Over-current protection circuit for frequency converter and frequency converter
By designing bridge arm current sampling circuit and overcurrent split trigger circuit in the inverter, directly monitoring and hardware triggering overcurrent protection, the problem of slow response speed of the existing inverter overcurrent protection is solved, and a more efficient protection effect is achieved.
Patent Information
- Application Number
- CN202520666358.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-10
- Publication Date
- 2025-05-13
- Estimated Expiration
- 2035-04-10
AI Technical Summary
The overcurrent protection mechanism of existing inverters has slow response speed, especially in application scenarios with poor operating conditions, which can easily lead to short-term failure, affecting the service life of power devices and the safe operation of the inverter system.
An overcurrent protection circuit for inverter is designed. The inverter bridge arm current is directly monitored through the bridge arm current sampling circuit to avoid the window restriction of traditional low-end sampling that needs to wait for the down tube to be turned on. The hardware direct contact is realized through the overcurrent break trigger circuit, and there is no need to go through the software decision process of the control unit.
It improves the response speed of overcurrent protection, ensures that power devices can be effectively protected in overcurrent situations, extends their service life, and improves the operational safety of the frequency conversion system.
Smart Images
Figure CN222868540U_ABST
Abstract
Description
Technical Field
[0001] The utility model relates to the technical field of frequency converters, and in particular to an overcurrent protection circuit for frequency converters and a frequency converter. Background Art
[0002] The variable-frequency drive (VFD) is a power control device that uses frequency conversion technology and microelectronics technology to control the AC motor by changing the working power frequency of the motor. The inverter is mainly composed of a rectifier unit, a filter unit, an inverter unit, a brake unit, a drive unit, a detection unit, and a control unit. The inverter adjusts the voltage and frequency of the output power supply by switching on and off the power devices inside the inverter unit, and provides the required power supply voltage according to the actual needs of the motor, thereby achieving the purpose of energy saving and speed regulation.
[0003] When the inverter is outputting inverter current, if the load is too large, it will cause overcurrent in the main circuit. Overcurrent is a very important factor affecting the safe operation of high-power inverters. Therefore, it is necessary to sample the current of the inverter and perform overcurrent protection based on the current sampling results. However, the existing inverter feeds back the current sampling to the inverter control unit, and then the control unit adjusts the switching frequency of the inverter unit power device to control the output current. This overcurrent control method has a slow response speed, especially in application scenarios with poor working conditions, and may even cause the overcurrent protection mechanism to fail for a short time, which greatly affects the service life of the power device and the safe operation of the inverter system.
[0004] In view of this, it is urgent to propose an overcurrent protection circuit for a frequency converter to overcome the problems existing in the existing overcurrent protection mechanism of the frequency converter. Summary of the invention
[0005] In order to solve the above problems, the utility model provides an overcurrent protection circuit for a frequency converter and a frequency converter.
[0006] In the first aspect of the utility model, there is provided an overcurrent protection circuit for a frequency converter, comprising a control unit and a rectifier circuit, a brake circuit and an inverter circuit connected in sequence, wherein the input end of the rectifier circuit is connected to an external power grid, the output end of the inverter circuit is connected to an external load, a current-limiting starting circuit is connected between the rectifier circuit and the brake circuit, the output end of the control unit is respectively connected to the input end of the brake circuit and the input end of the inverter circuit, and further comprising a bridge arm current sampling circuit, an overcurrent disconnection trigger circuit and a switching power supply circuit, the switching power supply circuit respectively providing working voltages for the control unit, the overcurrent disconnection trigger circuit and the bridge arm current sampling circuit, the input end of the bridge arm current sampling circuit is connected to the output end of the inverter circuit, the output end of the bridge arm current sampling circuit is respectively connected to the input end of the control unit and the input end of the overcurrent disconnection trigger circuit, the output end of the overcurrent disconnection trigger circuit is connected to the current-limiting starting circuit to control the disconnection of the current-limiting starting circuit, and the output end of the control unit is connected to the current-limiting starting circuit to realize buffered power-on of the frequency converter.
