Medium and low voltage direct current circuit breaker

Abstract

The invention discloses a medium and low voltage direct current circuit breaker which comprises a main through-flow branch, a buffer branch and an energy absorption branch which are connected in parallel. Wherein the main through-flow branch is of a two-way through-flow switch structure, when the system has no fault, the main through-flow branch is kept in a conducting state, and system current is conducted through the main through-flow branch; when the system has a short-circuit fault, the power electronic device on the main through-current branch is turned off, and the system current is transferred to the buffer branch and the energy absorption branch; the buffer branch is used for reducing the rising rate of the voltage at the two ends of the power electronic device when the power electronic device on the main through-flow branch is turned off, inhibiting the instantaneous voltage spike and preventing the power electronic device from being damaged due to the sudden change of the voltage at the two ends; the energy absorption branch is used for absorbing and consuming redundant energy when the system breaks down. The short-circuit current with the current peak value reaching 10 kA or above can be turned off within hundreds of microseconds, and the requirement for rapidly restraining the short-circuit current in a medium-low-voltage direct-current power grid is met.

Description

Technical Field

[0001] The present invention relates to the technical field of circuit breakers, and more particularly to a medium- and low-voltage direct current circuit breaker. Background Art

[0002] With the widespread integration of renewable energy sources, various energy storage power supply systems have become essential, typically in the form of regional DC grids incorporating energy storage devices. Currently, DC grids primarily rely on relay protection and DC circuit breakers to ensure reliable system operation. However, fault currents in DC grids rise rapidly, have high amplitudes, and lack zero crossings. Without fault current limiting measures, the di / dt (difference current) can reach over 3kA / ms, far exceeding the rate of rise of fault current amplitude during AC faults. This makes the protection devices and strategies used in traditional AC systems difficult to directly apply to DC grids, posing significant challenges to the safe and stable operation of DC grids. When a DC grid fault occurs, the rapidly increasing fault current can cause severe damage to power equipment in a very short period of time, such as overcurrent burnout of power electronic devices and capacitor breakdown. It also places increased strain on the dynamic and thermal stability of related equipment within the system, including transmission lines and circuit breakers.

[0003] To effectively address this challenge, it is imperative to develop new, fast-response DC circuit breakers. Solid-state current limiting technology using power electronics has become a research hotspot due to its advantages such as fast response and contactless operation.

[0004] A solid-state DC circuit breaker is a type of current limiting device based on fully controlled power electronic devices. It consists of fully controlled power electronic devices, their buffer circuits, and energy absorption branches. When a short-circuit fault is detected, the solid-state switch is controlled to shut down, quickly transferring the short-circuit current to the energy absorption branch (inductor or resistor). The current limiting element in the energy absorption branch limits the short-circuit current. The response time of a solid-state DC circuit breaker is mainly based on the power electronic devices it uses, and can generally reach microseconds, with a fast response speed.

[0005] The advantage of traditional mechanical DC circuit breakers is very low conduction loss. However, their disadvantage is that it is difficult to interrupt large currents and the current interruption time is long, generally tens of milliseconds, which cannot meet the rapid shutdown requirements of low-voltage DC systems.

[0006] The main problem with solid-state DC circuit breakers is the high overvoltage generated across power electronic devices during the shutdown process, which places high demands on their withstand voltage. This leads to high costs and difficulty in selecting the power electronic components used in circuit breakers. Limited by the current state of power electronic device development, solid-state DC circuit breakers are currently difficult to directly apply to high-voltage DC grids, and their primary application is in medium- and low-voltage DC regional grids. Summary of the Invention

[0007] The present invention provides a medium and low voltage DC circuit breaker to solve the problem of how to enable the DC circuit breaker to quickly limit the fault current.

[0008] In order to solve the above problem, according to one aspect of the present invention, a medium and low voltage DC circuit breaker is provided, wherein the medium and low voltage DC circuit breaker comprises: a main current branch, a buffer branch and an energy absorption branch connected in parallel with each other; wherein,

[0009] The main flow branch is a bidirectional flow switch structure. When there is no fault in the system, it remains in the on state and the system current is conducted through the main flow branch. When a short circuit fault occurs in the system, the power electronic devices on the main flow branch are turned off and the system current is transferred to the buffer branch and the energy absorption branch.

[0010] The buffer branch is used to reduce the rising rate of the voltage across the power electronic device to suppress the instantaneous voltage spike when the power electronic device on the main current branch is turned off, thereby preventing the power electronic device from being damaged due to a sudden change in the voltage across the power electronic device;

[0011] The energy absorption branch is used to absorb and consume excess energy when a system failure occurs.

