Method for controlling switching from working frequency converter to standby frequency converter of high-voltage frequency converter

Abstract

The invention particularly relates to a high-voltage frequency converter which comprises a working frequency converter, a standby frequency converter, a protection relay, a current transformer and a voltage transformer. A breaker is arranged on an inlet wire of the working frequency converter, a breaker is arranged on an outlet wire of the working frequency converter, the breaker of the outlet wire of the working frequency converter is connected with a protection relay, the protection relay is connected with a current transformer and a voltage transformer, and the voltage transformer is connected with the standby frequency converter. The standby frequency converter inlet wire is provided with a circuit breaker, and the standby frequency converter outlet wire is provided with a circuit breaker. An outgoing line of the working frequency converter is connected with an outgoing line of the standby frequency converter and a motor incoming line, the motor incoming line is connected with a first motor incoming line breaker and a second motor incoming line breaker in series, and a switching breaker is arranged on a line where the outgoing line of the working frequency converter is connected with the outgoing line of the standby frequency converter. Rapid switching from the working frequency converter to the standby frequency converter is achieved, and the standby frequency converter is automatically started under the working conditions that the working frequency converter breaks down and an outgoing line circuit breaker of the working frequency converter is not triggered to be opened.

Description

Technical Field

[0001] The present invention relates to the field of electronic power technology, and in particular to a control method for switching a working frequency converter of a high-voltage frequency converter to a standby frequency converter. Background Art

[0002] The AP1000 reactor coolant system introduced from the United States adopts a dual-loop layout, with two shielded main pumps arranged in each loop. Each main pump is powered by a main pump inverter. The rated voltage of the main pump motor is 6.9kV and the rated frequency is 60Hz. The frequency of the US power grid is 60Hz. The inverter was initially designed to reduce the impact on the busbar during the start-up and shutdown stages of the main pump. During stable operation, the main pump maintains industrial frequency operation and the inverter is out of operation. The domestic power grid frequency is 50Hz. The inverter of the domestic AP1000 unit needs to run continuously to ensure that the main pump runs at the design speed of 60Hz to achieve the design flow. Therefore, the reliability requirements of the main pump inverter of the domestic AP1000 unit are higher.

[0003] In order to reduce the number of unit non-stops caused by the failure of a single inverter, the domestic AP1000 unit has selected the "four in use and one standby" method to increase the redundancy of the main pump inverter. A new standby inverter is added to each unit as a hot standby for the four working inverters. When any working inverter fails and triggers the opening of the working inverter outgoing circuit breaker, it will automatically switch to the standby inverter to carry the load within a limited time, and the faulty working inverter will stop running. However, this method has the following problems:

[0004] 1. After the working inverter outgoing line circuit breaker is opened and the switching circuit breaker is closed, the standby inverter starts to run fast, resulting in a long time for the working inverter to switch to the standby inverter, causing the main pump speed to drop significantly, triggering the unit to shut down;

[0005] 2. For some working inverter failures but without triggering the opening of the working inverter outgoing circuit breaker, the standby inverter cannot be started, resulting in unplanned shutdown. Summary of the invention

[0006] Based on this, it is necessary to provide a high-voltage inverter and a control method for switching the working inverter of the high-voltage inverter to the standby inverter to address the above problems, so as to realize the rapid switching of the working inverter to the standby inverter, and automatically start the standby inverter when the working inverter fails and does not trigger the opening of the working inverter outgoing circuit breaker.

[0007] In order to solve the above problems, the present invention provides a high-voltage frequency converter, including a working frequency converter, a standby frequency converter, a protection relay, a current transformer and a voltage transformer, wherein the working frequency converter or the standby frequency converter carries the motor; a working frequency converter incoming line is provided with a working frequency converter incoming line circuit breaker, a working frequency converter outgoing line circuit breaker is provided with a working frequency converter outgoing line circuit breaker, the working frequency converter outgoing line circuit breaker is connected to the protection relay, the protection relay is respectively connected to the current transformer and the voltage transformer, and the voltage transformer is connected to the standby frequency converter; a standby frequency converter incoming line is provided with a standby frequency converter incoming line circuit breaker, and a standby frequency converter outgoing line circuit breaker is provided on the standby frequency converter outgoing line; the working frequency converter outgoing line is respectively connected to the standby frequency converter outgoing line and the motor incoming line, a motor first incoming line circuit breaker and a motor second incoming line circuit breaker are connected in series on the motor incoming line, and a switching circuit breaker is provided on the line connecting the working frequency converter outgoing line and the standby frequency converter outgoing line.

