CN116191368A

CN116191368A - Protection circuit and direct current system

Info

Publication number: CN116191368A
Application number: CN202310070622.0A
Authority: CN
Inventors: 胡光铖; 官威
Original assignee: Shanghai Baizhu Chenghang New Energy Co ltd
Current assignee: Shanghai Baizhu Chenghang New Energy Co ltd
Priority date: 2023-01-12
Filing date: 2023-01-12
Publication date: 2023-05-30

Abstract

The embodiment of the invention discloses a protection circuit and a direct current system. The protection circuit includes: a PWM circuit for outputting a control signal; a driving circuit for power amplifying the control signal; a switching circuit configured to turn on or off a connection between the main power unit and the interface unit in response to a control signal; a clamping circuit configured to introduce a feedback current to a control terminal of the switching circuit to clamp a voltage across the switching circuit at a stable voltage when the voltage across the switching circuit is greater than a preset threshold voltage; the output end of the driving circuit is connected to the control end of the switching circuit, and the switching circuit is connected in series between the positive bus or the negative bus. Through the mode, the embodiment of the invention can ensure the reliable turn-off of the switch circuit, and reduces the energy absorbed by the protection circuit when the fault current is turned off through rapidly detecting the fault. The fault can be judged by detecting the current of the capacitor, so that the cost of the detection element is reduced.

Description

Protection circuit and direct current system

Technical Field

The embodiment of the invention relates to the technical field of electronics, in particular to a protection circuit and a direct current system.

Background

In photovoltaic and energy storage application occasions, the direct current coupling scheme is more and more widely applied due to advantages in cost, efficiency and the like. However, when a dc system is shorted, the system short circuit impedance is small, the short circuit current increases dramatically, and there is no natural zero crossing, as compared to an ac system. If not timely protected, the short circuit current may damage equipment in the system. Short-circuit protection of a direct current system has a great challenge, and for safety of the direct current system, it is required to rapidly detect an abnormality and disconnect a fault point. In order to protect the equipment connected to the dc bus, it is common practice to add protection devices such as mechanical circuit breakers, fuses and the like at the equipment ports, however, these devices are costly and slow to protect, and the equipment is usually disabled before the protection devices act, resulting in larger secondary damage.

Compared with the traditional mechanical switch, the semiconductor switch can greatly improve the switching speed, and can be used for realizing quick turn-off. And the IGBT module is connected in series with the equipment port along the short-circuit fault current direction, and when fault abnormality is detected, the IGBT is turned off by driving of the IGBT module, and the flowing loop of fault current is blocked, so that equipment is protected. However, the rapid turn-off of the IGBT may cause serious voltage stress problems, which in turn damage the IGBT. Especially when the stray inductance of the fault loop is large, the energy of the stray inductance at the turn-off moment can generate a very large voltage spike. In order to reduce the voltage stress when the IGBT is turned off, the turn-off resistance is increased, soft turn-off is adopted, passive absorption circuits are added at two ends of the IGBT, and the passive absorption circuits are RC and RCD circuits. However, when the stray inductance of the fault loop is large, the voltage spike is absorbed by passive absorption, the RC parameter needs to be designed very large, and the cost and the volume cost are high.

In order to solve the problem when the stray inductance of the fault loop is large, diodes can be connected in parallel between +/-ports of the equipment nearby. When the IGBT turns off, the diode may provide a freewheeling circuit for most of the stray inductive current, thereby reducing the design requirements of the absorption loop. However, the added diode is a high-voltage diode, needs to be capable of bearing high surge current, needs to bear high blocking voltage for a long time in normal operation, and has high cost and low reliability.

