A method of high performance output voltage control of four-wire inverter 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 four-wire inverter is developed and the minimum loss discontinuous PWM method is derived. The design and analysis for the four-wire inverter UPS are proposed. Linear and nonlinear loads for balanced and unbalanced load operating conditions are implemented. The scalar control and PWM methods are proposed and implemented in MATLAB simulation.