[0007] Based on the first aspect, in a possible implementation, the current limiting starting circuit includes a first resistor, a contactor and a circuit breaker, the first resistor and the first tripping contact of the circuit breaker are connected in series to form a starting buffer branch, the normally open contact of the contactor and the second tripping contact of the circuit breaker are connected in series to form an operating conduction branch, and the starting buffer branch and the operating conduction branch are connected in parallel to each other.
[0008] Based on the first aspect, in a possible implementation manner, an output end of the control unit is connected to a coil of a contactor, and an output end of the overcurrent disconnection trigger circuit is connected to a tripping coil of a circuit breaker.
[0009] Based on the first aspect, in a possible implementation method, the bridge arm current sampling circuit samples the current of each bridge arm of the inverter circuit respectively, and the bridge arm current sampling circuit includes a second resistor, a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, a first capacitor, a second capacitor and a first operational amplifier. The second resistor is connected in series to the bridge arm loop of the inverter circuit, the first capacitor is connected in parallel to both ends of the second resistor, the two ends of the first capacitor are respectively connected to the first end of the third resistor and the first end of the fourth resistor, the second end of the third resistor is connected to the in-phase input end of the first operational amplifier, the second end of the fourth resistor is respectively connected to the inverting input end of the first operational amplifier and the first end of the fifth resistor, the output end of the first operational amplifier is respectively connected to the second end of the fifth resistor and the first end of the sixth resistor, the second capacitor is connected in parallel to both ends of the fifth resistor, and the second end of the sixth resistor is respectively connected to the input end of the control unit and the input end of the overcurrent disconnection trigger circuit.
[0010] Based on the first aspect, in a possible implementation, the overcurrent disconnect trigger circuit includes a bandpass filter unit, a hysteresis comparison unit and an isolation unit, the input end of the bandpass filter unit is connected to the output end of the bridge arm current sampling circuit, the output end of the bandpass filter unit is connected to the input end of the hysteresis comparison unit, the output end of the hysteresis comparison unit is connected to the input end of the isolation unit, and the output end of the isolation unit is connected to the coil of the circuit breaker.
[0011] Based on the first aspect, in a possible implementation, the bandpass filtering unit includes a seventh resistor, an eighth resistor, a ninth resistor, a tenth resistor, an eleventh resistor, a third capacitor, a fourth capacitor and a second operational amplifier, the first end of the seventh resistor is connected to the second end of the sixth resistor, the second end of the seventh resistor is respectively connected to the first end of the third capacitor, the first end of the fourth capacitor and the first end of the ninth resistor, the second end of the fourth capacitor is respectively connected to the in-phase input terminal of the second operational amplifier and the first end of the eighth resistor, the second end of the third capacitor and the second end of the eighth resistor are commonly connected, the inverting input terminal of the second operational amplifier is respectively connected to the first end of the tenth resistor and the first end of the eleventh resistor, the second end of the tenth resistor is grounded, and the output terminal of the second operational amplifier is respectively connected to the second end of the ninth resistor and the second end of the eleventh resistor.
[0012] Based on the first aspect, in a possible implementation, the hysteresis comparison unit includes a twelfth resistor, a thirteenth resistor and a comparator, the first end of the thirteenth resistor is connected to a reference voltage, the second end of the thirteenth resistor is connected to an inverting input of the comparator, the output of the second operational amplifier is respectively connected to the non-inverting input of the comparator and the first end of the twelfth resistor, and the second end of the twelfth resistor is connected to the output of the comparator.
