Control circuit and control method when power supply voltage of low voltage AC control loop is abnormal

Abstract

The present invention relates to a control circuit and a control method when the power supply voltage of a low-voltage AC control circuit is abnormal. The method comprises three parts: a voltage detection unit inputs to a main control unit, a main control unit controls a reset control unit, an interlocking control unit, and a start control unit. If there is an interlocking device with interlocking control in the low-voltage AC control circuit, or a protection device that needs to be reset before it can be re-run due to abnormal power supply voltage, when the short-term abnormal power supply voltage does not exceed the allowed time, the main control unit can control the interlocking control unit to output a closed contact so that the interlocking device does not stop because the power-consuming device has exited operation. After the voltage is normal, the main control unit uses the power-consuming device to re-operate according to the delay setting time of the power-consuming device; if there is a protection device in the control circuit that needs to be reset before it can be re-operated due to abnormal power supply voltage, the main control unit controls the reset control unit to output a short-term closed contact after the voltage is normal to reset the protection device.

Description

Technical Field

[0001] The present invention relates to the control of electrical equipment in a low-voltage AC control loop, in particular to a control circuit and a control method when the power supply voltage of the low-voltage AC control loop is abnormal, and belongs to the field of electromechanics. Background Art

[0002] A large number of electrical equipment such as motors are used in industrial control circuits. These electrical equipment are generally controlled by AC contactors. Due to the large capacity of electrical equipment, the impact current is large when starting, causing grid voltage fluctuations and affecting the normal operation of other equipment in the same grid. Therefore, these equipment will use a variety of starting methods such as auto-coupling step-down starting, star-delta starting, soft starting, and variable frequency starting when starting. These starting methods can significantly reduce the starting current and reduce grid voltage fluctuations when the motor starts, but make the control link complicated. When the grid voltage is abnormal, some control links will exit operation due to the influence of voltage, causing the motor to shut down and the control process to be interrupted. If the grid voltage abnormality is short, these equipment can be put back into operation in time after the voltage returns to normal, and will not affect normal production or have little impact. Therefore, restart devices are added to the control circuit, including restart controllers, restart control cabinets, anti-swaying devices, etc. However, since some control devices have interlocking control relationships, the shutdown of one device will cause other devices to shut down; some devices have protection functions, such as soft starters, frequency converters, motor controllers, etc., which will be protected when the voltage is abnormal, and the device will exit operation and must be reset before running again. Therefore, these restart devices can play a good role in the control circuit of a single AC contactor, but they cannot be used for the control circuit of AC contactor circuits with interlocking control and control circuits of frequency converters, soft starters, motor controllers and other control devices with protection functions. Summary of the invention

[0003] The purpose of the present invention is to overcome the problem that the existing restart device is only suitable for a single AC contactor control circuit, but not suitable for a control circuit of an electrical equipment with interlocking control or protection function. The present invention provides a control circuit and a control method for an abnormal power supply voltage in a low-voltage AC control circuit, so that when the power supply voltage is abnormal for a short time, the interlocking equipment of the interlocking control will not be affected, and the electrical equipment with protection function can be restarted after the power supply voltage returns to normal.

[0004] The technical solution adopted by the present invention is: a control circuit when the power supply voltage of a low-voltage AC control loop is abnormal, including a voltage detection unit, a main control unit, a reset control unit and a start control unit, the voltage detection unit is electrically connected to the main control unit, the main control unit is electrically connected to the reset control unit and the start control unit respectively, the voltage detection unit inputs a voltage signal to the main control unit, and the main control unit outputs control signals for controlling the reset control unit and the start control unit respectively.

[0005] Furthermore, the control circuit for when the power supply voltage of the low-voltage AC control loop is abnormal also includes an interlocking control unit, which is electrically connected to the main control unit, and the main control unit outputs a control signal for controlling the interlocking control unit.

