0 导语

随着柔性直流输电技术的逐步发展，采用架空线的柔性直流电网成为目前研究的热点。架空线具有瞬时性故障概率高的特性，因此需要具备重合闸能力的直流断路器（DCCB）进行故障隔离。现有的直流断路器的拓扑中，机械式DCCB不具备重合闸能力，而混合型DCCB由于使用了大量电力电子器件，成本较高且可靠性较低。为了解决这一问题，本文提出了一种具备重合闸能力的机械式直流断路器。

A Mechanical DCCB with Re-Closure Capability and Its Performance in MMC based DC Grid

Binye Ni, Wang Xiang, Meng Zhou, Xiaojun Lu, Wenping Zuo, Wei Yao, Jinyu Wen

期刊名字：International Journal of Electrical Power and Energy Systems（英）

Abstract/Highlight

For the modular multilevel converter (MMC) based DC grids using overhead line transmission, to restore the power transmission quickly, the DC circuit breakers (DCCB) are required to be able to re-close after DC line faults. To meet this requirement, an improved mechanical DCCB topology with re-closure capability is proposed in this paper. It consists of a pre-charged capacitor, an auxiliary capacitor, an oscillation inductor, and anti-parallel thyristors. Firstly, the topology and operating principle of the mechanical DCCB are presented in detail. Then, the general sizing methods associated with the impact of parameters on interruption capability are disclosed. The feasibility of the proposed mechanical DCCB is validated in a stiff DC system. Finally, the transient performance of the DC grid embedding the proposed mechanical DCCBs is investigated under various operating scenarios. The results verify the DC fault interruption and fast automatic re-closure capabilities of the proposed DCCB. It is shown that the mechanical DCCBs can be well applied to the overhead MMC based HVDC grids systems.

1 项目背景

柔性直流输电技术具有控制灵活、无需无功支撑等技术优势，在大规模可再生能源的汇集、输送和并网中都有较好的应用前景。由于我国可再生能源的分布特点，利用架空线构建多端柔性直流电网是未来的必然趋势。一方面，架空线的应用提高了直流电网的故障概率，带来了对DCCB的需求；另一方面，架空线瞬时性故障较多的特性，也要求DCCB具备重合闸能力。现有的直流断路器的拓扑中，机械式DCCB不具备重合闸能力，而混合型DCCB由于使用了大量电力电子器件，成本较高且可靠性较低。

2 论文所解决的问题及意义

针对现有DCCB拓扑的缺陷问题，本文提出了一种具备重合闸能力的机械式直流断路器，介绍并分析了其工作原理与动态特性，并在此基础上给出了DCCB参数的详细设计方法，最后在四端直流电网中仿真验证了其可行性。

3 论文重点内容

1）直流断路器拓扑

所提出的机械式直流断路器拓扑如图1所示。该拓扑的换流支路中包含预充电电容C_S，辅助电容C_A，电感L以及反并联晶闸管T₁、T₂。DCCB能够利用C_A的放电对进行C_S充电，从而获得重合闸能力。

图1 改进机械式DCCB拓扑

2）工作原理

所提出的机械式直流断路器的工作原理如图2所示。图2(a)、(b)解释了DCCB的跳闸过程，DCCB通过电容C_S放电以注入反向电流，使得MS上的电流过零并熄弧，之后电流转移至换流支路，并不断对电容充电直至避雷器导通。图2(c)、(d)解释了DCCB的重合闸过程，DCCB利用被充电至线路电压的C_A的放电过程，将C_S电压充电至预设值，之后C_A上的残余电压通过电阻放电至0，DCCB恢复至跳闸前的初态，从而获得重合闸能力。

图2 DCCB工作原理

3）仿真验证

对所提出的DCCB进行仿真以验证其跳闸与重合闸能力。图5给出了跳闸过程中DCCB内部的电流电压波形。晶闸管收到触发信号后导通，MS上电流I_main被转移至换流支路以熄弧，之后被转移的电流I_com持续对电容充电直至避雷器动作，电流再次被转移至避雷器支路进行耗散，最后当避雷器上的电流耗散完毕时，直流故障被成功清除。

图6给出了重合闸过程中DCCB内部的电流电压波形。机械开关重新合闸后，电容C_A开始放电，使得V_S在200 μs内被充至-320 kA，从而C_S重新获得产生反向注入电流的能力。之后，电感C_A放电，使其电压V_A降低至0。DCCB内的电压恢复至跳闸前的初态，从而具备了再次跳闸的能力。

（a） 电流波形

（b） 电压波形

图3 跳闸过程中的DCCB的电流电压波形

（a） 电流波形

（b） 电压波形

图4 重合闸过程中的DCCB的电流与电压波形

Conclusion（英文去写）

This paper proposes a novel mechanical DCCB with the twice-interruption capability to meet the requirement of overhead DC grid for automatic re-closure. This DCCB takes advantages of the discharging process of capacitor C_A to recharge capacitor C_S and thus achieve the second interruption capability. Taking the requirements of the representative four-terminal DC grid as an example, the parameter design methods of this DCCB are proposed. The DCCBs are designed as -320 kV pre-charged voltage of v_s, C_S of 15.5 μF, C_A of 7.6 μF, and L of 0.8 mH. It can interrupt the fault current of 25 kA within 3 ms. The breaking performance and re-closure capability of the proposed DCCB are verified in a stiff DC model.

A ±500kV four-terminal bipolar DC grid with the improved mechanical DCCB is tested. The simulation results for permanent pole-to-pole faults prove that the proposed DCCB can be well applied in the overhead DC grid. Two other simulations on the system in case of DCCBs malfunction show that the mechanical DCCB can work normally under extreme conditions and the energy absorption of the arrester would not be less than 103.91MJ. To further validate the effectiveness of the proposed DCCB, the experimental verification will be conducted in future work.

引文信息

Binye Ni, Wang Xiang, Meng Zhou, Xiaojun Lu, Wenping Zuo, Wei Yao and Jinyu Wen. “A mechanical DCCB with re-closure capability and its performance in MMC based DC grid.” International Journal of Electrical Power & Energy Systems, 121, 106128.

https://doi.org/10.1016/j.ijepes.2020.106128

作者简介：倪斌业(1995)，男，博士研究生，主要研究方向为直流电网，nibinye@foxmail.com；

期刊简介：International Journal of Electrical Power & Energy Systems (JEPE) 期刊关注在电能产生、传输、分配及利用过程中，电力系统各元件及其并网技术、交互作用和技术改进。期刊范围涵盖电力系统元件的建模、设计、性能分析，及其在各种规模和复杂程度的现代电力和能源系统的特定方面的典型应用。本期刊特别专注于能改变电力系统并确定其性能和运，行的新技术的研究。期刊2018年JCR影响因子为4.418。