CN101882927A - A Soft Switching Device for AC Solid State Power Controller - Google Patents

Abstract

The invention relates to a soft switching device of an AC solid-state power controller, which is characterized in that it includes a power circuit and a control circuit, the control circuit receives an input control signal, and combines the control signal with the current signal CUR and voltage signal obtained by sampling the power circuit VOL, and output the power switching tube driving signal QG to the power circuit; the soft switching device of the AC solid-state power controller proposed by the present invention replaces the bidirectional thyristor with a power MOSFET tube, and as the main switching device of the AC SSPC, it can overcome the aforementioned thyristor It can also realize the soft switching control of AC SSPC, and complete the two main power MOSFET tubes sharing a drive circuit. When the power supply voltage crosses zero, the two tubes are turned on at the same time; off.

Description

A Soft Switching Device for AC Solid State Power Controller

technical field

The invention relates to a soft switch device of an AC solid-state power controller, which belongs to an automatic circuit on-off control device.

Background technique

Solid-State Power Controller (SSPC) is an intelligent switching device composed of semiconductor devices, which is used to turn on or off the circuit, realize circuit protection and accept the control signal of the front-end computer and report its working status signal. Its function is similar to that of a traditional mechanical thermal automatic switch, a combination of a fuse and a relay in series, or other control protectors, but it is much superior to these traditional devices in terms of performance and function: it can quickly connect and disconnect circuits without No arcing, so high-altitude performance is good, especially suitable for aviation applications; there are no moving parts inside, so there is no mechanical wear, low failure rate, and high reliability; when overloaded, it will "trip" according to the anti-delay characteristic to protect electrical load equipment And lines; with electrical isolation measures, strong anti-interference ability, etc. ^[1] . As early as the 1970s, foreign countries began to study SSPC, but it has not been practically applied for many years. The main reason is that the on-state voltage drop of the transistor was large at that time, reaching 0.4 volts to 0.5 volts, and the on-state loss was much greater than that of the contact switch. In recent years, breakthroughs have been made in power electronics technology, and the on-state resistance of MOS tube devices is only at the milliohm level, creating conditions for the development of SSPC. At present, SSPC has been widely used in new foreign aircraft.

In AC SSPC, the soft switching technology of zero-voltage turn-on and zero-current turn-off of power switch is a key technology.

In the traditional hard switching circuit, due to the delay of the switching device at the moment of turning on and turning off, the voltage and current have a considerable overlapping part, which leads to a large power loss. Soft switching technology is to reduce the voltage to zero before the switch tube is turned on to achieve zero-voltage turn-on; before the switch tube is turned off, reduce the current to zero to achieve zero-current shutdown.

Soft switching technology can not only effectively reduce the turn-on and turn-off loss of the switch tube, but also reduce the voltage and current spikes caused by excessive dv/dt and di/dt caused by the sudden change of voltage and current at the moment of turn-on and turn-off, thereby Avoid the operation track of the switching tube beyond the safe operating area (SOA), ensure the reliable operation of the switching tube, and at the same time reduce the serious electromagnetic interference caused by excessively high di/dt and dv/dt.

At present, the main power transistors of foreign AC solid-state power controller products use bidirectional thyristors, such as the P111 series AC solid-state power controllers of LEACH Company ^[2] and the SSPC 90000 series products of NHI Company ^[3] . As a power semiconductor device, the bidirectional thyristor has the advantages of small size, light weight, high capacity, and good control characteristics. The bidirectional thyristor can realize the natural zero-crossing shutdown of the current, and is equipped with a special trigger chip, such as the MOC3061 produced by Motorola, and the bidirectional thyristor can also easily realize zero voltage turn-on.

Although bidirectional thyristors can achieve zero-voltage turn-on and current zero-crossing shutdown when used in AC applications, but when bidirectional thyristors are used as power switches for AC solid-state power controllers, they also bring some problems:

(1) When a high-current short-circuit fault occurs in the AC solid-state power controller, the protection circuit operates immediately and a protection shutdown signal is issued, but the bidirectional thyristor still cannot be turned off until the current crosses zero, which will cause the short-circuit current to last too long, The short-circuit current can last up to half a cycle.

