Failure of the commutation process is a serious malfunction in line-commutated high-voltage direct current (HVdc) converters, which mainly occurs due to inverter ac faults and may lead to outage of the HVdc system. In this paper, an improved strategy is developed that functions based on the SIEMENS HVdc control system under normal conditions and switches to a designed commutation failure inhibition module (CFIM) during an inverter ac fault. From the response speed point of view, since the designed CFIM does not require any proportional-integral controller, the inverter control system has a quick performance in prevention of the commutation failure. This is achieved by direct measurement of the overlap area using the waveforms of the valves anode-cathode and commuting voltages. In addition, from the accuracy aspect, the proposed method has a superior performance in comparison with the existing strategies. It is because of the fact that by direct measurement of the overlap area, variations of both direct current and the commutation inductance are considered, and hence, the unnecessary increase of the inverter reactive power consumption during the fault and the repetitive commutation failures are prevented. The practical performance and feasibility of the proposed strategy is validated through the laboratory testing, using the real-time Opal-RT hardware prototyping platform. The experimental results demonstrate that the proposed strategy can effectively inhibit the commutation failure or repetitive commutation failures under different fault types by considering the lowest possible reactive power consumption.

中文翻译：

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抑制线换相转换器换相失败的增强策略


换相过程故障是线路换相高压直流(HVdc)变流器中的一种严重故障，主要是由于逆变器交流故障而发生，并可能导致HVdc系统停电。本文提出了一种改进策略，该策略在正常情况下基于西门子高压直流控制系统运行，并在逆变器交流故障期间切换到设计的换相故障抑制模块（CFIM）。从响应速度来看，由于所设计的CFIM不需要任何比例积分控制器，因此逆变器控制系统具有快速的防止换相失败的性能。这是通过使用阀阳极-阴极和换向电压的波形直接测量重叠面积来实现的。此外，从准确性方面来看，所提出的方法与现有策略相比具有优越的性能。因为通过直接测量重叠面积，同时考虑了直流电流和换相电感的变化，从而避免了故障期间逆变器无功功率不必要的增加以及重复换相失败。使用实时 Opal-RT 硬件原型平台进行实验室测试，验证了所提出策略的实际性能和可行性。实验结果表明，该策略在考虑尽可能低的无功功率的情况下，能够有效抑制不同故障类型下的换相失败或重复换相失败。