Decoupled direct power control based on improved sector selection algorithm for three-level grid-connected inverter

Direct power control (DPC) is one of the most popular control strategies for grid-connected inverters due to its outstanding dynamic performance. However, the control coupling between active power and reactive power seriously depresses the steady-state performance of the conventional three-level DPC. By modifying the switching table of three-level DPC, the effect of power control coupling can be restrained, and the steady-state performance can be improved to some extent. But at the same time, the modified switching table will distinctly increase the switching frequency of the inverter because of the enlarged optional vector range, which is unacceptable to high power applications. In this paper, based on the analysis of power control coupling, a decoupled three-level DPC based on improved sector selection algorithm is proposed in order to eliminate the control coupling without increasing the switching frequency. The proposed strategy still adopts the conventional three-level switching table. Therefore, extra switching actions and high switching frequency are avoided. Experimental results verify the superiority of the proposed strategy. Compared with the conventional three-level DPC and the three-level DPC based on modified switching table, the proposed strategy achieves better steady-state performance.