Interference suppression circuit applied to frequency converter and frequency converter

Abstract

The utility model discloses an interference suppression circuit applied to a frequency converter and the frequency converter, and the frequency converter is provided with a passive common-mode suppression circuit, a surge lightning protection circuit, a DC bus electromagnetic anti-interference circuit and an active common-mode suppression circuit. Conductive interference brought by an external power supply, noise coupling generated by working of a power device and common-mode voltage output by the frequency converter are suppressed on the input side, the direct-current bus side and the output side of the frequency converter respectively, the quality of the external input power supply is improved, noise coupling of the power device is reduced, shaft voltage and shaft current on a motor bearing are reduced, and the service life of the motor is prolonged. The electromagnetic compatibility of the frequency converter is comprehensively improved, the stable operation of the frequency converter in a complex industrial environment is ensured, the service life of equipment is prolonged, and the maintenance and replacement cost of the frequency converter is reduced.

Description

Technical Field

[0001] The utility model relates to the technical field of frequency converters, and particularly relates to an interference suppression circuit and a frequency converter applied to a frequency converter. Background Art

[0002] A frequency converter is a power control device that applies frequency conversion technology and microelectronics technology to control an AC motor by changing the frequency of the motor's working power supply. The frequency converter mainly consists of a rectification unit, a filtering unit, an inversion unit, a braking unit, a driving unit, a detection unit, a microprocessing unit, etc. It adjusts the voltage and frequency of the output power supply by the on-off of the internal IGBT, and provides the required power supply voltage according to the actual needs of the motor, so as to achieve the purpose of energy saving and speed regulation.

[0003] The EMC (electromagnetic compatibility) circuit design of the frequency converter is to ensure that it is not affected by external electromagnetic interference during operation. The electromagnetic compatibility of the frequency converter is particularly important for four-quadrant frequency converters. The application site of the existing frequency converters used in industrial occasions is particularly complex. Not only is the power input distortion of power electronic devices relatively serious, which is prone to generating high-frequency harmonic interference and seriously affecting the normal operation of the equipment, but also the fixed pulse characteristics of the frequency converter cause the instantaneous voltage output by its inversion unit to be unbalanced, generating a large common-mode voltage, and coupling a very high shaft voltage and shaft current on the motor. The four-quadrant frequency converter uses IGBT modules to achieve bidirectional energy flow, and its PWM control will generate high-frequency harmonics, making it easier to generate strong voltage interference and endangering the reliable operation of surrounding equipment.

[0004] In view of this, it is urgent to design an interference suppression circuit and a frequency converter applied to a frequency converter to improve the electromagnetic compatibility of four-quadrant frequency converters. Summary of the Invention

[0005] To solve the above problems, the utility model provides an interference suppression circuit and a frequency converter applied to a frequency converter.

[0006] In the first aspect of the utility model, an interference suppression circuit applied to a frequency converter is provided, which includes a controllable rectification circuit, a current-limiting starting circuit, and an inversion circuit. The current-limiting starting circuit is connected to the loop between the controllable rectification circuit and the inversion circuit;

[0007] It further includes a passive common-mode suppression circuit, a surge lightning protection circuit, a DC bus electromagnetic immunity circuit, and an active common-mode suppression circuit;

[0008] The passive common-mode suppression circuit and the surge lightning protection circuit are both connected between the controllable rectification circuit and the external input power supply. The passive common-mode suppression circuit suppresses the conducted interference of the external input power supply and the harmonics generated by the frequency converter in the power generation state, and the surge lightning protection circuit is used to protect the external input power supply from transient overvoltage;

[0009] The DC bus electromagnetic interference suppression circuit is connected between the controllable rectifier circuit and the inverter circuit, and the DC bus electromagnetic interference suppression circuit suppresses the noise coupling of the power devices on the controllable rectifier circuit and the inverter circuit;

[0010] The active common-mode suppression circuit is connected between the inverter circuit and the external load, and the active common-mode suppression circuit suppresses the common-mode voltage and the high-frequency noise output by the frequency converter.

