Optimal Current Balance Control of Three-Level Inverter under Grid Voltage Unbalance: An Adaptive Dynamic Programming Approach

Abstract

When the grid voltage is unbalanced, the positive and negative sequence components in the grid voltage cause grid current to be disordered. Under current balance control, proportional integral (PI) closed-loop control will increase the grid currents instantaneously, which affects the safety and reliability of the inverter operation, and PI parameters are difficult to select without the complete system mathematical model. This paper introduces an adaptive dynamic programming (ADP) approach to solve this problem. The best state feedback controller for the system is obtained by driving the ADP by the value iteration ( V I ) algorithm without the need for an accurate mathematical model. In the simulations, the ADP approach can improve the dynamic performance of the system, the current increase can be suppressed when the grid voltage is unbalanced, and the harmonic rate of output currents is reduced.