A dual power supply switching device and its control method

Abstract

This invention relates to a dual-power switching device and its control method, which can operate in automatic, manual, and emergency modes. In automatic mode, the main power failure switching employs a phase synchronization judgment or phase-by-phase switching control strategy to ensure that the switching inrush current does not exceed the direct starting current of a three-phase asynchronous motor or a three-phase permanent magnet synchronous motor, thus preventing damage to the motor. The switching time is no more than 10ms, achieving rapid automatic switching. The manual mode allows the operator to set either the main power or the backup power supply. Forced switching uses synchronous switching, resulting in virtually no inrush current. When electronic components of the device malfunction, the device can operate in emergency mode, supplying power to the load via a mechanical transfer switch, improving the continuity of power supply to the load. This invention provides rapid main / backup power switching for three-phase asynchronous motors and three-phase permanent magnet synchronous motors, with the inrush current during switching being less than the direct starting current of the motor, and the switching time controlled within 10ms.

Description

Technical Field

[0001] This invention relates to a power supply technology, and more particularly to a dual-power fast switching device and control method for a three-phase asynchronous motor and a three-phase permanent magnet synchronous motor. Background Technology

[0002] In critical motor drive control systems, electrical loads are often configured with two power sources: a primary power source and a backup power source. If the primary power source fails, a rapid switch to the backup power source is required to maintain power supply. After repair, the system can switch back to the primary power source to ensure uninterrupted load operation and improve power supply reliability. Therefore, a dual-power rapid transfer switch is needed to achieve this function.

[0003] When a three-phase asynchronous motor or a three-phase permanent magnet synchronous motor experiences a power outage, the rotor continues to rotate due to inertia, inducing a voltage (often called residual voltage) on the stator. Reconnecting power after a short power outage often results in a significant current and torque surge. The transition process after reconnection varies depending on the power outage time and load conditions, and can be categorized into three cases: 1) If the power outage is extremely short, the magnitude and phase of the residual voltage on the motor stator are not significantly different from the power supply voltage, resulting in virtually no inrush current upon reconnection; 2) If the power outage is long and the speed has dropped considerably before power is restored, regardless of the residual voltage, the motor needs to undergo a surge current process lasting several seconds before returning to normal operation; 3) For motors with large rotational inertia, the back EMF may be out of phase with the backup power. If all three phases are connected simultaneously, a large transient inrush current, up to twice the direct starting current, will be generated, causing significant damage to the motor.

[0004] To reduce current and torque surges and limit switching inrush current, researchers have proposed delayed-start control and phase-by-phase soft-start control strategies. The delayed-start strategy involves switching on the backup power supply after a significant drop in motor rotor speed, essentially restarting the motor. However, the long switching time and excessive torque drop negatively impact the motor's mechanical load performance. The phase-by-phase soft-start control strategy switches on two phases first, then the third, then two phases again, then three, repeating this cycle five times to complete the switch. This strategy requires calculating the optimal thyristor firing angles for the two and third phases based on motor parameters, which can suppress inrush current. However, it heavily relies on the motor's inherent parameters, making widespread application inconvenient. Furthermore, the switching time of 100ms is too long for applications with strict switching time requirements. Summary of the Invention

[0005] To address the issues of current and torque surges and long switching times during power supply switching for motors during power outages, a dual-power switching device and its control method are proposed. This device provides a rapid dual-power conversion solution for three-phase asynchronous motors and three-phase permanent magnet synchronous motors, enabling selection between a primary power supply and a backup power supply. When the primary power supply fails, the device quickly switches to the backup power supply in less than 10ms. The switching inrush current is no greater than the direct starting current of the three-phase asynchronous motor or three-phase permanent magnet synchronous motor, thus preventing damage to the motor.

[0006] The technical solution of the present invention is as follows: a dual power supply switching device, wherein a main three-phase AC power supply and a backup three-phase AC power supply are selected to supply power to either a load three-phase AC asynchronous motor or a three-phase permanent magnet synchronous motor. The dual power supply switching device includes a first switching unit, a second switching unit, a mechanical transfer switch and a control unit.

[0007] One end of the first switching unit and the second switching unit are respectively connected to the three-phase output of the main three-phase AC power supply and the standby three-phase AC power supply, and the other end of the first switching unit and the second switching unit are connected to the common outputs A3, B3 and C3.

