A frequency converter

Abstract

The application discloses a frequency converter, comprising a control circuit, a power module, a slow start circuit, an AC switch, a third contactor and a breaking circuit; a first end of the power module is connected with a first end of a breaking switch in the breaking circuit, a second end of the breaking switch is used for being connected with a DC source, and a second end of the power module is used for being connected with a load through the AC switch; the slow start circuit comprises a slow start resistor and a first contactor which are connected in series; the slow start circuit is connected in parallel across the breaking switch; the slow start resistor, a contact of the first contactor and a contact of the third contactor are connected in series and then between a DC positive pole and a DC negative pole of the DC source; the control circuit is connected with the slow start circuit and the breaking circuit; and the control circuit is configured to control the first contactor and the breaking switch. The frequency converter can facilitate the dismounting of a faulty power module and the connection of a normal power module when the power module is faulty.

Description

Technical Field

[0001] This application relates to the field of electrical equipment protection technology, specifically to a frequency converter. Background Technology

[0002] In actual products, to ensure the reliable operation of the inverter's load, multiple inverters are typically connected in parallel and operate simultaneously. For example, the load can be a motor, and the inverter drives the motor. When one inverter fails, the others can continue to operate normally without affecting the load's operation.

[0003] In related technologies, when a faulty frequency converter is repaired, the components continue to be subjected to voltage stress. Utility Model Content

[0004] In view of this, this application provides a frequency converter that allows for easy disassembly of the faulty power module when the power module in the frequency converter fails, so that the components are no longer subjected to voltage stress.

[0005] The frequency converter provided in this application embodiment includes: a control circuit, a power module, a soft-start circuit, an AC switch, a third contactor, and a disconnecting circuit; a first terminal of the power module is connected to a first terminal of the disconnecting switch in the disconnecting circuit, a second terminal of the disconnecting switch is used to connect to a DC source, and a second terminal of the power module is used to connect to a load through the AC switch; the soft-start circuit includes a soft-start resistor and a first contactor connected in series; the soft-start circuit is connected in parallel across the two terminals of the disconnecting switch; the soft-start resistor, the contact of the first contactor, and the contact of the third contactor are connected in series between the positive and negative DC terminals of the DC source; the control circuit is connected to the soft-start circuit, the third contactor, the disconnecting circuit, and the AC switch; the control circuit is configured to control the first contactor, the third contactor, the disconnecting switch, and the AC switch.

[0006] In one possible implementation, the frequency converter further includes: a pre-charge cable and a second contactor; a first terminal of the soft-start circuit is connected to a second terminal of the disconnect switch, a first terminal of the second contactor is connected to a second terminal of the soft-start circuit via the pre-charge cable, and a second terminal of the second contactor is connected to a first terminal of the disconnect switch; the control circuit is used to control both the first contactor and the second contactor to disconnect when the frequency converter has completed pre-charging.

[0007] In one possible implementation, the first contactor includes a first contact and a second contact, the third contactor includes a third contact and a fourth contact, and the soft-start resistor, the first contact, the second contact, the third contact and the fourth contact are connected in series between the positive and negative DC terminals of the DC source.

[0008] In one possible implementation, the control circuit includes: a first relay, a second relay, and a third relay; the contacts of the first relay are connected in series with the coil of the first contactor, the contacts of the second relay are connected in series with the coil of the second contactor, and the contacts of the third relay are connected in series with the coil of the third contactor.

[0009] In one possible implementation, the control circuit further includes: a controller; the coil of the first relay is connected between the corresponding power supply and the first output pin of the controller, the coil of the second relay is connected between the corresponding power supply and the second output pin of the controller, and the coil of the third relay is connected between the corresponding power supply and the third output pin of the controller.

[0010] In one possible implementation, the disconnecting circuit further includes: a disconnecting relay and a closing relay; the coil of the closing relay is connected between the corresponding power supply and the fourth output pin of the controller; the coil of the disconnecting relay is connected between the corresponding power supply and the fifth output pin of the controller.