[0008] As one of the implementation schemes, the outgoing circuit breaker of the working inverter is connected to the protection relay through hard wiring, the protection relay is connected to the current transformer and the voltage transformer through hard wiring respectively, and the voltage transformer is connected to the standby inverter through hard wiring.

[0009] As one of the implementation solutions, a current transformer, a voltage transformer and a protection relay are installed in the working inverter outgoing circuit breaker switch cabinet.

[0010] As one of the implementation schemes, the number of working inverters is four, and the number of standby inverters is one; each working inverter incoming line is provided with a working inverter incoming line circuit breaker, and each working inverter outgoing line is provided with a working inverter outgoing line circuit breaker; each working inverter outgoing line is respectively connected to the standby inverter outgoing line and a motor incoming line, and each motor incoming line is respectively connected in series with the motor first incoming line circuit breaker and the motor second incoming line circuit breaker, and each working inverter outgoing line is respectively provided with a switching circuit breaker on the line connecting the standby inverter outgoing line; each working inverter outgoing line circuit breaker is respectively connected to a protection relay, each protection relay is respectively connected to a current transformer and a voltage transformer, and each voltage transformer is respectively connected to the standby inverter.

[0011] The present invention also provides a control method for switching a high-voltage inverter working inverter to a standby inverter, including the working inverter fault condition triggering the protection relay to open the working inverter output relay and the standby inverter starting phase locking at the same time, the working inverter output circuit breaker opening triggering the switching circuit breaker closing, the switching circuit breaker closing triggering the standby inverter flying start function, the standby inverter carrying the motor, and the faulty working inverter exiting operation.

[0012] As one of the implementation schemes, under normal working conditions of the working inverter, the working inverter incoming line is connected to the medium-voltage bus, the working inverter incoming line circuit breaker, the working inverter outgoing line circuit breaker, the motor first incoming line circuit breaker and the motor second incoming line circuit breaker are all in the closed state, and the working inverter carries the motor; the standby inverter incoming line is connected to the medium-voltage bus, the standby inverter incoming line circuit breaker and the standby inverter outgoing line circuit breaker are all in the closed state, the switching circuit breaker is in the open state, and the standby inverter is in a hot standby state without outputting current.

[0013] As one of the implementation schemes, the working inverter fault conditions include the working inverter fault triggering the working inverter output circuit breaker opening condition and the working inverter fault not triggering the working inverter output circuit breaker opening condition; under the working inverter fault triggering the working inverter output circuit breaker opening condition, the protection relay simultaneously opens the working inverter output circuit breaker according to the working inverter output circuit breaker opening logic; under the working inverter fault not triggering the working inverter output circuit breaker opening condition, the protection relay opens the working inverter output circuit breaker according to the working inverter output circuit breaker opening logic.

[0014] As one of the implementation schemes, the tripping logic of the working inverter output circuit breaker is: the current signal of the working inverter output circuit breaker is lower than its set value, the voltage signal of the working inverter output circuit breaker is lower than its set value, and the delay of the working inverter output circuit breaker reaches its set value.

[0015] As one of the implementation schemes, the working inverter output circuit breaker is connected to the protection relay, and the voltage signal and current signal of the working inverter output circuit breaker are respectively transmitted to the protection relay; the protection relay is respectively connected to the current transformer and the voltage transformer, the current transformer measures the current signal of the working inverter output circuit breaker, and the voltage transformer measures the voltage signal of the working inverter output circuit breaker; the voltage transformer is connected to the standby inverter, and the voltage signal of the working inverter output circuit breaker is transmitted to the standby inverter.

