An electric drive system, method and apparatus includes a rechargeable energy storage unit, a power inverter, and a rotary electric machine. Transfer of electrical power between the rechargeable energy storage unit and the rotary electric machine is governed by a pulse width modulation (PWM) switching frequency, which is one of a non-six-step switching mode or a six-step switching mode. Executable instructions determine a rotational speed, a torque command, a torque direction, a bus voltage, and a hysteresis band, determine a modulation index command in response to the rotational speed, the torque command, the torque direction, and the bus voltage, and command operation of the rotary electric machine in one of the non-six-step switching mode or the six-step switching mode employing the modulation index command.