[0006] Furthermore, the voltage detection unit includes at least two voltage inputs: power supply voltage and working voltage of the electrical equipment (hereinafter referred to as working voltage). The power supply voltage L and N terminals are respectively connected to the 1 and 2 terminals of the voltage detection unit input terminal, and the power supply voltage is provided to the voltage detection unit through the 1 and 2 terminals; the working voltage A of the electrical equipment is electrically connected to the 3 terminal of the voltage detection unit input terminal, and shares the N terminal with the power supply voltage. The output terminal of the voltage detection unit is electrically connected to the input terminal of the main control unit. The voltage detection unit inputs the voltage signal of the power supply voltage and the working voltage after the voltage is stepped down into the main control unit, and the main control unit determines the operating status of the electrical equipment and whether the power supply voltage is abnormal based on the two voltages; the main control unit The output ends are electrically connected to the input ends of the reset control unit, the interlocking control unit, and the start control unit respectively; the main control unit outputs voltage signals to control the closing or opening of the output contacts of the reset control unit, the interlocking control unit, and the start control unit respectively; the output contacts of the reset control unit are connected to the protection device to reset the protection device; the output contacts of the interlocking control unit are connected to the control circuit of the interlocking device that has an interlocking control relationship with the electrical equipment, and when the electrical equipment stops running, a false operation signal is provided to the interlocking device that has an interlocking control relationship with the electrical equipment to prevent the interlocking device from stopping running; the output contacts of the start control unit are connected in parallel to the 1 and 3 terminals of the voltage detection unit input or the two ends of the start button.

[0007] Furthermore, the voltage detection unit includes a circuit for reducing the AC voltage to a low voltage that can be recognized by the main control unit.

[0008] Furthermore, the main control unit is a single chip microcomputer, which can receive at least two voltage inputs and can output at least three voltage signals.

[0009] Furthermore, the reset control unit, interlocking control unit and starting control unit are all relays controlled by the main control unit, and the relay has at least one pair of normally open contacts, which are closed or opened by the main control unit.

[0010] A control method when the power supply voltage of a low-voltage AC control loop is abnormal. The voltage detection unit inputs a voltage signal after voltage reduction to a main control unit. The voltage detection unit includes at least two input voltages, namely, the power supply voltage and the working voltage of an electrical device. The main control unit detects the power supply voltage and the working voltage through the input of the voltage detection unit, judges the power supply voltage to determine whether the power supply voltage is abnormal, and judges the working voltage to determine whether the operating state of the electrical device is running or stopped. The main control unit controls the output contacts of the reset control unit, the interlocking control unit, and the start control unit to close or open according to the power supply voltage and the operating state of the electrical device.

[0011] Furthermore, the control method for the abnormal power supply voltage of the low-voltage AC control circuit is divided into three parts according to whether the power supply voltage is abnormal and whether the abnormal time exceeds the set value of the allowable voltage abnormal time of the electrical equipment (hereinafter referred to as the allowable time): the power supply voltage is normal, the power supply voltage abnormal time exceeds the allowable time, and the power supply voltage abnormal time does not exceed the allowable time. The control method is as follows:

[0012] A. When the power supply voltage is normal, the main control unit detects the input of the voltage detection unit and determines whether the electrical equipment is running or stopped according to the working voltage. If the working voltage is normal, the electrical equipment is running, and if the working voltage is abnormal, the electrical equipment is stopped. When the electrical equipment is running, the main control unit can control the interlocking control unit to output a closed contact or not. If the interlocking control unit outputs a closed contact, when the electrical equipment stops, the interlocking control unit needs to be controlled to open the closed contact.

