Synchronous-Frame Modeling and dq Current Control of an Unbalanced Nine-Phase Induction Motor Due to Open Phases

Multiphase machines have several benefits compared with three-phase machines. Their inherently higher reliability makes them attractive in several applications. For instance, the nine-phase motor can operate with up to six open phases in its stator but with torque ripple production. However, the modeling and control schemes for a balanced motor cannot be used since now the stator is unbalanced. In order to allow the multiphase machine to work magnetically balanced even in open-phase conditions, an adequate
dq
current control should be employed. To achieve this control scheme, it is necessary to have a synchronous-frame modeling of a nine-phase induction motor under open-phase faults, which is developed here. Using it, a synchronous-frame control is derived, still using proportional controllers in the
dq
current loops. This is possible due to the use of an appropriate voltage decoupling considering the fault condition. Hence, the unbalanced multiphase induction motor can be controlled very similarly as a balanced one, additionally resulting in the torque ripple minimization. Experimental results characterize the operation with open phases. Simulation and finite-element results show the success of the proposed control scheme.