Vector controlled multiphase induction machine: Harmonic injection using optimized constant gains

Torque enhancement by stator current harmonic injection is one possible use of the additional degrees of freedom offered by multiphase machines yielding a near rectangular air-gap flux. The number of injected harmonics depends on the phase order and the corresponding sequence planes. As the number of machine phases increases, the injected harmonic order can be increased where each plane requires two PI controllers, to control its current components, resulting in a complicated tuning process. Moreover, the deployment of conventional indirect vector control with multiple PI controller fails to maintain a near rectangular air-gap flux with different loading conditions due to synchronization problem between different planes. In this paper, the conventional indirect vector control based on multiple PI-controllers is replaced by only two PI-controllers to develop the fundamental dq voltage components from which the dq voltage components for other planes are determined using offline optimized constant gains. The proposed controller makes the tuning process is easier and achieve near rectangular air-gap flux during loading conditions. The proposed controller tested using a prototype eleven-phase induction machine where injection up to the ninth harmonic can be engaged. A comparison between the conventional controller, using multiple PI controllers, and the proposed controller is made for third harmonic injection. Practical results are introduced as a conformance to simulation results. (C) 2012 Elsevier B.V. All rights reserved.