A bridge-type constant current source clamping circuit, an AC SSPC and a control method

Abstract

The present invention discloses a bridge-type constant current source clamping circuit, an AC SSPC and a control method. The clamping circuit includes a full-bridge circuit, a constant current source circuit and a unidirectional power switch. The two AC input terminals of the full-bridge circuit are respectively connected to the power input terminal and the power ground of the AC solid state power controller. The constant current source circuit and the unidirectional power switch are connected in series between the two DC output terminals of the full-bridge circuit. The control input terminal of the unidirectional power switch is connected to a control instruction. The bridge-type constant current source clamping circuit of the present invention not only provides a path for the leakage current, but also greatly reduces the equivalent resistance on the load side, and realizes the constant current discharge of the capacitive load while reducing the voltage on the load side.

Description

Technical Field

[0001] The present invention relates to a bridge constant current source clamping circuit, an AC SSPC and a control method, belonging to the fields of power electronics technology and electrical engineering technology. Background Art

[0002] A solid state power controller (SSPC) uses power semiconductor devices as switches, integrating the switch control function of a relay and the protection function of a circuit breaker. It has advantages such as fast response, no arc, no mechanical contacts, low conduction power consumption, strong load adaptability, and high reliability, and is the key core of an advanced solid state power distribution system.

[0003] In an aerospace solid state power distribution system, there is a microampere-level leakage current in the off state of an AC SSPC. When a capacitive load is connected, the existence of the leakage current will cause the voltage on the load side to continuously accumulate; when the load is unloaded, a "virtual voltage" close to the power supply voltage will even appear on the load side, and as the system voltage level increases, it will endanger the normal operation of the system and the safety of personnel. Therefore, it is of great significance to study the leakage current problem of AC SSPC and its solutions.

[0004] The conventional solution is to connect a discharging resistor in parallel on the load side R , when the AC SSPC is turned off, the discharging resistor is incorporated into the load side for operation. This method reduces the equivalent resistance on the load side and dissipates the energy of the capacitor on the discharging resistor. There is a current spike at the initial discharge, and the R instantaneous power consumption on the resistor is the largest, and then the discharge current decays exponentially. In terms of the clamping time, relying on the power resistor for the natural discharge of the capacitor, the discharge current decays exponentially, and the discharge time is all above 100 ms, which is relatively long; in terms of safety, due to the unstable discharging current and the existence of a current spike at the initial discharge, the safety during the discharge process is relatively low; in terms of volume and weight, since all the energy is dissipated on the discharging resistor, the volume of this resistor is relatively large, resulting in a relatively large overall volume and weight of the power device.

[0005] In order to further shorten the capacitor discharge time, reduce the volume and weight of the power device, and improve the safety after the AC SSPC is turned off, it is necessary to conduct in-depth research on the clamping circuit of the AC SSPC. Summary of the Invention

[0006] The technical problem to be solved by the present invention is, aiming at the defects and deficiencies in the foregoing background, to provide a bridge constant current source clamping circuit, an AC SSPC and a control method, which can not only clamp the load voltage to a lower safe range, but also provide an energy release channel for the load capacitor and achieve controllable energy release time.

[0007] To solve the above technical problems, an embodiment of the present application first provides a bridge-type constant current source clamping circuit, which is applied to an AC solid-state power controller. It is characterized in that it includes a full-bridge circuit, a constant current source circuit, and a unidirectional power switch; two AC input terminals of the full-bridge circuit are respectively connected to the power input terminal and the power ground of the AC solid-state power controller, and the constant current source circuit and the unidirectional power switch are connected in series between two DC output terminals of the full-bridge circuit; a control input terminal of the unidirectional power switch is connected to a control instruction.

[0008] An embodiment of the present application also provides a main power circuit, a clamping circuit, and a clamping circuit control logic circuit. It is characterized in that the clamping circuit includes a full-bridge circuit, a constant current source circuit, and a unidirectional power switch; two AC input terminals of the full-bridge circuit are respectively connected to the power input terminal and the power ground of the AC solid-state power controller, and the constant current source circuit and the unidirectional power switch are connected in series between two DC output terminals of the full-bridge circuit; a control input terminal of the unidirectional power switch is connected to a control instruction output by the clamping circuit control logic circuit.

