Overmodulation Strategy for Seven-Phase Induction Motors With Optimum Harmonic Voltage Injection Based on Sequential Optimization Scheme

Overmodulation (OVM) strategy is widely utilized to enhance the dc-link voltage utilization. For five-phase and six-phase drives, various OVM strategies have been developed to reduce the reference voltage vector in one harmonic subspace (HS) and improve the output current total harmonic distortion (THD) performance. However, the performance of generic OVM strategies can be further improved to deal with the optimization problem of multiple HSs. This article presents a universal sequential optimization scheme and takes a seven-phase induction motor as study example. First, the OVM region is predivided by the principle of fully utilizing available degrees of freedom and the concept of virtual voltage vectors. Then, optimizations are carried out according to the voltage distribution in different HSs, and design guidelines are provided for multiphase drives with more than one HS. Without complex computations, the proposed OVM strategy can easily determine the desired voltage vectors and the corresponding duty ratio, which not only achieves overall good THD performance but also favors for more intuitive implementation. Finally, simulation and experimental results implemented on a seven-phase drive platform validate the feasibility of the proposed OVM strategy.