Inverter switching circuit

Abstract

The inverter switching circuit includes: a circuit breaker, which is connected to the main power line; a contactor, which is connected to the circuit breaker through a wire; a motor, which is connected to the contactor through an internal wire; and an inverter, wherein the input and output ends of the inverter are directly connected in parallel with the two ends of the contactor. The inverter switching circuit eliminates the contactor-type switch device used for switching the bypass at the output end of the inverter main circuit, and directly connects the inverter in parallel with the contactor, so that the power supply circuit in the circuit maintains the function of switching between each other, thereby reducing costs. Since there is no need to add additional contactors, the circuit structure is simplified, the possibility of circuit failure is reduced, and costs are saved.

Description

Technical Field

[0001] The present invention relates to the field of electronic information technology, and in particular to a frequency converter switching circuit. Background Art

[0002] The wiring diagram of the motor connected to the inverter is as follows Figure 1 As shown in the figure, the circuit breaker QF1 is a manual circuit switch for protection, and the contactor KM1 is used to control the circuit on and off to start and stop the motor M. The motor M is installed with the inverter VFD. In order to allow the motor M to be used in the original power circuit when the inverter fails, it is generally necessary to Figure 1 As in the example, a contactor KM2 is added to automatically switch the power supply circuit of the motor M. In addition, there are also Figure 2 As shown, compared to Figure 1 , it adds two contactors, namely contactor KM2 and contactor KM3, to achieve the purpose of switching the power supply circuit of motor M.

[0003] It can be seen that the existing inverter bypass switching function requires at least two contactor-type switch devices (contactor KM1 and contactor KM2), and often requires three contactor-type switch devices (contactor KM1, contactor KM2 and contactor KM3), which are responsible for the on and off of the industrial frequency power supply and the inverter circuit respectively, to ensure that when one of the circuits supplies power to the load, the other circuit is disconnected, thereby realizing the bypass switching function.

[0004] Since this circuit requires adding one or two or more contactors (that is, in addition to contactor KM1, contactor KM2 or even contactor KM3 is also needed), the equipment cost is increased, the circuit failure points are increased, and the system reliability is reduced. Summary of the invention

[0005] The problem solved by the present invention is to provide a frequency converter switching circuit, which reduces circuit space occupation, reduces equipment cost, makes line connection simpler, and reduces fault points.

[0006] To solve the above problems, the present invention provides a frequency converter switching circuit, comprising: a circuit breaker, which is connected to a main power line; a contactor, which is connected to the circuit breaker through a power line; a motor, which is connected to the contactor through an internal power line; and a frequency converter, wherein the input and output ends of the frequency converter are directly connected in parallel to the two ends of the contactor.

[0007] Optionally, the circuit further includes an intermediate relay, and a normally open contact of the intermediate relay is connected between a start terminal and a common terminal of an operation control loop of the frequency converter.

[0008] Optionally, the intermediate relay and the contactor form an electrical interlocking structure, and the electrical interlocking structure includes a normally closed contact of the contactor connected to the coil of the intermediate relay, and the coil of the contactor connected to the normally closed contact of the intermediate relay.

[0009] Optionally, the circuit also includes a relay starting circuit for controlling the intermediate relay.

[0010] Optionally, the output of the frequency converter adopts an IGBT power module.

[0011] Optionally, a three-phase power frequency voltage is directly applied to the load end of the frequency converter.

[0012] Optionally, the motor is a drive device for a water pump, a fan, a compressor, an air compressor or a transmission mechanism.

[0013] Optionally, the motor is a 110V three-phase AC motor, a 220V three-phase AC motor, a 380V three-phase AC motor or a medium-high voltage motor within 13.6kV. Optionally, the coil voltage level of the contactor is 24V DC voltage, 24V AC voltage, 120V AC voltage or 220V AC voltage.

[0014] Optionally, the coil voltage level of the intermediate relay is 24V DC voltage, 24V AC voltage, 120V AC voltage or 220V AC voltage.

[0015] In one aspect of the technical solution of the present invention, the contactor-type switch device used for switching the bypass at the output end of the inverter main circuit is eliminated, and the inverter is directly connected in parallel with a contactor, so that the power supply circuits in the circuit maintain the function of switching each other, thereby reducing costs. Since no additional contactor is required, the circuit structure is simplified, the possibility of circuit failure is reduced, and costs are saved.