[0009] Preferably, the main power circuit includes a first power tube and a second power tube connected in anti-series. A drain of the first power tube serves as the power input terminal of the AC solid-state power controller and is connected to an AC power supply, a drain of the second power tube serves as the power output terminal of the AC solid-state power controller and is connected to the clamping circuit and a load, a gate of the first power tube and a source of the second power tube are connected to the same analog ground, and gates of the first power tube and the second power tube are connected to different switching instructions.

[0010] Preferably, the clamping circuit control logic circuit includes a NOR gate, an OR gate, and an RS flip-flop. Two input terminals of the NOR gate are respectively connected to the switching instructions of the first power tube and the second power tube. Four input terminals of the OR gate are respectively connected to the switching instructions of the first power tube and the second power tube, and positive and negative logic signals of the load current direction; an output terminal of the NOR gate is connected to the terminal of the RS flip-flop, an output terminal of the OR gate is connected to the terminal of the RS flip-flop, and a terminal of the RS flip-flop outputs the control instruction.

[0011] An embodiment of the present application also provides a control method for the above AC solid-state power controller. It is characterized in that it includes:

[0012] When the AC solid-state power controller is turned on: in the positive half cycle of the AC power supply voltage, first turn on the second power tube, and then turn on the first power tube after the voltage passes through the zero point, and the unidirectional power switch is turned off; in the negative half cycle of the AC power supply voltage, first turn on the first power tube, and then turn on the second power tube after the voltage passes through the zero point, and the unidirectional power switch is turned off;

[0013] When the AC solid-state power controller is turned off: during the positive half-cycle of the load current, first turn off the second power transistor, and then turn off the first power transistor after the current passes through the zero-crossing point, and the unidirectional power switch is turned on; during the negative half-cycle of the load current, first turn off the first power transistor, and then turn off the second power transistor after the current passes through the zero-crossing point, and the unidirectional power switch is turned on.

[0014] The present invention has the following beneficial effects:

[0015] 1. The clamping circuit of the present invention can reduce the "virtual voltage" on the load side caused by the leakage current when the AC solid-state power controller is no-load to within a safe range;

[0016] 2. The clamping circuit of the present invention provides an energy release path for capacitive loads, preventing the continuous accumulation of voltage on the load side caused by the existence of leakage current. The capacitive load energy discharge current is stable, without current spikes, and the discharge current and discharge time are controllable;

[0017] 3. The present invention has simple control and strong practicability. Description of the Drawings

[0018] Figure 1 is the circuit diagram of the AC SSPC based on the bridge-type constant current source clamping circuit;

[0019] Figure 2 is the circuit diagram of the depletion-type constant current source;

[0020] Figure 3 is the control logic circuit diagram of the clamping circuit;

[0021] Figure 4 is the overall control timing diagram of the AC SSPC based on the bridge-type constant current source clamping circuit;

[0022] Figure 5 is the working timing diagram of the bridge-type constant current source clamping circuit;

[0023] Figure 6 is the working circuit diagram under the condition that the load is no-load and the SSPC is in the steady-state off;

[0024] Figure 7 is the working circuit diagram under the condition that the load is capacitive and the SSPC is in the steady-state off. Detailed Embodiment

[0025] The following details some key technologies involved in the present invention with reference to the drawings to support the claims section; for a clearer understanding of the purpose, technical solution and advantages of the present invention, the present invention will be further described in detail below with reference to the drawings and embodiments.

[0026] Embodiment 1

[0027] This embodiment provides a bridge-type constant current source clamping circuit, and an AC solid-state power controller is provided based on the bridge-type constant current source clamping circuit.