(2) The internal structure of the thyristor determines that its conduction voltage drop is relatively large, and its conduction voltage drop is basically the voltage drop of the base-emitter of the two transistors, which is equivalent to the voltage drop of two PN junctions.

(3) The turn-on time of the thyristor is about 1 to 4.5 microseconds, but its turn-off time is longer, about several hundred microseconds, because after turning off, it takes a while to extract minority carriers and recombine carriers. Therefore, the working frequency of the triac is low, and it is generally used in occasions below 400Hz, which does not meet the needs of the aircraft AC variable frequency power system.

These factors above limit the use of triacs in solid-state power controllers. In particular, the conduction voltage drop of the thyristor is large, so that the existing AC solid-state power controller can only be used in low-power applications. As the load current increases, the power consumption of the thyristor increases significantly, and the tube generates serious heat. Therefore, with the development of my country's aerospace industry, it is urgent to develop an AC solid-state power controller with new power electronic devices as the main power switch.

With the development of power electronics technology, power MOSFET is gradually emerging. Because it is a voltage-type control device, it has high input impedance, low driving power, fast switching speed, small on-resistance, and on-resistance has a positive temperature coefficient. These advantages make it possible for power MOSFETs to replace bidirectional thyristors and become the main switching device of new AC solid-state power controllers.

MOSFET is often used as a DC switch. In a DC circuit, an appropriate control voltage is applied between the gate and source of the MOSFET to control the on-off of the load. MOSFET can also control the AC circuit. Due to the parasitic diode in its structure, when a single MOSFET is used as an AC switch, it can only control the positive half cycle, and the negative half cycle current will turn on the circuit through the parasitic diode. Therefore power MOSFETs are not suitable for direct switching of AC waveforms.

Configuring a combined circuit with a series structure can solve the control of the AC waveform by the power MOSFET. The combined circuit is shown in Figure 1. Two power MOSFETs are connected in reverse series, and the sources of MOS1 and MOS2 are connected together. Parasitic anti-parallel diodes inside the MOSFETs prevent each other from turning on at the same time. The channel of the power MOSFET is a bidirectional switch, that is, when an appropriate control voltage is applied, the MOSFET can conduct current in the reverse direction. As long as the voltage on the channel is lower than the voltage on the internal diode (the voltage is generally higher than the voltage of the discrete diode), most Current will flow through the channel of the power MOSFET and not through the internal diode. Therefore, when the switch in the circuit shown in Figure 1 is turned on, a low switch voltage drop can be achieved.

Using power MOSFET as the switching tube of the AC solid-state power controller can overcome the above-mentioned shortcomings of the thyristor, but it also brings the problem that it is difficult to realize soft switching. Therefore, it is necessary to design a dedicated drive circuit to realize the "zero-voltage turn-on and zero-current turn-off" of the circuit.

The control driving signals of the two MOSFETs in the circuit are not sent out at the same time, but need to be organically combined with the positive and negative half cycles of the AC power supply to control the on-off of the MOSFETs in a certain order. When the power tube is in the cut-off state and the AC power is in the positive half cycle, firstly send a turn-on signal to the lower tube MOS2 of the anti-series structure to make it conduct, while the upper tube MOS1 remains in the off state, and the whole circuit is still in the off state at this time , no current flows; when the AC power supply changes from positive half cycle to negative half cycle, the main circuit has current flow at the moment when the AC power crosses zero, and the flow path is the conductive channel of MOS2 and the parasitic diode D1 of MOS1; in AC When the power supply works in the negative half cycle, it sends a turn-on signal to the upper tube MOS1, and the current in D1 will naturally commutate to the conductive channel of MOS1 (assuming that the voltage drop of the conductive channel is small, it is not enough to make the parasitic diode in the body conduct through clamp). In this way, the turn-on process of the AC solid-state power controller is realized. From the above analysis, it can be seen that the power tube is turned on by natural zero-crossing, so the zero-crossing accuracy is good, and there is no error in zero-crossing. Moreover, this control strategy does not have strict requirements for the detection of zero-crossing points. , it only needs to send a turn-on signal to the corresponding MOSFET within half a cycle. If the AC power supply is in the negative half cycle, according to the same principle, firstly send a turn-on signal to the upper tube MOS1 during the negative half cycle, and then send a turn-on signal to the lower tube when the power turns to the positive half cycle.

