In this thesis, a mathematical modeling and practical implementation of a three-phase PWM inverter is presented. The inverter design is based on a modular design approach to increase the capacity of the inverter output power to the desired rating. This is achieved by paralleling a sufficient number of inverter power modules. Each module utilises power MOSFET as the main switching device and a simple switching-aid network to ensure safe and reliable operation. The parallel operation of the inverter modules is considered by paralleling three modules without difficultly. The behavior and performance of inverter power circuit is analysed theoretically by deriving a mathematical model. The validity of proposed model is examined by comparing the predicted inverter performance with that measured experimentally. The PWM modulator which controls the switching of the inverter power circuit is developed by integrating the recent developments of an ultrasonic modulation strategy and a simple hardware implementation based on a microprocessor. Use "of such high modulation frequency avoids the use of ratio changing technique which was previously used to minimise the unwanted harmonics appearing on the output PWM waves. The essential hardware, software and performance considerations of the modulator is presented Finally, the performance of the complete inverter system is assessed with particular reference to a 2.3kVA prototype. It is demonstrated that the inverter considered has efficient and quiet operation over a wide operating frequency range.