Voltage sag protection circuit and method of alternating current contactor

Abstract

The invention provides a voltage sag protection circuit and method for an alternating current contactor, and the method comprises the steps: connecting a power input end of an alternating current contactor coil with an alternating current power supply through a first switching tube to form a first loop, and connecting a second switching tube and a first resistor to form a second loop; a third switch tube is connected to a high-voltage capacitor for power supply to form a third loop; when voltage sag occurs in the alternating current power supply, a control signal is output to control the switch tube to act, so that the first loop is controlled to be sequentially switched to the second loop, and the third loop is connected with the power supply input end of the alternating current contactor coil; the booster circuit is used for outputting the second direct-current voltage to the high-voltage capacitor, and the high-voltage capacitor maintains the fourth direct-current voltage after discharging and voltage reduction and outputs the fourth direct-current voltage to the power input end of the alternating-current contactor coil. The direct-current 300V switching voltage is provided for the contactor coil through the high-voltage capacitor during voltage sag, the 110V voltage can still be kept after discharging and voltage reduction, and an alternating-current contactor with the voltage being 300A or above can be kept in a closed state.

Description

Technical Field

[0001] The present invention relates to the technical field of power equipment protection, and in particular to a voltage sag protection circuit and method for an AC contactor. Background Art

[0002] A voltage sag is a sudden, sudden drop in voltage across a power supply line, typically within milliseconds to seconds, caused by an unexpected power system failure or the sudden increase in system load caused by the startup of large equipment. A voltage sag can cause AC contactors connected to the power source to trip, leading to unexpected downtime of production equipment, including equipment failure, data loss, and significant financial losses.

[0003] However, most existing voltage sag protection solutions are only applicable to AC contactors with a smaller capacity below 300A, and the solutions cannot be applied to AC contactors with larger capacity. In addition, they are unreliable during power switching. Existing solutions mainly use relays as power switching switches, but the action time from relay contact separation to closure is usually more than 5 milliseconds. In addition, the software detection and voltage sag judgment in the protection circuit all require time, and one cycle of AC power is 20 milliseconds. The switching needs to be completed before the AC contactor trips, which places high requirements on the response time of the protection circuit. Therefore, it is easy for the power switching to fail to be completed in time, resulting in the contactor tripping. In addition, when a voltage sag occurs, the coil still needs to be energized after switching the power supply to ensure closing. For large-capacity AC contactors, how to continuously provide a large holding voltage has become an issue that cannot be ignored.

[0004] Therefore, it is necessary to design a voltage sag protection circuit and method that can be applied to large-capacity AC contactors above 300A, enable the coil to safely discharge stored energy, ensure power switching reliability, and provide a voltage holding voltage. Summary of the Invention

[0005] The present invention provides a voltage sag protection circuit and method for an AC contactor, which are mainly used to solve the problems that existing voltage sag solutions are not applicable to large-capacity AC contactors above 300A, the contactor coils cannot safely discharge stored energy, switching is unreliable, and the holding voltage cannot be provided. The circuit and method can thus achieve the effect of being applicable to large-capacity AC contactors above 300A, enabling the coils to safely discharge stored energy, ensuring power switching reliability, and providing holding voltage.

[0006] The present invention achieves the above-mentioned purpose through the following technical solutions:

[0007] A voltage sag protection circuit for an AC contactor includes a power switching circuit, a control circuit, a high-voltage capacitor, a DC power supply circuit, and a boost circuit. The power switching circuit includes a first switching tube, a first resistor, a second switching tube, and a third switching tube. The power input end of the AC contactor coil is connected to the AC power supply through the first switching tube to form a first loop, and is connected to the second switching tube and the first resistor to form a second loop. The third loop is connected to the high-voltage capacitor through the third switching tube. The control circuit is connected to the control ends of the switching tubes and is used to control the operation of the switching tubes by outputting control signals when the AC power supply experiences a voltage sag, thereby controlling the first loop to switch to the second loop and the third loop in sequence to connect to the power input end of the AC contactor coil. The output end of the DC power supply circuit is connected to the input end of the boost circuit to provide a stable first DC voltage. The boost circuit is used to boost the first DC voltage and output a second DC voltage to the high-voltage capacitor. After the high-voltage capacitor discharges and reduces the voltage, it maintains a fourth DC voltage and outputs it to the power input end of the AC contactor coil.

