Abstract: Large-scale photovoltaic power plants use DC-collective boosting and delivery methods to have certain advantages in terms of transmission efficiency, cost and stability. This paper based on the scheme which the large-scale photovoltaic power station with input parallel output series (IPOS) is DC-boosted and then the modular multi-level single-ended flexible DC grid-connected, which deeply considers the voltage equalization and current sharing in the DC boost structure. To solve the problem, a DC-boost converter dynamic output voltage compensation control is combined with an optimized decoupling dual synchronous reference coordinate system phase-locked loop (DDSRF-PLL) for positive and negative sequence dual current loop control. Through the coordination between the pre-stage and the post-stage, the influence of the over-voltage and negative-sequence components of the DC bus on the grid-connected current is effectively suppressed. In addition, a soft start control strategy is proposed to suppress the system from overcurrent. Finally, the effectiveness of the control strategy is verified by simulation.

Solar power plants,IPOS DC boost,optimized DDSRF-PLL phase-locked loop,soft start,MMC-HVDC.