Diode protection circuit and half-bridge circuit based on power switch device

Abstract

The invention discloses a diode protection circuit and a half-bridge circuit based on a power switch device. The diode protection circuit comprises a bypass circuit which is connected to two ends of a diode and is used for bypassing the diode based on a trigger signal; and the constant voltage trigger circuit is connected between the bypass circuit and the anode of the diode and is used for sending the trigger signal when detecting that the diode is in an abnormal state so as to control the state of the bypass unit.

Description

Technical Field

[0001] This application belongs to the field of power technology, and in particular relates to a diode protection circuit and a half-bridge circuit based on power switching devices. Background Technology

[0002] The Half-Bridge Submodules Based Modular Multilevel Converter (HB-MMC) avoids the series voltage equalization problem of power semiconductor devices, easily improves system voltage levels, and is cost-effective, thus it is widely used in DC power transmission and distribution. When an inter-electrode short-circuit fault occurs on the DC side of the HB-MMC, it degenerates into a three-phase uncontrolled rectifier bridge. The AC side system voltage of the power semiconductor devices short-circuits through the lower arm diodes of each submodule, generating a huge inrush current that eventually causes the diode to overheat and fail. Therefore, a transition thyristor T is generally configured between the AC ports of the half-bridge submodules. On the one hand, it breaks down and short-circuits in the event of a submodule overvoltage fault, achieving reliable bypass of the submodule. On the other hand, it is triggered to conduct in the event of a bipolar short-circuit fault, shunting the diode and preventing it from overheating and failing.

[0003] In existing technology, when the thyristor is triggered to conduct, the power supply provides the triggering energy for the thyristor. The controller triggers the thyristor to conduct after detecting an overcurrent signal or receiving an instruction from the upper level. However, if any key component such as the overcurrent detection, controller, triggering circuit, or power supply fails, the thyristor cannot be successfully triggered, which in turn causes the lower bridge arm diode to fail under fault conditions, resulting in a decrease in the reliability of the protection circuit. Summary of the Invention

[0004] This application proposes a diode protection circuit and a half-bridge circuit based on power switching devices, which at least partially solves the technical problems such as reduced reliability of protection circuits in related technologies.

[0005] In a first aspect, this application provides a diode protection circuit, comprising:

[0006] A bypass circuit, connected to both ends of the diode, is used to bypass the diode based on a trigger signal;

[0007] A constant voltage trigger circuit is connected between the bypass circuit and the anode of the diode, and is used to issue the trigger signal when the diode is in an abnormal state, so as to control the state of the bypass unit.

[0008] A second aspect of this application provides a half-bridge circuit based on power switching devices, characterized in that it includes:

[0009] Bus capacitors are used to provide DC signals;

[0010] A first power switch and a second power switch connected in series are connected across the bus capacitor to convert the DC signal into an AC signal; the second power switch outputs the AC signal from its two ends.

[0011] The first diode is connected in reverse parallel with the first power switch for reverse freewheeling;

[0012] The second diode is connected in reverse parallel with the second power switch for reverse freewheeling.

[0013] According to the diode protection circuit described in the first aspect, it is connected in parallel with the second diode to protect the second diode.

[0014] As described above, this application provides a diode protection circuit and a half-bridge circuit based on power switching devices. The diode protection circuit consists of a bypass circuit and a constant-voltage trigger circuit. The bypass circuit is directly connected in parallel across the diode and can bypass the diode in response to a trigger signal. The constant-voltage trigger circuit is connected between the bypass circuit and the diode anode and can monitor the diode status in real time. Once an abnormality is detected, it immediately sends a trigger signal to regulate the working state of the bypass circuit. In the half-bridge circuit, the bus capacitor provides the DC input signal. The first and second power switches are connected in series across the bus capacitor to work together to convert the DC signal into an AC signal and output it from the second power switch. The first and second diodes are connected in reverse parallel with their corresponding power switches to undertake the task of reverse freewheeling. Furthermore, by connecting the diode protection circuit in parallel across the second diode, when the second diode encounters an abnormal condition, the protection circuit quickly activates the bypass protection mechanism, effectively preventing diode damage and thus enhancing the overall reliability and stability of the half-bridge circuit. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in this application or related technologies, the drawings used in the description of the embodiments or related technologies will be briefly introduced below. Obviously, the drawings described below are only embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a schematic diagram of the structure of an MMC converter in related technologies.