[0012] Preferably, the bidirectional flow switch structure is an anti-series structure, an anti-parallel structure and a diode bridge structure.

[0013] Preferably, the power electronic device on the main current branch is a fully controlled power electronic device.

[0014] Preferably, the buffer branch comprises: a buffer arrester, a buffer resistor and a buffer capacitor, wherein the buffer resistor and the buffer capacitor are connected in parallel and then in series with the buffer arrester;

[0015] The buffer capacitor is used to absorb the energy generated when the power electronic device on the main current branch is turned off;

[0016] The buffer arrester is used to limit the charging current of the buffer capacitor and consume excess energy when the buffer capacitor is discharged;

[0017] The buffer resistor is used to release the energy absorbed by the buffer capacitor.

[0018] Preferably, the absorption branch is a linear resistor or a nonlinear resistor.

[0019] Preferably, the energy absorbing branch adopts an energy absorbing arrester to absorb energy.

[0020] Preferably, the residual voltage of the buffer arrester is less than half of the residual voltage of the energy-absorbing arrester.

[0021] The present invention provides a medium- and low-voltage DC circuit breaker, comprising: a main current branch, a buffer branch, and an energy absorption branch connected in parallel; wherein the main current branch is a bidirectional current switch structure, which remains in an on state when no fault occurs in the system, and the system current is conducted through the main current branch; when a short-circuit fault occurs in the system, the power electronic devices on the main current branch are turned off, and the system current is transferred to the buffer branch and the energy absorption branch; the buffer branch is used to reduce the rising rate of the voltage across the power electronic devices when the power electronic devices on the main current branch are turned off, suppress the instantaneous voltage spike, and prevent the power electronic devices from being damaged due to the sudden change in the voltage across the two ends; the energy absorption branch is used to absorb and consume excess energy when a system fault occurs. The medium- and low-voltage DC circuit breaker of the present invention can be applied to medium- and low-voltage DC power grids to achieve a rapid suppression function for the short-circuit fault current of the DC power grid, and can shut off short-circuit currents with a current peak value of more than 10kA within hundreds of microseconds, meeting the demand for rapid suppression of short-circuit current in medium- and low-voltage DC power grids. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] A more complete understanding of exemplary embodiments of the present invention may be obtained by referring to the following drawings:

[0023] Figure 1 is a circuit diagram of a medium and low voltage DC circuit breaker according to an embodiment of the present invention;

[0024] Figure 2 Schematic diagrams of three bidirectional flow structures according to embodiments of the present invention;

[0025] Figure 3 A schematic diagram of four stages of a current path when a switch of an RC-MOV snubber circuit is disconnected according to an embodiment of the present invention;

[0026] Figure 4 is a schematic diagram of a short-circuit current waveform according to an embodiment of the present invention;

[0027] Figure 5 is a schematic diagram showing changes in current and voltage during the breaking process of a DC circuit breaker according to an embodiment of the present invention;

[0028] Figure 6 Schematic diagram of current transfer waveform during the breaking process of a DC circuit breaker according to an embodiment of the present invention. DETAILED DESCRIPTION

[0029] Exemplary embodiments of the present invention will now be described with reference to the accompanying drawings. However, the present invention may be embodied in many different forms and is not limited to the embodiments described herein. These embodiments are provided to provide a thorough and complete disclosure of the present invention and to fully convey the scope of the present invention to those skilled in the art. The terminology used in the exemplary embodiments shown in the accompanying drawings is not intended to limit the present invention. In the accompanying drawings, identical elements are denoted by the same reference numerals.

[0030] Unless otherwise specified, the terms used herein (including technical terms) have the meanings commonly understood by those skilled in the art. In addition, it is understood that terms defined in commonly used dictionaries should be understood to have the same meanings as those in the context of the relevant fields, and should not be understood as idealized or overly formal meanings.

[0031] In response to the DC regional power grid's need for rapid fault current limitation, the present invention proposes a medium- and low-voltage DC circuit breaker that can shut off short-circuit currents with a peak current of more than 10kA within hundreds of microseconds, meeting the need for rapid short-circuit current suppression in medium- and low-voltage DC power grids. The circuit breaker proposed in the present invention can achieve a bidirectional current-carrying function through a full-bridge diode bridge structure. At the same time, the innovative mov-RC buffer branch topology is adopted to reduce the voltage stress on both ends of the power electronic device at the moment of shutdown, reduce the parameter requirements of the solid-state circuit breaker for the power electronic device, and reduce the cost of the power electronic device in the circuit breaker while ensuring the performance of the circuit breaker.

