A system and method for switching a circulating pump from a power frequency to a variable frequency operation mode online

Abstract

The present invention belongs to the field of motor control technology, and specifically relates to a system and method for switching a circulating pump online from an industrial frequency to a variable frequency operation mode. The present invention includes a first circulating pump and a second circulating pump, the second circulating pump having the same structure and function as the first circulating pump, the first circulating pump being connected to the power supply busbar in sequence through the first circulating pump inverter outlet circuit breaker, the first circulating pump inverter, the first circulating pump inverter incoming circuit breaker, and the first circulating pump upstream circuit breaker, the first auxiliary oil pump provides lubricating oil to the first circulating pump gearbox during the start, stop, and switching of the circulating pump; the first high-pressure oil pump provides high-pressure oil to the bearing of the first circulating pump, supporting the rotor to form an oil film during the start, stop, and switching of the circulating pump, thereby ensuring the safe operation of the circulating pump; the circulating pump outlet pipe is connected to the first circulating pump water inlet electric valve to supply water to the auxiliary cooling water system. The present invention can realize the online rapid switching of the circulating water pump from the industrial frequency to the variable frequency operation mode without stopping the circulating water pump and without affecting the power of the unit.

Description

Technical Field

[0001] The present invention belongs to the technical field of motor control, and in particular relates to a system and method for switching a circulating pump online from an industrial frequency operation mode to a variable frequency operation mode. Background Art

[0002] Circulating water pumps (hereinafter referred to as "circulating pumps") in various power plants are primarily used to provide cooling water to the conventional island condenser, cooling the exhaust steam from the turbine after work, thereby ensuring the unit's normal thermal cycle. For many power plants in my country, particularly those located in northern China, the significant temperature difference between winter and summer seawater, with lower seawater temperatures in winter, can lead to overcooling of the condensate, resulting in elevated dissolved oxygen levels and accelerated corrosion of secondary circuit equipment. Furthermore, excessive condenser vacuum can lead to abnormal turbine vibration. To avoid this, it is necessary to adjust the circulating water flow rate by adjusting the circulating pump speed according to different operating conditions. Currently, some nuclear power plants in China have, for the first time, implemented advanced variable frequency speed regulation technology for high-power circulating pump motors (minimum 5000 kW), achieving online and stable regulation of the circulating water flow rate. To ensure system reliability, the circulating pump motor configuration utilizes a "variable frequency converter + power frequency bypass" system. This allows the circulating pump speed to be reduced in winter to minimize circulating water volume. In the event of a variable frequency converter failure or when variable frequency operation becomes uneconomical, the circulating pump can switch to power frequency bypass mode to continue operation. However, in the actual application of variable frequency speed regulation technology, when seawater temperature drops in winter and the circulating pump needs to be switched from "mains frequency operation mode" to "variable frequency operation mode", this switch cannot be made online. To switch, the unit must first be significantly reduced in power, and then the circulating pump must be manually shut down in "mains frequency operation mode". The inverter bypass switch must be disconnected and the inverter inlet and outlet switches closed. The circulating pump can then be restarted in variable frequency operation mode and the unit load increased to the power level before the switch. In addition, if the inverter stops operating due to a fault, once the fault is repaired and the unit can be put back into operation, the circulating pump must also be shut down in mains frequency operation mode and the unit power must be significantly reduced before switching to variable frequency operation mode.

[0003] Aiming at the problem that the existing circulating water pump cannot switch from the industrial frequency operation mode to the variable frequency operation mode online, a control method for online switching of the circulating water pump from the industrial frequency to the variable frequency operation mode is provided. The method can realize online "one-key switching" to the variable frequency operation mode when the circulating water flow rate needs to be reduced due to low seawater temperature in winter or when the variable frequency operation can be restored after the inverter fault is repaired. Summary of the Invention

[0004] The technical problem solved by the present invention is to provide a system and method for online switching of a circulating water pump from industrial frequency to variable frequency operation mode, which can realize online rapid switching of the circulating water pump from industrial frequency to variable frequency operation mode without stopping the circulating water pump and without affecting the power of the unit.