[0011] In one possible implementation, the disconnecting circuit further includes: a disconnecting relay, a closing relay, and a first button; the coil of the closing relay is connected between the corresponding power supply and the fourth output pin of the controller; the coil of the disconnecting relay and the first button are connected in series between the positive and negative terminals of the corresponding power supply.

[0012] In one possible implementation, the control circuit further includes: a disconnecting relay, a closing relay, a first button, a second button, a time-delayed closing relay, and a time-delayed opening relay; the coil of the first relay is connected between the corresponding power supply and the first output pin of the controller, and the coil of the third relay is connected between the corresponding power supply and the third output pin of the controller; the coil of the second relay is connected in series with the contact of the time-delayed opening relay and then connected between the positive and negative terminals of the corresponding power supply; the coil of the time-delayed opening relay is connected in series with the second button and then connected between the positive and negative terminals of the corresponding power supply; the coil of the time-delayed closing relay is connected in series with the contact of the time-delayed opening relay and then connected between the positive and negative terminals of the corresponding power supply; the contact of the time-delayed closing relay is connected in series with the coil of the closing relay and then connected between the positive and negative terminals of the corresponding power supply; the coil of the disconnecting relay is connected in series with the first button and then connected between the positive and negative terminals of the corresponding power supply.

[0013] In one possible implementation, the frequency converter further includes: a normally closed contact of a third relay; the normally closed contact of the third relay, the contact of the second relay, and the coil of the second contactor are connected in series, and the state of the normally closed contact of the third relay is opposite to the state of the contact of the third relay.

[0014] One possible implementation is that the power module includes at least one of a DC / DC converter circuit or a DC / AC converter circuit.

[0015] The inverter provided in this application embodiment has a disconnect switch between the DC source and the power module, and an AC switch on the AC side of the power module. This facilitates disconnecting the disconnect switch and the AC switch in case of a power module failure, allowing for the removal of the faulty inverter without affecting the operation of other normal inverters. It also facilitates the reconnection of a normal power module. During reconnection, the disconnect switch remains open, and the first contactor in the slow-start circuit closes, allowing the DC source to supply power to the power module through the slow-start resistor, preventing current surges and protecting the components in the power module. Only after the slow-start is complete does the disconnect switch close, and the power module resumes normal operation to drive the load. The inverter provided in this application embodiment can also discharge residual energy when the inverter is stopped. Generally, a DC support capacitor is connected between the second terminal of the disconnect switch and the DC source. When the power module stops, the energy in the DC support capacitor needs to be released quickly. The third contactor and the slow-start circuit provide an energy discharge path, relieving the components in the inverter from voltage stress. Attached Figure Description

[0016] Figure 1 A schematic diagram of a frequency converter provided in an embodiment of this application;

[0017] Figure 2AA schematic diagram of another frequency converter provided in the embodiments of this application;

[0018] Figure 2B A schematic diagram of yet another frequency converter provided in the embodiments of this application;

[0019] Figure 3 A schematic diagram of a control circuit provided in an embodiment of this application;

[0020] Figure 4 A schematic diagram of yet another control circuit provided in an embodiment of this application;

[0021] Figure 5 A schematic diagram of yet another control circuit provided in an embodiment of this application;

[0022] Figure 6 A schematic diagram of another control circuit provided in an embodiment of this application;

[0023] Figure 7 This is a schematic diagram of another control circuit provided in an embodiment of this application. Detailed Implementation

[0024] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the embodiments of this application will be further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0025] See Figure 1 The figure is a schematic diagram of a frequency converter provided in an embodiment of this application.

[0026] The frequency converter provided in this application embodiment includes: a control circuit 200, a power module 100, a soft-start circuit 300, an AC switch QS, a third contactor KM3, and a disconnecting circuit 400.

[0027] The first terminal of power module 100 is connected to the first terminal of disconnect switch Q in disconnect circuit 400. The second terminal of disconnect switch Q is used to connect to a DC source, which includes a positive DC terminal (DC+) and a negative DC terminal (DC-). The second terminal of power module 100 is used to connect to a load (not shown); for ease of control, the second terminal of power module 100 can be connected to the load via AC switch QS. The load can be, for example, a motor, and power module 100 drives the motor.

