Overmodulation region of multi-phase inverters

Overmodulation region control of multi-phase inverters is investigated from point of view of AC motor harmonic losses. It is shown that in full overmodulation region neither PWM inverter control nor the optimization of switching angles of inverter can ensure the decrease of motor harmonic losses to acceptable values. In the first half of overmodulation region these losses permanently increase leading to considerable values. Therefore the motor voltage region above 85-87% of the inverter maximal possible value is virtually restricted at least for steady state operation. The theoretical results are checked by simulation.