[0017] Figure 2 This is a schematic diagram of the current path in a bipolar short-circuit fault in related technologies.

[0018] Figure 3 This is a schematic diagram of the trigger circuit for a transition thyristor in related technologies.

[0019] Figure 4This is a schematic diagram of the diode protection circuit according to an embodiment of the present disclosure.

[0020] Figure 5 This is a schematic diagram of the diode protection circuit according to an embodiment of the present disclosure.

[0021] Figure 6 This is a schematic diagram of the structure of a half-bridge circuit based on a power switching device according to an embodiment of this disclosure.

[0022] Figure 7 This is a schematic diagram of the structure of a half-bridge circuit based on a power switching device according to an embodiment of this disclosure. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with specific embodiments and the accompanying drawings.

[0024] It should be noted that, unless otherwise defined, the technical or scientific terms used in the embodiments of this application should have the ordinary meaning understood by one of ordinary skill in the art to which this application pertains. The terms "first," "second," and similar terms used in the embodiments of this application do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed after the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are only used to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0025] Among related technologies, the Half-Bridge Submodules-Based Modular Multilevel Converter (HB-MMC) avoids the series voltage equalization problem of power semiconductor devices, easily improves system voltage levels, and has controllable costs. Therefore, it is widely used in DC power transmission and distribution, such as... Figure 1 As shown in the diagram, in the half-bridge submodule, fully controlled power semiconductor devices are connected in reverse parallel with diodes. The two sets of parallel structures are connected in series and then in parallel with the bus capacitor. The anode of the diode is connected to the low-voltage end of the bus capacitor to form an AC port, and the midpoint of the series diode forms the AC port.

[0026] When an inter-electrode short-circuit fault occurs on the DC side of the HB-MMC, the HB-MMC degenerates into a three-phase uncontrolled rectifier bridge, and the current path is as follows: Figure 2As shown, the AC system voltage of the power semiconductor device short-circuits through the lower arm diodes of each submodule, generating a huge inrush current that ultimately causes the diode to overheat and fail. Therefore, a bypass thyristor is generally configured between the AC ports of the half-bridge submodule. On the one hand, it breaks down and short-circuits in the event of a submodule overvoltage fault, realizing a reliable bypass of the submodule. On the other hand, it is triggered to conduct in the event of a bipolar short-circuit fault, shunting the diode and preventing it from overheating and failing.

[0027] The existing circuit block diagram for triggering thyristor conduction is as follows: Figure 3 As shown, the power supply provides the trigger energy for the thyristor. The controller triggers the thyristor to conduct after detecting an overcurrent signal or receiving a command from the upper level. However, if any key component—overcurrent detection, controller, triggering circuit, or power supply—fails, the thyristor cannot be successfully triggered, leading to the failure of the lower bridge arm diode under fault conditions. Therefore, the reliability of the protection circuit needs improvement. Thus, improving the reliability of the diode protection circuit, enhancing the reliability of the diode under bipolar short-circuit faults, and strengthening the overall reliability and stability of the half-bridge circuit have become urgent technical problems to be solved.

[0028] This disclosure provides a diode protection circuit, characterized in that it includes:

[0029] A bypass circuit, connected to both ends of the diode, is used to bypass the diode based on a trigger signal;

[0030] A constant voltage trigger circuit is connected between the bypass circuit and the anode of the diode, and is used to issue the trigger signal when the diode is in an abnormal state, so as to control the state of the bypass unit.