[0013] Based on the first aspect, in a possible implementation, the isolation unit includes an optocoupler, a fourteenth resistor, a fifteenth resistor, a thyristor and a first diode, the positive electrode of the optocoupler is connected to the output end of the comparator, the first end of the fourteenth resistor is connected to the negative electrode of the optocoupler, the second end of the fourteenth resistor is grounded, the collector of the optocoupler is connected to a high level, the emitter of the optocoupler is connected to the first end of the fifteenth resistor, the second end of the fifteenth resistor is connected to the gate of the thyristor, the anode of the thyristor is connected to the high level, the cathode of the thyristor is connected to the first end of the coil of the circuit breaker, the second end of the coil of the circuit breaker is grounded, and the first diode is anti-parallel connected at both ends of the coil of the circuit breaker.
[0014] Based on the first aspect, in a possible implementation, the rectifier circuit is a three-phase bridge fully-controlled rectifier circuit.
[0015] In a second aspect of the utility model, a frequency converter is provided, comprising the above-mentioned overcurrent protection circuit for the frequency converter.
[0016] Compared with the prior art, the technical solution provided by the utility model has the following beneficial effects:
[0017] The existing inverter overcurrent protection scheme relies on the control unit to process the current sampling signal and adjust the switching frequency, which has a long signal transmission and processing delay and is prone to failure in emergency situations such as short circuit or instantaneous overcurrent. The overcurrent protection circuit of the inverter used in this technical solution directly monitors the inverter bridge arm current through the bridge arm current sampling circuit, avoiding the window limitation of the traditional low-end sampling that needs to wait for the lower tube to turn on, and realizes the hardware direct triggering of overcurrent through the signal transmission between the bridge arm current sampling circuit and the overcurrent disconnection trigger circuit, without the need to go through the software decision-making process of the control unit. The overcurrent disconnection trigger circuit adopts an independent triggering mechanism, so that the overcurrent protection of the overcurrent disconnection trigger circuit and the overcurrent regulation protection of the control unit work in parallel. Even if the control unit fails, the protection action can still be triggered, which can effectively protect the power device in the overcurrent situation and improve the service life and operation safety of the power device. BRIEF DESCRIPTION OF THE DRAWINGS
[0018] Figure 1 The utility model is a block diagram of an overcurrent protection circuit for a frequency converter according to an embodiment of the present utility model.
[0019] Figure 2 This is a topological diagram of an overcurrent protection circuit for a frequency converter according to an embodiment of the utility model.
[0020] Figure 3 This is a schematic diagram of a bridge arm current sampling circuit according to an embodiment of the utility model.
[0021] Figure 4 This is a schematic diagram of an overcurrent disconnection trigger circuit according to an embodiment of the utility model.
[0022] Explanation of the accompanying drawings: 10, control unit; 20, rectification circuit; 30, braking circuit; 40, inverter circuit; 50, current limiting starting circuit; 60, bridge arm current sampling circuit; 70, overcurrent disconnection trigger circuit; 71, bandpass filter unit; 72, hysteresis comparison unit; 73, isolation unit; 80, switching power supply circuit. DETAILED DESCRIPTION
[0023] In order to make the purpose, technical solution and advantages of the embodiment of the utility model clearer, the technical solution in the embodiment of the utility model will be clearly and completely described below in conjunction with the drawings in the embodiment of the utility model. Obviously, the described embodiment is a part of the embodiment of the utility model, not all of the embodiments. Based on the embodiment of the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.