[0028] The bridge-type constant current source clamping circuit of this embodiment is applied to an AC solid-state power controller. As Figure 1 shown, the bridge-type constant current source clamping circuit of this embodiment includes a full-bridge circuit, a constant current source I CCS and a unidirectional power switch S aux . The AC side of the full-bridge circuit is connected in parallel with the load, and the DC side is connected in series with the constant current source I CCS , the unidirectional power switch S aux . Specifically, the two AC input terminals of the full-bridge circuit are respectively connected to the power output terminal Powerout and the power ground PGND of the AC solid-state power controller. A constant current source I CCS and a unidirectional power switch S aux are connected in series between the two DC output terminals of the full-bridge circuit.

[0029] The full-bridge circuit of this embodiment is composed of the first to fourth rectifying diodes (D1~D4). The first rectifying diode D1 and the second rectifying diode D2 are connected in series to form the first bridge arm. The third rectifying diode D3 and the fourth rectifying diode D4 are connected in series to form the second bridge arm. The two bridge arms are then connected in parallel to form a complete bridge structure. Among them, the connection end of the cathode of the first rectifying diode D1 and the anode of the second rectifying diode D2 serves as the positive pole of the AC input terminal of the full-bridge circuit and is connected to the power output terminal Powerout of the AC solid-state power controller. The connection end of the anode of the third rectifying diode D3 and the cathode of the fourth rectifying diode D4 serves as the negative pole of the AC input terminal of the full-bridge circuit and is connected to the power ground PGND of the AC solid-state power controller. The connection end of the anode of the first rectifying diode D1 and the anode of the fourth rectifying diode D4 serves as the negative pole of the DC output terminal of the full-bridge circuit and is connected to the analog ground AGND2. The connection end of the cathode of the third rectifying diode D3 and the cathode of the second rectifying diode D2 serves as the positive pole + V DD of the DC output terminal of the full-bridge circuit.

[0030] As Figure 2 shown, the constant current source I CCS of this embodiment is composed of a depletion-type N-MOSFET S1 and a negative feedback resistor R . The negative feedback resistor R is an adjustable resistor. The unidirectional power switch S auxIt is an enhanced N-MOSFET. The drain of the depletion-type N-MOSFET S1 is connected to +V DD , and the source is connected to one end of the negative feedback resistor R . The other end of the negative feedback resistor R is connected to the gate of the depletion-type N-MOSFET S1 and the source of the unidirectional power switch S aux . The gate of the unidirectional power switch S aux is connected to the control instruction CMD aux as the control input terminal of the clamping circuit, and the drain of the unidirectional power switch S aux is connected to the analog ground AGND2.

[0031] As Figure 1 , the AC SSPC based on the bridge constant current source clamping circuit in this embodiment is composed of an AC power supply V s , an AC SSPC power circuit, and a load. Among them, the AC power supply is a 115V AC source, and the load is composed of a resistor and a capacitor in parallel. The AC SSPC power circuit includes a main power circuit, the above-mentioned bridge constant current source clamping circuit, and Figure 3 the clamping circuit control logic circuit shown.

[0032] The main power circuit of the AC SSPC is composed of two identical N-channel enhanced Si MOSFETs, the first power transistor S upp and the second power transistor S low , connected in anti-series. The drain of the first power transistor S upp is connected to the AC power supply as the power input terminal of the AC solid-state power controller, and the drain of the second power transistor S low is connected to the clamping circuit and the load as the power output terminal of the AC solid-state power controller. The gate of the first power transistor S upp and the source of the second power transistor S low are connected to the same analog ground AGND1. The gate of the first power transistor S upp is connected to the first switch instruction CMD upp , and the gate of the second power transistor S low is connected to the second switch instruction CMD low .

[0033] For the constant current source in this embodiment, when the depletion-type N-MOSFET S1 operates in the saturation region, the drain current I D is:

[0034]

[0035] Among them, μ 0 is the electron mobility, C oxis the gate oxide capacitance per unit area, W is the channel width, L is the effective channel length; V GS and V TH represent the gate-source voltage and threshold voltage of the MOS transistor respectively.