[0031] The constant voltage trigger circuit continuously monitors the diode's electrical parameters to determine if it is in an abnormal state. When the diode malfunctions, such as when the voltage exceeds a safety threshold, the constant voltage trigger circuit sends a trigger signal. Upon receiving this trigger signal, the bypass circuit quickly activates, bypassing the diode and allowing current to flow around it, thus preventing further damage to the diode due to the abnormal state. The bypass circuit is directly connected across the diode; its main function is to provide a path for current to bypass the diode after receiving the trigger signal from the constant voltage trigger circuit. When the diode is in an abnormal operating state, such as experiencing an overvoltage surge, the bypass circuit conducts, allowing current to flow through the bypass, preventing excessive current or voltage from continuing to act on the diode, protecting it from breakdown or damage, and ensuring that the normal operation of other parts of the circuit is not severely affected by the diode failure. The constant voltage trigger circuit is connected between the bypass circuit and the diode anode, continuously monitoring parameters such as the voltage at the diode anode and other relevant points. By comparing these parameters with a preset safety threshold, it accurately determines whether the diode is in an abnormal state. Once the diode voltage or other parameters are detected to exceed the normal range and meet the abnormal state judgment criteria, the constant voltage trigger circuit will immediately send a trigger signal, providing instructions for the bypass circuit to activate and initiate the diode protection mechanism. This effectively protects the diode, responding quickly when an abnormal state occurs. By bypassing the diode through the bypass circuit, current is diverted around the diode, preventing damage due to overvoltage or overcurrent and extending its lifespan. It improves circuit reliability by promptly protecting the diode, reducing circuit interruptions or performance degradation caused by diode failure, ensuring stable operation of the entire circuit, and enhancing its reliability and stability. Furthermore, it enhances circuit safety by preventing potential short circuits, overheating, and other safety hazards that may arise from abnormal diode conditions, protecting other components in the circuit and reducing the risk of circuit failure and danger.

[0032] In some embodiments, the bypass circuit includes a controllable switch, a first terminal of which is connected to the cathode of the diode, a second terminal of which is connected to the anode of the diode, and a control terminal of which is connected to the constant voltage trigger circuit to receive the trigger signal.

[0033] The bypass circuit incorporates a controllable switch, with its first terminal connected to the diode's cathode and its second terminal connected to the diode's anode. The control terminal is connected to a constant-voltage trigger circuit to receive trigger signals. The constant-voltage trigger circuit monitors the diode's status in real time and issues a trigger signal upon detecting an anomaly. Upon receiving the signal, the controllable switch quickly conducts, allowing current to bypass the diode. This design enables timely response to diode anomalies, effectively preventing diode damage due to overcurrent or overvoltage, ensuring stable circuit operation, significantly improving circuit reliability and safety, and reducing various problems caused by diode failure.

[0034] In some embodiments, the controllable switch includes a thyristor, the cathode of which is connected to the cathode of the diode, the anode of which is connected to the anode of the diode, and the control terminal of which is connected to the cathode of the reverse blocking diode.

[0035] The controllable switch uses a thyristor, with its cathode connected to the cathode of a diode, its anode connected to the anode of the diode, and its control terminal connected to the cathode of the reverse blocking diode. A constant voltage trigger circuit sends a trigger signal to the thyristor control terminal by controlling the reverse blocking diode. When the diode malfunctions, the trigger signal turns on the thyristor, and the current bypasses through the thyristor. This allows for a rapid response to diode malfunctions, preventing damage from overvoltage or overcurrent, ensuring stable circuit operation, significantly improving circuit reliability and safety, and reducing the impact of diode failure on the overall circuit.

[0036] In some embodiments, the constant voltage trigger circuit includes a trigger switch and a reverse blocking diode connected in series. The first end of the trigger switch is connected to the anode of the diode, the second end of the trigger switch is connected to the anode of the reverse blocking diode, and the cathode of the reverse blocking diode is connected to the bypass circuit. The trigger switch includes a turnaround thyristor, a TVS diode, or a bidirectional trigger diode.