[0016] As one of the implementation schemes, when the voltage signal of the outgoing circuit breaker of the working inverter is lower than its set value, the standby inverter starts phase locking.

[0017] As one of the implementation solutions, after the standby inverter starts the phase lock, the standby inverter tracks the residual magnetic voltage of the motor in real time. After the switching circuit breaker is closed, the standby inverter immediately outputs voltage to the motor to increase the motor speed to 100% speed platform.

[0018] Beneficial technical effects of the present invention:

[0019] The control method for switching a working inverter of a high-voltage inverter to a standby inverter of the present invention can disconnect the working inverter output circuit breaker in two ways: the working inverter fault triggers the opening of the working inverter output circuit breaker and the protection relay disconnects the working inverter output circuit breaker, thereby solving the problem that the standby inverter cannot start switching under the condition that the working inverter fault cannot trigger the opening of the working inverter output circuit breaker; the standby inverter starts phase locking at the same time when the working inverter output circuit breaker is opened to trigger the working inverter to switch to the standby inverter, thereby shortening the time for switching the working inverter to the standby inverter to less than 58.7ms, thereby improving the success rate of switching the working inverter to the standby inverter. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a structural schematic diagram of an embodiment of an existing high-voltage frequency converter;

[0021] Figure 2 The figure is a schematic structural view of an embodiment of a high-voltage frequency converter of the present invention.

[0022] In the figure, 1, working inverter; 2, standby inverter; 3, motor; 4, switching circuit breaker; 5, medium voltage bus; 6, protection relay; 7, current transformer; 8, voltage transformer; 11-working inverter incoming circuit breaker; 12-working inverter outgoing circuit breaker; 21, standby inverter incoming circuit breaker; 22, standby inverter outgoing circuit breaker; 31, motor first incoming circuit breaker; 32, motor second incoming circuit breaker. DETAILED DESCRIPTION

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by technicians in the technical field of this application; the terms used in the specification of the application are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above-mentioned drawings are intended to cover non-exclusive inclusions. The terms "first", "second", etc. in the specification and claims of this application or the above-mentioned drawings are used to distinguish different objects, not to describe a specific order.

[0024] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0025] The technical solution of the present invention is clearly and completely described below in conjunction with the accompanying drawings and specific embodiments.

[0026] refer to Figure 1 Taking the main pump inverter of the domestic AP1000 unit as an example of the existing high-voltage inverter, the domestic AP1000 unit selects the "four-in-one" method to increase the redundancy of the main pump inverter. The main pump inverter includes four working inverters 1 and one standby inverter 2, and the working inverter 1 or the standby inverter 2 carries the motor 3; each working inverter 1 incoming line is provided with a working inverter incoming line circuit breaker 11, and each working inverter 1 outgoing line is provided with a working inverter outgoing line circuit breaker 12; the standby inverter 2 incoming line is provided with a standby inverter incoming line circuit breaker 21, and the standby inverter 2 outgoing line is provided with a standby inverter outgoing line circuit breaker 22; each working inverter 1 outgoing line is connected to the standby inverter 2 outgoing line and a motor 3 incoming line, and each motor 3 incoming line is connected in series with the motor first incoming line circuit breaker 31 and the motor second incoming line circuit breaker 32, and each working inverter 1 outgoing line connected to the standby inverter 2 outgoing line is provided with a switching circuit breaker 4.

[0027] Under normal working conditions of the working inverter 1, the incoming line of the working inverter 1 is connected to the 10kV medium-voltage bus 5, the working inverter incoming line circuit breaker 11, the working inverter outgoing line circuit breaker 12, the motor first incoming line circuit breaker 31 and the motor second incoming line circuit breaker 32 are all in the closed state, and the working inverter 1 converts the 10kV, 50Hz power supply into 6.9kV, 60Hz power supply to load the motor 3; the incoming line of the standby inverter 2 is connected to the 10kV medium-voltage bus 5, the standby inverter incoming line circuit breaker 21 and the standby inverter outgoing line circuit breaker 22 are all in the closed state, the switching circuit breaker 4 is in the open state, and the standby inverter 2 is in a hot standby state without outputting current.

