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).

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%.

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.

基于单边调制映射函数的LCC-HVDC直流侧阻抗精确建模

阻抗模型是电网换相换流器型高压直流输电系统小信号稳定性分析的重要基础,阻抗模型的准确程度直接影响系统小扰动稳定性分析。该文首先从同步触发原理出发,引入基于单边调制产生的映射函数,该函数蕴含控制及换相信息,可以准确建立换相/非换相期间交直流侧的映射关系;其次,考虑换相动态并通过谐波线性化和傅里叶变换建立完整的直流侧电压和交流侧电流的频域小信号动态模型;再次,考虑控制和换流阀阻尼回路,建立整流侧和逆变侧直流阻抗解析模型;最后,以CIGRE高压直流标准测试模型为例,基于PSCAD/EMTDC平台验证了直流侧阻抗模型的准确性及其用于小扰动稳定性分析的有效性。

集成有源开关电感和Y源倍压单元的高增益DC-DC变换器

针对光伏发电系统中光伏组件电压等级的提升,提出一种集成有源开关电感和Y源倍压单元的高增益DC-DC变换器。所提变换器能够实现低开关管电压应力,具有高自由度电压调节能力,在满足一定升压条件下仍能保证电路的效率,在光伏发电中具有较大的应用潜力。对变换器的工作模态、器件电压电流应力、参数设计和损耗效率进行详细阐述。最后通过实验验证所提拓扑结构的可行性。

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。

一种高频单片GaN DC-DC降压转换器设计

基于全耗尽型(D-mode)0.25μm硅基氮化镓(GaN-on-Si)工艺,设计了一款高频单片GaN DC-DC降压转换器芯片。该芯片集成了驱动电路和半桥功率级电路,驱动电路中电平放大功能通过有源上拉结构实现,在100~200 MHz频率范围内,单片GaN DC-DC降压转换器可直接被0.7 V的高速脉冲信号控制,无需片外模块,其峰值功率级效率达到92.2%,峰值总效率达到84.24%,峰值功率为7.7 W。相较于前期工作,芯片工作范围从100 MHz提升至200 MHz,在保证芯片效率性能的情况下,实现了对工作频率的大幅提升。

基于三绕组耦合电感的准Z源高增益DC-DC变换器

针对清洁能源并网发电系统中直流升压变换器的现有技术缺陷,提出一种新型的准Z源高升压DC-DC变换器。该变换器通过将准Z源网络与独特的耦合电感集成结构结合,能在较低的占空比和匝比下实现高电压增益。拓扑中的钳位回路回收了储存在耦合电感漏感中的能量,能有效缓解耦合电感漏感引起的尖峰电压。此外,变换器功率器件电压应力水平较低,便于使用低耐压器件来提高转换效率。输入电流连续以及输入输出共地的特点使得该变换器适合应用于可再生能源场景。详细介绍了所提变换器的工作原理,给出了关键性的公式推导和设计依据,并进行性能比较。最后,设计并搭建一台200 W额定功率的样机进行实验验证,实验结果与理论分析相吻合。

基于单神经元PID的高增益DC-DC变换器

为使光伏系统和燃料电池的输出电压适应于并网发电系统所需的电压等级,提出一种基于单神经元PID的高增益DC-DC变换器。基于耦合电感的升压单元,使变换器在原有的开关占空比D上,增加一个新的自由度来调节输出电压。钳位单元的引入,削弱了耦合电感漏感与半导体器件的电压尖峰,提升了变换器的效率。通过单神经元PID,增强变换器抗扰动能力。该文先分析所提变换器的工作模态,推出其性能特点,并与经典变换器做出比较。通过仿真模拟电路运行和搭建实验模型研究,验证理论分析的正确性和实验过程的准确性。

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。

高效单片AC/DC电源管理集成电路设计

随着科技快速发展,电子产品的复杂程度不断升级,日益向小型化、智能化、高效能方向迈进。电源管理系统作为电子产品中的重要系统之一,其重要作用逐渐凸显。本研究设计了一种单片AC/DC开关电源集成电路,该电路具有效率高、体积小、可靠性高等优点。因此,本文基于高效的单片AC/DC电源管理集成电路构成,对其进行了优化设计,希望能够为我国电源管理系统设计行业的相关工作提供参考和借鉴。

基于STM32的DC-DC降压变换电路设计与实现

文章提出了一种小型可调DC-DC降压变换器的电路系统。该系统由主控板(MCU)、辅助电源、Buck主电路组成,主控板基于STM32F103RC最小系统板设计,辅助电源为MCU和主电路供电,Buck主电路由MOSFET管、电感及滤波电容构成。利用PWM控制,设计驱动电路控制MOSFET管的通断;利用反馈电阻实现闭环电压控制,控制算法选用PID,通过改变PWM波的占空比来改变输出电压以达到调压的目的。该降压变换器设计简单、经济适用、通用性强、模块移植性强,适用于低压工作场合,其输入电压为24 V(可适当调整),输出电压在0~20 V连续可调。文章在Buck电路理论分析和仿真实现基础之上,设计了印刷电路板并完成实物制作,物理试验结果验证了该设计的正确性和电路的有效性。

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。

抑制DC/DC BOOST电路尖峰电压及振铃噪声的设计与应用

针对开关电源DC/DC BOOST电路易出现电磁辐射偏高甚至超标问题,通过对升压转换电路及其电磁辐射产生机理研究,提出一种DC/DC BOOST电路系统中寄生电容容值的确定方法及基于RC吸收电路的振铃噪声抑制方法,通过对RC吸收电路的元件参数进行计算取值并实测,测试数据显示,电路系统中尖峰电压有效降低2.2%,振铃噪声已无限趋近于0,电磁辐射峰值可有效降低4.2 dB;同时该方法不影响电路系统稳定性且成本低廉,契合大规模产业化设计需求,可有效提高产品开发效率。

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.

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.