[0036] When the gate-source voltage of the depletion-mode N-MOSFET S1 is zero-biased ( V GS = 0V), the drain current I DSS is:

[0037]

[0038] After adding the adjustable resistor R the drain current of the depletion-mode N-MOSFET S1 I D can be expressed as:

[0039]

[0040] Combining the above two formulas gives:

[0041]

[0042] Therefore, the drain current I D of the depletion-mode N-MOSFET S1 is determined jointly by the drain current I DSS when the gate-source voltage is zero-biased, the threshold voltage V TH and the adjustable resistor R . When a specific depletion-mode MOSFET device is determined, the drain current I D is then uniquely determined by the adjustable resistor R . The calculation expression for the value of the adjustable resistor R is:

[0043]

[0044] At the same time, the adjustable resistor R between the gate and source of the depletion-mode MOSFET has a negative feedback effect, which can effectively suppress the change in the output current caused by the fluctuation of the input voltage V DD . Therefore, the current source composed of the depletion-mode N-MOSFET S1 and the adjustable resistor R has the advantages of a wide allowable input voltage range and high output current accuracy.

[0045] Such as Figure 3, the clamping circuit control logic circuit of this embodiment includes a NOR gate OR1, an OR gate OR2, and an RS flip-flop composed of two NAND gates. The two input terminals of the NOR gate OR1 are respectively connected to the first switch command CMD upp , the second switch command CMD low . The four input terminals of the OR gate OR2 are respectively connected to the first switch command CMD upp , the second switch command CMD low , and the positive and negative logic signals of the load current direction I + and I -. I +, I - are respectively the logic signals representing the load current direction, and the high level indicates validity. I + indicates that the current direction is from the power input terminal Powerin of the AC SSPC to the power output terminal Powerout , I - indicates the opposite current direction. The output terminal of the NOR gate OR1 is connected to the terminal of the RS flip-flop, and the output terminal of the OR gate OR2 is connected to the terminal of the RS flip-flop. The terminal of the RS flip-flop outputs the control command CMD aux of the clamping circuit.

[0046] The following table is the function table of the clamping circuit control logic circuit:

[0047]

[0048] Figure 4 is the overall control timing diagram of the AC SSPC based on the bridge-type constant current source clamping circuit. This control timing diagram corresponds to the power supply voltage V s When the power supply voltage is in the negative half cycle, the AC SSPC is turned on, and when the load current I load is in the positive half cycle, the AC SSPC is turned off. Among them, t 0~ t 2 corresponds to the turn-on process of the AC SSPC, t 3~ t 5 corresponds to the turn-off process of the AC SSPC, t After 5, the bridge-type constant current source clamping circuit works.

[0049] t 0: The total switch command CMD of the AC SSPC becomes high, and the AC SSPC is turned on. Since the power supply voltage V s is in the negative half cycle, the first power transistor S upp of the main power circuit is first turned on. However, since the second power transistor S lowNot yet turned on, and the main power circuit is still in the reverse cut-off state;

[0050] t 1: Power supply voltage V s When entering the positive half cycle, the body diode of the second power transistor S of the main power circuit low and the channel of the first power transistor S of the already turned-on main power circuit upp form a forward path to enable the load current to change from zero;

[0051] t 2: Turn on the second power transistor S of the main power circuit low , and the AC SSPC enters the steady-state conduction state;

[0052] t 3: The total switch command CMD of the AC SSPC goes low, the AC SSPC turns off, and the load current I load is in the positive half cycle. First, turn off the second power transistor S of the main power circuit low , and the current of the second power transistor S of the main power circuit low switches from the MOSFET channel to the body diode, and the load current continues;

[0053] t 4: Load current I load When entering the negative half cycle, the AC SSPC is in the negative cut-off state, and the current naturally turns off at zero crossing;

[0054] t 5: Turn off the first power transistor S of the main power circuit upp , the AC SSPC enters the stable cut-off state of bidirectional cut-off, the load voltage is negative, and the control command CMD of the clamping circuit aux goes high, the unidirectional power switch S aux turns on, and the loop current flows from the power ground PGND through the third rectifier diode D3, the constant current source I CSS and the first rectifier diode D 1 to the power output terminal Powerout , and then the load voltage gradually decreases.

