电网换相换流器和电压源换流器串联组成的混合直流换流器控制和保护研究

基于电网换相换流器和电压源换流器串联的混合直流换流器在克服交流故障时的换相失败和直流故障时的重启动具有优势。分析了该混合直流换流器运行方式、控制策略、电压源换流器保护原理、抵御换相失败原理和直流线路重启过程,认为由该混合直流换流器组成的高压直流输电系统,可克服传统直流和柔性直流输电的主要缺点。当逆变侧的交流系统发生故障时,电压源换流器可提供电压支撑来抑制直流电流增加,缓解电网换相换流器换相失败效应。当直流线路发生故障时,逆变侧电网换相换流器可阻断电压源换流器产生的故障电流,具备直流线路故障重启能力。另外,电压源换流器还为电网换相换流器提供无功功率,从而减少换流站无功设备配置。

Control and protection of series hybrid DC converters with a line-commutated converter and a voltage source converter

A hybrid DC converter with a series Line-Commutated Converter (LCC) and a Voltage Source Converter (VSC) has advantages in avoiding commutation failure and blocking the DC fault. In this paper, the operation mode, control strategies, protection principle of the VSC, effect of commutation failure and process of the DC line restart are presented. The hybrid HVDC system constituted by the hybrid DC converters, which overcomes some drawbacks of the LCC HVDC and the VSC HVDC, has more advantages for fault toleration. For AC system faults in the inverter, the VSC can supply the constant or higher voltage to suppress the increasing direct current and to lower the effect of commutation failure in the LCC. For DC grid faults, the LCC in the inverter can block the large reversing fault direct current caused by the VSC, with DC line fault restart capability. In addition, the VSC can supply a large amount of reactive power for the LCC, thus reducing the converter station reactive equipment configuration. This work is supported by the Youth Science Fund of National Natural Science Foundation of China (No. 51607042).