Dynamic Capacitive Compensator for Photovoltaic Connection and Its Optimal Control

When photovoltaic power is connected to a weak grid via an inverter, the capacitive compensation is of great significance for enhancing the power transmission capacity of the inverter and the stability of the grid connection. In order to solve the contradiction between the performance and the cost of the traditional capacitive compensation device, a type of dynamic capacitive compensator is proposed. First, according to the fundamental frequency equivalent circuit model of the photovoltaic grid-connected system connected to the static var generator in the dq coordinate system, the influence of capacitive compensation on its power transmission capability is analyzed. Secondly, the topology and working principle of the dynamic capacitive compensator (DCC) circuit are introduced. considering the reactive power consumption of load and line impedance comprehensively, the reactive power command current calculation combining the instantaneous reactive power with the voltage droop adjustment is proposed. Based on this, the thyristor switching capacitor control strategy is given. At the same time, for the LC series resonance problem caused by the special structure of DCC, the active damping optimization control strategy and the feedback parameter design method of the LC branch current feedback are proposed. Finally, simulation and experimental results verify the effectiveness of the DCC topology and the optimized control strategy.