[0011] The present utility model is further configured such that the passive common-mode suppression circuit includes a first common-mode inductor group, a second common-mode inductor group, a differential-mode loop, and a common-mode capacitor. The first common-mode inductor group and the second common-mode inductor group are connected in series between the controllable rectifier circuit and the external input power supply. One end of the differential-mode loop is connected to the external input power supply, the other end of the differential-mode loop is connected to one end of the common-mode capacitor, and the other end of the common-mode capacitor is grounded.

[0012] The present utility model is further configured such that the differential-mode loop includes at least one differential-mode capacitor and a negative temperature coefficient thermistor, and the differential-mode capacitor and the negative temperature coefficient thermistor are connected in series.

[0013] The present utility model is further configured such that the surge lightning protection circuit includes a surge diversion loop and a gas discharge tube. One end of the surge diversion loop is connected to the external input power supply, the other end of the surge diversion loop is connected to one end of the gas discharge tube, and the other end of the gas discharge tube is connected to the frequency converter housing.

[0014] The present utility model is further configured such that the surge diversion loop is a varistor or a TVS diode.

[0015] The present utility model is further configured such that the DC bus electromagnetic interference suppression circuit includes a DC reactor, a thin-film capacitor group, and a clamping circuit. The DC reactor is symmetrically connected to the positive and negative buses of the frequency converter respectively. The thin-film capacitor group and the clamping circuit are connected in parallel between the positive and negative buses of the frequency converter respectively, and the clamping circuit is a TVS diode.

[0016] The present utility model is further configured such that the active common-mode suppression circuit includes a common-mode signal acquisition circuit, a first-stage active amplification circuit, a second-stage active amplification circuit, and a third common-mode inductor group. The input end of the common-mode signal acquisition circuit is connected to the output end of the inverter circuit, the output end of the common-mode signal acquisition circuit is connected to the input end of the first-stage active amplification circuit, the output end of the first-stage active amplification circuit is connected to the input end of the second-stage active amplification circuit, the output end of the second-stage active amplification circuit is connected to the primary winding of the third common-mode inductor group, and the secondary winding of the third common-mode inductor group is connected between the inverter circuit and the external load.

[0017] The present utility model is further configured such that the common-mode signal acquisition circuit includes a busbar unit and at least one common-mode acquisition unit. One end of the common-mode acquisition unit is connected to the output end of the inverter circuit, the other end of the common-mode acquisition unit is respectively connected to one end of the busbar unit and the input end of the first-stage active amplification circuit, and the other end of the busbar unit is grounded.

[0018] The present utility model is further configured such that the first-stage active amplification circuit is a triode push-pull amplification circuit, including two triodes connected in common-emitter; the second-stage active amplification circuit is a non-inverting operational amplifier circuit, the non-inverting input end of the second-stage active amplification circuit is connected to the emitter of the triode in the first-stage active amplification circuit, and the output end of the second-stage active amplification circuit is connected to the primary winding of the third common-mode inductor group.

[0019] In the second aspect of the present utility model, a frequency converter is provided, including the interference suppression circuit applied to the frequency converter as described above.

[0020] Adopting the technical solution provided by the present utility model, compared with the prior art, it has the following beneficial effects:

[0021] The interference suppression circuit applied to the frequency converter in this technical solution suppresses the conducted interference brought by the external power supply, the noise coupling generated by the operation of the power devices, and the common-mode voltage output by the frequency converter respectively on the input side, DC bus side and output side of the frequency converter through means of conducted interference suppression, electromagnetic immunity suppression and active common-mode suppression. It helps to improve the quality of the external input power supply, reduce the noise coupling of the power devices, reduce the shaft voltage and shaft current on the motor bearing, comprehensively improve the electromagnetic compatibility of the frequency converter, ensure its stable operation in a complex industrial environment, and at the same time help to extend the service life of the equipment and reduce the maintenance and replacement costs of the frequency converter.

[0022] The interference suppression circuit applied to the frequency converter in this technical solution is provided with a surge lightning protection circuit on the power input side of the frequency converter. When a transient overvoltage (such as lightning strike) occurs in the external input power supply, it can quickly absorb the overvoltage energy, protect the power devices and control circuits inside the frequency converter from damage. By providing transient overvoltage protection, the surge lightning protection circuit significantly improves the reliability of the frequency converter and reduces equipment failures and downtime caused by power anomalies. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a block diagram of the interference suppression circuit applied to the frequency converter in an embodiment of the present utility model.