Disclosure of Invention

In order to solve the technical problems, one technical scheme adopted by the embodiment of the invention is as follows: there is provided a protection circuit applied to a direct current system including a main power unit and an interface unit to which positive and negative bus bars of the main power unit are connected, respectively, the protection circuit comprising: a PWM circuit for outputting a control signal including an on signal and an off signal; a driving circuit for amplifying the power of the control signal; a switching circuit configured to turn on or off a connection between the main power unit and the interface unit in response to the control signal; a clamping circuit configured to introduce a feedback current to a control terminal of the switching circuit to clamp a voltage across the switching circuit at a stable voltage when a voltage across the switching circuit is greater than a preset threshold voltage; the output end of the driving circuit is connected to the control end of the switching circuit, and the switching circuit is connected in series between the positive bus or the negative bus.

In some embodiments, the protection circuit further comprises: and the auxiliary detection circuit is connected between the input end of the driving circuit and one end of the switching circuit and is used for feeding back the voltages at two ends of the switching circuit to the driving circuit.

In some embodiments, the protection circuit further comprises: and a first signal processing circuit configured to output an abnormal signal to the PWM circuit to cause the PWM circuit to output the off signal when it is detected that the output current of the main power unit is greater than or equal to a preset first current threshold.

In some embodiments, the protection circuit further comprises: and a second signal processing circuit configured to output a protection signal to the PWM circuit to cause the PWM circuit to output the off signal when it is detected that the output current change rate of the main power unit is greater than or equal to a first current change threshold.

In some embodiments, the protection circuit further comprises: a first capacitor arranged between the positive bus and the negative bus, wherein a first connection point is formed at the connection position of the first capacitor and the negative bus or at the connection position of the first capacitor and the positive bus; and a third signal processing circuit configured to output a protection signal to the PWM circuit to cause the PWM circuit to output the off signal when it is detected that the sampling current change rate of the first capacitor is greater than or equal to a preset second current change threshold, or the sampling current is greater than a preset second current threshold.

In some embodiments, the switching circuit is an IGBT tube, and if the switching circuit is connected in series between the negative bus bars, an emitter of the IGBT tube is connected to a negative electrode of the main power unit through the negative bus bars, and a collector of the IGBT tube is connected to the interface unit through the negative bus bars; and if the switch circuit is connected in series between the positive buses, the collector of the IGBT tube is connected to the positive electrode of the main power unit through the positive buses, and the emitter of the IGBT tube is connected to the interface unit through the positive buses.

In some embodiments, the clamping circuit comprises a transient diode and a current limiting unit, the current limiting unit comprises a second resistor, an RC circuit or an RCD circuit, wherein when the current limiting unit is the second resistor, a cathode of the transient diode is connected to a collector of the IGBT tube, and an anode of the transient diode is connected to one end of the second resistor; the other end of the second resistor is connected to the gate electrode of the IGBT tube.

In some embodiments, the drive circuit further comprises a first resistor, one end of the first resistor is connected to the gate electrode of the IGBT tube, and the other end of the first resistor is connected to the output end of the drive circuit.

In some embodiments, the auxiliary detection circuit comprises a first diode and a third resistor, wherein a cathode of the first diode is connected to one end of the switching circuit, and an anode of the first diode is connected to one end of the third resistor; the other end of the third resistor is connected to the driving circuit.

In some embodiments, the third signal processing circuit includes a current transformer, a fourth resistor, a second diode, a fifth resistor, a second capacitor, a comparator, and a latch, wherein a primary side of the current transformer is connected in series between the first capacitor and the first connection point, and a head end of a secondary side of the current transformer is connected to an anode of the second diode and one end of the fourth resistor, respectively; the tail end of the secondary side of the current transformer is respectively connected to the other end of the fourth resistor and one end of the second capacitor, and one end of the second capacitor is grounded; the cathode of the second diode is connected to one end of the fifth resistor, the other end of the fifth resistor is connected to the other end of the second capacitor and the first input end of the comparator respectively, and the second input end of the comparator is connected to the electric energy output end of the reference voltage source; the output end of the comparator is connected to the input end of the latch, and the output end of the latch is connected to the input end of the PWM circuit.

