Control strategy for inverters in microgrid based on repetitive and state feedback control

Abstract

As for an ac microgrid, it’s important to supply the loads with a sinusoidal voltage. However, due to the majority of the loads being naturally nonlinear, when the microgrid is operating in the island mode, the output voltage of the inverters is always deformed. To improve the total harmonic distortion (THD) of the output voltage, a control strategy based on repetitive and state feedback control is proposed in this paper. Firstly, the state feedback control is used to implement the pole assignment of the controlled object, i.e., the LC filter. By this way, the resonance of the filter can be well suppressed. And the open-loop gain of the system is also increased in the low frequency band, which can improve the system dynamics. Combined with this, the repetitive control is adopted to ensure good steady-state control performance. Based on the sensitivity function and the regeneration spectrum theory, a parameter design method is proposed to simplify the design of a repetitive controller. Both simulations and experiments are provided to demonstrate the good control performance of the proposed strategy when supplying nonlinear loads in comparison to the PI controller. Moreover, the microgrid simulation results of two inverters have been presented to validate the effectiveness of the designed control strategy.