A simplified hybrid vector model predictive control method for neutral-point-connected open-winding induction motor

Abstract For the neutral-point-connected open-winding induction motor based on auxiliary bridge arms topology (AB-NPC-OEWIM), the traditional single vector model predictive control (SVMPC) suffers from issues such as large current ripples and significant zero-sequence current (ZSC). To address these problems, a simplified hybrid vector model predictive control (HVMPC) method is proposed in this paper. The studied AB-NPC-OEWIM is supplied by double three-phase four-leg inverters, where the DC bus voltage ratio between the high-voltage inverter (INV1) and the low-voltage inverter (INV2) is set to 2:1. For the proposed HVMPC, the three-dimensional (3D) voltage vectors (VVs) of the three-phase four-leg inverter is first projected onto the αβ coordinate by the 3D voltage vector (VV) to two-dimensional (2D) VV conversion method. Then, the optimal VV of the INV1 is selected firstly. Next, six virtual VVs with the duty cycle calculated by the cost function values are defined for the INV2 and the optimal virtual VV is selected. Finally, by evaluating zero-sequence current using the redundant vectors, the optimal VVs for INV1 and INV2 are finally determined. Additionally, to show the effectiveness of the proposed virtual VV based MPC method for INV2, a new visualization analysis method is proposed, which depicts the control error vividly using a 3D diagram, indicating that the proposed MPC can reduce the control error obviously, resulting in reduced current ripples. Finally, experimental studies are carried out, which verify the effectiveness of the proposed HVMPC method for AB-NPC-OEWIM.