Harmonic content in VSI operated with homogeneous pulse width

Operation of inverters requires a subsystem to generate the gating signals for the semiconductor switches. In the case of simple modulating schemes such as PWM the gating signals can be obtained from inexpensive analog or digital electronic hardwired logic. In other situations a DSP or other kind of device with high computing power is needed. Then it is usual to have a control program that requires an homogeneous sampling period. In such cases, the actuation signal is kept constant for the whole duration of the sampling period. This is is in sharp contrast with methods that modulate via pulse width. In this paper a geometrical analysis is made over the set of waveforms that can be generated this way. The interest is in the harmonic content of the resulting voltage. The study identifies the key factors regarding harmonic content and provides bounds on the minimum harmonic content achievable by any homogeneous pulse width technique. Other related issues such as commutation losses are also considered.