Deep flux weakening control strategy for IPMSM with variable direct axis current limitations

To realize the smooth transition from the partial flux weakening zone I (FW-I Zone) to the deep flux weakening zone II (FW-II Zone) and avoid the current loop saturation during the deep flux weakening control for an interior permanent magnet synchronous motor, a novel deep flux weakening control strategy with variable direct axis (d-axis) current limitation (VDL-FWC) is proposed. In the framework of the traditional voltage closed-loop feedback regulation flux weakening control (FB-FWC) strategy, the d-axis flux weakening current is limited by the maximum torque per voltage, which is quickly obtained through a parabolic approximation that varies with the quadrature axis (q-axis) current. Therefore, when the d-axis weakening current exceeds its limitation, a closed-loop voltage feedback proportional-integral controller is used to adjust the q-axis current increment, which transfers the exceeding d-axis current to the q-axis current to prevent voltage saturation. This process helps the current loop avoid becoming out of control. The proposed deep flux weakening control strategy is compared with the FB-FWC strategy and flux weakening control strategy with a fixed direct d-axis current limitation (FDL-FWC). Studies show that the proposed strategy is effective and has a higher load capacity in the deep flux weakening zone.