Hybrid direct-current circuit breaker adopting novel buffer circuit

Abstract

The invention relates to a hybrid direct-current circuit breaker adopting a novel buffer circuit, which belongs to the field of direct-current systems and power electronics and comprises a through-current branch, a commutation branch, a buffer branch and a power electronic energy consumption branch which are connected in parallel. The through-current branch is connected in series with the direct-current bus; the commutation branch, the buffer branch and the power electronic energy consumption branch are connected in parallel with the through-flow branch; the commutation branch is connected in series with a power electronic switch device; the buffer branch comprises a first branch, and the first branch comprises an auxiliary metal oxide arrester and a first capacitor which are connected in series; a main metal oxide lightning arrester is connected in series in the power electronic energy consumption branch; the clamping voltage of the auxiliary metal oxide lightning arrester is smaller than the clamping voltage of the main metal oxide lightning arrester and is smaller than or equal to the sum of the clamping voltage of the auxiliary metal oxide lightning arrester and the rated voltage of the first capacitor. The circuit breaker can avoid the problem that the surge voltage is too high when a fault occurs.

Description

Technical Field

[0001] This invention relates to a hybrid DC circuit breaker employing a novel buffer circuit, belonging to the fields of DC systems and power electronics. Background Technology

[0002] DC systems, due to their advantages such as flexible power allocation, high system efficiency, large power supply capacity, low line loss, and high power quality, are increasingly widely used in high-voltage transmission, medium- and low-voltage power distribution, renewable energy integration, and shipbuilding and rail transportation. However, the complex main wiring structure and diverse operating modes of DC systems lead to numerous fault modes, rapid fault development, and a wide range of impacts. Therefore, breakthroughs in fault isolation and protection technologies for DC systems are urgently needed to ensure their safe and reliable operation. DC circuit breakers, as the most ideal fault isolation method for DC systems, have become a research hotspot in the electrical field. Based on topology and breaking principle, DC circuit breakers can be classified into mechanical DC circuit breakers, solid-state DC circuit breakers, and hybrid DC circuit breakers. Among them, mechanical DC circuit breakers have low conduction losses, but their switching mechanical and electrical stresses are high, their breaking speed is relatively slow, and their breaking dispersion is large; solid-state DC circuit breakers have extremely fast breaking speeds, but their conduction losses are high and their costs are high. Hybrid DC circuit breakers combine the low-loss current-carrying capacity and rapid insulation recovery of mechanical DC circuit breakers with the fast breaking capacity of solid-state DC circuit breakers, making them one of the main development directions for DC circuit breakers. However, existing DC circuit breakers suffer from excessively high surge voltages during fault current interruptions, which can adversely affect the safety and reliability of power systems. Summary of the Invention

[0003] The purpose of this invention is to provide a hybrid DC circuit breaker employing a novel buffer circuit to solve the problem of excessive surge voltage in DC circuit breakers during fault current interruption.

[0004] To achieve the above objectives, the present invention includes: This invention discloses a hybrid DC circuit breaker employing a novel buffer circuit, comprising a current-carrying branch, a converter branch, a buffer branch, and a power electronic energy-dissipating branch connected in parallel; the current-carrying branch is connected in series with the DC bus; the converter branch, buffer branch, and power electronic energy-dissipating branch are connected in parallel with the current-carrying branch; a power electronic switching device is connected in series on the converter branch; the buffer branch includes a first branch, which includes a secondary metal oxide surge arrester and a first capacitor connected in series; a primary metal oxide surge arrester is connected in series in the power electronic energy-dissipating branch; the clamping voltage of the secondary metal oxide surge arrester is less than the clamping voltage of the primary metal oxide surge arrester, which is less than or equal to the sum of the clamping voltage of the secondary metal oxide surge arrester and the rated voltage of the first capacitor.

[0005] Furthermore, the power electronic switching device in the commutation branch is an insulated-gate bipolar transistor (IGBT), with the collector and emitter of the IGBT connected in series in the commutation branch.

[0006] Furthermore, a first inductor is connected in series on the first branch of the buffer branch.

[0007] Furthermore, the buffer branch also includes a first resistor connected in parallel across the first inductor and the secondary metal oxide surge arrester connected in series.