[0024] Figure 2 It is a schematic diagram of the interference suppression circuit applied to the frequency converter in an embodiment of the present utility model.

[0025] Figure 3This is the schematic diagram of the passive common-mode suppression circuit and the surge lightning protection circuit in the embodiment of the present utility model.

[0026] Figure 4 This is the schematic diagram of the active common-mode suppression circuit in the embodiment of the present utility model. Detailed implementation manners

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present utility model clearer, the technical solutions in the embodiments of the present utility model will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present utility model. Apparently, the described embodiments are some but not all of the embodiments of the present utility model. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present utility model without creative efforts shall fall within the protection scope of the present utility model.

[0028] Embodiment 1

[0029] Combined with the attached Figure 1 to the attached Figure 4 In this embodiment, the technical solution of the present utility model is an interference suppression circuit applied to an inverter, including a controlled rectifier circuit 1, a current-limiting starting circuit 2, and an inverter circuit 3. The current-limiting starting circuit 2 is connected to the loop between the controlled rectifier circuit 1 and the inverter circuit 3, and further includes a passive common-mode suppression circuit 4, a surge lightning protection circuit 5, a DC bus electromagnetic immunity circuit 6, and an active common-mode suppression circuit 7;

[0030] Both the passive common-mode suppression circuit 4 and the surge lightning protection circuit 5 are connected between the controlled rectifier circuit 1 and an external input power supply. The passive common-mode suppression circuit 4 suppresses the conducted interference of the external input power supply and the harmonics generated by the inverter in the power generation state, and the surge lightning protection circuit 5 is used to protect the external input power supply from transient overvoltage;

[0031] The DC bus electromagnetic immunity circuit 6 is connected between the controlled rectifier circuit 1 and the inverter circuit 3, and the DC bus electromagnetic immunity circuit 6 suppresses the noise coupling of the power devices on the controlled rectifier circuit 1 and the inverter circuit 3;

[0032] The active common-mode suppression circuit 7 is connected between the inverter circuit 3 and an external load, and the active common-mode suppression circuit 7 suppresses the common-mode voltage and the high-frequency noise output by the inverter.

[0033] In this embodiment, this embodiment is described by taking a three-phase inverter as an example, as shown in the attached Figure 2As shown, both the controllable rectifier circuit 1 and the inverter circuit 3 are three-phase full-bridge switch circuits composed of six controllable power devices. By controlling the trigger angles of the power devices in the controllable rectifier circuit 1 and the inverter circuit 3, bidirectional energy flow of the frequency converter is achieved in the electric state and the power generation state.

[0034] In this embodiment, as shown in the appendix Figure 2 As shown, the current-limiting starting circuit 2 includes a parallel combination of a resistor R1 and a normally-open contact of a contactor KM. When the frequency converter starts, the coil of the contactor KM conducts electricity to close the normally-open contact of the contactor KM.

[0035] In this embodiment, as shown in the appendix Figure 3 As shown, the passive common-mode suppression circuit 4 includes a first common-mode inductor group, a second common-mode inductor group, a differential-mode loop, and a common-mode capacitor. The first common-mode inductor group and the second common-mode inductor group are connected in series between the controllable rectifier circuit and the external input power supply. One end of the differential-mode loop is connected to the external input power supply, the other end of the differential-mode loop is connected to one end of the common-mode capacitor, and the other end of the common-mode capacitor is grounded; the differential-mode loop includes at least one differential-mode capacitor and a negative temperature coefficient thermistor, and the differential-mode capacitor and the negative temperature coefficient thermistor are connected in series.

[0036] Specifically, the first common-mode inductor group includes an inductor L1, an inductor L3, and an inductor L5, and the second common-mode inductor group includes an inductor L2, an inductor L4, and an inductor L6. The inductor L1 and the inductor L2 are connected in series in the first-phase circuit of the external power supply, the inductor L3 and the inductor L4 are connected in series in the second-phase circuit of the external power supply, and the inductor L5 and the inductor L6 are connected in series in the third-phase circuit of the external power supply; there are three paths for the differential-mode loop, which respectively include a first loop formed by a series connection of a capacitor C1 and a thermistor NTC1, a second loop formed by a series connection of a capacitor C2 and a thermistor NTC2, and a third loop formed by a series connection of a capacitor C3 and a thermistor NTC3. The three differential-mode loops are connected in parallel and then connected to the common-mode capacitor Y.

