A Novel Control Method for D-STATCOM under Unbalanced Conditions

A novel control method for D-STATCOM under unbalanced condition is proposed in this paper. In the proposed method, the load and the compensator are taken as a whole comprehensive load, and the control object is that the line side only provides positive sequence active currents. The control scheme proposed is made up of DC voltage controller and current controller. The former mainly maintains the voltage of DC-capacitor at a desire value. The latter based on source currents detection, which has a close-loop structure, is presented in 'dq' reference frame. In the current controller, the reference of d-axis is provided by DC voltage controller and the reference current of q-axis is zero. So the control method proposed omits complicated load reactive current extraction which generates reference value for currents tracking controller in traditional control method based on load currents detection. It simplifies the control scheme. Compared to double 'dq' decoupled control method usually used for D-STATCOM under unbalanced conditions, the control scheme has a simpler structure, less calculation and is more convenient to realize. Simulation results show that D-STATCOM applying proposed control method can achieve good performance under unbalanced conditions.