[0008] A further solution is to further include a rectifier circuit, wherein the AC input end of the rectifier circuit is connected to the AC power supply, and the DC output end thereof is connected to the high-voltage capacitor, and is used to charge the high-voltage capacitor through the AC power supply.

[0009] A further solution is that the power switching circuit also includes a first diode, a second diode and a third diode, the first power input end of the AC contactor coil is connected to one end of the second switch tube through the first diode, the other end of the second switch tube is connected to one end of the high-voltage capacitor, and is connected to the second power input end of the AC contactor coil through the first resistor and the second diode; the other end of the high-voltage capacitor is connected to one end of the third switch tube, and the other end of the third switch tube is connected to the second power input end of the AC contactor coil through the third diode.

[0010] A further solution is that the control circuit includes a voltage detection unit and a main control unit, the voltage detection unit is used to detect the voltage value of the AC power supply and output a voltage detection signal to the main control unit, and the main control unit outputs the control signal to the control ends of the first switch tube, the second switch tube and the third switch tube respectively according to the voltage detection signal.

[0011] A further solution is that when the voltage value of the voltage detection signal is the allowable voltage value of the AC power supply, the main control unit outputs a first control signal to the first switch tube, which is used to control the first switch tube to be turned on, so that the AC contactor coil is powered by the AC power supply.

[0012] When a voltage sag occurs, the main control unit outputs a second control signal to the second switch tube to control the second switch tube to be turned on, so that the AC contactor coil discharges stored energy through the second circuit.

[0013] When the stored energy of the AC contactor coil is discharged, the main control unit outputs a third control signal to the third switch tube, which is used to control the third switch tube to be turned on, so that the high-voltage capacitor outputs a third DC voltage to the power input end of the AC contactor coil.

[0014] A further solution is that the duty cycle of the third control signal is set to match the discharge voltage curve of the high-voltage capacitor, so as to maintain the voltage output to the power input terminal of the AC contactor coil at the fourth DC voltage value.

[0015] A further solution is that the DC power supply circuit includes an AC-DC conversion circuit and a supercapacitor, the input end of the power conversion power supply is connected to the AC power supply, and is used to convert the AC voltage into the first DC voltage and supply it to both ends of the supercapacitor, and the supercapacitor is connected to the input end of the boost circuit to provide the first DC voltage.

[0016] A further solution is that the second DC voltage is 300V, the third DC voltage is a dynamic voltage of 110-300V, and the fourth DC voltage is 110V.

[0017] A voltage sag protection method for an AC contactor, applied to a voltage sag protection circuit for an AC contactor, comprises:

[0018] S1: AC power input, the first switch tube is turned on to make the AC contactor work normally.

[0019] S2: Determine whether the AC power source has a voltage sag. If not, repeat step S1; if so, control the first switch tube to be turned off and the second switch tube to be turned on.

[0020] S3: The coil of the AC contactor discharges stored energy through the first resistor.

[0021] S4: Controls the third switch tube to conduct, discharges the high-voltage capacitor, and provides a 300V DC voltage for the contactor coil.

[0022] S5: The DC power supply circuit provides a 300V DC voltage to the high-voltage capacitor through the boost circuit, and adjusts the supply voltage of the high-voltage capacitor to be maintained at 110V by controlling the duty cycle of the third switch tube.

[0023] Further plans include:

[0024] S6: Determine whether the voltage of the AC power supply returns to normal. If so, control the second switch tube and the third switch tube to be turned off and repeat step S1; if not, repeat step S5.

[0025] It can be seen that the present invention has the following beneficial effects:

[0026] 1. The present invention uses a high-voltage capacitor to provide a DC 300V switching voltage power supply to the coil of the AC contactor when an AC voltage sag occurs. This can ensure that the coil of the AC contactor with a capacity of 300A to 630A maintains a relatively high voltage, thereby keeping the AC contactor in a closed state, avoiding the problem of contactor tripping due to excessively low voltage in traditional solutions.

[0027] 2. The present invention provides a DC 300V voltage to the high-voltage capacitor through a DC power supply circuit and a boost circuit, so that the supercapacitor can still maintain a 110V voltage output after discharge and voltage reduction, ensuring the continuous voltage of the AC contactor coil, so that the AC contactor can continue to remain in the closed state before the voltage sag ends.

