Resonant and a new disturbance-observer combined control for off-grid voltage source inverter

A new control strategy that combines the resonant controller and the repetitive-controller based on the disturbance-observer (RSCDO) for offgrid four-leg voltage source inverter (VSI) has been presented in this paper. The aim of the new controller is to regulate the inverter output voltage, reducing as much as possible the voltage total harmonic distortion (THDv) in every load condition. The resonant controller allows to adjust the voltage at the fundamental harmonic, while the repetitive observer is able to compensate the voltage distortions due to inverter nonlinearity. The proposed strategy has been at first validated by means of simulation results performed in MATLAB/Simulink environment. Then, the new control strategy has been implemented in field-programmable gate array (FPGA) using LabView environmental and experimental results are performed on the 40 kVA three-phase 4-leg VSI prototype