Resolver-To-Digital Conversion Based on Acceleration-Compensated Angle Tracking Observer

Abstract

To obtain a rotary motor’s position, resolver-to-digital conversion conventionally adopts phase-locked loop-based type-II angle tracking observer (ATO), which generally performs well yet incurs steady-state position error when the motor accelerates. It inevitably weakens the motor drive system’s performance in applications such as electric vehicle, where the speed changes frequently. This paper proposes acceleration-compensated ATO that utilizes its own estimated speed to generate a signal proportional to the motor’s acceleration, and thus, compensate for the position error. First, it is theoretically verified that the proposed ATO can accurately estimate the rotor position of an accelerating motor. Also, its stability condition is deduced. Second, since the proposed observer, a third-order system, is too complicated to analyze directly, first-order and second-order systems are designated to approximate it, respectively, under two certain circumstances. Based on which, a simple guideline is summarized on how to tune the proposed ATO so that it may retain the merits of the conventional one while estimating the rotor position free of steady-state error. Finally, on a resolver mounted on a 20-kW permanent magnet synchronous motor, experiments are carried out. Experimental results demonstrate the ability of the acceleration-compensated ATO to precisely track an accelerating motor’s position in comparison with that of its conventional counterpart.