A dc microgrid solid-state protection converter overvoltage suppression system and method

Abstract

The application belongs to the technical field of low-voltage direct-current microgrid, and discloses a kind of overvoltage suppression system and method for solid-state protection of direct-current microgrid converter, which constructs a kind of system for inhibiting overvoltage of converter by connecting energy absorption path on solid-state switch device.When protection action triggers SSSD to shut down, the huge induced electromotive force generated by filter inductance due to sudden change of current path can drive current to divert to the parallel energy absorption path.Using the system eliminates the risk of high voltage breakdown of power devices caused by the release of electric energy in the original scheme, ensures that the protection action itself will not cause secondary voltage damage to the converter, while retaining the core protection capability of SSSD to quickly cut off fault current, thereby significantly improving the reliability and engineering practical value of the solid-state protection scheme.

Description

Technical Field

[0001] This invention belongs to the field of low-voltage DC microgrid technology, and particularly relates to an overvoltage suppression system and method for converters used in solid-state protection of DC microgrids. Background Technology

[0002] Low-voltage DC microgrids, due to their high efficiency and flexibility, are increasingly widely used in various fields such as new energy grid connection, data center power supply, and electric vehicle charging, and have become an important development direction in the current power electronics and microgrid field. In the actual operation of low-voltage DC microgrids, the reliability of the protection system directly determines the safety and stability of the grid operation. However, the rapid development speed and lack of natural zero-crossing point of DC fault current place stringent requirements on protection equipment, becoming a technical bottleneck restricting its development. To solve the above bottleneck, the industry has proposed a protection scheme using solid-state switching devices (SSSDs) to quickly isolate the converter in the early stage of a fault. This scheme operates the protection device before the DC filter capacitor has finished discharging, which can isolate the expensive and fragile power semiconductor devices inside the converter from the discharge circuit of the large-capacity support capacitor on the DC side, effectively avoiding the impact of capacitor discharge current on power devices. At the same time, it eliminates the need for expensive high-current breaking equipment, which has significant technical advantages.

[0003] While the aforementioned solid-state protection scheme based on SSSD successfully solved the problem of capacitor discharge current impacting power devices, it introduced a key technical defect that has not yet been resolved in practical applications: when the SSSD disconnects as expected, the magnetic field energy stored in the converter's own filter inductor (such as the AC side filter inductor of the VSC or the DC filter inductor of the Boost / Buck converter) cannot be released due to the sudden interruption of the current path, thus generating an inductive overvoltage with extremely high amplitude. v L = di L / dt This overvoltage will be directly superimposed on the power electronic switching devices of the converter. Since the amplitude of this instantaneous overvoltage far exceeds the rated withstand voltage of the power devices, it is very easy to cause the devices to be instantly broken down and damaged. This defect means that while existing solid-state protection schemes protect devices from "high current" impacts, they also expose them to the risk of "high voltage," which greatly reduces the reliability and practicality of the entire protection scheme. This not only makes the protection scheme unsafe to be applied in actual engineering, but may also cause secondary damage to the equipment when the protection is activated.

[0004] It is evident that existing protection schemes for low-voltage DC microgrid converters based on SSSD suffer from inductive overvoltage damage to power devices, severely restricting the engineering application of such protection schemes. Summary of the Invention

[0005] This invention provides an overvoltage suppression system and method for converters in DC microgrid solid-state protection. This device solves the problem of inductive overvoltage damaging power devices in existing low-voltage DC microgrid converter protection schemes based on SSSD (Self-Solid State Protection). It ensures that after SSSD operation, the energy stored in the converter's filter inductor can be safely absorbed and dissipated, thereby protecting the power electronic switching devices.

[0006] To achieve the above objectives, the present invention employs the following technical content: A converter overvoltage suppression system for solid-state protection of a DC microgrid includes: a protection device connected between the converter bridge and the DC bus, the protection device including solid-state switching equipment; The solid-state switchgear is connected to an energy absorption path; the energy absorption path is used to provide a controlled path for the freewheeling current of the filter inductor when the solid-state switchgear is turned off, so as to suppress overvoltage.

