Variable power frequency synchronous switching controller

Abstract

The utility model relates to the technical field of controllers, in particular to a variable-power-frequency synchronous switching controller, which realizes variable-power-frequency synchronous switching and comprises a control panel and a matched electrical loop, the control panel is externally connected with a 24V direct-current power supply and serves as a working power supply of the controller, the control panel is provided with a GND (ground) end which is grounded, and R, S and T terminals which are connected with a power grid. The U terminal, the V terminal and the W terminal are connected with the output of a frequency converter, the wiring sequence of the U terminal, the V terminal and the W terminal which are finally connected into a motor is consistent, the controller allows to drag 1-4 water pumps, and the enabling terminals X1, X2, X3 and X4 are selected, and in the following description, the main loop drags three water pumps as one. The frequency converter is mainly designed for being matched with frequency converters of various brands at home and abroad to play a variable power frequency synchronous switching role in multi-pump water supply. The controller is not limited to the field of water supply, and certainly, the controller can also be used in other occasions with variable power frequency switching requirements.

Description

Technical Field

[0001] This utility model relates to the field of switching controller technology, and in particular to a variable frequency synchronous switching controller. Background Technology

[0002] Currently, other brands of multi-pump controllers lack the function of variable frequency synchronous switching and limit the functions of the frequency converter itself, placing themselves in the master position. Therefore, the frequency converter in the slave position obviously cannot give full play to its powerful functions. In view of this waste of resources and lack of function, a more reasonable way to use frequency converters in multi-pump applications is proposed.

[0003] Therefore, this application proposes a variable frequency synchronous switching controller to solve the above problems. Utility Model Content

[0004] To address the shortcomings of existing technologies, this utility model provides a variable frequency synchronous switching controller to solve the technical problem that "current multi-pump controllers from other brands lack variable frequency synchronous switching functionality and limit the functions of the frequency converter itself, placing themselves in the master control position. As a result, the frequency converter in the slave position obviously cannot give full play to its powerful functions. In response to this waste of resources and functional deficiencies, a more reasonable method for using the frequency converter in multi-pump applications is proposed."

[0005] To achieve the above objectives, this utility model provides the following technical solution:

[0006] A variable frequency synchronous switching controller includes a control panel and matching electrical circuits.

[0007] The control panel is connected to an external 24V DC power supply, which is the working power supply for this controller. The control panel is equipped with a GND terminal for grounding, R, S, and T terminals for connecting to the power grid, and U, V, and W terminals for connecting to the inverter output. The final wiring sequence for connecting to the motor is consistent.

[0008] The control panel also includes the following terminals.

[0009] X0: Synchronization enable terminal, interlocked with inverter start input, short-circuit disables. X1: Motor M1 enable, short-circuited with GND, and manually interlocked with MT1 for mains frequency. X2: Motor M2 enable, short-circuited with GND, and manually interlocked with MT2 for mains frequency. X3: Motor M3 enable, short-circuited with GND, and manually interlocked with MT3 for mains frequency. X4: Motor M4 enable, short-circuited with GND, and manually interlocked with MT4 for mains frequency. X5: X5 is the inverter running status input, monitoring the inverter status. Short-circuited with GND for running, disconnected for stopping. X6: X6 short-circuited with GND, used to disable system switching between mains and mains frequency. X7: Terminal X7 short-circuited with GND, used to prevent the system from switching from mains frequency to inverter after switching between inverter and mains frequency. X8: X8 short-circuited with GND, disables the last inverter / mains frequency motor switching, disconnected with GND allows the last motor to switch between inverter and mains frequency. X9: Inverter fault input, used to mark the faulty motor as removed from the running array. Terminal UP indicates the mains voltage; the DC output terminal (DC 0-10V) corresponds to the AC input of terminals R, S, and T (AC 0-500V). Terminal UG indicates the inverter output voltage; the DC output terminal (DC 0-10V) corresponds to the AC output of terminals U, V, and W (AC 0-500V). Terminal FMI is the inverter speed setpoint input terminal. 0-10V corresponds to a frequency converter speed setting of 0-50HZ. K0: Y00-Y01: Motor M1 frequency converter contactor control terminal; K1: Y10-Y11: Motor M1 power frequency contactor control terminal; K2: Y20-Y21: Motor M2 frequency converter contactor control terminal; K3: Y30-Y31: Motor M2 power frequency contactor control; K4: Y40-Y41: Motor M3 frequency converter contactor control terminal; K5: Y50-Y51: Motor M3 power frequency contactor control terminal; K6: Y60-Y61: Motor M4 frequency converter contactor control terminal; K7: Y70-Y71: Motor M4 power frequency contactor control terminal; K8: K8 is used to control the start and stop of the frequency converter. TC is connected to the frequency converter's common terminal COM. TC-TB: Normally closed contact is connected to the frequency converter's free stop terminal. TC-TA: Normally open contact is connected in series to the frequency converter's start command terminal. The RS485 terminal is the remote communication terminal for the control board.