The turn-off process of this control method is that if the load is in the positive half cycle, a turn-off signal is sent to the lower tube MOS2 to turn it off, and the upper tube MOS1 remains on. At this time, the current of the MOS2 tube is controlled by its conductive channel. Natural commutation to the parasitic diode D2 in the body, the AC solid-state power controller remains on; when the load current is working from the positive half cycle to the negative half cycle, the loop current is blocked by the diode D2, no current flows in the main loop, and then only It is enough to send a shutdown signal to the upper tube MOS1. Similarly, if the load current is in the negative half cycle, it is necessary to send a shutdown signal to the upper tube MOS1 first, and then send a shutdown signal to the lower tube MOS2 when the load current turns to the positive half cycle. Since the turn-on and turn-off of this control strategy are at the natural zero-crossing of the AC signal, it can realize the precise zero-voltage turn-on and zero-current turn-off functions of the AC solid-state power controller, and completely suppress the du when turn-on and turn-off. /dt and di/dt.

The disadvantage of this control method is that the drive control circuit is complex, and the drive control circuits of the two power transistors MOS1 and MOS2 need to be designed separately, which will adversely affect the working reliability and device volume of the AC solid-state power controller.

As mentioned above, the bidirectional thyristor is used as the main switching device of the AC solid-state power controller. Due to its own structure and mature supporting driver chips, it can be relatively easy to achieve zero-voltage turn-on and zero-current turn-off, but the turn-on voltage of the bidirectional thyristor The disadvantages of large dropout, short-circuit protection cannot be shut down in time, and low operating frequency limit its application in solid-state power controllers.

If a power MOSFET is used to replace the bidirectional thyristor, although the aforementioned shortcomings of the thyristor can be overcome, it also brings about the problem that it is difficult to realize soft switching. Its application in solid-state power controllers.

Contents of the invention

In order to avoid the deficiencies of the prior art, the present invention proposes a soft switching device for an AC solid-state power controller, so that MOS1 and MOS2 share a drive circuit, and as long as the drive circuit sends a control signal, the two tubes will be turned on or off at the same time , realizing zero-voltage turn-on and zero-current turn-off of an AC solid-state power controller.

A soft switching device for an AC solid-state power controller, characterized in that it includes a power circuit and a control circuit, the control circuit receives an input control signal, and combines the control signal with the current signal CUR and voltage signal VOL sampled by the power circuit, and Output the power switch tube drive signal QG to the power circuit; the control circuit includes a detection circuit, a DSP circuit and a CPLD circuit, and the detection circuit performs zero-crossing detection on the voltage signal VOL and the current signal CUR of the AC power supply in the loop. A zero-crossing signal is sent to the CPLD circuit when a zero-crossing signal value occurs; the DSP circuit receives the on-off control signal input from the upper position, and sends an on-off control signal to the CPLD circuit; the CPLD circuit sends a control signal to the DSP circuit and the detection circuit. The voltage and current zero-crossing signal performs logic calculation, and then sends the power tube soft switch drive signal QG; the power circuit includes a MOSFET tube and a bias resistor, and two MOSFET tubes Q ₀ and Q ₁ are reversely connected in series to form a main switch tube, Capacitor C ₀ and resistor R ₆ are connected in series and connected to the drains of Q ₀ and Q ₁ to form an absorbing protection circuit connected in parallel to both ends of the main switch tube; resistors R ₄ and R ₅ are connected in parallel to the main switch tube to form a main circuit voltage divider The circuit provides the AC voltage signal VO1 of the power circuit to the control circuit; the sampling resistor R ₇ is connected in series with the power circuit, and converts the current flowing through the power circuit into a voltage signal CUR for the control circuit.