[0007] Furthermore, the energy absorption path employs a buffer circuit connected in parallel with the solid-state switching device; The buffer circuit includes a buffer resistor and a buffer capacitor connected in series; the buffer circuit and the solid-state switching device are integrated inside the protection device.

[0008] Furthermore, the converter is a Boost converter; the design of the buffer circuit is based on the following formula:

[0009]

[0010] In the formula, This refers to the voltage at the high-voltage side of the converter bridge. This is the rated voltage on the low-voltage side of the Boost converter. This is the rated voltage on the high-voltage side of the Boost converter. This is the initial value of the filter inductor current; The frequency of the damped oscillation; = R S / 2L f The damping coefficient; The moment after the failure; For buffer resistors; For buffer capacitors; This is a filter inductor.

[0011] Furthermore, the converter is a VSC converter; the design of the buffer circuit is based on the following formula:

[0012]

[0013] In the formula, This refers to the voltage at the high-voltage side of the converter bridge. This refers to the effective value of the rated phase voltage on the AC side of the VSC. This is the rated voltage of the DC side of the VSC; This is the initial value of the filter inductor current; The frequency of the damped oscillation; = R S / 2L f The damping coefficient; The moment after the failure; For buffer resistors; For buffer capacitors; This is a filter inductor.

[0014] Furthermore, the energy absorption path adopts an independent auxiliary circuit, which includes an auxiliary resistor and an auxiliary capacitor connected in series; the auxiliary circuit is connected in parallel across the converter bridge; and the auxiliary circuit is integrated with the solid-state switching device inside the protection device.

[0015] Furthermore, the converter is a Boost converter; the design of the auxiliary circuit is based on the following formula:

[0016]

[0017] In the formula, This refers to the voltage at the high-voltage side of the converter bridge. This is the rated voltage on the low-voltage side of the Boost converter. This is the rated voltage on the high-voltage side of the Boost converter. This is the initial value of the filter inductor current; The frequency of the damped oscillation; = R A / 2L f The damping coefficient; The moment after the failure; For auxiliary resistors; For auxiliary capacitors; This is a filter inductor.

[0018] Furthermore, the converter is a VSC converter; the design of the buffer circuit is based on the following formula:

[0019]

[0020] In the formula, This refers to the voltage at the high-voltage side of the converter bridge. This refers to the effective value of the rated phase voltage on the AC side of the VSC. This is the rated voltage of the DC side of the VSC; This is the initial value of the filter inductor current; The frequency of the damped oscillation; = R A / 2L f The damping coefficient; The moment after the failure; For auxiliary resistors; For auxiliary capacitors; This is a filter inductor.

[0021] A method for suppressing overvoltage in a converter used for solid-state protection of a DC microgrid, implemented based on the aforementioned overvoltage suppression system for a converter used for solid-state protection of a DC microgrid, includes: When a fault occurs in the DC microgrid, the solid-state switching equipment is turned off, providing a controlled path for the freewheeling current of the filter inductor through the energy absorption path, thus suppressing overvoltage.

[0022] Furthermore, the energy absorption path employs a buffer circuit connected in parallel with the solid-state switching device; The buffer circuit includes a buffer resistor and a buffer capacitor connected in series. After the solid-state switching device is turned off, the freewheeling current of the converter filter inductor is guided to the buffer circuit; The buffer capacitor in the buffer circuit provides a path for freewheeling current, limiting the rate of voltage rise and thus suppressing overvoltage peaks; the buffer resistor in the buffer circuit dissipates the energy stored in the filter inductor in the form of heat.