[0010] As a preferred embodiment of this utility model, the electrical circuit includes a first pump M1, a second pump M2, and a third pump M3. The first pump M1, the second pump M2, and the third pump M3 are electrically connected to thermal overload circuits RJ1, RJ2, and RJ3, respectively. Thermal overload circuits RJ1, RJ2, and RJ3 are electrically connected to contactors KM1, KM3, and KM5, respectively. Thermal overload circuits RJ1, RJ2, and RJ3 are also electrically connected to contactors KM2, KM4, and KM6, respectively. Contactors KM1, KM3, and KM5 are electrically connected to the same frequency converter, which is electrically connected to circuit breaker QF1. Contactors KM2, KM4, and KM6 are electrically connected to circuit breakers QF2, QF3, and QF4, respectively. Circuit breakers QF1, QF2, QF3, and QF4 are electrically connected to the same ammeter A, which is electrically connected to circuit breaker QF0. Circuit breakers QF2, QF3, and QF4 are also electrically connected to the same voltmeter V. Circuit breaker QF4 is connected to the live wire L.

[0011] As a preferred embodiment of this utility model, the electrical circuit further includes a fuse current-limiting resistor R1, a fuse current-limiting resistor R2, a fuse current-limiting resistor R3, and a fuse current-limiting resistor R4. Fuse current-limiting resistors R1 and R3 are both connected to the neutral wire N, while fuse current-limiting resistors R2 and R4 are connected to the live wire L. Axial fans F1 and F2, installed inside the cabinet, are electrically connected between fuse current-limiting resistors R1 and R2. A series of indicator lights connected in parallel between fuse current-limiting resistors R3 and R4 are connected in parallel: variable frequency pump 1 indicator light KM1-2, power frequency pump 1 indicator light KM2-2, variable frequency pump 2 indicator light KM3-2, power frequency pump 2 indicator light KM4-2, variable frequency pump 3 indicator light KM5-2, and power frequency pump 3 indicator light KM6-2.

[0012] As a preferred technical solution of this utility model, the inverter is a general-purpose inverter for both domestic and international markets. The contactors are electrically interlocked when the action time is short enough not to affect the synchronous switching, contactors KM1 and KM2 are electrically interlocked, contactors KM3 and KM4 are electrically interlocked, and contactors KM5 and KM6 are electrically interlocked.

[0013] As a preferred technical solution of this utility model, each of the No. 1 pump M1, No. 2 pump M2 and No. 3 pump M3 is equipped with a motor, motor excitation and rotor.

[0014] This utility model provides a variable power frequency synchronous switching controller, which has the following beneficial effects:

[0015] 1. This utility model is mainly designed to cooperate with various domestic and foreign brand frequency converters to play the role of synchronous switching between variable frequency and power frequency in multi-pump water supply. It can synchronously switch the number of frequency converter pumps according to the change of water volume to achieve the purpose of meeting high-quality water supply, and truly achieve smooth switching between variable and power frequency, and stable transition of water supply pressure and flow.

[0016] 2. The resulting system is still a pump frequency switching system with the inverter itself as the main PID controller and the multi-pump controller as the auxiliary controller. Therefore, the parameter setting is completed by the inverter itself, and the controller does not need to be set. It is only used as a functional component for frequency switching. The purpose of doing so is not to limit the role of the inverter, but to help the inverter play a greater role. Attached Figure Description

[0017] Figure 1 This is the control circuit diagram for the "one-to-N" system of this utility model;

[0018] Figure 2 This invention relates to the terminal wiring circuit for the soft start application of the high-power variable frequency / power frequency synchronous switching controller.

[0019] Figure 3 This is the main control circuit diagram for the "one-to-three" configuration of this utility model;

[0020] Figure 4 This is the control main circuit diagram for the "one-to-one" soft start application of this utility model;

[0021] Figure 5 This is a circuit diagram of Embodiment 1 of the present invention;

[0022] Figure 6 This is a circuit diagram of Embodiment 2 of the present invention. Detailed Implementation

[0023] To make the technical problems, technical solutions, and beneficial effects of this utility model clearer, the present utility model will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present utility model and are not intended to limit the present utility model.

