive the load more effectively and improve the output current capacity; 3) the output stage of the push-pull circuit can provide a lower output impedance when working, therefore, under the given load condition, the push-pull circuit can provide greater output current without reducing the output voltage, which is very advantageous for driving low-impedance loads or applications requiring greater output current.

[0045] Specifically, the fifth resistor R5 and the sixth resistor R6 in the current amplification circuit D are used to generate a bias voltage to determine the static operating point of the push-pull circuit, the seventh resistor R7 and the eighth resistor R8 are used to solve the problem of thermal runaway, and the first diode D1 and the second diode D2 are used to eliminate the dead zone effect of the input voltage, as shown in Figure 1 and Figure 3 As shown, the emitter follower and the current amplification circuit D are powered by the same power supply, and the power ground of the power supply is connected with the ground; in order not to affect the output of the active EMI filter, the third capacitor C3 and the fourth capacitor C4 need to be selected to have appropriate values so as not to affect the output of the active EMI filter in the frequency range of 150 kHz and above, in the embodiment, preferably, the third capacitor C3 and the fourth capacitor C4 have the same size of 47nF.

[0046] In specific embodiments, the common-mode current sampling circuit B comprises a current transformer and a first resistor R1, one end of the first resistor R1 is connected with one end of a secondary winding L2 of the current transformer, and is connected with a power supply ground of the active EMI filter, the other end of the first resistor R1 and the other end of the secondary winding L2 of the current transformer are connected with the other end of the first capacitor C1.

[0047] In specific embodiments, the first and second triodes T1 and T2 are NPN type triodes, and the third triode T3 is a PNP type triode. Specifically, in the present embodiment, the cost of the product is reduced by adding triodes in the active EMI filter.

[0048] Based on the same principle, an application system is constructed in the present application, comprising the active common-mode EMI filter and a power electronic converter, the active common-mode EMI filter being connected with the power electronic converter.

[0049] Specifically, in the application system of the present embodiment, two injection capacitors are set according to the number of bus bars of the power electronic converter, which are the third capacitor C3 and the fourth capacitor C4, and the other end of the ninth resistor R9 is connected with one end of the third capacitor C3 and one end of the fourth capacitor C4, and the other end of the third capacitor C3 and the other end of the fourth capacitor C4 are respectively connected with the L line and the N line in the DC bus A of the power electronic converter. In practice, the number of injection capacitors can be adjusted according to the device to be filtered.

[0050] Specifically, in the application system of the present embodiment, the primary winding of the current transformer comprises a first primary winding L1 and a second primary winding L1', and the two ends of the first primary winding L1 are respectively connected with the L line in the DC bus A of the power electronic converter, and the two ends of the second primary winding L1' are respectively connected with the N line in the DC bus A of the power electronic converter.

[0051] In the present embodiment, the current amplification circuit D can improve the injection capability of the active filter, ensure that the current injected by the active EMI filter to the power electronic converter is the same as the common-mode current generated by the power electronic converter through the parasitic capacitance to ground, and further suppress the common-mode interference of the power electronic converter.

[0052] In the present embodiment, in order to verify the effectiveness of the active EMI filter in suppressing common-mode interference, as shown in FIG. 6, a common-mode voltage source is added to the DC bus A of the power electronic converter, and the common-mode voltage source is connected with the L line and the N line in the DC bus A of the power electronic converter. Figure 2 and Figure 3As shown, the application system is connected with a DC power supply and a LISN (Line Impedance Stabilization Network) for EMI test as a test device, and there is a parasitic capacitance Co between the power electronic converter and the ground, as shown in the figure. Figure 4 As shown in the figure, V CM is the common-mode voltage source of the whole device, the power supply circuit E includes a first power supply V1 and a second power supply V2, and V1=12v and V2=-12v, and supplies power to the emitter follower C and the current amplification circuit D, V3 is the input voltage value of the emitter follower C, V4 is the voltage value amplified by the inverting amplifier, the third capacitor C3 and the fourth capacitor C4 are the same and equivalent to C5, the first primary winding L1 and the second primary winding L1' are equivalent to L3, Z CM is the equivalent common-mode impedance of the load, Z LISN is the equivalent common-mode impedance of the parallel LISN, I LISN is the common-mode current flowing through the DC side, I CM is the common-mode current flowing through the parasitic capacitance, Z INJ is the output resistance and capacitance impedance of the current amplification circuit, I INJ is the injected current generated by the active filter, in this embodiment, in order to reduce the volume of the current transformer, the number of turns of the primary winding L3 of the current transformer is 1, the number of turns of the secondary winding L2 is n, and the primary winding L3 of the current transformer, i.e. L1 and L1', and the secondary winding L2 share a magnetic core, and the coupling coefficient is 1; in an ideal case, the voltage amplification coefficient of the emitter follower is 1, and the current amplification circuit has no voltage amplification effect, and the current gain of the whole active EMI filter is A, which is the ratio of I INJ and I CM . According to the Norton theorem and the Thevenin theorem, the following equation can be obtained:

[0053]

[0054] Generally, the impedance of the capacitor C5 is small enough, so the impedance value of Z INJ is R9, and therefore, the current amplification coefficient A of the active EMI filter is obtained as follows:

[0055]

[0056]

[0057] By simplifying, the common-mode current on the DC side at this time is:

[0058]

[0059] At this time, it can be seen that when A = 1, the common-mode current on the DC side is theoretically 0, so the values of the first resistor R1, the ninth resistor R9 and n can be determined through equation (2), so that A = 1 can be ensured, that is, the active EMI filter injects the sampled common-mode current into the power electronic converter, so that the current I INJ with the common-mode current I CM generated by the parasitic capacitance to ground is the same, so that the common-mode current flowing through the LISN can be reduced, and sufficient suppression of the common-mode interference of the power electronic converter can be achieved.