[0024] Example 1
[0025] Combined with Figure 1 To Attachment Figure 4 The utility model technical solution is an overcurrent protection circuit for a frequency converter, comprising a control unit 10 and a rectifier circuit 20, a brake circuit 30 and an inverter circuit 40 connected in sequence, wherein the input end of the rectifier circuit 20 is connected to an external power grid, the output end of the inverter circuit 40 is connected to an external load, a limited current starting circuit 50 is connected between the rectifier circuit 20 and the brake circuit 30, the output end of the control unit 10 is respectively connected to the input end of the brake circuit 30 and the input end of the inverter circuit 40, and also includes a bridge arm current sampling circuit 60, an overcurrent disconnection trigger circuit 70 and a switch power supply circuit 80, the switch The power supply shutdown circuit 80 provides working voltage for the control unit 10, the overcurrent disconnection trigger circuit 70 and the bridge arm current sampling circuit 60 respectively. The input end of the bridge arm current sampling circuit 60 is connected to the output end of the inverter circuit 40, and the output end of the bridge arm current sampling circuit 60 is respectively connected to the input end of the control unit 10 and the input end of the overcurrent disconnection trigger circuit 70. The output end of the overcurrent disconnection trigger circuit 70 is connected to the current limiting start-up circuit 50 to control the disconnection of the current limiting start-up circuit. The output end of the control unit 10 is connected to the current limiting start-up circuit 50 to realize buffered power-on of the inverter.
[0026] In this embodiment, the bridge arm current sampling circuit 60 collects the current signal of each bridge arm of the inverter circuit 40. The number of the bridge arm current sampling circuits 60 is set specifically according to the number of bridge arms to meet the current sampling of all bridge arms of the inverter circuit 40.
[0027] In this embodiment, the braking circuit 30 is used to perform rapid braking when the bus voltage increases (the inverter is in a power generation state).
[0028] In this embodiment, the overcurrent protection circuit for the inverter of this embodiment directly monitors the inverter bridge arm current through the bridge arm current sampling circuit 60, avoiding the window limitation of the traditional low-end sampling that needs to wait for the lower tube to be turned on, and realizes the hardware direct triggering of overcurrent through the signal transmission between the bridge arm current sampling circuit 60 and the overcurrent disconnection trigger circuit 70, without going through the software decision process of the control unit 10. The overcurrent disconnection trigger circuit 70 adopts an independent trigger mechanism, so that the overcurrent protection of the overcurrent disconnection trigger circuit 70 and the overcurrent regulation protection of the control unit 10 work in parallel. Even if the control unit 10 fails, the protection action can still be triggered, which can effectively protect the power device in the overcurrent situation and improve the service life and operation safety of the power device.
[0029] In this embodiment, as shown in the attached Figure 2As shown, the current limiting starting circuit 50 includes a first resistor R1, a contactor KM1 and a circuit breaker QF, the first resistor R1 and the first tripping contact of the circuit breaker QF are connected in series to form a starting buffer branch, the normally open contact of the contactor KM1 and the second tripping contact of the circuit breaker QF are connected in series to form an operating conduction branch, and the starting buffer branch and the operating conduction branch are connected in parallel to each other.
[0030] In this embodiment, when the frequency converter is in normal operation, the circuit breaker QF is in the on state, that is, the first trip contact of the circuit breaker QF and the second trip contact of the circuit breaker QF are both in the closed state. At the moment of starting the frequency converter, the start buffer branch is in the on state, and the instantaneous impact current is reduced by connecting the first resistor R1 in series to protect the circuit components; after a delay, the control unit 10 controls the contactor KM1 to be energized, the operation conduction branch is in the on state, the start buffer branch is short-circuited, and the frequency converter enters the normalized working state.
[0031] In this embodiment, the output end of the control unit 10 is connected to the coil of the contactor KM1, and the output end of the overcurrent disconnection trigger circuit 70 is connected to the tripping coil of the circuit breaker QF; the on and off of the contactor KM1 is driven by the control unit 10, and the on and off of the circuit breaker QF is driven by the overcurrent disconnection trigger circuit 70.