[0005] The technical solution adopted in the present invention is:

[0006] A system for switching a circulating pump online from an industrial frequency to a variable frequency operation mode comprises a first circulating pump and a second circulating pump, wherein the second circulating pump has the same structure and function as the first circulating pump, the first circulating pump is connected to the power supply busbar in sequence through the first circulating pump inverter outlet circuit breaker, the first circulating pump inverter, the first circulating pump inverter incoming circuit breaker, and the first circulating pump upstream circuit breaker, a first auxiliary oil pump provides lubricating oil to the first circulating pump gearbox during the start-up, stop and switching of the circulating pump; a first high-pressure oil pump provides high-pressure oil to the bearing of the first circulating pump, supporting the rotor to form an oil film during the start-up, stop and switching of the circulating pump, thereby ensuring the safe operation of the circulating pump; the circulating pump outlet pipe is connected to the first circulating pump to the SEN system water inlet electric valve to supply water to the auxiliary cooling water system.

[0007] The first circulating pump is directly connected to the power supply busbar through the first circulating pump inverter bypass circuit breaker and the first circulating pump upstream circuit breaker.

[0008] A method for switching a circulating water pump operating mode online comprises the following steps:

[0009] Step 1: Confirm the initial status and confirm whether the first circulation pump can be manually switched. If not, proceed to step 2;

[0010] Step 2: The inverter sends a command to the switching module to switch from the industrial frequency to the variable frequency operation mode;

[0011] Step 3: Execute the process system operations before the inverter is switched

[0012] Step 4: Execute the electrical switch of the inverter from industrial frequency to variable frequency operation mode;

[0013] Step 5: If the first circulating pump inverter inlet circuit breaker and the first circulating pump inverter outlet circuit breaker are both in the "closed" position and the inverter is in the "variable frequency operation" mode, the switching is judged to be successful and the process goes to step 6; otherwise, the switching is judged to be failed and the process goes to step 7;

[0014] Step 6: Process system status recovery;

[0015] Step 7: Switch the inverter back to the "power frequency" operation mode;

[0016] Step 8: If the first pump circuit is in either the "open" or "open" state or the "closed" state, the switchback is successful and the process goes to step 9;

[0017] If the first pump circuit is in either the "open" or "open" state or the "open" state, the switchback fails and goes to step ten.

[0018] Step 9: After switching back to the "power frequency" operation mode, the status is restored: the inverter is reloaded to the "power frequency" operation mode; the first auxiliary oil pump and the first high-pressure oil pump automatically stop after running for 90 seconds; after the loading is completed and the system is confirmed to have no abnormalities, the operator opens the first electric valve; the switching back process is completed;

[0019] Step 10: Stop the circulating pump:

[0020] A "open" command was issued to the upstream circuit breaker of the first circulating pump, the first circulating pump stopped operating, and the switching failed.

[0021] If the first circulating pump can be switched manually, the following conditions must be met at the same time: the first circulating pump is running at the industrial frequency; the upstream circuit breaker of the first circulating pump is in the "closed" state; the bypass circuit breaker of the first circulating pump inverter is in the "remote control", "working position" and "closed" state; the first circulating pump inverter is in the "remote control" mode and there is no fault alarm; the incoming circuit breaker of the first circulating pump inverter and the outgoing circuit breaker of the first circulating pump inverter are both in the "remote control", "working position" and "open" states; the first auxiliary oil pump and the first high-pressure oil pump are in the "stop" and "standby" states; the second circulating pump is running; the second electric valve is in the "fully open" state; the first electric valve is in the "fully open", "remote control" and "automatic" states.

[0022] The step three specifically includes: after the instruction in step two is triggered, the first electric valve begins to close after receiving the closing instruction; after the first electric valve is fully closed, the first auxiliary oil pump and the first high-pressure oil pump issue a start-up and operation instruction for 90 seconds.

