For a PWM inverter system, the output ac current is expected to be a sinusoidal waveform after filtering; however, PWM inverters have two drawbacks causing distortion of output waveform. One is the presence of harmonics, and the other is the variations of the system parameters. In this paper, a robust Doubly Coprime Factorization Disturbance Observer (robust DCFDOB) is applied to a dc-to-ac inverter. The proposed robust DCFDOB involves the H∞-loop shaping method to guarantee the robust stability and robust performance. Experiment results are given to illustrate the effectiveness of the robust DCFDOB.