A TVS-MOV clamping based DC circuit breaker and a working method thereof
By using a TVS-MOV clamping structure and SCR-triggered circuit design, the problem of excessive MOV clamping voltage was solved, achieving a DC circuit breaker design with low voltage stress and high reliability, reducing system losses and improving the flexibility of device selection.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- ANHUI UNIV
- Filing Date
- 2026-01-15
- Publication Date
- 2026-05-29
Smart Images
Figure CN122118614A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of DC power grid protection technology, and in particular to a DC circuit breaker based on TVS-MOV clamping and its operating method. Background Technology
[0002] In the field of DC circuit breakers, metal oxide varistors (MOVs) are commonly used as clamping devices in traditional technologies. Since the clamping voltage of an MOV needs to be fixed at more than twice the rated DC voltage, this results in an excessively high clamping voltage. This not only increases the voltage stress on power devices and limits the flexibility of device selection, but also reduces the overcurrent capacity of the devices. Furthermore, the high clamping voltage leads to greater losses in the entire system, directly affecting the operating performance and reliability of the DC circuit breaker.
[0003] Therefore, how to reduce the clamping voltage of the MOV and decouple the DC bus voltage from the MOV clamping voltage has become a key issue in improving the performance of DC circuit breakers. Summary of the Invention
[0004] To address the existing problems, this invention provides a DC circuit breaker based on TVS-MOV clamping and its operating method, the specific solution of which is as follows:
[0005] A DC circuit breaker based on TVS-MOV clamping has a circuit topology comprising: a TVS-MOV branch, an RC buffer branch, and a back-to-back IGBT branch; the TVS-MOV branch, the RC buffer branch, and the back-to-back IGBT branch are connected in parallel across a DC bus; a silicon controlled thyristor (SCR) is also connected in series in the TVS-MOV branch, and the gate of the SCR is connected to the node between the cathode of the TVS and one end of the MOV, for receiving a trigger signal from the TVS;
[0006] Preferably, a pn diode is connected in parallel across the gate and cathode of the SCR to achieve reverse blocking capability and protect the thyristor.
[0007] Preferably, after the TVS and MOV are connected in series to form a TVS-MOV branch, a voltage equalization resistor is connected in parallel at both ends.
[0008] Preferably, a capacitor is connected in parallel across the two ends of the MOV.
[0009] This invention also discloses a method for operating a DC circuit breaker based on TVS-MOV clamping, applicable to any of the DC circuit breakers described above, comprising the following steps:
[0010] S1. In normal standby mode, the DC bus voltage is shared by the TVS and MOV connected in series, the back-to-back IGBTs are turned on, and the load current flows through the back-to-back IGBT branch.
[0011] S2. When a short circuit fault occurs in the DC system, the fault current flows through the conducting back-to-back IGBT branch; the control signal turns off the back-to-back IGBT, and the fault current is transferred to the RC buffer branch, causing the voltage across the circuit breaker to rise.
[0012] S3. When the voltage across the circuit breaker rises to the breakdown voltage of the TVS, the TVS breaks down and conducts, and the resulting current signal triggers the SCR to conduct.
[0013] After S4 and SCR are turned on, the fault current is switched to the path formed by SCR and MOV. MOV turns on and absorbs the fault energy, clamping the voltage at both ends of the circuit breaker and completing the fault clearing.
[0014] Preferably, in step S3, when the TVS breaks down, the MOV cannot change voltage due to the capacitor connected in parallel across its two ends, and the initial voltage is mainly established across the TVS.
[0015] The beneficial effects of this invention are as follows:
[0016] 1. This invention cleverly decouples the clamping voltage of the MOV from the DC bus operating voltage by introducing a TVS in series with the MOV for voltage equalization and using the TVS to trigger the SCR for commutation during a fault. This allows the selection of an MOV with a much lower turn-on voltage than traditional solutions, ultimately resulting in a significant reduction in the fault clamping voltage.
[0017] 2. Due to the reduction in the final clamping voltage, the voltage stress that the back-to-back IGBTs in the back-to-back IGBT branch, i.e. the main switch branch, need to withstand is greatly reduced, allowing the selection of IGBT devices with lower voltage ratings, stronger current carrying capacity, and lower cost.
[0018] 3. The entire fault detection, triggering and commutation process is achieved entirely by the physical characteristics of the devices in the circuit topology (TVS breakdown, SCR triggering, MOV conduction), without the need for additional complex control circuits, resulting in high reliability.