[0016] At the same time, the input and output ends of the inverter are directly connected in parallel with the two ends of the contactor to achieve the function of switching with the industrial frequency power supply circuit, reduce space occupancy, reduce equipment costs, make the connection on the line simpler, and reduce failure points.

[0017] Furthermore, the intermediate relay and contactor are used to form an electrical interlock, so that the motor, the industrial frequency power supply and the inverter circuit can switch with each other, and the switching between the original circuit and the inverter circuit can be realized without the need for additional on-off control of the main circuit contactor. The structure is simple and efficient, suitable for inverters of various voltages and similar electrical equipment, reducing the overall cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is the existing inverter switching circuit diagram;

[0019] Figure 2 It is another existing inverter switching circuit diagram;

[0020] Figure 3 is a frequency converter switching circuit diagram provided by an embodiment of the present invention;

[0021] Figure 4 is a frequency converter switching circuit diagram provided by another embodiment of the present invention;

[0022] QF1-circuit breaker; KM1-contactor; M-motor; VFD-frequency converter; KM2-contactor; KM3-contactor; KM11-contactor main contact; KM12-contactor normally closed contact; KM13-contactor coil; KA1-intermediate relay; KA11-intermediate relay normally open contact; KA12-intermediate relay coil; KA13-intermediate relay normally closed contact; VFD1-frequency converter control circuit; S1-control circuit start end; SC-control circuit common end; S6-control circuit switch. DETAILED DESCRIPTION

[0023] As can be seen from the background technology, the existing inverter bypass switching function circuit needs to use at least two contactor-type switch devices, which are responsible for the on-off of the industrial power supply and the inverter circuit respectively, to ensure that when one circuit supplies power to the load, the other circuit is disconnected to achieve the bypass switching function. This method adds one or two contactors, increases equipment costs, increases circuit failure points, and reduces system reliability.

[0024] To this end, the present invention provides a new inverter switching circuit to solve the above-mentioned shortcomings.

[0025] For a clearer representation, the present invention is described in detail below with reference to the accompanying drawings.

[0026] The embodiment of the present invention provides a frequency converter switching circuit, please refer to Figure 1 ,include:

[0027] Circuit breaker QF1, circuit breaker QF1 is connected to the main power line;

[0028] Contactor KM1, in this embodiment, contactor KM1 is an AC contactor KM1, and contactor KM1 is connected to circuit breaker QF1 through wires;

[0029] Motor M, motor M is connected to contactor KM1 through internal wires;

[0030] The frequency converter VFD, the input end and the output end (the output end is usually also the load end) of the frequency converter VFD are directly connected in parallel with the two ends of the contactor KM1 (usually, the positive and negative poles of the frequency converter VFD busbar can be connected to the circuit breaker QF1).

[0031] The inverter switching circuit provided in this embodiment eliminates the switch device (contactor) used for switching the bypass at the output end of the inverter VFD main circuit. However, through circuit design and circuit principle, the function of switching with the industrial frequency power supply circuit can still be guaranteed to reduce costs. Since there is no need to add additional contactors, the circuit structure is simplified, the possibility of circuit failure is reduced, and costs are saved. That is to say, in this embodiment, the input and output ends of the inverter VFD are directly connected in parallel with the two ends of the contactor KM1 to achieve the function of switching with the industrial frequency power supply circuit. Since a contactor-type switch device is eliminated, the space occupancy is reduced, the equipment cost is reduced, the connection on the line is simpler, and the number of failure points is reduced.

[0032] Another embodiment of the present invention provides another inverter switching circuit, comprising:

[0033] Circuit breaker QF1, circuit breaker QF1 is connected to the main power line;

[0034] Contactor KM1, contactor KM1 is connected to circuit breaker QF1 through wires;

[0035] Motor M, motor M is connected to contactor KM1 through internal wires;

[0036] The frequency converter VFD, the input end and the output end of the frequency converter VFD are directly connected in parallel with the two ends of the contactor KM1.

[0037] For the above content, reference can be made to the corresponding content of the aforementioned embodiments.