[0028] 3. In the initial stage of voltage sag, the present invention controls the second switch tube to conduct so that the charge stored in the AC contactor coil is discharged along the second circuit, thereby avoiding the problem that the energy stored in the coil is discharged along the circuit after the power is suddenly cut off, and the current shock causes interference with the circuit working sequence and damage to the device.

[0029] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 The figure is a schematic diagram of a voltage sag protection circuit of an AC contactor according to an embodiment of the present invention.

[0031] Figure 2 It is a circuit principle diagram of a capacitor charging according to an embodiment of the present invention.

[0032] Figure 3 This is a flow chart of a voltage sag protection method for an AC contactor according to an embodiment of the present invention. DETAILED DESCRIPTION

[0033] To make the purpose, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the described embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] An embodiment of a voltage sag protection circuit for an AC contactor

[0035] See also Figure 1 The present invention relates to a voltage sag protection circuit for an AC contactor, comprising a power switching circuit 40, a control circuit, a high-voltage capacitor C1, a DC power supply circuit 10, and a boost circuit 20. The power switching circuit 40 comprises a first switch tube Q1, a first resistor, a second switch tube Q2, and a third switch tube Q3. The power input end of the AC contactor coil 300 is connected to the AC power supply 200 through the first switch tube Q1 to form a first circuit, and is connected to the second switch tube Q2 and the first resistor to form a second circuit, and is connected to the high-voltage capacitor C1 through the third switch tube Q3 to form a third circuit. The control circuit is respectively connected to the above-mentioned switches. The control end of the tube is connected, and is used to control the action of the above-mentioned switching tube by outputting a control signal when a voltage sag occurs in the AC power supply 200, thereby controlling the first circuit to switch to the second circuit and the third circuit in sequence to connect to the power input end of the AC contactor coil 300; the output end of the DC power supply circuit 10 is connected to the input end of the boost circuit 20, and is used to provide a stable first DC voltage. The boost circuit 20 is used to boost the first DC voltage and output a second DC voltage to the high-voltage capacitor C1. The high-voltage capacitor C1 maintains a fourth DC voltage after the high-voltage capacitor is discharged and the voltage is reduced, and is output to the power input end of the AC contactor coil 300.

[0036] Specifically, in this embodiment, the first switch tube Q1, the second switch tube Q2, and the third switch tube Q3 are all insulated gate bipolar transistors (IGBTs) or field-effect transistors, which have a fast switching speed and a high switching frequency. Compared with the traditional method of using relay switches, the switching operation can be completed in a short time, meeting the need for timely power switching during voltage sags. In addition, IGBTs and field-effect transistors can withstand large currents and voltages and are suitable for the high-voltage environment of this embodiment. In addition, IGBTs and field-effect transistors have low on-resistance, which can reduce power loss, avoid arcing, and improve efficiency and life.

[0037] Specifically, this embodiment takes a single-phase 220V AC power supply 200 input and a 300A single-phase AC contactor as an example. The power input end of the AC contactor is connected to the AC power supply 200, one end of its main contact is connected to the live wire of the AC power supply 200, and the other end is connected to one end of the AC contactor coil 300 through the first switching tube Q1. The neutral wire of the AC power supply 200 is connected to the other end of the coil to form the first circuit.

[0038] See also Figure 2 In this embodiment, a rectifier circuit 30 is further included. The AC input end of the rectifier circuit 30 is connected to the AC power supply 200, and the DC output end thereof is connected to the high-voltage capacitor C1, which is used to charge the high-voltage capacitor C1 through the AC power supply 200.

[0039] Specifically, the rectifier circuit 30 of this embodiment adopts a rectifier bridge B2, which is used to perform bridge rectification on the input 220V AC power supply 200 and output about 311V DC power to charge the high-voltage capacitor C1.

[0040] In this embodiment, the power switching circuit 40 further includes a first diode D1, a second diode D2, and a third diode D3. The first power input terminal of the AC contactor coil 300 is connected to one end of the second switch tube Q2 through the first diode D1, the other end of the second switch tube Q2 is connected to one end of the high-voltage capacitor C1, and is connected to the second power input terminal of the AC contactor coil 300 through the first resistor R1 and the second diode D2; the other end of the high-voltage capacitor C1 is connected to one end of the third switch tube Q3, and the other end of the third switch tube Q3 is connected to the second power input terminal of the AC contactor coil 300 through the third diode D3.

