Design of PI controllers for a grid-connected VSC based on optimal disturbance rejection

Voltage source converter (VSC) plays a major role in the AC/DC interconnection. Its control stands as a significant issue as it determines the stability and performance of the system. Therefore, utilization of a control algorithm that can robustly reject disturbances is highly appreciated. This paper proposes a new approach for PI-parameters selection, used in the decoupled dq-vector control scheme, based on first-order-plus-time-delay (FOPTD) models, for which analytical formulas for optimal controller design/tuning can be obtained. Furthermore, a non-linear optimization algorithm is developed in order to achieve the optimum disturbance rejection in terms of minimizing the integral time absolute of the error (ITAE) performance index. The cost function employs a weighted-sum criterion for two sources of disturbances, namely AC input voltage fluctuation and load disturbances, which may affect the regulated voltage. Simulation results demonstrate a very similar system performance using the FOPTD tuning parameters compared to the optimum ones where both yield a robust system against disturbances. The obtained results are also verified experimentally.