[0023] The step three specifically includes: after the step three is executed, the system triggers a 10-second "power frequency to variable frequency" operation mode instruction, and the time of issuing the "power frequency to variable frequency" operation mode instruction is counted as 0s; at 0s: issuing an "opening" instruction to the bypass circuit breaker of the first circulating pump inverter and maintaining it for 5 seconds; issuing a 90-second switching to 50Hz operation signal instruction to the first circulating pump inverter; at 2s: after the bypass circuit breaker of the first circulating pump inverter is opened, issuing a "closing" instruction to the incoming circuit breaker of the first circulating pump inverter; at 4.5 seconds: issuing a "closing" instruction to the outgoing circuit breaker of the first circulating pump inverter;

[0024] The step six specifically includes: the first circulating pump inverter is quickly loaded to full power 50Hz operation for 60 seconds; the first auxiliary oil pump and the first high-pressure oil pump are automatically shut down after running for 90 seconds; after confirming that there is no abnormality in the system, the operator opens the first electric valve; and the switching process ends.

[0025] The step seven specifically includes: in the 6th second: triggering the "open" and "open" instructions; between the 6th and 8th seconds: after receiving the "open" and "open" states of the first circulating pump inverter incoming circuit breaker and the first circulating pump inverter outgoing circuit breaker, issuing a "close" instruction to the first circulating pump inverter bypass circuit breaker.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) The present invention provides a system and method for switching a circulating water pump from a power frequency operation mode to a variable frequency operation mode online. Under normal operating conditions of the circulating water pump, the method switches from the power frequency (bypass) operation mode to the variable frequency operation mode with one click, thereby enabling the circulating water pump to maintain low-frequency operation when the circulating water temperature is low, thereby achieving the goal of reducing power consumption and improving economy.

[0028] (2) The present invention provides a system and method for switching a circulating pump from an industrial frequency operation mode to a variable frequency operation mode online, and provides a method for determining the switching timing of the circulating pump from the variable frequency operation mode to the industrial frequency operation mode by comprehensively considering the measured motor residual pressure attenuation curve and the circulating water flow attenuation curve when the circulating pump of the process system is stopped, which is 4.5 seconds after the inverter input circuit breaker and the circuit breaker are fully disconnected. During the switching process, the operating safety of the circulating pump motor is guaranteed, and the circulating water flow rate is guaranteed not to change significantly;

[0029] (3) The present invention provides a system and method for switching a circulating pump from an industrial frequency to a variable frequency operation mode online, and introduces a criterion for unsuccessful switching of the circulating pump based on the position of the variable frequency dual switch and the operating status of the inverter, thereby improving the accuracy of judging the switching status of the circulating pump;

[0030] (4) The present invention provides a system and method for switching a circulating pump from a power frequency operation mode to a variable frequency operation mode online, and provides a solution for closing the auxiliary cooling water system water supply electric valve in advance when the circulating pump switches from the power frequency operation mode to the variable frequency operation mode, thereby ensuring the cooling water supply of conventional island equipment during the switching process;

[0031] (5) The present invention provides a system and method for switching a circulating pump from an industrial frequency operation mode to a variable frequency operation mode online, and provides a solution for starting an auxiliary oil pump and a high-pressure oil pump in advance when the circulating pump switches from an industrial frequency operation mode to a variable frequency operation mode, thereby ensuring the safety of the pump during the switching process of the circulating pump. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is the electrical wiring diagram of a single unit circulating pump-inverter group;

[0033] Figure 2 A flow chart of a method for switching an online operation mode of a circulating water pump provided by the present invention;

[0034] In the figure: 1-upstream circuit breaker of the first circulating pump; 2-incoming circuit breaker of the first circulating pump inverter; 3-outgoing circuit breaker of the first circulating pump inverter; 4-bypass circuit breaker of the first circulating pump inverter; 5-first circulating pump inverter; 6-first circulating pump; 7-upstream circuit breaker of the second circulating pump; 8-incoming circuit breaker of the second circulating pump inverter; 9-outgoing circuit breaker of the second circulating pump inverter; 10-bypass circuit breaker of the second circulating pump inverter; 11-second circulating pump inverter; 12-second circulating pump; 13-auxiliary oil pump of the first circulating pump; 14-high-pressure oil pump of the first circulating pump; 15-water inlet electric valve from the first circulating pump to the SEN system; 16-water inlet electric valve from the second circulating pump to the SEN system; 17-auxiliary oil pump of the second circulating pump; 18-high-pressure oil pump of the second circulating pump. DETAILED DESCRIPTION

