A Fault Current Limiting Hybrid DC Circuit Breaker

Due to the low impedance characteristic of the high voltage direct current(HVDC)grid,the fault current rises extremely fast after a DC-side fault occurs,and this phenomenon seriously endangers the safety of the HVDC grid.In order to suppress the rising speed of the fault current and reduce the current interruption requirements of the main breaker(MB),a fault current limiting hybrid DC circuit breaker(FCL-HCB)has been proposed in this paper,and it has the capability of bidirectional fault current limiting and fault current interruption.After the occurrence of the overcurrent in the HVDC grid,the current limiting circuit(CLC)of FCL-HCB is put into operation immediately,and whether the protected line is cut off or resumed to normal operation is decided according to the fault detection result.Compared with the traditional hybrid DC circuit breaker(HCB),the required number of semiconductor switches and the peak value of fault current after fault occurs are greatly reduced by adopting the proposed device.Extensive simulations also verify the effectiveness of the proposed FCL-HCB.

Key stress extraction and equivalent test method for hybrid DC circuit breaker

Firstly, relevant stress properties of millisecond level breaking process and microsecond level commutation process of hybrid HVDC circuit breaker are studied in detail on the basis of the analysis for the application environment and topological structure and operating principles of hybrid circuit breakers, and key stress parameters in transient state process of two time dimensions are extracted. The established digital simulation circuit for PSCAD/EMTDC device-level operation of the circuit breaker has verified the stress properties of millisecond level breaking process and microsecond level commutation process. Then, equivalent test method, circuits and parameters based on LC power supply are proposed on the basis of stress extraction. Finally, the results of implemented breaking tests for complete 200 kV circuit breaker, 100 kV and 50 kV circuit breaker units, as well as single power electronic module have verified the accuracy of the simulation circuit and mathematical analysis. The result of this paper can be a guide to electrical structure and test system design of hybrid HVDC circuit breaker.

Research on Parameter Collaborative Configuration of DC Circuit Breaker and DC Fault Current Limiter

Fault current suppression is the key technology to ensure the safe operation of the DC power distribution system. In order to realize the parameter collabora-tive configuration of the DC circuit breaker and the DC current limiter and improve the fault current suppression capability, the fault current suppression mechanism of the DC power distribution system is revealed based on the circuit model. Then, based on the mathematical model of the DC breaker, the characteristic parameters of DC breaking are extracted, and then the influence of different characteristic parameters on the breaking characteristics of fault current is studied. Finally, the mathematical model of the collaborative process between DC circuit breaker and DC current limiter is established. The charac-teristic parameters of fault current collaborative suppression are extracted. The coupling effects of different characteristic parameters on the fault current col-laborative suppression are studied. The principle of collaborative configuration of DC circuit breaker and DC current limiter is proposed, and the collaborative suppression ability of DC circuit breaker and DC current limiter to fault current is fully exploited to ensure the safe and reliable operation of the DC power distribution system.

Fluid-chemical modeling of the near-cathode sheath formation process in a high current broken in DC air circuit breaker

When the contacts of a medium-voltage DC air circuit breaker(DCCB) are separated, the energy distribution of the arc is determined by the formation process of the near-electrode sheath. Therefore, the voltage drop through the near-electrode sheath is an important means to build up the arc voltage, which directly determines the current-limiting performance of the DCCB. A numerical model to describe the near-electrode sheath formation process can provide insight into the physical mechanism of the arc formation, and thus provide a method for arc energy regulation. In this work, we establish a two-dimensional axisymmetric time-varying model of a medium-voltage DCCB arc when interrupted by high current based on a fluid-chemical model involving 16 kinds of species and 46 collision reactions. The transient distributions of electron number density, positive and negative ion number density, net space charge density, axial electric field, axial potential between electrodes, and near-cathode sheath are obtained from the numerical model. The computational results show that the electron density in the arc column increases, then decreases, and then stabilizes during the near-cathode sheath formation process, and the arc column's diameter gradually becomes wider. The 11.14 V–12.33 V drops along the17 μm space charge layer away from the cathode(65.5 k V/m–72.5 k V/m) when the current varies from 20 k A–80 k A.The homogeneous external magnetic field has little effect on the distribution of particles in the near-cathode sheath core,but the electron number density at the near-cathode sheath periphery can increase as the magnetic field increases and the homogeneous external magnetic field will lead to arc diffusion. The validity of the numerical model can be proven by comparison with the experiment.

