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Back-EMF-based sensorless control of permanent magnet synchronous machines (PMSMs) is preferred in many industrial applications due to its control simplicity and high machine efficiency. Position estimation based on the back-EMF is most reliable in the medium-to high-speed range. For applications where low-speed operation is not required, a simple-structure back-EMF-based sensorless controller coupled with a simple startup procedure offers an attractive low-cost solution. This paper proposes a new startup procedure based on closed-loop current regulation. Compared to the existing methods, the new starting method can work under different load conditions and allows smooth transition from the startup procedure to the back-EMF-based sensorless control mode. In order to determine the successful use of the proposed method in various applications, it stability under different load conditions is discussed in detail. The proposed method is robust when it comes to the motor parameter variation and can be used for both surface-mounted PMSMs (SPMSMs) and interior PMSMs. The method presented in this paper is validated using the experimental results on an SPMSM. A general design guideline is also given.
Date of Publication: Aug. 2012