Built-in electric energy meter switching device and method based on unidirectional silicon controlled rectifier and relay

Abstract

The invention discloses a built-in electric energy meter switching device and method based on a unidirectional silicon controlled rectifier and a relay. The device comprises a silicon controlled rectifier control module, a relay module and a control unit. The silicon controlled rectifier control module comprises two unidirectional silicon controlled rectifiers which are reversely connected in parallel, and the unidirectional silicon controlled rectifiers are respectively used for controlling on-off of a positive half cycle and a negative half cycle of alternating current. The relay module is connected in parallel with the silicon controlled rectifier control module and is used for keeping continuous conduction after the load is stable. The control unit is configured to perform zero-crossing switching control and load cutoff control. The built-in intelligent electric energy meter adopts a zero-crossing switching technology of two one-way silicon controlled rectifiers and a relay plate, the stability and the service life of the intelligent electric energy meter can be improved, positive and negative half cycles are respectively controlled through the two one-way silicon controlled rectifiers, accurate zero-crossing switching is realized, current abrupt change and electromagnetic interference are reduced, and the reliability of the intelligent electric energy meter is improved. And the unidirectional silicon controlled rectifier shares current load, and the relay is only switched on after being stabilized, so that the service life of the contact is obviously prolonged.

Description

Technical Field

[0001] The present invention relates to an in-built power meter switching device in the technical field of power metering, in particular to an in-built power meter switching device based on a unidirectional thyristor and a relay, and also relates to an in-built power meter switching method based on a unidirectional thyristor and a relay. Background Art

[0002] When a relay performs conventional switching, there are problems of large inrush current and arcing, which may cause component damage. In the prior art, a zero-crossing switching technology combining a thyristor and a relay is usually adopted, which can effectively avoid generating a large current at the moment of switching, reduce component loss, improve equipment reliability, and extend the service life.

[0003] The commonly used zero-crossing switching technologies mainly include: a pure relay version, a pure thyristor version, and a version with two unidirectional thyristors + a relay. The switching technology of the pure relay version relies on software implementation, is easily affected by power grid harmonics, the inrush current cannot be stably controlled within a small range, and there are problems such as low reliability. The pure thyristor version has a high cost and a large volume, and is not suitable for the case of an in-built power meter. In the version with two unidirectional thyristors + a relay, since a single two unidirectional thyristors needs to bear the current of the entire AC cycle, there are unstable characteristics and it is impossible to accurately achieve zero-crossing switching every time. Summary of the Invention

[0004] In order to solve the technical problems of insufficient reliability, low control accuracy, and large electromagnetic interference existing in the existing in-built power meter switching device, the present invention provides an in-built power meter switching device and method based on a unidirectional thyristor and a relay.

[0005] The present invention is implemented by adopting the following technical solutions: An in-built power meter switching device based on a unidirectional thyristor and a relay, which includes:

[0006] A thyristor control module, which includes two unidirectional thyristors connected in reverse parallel, and the two unidirectional thyristors are respectively used to control the on-off of the positive and negative half-cycles of the alternating current;

[0007] A relay module, which is connected in parallel with the thyristor control module and is used to keep continuously conducting after the load is stable;

[0008] A control unit, which is configured to execute:

[0009] (1) Zero-crossing switching control: (1.1) Read the zero-crossing acquisition signal of the metering chip of the power meter; (1.2) Determine the current steady state by collecting the zero-crossing points of several cycles; (1.3) After confirming the current steady state, synchronously trigger the zero-crossing conduction of the two unidirectional thyristors; (1.4) After the thyristors establish a path, energize the relay module to make the load conduct; (1.5) Turn off the thyristor control module;

[0010] (2) Load cut-off control: (2.1) When responding to a cut-off instruction, trigger the full conduction of two thyristors; (2.2) Disconnect the relay module to achieve zero-crossing turn-off of the current; (2.3) Turn off the thyristor control module to complete arc-free breaking.

[0011] By adopting the zero-crossing switching technology of two reverse-parallel thyristors + relay board on the built-in smart electricity meter, the present invention can improve the stability and service life of the smart electricity meter. By controlling the positive and negative half-cycles with two thyristors respectively, precise zero-crossing switching is achieved, reducing current mutation and electromagnetic interference. Moreover, the thyristors share the current load, and the relay is only turned on after stabilization, significantly extending the contact life, and solving the technical problems of the existing built-in electricity meter switching device such as short contact life, insufficient reliability, low control accuracy, and large electromagnetic interference.