In order to solve the technical problems, another technical scheme adopted by the embodiment of the invention is as follows: there is provided a direct current system comprising: a main power unit for outputting a power voltage, the main power unit including an inverter or a converter, the main power unit including a positive bus and a negative bus; an interface unit for filtering the power voltage or disconnecting or connecting the equipment to be powered; a protection circuit as described above; the protection circuit is arranged on the positive bus or the negative bus, and the positive bus and the negative bus are respectively connected to the interface unit.

In some embodiments, the interface unit includes a relay, a load switch, and/or EMI circuitry.

The beneficial effects of the embodiment of the invention are as follows: compared with the prior art, the method and the device are different from the situation of the prior art, when the short-circuit fault of the direct-current bus is detected, the IGBT tube connected in series on the fault current flowing loop is turned off in time, and the turn-off stress of the IGBT tube is controlled within a safety range through the clamping circuit, so that an additional freewheeling diode and a passive absorption circuit are not required to be added. And secondly, faults can be detected rapidly under various short circuit conditions, so that the energy required to be absorbed by the protection circuit when the fault current is turned off is reduced, and the reliable turn-off of the IGBT tube is ensured. Finally, the fault can be judged by detecting the current of the capacitor, so that the cost of the detection element can be reduced.

Drawings

Fig. 1 is a block diagram of a dc system as an application scenario;

fig. 2 is a schematic structural diagram of a first protection circuit according to an embodiment of the present invention;

fig. 3 is a schematic structural diagram of a second protection circuit according to an embodiment of the present invention;

fig. 4 is a schematic structural diagram of a third protection circuit according to an embodiment of the present invention;

fig. 5 is a schematic structural diagram of a fourth protection circuit according to an embodiment of the present invention;

fig. 6 is a schematic structural diagram of a fifth protection circuit according to an embodiment of the present invention;

fig. 7 is a schematic structural diagram of a sixth protection circuit according to an embodiment of the present invention;

fig. 8 is a schematic structural diagram of a seventh protection circuit according to an embodiment of the present invention;

fig. 9 is a schematic structural diagram of a seventh protection circuit according to an embodiment of the present invention, so as to illustrate a circuit topology of a third signal processing circuit;

fig. 10 is a schematic structural diagram of a dc system according to an embodiment of the present invention.

Detailed Description

The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the present invention, but are not intended to limit the invention in any way. It should be noted that variations and modifications could be made by those skilled in the art without departing from the inventive concept. These are all within the scope of the present invention.

In order to make the objects, technical solutions and advantages of the present application more apparent, the present application will be further described in detail with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the present application.

Fig. 1 is an application environment provided in an embodiment of the present invention. As shown in fig. 1, the application environment is a dc system, which includes a main power unit 10 and an interface unit 20.

In the present embodiment, the positive electrode of the dc bus of the main power unit 10 is referred to as a positive bus, and the negative electrode of the dc bus is referred to as a negative bus.

Wherein the positive and negative bus bars of the main power unit 10 are connected to the access terminals of the interface unit 20, respectively.

The main power unit 10 includes, as a power output unit, a power output device having a direct current bus, such as an inverter, a DC-DC converter, or the like.

The interface unit 20 performs filtering and/or protection functions, and the interface unit 20 includes a relay, a load switch, or an EMI circuit, or any combination of a relay, a load switch, and an EMI circuit. Or the lead can be directly adopted on the premise that filtering or protecting effect is not needed.

Based on the above application scenario, a schematic structural diagram of a protection circuit provided in an embodiment of the present invention is shown in fig. 2, where the protection circuit includes: a switching circuit 100, a clamping circuit 200, a driving circuit 300, and a PWM circuit 400.

Wherein the switching circuit 100 is connected in series between the positive bus or the negative bus.

In the present embodiment, the switching circuit 100 is illustrated as being connected in series between the negative bus bars, one end of the switching circuit 100 is connected to the main power unit through the negative bus bars, and the other end of the switching circuit 100 is connected to the interface unit through the negative bus bars.

The switching circuit 100 is configured to switch on or off a connection between the main power unit and the interface unit in response to a control signal. In particular in that the connection between the main power unit and the interface unit is maintained in response to an on signal or in that the connection between the main power unit and the interface unit is broken in response to an off signal.