[0038] Different from the above-mentioned embodiment, in this embodiment, the inverter switching circuit further includes an intermediate relay KA1, and the normally open contact of the intermediate relay KA1 is connected between the start terminal and the common terminal of the operation control loop of the inverter VFD.

[0039] Different from the above-mentioned embodiment, in this embodiment, the intermediate relay KA1 and the contactor KM1 form an electrical interlocking structure, which includes: the main contact KM11 of the contactor KM1 is connected to the circuit, connected between the circuit breaker QF1 and the motor M, the normally closed contact KM12 of the contactor KM1 is connected to the coil KA12 of the intermediate relay KA1, and the coil KM13 of the contactor KM1 is connected to the normally closed contact KA13 of the intermediate relay KA1. The interconnected circuit wires forming the electrical interlocking structure are Figure 4 The contactor KM1 includes a main contact KM11, a normally closed contact KM12, a coil KM13 and a normally open contact (the normally open contact is not shown in the figure because it is not needed in this embodiment).

[0040] At the same time, this embodiment also shows some circuit structures of the frequency converter VFD in the loop, that is, part of the control circuit of the frequency converter VFD, that is, part of the operation control loop VFD1. Specifically, as mentioned above, the normally open contact KA11 of the intermediate relay KA1 is connected between the start terminal S1 (start control terminal) and the common terminal SC of the operation control loop VFD1 of the frequency converter VFD. The intermediate relay KA1 does not distinguish between the main contact and the auxiliary contact, and includes the normally open contact KA11, the coil KA12 and the normally closed contact KA13.

[0041] When the start terminal S1 closes the common terminal SC, the circuit of the inverter VFD is connected, the inverter VFD starts, and the inverter VFD outputs the corresponding voltage to start the motor M; when the start terminal S1 is disconnected from the common terminal SC, the inverter VFD is turned off, and the inverter VFD turns off the output voltage. In other words, the inverter VFD starts when the start terminal S1 is closed to the common terminal SC, and does not start when it is not closed. This ensures that in the circuit of this embodiment, the contactor KM1 and the inverter VFD1 will not be used to supply power at the same time. Switch S6 is another switch of the inverter VFD operation control circuit VFD1.

[0042] The wiring method of this embodiment is simpler. The intermediate relay KA1 is not necessary and only needs to be added when electrical interlocking needs to be implemented. The main idea of ​​the present invention is that no additional contactors are required under (or above) the inverter, but it is directly connected in parallel with the contactor KM1.

[0043] Meanwhile, the present embodiment adopts the intermediate relay KA1, which is more cost-effective and smaller in size than a contactor.

[0044] It should be noted that, in other embodiments, the inverter switching circuit may further include a relay starting circuit for controlling the intermediate relay KA1. The corresponding starting circuit may be designed to be relatively simple and small in size, and may even be directly attached to the intermediate relay KA1.

[0045] In this embodiment, the output of the frequency converter VFD can adopt an IGBT (insulated gate bipolar transistor) power module. IGBT is a composite fully controlled voltage-driven power semiconductor device composed of BJT (bipolar junction transistor) and MOSFET (insulated gate field effect transistor), which has the advantages of high input impedance of MOSFET and low conduction voltage drop of GTR (power transistor).

[0046] In this embodiment, the load end of the frequency converter VFD is directly applied with the three-phase power supply voltage. This design also allows the power supply to connect the 380V AC voltage to the output interface of the frequency converter VFD for a long time, that is, the power supply can directly apply the power frequency AC voltage to the output end of the frequency converter for a long time. This means that when the frequency converter VFD is not started, the power supply can directly apply the power frequency AC voltage to the output end of the frequency converter for a long time, which will not cause damage to the frequency converter and circuit failure problems, such as Figure 4 .

[0047] In this embodiment, the motor M can be a drive device of a water pump, a fan, a compressor, an air compressor or a transmission mechanism. The motors of these devices are controlled by the inverter switching circuit provided in this embodiment, so the control effect is good and it is not easy to fail (because the connection points are reduced).

[0048] In this embodiment, the motor M may be a 110V three-phase AC motor, a 220V three-phase AC motor, a 380V three-phase AC motor, or a medium- and high-voltage motor within 13.6 kV. For medium- and high-voltage motors within 13.6 kV, specifically, motors of 6600V, 3800V, 1140V, 660V, or 460V may be used.