[0028] When the working inverter 1 fails and triggers the opening of the working inverter output circuit breaker 12, the opening of the working inverter output circuit breaker 12 triggers the closing of the switching circuit breaker 4. The closing of the switching circuit breaker 4 triggers the standby inverter 2 to start the phase lock and start the flying car. The standby inverter 2 estimates the speed of the motor 3, and then outputs a voltage to the motor 3. The standby inverter 2 loads the motor 3, and the faulty working inverter 1 exits operation.

[0029] The existing main pump inverter has the following problems:

[0030] 1. After the working inverter outgoing line circuit breaker 12 was opened and the switching circuit breaker 4 was closed, the standby inverter 2 started to run fast, resulting in a long switching time from the working inverter 1 to the standby inverter 2, causing the main pump speed to drop significantly, triggering the unit to shut down;

[0031] 2. For some working conditions where the working inverter 1 fails but does not trigger the opening of the working inverter outgoing circuit breaker 12, the standby inverter 2 cannot be started, resulting in an unplanned shutdown.

[0032] To solve the above problems, see Figure 2 The present embodiment provides a high-voltage frequency converter, including a working frequency converter 1, a standby frequency converter 2, a protection relay 6, a current transformer 7 and a voltage transformer 8, wherein the working frequency converter 1 or the standby frequency converter 2 carries the motor 3; a working frequency converter inlet circuit breaker 11 is provided on the working frequency converter 1 inlet line, a working frequency converter outlet circuit breaker 12 is provided on the working frequency converter 1 outlet line, the working frequency converter outlet circuit breaker 12 is connected to the protection relay 6, and the protection relay 6 is respectively connected to the current transformer 7 and the voltage transformer 8. Transformer 8, voltage transformer 8 is connected with standby inverter 2; standby inverter 2 incoming line is provided with standby inverter incoming line circuit breaker 21, and standby inverter 2 outgoing line is provided with standby inverter outgoing line circuit breaker 22; working inverter 1 outgoing line is respectively connected with standby inverter 2 outgoing line and motor 3 incoming line, and motor 3 incoming line is connected in series with motor first incoming line circuit breaker 31 and motor second incoming line circuit breaker 32, and switching circuit breaker 4 is provided on the line connecting working inverter 1 outgoing line and standby inverter 2 outgoing line.

[0033] In this embodiment, the working inverter outgoing circuit breaker 12 is connected to the protection relay 6, and the voltage signal and current signal of the working inverter outgoing circuit breaker 12 are respectively transmitted to the protection relay 6; the protection relay 6 is respectively connected to the current transformer 7 and the voltage transformer 8, the current transformer 7 measures the current signal of the working inverter outgoing circuit breaker 12, and the voltage transformer 8 measures the voltage signal of the working inverter outgoing circuit breaker 12; the voltage transformer 8 is connected to the standby inverter 2, and transmits the voltage signal of the working inverter outgoing circuit breaker 12 to the standby inverter 2.

[0034] In this embodiment, the working inverter outgoing circuit breaker 12 is connected to the protection relay 6 through hard wiring, the protection relay 6 is respectively connected to the current transformer 7 and the voltage transformer 8 through hard wiring, the voltage transformer 8 is connected to the standby inverter 2 through hard wiring, and the voltage signal and current signal of the working inverter outgoing circuit breaker 12 are respectively transmitted to the protection relay 6 through hard wiring; the voltage transformer 8 transmits the voltage signal of the working inverter outgoing circuit breaker 12 to the standby inverter 2 through hard wiring.

[0035] In this embodiment, a current transformer 7, a voltage transformer 8 and a protection relay 6 are installed in the switch cabinet of the outgoing circuit breaker 12 of the working frequency converter.