[0055] The following table summarizes the control logic of the zero-crossing switch of the AC SSPC.

[0056]

[0057] For the AC solid-state power controller based on the bridge-type constant current source clamping circuit of the present invention, when the AC solid-state power controller is turned on, the unidirectional power switch S auxTurn off, and the clamping circuit does not work; when the AC solid-state power controller is turned off, the unidirectional power switch S aux Turn on, the clamping circuit conducts, the clamping circuit is in series with the load, and the energy stored in the load capacitor ( C load ) is consumed on the load resistor ( R load ). This circuit can provide a path for the leakage current of the AC solid-state power controller and achieve constant-current discharge of capacitive loads. Since the equivalent resistance of this clamping circuit is much smaller than the equivalent resistance when the AC solid-state power controller is turned off, the voltage division value on the load side caused by the leakage current after turning off the AC solid-state power controller can be controlled within 1V, and the discharge time is reduced to within 10ms, effectively improving the safety of the AC solid-state power controller.

[0058] Figure 5 is the working timing diagram of the bridge-type constant-current source clamping circuit. When the unidirectional power switch S aux conducts, if the voltage of the power output terminal Powerout of the AC solid-state power controller is higher than the voltage of the power ground PGND , the working timing diagram of the clamping circuit is shown as (a); conversely, if the unidirectional power switch S aux conducts and the voltage of the power output terminal Powerout of the AC solid-state power controller is lower than the voltage of the power ground PGND , the working timing diagram of the clamping circuit is (b).

[0059] t 0: The total switch command CMD of the AC SSPC is set low, and the AC SSPC is turned off.

[0060] t 1: The control command CMD aux of the clamping circuit is set to high level, the unidirectional power switch S aux turns on. If the voltage of the power output terminal Powerout of the AC solid-state power controller is higher than the voltage of the power ground PGND at this time, the second rectifier diode D2 and the fourth rectifier diode D4 work, and the first rectifier diode D1 and the third rectifier diode D3 are reverse cut-off. The current I CSS + passes through the second rectifier diode D2, the fourth rectifier diode D4, and the constant current source I CSS to clamp the voltage on the load side V C ; if the voltage of the power output terminal Powerout of the AC solid-state power controller is lower than the voltage of the power ground PGNDWhen the voltage is applied, the first rectifier diode D1 and the third rectifier diode D3 conduct, while the second rectifier diode D2 and the fourth rectifier diode D4 are reverse-biased and non-conducting. The current I CSS - passes through the first rectifier diode D1, the third rectifier diode D3, and the constant current source I CSS to clamp the voltage on the load side V C .

[0061] Figure 6 Figure R shows the working circuit diagram when the load is unloaded and the SSPC is in the steady-state off condition. Since the main power topology of the single-phase AC SSPC is composed of two identical N-channel enhancement-mode MOSFETs connected in anti-parallel, according to the circuit equivalence principle, an equivalent two-terminal network model of the SSPC with a resistor R SSPC in parallel with a capacitor C SSPC can be established. Among them, the equivalent resistance R SSPC of the SSPC in the steady-state conduction state is in the milliohm range, and in the steady-state off state, it is in the megohm range.

[0062] If the clamping circuit is not added, in the SSPC control circuit, due to the existence of the load voltage sampling and conditioning circuit, that is, the differential amplifier circuit composed of the load and the operational amplifier is in parallel, and the differential-mode input impedance Z diff of the operational amplifier is generally 100 MΩ. Therefore, the unloaded state is approximately equivalent to a resistive load of 100 megohms. Assuming that the equivalent resistance of the SSPC main power circuit is 10 MΩ when it is turned off, when the load is unloaded and the SSPC is in the steady-state off condition, the voltage on the load side is:

[0063]

[0064] After adding the clamping circuit, since the equivalent resistance of the clamping circuit is much smaller than the equivalent resistance of the SSPC in the off state R SSPC , the voltage drop generated by the leakage current on the load side is much lower than the power supply voltage. The specific no-load clamping voltage V C is as follows:

