Efficiency-based optimization of steady-state operating points for parallel source converters in stand-alone power system

The operation efficiency is always considered to be a significant issue for power electronics system, such as parallel source converters in stand-alone power system. Quite a few solutions have been developed to increase power conversion efficiency of a single converter. However, existing work concerning efficiency issue on system level is scarce. On the basis of hierarchical multilevel control theory, this paper proposed a coordinative control strategy on tertiary level to optimize steady-state operating points for each source converter in the system, reducing losses and improving the overall efficiency. Based on the quadratic loss model, the optimal power distribution ratio between two converters is firstly analyzed. By introducing the concept of equivalent converter loss model, a forward-backward sweep calculation method is generalized to N-parallel-converter system. Furthermore, the successive switching points of N converters are precisely designed to maintain minimum system losses under full load range. According to datasheets of typical industrial products, calculation examples are presented to demonstrate the validity of this proposed strategy. The maximum and average efficiency improvement is 1.55 and 0.56 in percentage respectively. Considering the rising development of renewable energy generation and microgrids, this efficiency increase will contribute considerable energy and economic savings in the long run.