[0023] Furthermore, the energy absorption path employs an independent auxiliary circuit, which includes an auxiliary resistor and an auxiliary capacitor connected in series; the auxiliary circuit is connected in parallel across the converter bridge. After the solid-state switching equipment is turned off, the freewheeling current of the converter filter inductor is guided to an independent auxiliary circuit through the freewheeling diode in the converter bridge; The auxiliary circuit provides a path for freewheeling current, limits the rate of voltage rise, and thus suppresses overvoltage peaks; the auxiliary resistor in the auxiliary circuit dissipates the energy stored in the filter inductor in the form of heat.

[0024] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a converter overvoltage suppression system for solid-state protection of DC microgrids. By connecting an energy absorption path to the solid-state switching device, a system for suppressing converter overvoltage is constructed. When the protection action triggers the SSSD turn-off, the huge induced electromotive force generated by the sudden change in the current path of the filter inductor drives the current to the parallel energy absorption path. This path provides a controlled freewheeling path, allowing the magnetic field energy stored in the inductor to be gradually dissipated or transferred within it, rather than being directly applied to the power devices. By actively guiding and absorbing this critical energy, this system effectively suppresses the inductive overvoltage spike generated on the converter power switching devices at the moment of SSSD turn-off. This system eliminates the risk of high-voltage breakdown of power devices caused by the lack of energy release in the inductor in the original scheme, ensuring that the protection action itself does not cause secondary voltage damage to the converter, while retaining the core protection capability of SSSD to quickly cut off fault current. This significantly improves the reliability and engineering practicality of the solid-state protection scheme.

[0025] This invention also provides an overvoltage suppression method for converters used in solid-state protection of DC microgrids. Based on the aforementioned overvoltage suppression system for converters used in solid-state protection of DC microgrids, this method actively guides the freewheeling energy of the filter inductor into a controlled release path when a fault in the DC microgrid triggers the SSSD shutdown. When the SSSD cuts off the fault current path, the induced electromotive force generated by the magnetic field energy stored in the filter inductor due to the sudden change in current forces the current to turn towards the energy absorption path. This path, through a preset energy conduction mechanism (such as resistive dissipation and capacitive absorption), causes the inductor current to decay at a controlled rate, thereby transferring the inductive overvoltage originally acting on the power device to the energy absorption path for processing. This method effectively avoids the risk of overvoltage breakdown of power devices caused by the lack of release of inductor energy in the original scheme, ensuring that the protection action will not cause secondary voltage damage. At the same time, it fully retains the core advantage of the SSSD in quickly cutting off the fault current, significantly improving the reliability and engineering applicability of the protection system, and providing a key guarantee for the practical application of solid-state protection technology. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of a typical bidirectional non-isolated DC-DC converter circuit structure in the prior art provided by the embodiments of the present invention; Figure 2 This is a schematic diagram of the overvoltage suppression system for a DC microgrid solid-state protection converter provided in an embodiment of the present invention; wherein, (a) is a first type of overvoltage suppression system for a DC microgrid solid-state protection converter; and (b) is a second type of overvoltage suppression system for a DC microgrid solid-state protection converter. Figure 3 This is a schematic diagram of a simulation system for an overvoltage suppression system of a DC microgrid solid-state protection converter, provided in an embodiment of the present invention. Figure 4 This is a simulation result of an overvoltage suppression system for a DC microgrid solid-state protection converter provided in an embodiment of the present invention; Figure 5 A schematic diagram of a simulation system for an overvoltage suppression system for a DC microgrid solid-state protection converter, provided in an embodiment of the present invention; Figure 6 Simulation results of another DC microgrid solid-state protection converter overvoltage suppression system provided in this embodiment of the invention. Detailed Implementation

[0027] To make the technical problems solved by the present invention, the technical solutions, and the beneficial effects clearer, the following specific embodiments provide a further detailed description of the present invention. It should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the scope of the invention.

