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Tutorial Title: Active Thermal Control for More Reliable Power Electronics

Presenters: Giampaolo Buticchi (China), Abraham Marquez (Spain), Jose I. Leon (Spain), Marco Liserre (Germany)

Power semiconductor modules are built of different layers of copper and substrate to ensure electrical insulation on one hand and a good thermal conductivity on the other hand. For the electric connection between chips and terminals, aluminum bond wires are typically used, although copper has been recently introduced.

Variations of the ambient temperature and power variations create cyclic heating and cooling processes, also called thermal cycles. The thermal cycle magnitude is the most critical parameter for the scale of the aging.

Failures in power electronics impact safety in operation and cause downtimes, giving extra cost for the operators of the system. In order to increase lifetime and improve reliability of power electronic modules, improvements in the connection technology and assembly of the modules have been done. Active thermal control is a new concept recently introduced to regulate power losses and control the thermal stress, it has started from industry as an optimized thermal management for a better utilization of the semiconductor. The general principle is to vary temperature related control variables of the system to influence its junction temperature in order to prevent damages caused by thermal cycling.

Since the thermal behavior is changed via the control, there are as many possibilities as the control layers and variables. The lowest level is the gate driver, that can be used directly to influence the losses of the power devices. Also modified modulation patterns can be employed to this aim.

At the converter control level, the reference signal generation system can be affected and in this case active de-rating can be performed. Modification of the control variables (DC link, switching frequency) can be realized without altering the normal converter operation. At the highest level there is system control, where the presence of multiple power converters can be exploited to alter the losses distribution or to create additional losses without affecting the main converter’s goal.

The technique of controlling the power processed by different converters in a modular structure is called Power Routing, and allows for the fine control of the thermal stress of the system. Cascaded H-Bridge converters and multiple parallel converters will be analyzed via this technique.

This tutorial is open to postgraduate students and to professional engineers who whish to implement this kind of advanced thermal management system.