The detection circuit includes a voltage detection circuit and a current detection circuit, and the voltage detection circuit is composed of an operational amplifier LM741 to form an inverting amplifying circuit to amplify the obtained main circuit AC voltage signal VOL, and the amplified signal is sent to the photoelectric coupler The device HCPL-3700 performs zero-crossing detection, and sends out a pulse signal VZ00 at the zero-crossing point of the power supply voltage; R ₃₈ and R ₁₈ divide the voltage signal CUR on the main circuit sampling resistor and input it to VIN+ and VIN- of HCPL-788J, R ₁₈ and amplitude diode D ₆ , D ₇ are connected in parallel between VIN+ and VIN- of HCPL-788J, VREF is connected to the reference voltage of 3V, HCPL-788J isolates and amplifies the input signal and outputs it from VOUT, through R ₃₄ , R ₃₅ and R ₃₆ are sent to pin 2 of voltage comparator U1A and pin 5 of U1B, and the comparison level of 1.5V is applied to pin 3 of comparator U1A and pin 6 of U1B; the series connection of capacitors C18 and R16 The circuit is at the output terminal of U1A, and R ₂₈ and diode D ₄ are connected in parallel with the ground, and the series circuit of capacitor C ₁ 9 and R ₁₇ is at the output terminal of U1B, and R ₂₉ and diode D ₅ are connected in parallel with the ground.

The soft switching device of the AC solid-state power controller proposed by the present invention replaces the bidirectional thyristor with a power MOSFET tube as the main switching device of the AC SSPC, which can not only overcome the aforementioned shortcomings of the thyristor, but also realize the soft switching control of the AC SSPC, and complete The two main power MOSFET tubes share a drive circuit. When the power supply voltage crosses zero, the two tubes are turned on at the same time; when the current flowing through the power tube crosses zero, the two tubes are turned off at the same time.

Description of drawings

Figure 1: Power MOSFET AC switch in prior art;

Fig. 2: The functional block diagram of the soft switching device of the AC solid-state power controller proposed by the present invention;

Fig. 3: The principle diagram of the power circuit in the soft switching device of the AC solid-state power controller proposed by the present invention;

Fig. 4: The functional block diagram of the control circuit in the soft switching device of the AC solid-state power controller proposed by the present invention;

Figure 5: Schematic diagram of the voltage detection circuit;

Figure 6: Schematic diagram of the current detection circuit;

Figure 7: Internal schematic diagram of CPLD circuit;

Figure 8: AC SSPC zero-voltage turn-on waveform;

Figure 9: Waveform diagram of AC SSPC zero current shutdown.

Detailed ways

Now in conjunction with embodiment, accompanying drawing, the present invention will be further described:

The schematic diagram of the power circuit is shown in Figure 3. The rated current of this circuit design is 10A. After considering the margin, the main switching tubes Q ₀ and Q ₁ choose the MOSFET tube IXKH70N60 from IXYS Company in Germany. The rated current of this power tube is 70A; The capacitor C ₀ of the protection circuit is selected as 0.1 μF, the resistor R ₆ is selected as 47Ω; the sampling resistor R ₇ is selected as 10mΩ, so as to ensure that the sampling resistor can generate a voltage of 100mV when the rated current flows.

In the control circuit, the DSP chip adopts TMS320F2812 of TI Company, and the CPLD chip adopts EPM7128AETC100 of ALTERA Company; -3700 adopts the products of HP Company. The resistance and capacitance values of the peripheral circuit components in the figure are shown in the figure; the schematic diagram of the current detection circuit is shown in Figure 6. The isolation amplifier 788J in the figure is the product of HP Company. The operational amplifiers U1A and U1B are LM393 from NS Company, and the resistance and capacitance values of other peripheral circuit components are shown in the figure.

The principle block diagram of the soft switching device of the AC solid-state power controller in the present invention is shown in FIG. 2 .

In Figure 2, the device is divided into two parts, the power circuit and the control circuit. The power circuit is mainly composed of a power switch MOSFET and a sampling resistor to realize switching on and off the power supply and the load; the control circuit completes the drive and control of the power switch tube. Function. It can be seen from Figure 2 that the control circuit receives the control signal sent by the host computer, and at the same time samples the current signal CUR and voltage signal VOL of the circuit from the power circuit, performs analysis and calculation, and sends out the power switch tube drive signal QG.

The composition and principle of the power circuit and the control circuit will be described in detail below.

The schematic diagram of the power circuit is shown in Figure 3.