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0029] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0030] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0031] As mentioned in the background section, such as Figure 1 As shown, Figure 1 This is a typical bidirectional non-isolated DC-DC converter topology, used to address the problems of rapid DC fault current development, lack of natural zero-crossing, and stringent requirements for protection devices. However, when the SSSD operates as expected and disconnects, the magnetic field energy stored in the converter's own filter inductor (such as the AC-side filter inductor of the VSC or the DC-side filter inductor of the Boost / Buck converter) has nowhere to be released due to the sudden interruption of the current path. This energy generates a very high amplitude inductive overvoltage (…). v L = di L / dt This overvoltage will be directly superimposed across the power electronic switching devices of the converter. The amplitude of this instantaneous overvoltage far exceeds the rated withstand voltage of the power devices, which could very likely cause the devices to break down instantly. It is evident that while existing solid-state protection schemes protect devices from "high current" surges, they expose them to the risk of "high voltage," significantly reducing the reliability and practicality of the entire protection scheme. Without addressing this overvoltage issue, this protection scheme cannot be safely applied in practical engineering and may even cause secondary damage to the equipment during protection activation.

[0032] To address the aforementioned issues, this embodiment provides an overvoltage suppression system for converters used in solid-state protection of DC microgrids. This system adds an energy absorption path around the solid-state switchgear (SSSD) in the protection device. When the SSSD is turned off, it provides a controlled path for the freewheeling current of the filter inductor, suppressing the generation of overvoltage.

[0033] For example, this embodiment provides an overvoltage suppression system for a DC microgrid solid-state protection converter, including a protection device, wherein the protection device is connected between the converter bridge and the DC bus; The protection device includes a solid-state switchgear; the solid-state switchgear is connected to an energy absorption path, which provides a controlled path for the freewheeling current of the filter inductor when the solid-state switchgear is turned off, so as to suppress overvoltage.

[0034] The testing machine provided in this embodiment will be further described in detail below with reference to the accompanying drawings: like Figure 2 As shown, specifically as follows Figure 2 As shown in (a) of the figure, this embodiment provides an overvoltage suppression system for converters used in solid-state protection of DC microgrids, that is, an overvoltage suppression system based on a buffer circuit, as detailed below: Structural design: A buffer resistor is connected in parallel across the two ends of the solid-state switching device (SSSD). R s ) and buffer capacitor ( C s An RC snubber circuit composed of RC snubber circuits connected in series. This snubber circuit is integrated with the SSSD inside the protection device.

[0035] Working principle: When a fault occurs in the DC microgrid, the protection device detects the fault and issues a command. The SSSD quickly shuts down within microseconds, cutting off the discharge circuit of the large capacitor on the DC side. At this time, the converter filter inductor... L f The freewheeling current is directed to a parallel RC snubber circuit. Snubber capacitor C sIt provides a path for freewheeling, limiting the rate of voltage rise. dv / dt This suppresses overvoltage peaks. Simultaneously, the buffer resistor... R s The energy stored in the inductor is dissipated as heat.

[0036] Application Scenarios: This system can be widely used in various converters, such as Boost converters and VSCs (voltage source converters). Although the freewheeling paths and overvoltage generation mechanisms differ for different types of converters, configuring this buffer circuit across the SSSD terminals can effectively suppress overvoltages and protect the power devices within the converter bridge.

[0037] Parameter Design: This embodiment also provides design principles for buffer circuit parameters. Research has found that, in order to minimize the peak voltage on power devices, circuit parameters ( R s and C s The optimal choice is not to put the circuit in a critically damped or overdamped state, but in a specific underdamped state, where the damping effect and the voltage drop of the resistor itself reach the best balance, and the overvoltage suppression effect is the best.

[0038] For Boost converters, the design of this buffer circuit can be determined according to formula (1): (1) (2) In the formula, This refers to the voltage at the high-voltage side of the converter bridge. This is the rated voltage on the low-voltage side of the Boost converter. This is the rated voltage on the high-voltage side of the Boost converter. This is the initial value of the filter inductor current; The frequency of the damped oscillation; = R S / 2L f The damping coefficient; The moment after the failure; For buffer resistors; For buffer capacitors; This is a filter inductor.