[0008] The mechanical changeover switch is a three-position changeover switch with S0, S1, and S2 positions. When one position is selected, the corresponding contact is connected to the output terminal, and the contacts in the other positions are not connected.

[0009] The three contacts of the mechanical transfer switch in position SO are connected to the three phases of the common output A3, B3, and C3. The three contacts of the mechanical transfer switch in position S1 are connected to the three phase outputs of the main three-phase AC power supply. The three contacts of the mechanical transfer switch in position S2 are connected to the three phase outputs of the standby three-phase AC power supply. The three outputs of the mechanical transfer switches in positions SO, S1, and S2 are all connected to the load three-phase AC asynchronous motor or three-phase permanent magnet synchronous motor.

[0010] The control unit includes a control board, an automatic / manual / emergency working mode selection switch, a forced power supply selection switch, a confirmation button, and a human-machine interface terminal. The control board collects the current and voltage signals of the main three-phase AC power supply, the backup three-phase AC power supply, and the load, and outputs control signals to the first switching unit and the second switching unit to control their on or off.

[0011] Preferably, the first switching unit, as the core unit for power switching, consists of three solid-state switches connected in series at the three-phase output terminals of the main three-phase AC power supply. The solid-state switches include anti-parallel thyristors and isolation drivers. They are turned on momentarily when the drive signal is high and turned off when the current crosses zero when the drive signal is low.

[0012] Preferably, the second switching unit, as the core unit for power switching, consists of three solid-state switches connected in series at the three-phase output terminals of the backup three-phase AC power supply. The solid-state switches are mainly composed of anti-parallel thyristors and isolation drivers. They are turned on momentarily when the drive signal is high and turned off when the current crosses zero when the drive signal is low.

[0013] A dual power supply switching device control method: In automatic mode, the mechanical transfer switch is in the SO position. The main three-phase AC power supply and the backup three-phase AC power supply are selected by the dual power supply switching device to supply power to the load three-phase AC asynchronous motor or three-phase permanent magnet synchronous motor. The control board determines that one current is completely zero-crossing and then turns off the other one to prevent the main and backup power supplies from being connected in parallel during switching and generating inrush current.

[0014] In manual mode, you can set either forced main power supply or forced backup power supply. The forced switching will be performed after the control board performs a synchronization judgment on the main and backup power phases.

[0015] In emergency mode, when the mechanical changeover switch is rotated to position S1 or S2, the contacts of the mechanical changeover switch are interlocked. After one set of contacts is disconnected, the other set of contacts will be connected, thus physically achieving the principle of disconnecting before closing.

[0016] Furthermore, the specific method for switching in the automatic working mode is as follows:

[0017] After the main three-phase AC power supply is cut off, if the output residual voltage is maintained at 80%-90% of the rated voltage, a delayed phase judgment is added. The control board will switch to backup power supply after synchronously judging the phase of the backup power and the residual voltage to suppress the switching inrush current.

[0018] After the main three-phase AC power supply is cut off, if the output residual voltage drops rapidly to below 80% of the rated voltage, a phase-by-phase switching control strategy is adopted. Two phases are switched on first, and the third phase is switched on after a delay, so that the switching inrush current is less than the direct starting current of the motor.

[0019] In automatic operation mode, when the main power supply is restored to above 95% of the rated voltage during standby power supply, the control board switches to main power supply after synchronizing the main and standby power phases to suppress the switching inrush current.

[0020] Furthermore, the synchronization determination is that the phase difference between the two phases is within 5°.

[0021] Furthermore, the specific method for phase-by-phase activation control is as follows: the initial two-phase firing angle α and the impulse voltage phase θ satisfy the following formula; after the two phases are activated, there is a 5ms delay before the third phase is activated; the peak values ​​of the three-phase impulse currents are the same, and the impulse current is minimized.

[0022]

[0023] Define β as the initial two-phase firing angle and the phase difference between the backup power supply, where 0 ≤ β < 2π. The value of β determines which two phases are activated first to ensure the switching is completed within 10 ms.

[0024] 0≤β<2 / 3π, first introduce phase BC, then introduce phase A;

[0025] 2 / 3π≤β<4 / 3π, first put phase AB in, then put phase C in;

[0026] 4 / 3π≤β<2π, so phase AC is introduced first, followed by phase B;

[0027] The voltage difference between the applied backup voltage u2 and the residual voltage e after the main power is cut off is defined as the impulse voltage Δu. Then, Δu = u2 - e = ΔUsin(ωt + θ).