[0037] The constant voltage trigger circuit consists of a trigger switch and a reverse blocking diode connected in series. One end of the trigger switch is connected to the anode of the diode, and the other end is connected to the anode of the reverse blocking diode. The cathode of the reverse blocking diode is connected to the bypass circuit. The trigger switch can be a turnaround thyristor, TVS diode, or bidirectional trigger diode. When the diode malfunctions, such as when the voltage exceeds a set threshold, the trigger switch quickly conducts according to its characteristics. Current flows through the trigger switch and the reverse blocking diode to form a path, sending a trigger signal to the bypass circuit. This causes the controllable switch of the bypass circuit to operate, bypassing the diode. This allows for precise detection of abnormal diode voltage, rapid triggering of the protection mechanism, effective prevention of diode damage due to overvoltage, ensuring stable circuit operation, enhancing circuit reliability and safety, and reducing the negative impact of diode failure on the system.

[0038] In some embodiments, the constant voltage trigger circuit includes one or more Zener diodes connected in series.

[0039] Zener diodes, with their stable breakdown voltage characteristics, can be connected in series at specific locations in a circuit. The trigger voltage value can be precisely set based on the number of diodes connected in series. When the voltage across the associated diode abnormally rises and reaches the set value, the Zener diode breaks down and conducts, sending a trigger signal to the bypass circuit. This causes the bypass circuit to activate and bypass the diode. This precise response to overvoltage anomalies in the diode allows for timely activation of protection, effectively preventing diode damage due to overvoltage, improving circuit reliability and stability, and ensuring the safe operation of the entire system.

[0040] Specifically, see Figure 4 , Figure 4 A schematic diagram of a diode protection circuit according to an embodiment of this application is shown. Figure 4 In the circuit, the cathode of the bypass protection thyristor T (i.e., the bypass circuit) is connected to AC port A1, and the anode is connected to AC port A2. The constant voltage trigger circuit includes trigger switch D. T (e.g., a turnaround thyristor or TVS diode) and reverse blocking diode D F Connected in series between the anode and gate of the turnaround protection thyristor T, the constant voltage triggering circuit generates a bypass thyristor trigger current based on the voltage drop when the freewheeling diode D2 is in a surge state, and reverse blocking diode D... F Used to increase the reverse withstand voltage capability of bypass thyristor T.

[0041] In some embodiments, the constant voltage trigger circuit includes:

[0042] A first resistor, the first end of which is connected to the bypass circuit;

[0043] A transistor, wherein the collector of the transistor is connected to the second terminal of the first resistor;

[0044] A Zener diode, wherein the cathode of the Zener diode is connected to the second terminal of the first resistor, the anode of the Zener diode is connected to the base of the transistor, and the emitter of the transistor is connected to the anode of the diode;

[0045] The second resistor is connected between the base and the emitter of the transistor.

[0046] In this design, one end of the first resistor is connected to the bypass circuit, and the other end is connected to the collector of the transistor and the cathode of the Zener diode. The anode of the Zener diode is connected to the base of the transistor, and the emitter of the transistor is connected to the anode of the diode. The second resistor is connected between the base and emitter. The Zener diode has a set trigger voltage. When the diode voltage abnormally reaches this value, the Zener diode conducts, causing current to flow into the base of the transistor, which then sends a trigger signal to the bypass circuit. This design can accurately detect diode overvoltage, quickly trigger bypass protection, prevent diode damage, improve circuit reliability and stability, and ensure safe system operation.

[0047] Specifically, see Figure 5 , Figure 5 A schematic diagram of a diode protection circuit according to an embodiment of this application is shown. Figure 5In this circuit, the freewheeling diode is often connected in anti-parallel with a 4.5kV IGBT or IGCT in the VSC, with IFAV=2.69 kA and IFSM=40 kA. At 25℃ and 140℃, the typical forward voltage drops at a 40kA surge current are 9.5V and 11.8V, respectively. In the MMC's lower arm diode protection circuit, the bypass thyristor (i.e., the bypass circuit) has a gate trigger voltage of 2.6V and a trigger current of 400mA. When this voltage drop is reached, the diode's forward current is only 2.2kA, less than the diode's current limit. The self-triggered circuit voltage drop during bypass thyristor triggering is positively correlated with the freewheeling diode's surge current. The constant voltage trigger circuit uses a transistor to reduce the Zener diode's impedance and a larger capacity blocking diode to reduce the breakover voltage. The current selection has a total voltage drop of 5V, corresponding to a 10kA surge current.