[0041] Specifically, the first power input terminal of the AC contactor coil 300 of this embodiment is connected to the negative pole of the direct current, and the second power input terminal is connected to the positive pole of the direct current.

[0042] Specifically, the power switching circuit 40 of this embodiment further includes a fourth diode D4 , which is connected in reverse parallel to both ends of the second transistor to prevent current reverse flow and provide overvoltage protection.

[0043] In this embodiment, the control circuit includes a voltage detection unit and a main control unit. The voltage detection unit is used to detect the voltage value of the AC power supply 200 and output a voltage detection signal to the main control unit. The main control unit outputs the control signal to the control ends of the first switch tube Q1, the second switch tube Q2 and the third switch tube Q3 according to the voltage detection signal.

[0044] In this embodiment, when the voltage value of the voltage detection signal is the allowable voltage value of the AC power supply 200, the main control unit outputs a first control signal to the first switch tube Q1, which is used to control the first switch tube Q1 to be turned on, so that the AC contactor coil 300 is powered by the AC power supply 200.

[0045] Specifically, the allowable variation range of the input voltage of the AC power supply 200 in this embodiment is generally within ±10% of the rated voltage, that is, the allowable variation range of the voltage of the AC power supply 200 in this embodiment is 198V to 242V. When the voltage value of the voltage detection signal is within the above-mentioned allowable variation range, it is considered that the AC power supply 200 is normally supplying power, and the first switch tube Q1 is controlled to be continuously turned on.

[0046] When a voltage sag occurs, the main control unit outputs a second control signal to the second switch tube Q2 to control the second switch tube Q2 to be turned on, so that the AC contactor coil 300 discharges stored energy through the second circuit.

[0047] Specifically, in this embodiment, the first resistor R1 is a discharge resistor. The charge stored in the AC contactor coil 300 is discharged through the discharge resistor until all the charge is discharged. The discharge time is: t=RC, where R is the resistance of the discharge resistor and C is the charge capacity of the AC contactor coil 300.

[0048] When the stored energy of the AC contactor coil 300 is discharged, the main control unit outputs a third control signal to the third switch tube Q3 to control the third switch tube Q3 to be turned on, so that the high-voltage capacitor C1 outputs a third DC voltage to the power input terminal of the AC contactor coil 300.

[0049] Specifically, the third DC voltage in this embodiment is a DC dynamic voltage that is automatically adjusted in real time and has a voltage variation range of 110V to 300V.

[0050] Specifically, this embodiment determines whether the AC contactor coil 300 has discharged its stored energy by detecting the current signal from the AC contactor coil 300 and setting a discharge time within the control unit. During the initial discharge phase of high-voltage capacitor C1, its voltage is 300V, and the charge within it is rapidly released, causing the voltage to drop. When the voltage drops to 110V, the duty cycle of the control signal from the third switch Q3 is adjusted to stabilize at 110V.

[0051] In this embodiment, the duty cycle of the third control signal is set to match the discharge voltage curve of the high-voltage capacitor C1, so as to maintain the voltage output to the power input terminal of the AC contactor coil 300 at the fourth DC voltage value.

[0052] Specifically, in this embodiment, the duty cycle of the third control signal serves as a modulation factor for the discharge voltage of the high-voltage capacitor C1, thereby controlling the output voltage. As the duty cycle increases, the proportion of time the third control signal remains high increases. During each cycle, the third switch Q3 increases the duration of power flow in the third circuit, thereby increasing the output voltage. Conversely, the voltage decreases.

[0053] See also Figure 2 In this embodiment, the DC power supply circuit 10 includes an AC-DC conversion circuit and a supercapacitor C2. The input end of the power conversion circuit is connected to the AC power supply 200 for converting the AC voltage into the first DC voltage and supplying it to both ends of the supercapacitor C2. The supercapacitor C2 is connected to the input end of the boost circuit 20 for providing the first DC voltage.