[0028] The soft-start circuit 300 includes a soft-start resistor R1 and a first contactor KM1 connected in series; the soft-start circuit 300 is connected in parallel across the two ends of the disconnect switch Q. For example, the first contactor KM1 includes a first contact and a second contact. The first end of the first contact is connected to the positive DC terminal DC+ of the DC source through the soft-start resistor R1, and the second end of the first contact is connected to the positive terminal of the first end of the disconnect switch Q. The first end of the second contact is connected to the negative DC terminal DC- of the DC source, and the second end of the second contact is connected to the negative terminal of the first end of the disconnect switch Q.

[0029] The slow-start resistor R1, the contacts of the first contactor KM1, and the contacts of the third contactor KM3 are connected in series between the positive DC pole DC+ and the negative DC pole DC- of the DC source.

[0030] The frequency converter provided in this application embodiment can also discharge residual energy when the frequency converter is stopped. Generally, a DC support capacitor is connected between the second terminal of the disconnect switch Q and the DC source. When the power module 100 stops, the energy of the DC support capacitor needs to be released quickly. Therefore, the frequency converter provided in this application embodiment also includes an energy discharge path. Specifically, the contacts of the first contactor KM1 and the third contactor KM3 in the soft start circuit 300 are connected in series between the DC positive terminal DC+ and the DC negative terminal DC- of the DC source. When the power module 100 stops, the disconnect switch Q needs to be opened. At this time, the first contactor KM1, the second contactor KM2, and the third contactor KM3 are all in the open state. Figure 1 The third contactor KM3 in this embodiment includes one contact point. This application does not specifically limit whether the contact point of the third contactor KM3 is close to the DC positive terminal DC+ or close to the DC negative terminal DC-.

[0031] Another implementation method, such as Figure 2A As shown, for example, the third contactor KM3 includes two contacts, namely the third contact and the fourth contact, and the first contactor KM1 includes a first contact and a second contact. The soft-start resistor R1, the first contact of the first contactor KM1, the second contact of the first contactor KM1, the third contact of the third contactor KM3, and the fourth contact of the third contactor KM3 are connected in series between the positive DC+ and negative DC- terminals of the DC source. During energy discharge, the control circuit 200 controls both the first contactor KM1 and the third contactor KM3 to close. Since the soft-start resistor R1 is connected in series between the positive DC+ and negative DC- terminals of the DC source, energy can be dissipated, thus achieving energy discharge and preventing the components in the circuit from continuing to bear voltage stress.

[0032] The control circuit 200 is connected to the soft start circuit 300, the power module 100, and the disconnect circuit 400; the control circuit 200 is configured to control the first contactor KM1 and the disconnect switch Q.

[0033] The control circuit 200 is used to control the disconnect switch Q to open and the first contactor KM1 to close when the power module 100 is pre-charged; to control the disconnect switch Q to close and the first contactor KM1 to open when the power module 100 is pre-charged; and to control the disconnect switch Q to open in the event of a power module 100 malfunction.

[0034] It should be understood that when power module 100 malfunctions, the trip switch Q can be directly controlled to open. With AC switch QS open, there is no power to the second terminal of power module 100, and the first terminal of power module 100 is also disconnected from the DC source. Therefore, power module 100 can be safely removed. When a normal power module 100 needs to be connected, it is connected between the second terminal of the trip circuit 400 and the load. At this time, power needs to be supplied to power module 100. The first contactor KM1 closes, pre-charging power module 100 through the slow-start resistor R1 to prevent excessive inrush current from being generated when the DC source is directly connected to power module 100. At this time, trip switch Q is still in the open state.

[0035] When pre-charging is complete, the disconnect switch Q closes, the first contactor KM1 opens, and the DC source supplies power to the power module 100 through the disconnect switch Q. This application does not specifically limit the pre-charging time; it can be preset.