[0036] In this embodiment, the number of working inverters 1 is four, and the number of standby inverters 2 is one; each working inverter 1 incoming line is provided with a working inverter incoming line circuit breaker 11, and each working inverter 1 outgoing line is provided with a working inverter outgoing line circuit breaker 12; each working inverter 1 outgoing line is respectively connected to the standby inverter 2 outgoing line and an incoming line of a motor 3, and each motor 3 incoming line is respectively connected in series with the motor first incoming line circuit breaker 31 and the motor second incoming line circuit breaker 32, and each working inverter 1 outgoing line connected to the standby inverter 2 outgoing line is respectively provided with a switching circuit breaker 4; each working inverter outgoing line circuit breaker 12 is respectively connected to a protection relay 6, each protection relay 6 is respectively connected to a current transformer 7 and a voltage transformer 8, and each voltage transformer 8 is respectively connected to the standby inverter 2.

[0037] The present embodiment also provides a control method for switching a high-voltage inverter working inverter to a standby inverter, including the working inverter 1 fault condition triggering the protection relay 6 to open the working inverter output relay 12, while the standby inverter 2 starts phase locking, the working inverter output circuit breaker 12 is opened to trigger the switching circuit breaker 4 to close, the switching circuit breaker 4 is closed to trigger the flying start function of the standby inverter 2, the standby inverter 2 carries the motor 3, and the faulty working inverter 1 exits operation.

[0038] In this embodiment, under normal working conditions of the working inverter 1, the incoming line of the working inverter 1 is connected to the 10kV medium-voltage bus 5, the working inverter incoming line circuit breaker 11, the working inverter outgoing line circuit breaker 12, the first incoming line circuit breaker 31 of the motor and the second incoming line circuit breaker 32 of the motor are all in the closed state, and the working inverter 1 converts the 10kV, 50Hz power supply into 6.9kV, 60Hz power supply to load the motor 3; the incoming line of the standby inverter 2 is connected to the 10kV medium-voltage bus 5, the standby inverter incoming line circuit breaker 21 and the standby inverter outgoing line circuit breaker 22 are all in the closed state, the switching circuit breaker 4 is in the open state, and the standby inverter 2 is in a hot standby state without outputting current.

[0039] In this embodiment, the fault conditions of the working frequency converter 1 include the conditions where the fault of the working frequency converter 1 triggers the opening of the working frequency converter output circuit breaker 12 and the conditions where the fault of the working frequency converter 1 does not trigger the opening of the working frequency converter output circuit breaker 12; under the condition where the fault of the working frequency converter 1 triggers the opening of the working frequency converter output circuit breaker 12, the protection relay 6 simultaneously opens the working frequency converter output circuit breaker 12 according to the opening logic of the working frequency converter output circuit breaker 12; under the condition where the fault of the working frequency converter 1 does not trigger the opening of the working frequency converter output circuit breaker 12, the protection relay 6 opens the working frequency converter output circuit breaker 12 according to the opening logic of the working frequency converter output circuit breaker 12.

[0040] The working inverter 1 fault triggers the working inverter output circuit breaker 12 to open, and the protection relay 6 opens the working inverter output circuit breaker 12. Both ways can open the working inverter output circuit breaker 12. The opening of the working inverter output circuit breaker 12 triggers the working inverter 1 to switch to the standby inverter 2. At the same time, the standby inverter 2 starts the phase lock. The working inverter 1 switches to the standby inverter 2, that is, the switching circuit breaker 4 is closed.

[0041] In this embodiment, the tripping logic of the working inverter outgoing circuit breaker 12 is: the current signal of the working inverter outgoing circuit breaker 12 is lower than its set value, the voltage signal of the working inverter outgoing circuit breaker 12 is lower than its set value, and the delay of the working inverter outgoing circuit breaker 12 reaches its set value.

