A multiple-reference complex-based controller is proposed for three-phase power converters feeding nonlinear and unbalanced loads. The control scheme incorporates a stable multiple-complex coefficient filter with bandwidths that are set arbitrarily and independently for every harmonic under consideration. The multiple-reference complex-based control scheme is applied to an uninterruptible power supply system with a voltage source converter. Each harmonic is controlled using a standard complex proportional-resonant controller that is designed for stability and robustness using the Nyquist criterion. Similar stability and robustness properties follow for the overall system due to the frequency-domain properties of the filter and of the controllers. The proposed methodology is validated in simulation and experimental tests.