[0012] As a further improvement of the above solution, the built-in electricity meter switching device further includes:

[0013] A protection circuit, which is used to monitor the states of two thyristors and perform overvoltage protection, overcurrent protection, and temperature protection on the thyristor control module.

[0014] Further, the thyristor control module and the relay module are located in a hybrid switch circuit, and the hybrid switch circuit further includes a varistor, a fixed resistor, and a capacitor; the varistor is connected in parallel with the thyristor control module, one end is connected to one end of the fixed resistor, and the other end is connected to one end of the capacitor; the other end of the fixed resistor is connected to the other end of the capacitor.

[0015] As a further improvement of the above solution, the relay module adopts a magnetic latching relay, and the control unit includes a high-speed optocoupler isolation circuit with a zero-crossing detection accuracy better than ±100 μs.

[0016] As a further improvement of the above solution, the built-in electricity meter switching device further includes:

[0017] A zero-crossing detection unit, which is used to collect the pulse signal of the metering chip in real time and generate a zero-crossing flag to obtain the zero-crossing acquisition signal.

[0018] As a further improvement of the above solution, the built-in electricity meter switching device further includes:

[0019] A load monitoring unit, which is used to collect the load current waveform through a current transformer and determine it as a stable state when the harmonic distortion rate is not higher than a preset ratio.

[0020] As a further improvement of the above solution, the built-in electricity meter switching device further includes:

[0021] A temperature monitoring unit, which includes a thermistor provided on the radiator of the thyristor, and monitors the operating temperature of the thyristor through the thermistor.

[0022] As a further improvement of the above solution, the method for judging the current steady state includes the following steps:

[0023] (a) Perform signal sampling and remove high-frequency noise;

[0024] (b) Detect the sign change between two adjacent points in the discrete sampling sequence and calculate the actual zero-crossing moment;

[0025] (c) Statistically analyze the zero-crossing time intervals of multiple consecutive cycles and calculate the cycle standard deviation;

[0026] (d) Judge whether the cycle standard deviation is less than a preset standard deviation. If so, it is determined that the current is stable; otherwise, it is determined that the current is unstable.

[0027] Furthermore, the calculation formula for the actual zero-crossing moment is:

[0028]

[0029] In the formula, t z is the actual zero-crossing moment, I[n] is the discrete sampling sequence, t[n] is the discrete sampling point, and Δt is the sampling interval;

[0030] The calculation formula for the cycle standard deviation is:

[0031]

[0032] In the formula, σ T is the cycle standard deviation, N is the number of cycles, T k =t z,k+1 -t z,k ,T k is the zero-crossing time interval.

[0033] The present invention also provides an internal energy meter switching method based on a thyristor and a relay, which is applied to any one of the above internal energy meter switching devices based on a thyristor and a relay, and includes the following steps:

[0034] (1) Zero-crossing switching control: (1.1) Read the zero-crossing acquisition signal of the metering chip of the energy meter; (1.2) Determine the current steady state by collecting the zero-crossing points of several cycles; (1.3) After confirming the current steady state, synchronously trigger the zero-crossing conduction of two thyristors; (1.4) After the thyristor establishes a path, energize the relay module to turn on the load; (1.5) Turn off the thyristor control module;

[0035] (2) Load cut-off control: (2.1) When responding to the cut-off instruction, trigger the full conduction of two thyristors; (2.2) Disconnect the relay module to achieve zero-crossing turn-off of the current; (2.3) Turn off the thyristor control module to complete arc-free breaking.

[0036] Compared with the existing built-in electric energy meter switching device, the built-in electric energy meter switching device and method based on thyristors and relays of the present invention have the following beneficial effects:

[0037] 1. The built-in electric energy meter switching device based on thyristors and relays adopts the zero-crossing switching technology of two thyristors + relay version on the built-in intelligent electric energy meter, which can improve the stability and service life of the intelligent electric energy meter.

[0038] 2. The built-in electric energy meter switching device based on thyristors and relays has the characteristics of high-precision control. The switching device controls the positive and negative half-cycles respectively through two thyristors to achieve precise zero-crossing switching and more precise current control.