[0039] Given a fixed filter inductance value and rated voltage, calculate the peak voltage at the commutator bridge and the parameters of the buffer circuit before the capacitor discharges, according to formula (1). R s , C s The relationship between the surfaces is determined to identify the appropriate surfaces. R s, C s value.

[0040] For example, for a VSC converter, the buffer circuit design can be determined according to formula (3): (3) (4) In the formula, This refers to the voltage at the high-voltage side of the converter bridge. This refers to the effective value of the rated phase voltage on the AC side of the VSC. This is the rated voltage of the DC side of the VSC; This is the initial value of the filter inductor current; The frequency of the damped oscillation; = R S / 2L f The damping coefficient; The moment after the failure; For buffer resistors; For buffer capacitors; This is a filter inductor.

[0041] Given the specified filter inductance value and rated voltage, calculate the peak voltage at the commutator bridge and the parameters of the buffer circuit before the capacitor discharges, according to formula (3). R s , C s The relationship between the surfaces is determined to identify the appropriate surfaces. R s , C s value.

[0042] For example Figure 2 As shown, specifically as follows Figure 2 As shown in (b) of the figure, this embodiment also provides another overvoltage suppression system for DC microgrid solid-state protection converters, namely, an overvoltage suppression system based on an independent auxiliary circuit, as detailed below: Structural Design: In the protection device, in addition to SSSD, an independent auxiliary circuit is configured. This auxiliary circuit also consists of an auxiliary resistor ( R A ) and auxiliary capacitor ( C A They are connected in series and serve as a dedicated energy absorption unit to provide a path for the freewheeling current of the filter inductor.

[0043] Working Principle: When a fault occurs in the DC microgrid, the protection device detects the fault and issues a command. The SSSD quickly shuts off within microseconds, cutting off the discharge circuit of the large capacitor on the DC side. At this time, the freewheeling current of the converter filter inductor is guided to this independent auxiliary circuit through the freewheeling diode in the converter bridge. The auxiliary circuit absorbs and dissipates this portion of inductive energy. Its working principle is similar to that of the buffer circuit in the first embodiment, both using capacitors to limit the voltage rise rate and resistors to dissipate energy, thereby clamping the voltage across the converter bridge within a safe range.

[0044] The advantage of this system is that by setting up an independent auxiliary circuit, parameter design and function optimization can be performed more flexibly without directly affecting the switching characteristics of the SSSD itself.

[0045] Application scenarios: This system can be widely used in various converters, such as Boost converters and VSC (voltage source converters).

[0046] Parameter Design: This embodiment also provides design principles for auxiliary circuit parameters.

[0047] For Boost converters, the auxiliary circuit design can be determined according to formula (5): (5) (6) In the formula, This refers to the voltage at the high-voltage side of the converter bridge. This is the rated voltage on the low-voltage side of the Boost converter. This is the rated voltage on the high-voltage side of the Boost converter. This is the initial value of the filter inductor current; The frequency of the damped oscillation; = R A / 2L f The damping coefficient; The moment after the failure; For auxiliary resistors; For auxiliary capacitors; This is a filter inductor.

[0048] Given the specified filter inductance value and rated voltage, calculate the peak voltage at the commutator bridge and the parameters of the buffer circuit before the capacitor discharges, according to formula (5). R A , C A The relationship between the surfaces is determined to identify the appropriate surfaces. R A , C A value.

[0049] For VSC converters, the auxiliary circuit design can be determined according to the formula: (7) (8) In the formula, This refers to the voltage at the high-voltage side of the converter bridge. This refers to the effective value of the rated phase voltage on the AC side of the VSC. This is the rated voltage of the DC side of the VSC; This is the initial value of the filter inductor current; The frequency of the damped oscillation; = R A / 2L f The damping coefficient; The moment after the failure; For auxiliary resistors; For auxiliary capacitors; This is a filter inductor.

[0050] Given the specified filter inductance value and rated voltage, calculate the peak voltage at the commutator bridge and the parameters of the buffer circuit before the capacitor discharges, according to formula (7). R A , C A The relationship between the surfaces is determined to identify the appropriate surfaces. R A , C A value.