In Fig. 3, the main switching tube is formed by MOSFET tubes _Q0 and _Q1 being reversely connected in series, the capacitor _C0 and the resistor _R6 are connected in series, connected to the drains of _Q0 and _Q1 , that is, connected in parallel at both ends of the main switching tube, Form an absorption protection circuit; resistors R ₄ and R ₅ are connected in parallel with the main switch tube to form a main circuit voltage divider circuit, and provide the AC voltage signal VO1 of the power circuit to the control circuit; the sampling resistor R ₇ is connected in series with the power circuit, and will flow through the power circuit The current is converted into a voltage signal CUR, which is provided to the control circuit.

The control circuit in the device is the core part of the invention, which can complete the drive and control of the power switch tube in the device and realize the soft switching function.

The functional block diagram of the control circuit in the soft switch device is shown in Figure 4.

It can be seen from Figure 4 that the control circuit in the device is composed of several parts such as a detection circuit, a DSP circuit and a CPLD circuit. Among them, the detection circuit detects the zero-crossing of the voltage signal VOL of the AC power supply, and detects the zero-crossing of the current signal CUR flowing through the main circuit through the sampling resistor of the main circuit, and sends a zero-crossing signal to the CPLD circuit at the zero-crossing point of the voltage and current respectively; DSP The circuit receives the on-off control signal sent by the host computer through the CAN bus, and sends the on-off control signal to the CPLD circuit; the CPLD circuit performs logic calculation on the control signal sent by the DSP circuit and the voltage and current zero-crossing signal sent by the detection circuit, and sends out power The tube soft switch drive signal QG realizes the zero-voltage turn-on and zero-current turn-off of the power tube of the main circuit.

●DSP circuit

The DSP chip in this device adopts TMS320F2812 of TI Company, and the upper computer and DSP communicate through the CAN bus according to the communication protocol compiled. When the host computer needs to send commands to the device, it only needs to write the CAN message into the sending buffer of the CAN card installed in the host computer. After writing, the CAN message will be automatically sent to the CAN receiving buffer of the DSP chip of the device through the CAN bus, and a message receiving interrupt will be generated. When the interrupt signal is detected, the DSP main program immediately responds to the interrupt, reads the message in its receiving buffer, and transmits the switch command to the CPLD circuit through the I/O port according to the communication protocol between the DSP and the host computer.

●Detection circuit

The detection circuit is a voltage detection circuit and a current detection circuit. The schematic diagram of the voltage detection circuit is shown in Figure 5.

In Figure 5, the operational amplifier LM741 forms an inverting amplifier circuit to amplify the AC voltage signal VOL from the main circuit, and the amplified signal is sent to the photocoupler HCPL-3700.

HCPL-3700 is a voltage/current threshold detection optocoupler produced by FAIRCHILD Company, which detects the zero-crossing of the input AC signal. When HCPL-3700 detects the AC signal, it first performs full-wave rectification on the AC signal through the internal diode rectification circuit, and compares the rectified signal with the preset threshold, which is set to zero in the present invention. When the input AC signal is greater than zero, the circuit output is low level; when the input signal is less than zero level, that is, at the zero crossing point of the AC signal, the circuit output changes from low to high, and a pulse signal is sent out. The width of the pulse signal is determined by HCPL -3700 internal hysteresis decision. It can be seen from the above analysis that the voltage detection circuit can send out the pulse signal VZ00 at the zero crossing point of the power supply voltage. At the same time, HCPL-3700 isolates the input and output signals on the circuit.

The current detection circuit completes the tasks of isolation amplification and current zero-crossing detection, and its circuit schematic diagram is shown in Figure 6.