[0013] B. When the power-consuming equipment is running, when the main control unit detects abnormal power supply voltage through the voltage detection unit, if the power-consuming equipment is connected to other interlocking devices with interlocking control, the main control unit controls the interlocking control unit to output a closed contact, and the interlocking device can continue to run; if the power-consuming equipment is running, the interlocking control unit has output a closed contact, and this step can be omitted;

[0014] Due to the different durations of power supply voltage abnormality, there are two situations: exceeding the allowed time and not exceeding the allowed time:

[0015] 1) Exceeding the allowed time: If the power supply voltage abnormal time exceeds the allowed time, the main control unit controls the interlocking control unit to output the closed contact disconnected; if the interlocking control unit does not output the closed contact, this step can be omitted, exit the control process, and wait for the next operation of the power-consuming equipment;

[0016] 2) Does not exceed the allowed time: When the power supply voltage returns to normal within the allowed time, the main control unit controls the reset control unit to output a short-time closed contact to reset the protection device. If there is no protection device that needs to be reset, this step can be omitted. When the normal power supply voltage time reaches the delayed start setting time of the electrical equipment, the main control unit controls the start control unit to output a short-time closed contact, and the electrical equipment starts running again. After the electrical equipment starts running again, if the interlocking control unit does not need to output a closed contact during normal operation, the closed contact output by the interlocking control unit needs to be disconnected. If the contact is not closed, this step can be omitted.

[0017] The advantages of the present invention are: if there are interlocking devices with interlocking control in the low-voltage AC control loop, or protective devices that will trigger protective actions due to abnormal voltage and need to be reset before they can be re-operated, when the short-term abnormality of the power supply voltage does not exceed the allowed time, the main control unit can control the interlocking control unit to output a closed contact, so that the interlocking device does not stop because the electrical equipment has exited operation. After the power supply voltage is normal, the main control unit uses the electrical equipment to re-operate according to the delay setting time of the electrical equipment; if there are protective devices in the control loop that cause protective actions due to abnormal power supply voltage and need to be reset before they can be re-operated, the main control unit controls the reset control unit to output a closed contact after the power supply voltage is normal, so that the protective device is reset and can be re-operated. Through the above control, the electrical equipment can quickly re-operate after a short-term power supply voltage abnormality, maintaining the continuous operation of the production process.

[0018] The control method for abnormal power supply voltage of a low-voltage AC control loop of the present invention has all controls connected in parallel in the original control loop, does not affect the normal operation of the original electrical equipment, and does not require modification of the electrical equipment in the original control loop. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The present invention is further described below with reference to the accompanying drawings and embodiments, but is not intended to limit the present invention.

[0020] Figure 1 It is a schematic diagram of the control circuit of the present invention when the power supply voltage of the low-voltage AC control loop is abnormal;

[0021] Figure 2 is a circuit diagram of the practical application of the present invention, wherein (a) is a connection diagram of a low voltage AC control circuit, (b) is a connection diagram of a protection device, and (c) is a control circuit diagram of an interlocking device;

[0022] In the figure, 01, voltage detection unit; 02, main control unit; 03, reset control unit; 04, interlocking control unit; 05, start control unit; 06, electrical equipment; 07, stop button; 08, start button; 09, protection contact; 10, protection equipment; 11, interlocking contact; 12, interlocking equipment. DETAILED DESCRIPTION

[0023] Example 1

[0024] A control circuit for when the power supply voltage of a low-voltage AC control loop is abnormal includes a voltage detection unit 01, a main control unit 02, a reset control unit 03 and a start control unit 05. The voltage detection unit 01 is electrically connected to the main control unit 02, and the main control unit 02 is electrically connected to the reset control unit 03 and the start control unit 05 respectively. The voltage detection unit 01 inputs a voltage signal to the main control unit 02, and the main control unit 02 outputs a control signal for controlling the reset control unit 03 and the start control unit 05 respectively.