The clamp circuit 200 is configured to introduce a feedback current to the control terminal of the switch circuit 100 to slow down the turn-off speed of the switch circuit 100 and clamp the voltage across the switch circuit 100 at a stable voltage when the voltage across the switch circuit is greater than a preset threshold voltage.

The driving circuit 300 is used for power amplifying the control signal. The output terminal of the driving circuit 300 is connected to the switching circuit 100 and the clamping circuit 200 through a first resistor R1, respectively, and the second sample of the driving circuit 300 is connected to one terminal of the switching circuit 100.

The driving circuit 300 is a prior art, and a specific structure thereof is not described in the present embodiment.

The PWM circuit 400 is configured to output a control signal including an on signal and an off signal. An output terminal of the PWM circuit 400 is connected to a signal input terminal of the driving circuit 300.

It should be noted that the PWM circuit 400 may be implemented by a digital chip or a logic chip, such as DSP, CPLD, ARM, FPGA. The PWM circuit 400 is a prior art, and a specific structure thereof is not described in the present embodiment.

In this embodiment, the switching circuit 100 is an IGBT tube Q1, an emitter of the IGBT tube Q1 is connected to a negative electrode of the main power unit through a negative bus, and a collector of the IGBT tube Q1 is connected to the interface unit through a negative bus.

In some embodiments, the switch circuit may also be a MOSFET, and the corresponding connection method is not described herein.

The clamp circuit 200 includes a transient diode TVS1 and a current limiting unit 210, and the current limiting unit 210 includes a second resistor R2, an RC circuit, or an RCD circuit. In the embodiment of the present application, the current limiting unit 210 is illustrated by taking the second resistor R2 as an example.

The cathode of the transient diode TVS1 is connected to the collector of the IGBT tube Q1, and the anode of the transient diode TVS1 is connected to one end of the second resistor R2; the other end of the second resistor R2 is connected to the gate of the IGBT tube Q1.

In other embodiments, clamp 200 may include several transient diodes.

The protection circuit further includes a first resistor R1, one end of the first resistor R1 is connected to the gate of the IGBT tube Q1, and the other end of the first resistor R1 is connected to the output end of the driving circuit 300.

The specific working principle is as follows: when the main power unit works normally, the PWM circuit 400 sends out a conducting signal to keep the IGBT tube Q1 normally on.

When detecting that the output current of the main power unit is abnormal or needs to be stopped rapidly, the PWM circuit 400 sends a turn-off signal, and the turn-off signal is amplified by the driving circuit 300 and then output to the IGBT tube, so that the IGBT tube Q1 is turned off. In the turn-off process of the IGBT tube Q1, the voltages at the two ends of the collector and the emitter of the IGBT tube Q1 rise rapidly, and when the voltage is greater than the threshold diode voltage set by the transient diode TVS1, feedback current flows into the gate of the IGBT tube Q1 through the transient diode TVS1 and the second resistor R2, so that the turn-off speed of the IGBT tube Q1 is slowed down, and the rising speed of the voltages at the two ends of the collector and the emitter of the IGBT tube Q1 is slowed down.

When the feedback current flowing into the gate of the IGBT Q1 through the clamp circuit 200 and the turn-off speed of the IGBT Q1 reach a certain dynamic balance, the voltages at the collector and emitter ends of the IGBT Q1 will be clamped at a stable value, called a stable voltage, and the IGBT Q1 will continue to consume the energy of the loop stray inductance until the stray inductance energy is insufficient to maintain the voltages at the collector and emitter ends of the IGBT Q1, and the voltages at the two ends of the IGBT Q1 will gradually drop to the normal blocking voltage value of the IGBT Q1, so that a higher voltage spike will be generated when the turn-off fault current is avoided.

