Thermal balancing of multiphase battery chargers controlled by phase shift

Abstract

Power sources based on multiphase resonant converters, controlled by phase-shift at constant switching frequency, reduce conduction losses and enable current-mode operation for battery charger applications. However, phase-shift modulation in multiphase class D resonant converters inherently causes uneven current distribution among sections, leading to a thermal imbalances in transistors and inductors. To address this, a thermal balancing control strategy is proposed, which equalizes temperatures by modulating the amplitude (AM) of the resonant currents flowing through the transistors and inductors in each Class D section. A simple hysteresis band outer controller set up the average phase shift required to balance the temperature in the resonant branches. This method involves periodically exchanging the control signals of the inverter sections, which does not affect the output variables due to the symmetrical structure of the circuit. Thus, this approach enables thermal management without interfering with the inner output variable control set by the instantaneous phase shift. The proposal is validated experimentally using a four-phase LCpCs resonant converter designed for a Lithium-ion battery charger application.