[0025] Example 2

[0026] like Figure 1 As shown, the control circuit when the power supply voltage of the low-voltage AC control loop is abnormal includes a voltage detection unit 01, a main control unit 02, a reset control unit 03, an interlocking control unit 04 and a start control unit 05. The voltage detection unit 01 is electrically connected to the main control unit 02, and the main control unit 02 is electrically connected to the reset control unit 03, the interlocking control unit 04 and the start control unit 05 respectively. The voltage detection unit 01 inputs a voltage signal to the main control unit 02, and the main control unit 02 outputs a control signal for controlling the reset control unit 03, the interlocking control unit 04 and the start control unit 05 respectively.

[0027] The control method when the power supply voltage of the low-voltage AC control loop is abnormal is: the voltage detection unit 01 inputs the voltage signal after the voltage is stepped down to the main control unit 02, and the voltage detection unit 01 includes at least two input voltages, namely the power supply voltage and the working voltage of the electrical equipment 06; the main control unit 02 detects the power supply voltage and the working voltage through the input of the voltage detection unit 01, judges the power supply voltage to determine whether the power supply voltage is abnormal, and judges the working voltage to determine whether the operating state of the electrical equipment 06 is running or stopped; the main control unit 02 controls the output contacts of the reset control unit 03, the interlocking control unit 04, and the start control unit 05 to close or open according to the power supply voltage and the operating state of the electrical equipment 06.

[0028] Example 3

[0029] On the basis of Example 2, Figure 2As shown in the figure, the control circuit when the power supply voltage of the low-voltage AC control loop is abnormal: the voltage detection unit 01 includes at least two voltage inputs: the power supply voltage and the working voltage of the electrical equipment 06. The power supply voltage L and N terminals are respectively connected to the 1 and 2 terminals of the input end of the voltage detection unit 01, and the power supply voltage is provided to the voltage detection unit 01 through the 1 and 2 terminals; a stop button 07 and a start button 08 are connected in series between the power supply voltage L terminal and the working voltage A terminal of the electrical equipment 06; the working voltage A of the electrical equipment 06 is electrically connected to the 3 terminal of the input end of the voltage detection unit 01, and the power supply voltage is connected to the 1 and 2 terminals of the input end of the voltage detection unit 01. The output end of the voltage detection unit 01 is electrically connected to the input end of the main control unit 02. The voltage detection unit 01 inputs the voltage signal after the power supply voltage and the working voltage are stepped down to the main control unit 02, and the main control unit 02 determines the operating state of the electrical equipment 06 and whether the power supply voltage is abnormal according to the two voltages; the output end of the main control unit 02 is electrically connected to the input ends of the reset control unit 03, the interlocking control unit 04, and the start control unit 05 respectively. The main control unit 02 is electrically connected to the voltage detection unit 01, the reset control unit 03, the interlocking control unit 04, and the start control unit 05 common ground; the main control unit 02 outputs voltage signals to respectively control the closing or disconnection of the output contacts of the reset control unit 03, the interlocking control unit 04, and the start control unit 05; the output contacts of the reset control unit 03 are connected to the protection device 10 to reset the protection device 10, and the protection contacts 09 of the protection device 10 are connected in series in the control circuit of the power-consuming device 06; the output contacts of the interlocking control unit 04 are connected to the control circuit of the interlocking device 12 that has an interlocking control relationship with the power-consuming device 06, and are connected in parallel at both ends of the interlocking contacts 11 in the control circuit of the interlocking device 12, When 06 stops running, a false running signal is provided to the interlocking device 12 which has an interlocking control relationship with the electrical equipment 06 to prevent the interlocking device 12 from stopping running; the output contacts of the start control unit 05 are connected in parallel to the 1 and 3 terminals of the input end of the voltage detection unit 01 or the two ends of the start button 08; a normally open contact of the electrical equipment 06 is connected in series in the control circuit of the interlocking device 12 as an interlocking contact 11. After the electrical equipment 06 is running, the interlocking contact 11 is closed and the interlocking device 12 can run. When the electrical equipment 06 stops, the interlocking contact 11 is disconnected and the interlocking device 12 also stops running.