In other embodiments, the switch circuit 100 may be connected in series between the positive buses, but it should be noted that if the switch circuit 100 is connected in series between the positive buses, the collector of the IGBT tube Q1 is connected to the positive pole of the main power unit through the positive bus, and the emitter of the IGBT tube Q1 is connected to the interface unit through the positive bus.

Based on the above embodiment, the second protection circuit is provided in the embodiment of the present invention, and the schematic structural diagram of the second protection circuit is shown in fig. 3. The difference from the first protection circuit is that the second protection circuit adds the auxiliary detection circuit 500 in consideration of the stray inductances in different application scenarios.

The auxiliary detecting circuit 500 is connected between the input end of the driving circuit 300 and one end of the switching circuit 100, and is used for outputting the output voltage of the switching circuit 100 to the driving circuit 300, i.e. outputting the voltage across the switching circuit 100. The auxiliary detection circuit 500 is active when the stray inductance is small.

In the present embodiment, the auxiliary detection circuit includes a first diode D1 and a third resistor R3, wherein the cathode of the first diode D1 is connected to the other end of the switching circuit 100, i.e., the collector of the IGBT tube Q1. The anode of the first diode D1 is connected to one end of the third resistor R3; the other end of the third resistor R3 is connected to the first sampling end of the driving circuit 300.

Specifically, when the stray inductance is small, the output current of the main power unit rises rapidly, the IGBT tube Q1 is rapidly desaturated, the driving circuit 300 can rapidly detect that the voltage Vce between the emitter and the collector of the IGBT tube Q1 is abnormal through the auxiliary detection circuit 500, and then the IGBT tube Q1 is turned off through the clamp circuit 200.

It should be noted that, in the prior art, the desaturation detection technology of the integrated IGBT tube of the driving circuit 300, the driving circuit 300 determines whether the IGBT tube Q1 is desaturated according to the sampled voltage between the collector and the emitter of the IGBT tube Q1 and the control signal of the IGBT tube Q1, if so, outputs a turn-off signal to quickly turn off the IGBT tube and returns fault information.

When the stray inductance is large, the output current rises slowly, and it is difficult for the driving circuit 300 to quickly detect Vce abnormality by the auxiliary detecting circuit 500. For this purpose, the third protection circuit is provided in the embodiment of the present invention, and the schematic structural diagram is shown in fig. 4. The difference from the first protection circuit is that the third protection circuit adds the first signal processing circuit 600.

The first signal processing circuit 600 is configured to output an abnormal signal to the PWM circuit 400 when detecting that the output current is greater than or equal to a preset first current threshold, so that the PWM circuit 400 outputs a shutdown signal. The sampling end of the first signal processing circuit 600 is connected to one end of the switching circuit 100, i.e., the emitter of the IGBT tube Q1, and the output end of the first signal processing circuit 600 is connected to the input end of the PWM circuit 400. The first signal processing circuit 600 functions when the stray inductance is large.

When the stray inductance is large, the output current rises slowly, and it is difficult for the driving circuit 300 to quickly detect Vce abnormality by the auxiliary detecting circuit 500. At this time, the first signal processing circuit 600 may more rapidly determine abnormality and output an abnormality signal to the PWM circuit 400, so that the PWM circuit 400 outputs a turn-off signal to the driving circuit 300, and turns off the IGBT tube Q1 through the clamp circuit 200.

In other embodiments, the auxiliary detecting circuit 500 and the first signal processing circuit 600 may be disposed in the protection circuit at the same time to form a fourth protection circuit, the schematic structure of which is shown in fig. 5, and the corresponding connection relationship is described in the above embodiments, which is not repeated here. Through the effective combination of the two detection modes of the auxiliary detection circuit 500 and the first signal processing circuit 600, the abnormality under various working conditions can be detected rapidly, under the condition of abnormal output current, the IGBT tube Q1 is turned off in time, the continuous increase of the output current is avoided, the energy of a loop is reduced, and the energy of the loop is ensured not to exceed the upper power limit of the clamping circuit.