It can be seen from the figure that the voltage signal CUR from the sampling resistor of the main circuit is divided by R ₃₈ and R ₁₈ and then input to VIN+ and VIN- of 788J. In the figure, the circuit with 788J as the main device completes the isolation and amplification function. The 788J is an isolation amplifier with short circuit and overload detection. Its output level is directly compatible with the A/D converter, has a fast short-circuit detection (3us) function, and outputs an overload detection signal in the form of the absolute value of the input signal. 788J requires the maximum input voltage to be plus or minus 256mV, which should be limited to 200mV under normal circumstances. Therefore, two diodes D ₆ and D ₇ are connected in parallel between VIN+ and VIN- of the 788J to limit the amplitude of the input signal and prevent the chip from being damaged due to excessive current when the main circuit is overloaded or short-circuited. 788J isolates and amplifies the input signal, and outputs from VOUT, the output value varies between 0 and VREF, and its output gain is typically VREF/504mV. In this circuit, the external reference source connected to the VREF pin is a reference voltage of 3V, so the actual gain of HCPL-788J is about 6. Since VREF is 3V, the output AC signal of 788J is superimposed on the DC level of 1.5V.

HCPL-788J outputs the VOUT pin to send the output signal of the isolation amplifier circuit to pin 2 of the voltage comparator U1A and pin 5 of U1B. U1A and U1B use op amp LM393. Since the output signal of the isolation amplifier circuit is an AC signal superimposed on the 1.5V DC level, the 1.5V bias level must be subtracted before the zero-crossing comparison. Therefore, the comparison level REF1.5 of 1.5V is provided for the U1A3 pin of the comparator and the 6 pin of U1B through the reference source in the figure. When the input AC signal of the zero-crossing comparison circuit is greater than the comparison level, U1B outputs +5V high level; when the input AC signal of the zero-crossing comparison circuit is smaller than the comparison level, U1A outputs +5V high level. Capacitors _C18 and _C19 detect the rising edge of the output level of U1A and U1B, and convert the signal into a pulse signal.

From the above analysis, it can be seen that the current detection circuit will send out pulse signals CZ00-1 and CZ00-2 at the zero-crossing point of the current flowing through the main circuit.

●CPLD circuit

The CPLD circuit in this device performs logic calculation on the control signal CMD sent by the DSP circuit and the voltage zero-crossing signal VZ00 and current zero-crossing signals CZ00-1 and CZ00-2 sent by the detection circuit. When the upper computer issues a turn-on command, the CPLD sends a power tube turn-on signal at the zero-crossing point of the AC voltage; after the power tube is turned on, when the upper computer issues a turn-off command, the CPLD sends a turn-off signal at the zero-crossing point of the AC current to realize AC solid-state power control Zero-voltage turn-on and zero-current turn-off of the device.

The internal schematic diagram of the CPLD circuit is as follows:

In Fig. 7, in the initial state of the circuit, the power tube drive signal QG is low level, which blocks the AND gate inst8, and opens the AND gate inst9 through NOT inst26, that is, the initial state of the circuit, the current zero-crossing signal CZ00-1 and CZ00-2 will not get a response in the circuit, and the voltage zero-crossing signal VZ00 is valid. The voltage zero-crossing signal VZ00 is sent to the D flip-flop inst27 through the OR gate inst10. Through the D flip-flop, at each voltage zero-crossing point, the CPLD circuit sends the control signal CMD sent by the DSP circuit to the circuit output signal QG. Once the CMD signal is low level to high level, the power drive signal QG is flipped from low to high level at the voltage zero crossing point, and the zero voltage turn-on of the power tube is realized; at this time, the output signal QG of the CPLD circuit remains at high level, and the level Block the AND gate inst9 through NOT inst26, and open the AND gate inst8 at the same time, that is, after the power tube is turned on, the voltage zero-crossing signal VZ00 will not get a response in the circuit, and the current zero-crossing signals CZ00-1 and CZ00-2 become valid . The current zero-crossing signal is also sent to the D flip-flop. Through the D flip-flop, at each current zero-crossing point, the CPLD circuit sends the control signal CMD to the circuit output signal QG. Once the CMD signal changes from high level to low level, The power driving signal QG turns from high level to low level at the current zero-crossing point, so as to realize the zero-current shutdown of the power tube.

The effect of this embodiment:

The AC SSPC designed according to the above principles can conveniently and reliably realize the zero-voltage turn-on and zero-current turn-off functions of the device. The effect analysis is carried out according to the waveform diagram of the device after receiving the turn-on and turn-off commands respectively.

