Preventing Premature Failure of Frequency Converters Used in Cyclic Operation

Thermal cycling can lead to the failure of the frequency converter, therefore it is a serious issue. The failure is caused by bond wire lift-off or solder joint failure which occurs in the IGBT module due to the difference of coefficients of thermal expansion. Especially, frequency converters that are used in cranes and operate constantly with high currents are at risk. The goal of this thesis is to develop different methods to increase the lifetime of frequency converters used constantly in high currents. Therefore, the IGBT module structure and failure mechanisms were studied, the thermal model of the IGBT module was built, and the thermal model was used to develop different methods to reduce thermal cycling. Total of six methods were developed: magnetization current decrease, switching frequency decrease, zero-speed operation removal, heat sink temperature control, heat sink size increase, and IGBT chip size increase. From these methods magnetization current decrease showed the most promising results, since the largest temperature changes occurred during magnetization. The IGBT chip size increase had moderate results while remaining methods were ineffective and should not be implemented. Implementation of magnetization current decrease lowered the temperature changes up to 62 % during magnetization, which increased the lifetime of the module by 2900 %. Therefore, the thermal behavior of the IGBT module can be used to estimate the lifetime of the frequency converter