The impact of modulation technique on high power density synchronous machine characteristics

Next generation electrical machines used for future transportation such as electric-flying or electric driving, have highly challenging performance requirements in terms of maximizing the power-density to high kW/kg or kW/l, and maximizing the efficiency to ensure that maximum travel distance is achieved per battery charging cycle or minimize fuel consumption. The high power density often translates to higher fundamental frequencies, which makes the choice of switching frequency and modulation strategies critical both in terms of maximizing the efficiency as well as for maintaining acceptable temperature rise for the power density targeted. This paper considers three modulation strategies (PWM, FBQ and Six-step square wave) and evaluates in detail the performance tradeoffs (current THD, torque quality and efficiency) with the aim of selecting the appropriate modulation for a high power density PMSM.