[0039] 3. The built-in electric energy meter switching device based on thyristors and relays has the characteristics of high reliability, energy saving and high efficiency. The thyristor shares the current load, and the relay is only turned on after stabilization, avoiding direct switching of large current, significantly prolonging the contact life. Moreover, the conduction loss of the thyristor is low, and the relay only attracts when needed, reducing the system power consumption.

[0040] 4. The built-in electric energy meter switching device based on thyristors and relays has the characteristics of low electromagnetic interference and can be applied to large current application scenarios. In the process of controlling the thyristor control module and the relay module to perform zero-crossing switching by the control unit, the precise control of the thyristor reduces the current mutation and the electromagnetic interference. Since the two thyristors share the current load, the overall heat generation is less, so it is more suitable for large current occasions.

[0041] 5. The built-in electric energy meter switching device based on thyristors and relays can perform overvoltage protection, overcurrent protection and temperature protection on its protection circuit to ensure the safe operation of the system under abnormal conditions and prevent damage caused by overvoltage, overcurrent or overheating. Description of the Drawings

[0042] Figure 1 It is the circuit diagram of the thyristor control module and the relay module in the built-in electric energy meter switching device based on thyristors and relays of Embodiment 1 of the present invention.

[0043] Figure 2 It is the flow chart of zero-crossing switching in the built-in electric energy meter switching device based on thyristors and relays of Embodiment 1 of the present invention. Detailed Embodiment

[0044] In order to make the objectives, technical solutions and advantages of the present invention more clear and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0045] Embodiment 1

[0046] Please refer to Figure 1 and Figure 2 This embodiment provides an in-built electricity meter switching device based on a thyristor and a relay. This device is mainly used in cooperation with an in-built electricity meter and can either be independent of the in-built electricity meter or be part of the structure of the in-built electricity meter. Among them, the in-built electricity meter is a miniaturized and integrated electricity metering device, which is usually embedded in electronic devices such as smart home appliances, industrial equipment, new energy systems, and Internet of Things terminals to measure the electricity consumption of these electronic devices. The switching device can achieve zero-crossing switching and load cut-off control between the in-built electricity meter and the load. In this embodiment, the in-built electricity meter switching device mainly includes a thyristor control module, a relay module, a control unit, and a protection circuit.

[0047] The thyristor control module includes two reverse-parallel silicon-controlled rectifiers (SCRs), and the two SCRs are respectively used to control the on-off of the positive and negative half-cycles of the alternating current. The two SCRs achieve precise zero-crossing switching through zero-crossing detection, enabling more precise current control and reducing current mutation and electromagnetic interference.

[0048] The relay module is connected in parallel with the thyristor control module, and the relay module is used to maintain continuous conduction after the load is stable. In this embodiment, the relay module uses a magnetic latching relay. Since the SCR shares the current load, the relay module can be turned on only after stability, reducing heat generation and significantly extending the contact life.

[0049] The thyristor control module and the relay module are located in a hybrid switch circuit, and the hybrid switch circuit also includes a varistor, a fixed resistor, and a capacitor. The varistor is connected in parallel with the thyristor control module, one end is connected to one end of the fixed resistor, and the other end is connected to one end of the capacitor. The other end of the fixed resistor is connected to the other end of the capacitor.

[0050] The control unit is configured to execute two control strategies: (1) zero-crossing switching control; (2) load cut-off control. In this embodiment, the control unit may include a high-speed optocoupler isolation circuit with a zero-crossing detection accuracy better than ±100 μs.

[0051] The zero-crossing switching control method includes the following steps: (1.1) Read the zero-crossing acquisition signal of the metering chip of the electric energy meter; (1.2) Determine the current steady state by collecting zero-crossing points for several cycles; (1.3) After confirming the current steady state, synchronously trigger the zero-crossing conduction of two unilateral thyristors; (1.4) After the thyristor establishes a path, energize the relay module to turn on the load; (1.5) Turn off the thyristor control module.

[0052] Among them, the method for judging the current steady state includes the following steps (a-d). The basis for judging the current steady state is cycle stability and no attenuation or mutation. Cycle stability mainly means that the waveform shape, amplitude, and zero-crossing time interval of multiple consecutive cycles are the same. No attenuation or mutation can prevent oscillations or attenuation caused by startup or load mutation.

