Calibration of resolver sensors in electromechanical braking systems: a modified recursive weighted least-squares approach

Resolver sensors are utilized as absolute position transducers to control the position and speed of actuators in many industrial applications. The accuracy and convergence of the position and speed measurements provided by resolvers in electromechanical braking system (EMB) designs directly contribute to the braking performance and vehicle safety. In practice, the dc drifts, amplitudes, and phase shift of the resolver signals vary with aging and temperature, and adaptive techniques are required for the calibration of these parameters of resolvers. Existing classical adaptive techniques such as recursive least squares are unable to track the parameters during resting (low-speed actuation or stationary) periods and also a transient period after them. This paper proposes a new approach for real-time tracking of resolver parameters specially developed for actuator-control applications with varying speed and long resting periods. We formulate the algebraic relationship between the resolver parameters and the parameters of resolver characteristic ellipse, which is the ellipse formed by plotting the resolver signals versus each other. Having known the characteristic ellipse parameters, the resolver parameters are calculated using the formulated algebraic relation. Then, a new recursive and adaptive estimator is proposed to track the parameters of characteristic ellipse. The low computational complexity of the proposed method makes it desirable for real-time applications like the EMBs, where limited computational power and memory are available. Experimental results show that the proposed technique is able to track the resolver parameters and the accurate actuator position with a small error in real-time, while other adaptive estimators are unable to track the resolver parameters during and after resting periods.