[0060] Specifically, in the embodiment, preferably, the resistance value of the first resistor R1 is 10Ω, the resistance value of the second resistor R2 is 7500Ω, the resistance value of the third resistor R3 is 10000Ω, the resistance value of the fourth resistor R4, the fifth resistor R5 and the sixth resistor R6 is 1000Ω, the resistance value of the seventh resistor R7, the eighth resistor R8 and the ninth resistor R9 is 1Ω; the size of the first capacitor C1 and the second capacitor C2 is 10μF.

[0061] Finally, it should be pointed out that: the above embodiments are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. An active common-mode EMI filter based on feedforward current compensation, characterized in that, This includes a common-mode current sampling circuit (B), an emitter follower (C), a current amplifier circuit (D), and a power supply circuit (E). Several ports of the common-mode current sampling circuit B are respectively connected to one end of the emitter follower C and the power supply ground, and several ports of the current amplification circuit D are respectively connected to the other end of the emitter follower C and the power supply circuit E. The power supply circuit E is used to supply power to the emitter follower C and the current amplifier circuit D. The common-mode current sampling circuit B is used to sample the common-mode current and output a voltage signal; The emitter follower C is used as an isolation buffer circuit between the common-mode current sampling circuit B and the current amplification circuit D to keep the output voltage signal unchanged. The emitter follower C includes a first capacitor C1, a second resistor R2, a third resistor R3, a fourth resistor R4, a first transistor T1, and a second capacitor C2; the power supply circuit E includes a first power supply V1 and a second power supply V2. One end of the first capacitor C1 is connected to the common-mode current sampling circuit B. The base of the first transistor T1 is connected to the other end of the first capacitor C1, one end of the second resistor R2, and one end of the third resistor R3. The collector of the first transistor T1 is connected to the other end of the second resistor R2 and the first power supply V1. The emitter of the first transistor T1 is connected to one end of the fourth resistor R4 and one end of the second capacitor C2. The other end of the third resistor R3 is connected to the other end of the fourth resistor R4. The current amplifier circuit D is used to convert the voltage signal output by the emitter follower C into a current signal and provide additional current to the L and N lines in the DC bus so that the final output current is equal to the common-mode current. The current amplification circuit D includes a fifth resistor R5, a sixth resistor R6, a seventh resistor R7, an eighth resistor R8, a first diode D1, a second diode D2, a second transistor T2, a third transistor T3, a ninth resistor R9, and several injection capacitors. One end of the first diode D1 and one end of the second diode D2 are respectively connected to the other end of the second capacitor C2. The base of the second transistor T2 is connected to the other end of the first diode D1 and one end of the fifth resistor R5. The collector of the second transistor T2 is connected to the other end of the fifth resistor R5 and the first power supply V1. The emitter of the second transistor T2 is connected to one end of the seventh resistor R7. The base of the third transistor T3 is connected to the other end of the second diode D2 and one end of the sixth resistor R6. The collector of the third transistor T3 is connected to the other end of the sixth resistor R6 and the second power supply V2. The emitter of the third transistor T3 is connected to one end of the eighth resistor R8. The other end of the seventh resistor R7 and the other end of the eighth resistor R8 are respectively connected to one end of the ninth resistor R9, and the other end of the ninth resistor R9 is respectively connected to one end of one of the injection capacitors.

2. The active common-mode EMI filter based on feedforward current compensation according to claim 1, characterized in that, The common-mode current sampling circuit B includes a current transformer and a first resistor R1. One end of the first resistor R1 is connected to one end of the secondary winding L2 of the current transformer and is connected to the power ground of the active EMI filter. The other end of the first resistor R1 and the other end of the secondary winding L2 of the current transformer are both connected to the other end of the first capacitor C1.

3. The active common-mode EMI filter based on feedforward current compensation according to claim 2, characterized in that, The first transistor T1 and the second transistor T2 are NPN transistors, and the third transistor T3 is a PNP transistor.

4. An application system, characterized in that, Includes the active common-mode EMI filter and power electronic converter as described in claim 3, wherein the active common-mode EMI filter is connected to the power electronic converter, wherein: The plurality of injection capacitors are respectively the third capacitor C3 and the fourth capacitor C4; the other end of the ninth resistor R9 is connected to one end of the third capacitor C3 and one end of the fourth capacitor C4, and the other end of the third capacitor C3 and the other end of the fourth capacitor C4 are respectively connected to the L line and N line in the DC bus A of the power electronic converter. The primary winding of the current transformer includes a first primary winding L1 and a second primary winding L2. The two ends of the first primary winding L1 are respectively connected to the L line in the DC bus A of the power electronic converter, and the second primary winding L1 Both ends are connected to the N line in the DC bus A of the power electronic converter.

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