Evaluation of Thermal Performance of Three-Phase Systems With Zero Sequence Injection

Abstract

Zero-sequence injection (ZSI) techniques are widely adopted in Wye- and Delta-connected cascaded H-bridge (CHB) three-phase systems to cope with the unbalanced power generation from each phase. Recent studies have shown that a ZSI can allow a $\triangle-$connected CHB converter to cope with a large range of power imbalances among phases when compared to a standard Y-connected CHB converter. The superiority in the electrical performance under unbalanced input power has been well investigated, however the comparative thermal performance for both configurations under same power imbalance condition has not been investigated. In this work, the thermal performance of a CHB converter connected in both $\triangle-$configuration and Yconfiguration operating under an unbalanced power condition is studied. For this, the enquired ZSI for both $\triangle-$ and Y-connected CHB converters is firstly analyzed. Then, the impact of ZSI on the thermal performance and lifetime expectancy of the power switches in each phase is evaluated and compared for both configurations. The thermal analysis carried out in this work shows that even though a $\triangle-$connected CHB converter offer a wider power imbalance operation than Y-connected counterpart from the electrical viewpoint, this is achieved by thermally stressing the power switches in each phase in an uneven manner, and in some case overstressing them. Consequently, there is a trade-off between electrical performance and thermal stress when dealing with power imbalances in $\triangle$-connected and Y-connected CHB converters.