[0042] In this embodiment, the working inverter outgoing circuit breaker 12 is connected to the protection relay 6, and the voltage signal and current signal of the working inverter outgoing circuit breaker 12 are respectively transmitted to the protection relay; the protection relay 6 is respectively connected to the current transformer 7 and the voltage transformer 8, the current transformer 7 measures the current signal of the working inverter outgoing circuit breaker 12, and the voltage transformer 8 measures the voltage signal of the working inverter outgoing circuit breaker 12; the voltage transformer 8 is connected to the standby inverter 2, and transmits the current signal of the working inverter outgoing circuit breaker 12 to the standby inverter 2.

[0043] In this embodiment, when the voltage signal of the outgoing line circuit breaker 12 of the working inverter is lower than its set value, the standby inverter 2 starts phase locking.

[0044] In this embodiment, after the standby inverter 2 starts phase locking, the standby inverter 2 tracks the residual magnetic voltage of the motor 3 in real time. After the switching circuit breaker 4 is closed, the standby inverter 2 immediately outputs voltage to the motor 3 to increase the speed of the motor 3 to 100% speed platform.

[0045] The advantage of the standby inverter 2 tracking the residual magnetic voltage of the motor 3 in real time is that the standby inverter 2 can estimate the speed of the motor 3 through the vector control algorithm. Once the switching circuit breaker 4 is closed, the standby inverter 2 can immediately output voltage to the motor 3 to quickly stop the speed of the motor 3 from falling.

[0046] If the original solution is used, the standby inverter 2 cannot track the residual magnetic voltage of the motor 3 in real time. After the switching circuit breaker 4 is closed, the standby inverter 2 will need to spend more than 100ms to estimate the speed of the motor 3 and then output voltage to the motor 3. At this time, the speed of the motor 3 may not meet the requirements of the main pump operation, causing the main pump to stop operating.

[0047] In the control method for switching the working inverter of the high-voltage inverter of the present embodiment to the standby inverter, the working inverter outlet circuit breaker can be opened by two ways: the working inverter fault triggers the opening of the working inverter outlet circuit breaker and the protection relay opens the working inverter outlet circuit breaker, thereby solving the problem that the standby inverter cannot start switching under the condition that the working inverter fault cannot trigger the opening of the working inverter outlet circuit breaker; the working inverter outlet circuit breaker opening triggers the working inverter to switch to the standby inverter, and the standby inverter starts phase locking, thereby shortening the time for switching the working inverter to the standby inverter to less than 58.7ms, thereby improving the success rate of switching the working inverter to the standby inverter.

[0048] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A high-voltage frequency converter, comprising a working frequency converter (1) and a standby frequency converter (2), wherein the working frequency converter (1) or the standby frequency converter (2) carries a motor (3); a working frequency converter inlet circuit breaker (11) is provided on the working frequency converter (1) inlet line, and a working frequency converter outlet circuit breaker (12) is provided on the working frequency converter (1) outlet line; a standby frequency converter inlet circuit breaker (21) is provided on the standby frequency converter (2) inlet line, and a standby frequency converter outlet circuit breaker (22) is provided on the standby frequency converter (2) outlet line; the working frequency converter (1) outlet line is respectively connected to the standby frequency converter (2) outlet line and the motor (3) inlet line, a motor first inlet circuit breaker (31) and a motor second inlet circuit breaker (32) are connected in series on the motor (3) inlet line, and a switching circuit breaker (4) is provided on the line connecting the working frequency converter (1) outlet line and the standby frequency converter (2) outlet line; the characteristic is that It also includes a protection relay (6), a current transformer (7) and a voltage transformer (8); the working frequency converter output line circuit breaker (12) is connected to the protection relay (6), the protection relay (6) is respectively connected to the current transformer (7) and the voltage transformer (8), and the voltage transformer (8) is connected to the standby frequency converter (2).

2. The main pump frequency converter according to claim 1, characterized in that: The working inverter output circuit breaker (12) is connected in parallel with the protection relay (6) through hard wiring, the protection relay (6) is connected to the current transformer (7) and the voltage transformer (8) through hard wiring, and the voltage transformer (8) is connected to the standby inverter (2) through hard wiring.