[0028] ω is the angular velocity of the impulse voltage; θ is the phase of the impulse voltage.

[0029] The beneficial effects of this invention are as follows: The dual power supply switching device and its control method provide rapid switching between main and backup power for three-phase asynchronous motors and three-phase permanent magnet synchronous motors. During the switching process, the inrush current is less than the direct starting current of the motor, which will not cause damage to the motor. The switching time is controlled within 10ms, realizing rapid switching between dual power supplies. It can be widely used in the dual power supply of three-phase asynchronous motors and three-phase permanent magnet synchronous motors, providing reliable power supply for three-phase asynchronous motors and three-phase permanent magnet synchronous motors. Attached Figure Description

[0030] Figure 1 This is a system block diagram of the dual power supply switching device of the present invention;

[0031] Figure 2 This is a flowchart of the automatic / manual mode control of the dual power supply switching device of the present invention;

[0032] Figure 3 This is a flowchart of the emergency mode control of the dual power supply switching device of the present invention;

[0033] Figure 4 Three-phase current waveform diagram for direct starting of a 2.2kW three-phase AC asynchronous motor;

[0034] Figure 5 This is a waveform diagram of the automatic voltage switching when the main power fails and the backup power is 180° out of phase.

[0035] Figure 6 This invention provides a three-phase current waveform diagram for automatic switching when the main power fails, provided the main and backup power phases differ by 180°. Detailed Implementation

[0036] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0037] like Figure 1 The system block diagram of the dual power supply switching device shown includes a first input switching unit, a second switching unit, a mechanical changeover switch, and a control unit.

[0038] The first switching unit is connected at one end to phases A1, B1, and C1 of the three-phase AC power supply 1 (main power supply), and at the other end to phases A3, B3, and C3 of the mechanical transfer switch S0 and the second switching unit. As the core unit for power switching, the first switching unit consists of three solid-state switches (SSR1 to SSR3) connected in series at the three-phase output terminals of the three-phase AC power supply 1. The solid-state switches mainly consist of anti-parallel thyristors and isolation drivers, allowing for instantaneous turn-on when the drive signal is high and zero-crossing turn-off when the drive signal is low, exhibiting high voltage withstand capability and short-time current withstand capability.

[0039] The second switching unit is connected at one end to phases A2, B2, and C2 of the three-phase AC power supply 2 (backup power supply), and at the other end to the mechanical transfer switch S2 and phases A3, B3, and C3 of the first switching unit. As the core unit for power switching, the second switching unit consists of three solid-state switches (SSR4 to SSR6) connected in series at the three-phase output terminals of the three-phase AC power supply 2. The solid-state switches mainly consist of anti-parallel thyristors and isolation drivers, allowing for instantaneous turn-on when the drive signal is high and zero-crossing turn-off when the drive signal is low, exhibiting high voltage withstand capability and short-time current withstand capability.

[0040] The three contacts of the mechanical transfer switch S0 are connected to phases A3, B3, and C3 of the first and second switching units, respectively. The three contacts of the mechanical transfer switch S1 are connected to the three-phase output terminals of three-phase AC power supply 1 (main power supply), and the three contacts of the mechanical transfer switch S2 are connected to the three-phase output terminals of three-phase AC power supply 2 (standby power supply). All three output terminals of the mechanical transfer switches S0, S1, and S2 are connected to either a three-phase AC asynchronous motor or a three-phase permanent magnet synchronous motor as the load. The mechanical transfer switches are three-position switches, with S0, S1, and S2 positions. Selecting one position connects the corresponding contact to the output terminal, while the contacts in the other positions are not conductive. In automatic and manual operating modes, the mechanical transfer switch is in the S0 position, with the S0 contact conductive, and the output is connected to the load through the switching between the first and second switching units. When the first or second switching unit malfunctions and the system switches to emergency mode, the mechanical transfer switch can be turned to position S1. The S1 contact will be open, and three-phase AC power supply 1 (main power) will supply power to the three-phase AC asynchronous motor or three-phase permanent magnet synchronous motor through the mechanical switch. Similarly, the mechanical transfer switch can be turned to position S2. The S2 contact will be open, and three-phase AC power supply 2 (backup power) will supply power to the three-phase AC asynchronous motor or three-phase permanent magnet synchronous motor through the mechanical switch. The function of the mechanical transfer switch is to supply power to the load in emergency mode, improving the continuity of power supply to the device.