Low-loss and Compact Hybrid DC Circuit Breaker Scheme Using Self-commutated Semiconductor Switch Module

In traditional hybrid DC circuit breakers(HCBs)schemes,complex equipment is usually required to ensure current commutation from mechanical to semiconductor switches,which cause not only additional construction costs and volume but also additional losses and maintenance work.Different from this condition,a low-loss and compact HCB scheme that does not use separate current commutation equipment is proposed in this study.By rationally using the charge and discharge of the snubber capacitor,the self-commutated semiconductor switch(SCS)module can integrate both the current commutation and shutdown functions,thereby greatly reducing cost and volume.The working process is discussed and analyzed in detail,and then a 10-kA prototype is developed and tested,which verifies the feasibility and effectiveness of the proposed scheme.Index Terms-HVDC circuit breakers,hybrid DC circuit breakers(HCBs),self-commutated semiconductor switch(SCS).

Coordinated Control of DC Circuit Breakers in Multilink HVDC Grids

High voltage DC grids are developing in more terminals and with larger transmission capacity,thus the re-quirements for DC circuit breakers(DCCB)will continue to rise.Conventional methods only use the faulty line DCCB to withstand the fault stress,and therefore this paper presents a coordination method of multiple DCCBs to protect the system.As many adjacent DCCBs are tripped to interrupt the fault current,the fault energy is shared,and the requirement for the faulty line DCCB is reduced.Moreover,the adjacent DCCBs are actively controlled to help system recovery.The primary protection,backup protection,and reclosing logic of multiple DCCBs are studied.Simulations confirm that the proposed control reduces the energy dissipation requirement of faulty line DCCB by approximately 30%-42%,the required current rating for IGBTs is reduced,and the system recovery time is also reduced by 20-40 ms.

Study on Clamping Type DC Circuit Breaker with Short Fault Isolation Time and Low Energy Dissipation

The development of DC grids faces challenges from DC fault protection.The conventional DC circuit breaker(DCCB)employs metal-oxide varistor(MOV)to isolate the faulted line,in which the fault isolation process is coupled with the energy dissipation process.In this study,a clamping type DCCB(CTCB)using internal capacitors to clamp the converter voltage is proposed.Thanks to the proposed configuration,fault isolation and energy dissipation are decoupled,resulting in a fast fault isolation and low energy dissipation compared to the conventional DCCB.The working principle of the proposed CTCB is presented and verified in a DC grid simulation model.A comparison is made with the traditional DCCB.The fault isolation time can be reduced by 34.5%.The dissipated energy can be reduced by 17.4%.The energy dissipation power can be reduced by 76.2%.

含主动限流控制的MMC-HVDC电网直流短路故障电流解析计算

传统的MMC-HVDC电网直流短路故障电流计算一般采用等效RLC电路方法。但是该方法没有考虑主动限流控制(ACLC)对等效电路RLC参数的影响,因此无法直接用于含ACLC的MMC-HVDC电网的直流短路故障电流的解析计算问题。该文通过将ACLC的控制效果等效为虚拟阻抗产生的压降,建立了体现ACLC的控制影响的等效RLC电路,以包含电流变化率限流环节的典型ACLC算法为例,推导了直流双极短路故障条件下ACLC的控制参数与虚拟阻抗的映射关系以及相应的直流故障电流解析表达式。最后,以基于含ACLC的半桥型四端MMC-HVDC电网为例,建立PSCAD/EMTDC仿真模型,对采用ACLC的直流双极短路故障电流解析计算结果进行了验证。结果表明:故障后10ms内直流短路故障电流的PSCAD仿真结果与所提出的含ACLC的等效RLC电路解析计算结果的平均误差在8.29%以内,最大误差在10.99%。因此,使用所提出的方法具有工程实用性。

基于IAO-ELM的DC-DC电路软故障诊断

针对DC-DC电路软故障诊断精确度差的问题,提出了一种基于改进的天鹰算法(IAO)-优化极限学习机(ELM)的故障诊断方法。采用变分模态分解的方法对原始的故障信号进行分解重构,提取时频域特征作为特征向量。使用SPM混沌映射、透镜反向学习、自适应权重和柯西变异策略改进天鹰算法,提升其寻优性能。采用IAO对ELM的输入权值和隐含层偏置进行优化,得到IAO-ELM诊断模型,提高分类精度。结果显示,IAO-ELM诊断模型的准确率为99.375%,能有效地实现DC-DC电路软故障诊断。

