This thesis describes the implementation of microprocessor controlled single-phase and three-phase inverters for UPS applications. A carrier frequency of 18 kHz is employed in both cases, and the PWM pulses are generated directly by the microprocessor using the regular-sampled symmetric PWM strategy. Single-edge modulation as well as double-edge modulation has been implemented for single-phase and three-phase systems. Since in general, software implementation of PWM strategies require precalculated pulse width values, a scheme is proposed which enables the large quantity of such data to be handled efficiently. The scheme involves the use of a small program for calculating and transferring the data to the memory of the controller.