[0053] (a) Perform signal sampling and remove high-frequency noise. This step is mainly for signal acquisition and preprocessing. The current can be converted into a voltage signal through a current sensor (such as a CT or Hall sensor), and the high-frequency noise can be removed through an anti-aliasing filter (low-pass filter) to avoid false zero-crossing points. The sampling signal needs to meet the Nyquist theorem (sampling frequency ≥ 2 times the highest signal frequency), usually taking more than 10 × power frequency (50 / 60 Hz) (such as 1 kHz).

[0054] (b) Detect the sign change between adjacent two points in the discrete sampling sequence and calculate the actual zero-crossing moment. When there is a sign change, I[n] × I[n + 1] < 0. Therefore, the calculation formula for the actual zero-crossing moment is:

[0055]

[0056] In the formula, t z is the actual zero-crossing moment, I[n] is the discrete sampling sequence, t[n] is the discrete sampling point, and Δt is the sampling interval.

[0057] (c) Statistically calculate the zero-crossing time intervals of multiple consecutive cycles and calculate the cycle standard deviation. The calculation formula for the cycle standard deviation is:

[0058]

[0059] In the formula, σ T is the cycle standard deviation, N is the number of cycles, T k = t z,k+1 -t z,k ,T k is the zero-crossing time interval.

[0060] (d) Judge whether the cycle standard deviation is less than a preset standard deviation. If so, it is determined that the current is stable; otherwise, it is determined that the current is unstable. For example, set the preset standard deviation ∈ to If σ TIf <∈, it is considered cycle - stable. In some embodiments, the amplitude stability is verified by the peak value or the effective value between adjacent zero - crossing points (full - waveform sampling is required). In some strict scenarios, the percentage of 1% can be adjusted to a smaller value such as 0.5%, which can be determined according to the specific scenario.

[0061] Of course, in some embodiments, it is also possible to judge the T of the previous several cycles k Or whether the amplitude change exceeds the threshold. If so, it is determined as transient, and before judging the steady state, the previous cycles need to remain transient.

[0062] The load - cut - off control method includes the following steps: (2.1) Trigger two unilateral thyristors to conduct fully when responding to the cut - off instruction; (2.2) Disconnect the relay module to achieve zero - current turn - off; (2.3) Turn off the thyristor control module to complete arc - free breaking.

[0063] In this embodiment, when the electric energy meter detects that the load needs to be switched, it first reads the zero - crossing acquisition signal of the metering chip of the electric energy meter. By collecting the zero - crossing points of several cycles, it judges whether the current is stable. If the current is stable, the control unit first triggers two SCRs to achieve zero - crossing switching in the positive and negative half - cycles of the alternating current respectively. After the SCRs complete the switching, the control unit closes the relay to make the load conduct stably, and then turns off the SCRs. When the load needs to be cut off, first turn on the SCRs, then the control unit disconnects the relay, and finally turns off the SCRs to ensure arc - free switching. During the whole process, the protection circuit monitors the thyristor state in real - time to prevent damage caused by over - voltage, over - current or over - heat.

[0064] The protection circuit is used to monitor the states of two unilateral thyristors and perform over - voltage protection, over - current protection and temperature protection on the thyristor control module.

[0065] In summary, compared with the existing built - in electric energy meter switching device, the built - in electric energy meter switching device based on unilateral thyristors and relays in this embodiment has the following beneficial effects:

[0066] 1. The built - in electric energy meter switching device based on unilateral thyristors and relays adopts the zero - crossing switching technology of two unilateral thyristors + relay version on the built - in intelligent electric energy meter, which can improve the stability and service life of the intelligent electric energy meter.

[0067] 2. The built - in electric energy meter switching device based on unilateral thyristors and relays has the characteristics of high - precision control. The switching device controls the positive and negative half - cycles respectively through two unilateral thyristors to achieve precise zero - crossing switching and more precise current control.

[0068] 3. The built-in electric energy meter switching device based on thyristors and relays features high reliability, energy conservation, and high efficiency. The thyristor shares the current load, and the relay is only turned on after stabilization, avoiding direct switching of large currents, significantly extending the contact life. Moreover, the conduction loss of the thyristor is low, and the relay only pulls in when needed, reducing the system power consumption.

