Soft-Unbalance Operation for Power Routing in Multiphase Drives

The unbalanced operation of multiphase drives has been adopted for the fault-tolerance purpose in mission critical applications. However, the higher number of phases increases the number of devices and the probability of thermal mismatches among them. Indeed, parametric mismatches, thermal cross coupling, inhomogeneous cooling, and uneven degradation have been reported as root causes of critical thermal deviation among power semiconductor devices. Consequently, a higher temperature in a subset of devices provokes degradation unevenness and a lifetime reduction of the whole power converter. In modular systems, for example, power routing has been proposed to better distribute the temperature among the high number of devices and overcome this problem. Although not modular, the capability of a multiphase machine to operate under unbalanced condition allows an uneven power distribution without overloading the phases and degrading the machine magnetic performance. Therefore, this work investigates the soft-unbalance operation for power routing in multiphase drives. To validate the presented solutions, finite-element analysis based in a real multiphase system is conducted. Additionally, experimental results show the multiphase machine performance in soft-unbalanced conditions. Moreover, a case study is carried out to evaluate the impact of the power routing on the lifetime of a high power mission critical application.