[0035] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0036] In the description of the present invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate and simplify the description of the present invention. They are not intended to indicate or imply that the devices or components referred to must have, be constructed, or operate in a specific orientation, and therefore should not be construed as limitations on the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0037] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0038] Figure 1The present invention is a schematic diagram of the electrical connection of a circulating pump-inverter group of a single unit. Each unit is equipped with two circulating pumps, a first circulating pump (6) and a second circulating pump (12), each of which bears 50% of the circulating water supply task. The shutdown of either circulating pump will cause the unit power to be reduced to 50%. The first circulating pump (6) corresponds to the first auxiliary oil pump (13) and the first high-pressure oil pump (14), and supplies water to the auxiliary cooling water system through the first electric valve (15); the second circulating pump (12) corresponds to the second auxiliary oil pump (16) and the second high-pressure oil pump (17), and supplies water to the auxiliary cooling water system through the second electric valve (18).

[0039] Taking the first circulation pump (6) as an example, Figure 2 As shown, the present invention provides a method for switching the online operation mode of a circulating water pump, which specifically includes the following steps:

[0040] Step 1: Confirm the initial state;

[0041] Confirm the initial status of the circulation pump system and determine whether it meets the following conditions at the same time:

[0042] ① The first circulating pump (6) is operating at the power frequency;

[0043] ② The upstream circuit breaker (1) of the first circulating pump is in the "closed" state;

[0044] ③ The bypass circuit breaker (4) of the first circulating pump inverter is in the "remote control", "working position" and "closed" state;

[0045] ④ The first circulating pump inverter (5) is in the "remote control" mode and there is no fault alarm;

[0046] ⑤ The first circulating pump inverter incoming line circuit breaker (2) and the first circulating pump inverter outgoing line circuit breaker (3) are both in

[0047] In the "remote control", "working position" and "opening" states

[0048] ⑥ The first auxiliary oil pump (13) and the first high-pressure oil pump (14) are in the "out of service" and "standby" states;

[0049] ⑦ The second circulation pump (12) is in operation;

[0050] ⑧ The second electric valve (18) is in the "fully open" state;

[0051] ⑨ The first electric valve (15) is in the "full open", "remote control" and "automatic" states.

[0052] Step 2: The inverter sends a command to the switching module to switch from the "power frequency" to the "variable frequency" operation mode;

[0053] The switching module emits a 60-second high-level pulse inside;

[0054] Step 3: Execute the process system operations before the inverter is switched;

[0055] ① After the instruction in step 2 is triggered, the first electric valve (15) begins to close after receiving the closing instruction;

[0056] ② After the first electric valve (15) is fully closed (the valve closing time is about 50 seconds), the first auxiliary oil pump (13) and the first high-pressure oil pump (14) issue a start-up operation instruction for 90 seconds.

[0057] Step 4: Execute the electrical switch of the inverter from "power frequency" to "variable frequency" operation mode;

[0058] ① After step 3 is completed, the system triggers the 10-second "power frequency to variable frequency" operation mode instruction, and the time of issuing the "power frequency to variable frequency" operation mode instruction is counted as 0s;

[0059] ② At 0s: a “open” command is issued to the bypass circuit breaker (4) of the first circulating pump inverter and maintained for 5 seconds; a 90-second switchover signal command to the first circulating pump inverter (5) is issued;

[0060] ③ Second second: After the bypass circuit breaker (4) of the first circulating pump inverter is opened, a "close" command is sent to the incoming circuit breaker (2) of the first circulating pump inverter;

[0061] ④ 4.5 seconds: Send a “close” command to the output circuit breaker (3) of the first circulating pump inverter;

[0062] Step 5:

[0063] If the first circulating pump inverter inlet circuit breaker (2) and the first circulating pump inverter outlet circuit breaker (3) are both in the "closed" position and the inverter is in the "variable frequency operation" mode (fault-tolerant processing to prevent poor contact of auxiliary contacts), the switching is judged to be successful and the process goes to step 6; otherwise, the switching is judged to be failed and the process goes to step 7.