[0037] In this embodiment, the function of connecting the negative temperature coefficient thermistor in series with the differential-mode capacitor is as follows: At the moment when the frequency converter starts, a relatively large inrush current may be generated on the input side; as the operating current of the frequency converter passes through, the temperature of the thermistor rises, and its resistance value gradually decreases. After entering the normal operating state, the influence on the circuit is relatively small.

[0038] In this embodiment, by suppressing conducted interference and harmonics, the passive common-mode suppression circuit helps to improve the quality of the power supply, ensuring that the frequency converter obtains a more stable and cleaner input power supply; at the same time, when the frequency converter is in the power generation state, the passive common-mode suppression circuit can reduce the generation and propagation of harmonics and reduce the pollution of harmonics to the power network.

[0039] In this embodiment, the surge lightning protection circuit 5 includes a surge diversion circuit and a gas discharge tube. One end of the surge diversion circuit is connected to an external input power supply, the other end of the surge diversion circuit is connected to one end of the gas discharge tube, and the other end of the gas discharge tube is connected to the frequency converter housing.

[0040] In this embodiment, the surge diversion circuit is a varistor or a TVS diode.

[0041] Specifically, as shown in the appendix Figure 3 As shown, one end of the TVS diode TVS1, one end of the TVS diode TVS2, and one end of the TVS diode TVS1 are respectively connected to the three-phase power of the external power supply. The other end of the TVS diode TVS1, the other end of the TVS diode TVS2, and the other end of the TVS diode TVS1 are commonly connected to one end of the gas discharge tube SPD, and the other end of the gas discharge tube SPD is grounded.

[0042] In this embodiment, as shown in the appendix Figure 2 As shown, the DC bus electromagnetic immunity circuit 6 includes a DC reactor, a thin-film capacitor bank, and a clamping circuit. The windings L7 and L7' of the DC reactor are symmetrically connected to the positive and negative buses of the frequency converter respectively. The thin-film capacitor bank and the clamping circuit are respectively connected in parallel between the positive and negative buses of the frequency converter. The thin-film capacitor bank includes series-connected thin-film capacitors C4 and C5, and the clamping circuit is the TVS diode TVS4. The DC bus electromagnetic immunity circuit effectively suppresses the noise coupling generated by the power devices during the switching process in the controlled rectifier circuit and the inverter circuit by optimizing the bus capacitor design and adding a DC reactor, reduces the noise coupling of the power devices, can reduce the temperature rise and stress of the devices, and thus extends the service life of the equipment.

[0043] In this embodiment, as shown in the appendix Figure 4 As shown, the active common-mode suppression circuit 7 includes a common-mode signal acquisition circuit 71, a first-stage active amplifier circuit 72, a second-stage active amplifier circuit 73, and a third common-mode inductor group 74. The input end of the common-mode signal acquisition circuit 71 is connected to the output end of the inverter circuit 3, the output end of the common-mode signal acquisition circuit 71 is connected to the input end of the first-stage active amplifier circuit 72, the output end of the first-stage active amplifier circuit 72 is connected to the input end of the second-stage active amplifier circuit 73, the output end of the second-stage active amplifier circuit 73 is connected to the primary winding of the third common-mode inductor group 74, and the secondary winding of the third common-mode inductor group 74 is connected between the inverter circuit 3 and the external load.

[0044] In this embodiment, as shown in the appendix Figure 4 As shown, the third common-mode inductor group 74 is the inductor L8, and the inductor L8 includes a primary winding and three secondary windings.

[0045] In this embodiment, the common-mode signal acquisition circuit 71 includes a busbar unit and at least one common-mode acquisition unit. One end of the common-mode acquisition unit is connected to the output end of the inverter circuit, and the other end of the common-mode acquisition unit is respectively connected to one end of the busbar unit and the input end of the first-stage active amplification circuit. The other end of the busbar unit is grounded.