[0036] The control circuit 200 may include a controller, which may be a digital processor, a microprocessor, or a single-chip microcomputer, etc.

[0037] The frequency converter provided in this application embodiment has a disconnect switch between the DC power source and the power module. This facilitates disconnecting the switch and disassembling the faulty frequency converter in case of a power module failure, without affecting the operation of other normal frequency converters. It also facilitates the reconnection of a normal power module. During reconnection, the disconnect switch remains open, and the first contactor in the slow-start circuit closes, allowing the DC power source to supply power to the power module through the slow-start resistor, preventing current surges and protecting the components in the power module. Only after the slow-start is complete does the disconnect switch close, and the power module resumes normal operation to drive the load.

[0038] The embodiments of this application do not specifically limit the specific type of power module, but may include at least one of DC / DC (Direct Current / Direct Current) conversion circuit and DC / AC (Direct Current / Alternating Current) conversion circuit.

[0039] See Figure 2B This figure is a schematic diagram of another frequency converter provided in an embodiment of this application.

[0040] The frequency converter provided in this application embodiment also includes: a pre-charge cable 10 and a second contactor KM2;

[0041] from Figure 2B As can be seen, the pre-charging cable 10 is connected between the first contactor KM1 and the second contactor KM2. The control circuit 200 is used to control both the first contactor KM1 and the second contactor KM2 to disconnect when the power module 100 has completed pre-charging. The main function of the pre-charging cable 10 and the second contactor KM2 is that when the power module 100 has completed charging, both the second contactor KM2 and the first contactor KM1 are disconnected, and the pre-charging cable 10 can be removed from the circuit for pre-charging of other power modules, thus sharing the same pre-charging cable 10, saving cable costs, and consequently saving the overall cost of the converter.

[0042] Specifically, the first terminal of the soft-start circuit 300 is connected to the second terminal of the disconnect switch Q, and the first terminal of the second contactor KM2 is connected to the second terminal of the soft-start circuit 300 via the pre-charge cable 10. The second terminal of the second contactor KM2 is connected to the first terminal of the disconnect switch Q. For example, the second contactor KM2 includes a fifth contact and a sixth contact. The first terminal of the fifth contact is connected to the second terminal of the first contact of the first contactor KM1 via the pre-charge cable 10, and the second terminal of the fifth contact is connected to the positive terminal of the first terminal of the disconnect switch Q. The first terminal of the sixth contact is connected to the second terminal of the second contact of the first contactor KM1 via the pre-charge cable 10, and the second terminal of the sixth contact is connected to the negative terminal of the first terminal of the disconnect switch Q. That is, the first terminal of the second contactor KM2 is connected to the second terminal of the first contactor KM1, and the second terminal of the second contactor KM2 is connected to the first terminal of the disconnect switch Q.

[0043] Since the first, second, and third contactors are all connected to a high-voltage circuit, the low-voltage circuitry of the control circuit cannot directly drive these contactors. Therefore, an intermediate relay is required to drive these contactors. The following is a detailed description with reference to the attached diagram.

[0044] See Figure 3 The figure is a schematic diagram of a control circuit provided in an embodiment of this application.

[0045] The inverter provided in this application embodiment has a control circuit 200 including a first relay K1, a second relay K2, and a third relay K3.

[0046] The contacts of the first relay K1 are connected in series with the coil of the first contactor KM1, the contacts of the second relay K2 are connected in series with the coil of the second contactor KM2, and the contacts of the third relay K3 are connected in series with the coil of the third contactor KM3.

[0047] To prevent a short circuit on the DC side of the power module caused by abnormal closure of the third contactor, the inverter provided in this application embodiment also interlocks the states of the second and third contactors. A specific implementation method is described below with reference to the accompanying drawings.

[0048] See Figure 4 This figure is a schematic diagram of another control circuit provided in an embodiment of this application.

[0049] The interlocking circuit provided in this application takes the normally closed contact KM31 of the third contactor connected in series in the second contactor circuit as an example.