[0064] Step 6: Process system status recovery;

[0065] ① The first circulating pump inverter (5) is quickly loaded to full power 50Hz operation for 60 seconds;

[0066] ② The first auxiliary oil pump (13) and the first high-pressure oil pump (14) automatically stop operating after running for 90 seconds;

[0067] ③ After confirming that there is no abnormality in the system, the operator opens the first electric valve (15);

[0068] ④The switching process ends.

[0069] Step 7: Switch the inverter back to the "power frequency" operation mode.

[0070] ①6th second: trigger the “open” and “open” commands;

[0071] ② Between the 6th and 8th seconds: after receiving the "open" and "open" status of the first circulating pump inverter inlet circuit breaker (2) and the first circulating pump inverter outlet circuit breaker (3), a "close" command is sent to the first circulating pump inverter bypass circuit breaker (4);

[0072] Step 8: If the first pump circuit is in either the "open" or "open" state or the "closed" state, the switchback is successful and the process goes to step 9;

[0073] If the first pump circuit is in either the "open" or "open" state or the "open" state, the switchback fails and goes to step ten.

[0074] Step 9: Switch back to the "power frequency" operation mode and the status is restored:

[0075] ①The inverter is reloaded to the "power frequency" mode;

[0076] ② The first auxiliary oil pump (13) and the first high-pressure oil pump (14) automatically stop operating after running for 90 seconds;

[0077] ③ After loading is completed and the system is confirmed to be normal, the operator opens the first electric valve (15);

[0078] ④The switchback process ends

[0079] Step 10: Stop the circulating pump:

[0080] A "open" command is sent to the upstream circuit breaker (1) of the first circulating pump, the first circulating pump stops operating, and the switching fails.

[0081] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims, not the foregoing description, and all variations within the meaning and range of equivalents of the claims are intended to be included therein. Any reference sign in a claim should not be construed as limiting the claim to which it relates.

[0082] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A switching method for a system for online switching of a circulating water pump operation mode, based on a system for online switching of a circulating pump from a power frequency to a variable frequency operation mode, comprising a first circulating pump (6) and a second circulating pump (12), wherein the second circulating pump (12) has the same structure and function as the first circulating pump (6), the first circulating pump (6) is connected to the power supply busbar in sequence through the first circulating pump frequency converter output circuit breaker (3), the first circulating pump frequency converter (5), the first circulating pump frequency converter input circuit breaker (2), and the first circulating pump upstream circuit breaker (1), the first auxiliary oil pump (13) is connected to the power supply busbar in sequence through the first circulating pump frequency converter output circuit breaker (3), the first circulating pump frequency converter (5), the first circulating pump frequency converter input circuit breaker (2), and the first circulating pump upstream circuit breaker (1). ) provides lubricating oil to the gear box of the first circulating pump (6) during the start, stop and switching of the circulating pump; the first high-pressure oil pump (14) provides high-pressure oil to the bearing of the first circulating pump (6), supporting the rotor to form an oil film during the start, stop and switching of the circulating pump, thereby ensuring the safe operation of the circulating pump; the circulating pump outlet pipe is connected to the first circulating pump to the SEN system water inlet electric valve (15) to supply water to the auxiliary cooling water system, and the first circulating pump (6) is directly connected to the power supply busbar through the first circulating pump inverter bypass circuit breaker (4) and the first circulating pump upstream circuit breaker (1); it is characterized in that The steps include: Step 1: Confirm the initial state and confirm whether the first circulation pump (6) can be manually switched. If not, proceed to step 2; Step 2: The inverter sends a command to the switching module to switch from the industrial frequency to the variable frequency operation mode; Step 3: Execute the process system operations before the inverter is switched; Step 4: Execute the electrical switch of the inverter from industrial frequency to variable frequency operation mode; Step 5: If the first circulating pump inverter inlet circuit breaker (2) and the first circulating pump inverter outlet circuit breaker (3) are both in the "closed" position and the inverter is in the "variable frequency operation" mode, it is determined that the switching is successful and the process goes to step 6; otherwise, it is determined that the switching fails and the process goes to step 7; Step 6: Process system status recovery; Step 7: Switch the inverter back to the "power frequency" operation mode; Step 8: If the first pump circuit is in either the "open" or "open" state or the "closed" state, the switchback is successful and the process goes to step 9; If the first pump circuit is in either the "open" or "open" state and the "open" state exists, the switchback fails and the process goes to step 10. Step 9: After switching back to the "power frequency" operation mode, the state is restored: the frequency converter is reloaded to the "power frequency" mode; the first auxiliary oil pump (13) and the first high-pressure oil pump (14) automatically stop after running for 90 seconds; after the loading is completed and the system is confirmed to have no abnormalities, the operator opens the first electric valve (15); the switching back process is completed; Step 10: Stop the circulating pump: Send an "open" command to the upstream circuit breaker (1) of the first circulating pump, and the first circulating pump stops operating, and the switching fails.