[0041] The control unit, as the carrier of the control method, controls the opening and closing of solid-state switches and plays a crucial role as the "brain" for achieving rapid switching. The control unit consists of a control board, an automatic / manual / emergency operating mode selection switch, a forced power supply selection switch, a confirmation button, and a human-machine interface terminal.

[0042] The control board receives control information from the automatic / manual / emergency working mode selection switch and the forced main power supply, forced backup power supply, and non-forced power supply selection switch. It detects the main power voltage and current (ua1, ub1, uc1, ia1, ib1, ic1), backup power voltage and current (ua2, ub2, uc2, ia2, ib2, ic2), and load voltage and current (ua3, ub3, uc3, ia3, ib3, ic3). Through the control method, it generates corresponding drive signals to control the opening and closing of the solid-state switches of the first switching unit and the second switching unit, thereby realizing the power supply conversion function.

[0043] The automatic / manual / emergency operating mode selection switch is located on the device panel, offering three operating modes: automatic, manual, and emergency. Users can manually select the device's operating mode. Under normal circumstances, automatic or manual operating mode is selected; in case of a malfunction or emergency, the emergency operating mode is selected.

[0044] The forced power supply selection switch is located on the device panel, offering three modes: forced main power supply, forced backup power supply, and no forced power supply. In manual operation mode, one of the main or backup power sources can be manually selected for forced power supply. The forced power supply function is disabled in automatic and emergency operation modes. During forced power supply switching, the device detects the phase of the main and backup power sources; forced power supply switching only occurs when the phases are identical, resulting in virtually no inrush current.

[0045] The confirmation button is located on the device panel. It does not take effect immediately after the status of the automatic / manual / emergency working mode selection switch and the forced power supply selection switch changes. It only takes effect after the confirmation button is pressed. Its main functions are to prevent undesirable intermediate states during the selection process of the two three-position rotary switches and to prevent accidental touch or misoperation.

[0046] The human-machine interface terminal displays relevant operating information, fault information, and power supply information collected by the control board via CAN communication, intuitively showing the main and backup power voltage and current, fault information, and power supply status of the device.

[0047] This invention follows the principle of "disconnect before closing". In automatic mode, one current is turned off after it has completely crossed zero, so as to prevent the main and backup power supplies from being connected in parallel during switching and generating inrush current. In emergency mode, the contacts of the mechanical transfer switch are interlocked. After one set of contacts is disconnected, the other set of contacts is turned on, thus physically realizing "disconnect before closing".

[0048] When the main power is cut off, the speed of a three-phase asynchronous motor or a three-phase permanent magnet synchronous motor does not immediately drop to zero due to rotational inertia. The rotating rotor cuts magnetic lines of force, generating an induced electromotive force at the input terminal, forming a "residual voltage". The amplitude and frequency of the residual voltage decrease as the speed decreases. The formula for the residual voltage is:

[0049] Where: e is the residual voltage; E is the residual voltage amplitude; ω e This is the residual pressure angular velocity, which is related to the rotational speed. This is the residual voltage phase.

[0050] The voltage difference between the applied backup voltage and the residual voltage is defined as the impulse voltage Δu.

[0051] Δu=u2-e=ΔUsin(ωt+θ) (2)

[0052] in: Δu is the impulse voltage; ΔU is the impulse voltage amplitude; ω is the impulse voltage angular velocity; θ is the impulse voltage phase.

[0053] An inrush voltage generates an inrush current across the motor's internal impedance. Given a fixed internal impedance, the magnitude of the inrush current is determined by the inrush voltage. A smaller inrush voltage results in a smaller inrush current. When the phase of the backup voltage is equal to the phase of the residual voltage, the inrush voltage is minimal, less than the rated voltage, and the resulting inrush current is less than the direct starting current. When the phase of the backup voltage is opposite to the phase of the residual voltage, the inrush voltage is maximum, reaching twice the rated voltage, generating twice the direct starting current, which may damage the motor. Therefore, controlling the inrush voltage during switching is an effective measure to suppress inrush current.

[0054] In automatic operation mode, when the output residual voltage is maintained at 80%-90% of the rated voltage after the main power is cut off, a delayed phase judgment is added, and the backup power and the residual voltage are switched when they are "quasi-synchronous" to suppress the switching inrush current.