[0024] Therefore, a feature pointed out in this specification is used to describe one feature of one embodiment of the present invention, and does not imply that every embodiment of the present invention must have the described feature. Furthermore, it should be noted that this specification describes many features. Although certain features may be combined to illustrate possible system designs, these features may also be used in other combinations not explicitly stated. Therefore, unless otherwise stated, the described combinations are not intended to be limiting.

[0025] The principle and structure of this utility model will be described in detail below with reference to the accompanying drawings and embodiments:

[0026] refer to Figures 1 to 6 A variable frequency synchronous switching controller is provided to realize variable frequency synchronous switching. It includes a control panel and a matching electrical circuit. The control panel is connected to an external 24V DC power supply, which is the working power supply of this controller. The control panel is provided with a GND terminal for grounding, R, S, and T terminals for connecting to the power grid, and U, V, and W terminals for connecting to the inverter output. The final wiring sequence of the motor is consistent. This controller allows driving 1-4 water pumps, which can be selected by the enable terminals X1, X2, X3, and X4.

[0027] The control panel also includes the following terminals;

[0028] X0: Synchronization enable terminal, interlocked with inverter start input (shares start button), short-circuit disables; X1: Motor M1 enable, short-circuit valid with GND, disconnect invalid; used for manual power frequency interlock with MT1; X2: Motor M2 enable, short-circuit valid with GND, disconnect invalid; used for manual power frequency interlock with MT2; X3: Motor M3 enable, short-circuit valid with GND, disconnect invalid; used for manual power frequency interlock with MT3; X4: Motor M4 enable, short-circuit valid with GND, disconnect invalid; used for manual power frequency interlock with MT4; X5: Inverter running status input, this input is valid only when the inverter is running, allowing switching. When terminal X7 is high and invalid, if terminal X5 changes from valid to invalid for more than the stop interval, the inverter will be disabled. Motors in frequency mode are deactivated one by one; if no stop signal is received within a timeout period when the variable frequency synchronous switching signal is issued, the synchronous switching signal is invalid and the machine enable is disabled. It is necessary to check wiring, parameter settings and other issues. After troubleshooting, the terminal can be re-enabled and the frequency converter can be started again (if the terminal X5 is invalid, i.e., normally open or normally closed, switching will be prohibited). X6: The upper limit of the frequency converter has reached the switching allow input (short-circuiting X6 with GND prohibits the system from switching between variable frequency and power frequency, disconnecting it allows). When variable frequency switching is not required, terminal X6 can be short-circuited with GND. X7: The lower limit of the frequency converter has reached the switching allow input (short-circuiting X7 with GND prohibits power frequency exit, disconnecting it allows). If the system is used as a pure soft start, terminal X7 must be short-circuited with GND. Each motor can operate independently. The operating status of a motor that has already switched between variable frequency and mains frequency is not affected by the current variable frequency speed. The condition for exiting mains frequency is that the stop command or the corresponding enable terminal is invalid. X8: Whether the inverter is allowed to drive the last motor for variable frequency / mains frequency switching. Disconnecting from GND allows switching, shorting from GND prohibits the last motor from switching to mains frequency. The purpose of keeping the inverter online is for the need of continuous adjustment. When the indicator D33 is lit, it means that the inverter is prohibited from switching to mains frequency, and when it is off, it means that it is allowed. In actual use, there are two options: one is to directly short-circuit with GND, and the other is to indirectly use the GND command by interlocking with the inverter start / stop (sharing the start button). When used as a soft starter, this terminal is left floating (the difference from X6 is that X6 prohibits all motors from switching between variable frequency and mains frequency, while X8 only prohibits the last motor from switching between variable frequency and mains frequency). X9: Inverter fault input. The purpose is to mark the faulty motor to exit the running array. During the fault, the inverter is prohibited from running. If the fault holding time exceeds the effective shutdown time, the motors in the mains frequency running state will be shut down one by one. The terminal FMI is connected to the inverter's given analog input, corresponding to the given frequency. When the inverter's given value is lower than the return set value, the motor will return from the mains frequency to the inverter state. The set value can be adjusted by the potentiometer Rset, and the jumper is set to the 1-2 position.If this function is not used, connect terminal FMI to 10V or short terminal X7 to GND. Terminal UP is the standard AC 0-500V input, and terminal RST outputs a DC voltage of 0-10V, which can be calibrated by potentiometer Rrst. Terminal UVW is the inverter input, which can be calibrated by potentiometer Ruvw. Terminal UG corresponds to 0-10V. Because the waveforms of the two are different, the DC voltages obtained under equivalent voltage may be different. For easy observation and control, potentiometers are needed to calibrate the voltages of RST and UVW to make the inverter output completely consistent with the AC 0-500V conversion in terms of the corresponding 0-10V. The purpose is to ensure consistent voltage acquisition and achieve voltage synchronization. K0: Y00-Y01: Motor M1 frequency converter contactor control; indicator D19 is lit when engaged and off when released. K1: Y10-Y11: Motor M1 power frequency contactor control; indicator D20 is lit when engaged and off when released. K2: Y20-Y21: Motor M2 frequency converter contactor control; indicator D13 is lit when engaged and off when released. K3: Y30-Y31: Motor M2 power frequency contactor control; indicator D21 is lit when engaged. K4: Y40-Y41: Motor M3 frequency converter contactor control, light D14 indicates engagement, off indicates release; K5: Y50-Y51: Motor M3 power frequency contactor control, light D22 indicates engagement, off indicates release; K6: Y60-Y61: Motor M4 frequency converter contactor control, light D15 indicates engagement, off indicates release; K7: Y70-Y71: Motor M4 power frequency contactor control, light D23 indicates engagement, off indicates release; K8: TC common terminal, TC-TB: normally closed contact connected to the frequency converter free stop terminal; TC-TA: normally open contact connected to the frequency converter run enable terminal. Engaging K8 is to disconnect the frequency converter free stop terminal and enable the run terminal. Light D24 indicates engagement, off indicates release.