[0032] In this embodiment, as shown in the attached Figure 3 As shown, the bridge arm current sampling circuit 60 samples the current of each bridge arm of the inverter circuit 40 respectively, and the bridge arm current sampling circuit 60 includes a second resistor R2, a third resistor R3, a fourth resistor R4, a fifth resistor R5, a sixth resistor R6, a first capacitor C1, a second capacitor C2 and a first operational amplifier U1, the second resistor R2 is connected in series to the bridge arm loop of the inverter circuit (the DC bus voltage Ud is loaded at both ends of the bridge arm loop), the first capacitor C1 is connected in parallel to both ends of the second resistor R2, and both ends of the first capacitor C1 are connected to the first end of the third resistor R3 and the first end of the fourth resistor R4 respectively, and the third resistor R2 is connected in series to the bridge arm loop of the inverter circuit (the DC bus voltage Ud is loaded at both ends of the bridge arm loop), the first capacitor C1 is connected in parallel to both ends of the second resistor R2, and the two ends of the first capacitor C1 are connected to the first end of the third resistor R3 and the first end of the fourth resistor R4 respectively. The second end of the resistor R3 is connected to the non-inverting input end of the first operational amplifier U1, the second end of the fourth resistor R4 is respectively connected to the inverting input end of the first operational amplifier U1 and the first end of the fifth resistor R5, the output end of the first operational amplifier U1 is respectively connected to the second end of the fifth resistor R5 and the first end of the sixth resistor R6, the second capacitor C2 is connected in parallel to the two ends of the fifth resistor R5, the second end of the sixth resistor R6 is respectively connected to the input end of the control unit 10 and the input end of the over-current disconnection trigger circuit 70, and the second end of the sixth resistor R6 outputs the bridge arm current sampling signal Signal_Bac.
[0033] In this embodiment, the overcurrent disconnect trigger circuit 70 includes a bandpass filter unit 71, a hysteresis comparison unit 72 and an isolation unit 73, the input end of the bandpass filter unit 71 is connected to the output end of the bridge arm current sampling circuit 60, the output end of the bandpass filter unit 71 is connected to the input end of the hysteresis comparison unit 72, the output end of the hysteresis comparison unit 72 is connected to the input end of the isolation unit 73, and the output end of the isolation unit 73 is connected to the coil of the circuit breaker QF.
[0034] In this embodiment, the bridge arm current sampling signal Signal_Bac output by the bridge arm current sampling circuit 60 is connected to the input end of the bandpass filtering unit 71; the bandpass filtering unit 71 improves the signal-to-noise ratio of the signal by attenuating or suppressing the noise frequency component, the hysteresis comparison unit 72 can effectively avoid false triggering due to signal noise or fluctuations, and the isolation unit 73 can improve the safety and stability of the overcurrent disconnection triggering action.
[0035] In this embodiment, the bandpass filtering unit 71 includes a seventh resistor R7, an eighth resistor R8, a ninth resistor R9, a tenth resistor R10, an eleventh resistor R11, a third capacitor C3, a fourth capacitor C4 and a second operational amplifier U2, the first end of the seventh resistor R7 is connected to the second end of the sixth resistor R6, the second end of the seventh resistor R7 is respectively connected to the first end of the third capacitor C3, the first end of the fourth capacitor C4 and the first end of the ninth resistor R9, the second end of the fourth capacitor C4 is respectively connected to the in-phase input end of the second operational amplifier U2 and the first end of the eighth resistor R8, the second end of the third capacitor C3 and the second end of the eighth resistor R8 are commonly connected, the inverting input end of the second operational amplifier U2 is respectively connected to the first end of the tenth resistor R10 and the first end of the eleventh resistor R11, the second end of the tenth resistor R10 is grounded, and the output end of the second operational amplifier U2 is respectively connected to the second end of the ninth resistor R9 and the second end of the eleventh resistor R11.
[0036] In this embodiment, the hysteresis comparison unit 72 includes a twelfth resistor R12, a thirteenth resistor R13 and a comparator U3, the first end of the thirteenth resistor R13 is connected to the reference voltage Vref, the second end of the thirteenth resistor R13 is connected to the inverting input end of the comparator U3, the output end of the second operational amplifier U2 is respectively connected to the non-inverting input end of the comparator U3 and the first end of the twelfth resistor R12, and the second end of the twelfth resistor R12 is connected to the output end of the comparator U3.