[0048] This disclosure provides a half-bridge circuit based on power switching devices, including:

[0049] Bus capacitors are used to provide DC signals;

[0050] A first power switch and a second power switch connected in series are connected across the bus capacitor to convert the DC signal into an AC signal; the second power switch outputs the AC signal from its two ends.

[0051] The first diode is connected in reverse parallel with the first power switch for reverse freewheeling;

[0052] The second diode is connected in reverse parallel with the second power switch for reverse freewheeling.

[0053] According to the diode protection circuit described in the embodiments of this disclosure, it is connected in parallel with the second diode to protect the second diode.

[0054] Among them, such as Figure 6 As shown, the bus capacitor provides a DC signal. The first and second power switches are connected in series across the bus capacitor, converting the DC to AC and outputting it from the second power switch. The first and second diodes are connected in reverse parallel with their respective power switches to achieve reverse freewheeling. Simultaneously, a specific diode protection circuit is connected in parallel with the second diode. This scheme effectively achieves DC-to-AC conversion, and the reverse freewheeling diode prevents excessive voltage from being generated when the power switches are turned off. The parallel diode protection circuit can quickly bypass the second diode when it encounters overvoltage, overcurrent, or other abnormalities, preventing damage to the second diode, ensuring the stable and reliable operation of the half-bridge circuit, and improving the overall circuit's anti-interference capability and lifespan.

[0055] In some embodiments, the first power switch and the second power switch are IGCTs or IGBTs.

[0056] The first and second power switches utilize either IGCTs (Integrated Gate Commutated Thyristors) or IGBTs (Insulated Gate Bipolar Transistors), connected in series across the bus capacitor. This efficiently converts DC signals into AC signals, which are then output from the second power switch. The first and second diodes are connected in reverse parallel with their corresponding power switches, providing reverse freewheeling. Simultaneously, a specific diode protection circuit is connected in parallel with the second diode. IGCTs and IGBTs offer advantages such as high switching speed, low loss, and flexible control, improving circuit conversion efficiency and performance. The reverse freewheeling diode prevents excessive voltage when the power switch is turned off, protecting the switching devices. The diode protection circuit provides timely bypass protection in case of second diode malfunction, comprehensively ensuring the stable and reliable operation of the half-bridge circuit and enhancing its anti-interference capability and overall reliability.

[0057] In some embodiments, the half-bridge circuit further includes:

[0058] A buffer circuit, connected to both ends of the bus capacitor, is used to suppress voltage spikes in the DC signal.

[0059] Among them, the IGCT or IGBT ensures efficient DC-AC conversion, the reverse freewheeling diode prevents overvoltage during power switch turn-off, and the diode protection circuit safeguards the second diode. The buffer circuit effectively suppresses DC signal voltage spikes generated during circuit operation, such as those caused by switching, reducing the impact of voltage fluctuations on circuit components, further improving the stability and reliability of the half-bridge circuit, and extending the lifespan of each component.

[0060] In some embodiments, the buffer circuit includes:

[0061] A buffer inductor is connected between the bus capacitor and the first power switch;

[0062] A buffer resistor is connected between the buffer inductor and the bus capacitor;

[0063] A buffer diode is connected between the buffer inductor and the first power switch;

[0064] A buffer capacitor is connected between the connection point of the buffer resistor and the buffer diode and the bus capacitor.

[0065] Among them, such as Figure 7As shown, a buffer inductor is connected between the bus capacitor and the first power switch, a buffer resistor is connected between the buffer inductor and the bus capacitor, a buffer diode is connected between the buffer inductor and the first power switch, and a buffer capacitor is connected between the connection point of the buffer resistor and the buffer diode and the bus capacitor. When the power switch operates and generates a voltage spike, the buffer inductor impedes the sudden current change, the buffer capacitor absorbs energy to suppress the voltage rise, the buffer resistor consumes excess energy, and the buffer diode provides a freewheeling path for the inductor current. This effectively suppresses DC signal voltage spikes, reduces damage to circuit components, and improves the stability and reliability of the half-bridge circuit.