[0050] The frequency converter also includes: the normally closed contact KM31 of the third contactor;

[0051] The normally closed contact KM31 of the third contactor is connected in series with the contact of the second relay K2 and the coil of the second contactor KM2. The state of the normally closed contact KM31 of the third contactor is opposite to the state of the third relay K3. When the third relay K3 is closed, the coil of the third contactor KM3 is energized. At this time, the normally closed contact KM31 of the third contactor is open, so the coil of the second contactor KM2 cannot be energized. Therefore, the second contactor KM2 is disconnected.

[0052] The control circuit provided in this application embodiment adds an interlock function between the second contactor and the third contactor to prevent abnormal closure of the third contactor from causing a short circuit on the DC side of the power module.

[0053] The operation of the first relay K1, the second relay K2, and the third relay K3 can be controlled by the controller in the control circuit. A specific implementation method is described below.

[0054] See Figure 5 This figure is a schematic diagram of another control circuit provided in an embodiment of this application.

[0055] The frequency converter provided in this application embodiment further includes a controller (not shown) in the control circuit 200.

[0056] The coil of the first relay K1 is connected between the positive terminal of the corresponding power supply VDC and the first output pin A1 of the controller; the coil of the second relay K2 is connected between the positive terminal of the corresponding power supply VDC and the second output pin A2 of the controller; and the coil of the third relay is connected between the positive terminal of the corresponding power supply VDC and the third output pin A3 of the controller.

[0057] The controller is also used to control the energization or de-energization of the coils of the first relay K1, the second relay K2, and the third relay K3. For example, if the corresponding output pin of the controller outputs a low level, the coil of the corresponding relay is energized, and the relay operates.

[0058] In addition, the disconnecting circuit 400 also includes a closing relay K4 and a disconnecting relay K5. The disconnection and closing of the disconnecting switch Q of the disconnecting circuit 400 provided in this application embodiment are controlled by the disconnecting relay K5 and the closing relay K4, respectively.

[0059] The coil of the closing relay K4 is connected between the positive terminal of the corresponding power supply VDC and the fourth output pin A4 of the controller; the coil of the opening relay K5 is connected between the positive terminal of the corresponding power supply VDC and the fifth output pin A5 of the controller. The opening relay K5 is used to control the opening switch Q to open, and the closing relay K4 is used to control the opening switch Q to close.

[0060] The controller is also used to control the energization or de-energization of the coil of the disconnecting relay K5, and the energization or de-energization of the coil of the closing relay K4. For example, if the corresponding output pin of the controller outputs a low level, the coil of the corresponding relay is energized, and the relay contacts actuate.

[0061] The frequency converter provided in this application embodiment, in addition to Figure 5 In addition to automatic control, the disconnect relay K5 can also be manually controlled, as detailed below with reference to the attached diagram.

[0062] See Figure 6 This figure is a schematic diagram of another control circuit provided in an embodiment of this application.

[0063] Figure 6 and Figure 5 The difference is, Figure 6 The disconnecting relay K5 is manually controlled, rather than automatically controlled by the controller. That is, the disconnecting circuit 400 provided in this embodiment also includes: disconnecting relay K5, closing relay K4, and first button S1.

[0064] The coil of the closing relay K4 is connected between the positive terminal of the corresponding power supply VDC and the fourth output pin A4 of the controller; the coil of the disconnecting relay K5 is connected in series with the first button S1 and between the positive terminal and the negative terminal VDC- of the corresponding power supply VDC.

[0065] When the first button S1 is pressed, the coil of the disconnecting relay K5 is energized, and the corresponding contact of the disconnecting relay K5 is activated.

[0066] The control circuit provided in this application embodiment adds a first button S1 for manual control of disconnecting the relay, which can save one output pin of the controller, thereby facilitating the controller to perform other controls.

[0067] The following describes another frequency converter provided in the embodiments of this application, which includes two manual buttons and uses a time delay relay to save one output pin of the controller, thus saving a total of three output pins and conserving controller resources.