3. The main pump frequency converter according to claim 1, characterized in that: A current transformer (7), a voltage transformer (8) and a protection relay (6) are installed in the switch cabinet of the output circuit breaker (12) of the working frequency converter.

4. A control method for switching a main pump working frequency converter to a standby frequency converter, characterized in that: The fault condition of the working frequency converter (1) triggers the protection relay (6) to open the working frequency converter output circuit breaker (12), and at the same time, the standby frequency converter (2) starts the phase lock. The opening of the working frequency converter output circuit breaker (12) triggers the switching circuit breaker (4) to close. The closing of the switching circuit breaker (4) triggers the flying start function of the standby frequency converter (2). The standby frequency converter (2) loads the motor (3), and the faulty working frequency converter (1) exits operation.

5. The control method for switching the main pump working inverter to the standby inverter according to claim 4 is characterized in that: Under normal working conditions of the working frequency converter (1), the incoming line of the working frequency converter (1) is connected to the medium voltage bus (5), the incoming line circuit breaker (11) of the working frequency converter, the outgoing line circuit breaker (12) of the working frequency converter, the first incoming line circuit breaker (31) of the motor and the second incoming line circuit breaker (32) of the motor are all in a closed state, and the working frequency converter (1) carries the motor (3); the incoming line of the standby frequency converter (2) is connected to the medium voltage bus (5), the incoming line circuit breaker (21) of the standby frequency converter and the outgoing line circuit breaker (22) of the standby frequency converter are all in a closed state, the switching circuit breaker (4) is in an open state, and the standby frequency converter (2) is in a hot standby state.

6. The control method for switching the main pump working inverter to the standby inverter according to claim 4 is characterized in that: The working frequency converter (1) fault condition includes a working frequency converter (1) fault triggering the working frequency converter output circuit breaker (12) to open and a working frequency converter (1) fault not triggering the working frequency converter output circuit breaker (12) to open. In the working frequency converter (1) fault triggering the working frequency converter output circuit breaker (12) to open, the protection relay (6) simultaneously opens the working frequency converter output circuit breaker (12) according to the opening logic of the working frequency converter output circuit breaker (12). In the working frequency converter (1) fault not triggering the working frequency converter output circuit breaker (12) to open, the protection relay (6) opens the working frequency converter output circuit breaker (12) according to the opening logic of the working frequency converter output circuit breaker (12).

7. The control method for switching the main pump working inverter to the standby inverter according to claim 6 is characterized in that: The opening logic of the working frequency converter output circuit breaker (12) is as follows: the current signal of the working frequency converter output circuit breaker (12) is lower than its set value, the voltage signal of the working frequency converter output circuit breaker (12) is lower than its set value, and the delay of the working frequency converter output circuit breaker (12) reaches its set value.

8. The control method for switching the main pump working inverter to the standby inverter according to claim 4 is characterized in that: The working frequency converter output circuit breaker (12) is connected to the protection relay (6), and the voltage signal and current signal of the working frequency converter output circuit breaker (12) are respectively transmitted to the protection relay (6); the protection relay (6) is respectively connected to the current transformer (7) and the voltage transformer (8), the current transformer (7) measures the current signal of the working frequency converter output circuit breaker (12), and the voltage transformer (8) measures the voltage signal of the working frequency converter output circuit breaker (12); the voltage transformer (8) is connected to the standby frequency converter (2), and transmits the voltage signal of the working frequency converter output circuit breaker (12) to the standby frequency converter (2).

9. The control method for switching the main pump working inverter to the standby inverter according to claim 4 is characterized in that: When the voltage signal of the output circuit breaker (12) of the working frequency converter is lower than its set value, the standby frequency converter (2) starts phase locking.

10. The control method for switching the main pump working inverter to the standby inverter according to claim 4, characterized in that: After the standby frequency converter (2) starts the phase lock, the standby frequency converter (2) tracks the residual magnetic voltage of the motor (3) in real time. After the switching circuit breaker (4) is closed, the standby frequency converter (2) immediately outputs voltage to the motor (3) to increase the speed of the motor (3) to a 100% speed platform.

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