[0055] In automatic operation mode, when the main power supply is restored to above 95% of the rated voltage during standby power supply, the main power supply will switch to main power supply when the main and standby power phases are "quasi-synchronized" to suppress the switching inrush current.

[0056] In manual operation mode, the system can be set to either forced main power supply or forced backup power supply. The forced switching will occur when the main and backup power phases are "quasi-synchronous" to suppress the switching inrush current.

[0057] In automatic operation mode, when the output residual voltage drops rapidly to below 80% of the rated voltage after the main power is cut off, it is required to switch to backup power supply within 10ms. Waiting for the backup power and residual voltage to switch "quasi-synchronously" is not allowed. A rapid switch is required. The first switching unit is turned off, and a phase-by-phase input control strategy is adopted. When the initial two-phase trigger angle is α, two phases are put into operation first, and the third phase is put into operation after a delay, so that the switching inrush current is less than the direct starting current of the motor.

[0058] Studies have shown that when the initial two-phase trigger angle α and the impulse voltage phase θ satisfy formula (3), after the two phases are put into operation, the third phase is put into operation after a 5ms delay. The peak values ​​of the three-phase impulse currents are the same, and the impulse current is minimized.

[0059]

[0060] Define β as the initial two-phase firing angle and the phase difference between the backup power supply, i.e. (0≤β<2π), determine which two phases to switch on first based on the value of β, so as to complete the conversion within 10ms.

[0061] 0≤β<2 / 3π, first introduce phase BC, then introduce phase A;

[0062] 2 / 3π≤β<4 / 3π, first put phase AB in, then put phase C in;

[0063] 4 / 3π≤β<2π, so phase AC is introduced first, followed by phase B.

[0064] The control algorithm of this invention adopts a power supply state-based control method, such as... Figure 2 , Figure 3 :

[0065] Step 1: Determine the device's operating mode. If it is in automatic mode, proceed to Step 2; if it is in manual mode, proceed to Step 6; if it is in emergency mode, proceed to Step 10.

[0066] Step 2: In automatic mode, determine the current power supply status of the device: main power supply, backup power supply, or neither main nor backup power supply. If it is in main power supply status, proceed to step 3; if it is in backup power supply status, proceed to step 4; if it is in neither main nor backup power supply status, proceed to step 5.

[0067] Step 3: Under main power supply, if the output residual voltage remains at 80% to 90% of the main power rated voltage after the main power is cut off, and the phase difference between the backup power phase and the output residual voltage is within 5°, turn off the main power solid-state switch. After the main power solid-state switch current crosses zero and turns off, turn on the backup power solid-state switch and switch to backup power supply mode, then proceed to step 4. If the output residual voltage drops below 80% of the rated voltage, turn off the main power solid-state switch. After the main power solid-state switch current crosses zero and turns off, turn on the corresponding two-phase backup power solid-state switches after a delay of the initial two-phase trigger angle α, and then turn on the other phase backup power solid-state switch after a further delay of 5ms, switch to backup power supply mode, and proceed to step 4.

[0068] Step 4: In standby power supply mode, determine whether the main power has recovered to 95% of the rated voltage. If it has not recovered to 95% of the rated voltage, maintain standby power supply and continue to monitor the main power voltage. If the main power has recovered to 95% of the rated voltage, when the phase difference between the standby power and the main power is within 5°, turn off the standby solid-state switch. After the standby solid-state switch current crosses zero and turns off, turn on the main power solid-state switch, switch to main power supply mode, and proceed to step 3.

[0069] Step 5: When neither the main nor backup power supply is working, first determine if the main power supply is normal. If the main power supply is normal, turn on the main power solid-state switch, turn off the backup power solid-state switch, switch to main power supply, and proceed to step 3. If the main power supply is not working but the backup power supply is normal, turn on the backup power solid-state switch, turn off the main power solid-state switch, switch to backup power supply, and proceed to step 4. If neither the main nor backup power supply is working, turn off both the main and backup power solid-state switches, maintain the state where neither the main nor backup power supply is working, repeat step 5, and wait for other instructions.

[0070] Step 6: In manual mode, determine the forced power supply mode. If forced mains power supply is enabled, proceed to step 7; if forced backup power supply is enabled, proceed to step 8; if forced power supply is not enabled, proceed to step 9.