[0029] In actual use, the individual contacts are connected together to form a common terminal, which is then connected to the live wire L (or 24V, depending on the device being driven). To facilitate wiring, simply short-circuit the reserved pads on the back of the control board.

[0030] The electrical circuit also includes fuse current-limiting resistors R1, R2, R3, and R4. Fuse current-limiting resistors R1 and R3 are connected to the neutral wire N, while fuse current-limiting resistors R2 and R4 are connected to the live wire L. Axial fans F1 and F2, mounted inside the cabinet, are electrically connected between fuse current-limiting resistors R1 and R2. Variable frequency pumps 1, connected in parallel, are electrically connected between fuse current-limiting resistors R3 and R4. Indicator lights KM1-2, KM2-2 for mains frequency pump 1, KM3-2 for variable frequency pump 2, KM4-2 for mains frequency pump 2, KM5-2 for variable frequency pump 3, and KM6-2 for mains frequency pump 3. The variable frequency drive is a common type of variable frequency drive for both domestic and international applications. The contactors are electrically interlocked when the action time is short enough not to affect synchronous switching, contactors KM1 and KM2 are electrically interlocked, contactors KM3 and KM4 are electrically interlocked, and contactors KM5 and KM6 are electrically interlocked.

[0031] As a preferred technical solution of this utility model, each of the No. 1 pump M1, No. 2 pump M2 and No. 3 pump M3 is equipped with a motor, motor excitation and rotor.

[0032] During operation, the monitoring circuit for the variable frequency pump 1, fixed frequency pump 1, variable frequency pump 2, fixed frequency pump 2, variable frequency pump 3, and fixed frequency pump 3 is visible. For example, if the water volume is insufficient when pump M1 reaches 50Hz, pump M1 is directly connected to the fixed frequency pump, and pump M2 is started using the variable frequency pump. If the water volume is still insufficient when pump M2 reaches 50Hz, pump M2 is connected to the fixed frequency pump, and pump M3 is started using the variable frequency pump. Conversely, the pumps will gradually disconnect. During the connection process, the water supply volume changes continuously without sudden changes, thus ensuring a stable water supply and meeting the user's water comfort requirements. In actual use of multiple pumps, the back EMF frequency, angle, amplitude, and phase sequence of the motor are compared with the power grid. When synchronized, the system switches to the fixed frequency pump, overcoming the current surge caused by asynchrony. The variable frequency / fixed frequency switching is crucial. If the upper limit frequency of the motor operation is appropriately increased to compensate for slip, the system switching will be even smoother.