In other embodiments, based on the first protection circuit, a fifth protection circuit is provided according to an embodiment of the present invention, and a schematic structural diagram of the fifth protection circuit is shown in fig. 6. The difference from the first protection circuit is that the fifth protection circuit adds the second signal processing circuit 700.

The second signal processing circuit 700 is connected between the input terminal of the PWM circuit 400 and one terminal of the switching circuit 100 (i.e., the emitter of the IGBT tube Q1). The second signal processing circuit 700 is configured to output a protection signal to the PWM circuit 400 to cause the PWM circuit 400 to output an off signal when it is detected that the output current change rate of the main power unit is greater than or equal to the first current change threshold.

Specifically, the second signal processing circuit 700 detects the rate of increase of the output current per unit time, i.e., the rate of change of the output current, by collecting the output current of the main power unit and by a sensor. Then, whether the output current change rate is larger than or equal to a preset first current change threshold value is judged. If yes, a protection signal is output to the PWM circuit 400, so that the PWM circuit 400 outputs a turn-off signal to the driving circuit 300, and the IGBT tube Q1 is turned off by the clamp circuit 200.

In some embodiments, the rate of change of the output current may be detected directly using a Rogowski coil, or an electromagnetic field of the output current may be induced using a coil to obtain the rate of change of the output current.

In other embodiments, the auxiliary detecting circuit 500 and the second signal processing circuit 700 may be simultaneously disposed in the protection circuit to form a sixth protection circuit, the schematic structure of which is shown in fig. 7, and the corresponding connection relationship is described in the above embodiments, which is not repeated here. Through the effective combination of the two detection modes of the auxiliary detection circuit 500 and the second signal processing circuit 700, the abnormality under various working conditions can be detected quickly, under the condition of abnormal output current, the IGBT tube Q1 is turned off in time, the continuous increase of the output current is avoided, the energy of a loop is reduced, and the energy of the loop is ensured not to exceed the upper power limit of the clamping circuit.

In other embodiments, based on the first protection circuit, the embodiment of the present invention provides a seventh protection circuit, and a schematic structural diagram of the seventh protection circuit is shown in fig. 8. The difference from the first protection circuit is that the seventh protection circuit adds the first capacitance C1 and the third signal processing circuit 800 provided between the positive bus bar and the negative bus bar.

In this embodiment, a first connection point is formed at a connection point between the first capacitor C1 and the negative bus, an input end of the third signal processing circuit 800 is connected to the first connection point, and an output end of the third signal processing circuit 800 is connected to the PWM circuit 100.

In other embodiments, the first connection point is formed at the connection of the first capacitor C1 and the positive bus.

It should be noted that, the setting position of the first capacitor C1 is flexible. In the present embodiment, the first capacitor C1 is disposed on the main power unit side, and in other embodiments, the first capacitor C1 may also be disposed on the interface unit side.

It should be noted that the first capacitor C1 may be omitted, and the input terminal of the third signal processing circuit 800 may be directly connected to the capacitor connected between the positive bus and the negative bus in the main power unit.

The third signal processing circuit 800 is configured to output a protection signal to the PWM circuit 400 to cause the PWM circuit 400 to output a shutdown signal when it is detected that the sampling current change rate of the first capacitor C1 is greater than or equal to a preset second current change threshold, or the sampling current is greater than or equal to a preset second current threshold.

In some embodiments, the circuit topology of the third signal processing circuit 800 is as shown in fig. 9, and the third signal processing circuit 800 includes a current transformer CT1, a fourth resistor R4, a second diode D2, a fifth resistor R5, a second capacitor C2, a comparator Com1, and a latch Com2.

The primary side of the current transformer CT1 is connected in series between the first capacitor C1 and the first connection point, and the head end of the secondary side of the current transformer CT1 is connected to the anode of the second diode D2 and one end of the fourth resistor R4, respectively.

The tail end of the secondary side of the current transformer CT1 is respectively connected to the other end of the fourth resistor R4 and one end of the second capacitor C2, and one end of the second capacitor C2 is connected to the circuit ground.