[0032] Figure 1 FIG. 1 is a circuit diagram of a medium and low voltage DC circuit breaker according to an embodiment of the present invention. Figure 1 As shown, the medium- and low-voltage DC circuit breaker provided in the embodiments of the present invention can be applied to medium- and low-voltage DC power grids to achieve rapid suppression of short-circuit fault currents in the DC power grid. It can shut off short-circuit currents with a peak current exceeding 10kA within hundreds of microseconds, meeting the demand for rapid short-circuit current suppression in medium- and low-voltage DC power grids. The medium- and low-voltage DC circuit breaker provided in the embodiments of the present invention includes: a main current-carrying branch, a buffer branch, and an energy-absorbing branch connected in parallel.

[0033] The main current branch is a bidirectional current switch. When the system is fault-free, it remains on, conducting system current through the main current branch. In the event of a short-circuit fault, the power electronic devices on the main current branch are shut down, diverting the system current to the buffer branch and energy absorption branch. The buffer branch is designed to reduce the rate of voltage rise across the power electronic devices when the power electronic devices on the main current branch are shut down, suppressing transient voltage spikes and preventing damage to the power electronic devices due to sudden voltage changes. The energy absorption branch is designed to absorb and dissipate excess energy in the event of a system fault.

[0034] Preferably, the bidirectional flow switch structure is an anti-series structure, an anti-parallel structure and a diode bridge structure.

[0035] Preferably, the power electronic device on the main current branch is a fully controlled power electronic device.

[0036] Preferably, the buffer branch comprises: a buffer arrester, a buffer resistor and a buffer capacitor, wherein the buffer resistor and the buffer capacitor are connected in parallel and then in series with the buffer arrester;

[0037] The buffer capacitor is used to absorb the energy generated when the power electronic device on the main current branch is turned off;

[0038] The buffer arrester is used to limit the charging current of the buffer capacitor and consume excess energy when the buffer capacitor is discharged;

[0039] The buffer resistor is used to release the energy absorbed by the buffer capacitor.

[0040] Preferably, the absorption branch is a linear resistor or a nonlinear resistor.

[0041] Preferably, the energy absorbing branch adopts an energy absorbing arrester to absorb energy.

[0042] Preferably, the residual voltage of the buffer arrester is less than half of the residual voltage of the energy-absorbing arrester.

[0043] In the present invention, the main circuit of the medium and low voltage circuit breaker includes three parts: the main flow branch, the buffer branch and the energy absorption branch. The main flow branch, the buffer branch and the energy absorption branch are connected in parallel. The specific structure is as follows: Figure 1 As shown in FIG. , D1-D4 are diodes, G1 is a power electronic device, Cs is a snubber capacitor, and Rs is a snubber resistor. The main current branch uses a diode bridge structure as an example, but can also be an anti-series structure or an anti-parallel structure.

[0044] In the present invention, the main flow branch is composed of power electronic devices, which can be turned on and off by control signals. When no fault occurs, the main flow branch remains on, and the system current is conducted through the main flow branch. When a short-circuit fault occurs in the system, the current flowing through the main flow branch increases rapidly, the power electronic devices on the main flow branch shut down, and the system current is transferred to the buffer branch and energy absorption branch.

[0045] The main current flow circuit is a bidirectional current flow switch structure, which can realize the bidirectional current flow function. Therefore, both ends of the DC circuit breaker of the present invention can be used as both the input end and the output end. The power electronic devices that constitute the main current flow branch can be fully controlled power electronic devices such as IGBT and IGCT. Through the mutual combination of multiple power electronic devices, the bidirectional flow function of the main current flow branch can be realized. The specific composition structure of the bidirectional switch can be an anti-series type, anti-parallel type or diode bridge type bidirectional flow structure, respectively as follows: Figure 2 As shown in (a), (b) and (c), the main current branch of the diode bridge structure is taken as an example for introduction.

[0046] In the present invention, the main components of the buffer branch include a metal-oxide varistor (MOV), a buffer resistor, and a buffer capacitor. In the buffer branch, the buffer capacitor and the buffer resistor are connected in parallel, and then connected in series with the buffer MOV.

[0047] During circuit operation, especially when power electronic devices in the main current-carrying branch are turned off, high voltage spikes are generated, posing a serious threat to their safe operation. This is when the snubber branch comes into play. Capacitor C can quickly absorb this energy, slowing the rate of voltage change and preventing damage to the device from excessive voltage spikes. The snubber MOV limits the capacitor's charging current and dissipates excess energy during discharge, ensuring the stability and reliability of the buffering process. Because the snubber MOV only assumes a low-resistance state above a certain voltage, the energy stored in the snubber capacitor C cannot be released. Therefore, a snubber resistor R is connected in parallel across the snubber capacitor C to release the stored energy.

