Improved Finite Set Model Predictive Current Control of Grid Side Converter in Weak Grid Using Kalman Filter

Abstract

When GSC is connected to weak grid, the small signal instability can happen due to incompatible terminal characteristic of GSC and the grid impedance. Since higher disturbance rejection capability of GSC benefits the resolving of such stability problem, finite set model predictive control (FS-MPC) is applied. However, in weak grid, conventional FS-MPC shows poor performance as the total harmonic distortion (THD) of GSC output current is too high. To solve the problem, Kalman filter (KF) is used. The filtered signals are fed into the predictive controller instead of the directly measured current and voltage, which significantly reduce the harmonic distortion of GSC output current in the middle frequency range around 300~600Hz. Besides, in order to reduce the THD of output current, a three-level neutral point clamped (3L-NPC) grid side converter (GSC) is used. A simple sequential finite set prediction is applied to reduce the computational burden. The performance of proposed strategy is verified by simulation. Moreover, the impedance characteristic of the proposed MPC controller is presented, which is obtained by the perturbation test. From impedance viewpoint, the stability performance of proposed method in weak grid is analyzed, which is found promising.