Sound power radiated from an inverter-driven induction motor: experimental investigation

The effects of various inverter strategies, switching frequency, random modulation levels and motor speeds on the radiated noise of a 2.2 kW induction motor with and without load were examined by measuring the sound power spectrum, rather than the sound pressure spectrum at a single point in space. Results show that the sound power level due to the aerodynamic and mechanical noise increases at a rate of 12 dB per doubling of the motor speed. For an ideal, almost purely sinusoidal supply, electromagnetic noise dominates at low motor speeds. For a PWM inverter drive, the electromagnetic noise due to the switching harmonics could dominate the total sound power level at low motor speeds; however, the effects of switching harmonics appear to be insignificant at high motor speeds where the noise due to the fundamental frequency is dominant. At high speeds, the variation of sound power level with load is small, whereas at low speeds the total sound power level normally increases due to the low-frequency component.