[0048] In the present invention, the energy absorption branch primarily absorbs excess energy from the fault current diverted by the current limiting device. This energy absorption branch dissipates this excess energy in the form of heat, preventing energy accumulation in the circuit and damage to other critical components, thereby ensuring the safe and stable operation of the entire current limiting device. Linear or nonlinear resistors are typically used; in this example, an energy-absorbing arrester is employed to absorb the diverted fault current.

[0049] Among them, the residual pressure of the buffer lightning arrester should not be higher than half of the residual pressure of the energy-absorbing lightning arrester.

[0050] The branches of the medium and low voltage circuit breaker of the present invention work closely together to achieve stable operation of the current limiting device under different working conditions and an efficient energy transfer process.

[0051] In the DC circuit breaker structure proposed in this invention, a nonlinear resistor (MOV) is connected in series with a snubber capacitor (C) in the snubber branch. At the moment the switch opens, the snubber MOV performs a voltage-limiting function, effectively suppressing abnormal voltage increases and preventing excessive voltage from damaging the power electronic switches in the main current loop. When the switch closes, the MOV exhibits a current-limiting characteristic, suppressing the capacitor's discharge current through the main current loop, limiting instantaneous current surges and protecting the power electronic devices within the loop.

[0052] In addition, the buffer MOV has a significant advantage: its ability to effectively block AC harmonics. The presence of AC harmonics can adversely affect capacitors, accelerating capacitor aging and shortening their service life. MOVs effectively filter out AC harmonics through their inherent characteristics, significantly reducing the negative effects of harmonics on capacitors, extending the service life of capacitors, and thereby improving the stability and reliability of the entire circuit system. Simultaneously, by connecting a buffer resistor in parallel across the buffer capacitor, the energy stored in capacitor C is effectively discharged. This measure avoids the long-term accumulation of capacitor energy and can effectively extend the operating life of capacitor C. Furthermore, since the capacitor energy is properly processed, the risk of failure caused by abnormal energy accumulation is reduced, significantly improving the reliability of the current limiting device.

[0053] In the present invention, the different operating states of the DC circuit breaker are as follows: Figure 3 shown.

[0054] In normal operation, G1 is turned on and current flows through D1-G1-D4. The current path is as follows: Figure 3 As shown in (a).

[0055] When a fault occurs and abnormal energy such as overcurrent appears in the circuit, the solid-state switch G1 acts quickly. At the moment the switch is disconnected, the current flows through the buffer branch, and the buffer mov enters the working area. The buffer mov presents a low resistance state, thereby ensuring that the voltage across it will not be too large, playing a role in voltage limiting. At this time, the capacitor C s In charging state. The current path is as follows Figure 3 (b) shown.

[0056] Since the fault current is large, the capacitor C s The voltage across the terminals quickly exceeds the arrester's reference voltage. Once the buffer branch voltage exceeds the arrester's reference voltage on the energy-absorbing branch, the fault current is transferred to the energy-absorbing branch. The fault current flows through the energy-absorbing branch, suppressing the fault current. Excess energy from the fault current is dissipated through heat and other means, preventing energy accumulation.

[0057] Since the capacitor C S The difference between the voltage at both ends and the voltage at both ends of the energy absorption branch is less than the reference voltage of the buffer arrester, and the capacitor C s Stop discharging to the energy absorption branch and release the remaining energy through the parallel buffer resistor. Figure 3 (c) shown.

[0058] When the main current loop switch is closed, the capacitor C s The residual energy on the capacitor will be released to the main current loop through the buffer MOV. The MOV plays a current limiting role at this time to prevent the capacitor discharge current from being too large and causing damage to the fully controlled switching device. The current path is as follows Figure 3 (d)

[0059] In order to analyze the electrical distribution of the designed DC circuit breaker during the breaking process, a model was built in the simulation software PSCAD / EMTDC and the designed DC circuit breaker was simulated. When the circuit breaker is not operating, the short-circuit current waveform is as follows: Figure 4 As shown, the short-circuit current peak is 10.5kA and the average current rise rate is about 7kA / ms.

