The increasing availability of digital computers now makes the computer-aided design of powerelectronic systems an attractive and cost-effective development tool. The paper describes the detailed development of an extremely versatile PWM computer modelling package which can be used as a ‘stand-alone’ package for harmonic analysis, or alternatively as a ‘building-block’ for developing more complex systems. The capabilities of the package are demonstrated, using a number of examples of single-phase and 3-phase PWM inverters, which serve to highlight a number of important operational characteristics of PWM inverters. The validity and accuracy of the computer simulations are confirmed, using experimental results obtained from a microprocessor-controlled PWM inverter-drive system.