[0054] Specifically, the AC power supply 200 of this embodiment converts 220V AC power into 15V DC power through the AC-DC conversion circuit to charge the supercapacitor C2, and the boost circuit 20 is used to boost the 15V DC power to DC300V for output.

[0055] Specifically, this embodiment can enable the coil of an AC contactor with a voltage of up to 630A to maintain voltage when the voltage temporarily sags, thereby allowing the AC contactor to remain in a closed state without tripping.

[0056] A voltage sag protection method for an AC contactor, applied to a voltage sag protection circuit for an AC contactor, comprises:

[0057] S1: AC power supply 200 is input, and the first switch tube Q1 is turned on to enable the AC contactor to work normally.

[0058] S2: Determine whether the AC power source 200 has a voltage sag. If not, repeat step S1; if so, control the first switch tube Q1 to be turned off and the second switch tube Q2 to be turned on.

[0059] S3: The coil of the AC contactor discharges stored energy through the first resistor.

[0060] S4: Control the third switch tube Q3 to be turned on, and the high-voltage capacitor C1 is discharged to provide a 300V DC voltage to the contactor coil 300.

[0061] S5: The DC power supply circuit 10 provides a 300V DC voltage to the high-voltage capacitor C1 through the boost circuit 20, and adjusts the supply voltage of the high-voltage capacitor C1 to be maintained at 110V by controlling the duty cycle of the third switch tube.

[0062] Specifically, in this embodiment, when AC power source 200 is operating normally, the control unit turns on first switch Q1, connecting contactor coil 300 to AC power source 200 via first switch Q1. At this point, the AC voltage charges high-voltage capacitor C1 to 300V DC via rectifier bridge B2.

[0063] When a voltage sag occurs on the AC power supply 200, the control unit controls the first switch Q1 to turn off and the second switch Q2 to turn on. The second switch Q2, along with the first resistor R1 and the second diode D2, forms a channel, short-circuiting the AC contactor coil 300 and releasing its stored energy. Once the energy has been released, the control unit controls the third switch Q3 to turn on, connecting the 300V DC power supply from the high-voltage capacitor C1 to the AC contactor coil 300, ensuring that the AC voltage sag does not cause the contactor to trip. The voltage curve of the high-voltage capacitor C1 is adjusted by the main control unit, controlling the on / off time ratio of the third switch Q3 and the boost circuit 20, so that the voltage of the high-voltage capacitor C1 drops to 110V DC and remains stable, preventing the AC contactor from tripping.

[0064] In this embodiment, it also includes:

[0065] S6: Determine whether the voltage of the AC power source 200 returns to normal. If so, control the second switch tube Q2 and the third switch tube Q3 to turn off and repeat step S1; if not, repeat step S5.

[0066] Specifically, in step S6 of this embodiment, when the voltage of the AC power source 200 has not returned to normal, the following steps are further included:

[0067] S61: Determine whether the set time has been reached. If so, control the second switch tube Q2 and the third switch tube Q3 to turn off and open the AC contactor. If not, repeat step S6.

[0068] Specifically, in this embodiment, if the voltage sag has not ended after the set time, it means that a fault has occurred in the power system and cannot be resolved in a short time. In order to protect the power equipment, the AC contactor is opened.

[0069] The above embodiments are only preferred embodiments of the present invention and cannot be used to limit the scope of protection of the present invention. Any non-substantial changes and replacements made by technicians in this field on the basis of the present invention fall within the scope of protection required by the present invention.

Claims

1. A voltage sag protection circuit for an AC contactor, characterized in that: include: A power switching circuit, a control circuit, a high-voltage capacitor, a DC power supply circuit and a boost circuit, wherein the power switching circuit comprises a first switch tube, a first resistor, a second switch tube and a third switch tube, wherein the power input end of the AC contactor coil is connected to the AC power supply through the first switch tube to form a first loop, and is connected to the second switch tube and the first resistor to form a second loop, and is connected to the high-voltage capacitor to form a third loop through the third switch tube; the control circuit is respectively connected to the control ends of the above-mentioned switch tubes, and is used to control the action of the above-mentioned switch tubes by outputting control signals when the AC power supply has a voltage sag, thereby controlling the first loop to switch to the second loop and the third loop in sequence to connect to the power input end of the AC contactor coil; the output end of the DC power supply circuit is connected to the input end of the boost circuit to provide a stable first DC voltage, and the boost circuit is used to boost the first DC voltage and output a second DC voltage to supply the high-voltage capacitor, and the high-voltage capacitor maintains a fourth DC voltage after discharge and voltage reduction and outputs it to the power input end of the AC contactor coil.

