A Medium Voltage Photovoltaic DC Transmission System Based on Current Source Actively Commutated Converter

In order to improve power efficiency of medium voltage photovoltaic dc transmission system, a novel topology based on current source actively commutated converter (ACC) is proposed. It mainly consists of ACC on the medium/low voltage side and uncontrolled rectifier bridge unit. The most significant feature of the topology is that the operating frequency of ACC on the medium voltage side is consistent with the grid frequency. Thus, it significantly reduces switching losses of power semiconductor devices. Moreover, it changes the photovoltaic port voltage by adjusting the output current duty cycle of ACC on the low voltage side, thereby achieving maximum power point tracking (MPPT) control. The matched control strategy is also proposed in this paper. Simulations on a 6MW 20 kV ac/35 kV dc photovoltaic dc transmission system verifies feasibility of the topology and control strategy.