[0008] Furthermore, the buffer branch also includes a second branch connected in parallel across the two ends of the first branch, and the second branch includes a second resistor and a second capacitor connected in series.

[0009] Furthermore, the power electronic energy dissipation branch also includes a second inductor connected in series with the main metal oxide surge arrester.

[0010] The beneficial effects of this invention are as follows: This invention is groundbreaking. It presents a hybrid DC circuit breaker employing a novel buffer circuit. Utilizing two metal oxide varistors (MOVs) with different clamping voltages, the function of each MOV can be specified based on the difference in energy absorption at different voltage levels. This effectively suppresses surge voltage, solving the problem of excessively high surge voltage during fault current interruptions. Consequently, it enhances the performance of the SSCB (Solid State Circuit Breaker) in the hybrid DC circuit breaker, improves the safety of the power system, and is expected to enhance the safety and reliability of the power system. Attached Figure Description

[0011] Figure 1 This is a schematic diagram of the main structure of a hybrid DC circuit breaker that uses a novel buffer circuit. Figure 2 This is a schematic diagram of the normal flow process of a hybrid DC circuit breaker using a new type of buffer circuit. Figure 3 This is a schematic diagram of the current transfer process of a hybrid DC circuit breaker using a novel buffer circuit. Figure 4 This is a schematic diagram of the buffering process of a hybrid DC circuit breaker using a novel buffer circuit. Figure 5 This is a schematic diagram of the energy dissipation process of a hybrid DC circuit breaker using a novel buffer circuit. Figure 6 This is a schematic diagram of the resonant process of a hybrid DC circuit breaker using a novel buffer circuit. Figure 7 This is a schematic diagram of the capacitor discharge process of a hybrid DC circuit breaker using a novel buffer circuit. Detailed Implementation

[0012] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0013] The present invention provides a hybrid DC circuit breaker employing a novel buffer circuit. This circuit breaker consists of a current-carrying branch, a converter branch, a buffer branch, a power electronic energy dissipation branch, and a capacitor discharge branch. By utilizing two metal oxide varistors (metal oxide surge arresters) with different clamping voltages in the buffer branch and the power electronic energy dissipation branch, the function of each MOV can be specified according to the difference in energy absorption of MOVs at different voltage levels, thereby effectively suppressing surge voltage and solving the problem of excessively high surge voltage during fault current interruption.

[0014] Example: like Figure 1 The hybrid DC circuit breaker shown employs a novel buffer circuit and comprises a current-carrying branch, a commutation branch, a buffer branch, a power electronic energy dissipation branch, and a capacitor discharge branch. The current-carrying branch, commutation branch, buffer branch, and power electronic energy dissipation branch are connected in parallel. The current-carrying branch consists of a fast mechanical switch (FMS); the commutation branch consists of power electronic switching devices (IGBTs); the buffer branch consists of a first inductor Ls, a first resistor Rs, a second resistor Rm, a first capacitor Cs, a second capacitor Cm, and a secondary metal oxide surge arrester (MOVs); the power electronic energy dissipation branch consists of a second inductor Lm and a main metal oxide surge arrester (MOVm); and the capacitor discharge branch consists of the fast mechanical switch (FMS), the first resistor Rs, the second resistor Rm, the first capacitor Cs, and the second capacitor Cm.

[0015] The line resistance Rline, the line inductance Lline, the fast mechanical switch FMS in the current-carrying branch, and the load resistance Rload are connected in series. In the commutation branch, the collector and emitter of the IGBT are connected in series in the commutation branch; In the buffer branch, Ls, MOVs and Cs are connected in series to form the first branch, Rs is connected in parallel at both ends of Ls and MOVs connected in series, Rm and Cm are connected in series to form the second branch, and the second branch is connected in parallel with the first branch. In the power electronic energy-consuming branch, Lm and MOVm are connected in series.

[0016] Among them, MOVm is the main MOV and MOVs is the auxiliary MOV. The voltage level of the main MOV is higher than that of the auxiliary MOV. The sum of the voltage level of the auxiliary MOV and the rated voltage of Cs is greater than or equal to the voltage level of the main MOV. The main MOV is responsible for absorbing most of the energy during a fault. The auxiliary MOV is responsible for clamping and suppressing the initial surge voltage and rectifying the primary fault current.