[0019] 4. The topology is symmetrical, retaining the bidirectional current conduction and interruption function achieved by bidirectional TVS and back-to-back IGBTs, without adding extra circuit complexity. Attached Figure Description
[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0021] Figure 1This is a topology diagram of the DC circuit breaker of the present invention;
[0022] Figures 2a to 2d This is a schematic diagram illustrating different stages of the working principle of the present invention;
[0023] Figure 3 This is a diagram of a simulation system built in LTspice software based on an embodiment of the present invention.
[0024] Figure 4 The waveform diagram of surge current under a 300V / 60A system is shown.
[0025] Figure 5 The simulation waveform diagram is shown at the moment of IGBT turn-on in a 300V / 60A system.
[0026] Figure 6 The simulation waveform diagram is shown at the moment of IGBT turn-off in a 300V / 60A system. Detailed Implementation
[0027] 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. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0028] like Figure 1 This invention discloses a DC circuit breaker based on TVS-MOV clamping and its working method, involving the analysis of the topology and working principle of the clamping branch of the DC circuit breaker and the verification through simulation.
[0029] This paper proposes a novel clamping circuit to decouple the DC bus voltage from the MOV clamping voltage, thereby improving the DC bus voltage suppression coefficient and reducing the overall system losses. A TVS transient suppression diode and a silicon controlled thyristor (SCR) are introduced to share the voltage under normal conditions and commutate the current to the MOV during fault conditions to clear the fault. In standby mode, the TVS and MOV share the DC bus voltage. During a fault transient, the voltage initially rises to the TVS clamping voltage, causing the TVS to conduct. Since the TVS and MOV form a circuit, the MOV is not conducting at this time due to its high impedance limitation. The TVS current is very small, and the current signal is sent to the gate of the SCR, causing the SCR to conduct. The fault current is then commutated to the MOV, which absorbs energy and clears the fault. The pn diodes at the gate and cathode of the SCR provide reverse blocking capability, protecting the thyristor.
[0030] The specific current flow direction is as follows: Figures 2a to 2d As shown. Among them, Figure 2a At this point, the fault current flows through the back-to-back IGBTs, and the impedance is almost negligible. The fault current rises rapidly at this time. Figure 2b At this point, the IGBT disconnects, and the fault current is transferred to the RC buffer branch. The current then begins to charge C1, and the voltage is quickly established. Figure 2c When the voltage rises to the point where the TVS breaks down, the TVS turns on, instantly giving the SCR thyristor a turn-on signal. Figure 2d At this point, the current is switched to the SCR, the MOV turns on, and the voltage eventually rises to the MOV clamping voltage. The MOV absorbs energy and completes the fault clearing.
[0031] The simulation verification of this invention is as follows:
[0032] Table 1 Key Component Parameters
[0033]
[0034] Simulation verification was performed in LTspice software, and the device parameters used were obtained from the imported LTspice model. Using these parameters, this topology was built for a 300V 60A DC system. Figure 3 As shown, a fault current is generated when the IGBT is turned on, and the IGBT is turned off after 25µs.
[0035] Simulated waveforms such as Figure 4As shown, V(igbt) represents the IGBT voltage (i.e., the DC bus voltage), V(igbt,tvs) represents the voltage across the TVS, and V(mov) represents the voltage across the MOV. Ix(IGBT:1) represents the current across the IGBT, I(RC) represents the current flowing through the RC buffer branch, Ix(U1:2) represents the current flowing through the TVS, and Ix(SCR:A) represents the current flowing through the SCR. The figure shows that before 20µs, the DC bus voltage is shared by the TVS and MOV, and no current flows through the line. Between 20µs and 45µs, the IGBT turns on, causing a voltage drop. The energy in the RC buffer branch capacitor is released instantaneously, flowing through the TVS and ultimately to the IGBT branch. Therefore, a voltage spike is observed across the IGBT and TVS, as the simulation needs to reflect the static voltage sharing between the TVS and MOV at the beginning. Subsequently, a fault current is generated and gradually increases. After 45µs, the IGBT turns off, and the current transfers to the RC snubber branch, establishing voltage. The TVS breaks down, causing the SCR to turn on, and the current is ultimately clamped above the MOV, achieving energy absorption and fault clearing. As shown in the diagram, the final clamping voltage is only around 360V, significantly reducing the clamping voltage, and fault clearing is also very rapid. If the traditional clamping voltage is generally more than double the DC bus voltage, by decoupling the DC bus voltage and the MOV clamping voltage, a lower clamping voltage MOV can be selected, reducing the final energy absorption clamping voltage.