[0066] Additionally, to simplify the description and discussion, and to avoid obscuring the embodiments of this application, the well-known power / ground connections to integrated circuit (IC) chips and other components may or may not be shown in the provided drawings. Furthermore, the apparatus may be shown in block diagram form to avoid obscuring the embodiments of this application, and this also takes into account the fact that the details of the implementation of these block diagram apparatuses are highly dependent on the platform on which the embodiments of this application will be implemented (i.e., these details should be fully understood by those skilled in the art). While specific details (e.g., circuits) have been set forth to describe exemplary embodiments of this application, it will be apparent to those skilled in the art that the embodiments of this application can be implemented without these specific details or with variations thereof. Therefore, these descriptions should be considered illustrative rather than restrictive.

[0067] Although this application has been described in conjunction with specific embodiments thereof, many substitutions, modifications, and variations of these embodiments will be apparent to those skilled in the art from the foregoing description. For example, other memory architectures (e.g., dynamic RAM (DRAM)) may be used with the embodiments discussed.

[0068] The embodiments of this application are intended to cover all such substitutions, modifications, and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the embodiments of this application should be included within the protection scope of this application.

Claims

1. A diode protection circuit, characterized by, include: A bypass circuit, connected to both ends of the diode, is used to bypass the diode based on a trigger signal; A constant voltage trigger circuit is connected between the bypass circuit and the anode of the diode, and is used to issue the trigger signal when the diode is in an abnormal state, so as to control the state of the bypass unit.

2. The diode protection circuit of claim 1, wherein, The bypass circuit includes a controllable switch, the first end of which is connected to the cathode of the diode, the second end of which is connected to the anode of the diode, and the control terminal of which is connected to the constant voltage trigger circuit to receive the trigger signal.

3. The diode protection circuit of claim 2, wherein, The controllable switch includes a thyristor, the cathode of which is connected to the cathode of the diode, the anode of which is connected to the anode of the diode, and the control terminal of which is connected to the cathode of the reverse blocking diode.

4. The diode protection circuit of claim 1, wherein, The constant voltage trigger circuit includes a trigger switch and a reverse blocking diode connected in series. The first end of the trigger switch is connected to the anode of the diode, the second end of the trigger switch is connected to the anode of the reverse blocking diode, and the cathode of the reverse blocking diode is connected to the bypass circuit. The trigger switch includes a thyristor, a TVS diode, or a bidirectional trigger diode.

5. The diode protection circuit of claim 1, wherein, The constant voltage trigger circuit includes one or more Zener diodes connected in series.

6. The diode protection circuit of claim 1, wherein, The constant voltage trigger circuit includes: A first resistor, the first end of which is connected to the bypass circuit; A transistor, wherein the collector of the transistor is connected to the second terminal of the first resistor; A Zener diode, wherein the cathode of the Zener diode is connected to the second terminal of the first resistor, the anode of the Zener diode is connected to the base of the transistor, and the emitter of the transistor is connected to the anode of the diode; The second resistor is connected between the base and the emitter of the transistor.

7. A half bridge circuit based on power switching devices, characterized in that include: Bus capacitors are used to provide DC signals; A first power switch and a second power switch connected in series are connected across the bus capacitor to convert the DC signal into an AC signal; the second power switch outputs the AC signal from its two ends. The first diode is connected in reverse parallel with the first power switch for reverse freewheeling; The second diode is connected in reverse parallel with the second power switch for reverse freewheeling. The diode protection circuit according to any one of claims 1-6 is connected in parallel with the second diode to protect the second diode.

8. The half bridge circuit of claim 7, characterized in that, Also includes: A buffer circuit, connected to both ends of the bus capacitor, is used to suppress voltage spikes in the DC signal.

9. The half bridge circuit of claim 8, characterized in that, The buffer circuit includes: A buffer inductor is connected between the bus capacitor and the first power switch; A buffer resistor is connected between the buffer inductor and the bus capacitor; A buffer diode is connected between the buffer inductor and the first power switch; A buffer capacitor is connected between the connection point of the buffer resistor and the buffer diode and the bus capacitor.

10. The half bridge circuit of claim 7, wherein, The first power switch and the second power switch are IGCT or IGBT.

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