SENSORLESS CONTROL OF BRUSHLESS PERMANENT-MAGNET MACHINES FOR POWER TOOL APPLICATION

Permanent-magnet-synchronous-machine (PMSM) drives are widely used in industrial and commercial applications which requires fast dynamic response and accurate control over wide speed ranges. Although, there exists challenges to develop position-sensorless based vector control of PMSM operating in wide speed range covering both constant-torque and constant-power regions. The research objective is to maintain and improve its control robustness and adaptability to variations of operating conditions as well as dynamic performance as compared to sensored rotor estimation technique which is currently employed in the system. Sensorless operation at zero or low speeds is problematic due to motor parameters and initial rotor position error. Also, since most model-based approaches rely on amplitude of back-emf, which is proportional to the rotor speed, these techniques fail in zero and low-speed regions. There is no single sensorless technique suitable for whole speed range therefore suitable sensorless scheme is applied to the zero, low and high speed range for seamless operation of the drive. First, Initial Position Detection algorithm is implemented at zero speed which helps in initial position estimation with higher resolution followed by parking stage implementation to ensure rotor rotates in correct direction essential for most PMSM drive application. Secondly, at low speeds High Frequency Injection (HFI) based technique is employed which is suitable for Interior Permanent Magnet (IPM) type motors due to the inherent rotor pole saliency as well as its accuracy being independent of rotor speed. At high speeds above 60 Hz, sliding mode observer-based position estimation is employed which is fundamentally based on back-emf information. These methods are implemented on PMSM drive based power tool application like SBD power drill and grinder.Electrical and Computer Engineering, Department o