"Multi-objective control of power converters, including active lifetime extension"

Switching devices (IGBT, IGCT, etc.) of Three-level Neutral-Point-Clamped Voltage Source Inverters (3L-NPC-VSI) for high-power applications are typically mounted on dedicated heatsinks, which results in a lack of heat sharing among the switches. Several control strategies have been proposed to enable even distrubtion of losses among the switches in normal operation, however a local thermal overload can occur due to adverse operating conditions such as: degradation of cooling system, inappropriate placing of semiconductor device, failures in electronics, etc. The thermal incrases the risk of thermal breakdown of the affected device and reduses consequently the expected lifetime of inverter.

A new fault-tolerant control approach is proposed in the work to deal with this matter. In case of thermal overload, the control method of inverter is immediately adapted, so that the stressed switch is relieved, the heat is distributed to the other devices which are not affected by the overload. Here, redundant states of multi-level inverter are taken advantage of, since redundancies of voltage space vector deliver the same line-to-line output voltage, but having different impact on the loss distribution among the switches of the inverter. Thanks to the active redistribution of losses among the switches, the temperature of the affected device is kept under the critical limit. In this way, the lifetime of the inverter is maximized even in case of thermal overload.

The proposed startegy will be examined with two control methods for the inverter feeding an induction machine: Fields Oriented Control (FOC) and Direct Torque Control (DTC), which are very widespread in the practice. The implementation of each control method requires diffrent considerations and strategies. Finally, the impact of the optimized switching pattern on loss distribution among the switches will be verfied by menas of simulation and measurements on a laboratory set-up. During operation of the proposed control methods, the stability of the neutral-piont potential of the inverter is ensured without any additional hardware.

2015 

"Active thermal protection and lifetime extension in 3L-NPS-Inverter in the low modulation range", Applied Power Electronics Conference and  Exposition (APEC), 2015 IEEE, Charlotte - USA

 "Active Lifetime Extension for a 3L-NPC-Inverter with Direct Torque Control" 2015 Intl Aegean Conference on Electrical Machines & Power  Electronics (ACEMP), 2015 Intl Conference on Optimization of Electrical and Electronic Equipment (OPTIM) & 2015 Intl Symposium on  Advanced Electromechanical Motion Systems (ELECTROMOTION), Side, 2015, pp. 468-475.