[0051] Based on the above-mentioned overvoltage suppression system for converters used in solid-state protection of DC microgrids, this embodiment also provides an overvoltage suppression method for converters used in solid-state protection of DC microgrids, including: When a fault occurs in the DC microgrid, the solid-state switching equipment is turned off, providing a controlled path for the freewheeling current of the filter inductor through the energy absorption path, thus suppressing overvoltage.

[0052] The energy absorption path employs a buffer circuit connected in parallel with the solid-state switching device. The buffer circuit includes a buffer resistor and a buffer capacitor connected in series. After the solid-state switching device is turned off, the freewheeling current of the converter filter inductor is guided to the buffer circuit; The buffer capacitor in the buffer circuit provides a path for freewheeling current, limiting the rate of voltage rise and thus suppressing overvoltage peaks; the buffer resistor in the buffer circuit dissipates the energy stored in the filter inductor in the form of heat.

[0053] Alternatively, the energy absorption path may employ an independent auxiliary circuit, which includes an auxiliary resistor and an auxiliary capacitor connected in series. After the solid-state switching equipment is turned off, the freewheeling current of the converter filter inductor is guided to an independent auxiliary circuit through the freewheeling diode in the converter bridge; The auxiliary circuit provides a path for freewheeling current, limits the rate of voltage rise, and thus suppresses overvoltage peaks; the auxiliary resistor in the auxiliary circuit dissipates the energy stored in the filter inductor in the form of heat.

[0054] For example, a specific implementation application of the above-mentioned overvoltage suppression system and method for solid-state protection of DC microgrids is carried out, and the specific implementation process is as follows: Example 1: Overvoltage suppression scheme based on buffer circuit: The overvoltage suppression scheme in this embodiment is applied to a Boost converter system, such as... Figure 3 As shown. The system includes a low-voltage side power supply (400V), a high-voltage side load, and a filter inductor. L f Low-voltage side switching transistor S 1. High-voltage side switch tube S 2 (and its anti-parallel diode), high-voltage side filter capacitor C According to the overvoltage suppression method for converters used in solid-state protection of DC microgrids provided in this embodiment, the switching transistor S2 and the filter capacitor... C A protection device SSSD is connected in series between them, and a buffer circuit is connected in parallel at both ends of it.

[0055] In this embodiment, the specific parameter settings are as follows: high-voltage side voltage level is 750V, low-voltage side power supply voltage is 400V, rated resistive load is 37.5W, and buffer circuit parameters are as follows. R s =3 W, C s =10 mF. When the simulation time is set to 0.3s, a bipolar short-circuit fault occurs in the system, and the fault resistance is... R f =0.1 W.

[0056] based on Figure 4 The simulation results of the overvoltage suppression scheme based on the buffer circuit for the simulated system are as follows: Figure 5 As shown. The simulation results, from top to bottom, represent the buffer circuit current. i snu SSSD current i SSSD Converter bridge port voltage v Bridge Buffer circuit voltage v snu .

[0057] Depend on Figure 4 It can be seen that the fault occurs at 0.3 seconds of simulation time. After a fault detection delay of about ten microseconds, the controller will immediately send a shutdown signal to the SSSD. i SSSD When the current drops to 0, the inductor freewheeling current is forcibly guided into the buffer circuit, generating an overvoltage across the commutation bridge. This overvoltage is effectively suppressed by the buffer circuit.

[0058] Example 2: Overvoltage suppression scheme based on independent auxiliary circuit: The overvoltage suppression scheme in this embodiment is applied to a Boost converter system, such as... Figure 5 As shown. The system includes a low-voltage side power supply (400V), a high-voltage side load, and a filter inductor. L f Low-voltage side switching transistor S 1. High-voltage side switch tube S 2 (and its anti-parallel diode), high-voltage side filter capacitor C According to the overvoltage suppression method for converters used in solid-state protection of DC microgrids provided in this embodiment, the switching transistor S2 and the filter capacitor... C The SSSD protection device is connected in series between the two sides, and auxiliary circuits are connected in parallel across the two ends of the converter bridge.

