Methodology for Active Thermal Cycle Reduction of Power Electronic Modules

This paper proposes a methodology for active thermal control of power electronic modules in ac applications, which includes a loss manipulation unit, a thermal observer structure, and an active thermal cycle reduction algorithm. It aims to reduce the thermo-mechanical strain in the inter-connects of the module in order to enhance its reliability and lifetime. The loss manipulation unit operates in a minimally invasive manner by manipulating adaptive gate resistances and the pulsewidth modulation frequency. This allows the individual thermal control of multiple devices within a power module, which has not been achieved in prior work. A thermal observer structure that estimates averaged junction temperatures by combination of a thermal model and sensor information is introduced. The observer technology makes this paper the first to realize closed-loop control of averaged temperatures achieving an increased robustness and insensitivity to modeling errors. A key element of the active thermal cycle reduction algorithm is the virtual heat sink that derives feasible and stress relieving thermal trajectories. The trajectories are applied with a unique thermal feedback control that smoothly manipulates the averaged junction temperature of the power module even in the presence of loss manipulation limits. The active thermal control methodology is evaluated experimentally with a state-of-the-art insulated-gate bipolar transistor (IGBT) power module.