Study on dual-loop control for inverters based on state observer with repetitive compensation

In order to obtain good performance for inverters and to solve the problem of time delay in digital control, a novel dual-loop control based on state observer with repetitive compensation is proposed. Dual-loop control for PWM inverter can achieve fast dynamic response and inhibit nonlinear load disturbances while observer can solve the problem of duty-cycle regulation caused by sampling and computing delay, and repetitive compensation to state observer could reduce the predictive error induced by model deviation. First in this paper the mathematical model of PWM inverter is established based on the state-space theory, using state-average method. Then a digital dual-loop control (inner loop is inductor current and outer loop is output voltage) with output current feed-forward is adopted. In order to get predictive value of feedback variables, observer is introduced and designed. Meanwhile, repetitive compensation is accordingly added to state observer to increase prediction accuracy. Finally the control method mentioned above is validated by experiment on a 50Hz single-phase PWM inverter. Results show that this method could obtain nice dynamic and static characteristics under various loads.