Redundant Module based Control Scheme for Grid-Forming Cascaded H-Bridge PV Converters to Enhance Overcurrent Capability

Medium-voltage Photovoltaic (PV) converter based on the cascaded H-bridge (CHB) topology is an emerging solution for large-scale PV grid-connected power generation systems. In order to better support the operation of the power grid with high penetration of renewable energy and power electronics, to output a large short-circuit current (⩾1.5pu) under the short-circuit fault of the grid so as to provide enough reactive power and effectively trigger the relay protection action becomes one key requirements for the grid-forming PV converters. In our study, a large short-circuit current output control strategy based on redundant module rotation is proposed for CHB grid-forming PV converters. By making use of the parallel bypass switch of the H-bridge and combining with the modulation strategy of module rotation, the maximum junction temperature of all devices are reduced during the short-circuit fault of the power grid. The overcurrent capability of the converter are thus enhanced. And by establishing the system thermal circuit model, the maximum output overcurrent capability of the system after adding the redundant module rotation strategy is investigated. This digest firstly shows the structure and operation principle of the control system. The results of simulations are shown to verify the effectiveness of the strategy.