Control of Junction Temperature and Its Rate of Change at Thermal Boundaries via Precise Loss Manipulation

To optimize the lifetime of switching power semiconductors, this paper presents a methodology to control power device junction temperature T-j and its change during power cycles Delta T-j at thermal boundaries. This paper proposes a supervisory state machine to interrupt nominal system-level control only when temperature bounds are exceeded, and coordinates smooth transitions as T-j (k) and Delta T-j (k) approach their respective boundaries. To ensure that thermal states are regulated via precise and independent modulation of conduction and switching loss elements, decoupling methods are proposed. Also proposed is a Delta T-j control law that closes a control loop on the rate of change state T-j, and introduces active thermal capacitance and conductance into the closed-loop thermal system dynamics. Experimental evaluation of the proposed system illustrates well damped T-j (k) and Delta Tj (k) responses, and gradual adjustment of the manipulated inputs switching frequency and duty ratio. Finally, comparison with a current limit-based T-j regulation method illustrates how the proposed system allows power converters to push harder against their thermal limits.