Analysis of the Acoustic Noise Spectrum of Domestic Induction Heating Systems Controlled by Phase-Accumulator Modulators

In domestic induction heating applications, the modulation technique applied to the inverter has a high influence on the acoustic noise emissions. These noise emissions must be avoided, since they may be audible and annoying to the final user. This paper analyzes the acoustic noise emissions that appear when a series half-bridge resonant inverter is operated with a phase-accumulator-based modulator. This modulation technique has the advantage of operating in the frequency domain, and it is compared with the classical pulsewidth modulator regarding the audible noise generated. The frequencies of the tones in the acoustic noise spectrum are theoretically calculated from the parameters of the phase-accumulator-based modulator. The spectral flatness measure is used to quantify the number of cases in which tones are generated by the modulation. Two techniques are applied to the phase-accumulator-based modulator, and their effect is tested. Theoretical results are experimentally verified.