[0065] V C = 2 V F + V DS_aux + ( V DS_CCS + Ri leak ) (7)

[0066] In the above formula V F is the forward conduction voltage drop of a single diode in the rectifier bridge, V DS_aux is the drain-source conduction voltage drop of the enhancement-mode MOSFET, V DS_CCS is the drain-source conduction voltage drop of the depletion-mode MOSFET, R is the negative feedback resistor in the constant current source circuit, i leak is the branch leakage current. After adding this clamping circuit, the voltage on the load side is much lower than that without the clamping circuit, greatly improving the safety of the system.

[0067] Figure 7 is the working circuit diagram of the capacitive load and the SSPC under the steady-state off condition. Among them, (a) is the circuit without the clamping circuit. For solid-state switches such as MOSFETs or IGBTs, even in the off state, there is still a very small leakage current (in the order of μA) in these devices. When the SSPC is turned off, this leakage current will slowly charge the capacitive load:

[0068]

[0069] Although the off-state leakage current of the SSPC is small, the continuous charging of the capacitive load will cause the voltage to rise linearly with time, and this voltage may pose a hazard to personnel or equipment and needs to be suppressed through circuit design or protection measures.

[0070] Figure 7 In (b) is the circuit after adding the clamping circuit. Ignoring the current of the capacitive load, the voltage on the load side at this time is:

[0071] V C =2 V F + V DS_aux +( V DS_CCS + Ri leak ) (9)

[0072] Where V F is the forward conduction voltage drop of a single diode in the rectifier bridge, V DS_aux is the drain-source conduction voltage drop of the enhancement-mode MOSFET, V DS_CCS is the drain-source conduction voltage drop of the depletion-mode MOSFET, R is the negative feedback resistor in the constant current source circuit, i leak is the branch leakage current.

[0073] When the power MOSFET is turned on, the voltage between its drain and source is usually maintained at the millivolt level; while in the off state, the leakage current is only in the microampere range. By introducing a clamping circuit and setting a negative feedback resistor of dozens of ohms, the voltage on the load side can be effectively limited within a few volts. Compared with the situation without adding a clamping circuit, after adding the clamping circuit, the voltage on the load side can remain basically stable, avoiding the continuous accumulation of "virtual voltage" caused by leakage current. This design not only ensures the reliability of the system, but also eliminates potential safety hazards, effectively protecting the safety of personnel and equipment.

[0074] The above embodiments are only used to illustrate the technical idea of the present invention, and the protection scope of the present invention cannot be limited thereby. Any changes made on the basis of the technical solution according to the technical idea proposed by the present invention shall fall within the protection scope of the present invention.

Claims

1. A bridge-type constant current source clamping circuit is applied to an AC solid-state power controller, and is characterized in that, It includes a full-bridge circuit, a constant current source circuit and a unidirectional power switch; two AC input terminals of the full-bridge circuit are respectively connected to the power input terminal and the power ground of the AC solid-state power controller, and the constant current source circuit and the unidirectional power switch are connected in series between two DC output terminals of the full-bridge circuit; a control input terminal of the unidirectional power switch is connected to a control instruction output by a clamping circuit control logic circuit; the clamping circuit control logic circuit includes a NOR gate, an OR gate and an RS flip-flop, two input terminals of the NOR gate are respectively connected to switching instructions of a first power transistor and a second power transistor of a main power circuit of the AC solid-state power controller, and four input terminals of the OR gate are respectively connected to the switching instructions of the first power transistor and the second power transistor, and positive and negative logic signals of the load current direction; an output terminal of the NOR gate is connected to the terminal of the RS flip-flop, an output terminal of the OR gate is connected to the terminal of the RS flip-flop, and the terminal of the RS flip-flop outputs the control instruction.