[0049] In this embodiment, the voltage level of the coil KM13 of the contactor KM1 can be 24V DC voltage, 24V AC voltage, 120V AC voltage or 220V AC voltage.

[0050] In this embodiment, the voltage level of the coil KA12 of the intermediate relay KA1 can be 24V DC voltage, 24V AC voltage, 120V AC voltage or 220V AC voltage.

[0051] This embodiment provides a new wiring and control method for switching the output end of a frequency converter (frequency converter switching circuit), and adopts a frequency converter VFD, whose input and output ends are directly connected in parallel with the two ends of the contactor KM1.

[0052] Furthermore, by using the intermediate relay KA1 and the contactor KM1 to form an electrical interlock, the switching between the original circuit and the inverter circuit can be realized without the need for additional on-off control of the main circuit contactor. When the inverter VFD is not started, the power supply can directly apply the industrial frequency AC voltage to the output end of the inverter for a long time without causing damage to the inverter and circuit problems.

[0053] This wiring method eliminates a contactor switch device, reduces space occupancy, reduces equipment costs, simplifies line connections, and reduces failure points. Compared with the original solution, it has obvious cost advantages and good technical and economic benefits.

[0054] The new inverter output switching wiring and control method is to cancel the contact switch device used for switching bypass at the inverter main circuit output, and directly connect the inverter input and output terminals in parallel with the two ends of contactor KM1, and use the intermediate relay KA1 and contactor KM1 to form an electrical interlock, so as to realize the function of switching between the motor, the industrial power supply and the inverter circuit, and to realize the switching between the original circuit and the inverter circuit without the need for additional main circuit contactor on-off control. The structure is simple and efficient, suitable for inverters of various voltages and similar electrical equipment, greatly reducing the overall cost.

[0055] The new wiring and control method for switching the inverter output end adopts the method of directly connecting the inverter VFD input and output ends in parallel with the two ends of the contactor KM1, and cancels the switch device used for switching the bypass at the output end of the inverter VFD main circuit. For the load motor, it better realizes the function of maintaining mutual switching between the inverter and the industrial frequency power supply circuit, and realizes the electrical interlocking effect, which plays a better protective role.

[0056] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the scope defined by the claims.

Claims

1. A frequency converter switching circuit, characterized in that: include: A circuit breaker connected to the main electric line; A contactor, the contactor being connected to the circuit breaker via an electric wire; A motor connected to the contactor via an internal wire; A frequency converter, wherein the input terminal and the output terminal of the frequency converter are directly connected in parallel with the two ends of the contactor; It also includes an intermediate relay, the normally open contact of the intermediate relay is connected between the start end and the common end of the operation control loop of the frequency converter; The contactor comprises a main contact, a normally closed contact, a coil and a normally open contact; The intermediate relay and the contactor form an electrical interlocking structure, wherein the electrical interlocking structure includes a normally closed contact of the contactor connected to a coil of the intermediate relay, and a coil of the contactor connected to a normally closed contact of the intermediate relay; The output of the frequency converter adopts an IGBT power module.

2. The inverter switching circuit according to claim 1, characterized in that: It also includes a relay starting circuit for controlling the intermediate relay.

3. The inverter switching circuit according to claim 1, characterized in that: The load end of the frequency converter is directly applied with a three-phase power supply frequency voltage.

4. The inverter switching circuit according to claim 1, characterized in that: The motor is a driving device for a water pump, a fan, a compressor, an air compressor, a transmission mechanism or a lifting mechanism.

5. The inverter switching circuit according to claim 1, characterized in that: The motor is a 110V three-phase AC motor, a 220V three-phase AC motor, a 380V three-phase AC motor or a medium or high voltage motor within 13.6kV.

6. The inverter switching circuit according to claim 1, characterized in that: The coil voltage level of the contactor is 24V DC voltage, 24V AC voltage, 120V AC voltage or 220V AC voltage.

7. The inverter switching circuit according to claim 1, characterized in that: The coil voltage level of the intermediate relay is 24V DC voltage, 24V AC voltage, 120V AC voltage or 220V AC voltage.

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