Flux-Weakening Control for Variable Flux Reluctance Machine Excited by Zero-Sequence Current Considering Zero-Sequence Resistive Voltage Drop

In the control of variable flux reluctance machine (VFRM) excited by zero-sequence current, neglecting the zero-sequence resistive voltage drop would cause a large calculation deviation of the stator voltage, which can saturate the inverter and influence the switching from constant torque region to flux-weakening region. To solve with this problem, a flux-weakening control method considering the zero-sequence resistive voltage drop for VFRM is proposed. Firstly, the relationship between dq-axis voltages, zero-sequence voltage and the maximum voltage is presented. Secondly, based on the deduced voltage constraint, the calculation of optimal reference currents in flux-weakening region is presented by using Lagrange multiplier method. Since the zero-sequence voltage is considered, the calculation accuracy of the stator voltage and the utilization rate of DC link voltage are improved, which improves the output power capability. Finally, the proposed method is verified by the experimental results.