Audible noise reduction for medium power inverters

An audible noise reduction for medium power inverters which involves the application of a specialized inverter PWM (pulse width modulated) technique combined with a preregulation stage offering an improved inverter output voltage spectrum is proposed. Consequently, inverter switching losses are kept low, while the dominant harmonic generated should not contribute to audible noise measured. Thus, inverter stages previously limited by switching losses can process larger power levels. The carrier-based PWM technique presented here has its first harmonic family at 2.5 times the switching frequency. The technique allows base frequency changes identical to that of sine PWM, yet offers a 15% higher voltage gain. Since the technique is most effective at full modulation index, medium power DC-DC converters capable of inverter input regulation are discussed. Selected experimental results are presented to validate the PWM technique, and a high-frequency preregulation stage is proposed for applications requiring galvanic isolation between source and load.<>