A method for high performance output voltage control of a four-leg inverter (FLI) based three-phase UPS is proposed. Stationary frame resonant filter bank based output voltage control loop, which is complemented by capacitor current feedback based active damping loop, is employed. Utilizing the zero-state partitioning variable, a generalized form of scalar PWM for the FLI is developed and the minimum loss discontinuous PWM method is derived. The controller and modulator design and implementation details for the FLI-UPS are given. Linear and nonlinear loads for balanced and unbalanced load operating conditions are considered. The scalar control and PWM methods are proven by means of theory, simulations, and experiments.