Dynamic Overmodulation Methods for Dual Three-Phase Permanent Magnet Synchronous Machines

Abstract

For dual three-phase permanent magnet synchronous machines (DPMSMs), this article presents three dynamic overmodulation methods for selecting optimal duty cycles with maximum dc-link utilization. Concretely, the voltage references computed by the current controller exceed the modulating constraints when suffering a large reference or sudden load change, resulting in a reduced performance under transient. To address this issue, this article uses geometric projection to synthesize the voltage reference by selecting one or two active vectors, which are produced by two separate three-phase frames. Moreover, as vector space decomposition (VSD) models dual three-phase machines into 2-D orthogonal $\alpha \beta $ and xy subspaces, the other two proposed methods solve the optimal duty cycles by a quadratic program (QP) solver for the four active voltage vectors. The difference between these two methods lies in the different selection of active voltage vectors in $\alpha \beta $ and xy frames. Specifically, these two strategies based on the QP solver allow the cost function formulated as a single linear and bound constraint QP, which is calculated by an active set method. Finally, the experimental investigations for a DPMSM are presented to prove the viability and flexibility of the proposed overmodulation methodologies.