High Frequency Injection Based Rotor Position Self-Sensing for Synchronous Electrostatic Machines

The low loss during high torque, low speed operation demonstrated by synchronous electrostatic machines make them an attractive choice for low speed servo applications. The high pole count (p >50) of these machines necessitates the use of high resolution position sensors. This work proposes methods of rotor position self-sensing for separately excited synchronous electrostatic machines to reduce cost and complexity associated with using an external encoder. A high-frequency injection based self-sensing method, which takes advantage of the separate excitation of the machine is proposed for estimating rotor position at zero and low speeds. The performance of the proposed estimation method is experimentally verified using a current source inverter driving the electrostatic machine. Closed loop speed control without encoder feedback is demonstrated. A compensation technique to mitigate the effect of filter delays is implemented to improve estimation accuracy at higher fundamental frequencies.