Flux Control of a CPPM Machine for Both a Wide Speed Range and High Efficiency

This paper proposes a flux control strategy for a consequent-pole permanent-magnet (CPPM) machine that increases torque capability over a wide speed range and enhances efficiency with a fast convergence. After a brief analysis of the parameters of the CPPM machine, a new flux-weakening algorithm is proposed to achieve maximum torque output over the entire speed range. The optimal flux reference is determined by the preset output flux generated by the 1/ω method and compensated by the voltage closed-loop controller to improve dynamics response. A variable structure voltage controller incorporated with a limiter is designed to generate the antiwindup control. Furthermore, the loss model of the CPPM machine is derived to demonstrate that a 1-D search is suitable for optimizing the machine´s efficiency. Then, an adaptive flux step search algorithm, which calculates the flux step proportional to the derivative of the input power with respect to the q-axis voltage, is proposed to minimize the power losses online. The experimental results are compared with the traditional flux control strategy on a CPPM prototype machine, which confirmed the robustness of the presented flux control strategy to obtain the maximum torque output over the entire flux-weakening speed range. The convergence speed is also increased in the efficiency optimization process.