[0059] In this embodiment, the specific parameter settings are as follows: high-voltage side voltage level is 750V, low-voltage side power supply voltage is 400V, rated resistive load is 37.5W, and auxiliary circuit parameters are as follows: R A =5.71 W, C A =5 mF. When the simulation time is set to 0.3s, a bipolar short-circuit fault occurs in the system, and the fault resistance is... R f =0.1 W.

[0060] based on Figure 6 The simulation results of the overvoltage suppression scheme based on the buffer circuit for the simulated system are as follows: Figure 6 As shown. The simulation results, from top to bottom, represent the auxiliary circuit currents. i aux SSSD current i SSSD Converter bridge port voltage v Bridge Auxiliary circuit voltage v aux .

[0061] like Figure 6As shown, the fault occurs at 0.3 seconds of simulation time. After a fault detection delay of approximately ten microseconds, the controller immediately sends a shutdown signal to the SSSD. i SSSD When the current drops to 0, the inductor freewheeling current is forcibly guided into the buffer circuit, generating an overvoltage across the commutation bridge. This overvoltage is effectively suppressed by the buffer circuit.

[0062] In summary, this invention provides an overvoltage suppression system and method for converters used in solid-state protection of DC microgrids, which has the following advantages compared to existing suppression measures: First, this system solves the critical bottleneck of overvoltage and ensures the safety of power devices: This invention directly solves the problem of inductive overvoltage generated when the SSSD is turned off, effectively protecting the core power devices such as IGBTs and MOSFETs inside the converter and preventing them from being damaged due to overvoltage.

[0063] Secondly, the adoption of this system improves the overall reliability and practicality of the solid-state protection scheme: by overcoming the fatal defects of the existing scheme, this invention transforms the circuit breaker-free solid-state protection scheme from a theoretical concept into a safe, reliable, and engineerable complete solution.

[0064] Third, the system has a simple structure and low cost: the overvoltage suppression scheme proposed in this invention mainly uses passive components such as resistors and capacitors, which has a simple structure, low cost, high reliability, and is easy to integrate into existing protection devices without significantly increasing the complexity and cost of the entire protection system.

[0065] Fourth, the system has wide applicability: the principles and implementation schemes of this invention are not limited to specific types of converters, but are applicable to converters with various topologies such as VSC and Boost commonly found in DC microgrids, and have good versatility and scalability.

[0066] The above embodiments are merely one of the implementation methods for achieving the technical solution of the present invention. The scope of protection claimed by the present invention is not limited to this embodiment, but also includes any variations, substitutions and other implementation methods that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention.

Claims

1. A converter overvoltage suppression system for solid-state protection of DC microgrids, characterized in that, include: A protection device connected between the converter bridge and the DC bus, the protection device including a solid-state switchgear; The solid-state switchgear is connected to an energy absorption path; the energy absorption path is used to provide a controlled path for the freewheeling current of the filter inductor when the solid-state switchgear is turned off, so as to suppress overvoltage.

2. The converter overvoltage suppression system for solid-state protection of DC microgrids according to claim 1, characterized in that, The energy absorption path employs a buffer circuit connected in parallel with the solid-state switching device; The buffer circuit includes a buffer resistor and a buffer capacitor connected in series; the buffer circuit and the solid-state switching device are integrated inside the protection device.

3. The converter overvoltage suppression system for solid-state protection of DC microgrids according to claim 2, characterized in that, The converter is a Boost converter; the design of the buffer circuit is based on the following formula: In the formula, This refers to the voltage at the high-voltage side of the converter bridge. This is the rated voltage on the low-voltage side of the Boost converter. This is the rated voltage on the high-voltage side of the Boost converter. This is the initial value of the filter inductor current; The frequency of the damped oscillation; = R S / 2L f The damping coefficient; The moment after the failure; For buffer resistors; For buffer capacitors; This is a filter inductor.

