Development of digital constant frequency shift-phase power regulation series resonant inverter source

When two or more inductive heating coils are near and their sources are operating with different switching frequency, low-frequency noise occurs. In order to avoid such noises, this paper presents the constant frequency shift-phase power regulation for series resonant inverters. Leading leg switches always work at ZVS. Lagging leg switches work at ZCS when shift phase angle is bigger than load impedance angle, otherwise lagging leg switches work at ZVS. This paper analyses switch modes in detail, and presents choice principles of capacitance which paralleled with leading leg switches and corresponding experiment waveforms. Long-term practical engineering operation results show that this new power modulation can eliminate audible noises, decrease switch loss, and improve reliability, which has enormous engineering application value.