Construction of nonlinear droop relations to optimize islanded microgrids operation

In this digest nonlinear droop relations are suggested to optimize the operation of islanded microgrids. By using nonlinear droop, many microgrid operation aspects can be optimized in addition to the inherent advantages of the droop control. In the proposed method, the droop relations are allowed to have any nonlinear shape as along as that shape satisfies certain characteristics required for the stability and proper operations of the microgrid. One case is studied in detail in the paper to explain the procedure of constructing the nonlinear droops that minimize the operation cost and share the reactive power effectively among the sources. The selected droop structure is a mixture of polynomials and fractional-exponents polynomials whose parameters are selected using two-stage particle swarm optimization algorithm. Through simulation, the proposed method is explained and its effectiveness is verified.