2. The voltage sag protection circuit of the AC contactor according to claim 1, characterized in that: It also includes a rectifier circuit, wherein the AC input end of the rectifier circuit is connected to the AC power supply, and the DC output end of the rectifier circuit is connected to the high-voltage capacitor, and is used to charge the high-voltage capacitor through the AC power supply.

3. The voltage sag protection circuit of the AC contactor according to claim 1, characterized in that: The power switching circuit also includes a first diode, a second diode and a third diode. The first power input end of the AC contactor coil is connected to one end of the second switch tube through the first diode, the other end of the second switch tube is connected to one end of the high-voltage capacitor, and is connected to the second power input end of the AC contactor coil through the first resistor and the second diode; the other end of the high-voltage capacitor is connected to one end of the third switch tube, and the other end of the third switch tube is connected to the second power input end of the AC contactor coil through the third diode.

4. The voltage sag protection circuit of the AC contactor according to claim 1, characterized in that: The control circuit includes a voltage detection unit and a main control unit. The voltage detection unit is used to detect the voltage value of the AC power supply and output a voltage detection signal to the main control unit. The main control unit outputs the control signal to the control ends of the first switch tube, the second switch tube and the third switch tube respectively according to the voltage detection signal.

5. The voltage sag protection circuit of the AC contactor according to claim 4, characterized in that: When the voltage value of the voltage detection signal is the allowable voltage value of the AC power supply, the main control unit outputs a first control signal to the first switch tube, which is used to control the first switch tube to be turned on so that the AC contactor coil is powered by the AC power supply; When a voltage sag occurs, the main control unit outputs a second control signal to the second switch tube, which is used to control the second switch tube to be turned on, so that the AC contactor coil discharges stored energy through the second circuit; When the energy storage of the AC contactor coil is discharged, the main control unit outputs a third control signal to the third switch tube to control the third switch tube to be turned on, so that the high-voltage capacitor outputs a third DC voltage to the power input terminal of the AC contactor coil.

6. The voltage sag protection circuit for AC contactor according to claim 5, characterized in that: The duty cycle of the third control signal is set to match the discharge voltage curve of the high-voltage capacitor, and is used to maintain the voltage output to the power input terminal of the AC contactor coil at the fourth DC voltage value.

7. The voltage sag protection circuit of the AC contactor according to claim 1, characterized in that: The DC power supply circuit includes an AC-DC conversion circuit and a super capacitor. The input end of the power conversion power supply is connected to the AC power supply for converting the AC voltage into the first DC voltage and supplying it to both ends of the super capacitor. The super capacitor is connected to the input end of the boost circuit for providing the first DC voltage.

8. The voltage sag protection circuit for an AC contactor according to any one of claims 1 to 7, characterized in that: The second DC voltage is 300V, the third DC voltage is a dynamic voltage of 110-300V, and the fourth DC voltage is 110V.

9. A voltage sag protection method for an AC contactor, characterized in that: A voltage sag protection circuit for an AC contactor according to any one of claims 1 to 8, comprising: S1: AC power input, the first switch tube is turned on to make the AC contactor work normally; S2: Determine whether the AC power source has a voltage sag, if not, repeat step S1; if yes, control the first switch tube to be turned off and the second switch tube to be turned on; S3: the coil of the AC contactor discharges stored energy through a first resistor; S4: Control the third switch tube to conduct, the high-voltage capacitor discharges, and provides a 300V DC voltage for the contactor coil; S5: The DC power supply circuit provides a 300V DC voltage to the high-voltage capacitor through a boost circuit, and adjusts the supply voltage of the high-voltage capacitor to be maintained at 110V by controlling the duty cycle of the third switch tube.

10. The voltage sag protection method for AC contactor according to claim 9, characterized in that: Also includes: S6: Determine whether the voltage of the AC power source returns to normal. If so, control the second switch tube and the third switch tube to be turned off, and repeat step S1; If not, repeat step S5.

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