Current Gradient Based Modified Hysteresis Controller for Asymmetrical Six-Phase Induction Motor

This article proposes a simple current controller for asymmetrical six-phase induction motor (A6P-IM). The proposed controller is based on allocating both α and β current components in one of the eight regions. These regions are classified based on two factors: 1) tracking error, which is assessed by current hysteresis band (HB) and 2) future tendency of α β currents, which can be predicted by calculating current gradients (CGs). In order to minimize α β current errors, appropriate control action (V_αβ) should be applied. On the other hand, xy components need to be neutralized. As a result, virtual voltage vectors (VVVs) are considered and classified based on their α β components. For both α and β current regions, the best magnitude and direction of the available VVV components are assigned. Knowing α β current regions and the best-fit α β components, a lookup table is designed to directly select the best VVV to be applied. Thus, no iterations or optimization steps are required. The proposed method is characterized by its simplicity and robustness as it does not depend on any machine parameters. The validity of the proposed method is tested experimentally using a 1-kW A6P-IM. Moreover, its performance is assessed against conventional predictive current control (PCC) and VVV-based predictive controller VVV-PCC. The experimental results indicate that the proposed method has 25% less average switching frequency compared to the VVV-PCC method.