In Figure 8, channel 1 detects the MOSFET drive signal, which is 0V at low level and 12V at high level; channel 2 detects the load voltage of SSPC. It can be seen that the load voltage is 115V effective value and 162V peak value. It can be seen from Fig. 8 that the zero-voltage turn-on circuit in the present invention can accurately detect the voltage zero-crossing point. After the turn-on control signal is sent out, the MOSFET drive signal is accurately sent at the moment when the power supply voltage crosses zero through the zero-voltage turn-on circuit, realizing power Zero-voltage turn-on of the switch.

In Figure 9, channel 2 detects the MOSFET drive signal; channel 1 detects the load current of the SSPC, and it can be seen from the figure that the effective value of the load current is 5A. It can be seen from Figure 9 that when the shutdown command is issued, the SSPC does not shut down immediately, but through the function of the zero-current shutdown circuit, the shutdown signal is accurately issued at the zero-crossing point of the load current to achieve zero-current shutdown.

From the waveforms in Figure 8 and Figure 9, it can be seen that since the circuit effectively realizes zero-voltage turn-on and zero-current turn-off, the power loop will not generate voltage and current due to dv/dt and di/dt at the moment of SSPC turn-on and turn-off The sharp peak ensures the reliable operation of the switch tube, and at the same time reduces the electromagnetic interference generated by di/dt and dv/dt, effectively improving the reliability of the device.

Claims (2)

1. A soft switching device of an AC solid-state power controller, characterized in that it comprises a power circuit and a control circuit, the control circuit receives an input control signal, and the control signal is combined with the current signal CUR and the voltage signal VOL obtained by power circuit sampling , and output the power switch tube drive signal QG to the power circuit; the control circuit includes a detection circuit, a DSP circuit and a CPLD circuit, and the detection circuit performs zero-crossing detection on the voltage signal VOL and the current signal CUR of the AC power supply in the loop, and the two signals When any of the zero-crossing signal values occurs, a zero-crossing signal is sent to the CPLD circuit; the DSP circuit receives the on-off control signal input from the upper position, and sends an on-off control signal to the CPLD circuit; the CPLD circuit detects the control signal sent by the DSP circuit The voltage and current zero-crossing signal sent by the circuit is logically calculated, and then the power tube soft switch driving signal QG is sent out; the power circuit includes a MOSFET tube and a bias resistor, and two MOSFET tubes Q ₀ and Q ₁ are reversely connected in series to form a main switch The capacitor C ₀ and the resistor R ₆ are connected in series with the drains of Q ₀ and Q ₁ to form an absorbing protection circuit connected in parallel to both ends of the main switch tube; resistors R ₄ and R ₅ are connected in parallel with the main switch tube to form a main circuit The voltage divider circuit provides the AC voltage signal VO1 of the power circuit to the control circuit; the sampling resistor R ₇ is connected in series with the power circuit, and converts the current flowing through the power circuit into a voltage signal CUR for the control circuit. 2. The soft switching device of the AC solid-state power controller according to claim 1, characterized in that: the detection circuit includes a voltage detection circuit and a current detection circuit, and the voltage detection circuit is composed of an operational amplifier LM741 inverting The amplifying circuit amplifies the obtained main circuit AC voltage signal VOL, and the amplified signal is sent to the photocoupler HCPL-3700 for zero-crossing detection, and sends out a pulse signal VZ00 at the zero-crossing point of the power supply voltage; R ₃₈ and R ₁₈ connect the main circuit The voltage signal CUR on the sampling resistor is divided and input to VIN+ and VIN- of HCPL-788J, R ₁₈ and amplitude diodes D ₆ and D ₇ are connected in parallel between VIN+ and VIN- of HCPL-788J, VREF is connected to 3V HCPL-788J isolates and amplifies the input signal and then outputs it from VOUT, and sends it to pin 2 of voltage comparator U1A and pin 5 of U1B through R ₃₄ , R ₃₅ and R ₃₆ , and the comparison voltage of 1.5V Applied to comparator U1A's 3-pin and U1B's 6-pin; the series circuit of capacitor C ₁₈ and R ₁₆ is at the output of U1A, and R ₂₈ and diode D ₄ are connected in parallel with the ground, and the capacitor C ₁₉ and R ₁₇ The series circuit is at the output of U1B with R ₂₉ and diode D ₅ in parallel with ground.

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