DC-DC转换器高低温测试方案研究

高低温测试是DC-DC转换器筛选过程中的重要环节之一,直接关系到对电路的判定。以传统DC-DC转换器测试方案来进行高低温测试,壳温变化较大,影响测试的稳定性。针对传统测试方案存在的问题,提出了一种基于ATE、热流罩的高低温测试方案,介绍了物理结构设计、选材侧重点和板卡布局等要点。通过对方案优化前后的测试效果进行对比,展现新方案测试能力的提升,可以为DC-DC转换器的测试筛选和应用验证方案设计提供参考。

Coordination Control of Power Flow Controller and Hybrid DC Circuit Breaker in MVDC Distribution Networks

The two main challenges of medium voltage direct current(MVDC)distribution network are the flexible control of power flow(PF)and fault protection.In this paper,the power flow controller(PFC)is introduced to regulate the PF and inhibit the fault current during the DC fault.The coordination strategy of series-parallel PFC(SP-PFC)and hybrid DC circuit breaker(DCCB)is proposed.By regulating the polarity and magnitude of SP-PFC output voltage during the fault,the rising speed of fault current can be suppressed so as to reduce the breaking current of hybrid DCCB.The access mode of SP-PFC to the MVDC distribution network and its topology are analyzed,and the coordination strategy between SP-PFC and hybrid DCCB is investigated.Moreover,the emergency control and bypass control strategies of SP-PFC are developed.On this basis,the mathematical model of SP-PFC in different fault stages is derived.With the equivalent model of SP-PFC,the fault current of the MVDC distribution network can be calculated accurately.A simulation model of the MVDC distribution network containing SP-PFC is established in MATLAB/Simulink.The fault current calculation result is compared with the simulation result,and the effectiveness of the proposed coordination strategy is verified.

Topology of Current-limiting and Energy-transferring DC Circuit Breaker for DC Distribution Networks

With the development of power electronic technologies and distributed power generation,DC distribution networks attract increasing attention due to their various advantages compared with traditional AC distribution networks.However,DC fault protection is one of the major issues in DC distribution networks.To improve their reliability and protect the semiconductor devices under DC faults,a current-limiting and energy-transferring DC circuit breaker topology is proposed in this paper.By applying passive components and thyristors,the proposed topology is capable of quickly limiting the fault current and transferring the faulty energy.The working principle,mathematical model and parameter designing method of the proposed topology are presented in this paper.The simulation results verify that the proposed DC circuit breaker could effectively limit the fault current and quickly interrupt the fault current.Cost and conduction power loss evaluation proves the practicality of the proposed topology in medium-voltage DC distribution networks.

Novel Fast Operating Moving Coil Actuator with Compensation Coil for HVDC Circuit Breakers

DC circuit breakers are major enabling components for multi-terminal HVDC systems.Their key design targets are operating speed and efficiency.This paper proposes a novel moving coil actuator using a compensation coil topology to operate mechanical circuit breakers.This topology aims to significantly improve the magnetic field saturation and reduce the system inductance,so that the operating speed is increased.Four possible connection methods for the compensation coils are proposed and analyzed using finite element modeling,ensuing simulation results are compared and discussed.The operating speed of the moving coil actuator with compensation coils is significantly improved compared with the original moving coil actuator.The moving coil actuator with compensation coils can open a distance of 5 mm within 2.8 ms and the peak efficiency is 47%.

Circuit Model with Current Interruption for Hybrid High Voltage DC Circuit Breakers to Achieve Precise Current Experiments

The current interruption test based on an LC resonance circuit for hybrid DC circuit breakers(HVDC CBs)is widely employed to characterize the current interruption capability of CBs.In order to ensure a high-fidelity replica of the fault current in a high voltage application,this paper first proposes an equivalent model of the test circuit,where not only parasitic resistances but also the threshold voltages and on-state resistances of various semiconductor devices are considered.Moreover,the analytical formula of the test current is derived by including the working principle of the HVDC CB.Secondly,the parameter extraction method,which combines finite element analysis and measurements by an impedance analyzer,is given in this paper.The extracted result implies that,in current interruption transients,equivalent resistances of 500 kV CB are as large as 535 mS,which have a significant influence on current waveforms.Thirdly,the 34 kV/25 kA current interruption test for the 500 kV CB is conducted.The measured results are proved to be consistent with the analytical results obtained from the proposed model,and the relative error is less than 2%.

