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

Abstract

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.