Seamless transition scheme between grid-tied and stand-alone modes of distributed generation inverters

In this paper, an enhanced control strategy of the smooth transition between the grid-tied and stand-alone operation modes of the distributed generation (DG) inverter is proposed. In the grid-connected mode, the DG inverter controls active and reactive powers flowing into the grid by regulating grid currents using typical proportional integral plus resonant (PI+R) controllers, while direct voltage controllers utilizing a feedback linearization (FBLN) technique are applied to control the load voltages in the stand-alone mode. Applying the FBLN control gives a better performance than those of using the linear control methods for the DG inverter, which possesses a nonlinear relation between the inverter terminal and load voltages. Furthermore, initiating the value of integral terms in the PI+R regulators and FBLN as null at the instances of the operation mode changes results in a smooth transition between the current and voltage controllers for the grid-tied and stand-alone modes, respectively. The PSIM simulation results are shown to verify the feasibility of the proposed control strategy.