The cathode of the second diode D2 is connected to one end of the fifth resistor R5, the other end of the fifth resistor R5 is connected to the other end of the second capacitor C2 and the first input end of the comparator Com1, and the second input end of the comparator Com1 is connected to the power output end of the reference voltage source Vref.

The output of the comparator Com1 is connected to the input of the latch Com2, and the output of the latch Com2 is connected to the input of the PWM circuit 100.

The latch Com2 is a prior art, and may be implemented by a digital chip or a logic chip, such as a latch chip or DSP, CPLD, ARM, FPGA. And will not be described in detail herein.

Specifically, the current transformer CT1 detects the sampling current of the first capacitor C1, and converts the sampling current into a voltage signal through the fourth resistor R4, and the voltage signal is input to the comparator Com1 after being processed by the second diode D2, the fifth resistor R5, and the second capacitor C2. The comparator Com1 compares the processed voltage signal with the reference voltage Vref to determine whether the discharge current of the first capacitor C1 is abnormal. If it is determined that the discharge current of the first capacitor C1 is abnormal, the comparator Com1 outputs an abnormal signal to the latch Com2. The abnormal signal generates a stable protection signal through the latch Com2 and transmits the stable protection signal to the input terminal of the PWM circuit 400. The PWM circuit 400 is caused to output a turn-off signal to the driving circuit 300 to rapidly turn off the IGBT tube by the clamp circuit 200.

It should be noted that any of the protection circuits described above may be widely used in applications with dc buses, for example: the direct current system, the optical storage system and the like can effectively protect equipment such as an inverter, a DC-DC converter and the like connected to the bus when the bus is short-circuited.

Compared with the prior art, the method and the device have the advantages that when the short-circuit fault of the direct-current bus is detected, the IGBT tube connected in series on the circuit through which the fault current flows is turned off in time, and the turn-off stress of the IGBT tube is controlled within a safety range through the clamping circuit, so that an additional freewheeling diode and a passive absorption circuit are not required to be added. And secondly, faults can be detected rapidly under various short circuit conditions, so that the energy required to be absorbed by the protection circuit when the fault current is turned off is reduced, and the reliable turn-off of the IGBT tube is ensured. Finally, the fault can be judged by detecting the current of the capacitor, so that the cost of the detection element can be reduced.

Based on any one of the protection circuits in the foregoing embodiments, a dc system is provided, and a schematic structural diagram of the dc system is shown in fig. 10, where the dc system includes a main power unit 10, an interface unit 20, and any one of the protection circuits 30 in the foregoing embodiments.

Wherein the positive and negative bus bars of the main power unit 10 are connected to the access terminals of the interface unit 20, respectively. One end of the protection circuit 30 is connected to the main power unit 10 through a negative bus, and the other end of the protection circuit 30 is connected to the interface unit 20 through a negative bus.

The interface unit 20 has a disconnection or connection function for the device to be powered and/or the interface unit 20 also has a filtering function.

In some embodiments, the interface unit 20 includes a relay, load switch, or EMI circuit, or any combination of a relay, load switch, and EMI circuit. Or the lead can be directly adopted on the premise that filtering or protecting effect is not needed.

Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and are not limiting; the technical features of the above embodiments or in the different embodiments may also be combined within the idea of the invention, the steps may be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A protection circuit applied to a direct current system, the direct current system comprising a main power unit and an interface unit, a positive bus and a negative bus of the main power unit being respectively connected to the interface unit, the protection circuit comprising:

a PWM circuit for outputting a control signal including an on signal and an off signal;

a driving circuit for amplifying the power of the control signal;

a switching circuit configured to turn on or off a connection between the main power unit and the interface unit in response to the control signal;

a clamping circuit configured to introduce a feedback current to a control terminal of the switching circuit to clamp a voltage across the switching circuit at a stable voltage when a voltage across the switching circuit is greater than a preset threshold voltage;

the output end of the driving circuit is connected to the control end of the switching circuit, and the switching circuit is connected in series between the positive bus or the negative bus.

