Practical performance limitations for PWM strategies

Pulse width modulation is a most important part of power electronic systems, and there has been considerable research effort over the years to determine optimum PWM strategies and operating criteria for various applications. Much of this work has investigated the benefits of alternative theoretical approaches, but there has been somewhat less emphasis on the more practical issues of implementation and output filter design in terms of optimising the system performance. However, these issues become increasingly important as overall distortion levels reduce, and switching frequencies become higher with new devices and controllers. Under some operating conditions, second order effects may be the significant harmonic influence, and must also be considered if the distortion of an inverter is to be fully minimised. This paper presents an investigation into the influence of second order effects on the overall performance of a PWM inverter. The investigation compares the theoretically expected performance of a PWM system with that predicted when second order effects are considered. The performances are investigated over varying modulation depths and output filter cut off frequencies, and the results show the influence of these practical factors in overall inverter design.