[0030] The control method for abnormal power supply voltage in low-voltage AC control circuit: According to whether the power supply voltage is abnormal and whether the abnormal time exceeds the setting value of the voltage abnormal time allowed by the electrical equipment 06, it is divided into three parts: the power supply voltage is normal, the power supply voltage abnormal time exceeds the allowed time, and the power supply voltage abnormal time does not exceed the allowed time. The control method is as follows:

[0031] A. When the power supply voltage is normal, the main control unit 02 detects the input of the voltage detection unit 01, and determines whether the electric device 06 is running or stopped according to the working voltage. If the working voltage is normal, the electric device 06 is running, and if the working voltage is abnormal, the electric device 06 is stopped. When the electric device 06 is running, the main control unit 02 can control the interlocking control unit 04 to output a closed contact, or not to output a closed contact. If the interlocking control unit 04 outputs a closed contact, when the electric device 06 stops, it is necessary to control the interlocking control unit 04 to open the closed contact.

[0032] B. When the power consumption device 06 is running, when the main control unit 02 detects abnormal power supply voltage through the voltage detection unit 01, if the power consumption device 06 is connected to other interlocking devices 12 with interlocking control, the main control unit 02 controls the interlocking control unit 04 to output a closed contact, and the interlocking device 12 can continue to run; if the power consumption device 06 is running, the interlocking control unit 04 has output a closed contact, and this step can be omitted;

[0033] Due to the different durations of power supply voltage abnormality, there are two situations: exceeding the allowed time and not exceeding the allowed time:

[0034] 1) Exceeding the allowed time: If the power supply voltage abnormal time exceeds the allowed time, the main control unit 02 controls the interlocking control unit 04 to output the closed contact disconnection. If the interlocking control unit 04 does not output the closed contact, this step can be omitted, and the control process is exited until the next operation of the power-consuming device 06;

[0035] 2) Does not exceed the allowed time: If the power supply voltage returns to normal within the allowed time, the main control unit 02 controls the reset control unit 03 to output a short-time closed contact to reset the protection device 10, so that the protection contact 09 of the protection device 10 is closed. If there is no protection device 10 that needs to be reset, this step can be omitted; the reset control unit 03 must output the closed contact before the normal time of the power supply voltage reaches the delayed start setting time of the electrical equipment 06. When the normal time of the power supply voltage reaches the delayed start setting time of the electrical equipment 06, the main control unit 02 controls the start control unit 05 to output a short-time closed contact, and the electrical equipment 06 starts running again; after the electrical equipment 06 starts running again, if the interlocking control unit 04 does not need to output the closed contact during normal operation, the closed contact output by the interlocking control unit 04 needs to be disconnected. If the contact is not closed, this step can be omitted.

[0036] Example 4

[0037] Based on the embodiment 2 or 3, preferably, the voltage detection unit 01 includes a circuit for reducing the AC voltage to a low voltage that can be recognized by the main control unit 02. This is a well-known technology for those skilled in the art and will not be described here one by one.

[0038] Preferably, the main control unit 02 is a single chip microcomputer, which can receive at least two voltage inputs and output at least three voltage signals.

[0039] Further preferably, the main control unit 02 is a single chip microcomputer XC866 or other control elements.

[0040] Preferably, the reset control unit 03, the interlocking control unit 04 and the start control unit 05 are all relays controlled by the main control unit 02, and the relay has at least one pair of normally open contacts, which are controlled to be closed or opened by the main control unit 02.