[0069] 4. The built-in electric energy meter switching device based on thyristors and relays has the characteristic of low electromagnetic interference and can be applied to large-current application scenarios. During the zero-crossing switching control of the thyristor control module and the relay module by the control unit, the precise control of the thyristor reduces current mutation and electromagnetic interference. Since two thyristors share the current load, the overall heat generation is less, so it is more suitable for large-current occasions.

[0070] 5. The protection circuit of the built-in electric energy meter switching device based on thyristors and relays can perform overvoltage protection, overcurrent protection, and temperature protection to ensure the safe operation of the system under abnormal conditions and prevent damage caused by overvoltage, overcurrent, or overheating.

[0071] Embodiment 2

[0072] This embodiment provides a built-in electric energy meter switching device based on thyristors and relays, which adds a zero-crossing detection unit, a load monitoring unit, and a temperature monitoring unit on the basis of Embodiment 1.

[0073] The zero-crossing detection unit is used to collect the pulse signal of the metering chip in real time and generate a zero-crossing flag to obtain a zero-crossing acquisition signal. The zero-crossing detection unit includes a high-speed optocoupler and a Schmitt trigger. The high-speed optocoupler realizes electrical isolation between the power grid side and the control system side and accurately transmits the zero-crossing signal at the same time. The Schmitt trigger shapes the waveform of the optocoupler output signal, eliminates jitter, and generates a standard digital signal.

[0074] The load monitoring unit is used to collect the load current waveform through a current transformer and determine it as a stable state when the harmonic distortion rate is not higher than a preset ratio. Here, the stability of the current can be detected through the current waveform, and the harmonic distortion rate THD≤5% can be determined as a stable state.

[0075] The temperature monitoring unit includes a thermistor arranged on the radiator of the thyristor and monitors the operating temperature of the thyristor through the thermistor. The temperature monitoring unit can detect the temperature of the thyristor in real time, and it can play the role of temperature protection of the protection circuit, so it can also be a part of the protection circuit.

[0076] Embodiment 3

[0077] This embodiment provides a method for switching an in-built electric energy meter based on a thyristor and a relay. This method is applied to the in-built electric energy meter switching device based on a thyristor and a relay in Embodiment 1 or 2, and mainly includes two steps (zero-crossing switching control and load cut-off control). These two steps have no sequence and can be selected according to the actual situation.

[0078] Zero-crossing switching control process: (1.1) Read the zero-crossing acquisition signal of the metering chip of the electric energy meter; (1.2) Determine the current steady state by collecting zero-crossing points for several cycles; (1.3) After confirming the current steady state, synchronously trigger the zero-crossing conduction of two thyristors; (1.4) After the thyristors establish a path, energize the relay module to turn on the load; (1.5) Turn off the thyristor control module.

[0079] Load cut-off control process: (2.1) Trigger the full conduction of two thyristors when responding to a cut-off instruction; (2.2) Disconnect the relay module to achieve zero-crossing turn-off of the current; (2.3) Turn off the thyristor control module to complete arc-free breaking.

[0080] Embodiment 4

[0081] This embodiment provides an in-built electric energy meter, which includes the in-built electric energy meter switching device based on a thyristor and a relay in Embodiment 1 or 2. The in-built electric energy meter can measure the electricity consumption of electrical equipment such as air conditioners, refrigerators, charging piles, motors, frequency converters, power modules, photovoltaic inverters, energy storage systems, smart sockets, and energy gateways, and has the functions of zero-crossing switching and load cut-off control. The in-built electric energy meter can also measure the voltage, current, and power (active / reactive) of the aforementioned loads, and upload data through a communication interface (such as RS-485, Modbus, Bluetooth, Wi-Fi). It can support peak-valley electricity price statistics, has functions such as overload, short-circuit, and leakage alarms, and can record historical electricity consumption data (such as daily / monthly / yearly electricity consumption).

[0082] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A built-in electric energy meter switching device based on a thyristor and a relay, characterized in that, It includes: A thyristor control module, which includes two reverse-parallel unidirectional thyristors, and the two unidirectional thyristors are respectively used to control the on-off of the positive and negative half-cycles of alternating current; A relay module, which is connected in parallel with the thyristor control module and is used to maintain continuous conduction after the load is stable; A control unit, which is configured to execute: (1) Zero-crossing switching control: (1.1) Read the zero-crossing acquisition signal of the metering chip of the electric energy meter; (1.2) Determine the current steady state by collecting the zero-crossing points of several cycles; (1.3) After confirming the current steady state, synchronously trigger the zero-crossing conduction of the two unidirectional thyristors; (1.4) After the thyristor establishes a path, attract the relay module to turn on the load; (1.5) Turn off the thyristor control module; (2) Load cut-off control: (2.1) Trigger the full conduction of the two unidirectional thyristors when responding to the cut-off instruction; (2.2) Disconnect the relay module to achieve zero-crossing turn-off of the current; (2.3) Turn off the thyristor control module to complete arc-free breaking.