2. The bridge-type constant current source clamping circuit according to claim 1, wherein, The constant current source circuit includes a depletion-type N-MOSFET and a variable resistor. The drain of the depletion-type N-MOSFET is connected to the positive output terminal of the two DC output terminals of the full-bridge circuit. The source of the depletion-type N-MOSFET is connected to one end of the variable resistor. The other end of the variable resistor is connected to the gate of the depletion-type N-MOSFET and the unidirectional power switch.

3. The bridge-type constant current source clamping circuit according to claim 1, characterized in that The unidirectional power switch is an enhancement-type N-MOSFET. The gate of the enhancement-type N-MOSFET is connected to the control instruction. The source of the enhancement-type N-MOSFET is connected to the constant current source circuit. The drain of the enhancement-type N-MOSFET is connected to the negative output terminal of the two DC output terminals of the full-bridge circuit.

4. An AC solid-state power controller, comprising a main power circuit, a clamping circuit and a clamping circuit control logic circuit, characterized in that The clamping circuit includes a full-bridge circuit, a constant-current source circuit, and a unidirectional power switch; two AC input terminals of the full-bridge circuit are respectively connected to the power input terminal and the power ground of the AC solid-state power controller, and the constant-current source circuit and the unidirectional power switch are connected in series between two DC output terminals of the full-bridge circuit; a control input terminal of the unidirectional power switch is connected to a control instruction output by the clamping circuit control logic circuit; the clamping circuit control logic circuit includes a NOR gate, an OR gate, and an RS flip-flop, two input terminals of the NOR gate are respectively connected to switch instructions of a first power transistor and a second power transistor of the main power circuit of the AC solid-state power controller, four input terminals of the OR gate are respectively connected to the switch instructions of the first power transistor and the second power transistor, and positive and negative logic signals of the load current direction; an output terminal of the NOR gate is connected to the terminal of the RS flip-flop, an output terminal of the OR gate is connected to the terminal of the RS flip-flop, and the terminal of the RS flip-flop outputs the control instruction.

5. The AC solid-state power controller according to claim 4, characterized in that, The constant current source circuit includes a depletion-type N-MOSFET and a variable resistor. The drain of the depletion-type N-MOSFET is connected to the positive output terminal of the two DC output terminals of the full-bridge circuit. The source of the depletion-type N-MOSFET is connected to one end of the variable resistor. The other end of the variable resistor is connected to the gate of the depletion-type N-MOSFET and the unidirectional power switch.

6. The AC solid state power controller according to claim 4, characterized in that The unidirectional power switch is an enhancement-type N-MOSFET. The gate of the enhancement-type N-MOSFET is connected to the control instruction. The source of the enhancement-type N-MOSFET is connected to the constant current source circuit. The drain of the enhancement-type N-MOSFET is connected to the negative output terminal of the two DC output terminals of the full-bridge circuit.

7. The AC solid-state power controller according to any one of claims 4-6, characterized in that, The main power circuit includes a first power transistor and a second power transistor connected in anti-series. The drain of the first power transistor serves as the power input terminal of the AC solid-state power controller and is connected to the AC power supply. The drain of the second power transistor serves as the power output terminal of the AC solid-state power controller and is connected to the clamping circuit and the load. The gate of the first power transistor and the source of the second power transistor are connected to the same analog ground. The gates of the first power transistor and the second power transistor are connected to different switching instructions.

8. The control method of the AC solid-state power controller according to claim 7, characterized in that, Including: When the AC solid-state power controller is turned on: In the positive half-cycle of the AC power supply voltage, first turn on the second power transistor, and then turn on the first power transistor after the voltage passes through the zero point. The unidirectional power switch is turned off. In the negative half-cycle of the AC power supply voltage, first turn on the first power transistor, and then turn on the second power transistor after the voltage passes through the zero point. The unidirectional power switch is turned off. When the AC solid-state power controller is turned off: In the positive half-cycle of the load current, first turn off the second power transistor, and then turn off the first power transistor after the current passes through the zero point. The unidirectional power switch is turned on. In the negative half-cycle of the load current, first turn off the first power transistor, and then turn off the second power transistor after the current passes through the zero point. The unidirectional power switch is turned on.

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