[0033] Specific soft-start applications such as Figure 2 , Figure 4 , Figure 6Because the inverter and motor M1 have relatively high power, two contactors (KM11 and KM12, KM21 and KM22) are used in parallel to handle the motor current when switching to the power frequency. In fact, when using this product for switching, the inverter's own bus capacitor first absorbs the sudden current change Ldi / dt effect after the motor's instantaneous emergency stop, and then KM11 and KM12 are disconnected. This fundamentally eliminates the arcing phenomenon that would occur if KM11 and KM12 were directly disconnected. Secondly, by engaging KM21 and KM22, the motor is smoothly connected to the grid as a generator power source that meets the grid connection requirements. The engaging of contactors KM21 and KM22 does not need to withstand the large current similar to that of direct power frequency start-up. Therefore, there is no disaster to the public grid caused by asynchronous grid connection, and the mechanical violent impact caused by large current to the motor is also avoided.

[0034] This invention is primarily designed to work with ABB, Siemens, and other foreign frequency converters, as well as various domestic brands, to enable synchronous switching between variable and fixed frequency pumps in multi-pump water supply systems. It can synchronously switch the number of variable frequency pumps according to changes in water volume, achieving high-quality water supply and ensuring smooth transitions between variable and fixed frequency pumps with stable pressure and flow. The resulting system is still a pump variable and fixed frequency switching system primarily based on the frequency converter's PID control, supplemented by a multi-pump controller. Therefore, parameter settings are completed by the frequency converter itself; the controller requires no configuration and functions solely as a variable and fixed frequency switching component. This approach not only avoids limiting the frequency converter's capabilities but also helps it achieve greater efficiency.

[0035] Example 1: Multi-pump application

[0036] refer to Figure 1 , Figure 3 and Figure 5 As shown, a general-purpose frequency converter should have the following basic function terminals to work with the power frequency synchronous control board: DI1 for start, DI2 for emergency stop, 1TA / 1TB / 1TC for fault output, 2TA / 2TB / 2TC for operation output, FM for frequency setting (optional if no power frequency return is required), and AM for current setting (optional if no slip compensation function is available). Select the FM terminal on the frequency converter and connect it to the FMI controller. In power frequency mode, if a frequency value below 50Hz (e.g., 45Hz) is given, the frequency converter will exit power frequency mode, and after connecting to the frequency converter, speed tracking will initiate deceleration and braking until the circuit stops.

[0037] Example 2: Soft Start Application

[0038] refer to Figure 2 , Figure 4 and Figure 6 As shown, the corresponding circuits for the control terminals of this product and the inverter control terminals are as follows:

[0039] Terminal X0: Must be connected, equivalent to start / stop;

[0040] Terminal X1: Must be connected, equivalent to motor enable;

[0041] Terminal X5: Must be connected; indicates the inverter is in operation.

[0042] Terminal X7: Must be connected. Considering that some frequency converters do not have speed tracking start function, it is forbidden to connect to the frequency converter for start-up when switching off from the mains frequency, which will cause current surge.

[0043] Terminal X9: Must be connected, inverter fault input.

[0044] Terminal FMI: Must be connected to the inverter's given frequency output. Switching to the mains frequency is allowed after the given upper limit speed is reached.

[0045] Other terminals can be left unconnected; this is the default setting.

[0046] The inverter terminals should be configured accordingly: DI1, terminal start / stop; DI2, terminal emergency stop; 1TA / 1TB / 1TC are fault outputs; 2TA / 2TB / 2TC are running outputs. When using soft start, select the inverter terminal FM to connect to the controller FMI. At 50Hz, the operation will switch to mains frequency operation, but if a frequency value below 50Hz (such as 45Hz) is given, it will not exit the mains frequency operation.

[0047] The above description is merely a specific embodiment of this utility model, but the protection scope of this utility model is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this utility model, and these modifications or substitutions should all be covered within the protection scope of this utility model. Therefore, the protection scope of this utility model should be determined by the scope of the claims.