[0071] Step 7: When manually forcing main power supply, determine the current power supply status. If under main power supply status, switch to forced main power supply status; if neither is under power supply status, turn on the main power solid-state switch, turn off the backup power solid-state switch, and switch to forced main power supply status; if under backup power supply status, wait until the phase difference between the backup power and main power is within 5°, turn off the backup power solid-state switch, and turn on the main power solid-state switch after the backup power solid-state switch current crosses zero and turns off, switching to forced main power supply status.

[0072] Step 8: When manually forcing backup power supply, determine the current power supply status. If in backup power supply status, switch to forced backup power supply status; if neither is powered, turn on the backup solid-state switch, turn off the main solid-state switch, and switch to forced backup power supply status; if in main power supply status, wait until the phase difference between the backup and main power is within 5°, turn off the main solid-state switch, and turn on the backup solid-state switch after the main solid-state switch current crosses zero and turns off, switching to forced backup power supply status.

[0073] Step 9: When manually powering on without forcing, turn off the main and backup solid-state switches and switch to a state where neither is powered on.

[0074] Step 10: In emergency mode, turn off the main and backup power solid-state switch, rotate the mechanical transfer switch to position S1 or S2, select the main power or backup power to supply power to the load, switch to emergency power supply mode, and execute step 1.

[0075] The experimental waveforms of the prototype of this invention, powered by a 2.2kW three-phase AC asynchronous motor, are shown. Figure 4 The waveforms show the three-phase current waveforms for direct starting of a 2.2kW three-phase AC asynchronous motor, with a peak starting current of 58.6A. Channels C2, C3, and C4 represent the currents of phases A, B, and C, respectively, with the vertical axis at 20A / div and the horizontal axis at 200ms / div.

[0076] Figure 5 When the main and backup power supplies are 180° out of phase, the voltage waveform automatically switches when the main power fails. C1, C2, and C3 represent the load line voltage (AB, BC, CA) waveforms, and C4 represents the backup power AB line voltage waveform. The vertical axis is 200V / div, and the horizontal axis is 10ms / div. When the main power fails, the load line voltage and the backup line voltage are 180° out of phase, which is the most severe situation. The load voltage drops rapidly to below 80% of the rated voltage. The prototype first switches to phase AB, and then switches to phase C after a 5ms delay, with a switching time of approximately 7ms.

[0077] Figure 6 When the main and backup power phases are 180° apart, the three-phase current waveforms automatically switch when the main power fails. Channels C1, C2, and C3 represent the currents of phases A, B, and C, respectively, with a vertical axis of 20A / div and a horizontal axis of 50ms / div. The switching inrush current is 50A, which is less than the peak value of the direct starting current.

[0078] This invention provides a dual-power rapid switching device, which can operate in automatic, manual, and emergency modes. In automatic mode, the main power failure switching uses phase synchronization judgment or phase-by-phase switching control strategies to ensure that the switching inrush current does not exceed the direct starting current of a three-phase asynchronous motor or a three-phase permanent magnet synchronous motor, thus preventing damage to the motor. The switching time is no more than 10ms, achieving rapid automatic switching. The manual mode allows the operator to set either the main power or the backup power supply. Forced switching uses synchronous switching, with virtually no inrush current. When electronic components of the device fail, it can operate in emergency mode, supplying power to the load via a mechanical transfer switch, improving the continuity of power supply. This invention provides rapid main / backup power switching for three-phase asynchronous motors and three-phase permanent magnet synchronous motors. The inrush current during switching is less than the direct starting current of the motor, preventing damage. The switching time is controlled within 10ms, achieving rapid dual-power switching. It can be widely used in dual-power supply systems for three-phase asynchronous motors and three-phase permanent magnet synchronous motors, providing reliable power supply.

