Disturbance observer based fully digital controlled PWM inverter for CVCF operation

A new approach for digital feedback control of a PWM inverter is proposed, in which an output DB (deadbeat) control is achieved combined with a disturbance observer. In the proposed scheme, the pole placements of the state observer and the disturbance observer are chosen separately. When the two observers employed the same pole placements, the experimental setup had a tendency to become unstable due to the detection error. By selection of the different pole placements, the disturbance observer quickly estimates the disturbance and feedforward disturbance cancellation is achieved. Then the state observer estimates the state variables at the next sampling instant, and the deadbeat controller is applied to the nominal system. This scheme has advantages in robustness in the practical application. From the view point of UPS applications, the advantages and disadvantages are discussed through simulations and experiments. Compared with other digital control laws, the superiority of the proposed control law is verified