Claims

1. A variable frequency synchronous switching controller, comprising a control panel and matching electrical circuits, characterized in that, The control panel is connected to an external 24V DC power supply, which is the working power supply for this controller. The control panel is equipped with a GND terminal for grounding, R, S, and T terminals for connecting to the power grid, and U, V, and W terminals for connecting to the inverter output. The final wiring sequence for connecting to the motor is consistent. The control panel also includes the following terminals: X0: Synchronization enable terminal, interlocked with inverter start input, short-circuit disables. X1: Motor M1 enable, short-circuited with GND, and manually interlocked with MT1 (power frequency). X2: Motor M2 enable, short-circuited with GND, and manually interlocked with MT2 (power frequency). X3: Motor M3 enable, short-circuited with GND, and manually interlocked with MT3 (power frequency). X4: Motor M4 enable, short-circuited with GND, and manually interlocked with MT4 (power frequency). X5: X5 is the inverter operating status input, monitoring inverter status, and is interlocked with GN... D short-circuit for operation, open for stop; X6: X6 short-circuited with GND to disable system frequency / inverter switching; X7: Terminal X7 short-circuited with GND to prevent the system from switching from inverter to inverter after frequency / inverter switching; X8: X8 short-circuited with GND to disable the last frequency / inverter motor switching, disconnected from GND allows the last motor to switch between frequency / inverter; X9: Inverter fault input, used to indicate that a faulty motor has been removed from the operating array; Terminal UP is the mains voltage indicator, DC output terminal DC 0-10V corresponds to AC 0-500V input at AC terminals R, S, T; Terminal UG is the inverter output voltage indicator, DC output terminal DC 0-10V corresponds to AC 0-500V output at inverter terminals U, V, W; Terminal FMI is the inverter speed setpoint input terminal, DC 0-10V corresponds to inverter speed setpoint 0-50HZ; K0: Y00-Y01: Motor M1 inverter contactor control terminal; K1: Y10-Y11: Control terminal of motor M1 power frequency contactor; K2: Y20-Y21: Control terminal for motor M2 frequency converter contactor; K3: Y30-Y31: Control terminal for motor M2 power frequency contactor; K4: Y40-Y41: Control terminal for motor M3 frequency converter contactor; K5: Y50-Y51: Control terminal for motor M3 power frequency contactor; K6: Y60-Y61: Control terminal for motor M4 frequency converter contactor; K7: Y70-Y71: Control terminal for motor M4 power frequency contactor; K8: K8 is used to control the start and stop of the frequency converter. TC is connected to the frequency converter's common terminal COM. TC-TB: Normally closed contact is connected to the frequency converter's free stop terminal. TC-TA: Normally open contact is connected in series to the frequency converter's start command terminal. Terminal RS485 is the remote communication terminal for the control board.

2. The variable frequency synchronous switching controller according to claim 1, characterized in that, The electrical circuit includes pump M1, pump M2, and pump M3. Pumps M1, M2, and M3 are electrically connected to thermal overload circuits RJ1, RJ2, and RJ3, respectively. Thermal overload circuits RJ1, RJ2, and RJ3 are electrically connected to contactors KM1, KM3, and KM5, respectively. Thermal overload circuits RJ1, RJ2, and RJ3 are also electrically connected to contactors KM2, KM4, and KM6, respectively. The contactors KM1, KM2, and KM5... Contactors M1, KM3, and KM5 are electrically connected to the same frequency converter. The frequency converter is electrically connected to circuit breaker QF1. Contactors KM2, KM4, and KM6 are electrically connected to circuit breakers QF2, QF3, and QF4, respectively. Circuit breakers QF1, QF2, QF3, and QF4 are electrically connected to the same ammeter A. Ammeter A is electrically connected to circuit breaker QF0. Circuit breakers QF2, QF3, and QF4 are also electrically connected to the same voltmeter V. Circuit breaker QF4 is connected to the live wire L.

3. A variable frequency synchronous switching controller according to claim 2, characterized in that, The electrical circuit also includes fuse current-limiting resistors R1, R2, R3, and R4. Fuse current-limiting resistors R1 and R3 are connected to the neutral wire N, while fuse current-limiting resistors R2 and R4 are connected to the live wire L. Axial fans F1 and F2, installed inside the cabinet, are electrically connected between fuse current-limiting resistors R1 and R2. Indicator lights KM1-2 for variable frequency pump 1, KM2-2 for fixed frequency pump 1, KM3-2 for variable frequency pump 2, KM4-2 for fixed frequency pump 2, KM5-2 for variable frequency pump 3, and KM6-2 for fixed frequency pump 3 are electrically connected in parallel between fuse current-limiting resistors R3 and R4.

4. A variable frequency synchronous switching controller according to claim 2, characterized in that, The inverter is a general-purpose inverter for both domestic and international markets. The contactors are electrically interlocked when the action time is short enough not to affect the synchronous switching, contactors KM1 and KM2 are electrically interlocked, contactors KM3 and KM4 are electrically interlocked, and contactors KM5 and KM6 are electrically interlocked.

5. A variable frequency synchronous switching controller according to claim 2, characterized in that, Each of the pumps M1, M2, and M3 is equipped with a motor, motor excitation, and rotor.

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