[0041] like Figure 2 As shown, the voltage detection unit 01 includes at least two voltage inputs: power supply voltage and working voltage of the electrical equipment. The power supply voltages L and N are connected to terminals 1 and 2 of the voltage detection unit 01 respectively. The working voltage A of the electrical equipment is connected to terminal 3 of the voltage detection unit 01, and the N terminal is shared with the power supply voltage. A stop button 07 and a start button 08 are connected in series between the power supply voltage L terminal and the working voltage A terminal of the electrical equipment 06. The electrical equipment 06 has a normally open contact connected to both ends of the start button 08 (i.e.: Figure 2 (B terminal in (a), working voltage terminal A), the voltage detection unit 01 inputs the voltage signal of the power supply voltage and the working voltage after the voltage is stepped down to the main control unit 02, and the main control unit 02 determines the operating status of the electrical equipment and whether the power supply voltage is abnormal based on the two voltages. The main control unit can receive at least two voltage inputs and can output at least three voltage signals. The output voltage signals respectively control the closing or opening of the contacts of the reset control unit 03, the interlocking control unit 04, and the start control unit 05. The main control unit 02 shares a common ground with the voltage detection unit 01, the reset control unit 03, the interlocking control unit 04, and the start control unit 05. The protection contact 09 of the protection device 10 is connected in series in the control circuit of the electrical equipment 06. The wiring terminals 4 and 5 of the reset control unit 03 are connected in parallel to the reset terminals 101 and 102 of the protection device 10, see Figure 2 (b) The terminals 6 and 7 of the interlocking control unit 04 are connected in parallel to the two ends of the interlocking contact 11. The terminals 8 and 9 of the start control unit 05 are connected in parallel to the terminals 1 and 3 of the voltage detection unit 01 or the two ends of the start button 08. The interlocking contact 11 of the power-consuming device 06 is connected in series in the control circuit of the interlocking device 12. Figure 2 (c).

[0042] by Figure 2The wiring shown illustrates the control method when the power supply voltage of the low-voltage AC control circuit is abnormal. This method assumes that there is an interlocking device 12 and a protection device 10 that needs to be reset before it can be re-operated in the control circuit. If there is no such device, these components and control links are not required, or the corresponding wiring terminals are not connected to the device. When the power supply voltage is abnormal, the protection device 10 will exit operation, the protection contact 09 of the protection device 10 will be disconnected, and the control circuit of the user electrical device 06 will be interrupted. After the voltage is normal, the protection contact 09 will not automatically close. The reset terminals 101 and 102 of the protection device 10 need to be short-circuited and reset before the protection contact 09 will close. The electrical device 06 has an interlocking control relationship with the interlocking device 12. After the electrical device 06 is running, the interlocking contact 11 is closed, and the interlocking device 12 can run. When the interlocking device 12 is running, if the electrical device 06 exits operation, the interlocking contact 11 will be disconnected, and the interlocking device 12 will also exit operation.

[0043] When the power supply voltage is normal, L and N are input to the main control unit 02 through the voltage detection unit 01, and the main control unit 02 determines that the power supply voltage is normal. After the start button 08 is turned on, the electrical equipment 06 starts to run, and the voltage at point A is input to the main control unit 02 through the voltage detection unit 01. The main control unit 02 determines that the working voltage is normal, and the electrical equipment starts to operate normally. When the electrical equipment is running, the main control unit 02 can control the interlocking control unit 04 to output a closed contact, or it can not output a closed contact. If the electrical equipment needs to stop, press the stop button 07, and the electrical equipment 06 stops running. At this time, the power supply voltage is normal, but the working voltage is abnormal. The main control unit 02 determines that the electrical equipment stops normally. If the interlocking control unit 04 outputs a closed contact during normal operation, the main control unit 02 disconnects the contact.