[0017] The operation of a circuit breaker consists of the following processes: normal current flow, current transfer, buffering, energy dissipation, resonance, and capacitor discharge. Normal circulation process such as Figure 2 As shown, under normal current conditions, the system current flows through the line resistance Rline, the line inductance Lline, the load resistance Rload, and the fast mechanical switch FMS. Current transfer process as follows Figure 3 As shown, when a fault occurs, the fast mechanical switch FMS is disconnected, and at the same time the power electronic device IGBT in the converter branch is turned on, and the fault current is transferred to the converter branch. Buffering process as Figure 4 As shown, when the fault current is completely transferred to the converter branch, the power electronic device IGBT in the converter branch is turned off. At this time, the voltage across MOVs in the buffer branch and MOVm in the power electronic energy dissipation branch increases sharply. MOVs reaches its operating voltage and begins the first clamping. MOVm does not reach its operating voltage and therefore does not work. At this time, Cs and Cm in the buffer branch are charged. Energy dissipation process such as Figure 5 As shown, as the voltage of Cs in the buffer branch increases, the sum of the voltages of MOVs and Cs begins to drive the parallel MOVm to work. As the fault current begins to flow through MOVm, the fault current flowing into MOVs decreases, and finally the energy is dissipated in MOVm. The resonance process is as follows Figure 6 As shown, when the MOVs stop working, Cm, Cs resonate with Lline. When the resonance ends, the voltage across Cm and Cs is equal to the input voltage. The capacitor discharge process is as follows Figure 7 As shown, after the fault current is completely dissipated, the FMS is closed, and the energy stored in Cs and Cm is discharged through Rs and Rm connected in series. At this time, the second branch composed of Rm and Cm is used to adjust the resonant discharge.

[0018] As another implementation method: the buffer branch consists of a first inductor Ls, a secondary metal oxide surge arrester MOVs, a first capacitor Cs, and a first resistor Rs. Ls, MOVs, and Cs are connected in series, and Rs is connected in parallel across the two ends of Ls and MOVs connected in series.

Claims

1. A hybrid DC circuit breaker employing a novel buffer circuit, characterized in that, It includes a current-carrying branch, a converter branch, a buffer branch, and a power electronic energy-dissipating branch connected in parallel; the current-carrying branch is connected in series with the DC bus; the converter branch, buffer branch, and power electronic energy-dissipating branch are connected in parallel with the current-carrying branch; a power electronic switching device is connected in series on the converter branch; the buffer branch includes a first branch, which includes a secondary metal oxide surge arrester and a first capacitor connected in series; a primary metal oxide surge arrester is connected in series in the power electronic energy-dissipating branch; the clamping voltage of the secondary metal oxide surge arrester is less than the clamping voltage of the primary metal oxide surge arrester, which is less than or equal to the sum of the clamping voltage of the secondary metal oxide surge arrester and the rated voltage of the first capacitor.

2. The hybrid DC circuit breaker employing a novel buffer circuit according to claim 1, characterized in that, The power electronic switching device of the commutation branch is an insulated gate bipolar transistor (IGBT), with the collector and emitter of the IGBT connected in series in the commutation branch.

3. The hybrid DC circuit breaker employing a novel buffer circuit according to claim 2, characterized in that, A first inductor is also connected in series on the first branch of the buffer branch.

4. The hybrid DC circuit breaker employing a novel buffer circuit according to claim 3, characterized in that, The buffer branch also includes a first resistor connected in parallel across the first inductor and the secondary metal oxide surge arrester connected in series.

5. The hybrid DC circuit breaker employing a novel buffer circuit according to claim 2, characterized in that, The buffer branch also includes a second branch connected in parallel at both ends of the first branch, the second branch including a second resistor and a second capacitor connected in series.

6. The hybrid DC circuit breaker employing a novel buffer circuit according to claim 1, characterized in that, The power electronic energy dissipation branch also includes a second inductor connected in series with the main metal oxide surge arrester.

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