Adaptive voltage reference regulation for grid-connected MMCs based on P–V characteristics

Abstract When the modular multilevel converter is connected to the grid, the voltage reference command issued by the dispatching system to the MMC is updated at 15-min intervals, but the rapid fluctuation of the DC side power can be close to a few seconds. This kind of phenomenon leads to the mismatch of time scale between the update of the voltage reference command and the change of the actual operating state. It is difficult to track the change of the operating point in time, which is easy to cause the voltage offset of the grid-connected point. The scheduling level automatic voltage control and local reactive power regulation are designed for minute-level global optimization and reactive power disturbance scenarios, respectively. The design objectives do not directly cover the voltage offset caused by the rapid change of active power in the scheduling gap. In view of this scenario, this paper proposes a voltage reference adaptive adjustment method based on power-voltage characteristics. This method constructs a unified equivalent P–V curve through multi-condition power flow calculation and quadratic fitting, establishes a mapping relationship between DC-side power and voltage reference, and designs a piecewise correction mechanism with disturbance threshold and voltage limiting, so as to realize adaptive correction of voltage reference without changing the original control structure. The simulation results show that the proposed method can effectively suppress the grid-connected point voltage offset caused by the power disturbance in the scheduling gap, significantly improve the dynamic response performance, and maintain the stable current and circulating current response, which can provide an effective technical solution for PCC voltage deviation suppression of grid-connected MMC.