[0036] The simulated IGBT turn-on and turn-off moment magnification diagram is shown below. Figure 5 , 6 As shown, at the instant of conduction, the bus voltage, TVS, and MOV voltage drop rapidly. The reverse current in the RC snubber branch and TVS is due to the capacitor charging during the static state. Once the IGBT turns on, a loop is formed, and part of the capacitor's energy flows to the IGBT, and the other part flows to the TVS and then back to the IGBT. This is why such a reverse current is observed immediately upon turn-on. At the instant of turn-off, the voltage instantly establishes itself across the TVS after the IGBT turns off. This is because a capacitor is connected in parallel across the MOV in the topology. The voltage across the MOV does not change abruptly, so the initial voltage instantly establishes itself across the TVS. At this moment, the TVS is momentarily broken down, and a very small current is generated across it. Subsequently, the thyristor turns on, and the current is commutated to the MOV branch, ultimately clearing the fault current. This process also occurs on the order of microseconds.
[0037] Those skilled in the art will further appreciate that the various illustrative logic blocks, modules, circuits, and algorithm steps described in conjunction with the embodiments disclosed herein can be implemented as electronic hardware, computer software, or a combination of both. To clearly illustrate this interchangeability between hardware and software, the various illustrative components, blocks, modules, circuits, and steps are described above in a generalized manner in terms of their functionality. Whether such functionality is implemented as hardware or software depends on the specific application and the design constraints imposed on the overall system. Those skilled in the art may implement the described functionality in different ways for each specific application, but such implementation decisions should not be construed as departing from the scope of the invention.
[0038] The prior description of this disclosure is provided to enable any person skilled in the art to make or use this disclosure. Various modifications to this disclosure will be apparent to those skilled in the art, and the general principles defined herein may be applied to other variations without departing from the spirit or scope of this disclosure. Therefore, this disclosure is not intended to be limited to the examples and designs described herein, but should be accorded the widest scope consistent with the principles and novel features disclosed herein.
[0039] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.
Claims
1. A DC circuit breaker based on TVS-MOV clamping, characterized in that, The circuit topology includes: a TVS-MOV branch, an RC buffer branch, and a back-to-back IGBT branch; the TVS-MOV branch, RC buffer branch, and back-to-back IGBT branch are connected in parallel across the DC bus; a silicon controlled thyristor (SCR) is also connected in series in the TVS-MOV branch, and the gate of the SCR is connected to the node between the cathode of the TVS and one end of the MOV, for receiving trigger signals from the TVS.
2. The DC circuit breaker according to claim 1, characterized in that: A pn diode is connected in parallel across the gate and cathode of the SCR to provide reverse blocking capability and protect the thyristor.
3. The DC circuit breaker according to claim 1, characterized in that: After the TVS and MOV are connected in series to form a TVS-MOV branch, a voltage equalization resistor is connected in parallel at both ends.
4. The DC circuit breaker according to claim 1, characterized in that: A capacitor is connected in parallel across the two ends of the MOV.
5. A method for operating a DC circuit breaker based on TVS-MOV clamping, applied to the DC circuit breaker according to any one of claims 1-4, characterized in that, Includes the following steps: S1. In normal standby mode, the DC bus voltage is shared by the TVS and MOV connected in series, the back-to-back IGBTs are turned on, and the load current flows through the main switch branch. S2. When a short circuit fault occurs in the DC system, the fault current flows through the conducting back-to-back IGBTs; the control signal turns off the back-to-back IGBTs, and the fault current is transferred to the RC buffer branch, causing the voltage across the circuit breaker to rise. S3. When the voltage across the circuit breaker rises to the breakdown voltage of the TVS, the TVS breaks down and conducts, and the resulting current signal triggers the SCR to conduct. After S4 and SCR are turned on, the fault current is switched to the path formed by SCR and MOV. MOV turns on and absorbs the fault energy, clamping the voltage at both ends of the circuit breaker and completing the fault clearing.
6. The method according to claim 5, characterized in that: In step S3, when the TVS breaks down, the MOV cannot change voltage due to the capacitor connected in parallel across its two ends, and the initial voltage is mainly established across the TVS.