[0068] See Figure 7 This figure is a schematic diagram of another control circuit provided in an embodiment of this application.

[0069] The control circuit provided in this application embodiment further includes: a disconnecting relay K5, a closing relay K4, a first button S1, a second button S2, a time-delayed closing relay K6, and a time-delayed opening relay K7.

[0070] The coil of the first relay K1 is connected between the positive terminal of the corresponding power supply VDC and the first output pin A1 of the controller; the coil of the third relay K3 is connected between the positive terminal of the corresponding power supply VDC and the third output pin A3 of the controller; the coil of the second relay K2 is connected in series with the contact of the time-delay disconnect relay K7 and then connected between the positive terminal and the negative terminal VDC- of the corresponding power supply VDC.

[0071] The coil of the time-delay disconnect relay K7 is connected in series with the second button S2 and then connected between the positive and negative terminals VDC- of the corresponding power supply VDC; the coil of the time-delay closing relay K6 is connected in series with the contacts of the time-delay disconnect relay K7 and then connected between the positive and negative terminals VDC- of the corresponding power supply VDC.

[0072] The contacts of the time-delay closing relay K6 are connected in series with the coil of the closing relay K4 and then connected between the positive and negative terminals of the corresponding power supply VDC and VDC-.

[0073] The coil of the disconnect relay K5 is connected in series with the first button S1 and then connected between the positive and negative terminals of the corresponding power supply VDC.

[0074] The following is a reference to Figure 2 and... Figure 7 The working principle of the frequency converter provided in the embodiments of this application is introduced.

[0075] The first button S1 manually disconnects the coil of the disconnect relay K5, causing the disconnect switch Q to open.

[0076] The controller's first output pin energizes the coil of the first relay K1, which in turn closes the contacts of the first contactor KM1. When the second button S2 is pressed, the time-delayed disconnect relay K7 immediately activates and remains closed for a period of time, energizing the coil of the second relay K2 and closing its contacts. This, in turn, energizes the coil of the second contactor KM2 and closes its contacts, allowing the power module 100 to precharge.

[0077] After pre-charging, the time-delayed disconnect relay K7 disconnects after the set time, de-energizing the coil of the second relay K2 and causing its contacts to open, which in turn causes the contacts of the second contactor KM2 to open. At this time, the controller de-energizes the coil of the first relay K1, causing its contacts to open, which in turn causes the contacts of the first contactor KM1 to open as well. The time-delayed closing relay K6 closes exactly after the set time, energizing the coil of the closing relay K4 and causing its contacts to close, thus closing the trip switch Q. In practical operation, a time difference can be set between the time-delayed disconnect relay K7 and the time-delayed closing relay K6, meaning the time-delayed disconnect relay K7's time is greater than the time-delayed closing relay K6's time. For example, the time-delayed disconnect relay K7's time is 10 seconds, and the time-delayed closing relay K6's time is 9 seconds, resulting in a 1-second time difference. This means that the coil of the time-delayed closing relay K6 is energized before the contacts of the time-delayed disconnect relay K7 open.

[0078] It should be understood that the time-delay closing relay K6 and time-delay opening relay K7 provided in the embodiments of this application are both time-delay relays. The delay time of the time-delay relay can be configured according to the actual capacitance value of the capacitor in the power module 100, for example, by setting the time according to t=RC, and retaining a certain time margin.

[0079] The frequency converter provided in this application embodiment enables maintenance of the power module without shutting down the entire frequency converter. It allows for disassembly and assembly without shutdown, uses fewer components, and has pre-charging and discharging functions. The combined control of button control and time-delay relay added in this embodiment enables one-button power-on of the frequency converter.