2. The circuit of claim 1, further comprising:

and the auxiliary detection circuit is connected between the first sampling end of the driving circuit and one end of the switching circuit and is used for feeding back the voltages at two ends of the switching circuit to the driving circuit.

3. The circuit of claim 1 or 2, further comprising:

and a first signal processing circuit configured to output an abnormal signal to the PWM circuit to cause the PWM circuit to output the off signal when it is detected that the output current of the main power unit is greater than or equal to a preset first current threshold.

4. The circuit of claim 1 or 2, further comprising:

and a second signal processing circuit configured to output a protection signal to the PWM circuit to cause the PWM circuit to output the off signal when it is detected that the output current change rate of the main power unit is greater than or equal to a first current change threshold.

5. The circuit of claim 1, further comprising:

a first capacitor arranged between the positive bus and the negative bus, wherein a first connection point is formed at the connection position of the first capacitor and the negative bus or at the connection position of the first capacitor and the positive bus;

and a third signal processing circuit configured to output a protection signal to the PWM circuit to cause the PWM circuit to output the off signal when it is detected that the sampling current change rate of the first capacitor is greater than or equal to a preset second current change threshold, or the sampling current is greater than a preset second current threshold.

6. The circuit according to any one of claims 1-5, wherein the switching circuit is an IGBT tube, an emitter of the IGBT tube is connected to a negative electrode of the main power unit through the negative bus, and a collector of the IGBT tube is connected to the interface unit through the negative bus if the switching circuit is connected in series between the negative buses;

and if the switch circuit is connected in series between the positive buses, the collector of the IGBT tube is connected to the positive electrode of the main power unit through the positive buses, and the emitter of the IGBT tube is connected to the interface unit through the positive buses.

7. The circuit of claim 6, wherein the clamp circuit comprises a transient diode and a current limiting unit comprising a second resistor, an RC circuit, or an RCD circuit, wherein,

when the current limiting unit is a second resistor, the cathode of the transient diode is connected to the collector of the IGBT tube, and the anode of the transient diode is connected to one end of the second resistor;

the other end of the second resistor is connected to the gate electrode of the IGBT tube.

8. The circuit of claim 7, further comprising a first resistor, one end of the first resistor being connected to a gate of the IGBT tube, the other end of the first resistor being connected to an output of the drive circuit.

9. The circuit of claim 2, wherein the auxiliary detection circuit comprises a first diode and a third resistor, wherein,

the cathode of the first diode is connected to one end of the switch circuit, and the anode of the first diode is connected to one end of the third resistor;

the other end of the third resistor is connected to the driving circuit.

10. The circuit of claim 5, wherein the third signal processing circuit comprises a current transformer, a fourth resistor, a second diode, a fifth resistor, a second capacitor, a comparator, and a latch, wherein,

the primary side of the current transformer is connected in series between the first capacitor and the first connection point, and the head end of the secondary side of the current transformer is respectively connected to the anode of the second diode and one end of the fourth resistor;

the tail end of the secondary side of the current transformer is respectively connected to the other end of the fourth resistor and one end of the second capacitor, and one end of the second capacitor is grounded;

the cathode of the second diode is connected to one end of the fifth resistor, the other end of the fifth resistor is connected to the other end of the second capacitor and the first input end of the comparator respectively, and the second input end of the comparator is connected to the electric energy output end of the reference voltage source;

the output end of the comparator is connected to the input end of the latch, and the output end of the latch is connected to the input end of the PWM circuit.

11. A dc system, comprising:

a main power unit for outputting a power voltage, the main power unit including an inverter or a converter, the main power unit including a positive bus and a negative bus;

an interface unit for filtering the power voltage or disconnecting or connecting the equipment to be powered;

and a protection circuit as claimed in any one of claims 1 to 10;

the protection circuit is arranged on the positive bus or the negative bus, and the positive bus and the negative bus are respectively connected to the interface unit.

12. The system of claim 11, wherein the interface unit comprises a relay, a load switch, and/or an EMI circuit.