[0046] Specifically, as shown in the attached Figure 4 figure, there are 3 common-mode acquisition units, including: a first common-mode acquisition unit composed of a series connection of resistor R2 and capacitor C6, a second common-mode acquisition unit composed of a series connection of resistor R3 and capacitor C7, and a third common-mode acquisition unit composed of a series connection of resistor R4 and capacitor C8; the busbar unit includes a series connection of resistor R5 and capacitor C9; the first common-mode acquisition unit, the second common-mode acquisition unit, and the third common-mode acquisition unit are connected in parallel and then connected to the busbar unit.

[0047] In this embodiment, as shown in the attached Figure 4 figure, the first-stage active amplification circuit 72 is a transistor push-pull amplification circuit, including resistor R6, resistor R7, resistor R8, resistor R9, diode D1, diode D2, transistor Q13, and transistor Q14. Resistor R6, diode D1, diode D2, and resistor R7 are connected in series in sequence. One end of resistor R6 and the collector of transistor Q13 are connected to a high level, one end of resistor R7 and the collector of transistor Q14 are connected to a low level, the other end of resistor R6 is connected to the base of Q13, the other end of resistor R7 is connected to the base of Q14, the negative electrode of diode D1 is connected to the output end of the common-mode signal acquisition circuit 71, and resistor R8 and resistor R9 are connected in series between the emitter of transistor Q13 and the emitter of transistor Q14.

[0048] In this embodiment, the second-stage active amplification circuit 73 is a non-inverting operational amplifier circuit. The non-inverting input end of the second-stage active amplification circuit is connected to the emitter of the transistor in the first-stage active amplification circuit, and the output end of the second-stage active amplification circuit is connected to the primary winding of the third common-mode inductor group.

[0049] Specifically, as shown in the attached Figure 4As shown, the second-stage active amplification circuit 73 includes an operational amplifier U1, a resistor R10, and a resistor R11. The non-inverting input terminal of the operational amplifier U1 is connected to one end of the resistor R8. The inverting input terminal of the operational amplifier U1 is respectively connected to one end of the resistor R10 and one end of the resistor R11. The other end of the resistor R11 is grounded. The output terminal of the operational amplifier U1 is respectively connected to the other end of the resistor R10 and one end of the primary winding of the inductor L8. The other end of the primary winding of the inductor L8 is grounded.

[0050] In this embodiment, the combination of the signal push-pull amplification of the first-stage active amplification circuit 72 and the signal operational amplification of the second-stage active amplification circuit 73 provides a high-gain signal amplification ability, which can accurately amplify weak common-mode sampling signals. The high-gain amplification ensures that the common-mode rejection inductor can receive a driving signal with sufficient intensity. At the same time, by accurately amplifying the common-mode sampling signal, the active common-mode rejection circuit can ensure that the rejection signal generated by the common-mode rejection inductor is accurately matched with the common-mode voltage in amplitude and phase, so as to achieve efficient and accurate common-mode voltage suppression, effectively reduce the shaft voltage and shaft current, and extend the service life of the motor.

[0051] The technical solution of this application is applied to the interference suppression circuit of the frequency converter. By means of conducted interference suppression, electromagnetic immunity suppression, and active common-mode suppression, it suppresses the conducted interference brought by the external power supply, the noise coupling generated by the operation of power devices, and the common-mode voltage output by the frequency converter on the input side, DC bus side, and output side of the frequency converter respectively. It helps to improve the quality of the external input power supply, reduce the noise coupling of power devices, reduce the shaft voltage and shaft current on the motor bearing, comprehensively improve the electromagnetic compatibility of the frequency converter, ensure its stable operation in a complex industrial environment, and at the same time help to extend the service life of the equipment and reduce the maintenance and replacement costs of the frequency converter.

[0052] Embodiment 2

[0053] Combined with the attached Figure 1 to the attached Figure 4 , the technical solution of the present utility model is a frequency converter, including the interference suppression circuit applied to the frequency converter described in Embodiment 1.

[0054] It should also be noted that in this specification, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, such that a process, method, article or device comprising a series of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article or device. Without further limitation, an element defined by the phrase "comprising an..." does not exclude the presence of additional identical elements in the process, method, article or device comprising the element.