[0037] In this embodiment, the isolation unit 73 includes an optocoupler U4, a fourteenth resistor R14, a fifteenth resistor R15, a thyristor SCR and a first diode D1, the positive electrode of the optocoupler U4 is connected to the output end of the comparator U3, the first end of the fourteenth resistor R14 is connected to the negative electrode of the optocoupler U4, the second end of the fourteenth resistor R14 is grounded, the collector of the optocoupler U4 is connected to a high level VCC_1, the emitter of the optocoupler U4 is connected to the first end of the fifteenth resistor R15, the second end of the fifteenth resistor R15 is connected to the gate of the thyristor SCR, the anode of the thyristor SCR is connected to the high level VCC_2, the cathode of the thyristor SCR is connected to the first end of the coil of the circuit breaker QF, the second end of the coil of the circuit breaker QF is grounded, and the first diode D1 is anti-parallel connected to the two ends of the coil of the circuit breaker QF.
[0038] In this embodiment, the rectifier circuit 20 is a three-phase bridge fully controlled rectifier circuit.
[0039] In this embodiment, the high level VCC_1 , the high level VCC_2 and the reference voltage Vref are all provided by the switch power supply circuit 80 .
[0040] Example 2
[0041] Combined with Figure 2 The technical solution of the utility model is a frequency converter, including the overcurrent protection circuit for the frequency converter described in Example 1.
[0042] The various embodiments in the specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.
[0043] It should also be noted that, in this specification, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "comprises", "comprising" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the statement "comprising a ..." does not exclude the presence of other identical elements in the process, method, article or device including the element.
[0044] 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 may 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 will conform to the widest scope consistent with the principles and novel features disclosed herein.
Claims
1. An overcurrent protection circuit for a frequency converter, comprising a control unit and a rectifier circuit, a brake circuit and an inverter circuit connected in sequence, wherein the input end of the rectifier circuit is connected to an external power grid, the output end of the inverter circuit is connected to an external load, a current-limited starting circuit is connected between the rectifier circuit and the brake circuit, and the output end of the control unit is respectively connected to the input end of the brake circuit and the input end of the inverter circuit, characterized in that: It also includes a bridge arm current sampling circuit, an overcurrent disconnection trigger circuit and a switching power supply circuit. The switching power supply circuit provides working voltage for the control unit, the overcurrent disconnection trigger circuit and the bridge arm current sampling circuit respectively. The input end of the bridge arm current sampling circuit is connected to the output end of the inverter circuit, and the output end of the bridge arm current sampling circuit is respectively connected to the input end of the control unit and the input end of the overcurrent disconnection trigger circuit. The output end of the overcurrent disconnection trigger circuit is connected to the current limiting start-up circuit to control the disconnection of the current limiting start-up circuit, and the output end of the control unit is connected to the current limiting start-up circuit to realize buffered power-on of the inverter.
2. The overcurrent protection circuit for a frequency converter according to claim 1, characterized in that: The current limiting starting circuit includes a first resistor, a contactor and a circuit breaker. The first resistor and the first tripping contact of the circuit breaker are connected in series to form a starting buffer branch. The normally open contact of the contactor and the second tripping contact of the circuit breaker are connected in series to form an operating conduction branch. The starting buffer branch and the operating conduction branch are connected in parallel with each other.
3. The overcurrent protection circuit for a frequency converter according to claim 2, characterized in that: The output end of the control unit is connected to the coil of the contactor, and the output end of the overcurrent disconnection trigger circuit is connected to the tripping coil of the circuit breaker.