[0044] When the electrical equipment is running, if the power supply voltage is abnormal, L and N are input to the main control unit 02 through the voltage detection unit 01; the main control unit 02 detects the power supply voltage abnormality and controls the interlocking control unit 04 to output the closed contact (6, 7 terminals are closed). If the electrical equipment is operating normally, the interlocking control unit 04 has output the closed contact, this step can be omitted. At this time, although the electrical equipment 06 stops running and the interlocking contact 11 is disconnected, the 6, 7 terminals of the interlocking control unit 04 are closed, and the interlocking device 12 can continue to run and will not exit the operation due to the stop of the electrical equipment 06; when the power supply voltage is abnormal, the protection contact 09 of the protection device 10 will be disconnected; due to the different lengths of power supply voltage abnormality, if the power supply voltage abnormality time exceeds the allowed time, the main control unit 02 controls the interlocking control unit 04 to disconnect the closed contact (6, 7 terminals are disconnected), exit the control process, and wait for the next operation of the electrical equipment. If the power supply voltage abnormal time does not exceed the allowed time, when the power supply voltage is normal, the main control unit 02 controls the reset control unit 03 to output a short-time closed contact (4, 5 terminals are closed for a short time), resets the protection device 10, and closes the protection contact 09 of the protection device 10. When the power supply voltage is normal for a time that reaches the delayed start time of the power-consuming device 06, the main control unit 02 controls the start control unit 05 to output a short-time closed contact (8, 9 terminals are closed), and the power-consuming device starts running again. After the power-consuming device starts running again, if the interlocking control unit 04 does not need to output a closed contact during normal operation, the main control unit 02 disconnects the closed contact of the interlocking control unit 04, and the restart process ends, and the power-consuming device re-enters the normal operation process.

[0045] Further preferably, the protection device may be a soft starter, a frequency converter, a motor controller, or the like.

[0046] It will be understood by those skilled in the art that the above embodiments are specific examples of the present invention, and in practical applications, various changes may be made to them in form and detail without departing from the spirit and scope of the present invention. The components and structures not described in detail in this embodiment are well-known components and commonly used structures or commonly used means in the industry, and are not described here one by one.

Claims

1. A control circuit when the power supply voltage of a low-voltage AC control circuit is abnormal, characterized by: The device comprises a voltage detection unit (01), a main control unit (02), a reset control unit (03) and a start control unit (05); the voltage detection unit (01) is electrically connected to the main control unit (02); the main control unit (02) is electrically connected to the reset control unit (03) and the start control unit (05); the voltage detection unit (01) inputs a voltage signal to the main control unit (02); the main control unit (02) outputs a control signal for controlling the reset control unit (03) and the start control unit (05); It also includes an interlocking control unit (04), the interlocking control unit (04) being electrically connected to the main control unit (02), and the main control unit (02) outputting a control signal for controlling the interlocking control unit (04); The voltage detection unit (01) comprises at least two voltage inputs: a power supply voltage and an operating voltage of an electrical device (06); the power supply voltage L and N terminals are respectively connected to terminals 1 and 2 of an input terminal of the voltage detection unit (01); the power supply voltage is provided to the voltage detection unit (01) via terminals 1 and 2; the operating voltage A of the electrical device (06) is electrically connected to terminal 3 of the input terminal of the voltage detection unit (01); the N terminal is shared with the power supply voltage; the output terminal of the voltage detection unit (01) is electrically connected to the input terminal of a main control unit (02); the voltage detection unit (01) inputs a voltage signal after the power supply voltage and the operating voltage are stepped down into the main control unit (02); the main control unit (02) determines the operating state of the electrical device (06) and whether the power supply voltage is abnormal based on the two voltages; the output terminal of the main control unit (02) is respectively connected to a reset control unit (03) and an interlocking control unit (03); The main control unit (02) outputs a voltage signal to control the closing or opening of the output contacts of the reset control unit (03), the interlocking control unit (04) and the start control unit (05), respectively. The output contact of the reset control unit (03) is connected to the protection device (10) to perform a reset operation on the protection device (10). The output contact of the interlocking control unit (04) is connected to the control circuit of the interlocking device (12) having an interlocking control relationship with the power-consuming device (06). When the power-consuming device (06) stops running, a false operation signal is provided to the interlocking device (12) having an interlocking control relationship with the power-consuming device (06) to prevent the interlocking device (12) from stopping running. The output contact of the start control unit (05) is connected in parallel to the 1st and 3rd terminals of the input end of the voltage detection unit (01) or the two ends of the start button (08); The voltage detection unit (01) comprises a circuit for reducing the AC voltage to a low voltage that can be identified by the main control unit (02).

