Using Optimal Controller to Parallel Three-phase 4-leg Inverters with Unbalance Loads

摘要

In this paper; control and parallel operation of multi-modular 3-phase inverters are investigated. Active current sharing approach is selected as the fundamental control technique for parallel operation of inverters due to its high reliability. Among different methods for active current sharing; average load sharing is employed due to its acceptable stability. For this purpose; optimal control strategy and Linear Quadratic Regulator (LQR) method is proposed to parallel 3-phase 4-leg inverters. The system is modeled to be compatible and solvable with LQR equations. Using dq technique; 3-phase inverters are paralleled and controlled. The proposed method obtains both current sharing and voltage tracking and addresses supplying of balanced and unbalanced linear loads in spite of sudden changes. Other advantages of the suggested method include the smallest input energy; simplicity in control circuit; low output voltage Total Harmonic Distortion (THD); low circulating current; robustness to the change in the number of inverters and the possibility of parallel different inverters with different capacities. The results of the simulation verify the performance of the proposed method.