4. The overcurrent protection circuit for a frequency converter according to claim 3, characterized in that: The bridge arm current sampling circuit samples the current of each bridge arm of the inverter circuit respectively. The bridge arm current sampling circuit includes a second resistor, a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, a first capacitor, a second capacitor and a first operational amplifier. The second resistor is connected in series to the bridge arm loop of the inverter circuit. The first capacitor is connected in parallel to both ends of the second resistor. Both ends of the first capacitor are connected to the first end of the third resistor and the first end of the fourth resistor respectively. The second end of the third resistor is connected to the in-phase input end of the first operational amplifier. The second end of the fourth resistor is connected to the inverting input end of the first operational amplifier and the first end of the fifth resistor respectively. The output end of the first operational amplifier is connected to the second end of the fifth resistor and the first end of the sixth resistor respectively. The second capacitor is connected in parallel to both ends of the fifth resistor. The second end of the sixth resistor is connected to the input end of the control unit and the input end of the overcurrent disconnection trigger circuit respectively.
5. The overcurrent protection circuit for a frequency converter according to claim 4, characterized in that: The overcurrent disconnection trigger circuit includes a bandpass filter unit, a hysteresis comparison unit and an isolation unit, the input end of the bandpass filter unit is connected to the output end of the bridge arm current sampling circuit, the output end of the bandpass filter unit is connected to the input end of the hysteresis comparison unit, the output end of the hysteresis comparison unit is connected to the input end of the isolation unit, and the output end of the isolation unit is connected to the coil of the circuit breaker.
6. The overcurrent protection circuit for a frequency converter according to claim 5, characterized in that: The bandpass filtering unit includes a seventh resistor, an eighth resistor, a ninth resistor, a tenth resistor, an eleventh resistor, a third capacitor, a fourth capacitor and a second operational amplifier, the first end of the seventh resistor is connected to the second end of the sixth resistor, the second end of the seventh resistor is respectively connected to the first end of the third capacitor, the first end of the fourth capacitor and the first end of the ninth resistor, the second end of the fourth capacitor is respectively connected to the in-phase input terminal of the second operational amplifier and the first end of the eighth resistor, the second end of the third capacitor and the second end of the eighth resistor are commonly connected, the inverting input terminal of the second operational amplifier is respectively connected to the first end of the tenth resistor and the first end of the eleventh resistor, the second end of the tenth resistor is grounded, and the output terminal of the second operational amplifier is respectively connected to the second end of the ninth resistor and the second end of the eleventh resistor.
7. The overcurrent protection circuit for a frequency converter according to claim 6, characterized in that: The hysteresis comparison unit includes a twelfth resistor, a thirteenth resistor and a comparator, the first end of the thirteenth resistor is connected to a reference voltage, the second end of the thirteenth resistor is connected to an inverting input of the comparator, the output of the second operational amplifier is respectively connected to the non-inverting input of the comparator and the first end of the twelfth resistor, and the second end of the twelfth resistor is connected to the output of the comparator.
8. The overcurrent protection circuit for a frequency converter according to claim 7, characterized in that: The isolation unit includes an optocoupler, a fourteenth resistor, a fifteenth resistor, a thyristor and a first diode, the positive electrode of the optocoupler is connected to the output end of the comparator, the first end of the fourteenth resistor is connected to the negative electrode of the optocoupler, the second end of the fourteenth resistor is grounded, the collector of the optocoupler is connected to a high level, the emitter of the optocoupler is connected to the first end of the fifteenth resistor, the second end of the fifteenth resistor is connected to the gate of the thyristor, the anode of the thyristor is connected to a high level, the cathode of the thyristor SCR is connected to the first end of the coil of the circuit breaker, the second end of the coil of the circuit breaker is grounded, and the first diode is anti-parallel connected to the two ends of the coil of the circuit breaker.
9. An overcurrent protection circuit for a frequency converter according to any one of claims 1 to 8, characterized in that: The rectifier circuit is a three-phase bridge-type fully-controlled rectifier circuit.
10. A frequency converter, characterized in that: The invention comprises an overcurrent protection circuit for a frequency converter as claimed in any one of claims 1 to 9.