2. The control circuit for abnormal power supply voltage of a low-voltage AC control loop according to claim 1, characterized in that: The main control unit (02) is a single chip microcomputer, which can receive at least two voltage inputs and can output at least three voltage signals.

3. The control circuit for abnormal power supply voltage of a low-voltage AC control loop according to claim 1, characterized in that: The reset control unit (03), interlocking control unit (04) and starting control unit (05) are all relays controlled by the main control unit (02), and the relays have at least one pair of normally open contacts, which are closed or opened under the control of the main control unit (02).

4. A control method for low voltage AC control circuit when the power supply voltage is abnormal, characterized by: The voltage detection unit (01) inputs a voltage signal after voltage reduction to the main control unit (02), wherein the voltage detection unit (01) comprises at least two input voltages, namely a power supply voltage and an operating voltage of an electrical device (06); the main control unit (02) detects the power supply voltage and the operating voltage through the input of the voltage detection unit (01), judges the power supply voltage to determine whether the power supply voltage is abnormal, and judges the operating voltage to determine whether the operating state of the electrical device (06) is running or stopped; the main control unit (02) controls the output contacts of the reset control unit (03), the interlocking control unit (04), and the start control unit (05) to close or open according to the power supply voltage and the operating state of the electrical device (06); According to whether the power supply voltage is abnormal and whether the abnormal time exceeds the allowed time of the power-consuming equipment (06), it is divided into three parts: the power supply voltage is normal, the power supply voltage abnormal time exceeds the allowed time, and the power supply voltage abnormal time does not exceed the allowed time. The control method is as follows: A. When the power supply voltage is normal, the main control unit (02) detects the input of the voltage detection unit (01) and determines whether the electric device (06) is running or stopped according to the working voltage. If the working voltage is normal, the electric device (06) is running. If the working voltage is abnormal, the electric device (06) is stopped. When the electric device (06) is running, the main control unit (02) may control the interlocking control unit (04) to output a closed contact or may not output a closed contact. If the interlocking control unit (04) outputs a closed contact, when the electric device (06) is stopped, the interlocking control unit (04) needs to be controlled to open the closed contact. B. When the power-consuming device (06) is running, when the main control unit (02) detects an abnormal power supply voltage through the voltage detection unit (01), if the power-consuming device (06) is connected to other interlocking devices (12) of interlocking control, the main control unit (02) controls the interlocking control unit (04) to output a closed contact, and the interlocking device (12) can continue to operate; if the interlocking control unit (04) has already output a closed contact when the power-consuming device (06) is running, this step can be omitted; Due to the different durations of power supply voltage abnormality, there are two situations: exceeding the allowed time and not exceeding the allowed time: 1) Exceeding the allowed time: If the power supply voltage abnormality time exceeds the allowed time, the main control unit (02) controls the interlocking control unit (04) to open the output closed contact; if the interlocking control unit (04) does not output the closed contact, this step can be omitted, and the control process is exited, waiting for the next operation of the power-consuming equipment (06); 2) Not exceeding the allowed time: When the power supply voltage returns to normal within the allowed time, the main control unit (02) controls the reset control unit (03) to output a short-time closed contact to reset the protection device (10). If there is no protection device (10) that needs to be reset, this step can be omitted. When the power supply voltage normal time reaches the delayed start setting time of the electrical equipment (06), the main control unit (02) controls the start control unit (05) to output a short-time closed contact, and the electrical equipment (06) starts to run again. After the electrical equipment (06) starts to run again, if the interlocking control unit (04) does not need to output a closed contact during normal operation, the closed contact output by the interlocking control unit (04) needs to be disconnected. If the contact is not closed, this step can be omitted.

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