4. The converter overvoltage suppression system for solid-state protection of DC microgrids according to claim 2, characterized in that, The converter is a VSC converter; the design of the buffer circuit is based on the following formula: In the formula, This refers to the voltage at the high-voltage side of the converter bridge. This refers to the effective value of the rated phase voltage on the AC side of the VSC. This is the rated voltage of the DC side of the VSC; This is the initial value of the filter inductor current; The frequency of the damped oscillation; = R S / 2L f The damping coefficient; The moment after the failure; For buffer resistors; For buffer capacitors; This is a filter inductor.

5. The converter overvoltage suppression system for solid-state protection of DC microgrids according to claim 1, characterized in that, The energy absorption path adopts an independent auxiliary circuit, which includes an auxiliary resistor and an auxiliary capacitor connected in series; the auxiliary circuit is connected in parallel across the converter bridge; the auxiliary circuit and the solid-state switch are integrated inside the protection device.

6. The converter overvoltage suppression system for solid-state protection of DC microgrids according to claim 5, characterized in that, The converter is a Boost converter; the design of the auxiliary circuit is based on the following formula: In the formula, This refers to the voltage at the high-voltage side of the converter bridge. This is the rated voltage on the low-voltage side of the Boost converter. This is the rated voltage on the high-voltage side of the Boost converter. This is the initial value of the filter inductor current; The frequency of the damped oscillation; = R A / 2L f The damping coefficient; The moment after the failure; For auxiliary resistors; For auxiliary capacitors; This is a filter inductor.

7. The converter overvoltage suppression system for solid-state protection of DC microgrids according to claim 5, characterized in that, The converter is a VSC converter; the design of the buffer circuit is based on the following formula: In the formula, This refers to the voltage at the high-voltage side of the converter bridge. This refers to the effective value of the rated phase voltage on the AC side of the VSC. This is the rated voltage of the DC side of the VSC; This is the initial value of the filter inductor current; The frequency of the damped oscillation; = R A / 2L f The damping coefficient; The moment after the failure; For auxiliary resistors; For auxiliary capacitors; This is a filter inductor.

8. A method for suppressing overvoltage in a converter for solid-state protection of a DC microgrid, characterized in that, Based on the DC microgrid solid-state protection converter overvoltage suppression system according to any one of claims 1-7, it includes: When a fault occurs in the DC microgrid, the solid-state switching equipment is turned off, providing a controlled path for the freewheeling current of the filter inductor through the energy absorption path, thus suppressing overvoltage.

9. The method for suppressing overvoltage of a converter for solid-state protection of a DC microgrid according to claim 8, characterized in that, The energy absorption path employs a buffer circuit connected in parallel with the solid-state switching device; The buffer circuit includes a buffer resistor and a buffer capacitor connected in series. After the solid-state switching device is turned off, the freewheeling current of the converter filter inductor is guided to the buffer circuit; The buffer capacitor in the buffer circuit provides a path for freewheeling current, limiting the rate of voltage rise and thus suppressing overvoltage peaks; the buffer resistor in the buffer circuit dissipates the energy stored in the filter inductor in the form of heat.

10. The method for suppressing overvoltage of a converter for solid-state protection of a DC microgrid according to claim 8, characterized in that, The energy absorption path adopts an independent auxiliary circuit, which includes an auxiliary resistor and an auxiliary capacitor connected in series; the auxiliary circuit is connected in parallel across the converter bridge. After the solid-state switching equipment is turned off, the freewheeling current of the converter filter inductor is guided to an independent auxiliary circuit through the freewheeling diode in the converter bridge; The auxiliary circuit provides a path for freewheeling current, limits the rate of voltage rise, and thus suppresses overvoltage peaks; the auxiliary resistor in the auxiliary circuit dissipates the energy stored in the filter inductor in the form of heat.

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