2. The built-in electric energy meter switching device based on a thyristor and a relay according to claim 1, wherein, The built-in electric energy meter switching device further includes: A protection circuit, which is used to monitor the states of the two unidirectional thyristors and perform over-voltage protection, over-current protection and temperature protection on the thyristor control module.

3. The built-in electric energy meter switching device based on a thyristor and a relay according to claim 2, characterized in that The thyristor control module and the relay module are located in a hybrid switch circuit, and the hybrid switch circuit further includes a varistor, a fixed resistor and a capacitor; the varistor is connected in parallel with the thyristor control module, one end is connected to one end of the fixed resistor, and the other end is connected to one end of the capacitor; the other end of the fixed resistor is connected to the other end of the capacitor.

4. The built-in electric energy meter switching device based on a thyristor and a relay according to claim 1, characterized in that, The relay module uses a magnetic latching relay, and the control unit includes a high-speed optocoupler isolation circuit with a zero-crossing detection accuracy better than ±100 μs.

5. The built-in electric energy meter switching device based on a thyristor and a relay according to claim 1, characterized in that The built-in electric energy meter switching device further includes: A zero-crossing detection unit, which is used to collect the pulse signal of the metering chip in real time and generate a zero-crossing flag to obtain the zero-crossing acquisition signal.

6. The built-in energy meter switching device based on a thyristor and a relay according to claim 1, characterized in that The built-in electric energy meter switching device further includes: A load monitoring unit, which is used to collect the load current waveform through a current transformer and determine it as a stable state when the harmonic distortion rate is not higher than a preset ratio.

7. The built-in electric energy meter switching device based on a thyristor and a relay according to claim 1, characterized in that, The built-in electric energy meter switching device further includes: A temperature monitoring unit, which includes a thermistor arranged on the radiator of the unidirectional thyristor and monitors the working temperature of the unidirectional thyristor through the thermistor.

8. The built-in electric energy meter switching device based on a thyristor and a relay according to claim 1, characterized in that, The method for judging the current steady state includes the following steps: (a) Perform signal sampling and remove high-frequency noise; (b) Detect the sign change between two adjacent points in the discrete sampling sequence and calculate the actual zero-crossing moment; (c) Statistically calculate the zero-crossing time intervals of multiple consecutive cycles and calculate the cycle standard deviation; (d) Judge whether the cycle standard deviation is less than a preset standard deviation. If so, it is determined that the current is stable; otherwise, it is determined that the current is unstable.

9. The built-in electric energy meter switching device based on a thyristor and a relay according to claim 8, characterized in that, The calculation formula for the actual zero-crossing moment is: where t z is the actual zero-crossing moment, I[n] is the discrete sampling sequence, t[n] is the discrete sampling point, and Δt is the sampling interval; The calculation formula for the cycle standard deviation is: Where, σ T is the standard deviation of the period, N is the number of periods, and T k = t z,k+1 - t z,k , and T k is the zero-crossing time interval.

10. A built-in electric energy meter switching method based on a thyristor and a relay, characterized in that, It is applied to the built-in electric energy meter switching device based on unidirectional thyristors and relays as described in any one of claims 1-9, and it includes the following steps: (1) Zero-crossing switching control: (1.1) Read the zero-crossing acquisition signal of the metering chip of the electric energy meter; (1.2) Determine the current steady state through zero-crossing points by collecting several cycles; (1.3) After confirming the current steady state, synchronously trigger the zero-crossing conduction of two unilateral thyristors; (1.4) After the thyristors establish a path, energize the relay module to turn on the load; (1.5) Turn off the thyristor control module; (2) Load cut-off control: (2.1) Trigger full conduction of two unilateral thyristors when a cut-off instruction is responded to; (2.2) Disconnect the relay module to achieve zero-crossing turn-off of the current; (2.3) Turn off the thyristor control module to complete arc-free breaking.

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