2. The method according to claim 1, characterized in that If the first circulating pump (6) can be switched manually, the following conditions must be met simultaneously: the first circulating pump (6) is in power frequency operation; the upstream circuit breaker (1) of the first circulating pump is in the "closed" state; the bypass circuit breaker (4) of the first circulating pump frequency converter is in the "remote control", "working position", and "closed" state; the first circulating pump frequency converter (5) is in the "remote control" mode and has no fault alarm; the incoming circuit breaker (2) of the first circulating pump frequency converter and the outgoing circuit breaker (3) of the first circulating pump frequency converter are both in the "remote control", "working position", and "open" states; the first auxiliary oil pump (13) and the first high-pressure oil pump (14) are in the "stopped" and "standby" states; the second circulating pump (12) is in operation; the second electric valve (18) is in the "fully open" state; and the first electric valve (15) is in the "fully open", "remote control", and "automatic" states.

3. The method according to claim 1, characterized in that The step three specifically includes: after the instruction in step two is triggered, the first electric valve (15) starts to close after receiving the closing instruction; after the first electric valve (15) is fully closed, the first auxiliary oil pump (13) and the first high-pressure oil pump (14) issue a start-up operation instruction for 90 seconds.

4. The method according to claim 1, wherein The step three specifically includes: after the step three is executed, the system triggers a 10-second "power frequency cut to variable frequency" operation mode instruction, and the time of issuing the "power frequency cut to variable frequency" operation mode instruction is counted as 0s; 0s: issuing an "opening" instruction to the bypass circuit breaker (4) of the first circulating pump inverter and maintaining it for 5 seconds; issuing a 90-second switch to 50Hz operation signal instruction to the first circulating pump inverter (5); 2s: after the bypass circuit breaker (4) of the first circulating pump inverter is opened in place, issuing a "closing" instruction to the incoming circuit breaker (2) of the first circulating pump inverter; 4.5 seconds: issuing a "closing" instruction to the outgoing circuit breaker (3) of the first circulating pump inverter.

5. The method according to claim 1, wherein The step six specifically includes: the first circulating pump frequency converter (5) is quickly loaded to full power 50Hz operation for 60 seconds; the first auxiliary oil pump (13) and the first high-pressure oil pump (14) are automatically shut down after running for 90 seconds; after confirming that there is no abnormality in the system, the operator opens the first electric valve (15); and the switching process ends.

6. The method according to claim 1, characterized in that The step seven specifically includes: in the 6th second: triggering the "open" and "open" instructions; between the 6th and 8th seconds: after receiving the "open" and "open" states of the first circulating pump inverter inlet circuit breaker (2) and the first circulating pump inverter outlet circuit breaker (3), issuing a "close" instruction to the first circulating pump inverter bypass circuit breaker (4).

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