State-space modeling, analysis, and implementation of paralleled inverters for microgrid applications

The state-space model and implementation results of a power conditioning system are presented in this paper. Eigenvalues with different controller gains and load conditions for grid-tie mode and standalone mode are utilized to analyze the system stability. For standalone mode, higher controller gain and higher load resistance tend to make system more unstable. In grid-tie mode, higher controller gain is also found to make the system more unstable but load variation will not change the system stability much. Experimental and simulation results also verify the model. The state-space model is extended to a parallel-inverter system for investigation of the load variation and current-sharing controller effects to the system stability. A time-domain current ripple criterion is also suggested for light-load operation of the parallel-inverter microgrid system.