[0055] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An interference suppression circuit for a frequency converter, comprising a controlled rectifier circuit, a current limiting start circuit and an inverter circuit, wherein the current limiting start circuit is connected to a loop between the controlled rectifier circuit and the inverter circuit, and characterized in that: It also includes a passive common mode suppression circuit, a surge lightning protection circuit, a DC bus electromagnetic interference prevention circuit and an active common mode suppression circuit; The passive common-mode suppression circuit and the surge lightning protection circuit are both connected between the controllable rectifier circuit and the external input power supply, the passive common-mode suppression circuit suppresses the conducted interference of the external input power supply and the harmonics generated by the inverter in the power generation state, and the surge lightning protection circuit is used to protect the external input power supply from transient overvoltage; The DC bus electromagnetic anti-interference circuit is connected between the controllable rectifier circuit and the inverter circuit, and the DC bus electromagnetic anti-interference circuit suppresses noise coupling of power devices on the controllable rectifier circuit and the inverter circuit; The active common-mode suppression circuit is connected between the inverter circuit and an external load, and the active common-mode suppression circuit suppresses the common-mode voltage and high-frequency noise output by the inverter.

2. The interference suppression circuit for frequency converter according to claim 1, characterized in that: The passive common-mode suppression circuit includes a first common-mode inductor group, a second common-mode inductor group, a differential-mode loop and a common-mode capacitor. The first common-mode inductor group and the second common-mode inductor group are connected in series between the controllable rectifier circuit and an external input power supply. One end of the differential-mode loop is connected to the external input power supply, the other end of the differential-mode loop is connected to one end of the common-mode capacitor, and the other end of the common-mode capacitor is grounded.

3. The interference suppression circuit for frequency converter according to claim 2, characterized in that: The differential mode loop includes at least one differential mode capacitor and a negative temperature coefficient thermistor, and the differential mode capacitor and the negative temperature coefficient thermistor are connected in series.

4. The interference suppression circuit for frequency converter according to claim 1, characterized in that: The surge lightning protection circuit includes a surge diversion circuit and a gas discharge tube, one end of the surge diversion circuit is connected to an external input power supply, the other end of the surge diversion circuit is connected to one end of the gas discharge tube, and the other end of the gas discharge tube is connected to the inverter housing.

5. The interference suppression circuit for frequency converter according to claim 4, characterized in that: The surge diversion circuit is a varistor or a TVS diode.

6. The interference suppression circuit for frequency converter according to claim 1, characterized in that: The DC bus electromagnetic anti-interference circuit includes a DC reactor, a film capacitor group and a clamping circuit. The DC reactor is symmetrically connected to the positive and negative buses of the inverter, respectively. The film capacitor group and the clamping circuit are respectively connected in parallel between the positive and negative buses of the inverter. The clamping circuit is a TVS diode.

7. The interference suppression circuit for a frequency converter according to claim 1, characterized in that: The active common-mode suppression circuit includes a common-mode signal acquisition circuit, a first-level active amplifier circuit, a second-level active amplifier circuit and a third common-mode inductor group. The input end of the common-mode signal acquisition circuit is connected to the output end of the inverter circuit, the output end of the common-mode signal acquisition circuit is connected to the input end of the first-level active amplifier circuit, the output end of the first-level active amplifier circuit is connected to the input end of the second-level active amplifier circuit, the output end of the second-level active amplifier circuit is connected to the primary winding of the third common-mode inductor group, and the secondary winding of the third common-mode inductor group is connected between the inverter circuit and an external load.

8. The interference suppression circuit for frequency converter according to claim 7, characterized in that: The common-mode signal acquisition circuit includes a confluence unit and at least one common-mode acquisition unit, one end of the common-mode acquisition unit is connected to the output end of the inverter circuit, the other end of the common-mode acquisition unit is respectively connected to one end of the confluence unit and the input end of the first-level active amplifier circuit, and the other end of the confluence unit is grounded.

9. The interference suppression circuit for frequency converter according to claim 7, characterized in that: The first-level active amplifier circuit is a transistor push-pull amplifier circuit, including two transistors connected with a common emitter; the second-level active amplifier circuit is a common-phase operational amplifier circuit, the common-phase input end of the second-level active amplifier circuit is connected to the emitter of the transistor in the first-level active amplifier circuit, and the output end of the second-level active amplifier circuit is connected to the primary winding of the third common-mode inductor group.

10. A frequency converter, characterized in that: The invention comprises the interference suppression circuit applied to the frequency converter as claimed in any one of claims 1 to 9.

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