[0060] At t = 1.0005s, the fault current is generated, which is regarded as the fault start time. 0.5ms after the fault occurs, the DC circuit breaker is activated. After the DC circuit breaker receives the command, the power electronic switch G1 is immediately turned off and the voltage is established. As the voltage rises, the current is commutated to the buffer branch. When the capacitor voltage reaches a higher amplitude, the current is commutated from the buffer branch to the energy-consuming branch, and the voltage at both ends is maintained at the residual voltage of the energy-consuming MOV. Subsequently, all the current is commutated to the energy-consuming branch and absorbed by the energy-consuming MOV, completing the entire breaking process. The circuit breaker breaking waveform is as follows Figure 5 As shown in Figure 1, at 1.001s, the circuit breaker is activated and the fault current is quickly suppressed, while the voltage across the circuit breaker is limited to a tolerable range by the buffer branch. The changes in the current in each branch are shown in Figure 1. Figure 6 As shown, I_trans represents the current waveform on the main flow branch, I_MOV1 represents the current waveform of the buffer branch, and I_MOV2 represents the current waveform of the energy absorption branch.

[0061] After the breaking process is complete, the voltage across the energy-consuming MOV rapidly drops to the bus voltage. At this point, because the capacitor voltage has not been fully released and the rate of voltage drop across the capacitor is much slower than that across the energy-consuming MOV, the snubber arrester is subjected to a reverse voltage. However, the reverse voltage to which the snubber arrester is subjected does not exceed its reference voltage. The reverse current generated by the snubber branch is less than 1mA and can be ignored, with no impact on components external to the circuit breaker. As the snubber capacitor slowly releases energy into the snubber resistor, the voltage across the snubber resistor Cs gradually drops to zero. At this point, the voltage across the snubber arrester also returns to the bus voltage, completing the circuit breaker's breaking process.

[0062] During the overall process, the buffer branch can effectively suppress the voltage spike during the circuit breaker opening process. At the same time, the proposed DC circuit breaker topology can suppress the fault current from 6kA to close to 0A within 200μs, which can meet the requirements of rapid fault current suppression in medium and low voltage DC power grids.

[0063] The present invention has been described with reference to a few embodiments. However, it is apparent to those skilled in the art that other embodiments than the ones disclosed above are equally within the scope of the present invention.

[0064] Generally, all terms used in this disclosure are to be interpreted according to their ordinary meaning in the art, unless explicitly defined otherwise herein. All references to "a / the / the [device, component, etc.]" are to be interpreted openly as referring to at least one instance of the device, component, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not necessarily need to be performed in the exact order disclosed, unless explicitly stated otherwise.

[0065] It will be understood by those skilled in the art that embodiments of the present invention may be provided as methods, systems, or computer program products. Thus, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware. Furthermore, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0066] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowcharts and / or block diagrams, as well as combinations of processes and / or blocks in the flowcharts and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowcharts and / or block diagrams. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0067] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0068] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0069] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered by the scope of protection of the present invention.

Claims

1. A medium and low voltage DC circuit breaker, characterized in that: The medium and low voltage DC circuit breaker includes: a main current branch, a buffer branch and an energy absorption branch connected in parallel; wherein, The main flow branch is a bidirectional flow switch structure. When there is no fault in the system, it remains in the on state and the system current is conducted through the main flow branch. When a short circuit fault occurs in the system, the power electronic devices on the main flow branch are turned off and the system current is transferred to the buffer branch and the energy absorption branch. The buffer branch is used to reduce the rising rate of the voltage across the power electronic device when the power electronic device on the main current branch is turned off, suppress the instantaneous voltage spike, and prevent the power electronic device from being damaged due to the sudden change of the voltage across the power electronic device; The energy absorption branch is used to absorb and consume excess energy when a system failure occurs.

2. The medium and low voltage DC circuit breaker according to claim 1, characterized in that: The bidirectional flow switch structure is an anti-series structure, an anti-parallel structure and a diode bridge structure.

3. The medium and low voltage DC circuit breaker according to claim 1, characterized in that: The power electronic devices on the main current branch are fully controlled power electronic devices.

4. The medium and low voltage DC circuit breaker according to claim 1, characterized in that: The buffer branch includes: a buffer arrester, a buffer resistor and a buffer capacitor, wherein the buffer resistor and the buffer capacitor are connected in parallel and then in series with the buffer arrester; The buffer capacitor is used to absorb the energy generated when the power electronic device on the main current branch is turned off; The buffer arrester is used to limit the charging current of the buffer capacitor and consume excess energy when the buffer capacitor is discharged; The buffer resistor is used to release the energy absorbed by the buffer capacitor.

5. The medium and low voltage DC circuit breaker according to claim 4, characterized in that: The absorption branch is a linear resistor or a nonlinear resistor.

6. The medium and low voltage DC circuit breaker according to claim 4, characterized in that: The energy absorbing branch adopts an energy absorbing arrester to absorb energy.

7. The medium and low voltage DC circuit breaker according to claim 6, characterized in that: The residual voltage of the buffer arrester is less than half of the residual voltage of the energy-absorbing arrester.

Images