一种新型超高升压DC-DC变换器的设计

为使光伏系统可稳定输出高直流电压,提出一种新型超高升压DC-DC变换器的设计。变换器采用耦合电路升压结构增加了新的增益调节单元。新型开关单元降低了开关器件的电压应力和电压尖峰。耦合电感与开关电容结合,降低了器件的电压、电流尖峰,吸收了耦合电感的漏感能量。对变换器进行闭环控制,稳定变换器的输出。分析电路的工作模态,与近几年典型高升压变换器做性能对比,测试变换器的抗扰动性能。根据仿真和实验,验证变换器在闭环控制下的稳定性和鲁棒性。

Magneto-hydrodynamic simulation study of direct current multi-contact circuit breaker for equalizing breaking arc

This work is based on a direct current(DC)natural current commutation topology,which uses load-carrying branch contacts carrying rated current and multiple sets of series arcing branch contacts in parallel to achieve circuit breaking.The proposed topology can meet the new requirements of higher voltage DC switches in aviation,aerospace,energy and other fields.First,a magneto-hydrodynamic arc model is built using COMSOL Multiphysics,and the different arc breaking characteristics of the arcing branch contacts in different gas environments are simulated.Then,a voltage uniformity coefficient is used to measure the voltage sharing effect in the process of dynamic interruption.In order to solve the dispersion of arcing contact action,a structural control method is adopted to improve the voltage uniformity coefficient.The uniform voltage distribution can improve the breaking capacity and electrical life of the series connection structure.

Adaptive Reclosing Scheme Based on Traveling Wave Injection For Multi-Terminal dc Grids

The hybrid dc circuit breaker(HCB)has the advantages of fast action speed and low operating loss,which is an idealmethod for fault isolation ofmulti-terminal dc grids.Formulti-terminal dc grids that transmit power through overhead lines,HCBs are required to have reclosing capability due to the high fault probability and the fact that most of the faults are temporary faults.To avoid the secondary fault strike and equipment damage that may be caused by the reclosing of the HCB when the permanent fault occurs,an adaptive reclosing scheme based on traveling wave injection is proposed in this paper.The scheme injects traveling wave signal into the fault dc line through the additionally configured auxiliary discharge branch in the HCB,and then uses the reflection characteristic of the traveling wave signal on the dc line to identify temporary and permanent faults,to be able to realize fast reclosing when the temporary fault occurs and reliably avoid reclosing after the permanent fault occurs.The test results in the simulation model of the four-terminal dc grid show that the proposed adaptive reclosing scheme can quickly and reliably identify temporary and permanent faults,greatly shorten the power outage time of temporary faults.In addition,it has the advantages of easiness to implement,high reliability,robustness to high-resistance fault and no dead zone,etc.

基于双向DC-DC变换器的串联电池组主动均衡电路

针对单体电池串联成组使用时出现不一致性的问题,提出了一种基于双向DC-DC变换器的串联电池组主动均衡电路。使用双向DC-DC变换器将单体电池中的高能量输送到能量低的单体电池中,无需额外的存储组件来存储和传送能量,减少了能量损失,提高了均衡效率。根据电池开路电压(open circuit voltage,OCV)与荷电状态(state of charge,SOC)之间近似分段线性的关系,采用以电压和SOC双变量作为均衡策略,通过相互实时修正电压均衡和SOC均衡,使得电池组间能量动态趋于一致。最后通过搭建由4节单体电池组成的均衡电路实验平台,对提出的均衡电路和均衡控制策略进行有效性验证。

新能源汽车DC/AC变换电路教学模型设计

DC/AC变换电路作为新能源汽车上的核心电路之一,在实车上,由于集成度高、高电压等特性,非常不利于初学者进行学习。本文中设计的DC/AC变换电路教学模型,学生不仅能直观认识其主电路和控制电路的结构,而且还能通过预留的接线端子进行电路再次搭建和测量其关键信号线上的电路参数,进而快速掌握DC/AC变换电路的基本结构和工作原理,为后续实车故障诊断打下较好的基础。

基于电弧磁流体仿真的DC 1500V两极塑壳断路器气道优化设计

该文开发了用于DC 1500V光伏和储能系统的新一代两极直流塑壳断路器样机。通过DC 1500V/15 kA,时间常数10 ms的短路分断实验发现,电弧电压快速升至350 V是提升断路器限流和分断性能的关键。为了加快初始燃弧阶段电弧运动速度使弧压快速上升,建立了断路器触头区域的二维局部电弧磁流体仿真模型,通过分析灭弧室温度、压力分布和气流速度变化曲线,明确了初始样机中电弧运动停滞的机理,并以此为依据提出了参差栅片排布和添加导流锥的气道优化设计方案。使用优化后的样机进行分断实验,比较优化前后的电压变化曲线和电弧运动高速摄像,验证了优化方案的有效性,对于DC 1500V两极直流塑壳的设计开发具有很强的实践指导意义。