Overmodulation strategies of inverter-fed ac drives

The three optimized and two carrier-based PWM strategies of the overmodulation region of inverter-fed ac drives are suggested and investigated from the point of view of motor harmonic losses, torque ripples and voltage gain of the control system. The 1(st) optimized solution produces the lowest value of motor harmonic losses if the skin effect in the rotor bar is not significant while the 2(nd) one gives the lowest value of these losses for the strong skin effect. It is shown that the harmonic losses of the optimized and the commonly used carrier based three-phase and two-phase overmodulation strategies ensure acceptable values of harmonic losses even if the skin effect is taken into account but only tip to 96% of the maximal possible voltage region, In this case for the presently used switching frequencies the motor harmonic losses will rarely exceed the maximal losses of the normal voltage region. The near constant voltage gain can be ensured for the overmodulation region too. The torque ripples of different overmodulation strategies have about the same values.