[0080] It should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0081] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily 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 this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A frequency converter, characterized in that, include: Control circuit, power module, soft start circuit, AC switch, third contactor and disconnecting circuit; The first terminal of the power module is connected to the first terminal of the disconnecting switch in the disconnecting circuit, the second terminal of the disconnecting switch is used to connect to a DC source, and the second terminal of the power module is used to connect to a load through the AC switch; The soft-start circuit includes a soft-start resistor and a first contactor connected in series; the soft-start circuit is connected in parallel across the two ends of the disconnect switch. The soft-start resistor, the contact of the first contactor, and the contact of the third contactor are connected in series between the positive and negative DC terminals of the DC source. The control circuit is connected to the soft-start circuit, the control circuit is connected to the third contactor, the control circuit is connected to the disconnecting circuit, and the control circuit is connected to the AC switch. The control circuit is configured to control the first contactor, control the third contactor, control the disconnect switch, and control the AC switch.

2. The frequency converter according to claim 1, characterized in that, The frequency converter also includes: a pre-charge cable and a second contactor; The first end of the soft-start circuit is connected to the second end of the disconnect switch, the first end of the second contactor is connected to the second end of the soft-start circuit through the pre-charge cable, and the second end of the second contactor is connected to the first end of the disconnect switch. The control circuit is used to control both the first contactor and the second contactor to disconnect when the inverter pre-charging is completed.

3. The frequency converter according to claim 2, characterized in that, The first contactor includes a first contact and a second contact, and the third contactor includes a third contact and a fourth contact. The soft-start resistor, the first contact, the second contact, the third contact, and the fourth contact are connected in series between the positive and negative DC terminals of the DC source.

4. The frequency converter according to claim 2, characterized in that, The control circuit includes: a first relay, a second relay, and a third relay; The contacts of the first relay are connected in series with the coil of the first contactor, the contacts of the second relay are connected in series with the coil of the second contactor, and the contacts of the third relay are connected in series with the coil of the third contactor.

5. The frequency converter according to claim 4, characterized in that, The control circuit further includes: a controller; The coil of the first relay is connected between the corresponding power supply and the first output pin of the controller, the coil of the second relay is connected between the corresponding power supply and the second output pin of the controller, and the coil of the third relay is connected between the corresponding power supply and the third output pin of the controller.

6. The frequency converter according to claim 5, characterized in that, The disconnecting circuit also includes: a disconnecting relay and a closing relay; The coil of the closing relay is connected between the corresponding power supply and the fourth output pin of the controller; the coil of the disconnecting relay is connected between the corresponding power supply and the fifth output pin of the controller.

7. The frequency converter according to claim 5, characterized in that, The disconnect circuit also includes: a disconnect relay, a closing relay, and a first button; The coil of the closing relay is connected between the corresponding power supply and the fourth output pin of the controller; the coil of the disconnecting relay and the first button are connected in series between the positive and negative terminals of the corresponding power supply.

8. The frequency converter according to claim 5, characterized in that, The control circuit also includes: a disconnect relay, a closing relay, a first button, a second button, a time-delay closing relay, and a time-delay opening relay; The coil of the first relay is connected between the corresponding power supply and the first output pin of the controller, and the coil of the third relay is connected between the corresponding power supply and the third output pin of the controller; the coil of the second relay is connected in series with the contact of the time-delay disconnect relay and then connected between the positive and negative terminals of the corresponding power supply. The coil of the time-delay disconnect relay is connected in series with the second button and then connected between the positive and negative terminals of the corresponding power supply; the coil of the time-delay close relay is connected in series with the contacts of the time-delay disconnect relay and then connected between the positive and negative terminals of the corresponding power supply. The contacts of the time-delay closing relay are connected in series with the coil of the closing relay and then connected between the positive and negative terminals of the corresponding power supply. The coil of the disconnect relay is connected in series with the first button and then connected between the positive and negative terminals of the corresponding power supply.

9. The frequency converter according to claim 4, characterized in that, The frequency converter also includes: the normally closed contact of the third relay; The normally closed contact of the third relay, the contact of the second relay, and the coil of the second contactor are connected in series, and the state of the normally closed contact of the third relay is opposite to the state of the contact of the third relay.

10. The frequency converter according to any one of claims 1-9, characterized in that, The power module includes at least one of a DC / DC converter circuit or a DC / AC converter circuit.

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