[0079] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A control method for a dual-power switching device, wherein the dual-power switching device provides power to either a primary three-phase AC power supply or a backup three-phase AC power supply for a load three-phase AC asynchronous motor or a three-phase permanent magnet synchronous motor. The dual-power switching device includes a first switching unit, a second switching unit, a mechanical transfer switch, and a control unit. One end of the first switching unit and the second switching unit are respectively connected to the three-phase outputs of the primary three-phase AC power supply and the backup three-phase AC power supply, and the other end of the first switching unit and the second switching unit are connected to the common outputs A3, B3, and C3. The mechanical transfer switch is a three-position switch. The changeover switch has three positions: S0, S1, and S2. Selecting one position connects the corresponding contact to the output terminal, while the contacts in the other positions are not connected. The three contacts of the mechanical changeover switch in position S0 are connected to the three phases of the common output A3, B3, and C3. The three contacts of the mechanical changeover switch in position S1 are connected to the three phase outputs of the main three-phase AC power supply. The three contacts of the mechanical changeover switch in position S2 are connected to the three phase outputs of the standby three-phase AC power supply. The three outputs of the mechanical changeover switches in positions S0, S1, and S2 are all connected to the load three-phase AC asynchronous motor or three-phase permanent magnet synchronous motor. The control unit includes a control board, an automatic / manual / emergency working mode selection switch, a forced power supply selection switch, a confirmation button, and a human-machine interface terminal. The control board collects current and voltage signals from the main three-phase AC power supply, the backup three-phase AC power supply, and the load, and outputs control signals to the first and second switching units to control their on / off states. The first switching unit, as the core unit for power switching, consists of three solid-state switches connected in series at the three-phase output terminals of the main three-phase AC power supply. Each solid-state switch includes anti-parallel thyristors and an isolation driver; it instantaneously turns on when the drive signal is high and turns off when the drive signal is low. The second switching unit, also as the core unit for power switching, consists of three solid-state switches connected in series at the three-phase output terminals of the backup three-phase AC power supply. Each solid-state switch mainly consists of anti-parallel thyristors and an isolation driver; it instantaneously turns on when the drive signal is high and turns off when the drive signal is low. Its characteristic is that… When the automatic / manual / emergency working mode selection switch is in automatic working mode, the mechanical changeover switch is in the SO position. Under the control of the dual power supply switching device, the main three-phase AC power supply and the backup three-phase AC power supply can be selected to supply power to the load three-phase AC asynchronous motor or three-phase permanent magnet synchronous motor. The control board determines that one current is completely zero-crossing and then turns off the other one to prevent the main and backup power supplies from being connected in parallel during switching and generating inrush current. When the automatic / manual / emergency working mode selection switch is in manual working mode, it is set to force main power supply or force backup power supply. The forced switching is performed after the control board makes a synchronous judgment on the main and backup power phases. When the automatic / manual / emergency working mode selection switch is in emergency working mode, rotate the mechanical changeover switch to position S1 or S2. The contacts of the mechanical changeover switch are interlocked. After one set of contacts is disconnected, the other set of contacts will be connected, thus physically realizing the disconnection before connection. When the automatic / manual / emergency working mode selection switch is in automatic working mode, the specific method for dual power supply switching is as follows: After the main three-phase AC power supply is cut off, if the output residual voltage is maintained at 80%-90% of the rated voltage, a delayed phase judgment is added. The control board will switch to backup power supply after synchronously judging the phase of the backup power and the residual voltage to suppress the switching inrush current. After the main three-phase AC power supply is cut off, if the output residual voltage drops rapidly to below 80% of the rated voltage, a phase-by-phase switching control strategy is adopted. Two phases are switched on first, and the third phase is switched on after a delay, so that the switching inrush current is less than the direct starting current of the motor. In automatic operation mode, when the main power supply is restored to above 95% of the rated voltage during standby power supply, the control board switches to main power supply after synchronizing the main and standby power phases to suppress the switching inrush current.

2. The control method for a dual-power switching device according to claim 1, characterized in that, The synchronization determination is that the phase difference between the two phases is within 5°.

3. The control method for a dual-power switching device according to claim 2, characterized in that, The specific method for phase-by-phase input control: initial two-phase firing angle α Phase with impulse voltage θ If the following formula is satisfied, and the third phase is connected after a 5ms delay following the connection of the first two phases, the peak inrush current of all three phases will be the same, and the inrush current will be minimized. ， definition β The initial two-phase firing angle and the phase difference of the backup power supply. 0≤β< 2 π ,according to β The size determines which two phases are activated first, ensuring the conversion is completed within 10ms. First, phases BC are introduced, then phase A is introduced; First, phases AB are introduced, then phase C is introduced; First, phase AC is introduced, then phase B is introduced; The backup power voltage that is put into operation u 2. Residual voltage after main power failure e The voltage difference between them is defined as the impulse voltage. ,but , ω The impulse voltage angular velocity; θ This is the phase of the impulse voltage.

Images