Power Control in Series-Resonant Bridge Inverters

摘要

Direct phase or indirect frequency control methodsudare used in series-resonant bridge power inverters for inductionudheating to maintain maximum power transfer as the load equivalentudelectrical parameters change during the heating process. Inudthese applications, to control the power level it is common to useudthe above resonance operating frequency, where only measurementudof the deviation of the phase angle from its reference valueudis used to calculate the new bridge switching frequency. Belowudresonance is not used since its control is non-linear, has high leveludof harmonics and is considered unstable, so no detailed analysisudhave been carried out. The paper present mathematical analysisudof the output power, voltage and current phase angle dependenceudon the resonant circuit damping frequency when it is excited withudpulse voltage with a different frequency than the resonant one, inudboth above and below resonance regions. Based on this analysis,udpossibilities of below resonance power control are investigatedudand new insight in circuit behavior is presented based on variationudin resonant tank parameter values.