Improved control strategy for stand-alone distributed generation system under unbalanced and non-linear loads

This study presents an improved control strategy for a distributed generation system under stand-alone mode. Since there is no grid supply in a stand-alone system, the output voltage has to be controlled in the constant amplitude and frequency by the load-side inverter under the unbalanced and non-linear loads. The mathematic model of the load-side inverter is described. The dual-loop control method based on the stationary αβ reference coordinate is used for the load-side inverter so that the coordinate transformation is not needed. The outer-loop voltage controller consists of a proportional controller and a resonant regulator tuned at low-order harmonic frequency to compensate for the low-order harmonic components of the output voltage. A predictive current control scheme based on space vector modulation is adopted in the inner-loop current controller to improve the transient performance under the sudden load disturbances. Finally, experiment studies are carried out on a 5 kW stand-alone generation system. The experiment results show the excellent output voltage performance under both the steady-state and dynamic process with the load-adaptive ability.