Contents I. Introduction
In Recent years, the use of the electric motors in automotive applications such as electric power steering and hybrid and electric vehicles has increased. Resolvers have been used for position sensors to provide the absolute position information in industrial applications for many years. Their robustness and reliability make them particularly suitable to harsh industrial environments [1]–[3]. The resolver output signals contain the angular position information, and they have a digital form, which is obtained from a resolver-to-digital (R/D) converter. Several methods exist in the literature, focusing on ways to improve the measurement accuracy of the R/D converter [4]–[6]. These techniques are cost effective, and they can be implemented using a less hardware in order to reduce the weight and size. These methods state the position resolution and accuracy specifications under the assumption that the ideal resolver signals are supplied to an R/D converter. However, in a real system, the resolver output signals include the position errors in the resolver itself as well as in the resolver signal conditioning circuits [7]–[11]. As a result, the actual resolver output signals have nonideal characteristics such as amplitude imbalance, imperfect quadrature, inductive harmonics, reference phase shift, excitation signal distortion, and disturbance signals [7], [8]. Due to these nonideal characteristics of the resolver signals, the position information of the R/D converter can be considerably distorted. In particular, the amplitude imbalance and the imperfect quadrature are dominant components [7]–[11]. Therefore, this paper only focuses on the effects of the position errors caused by the amplitude imbalance and the imperfect quadrature. In order to solve these problems, the compensation algorithms have already been suggested [7]–[11]. In [7] and [8], these methods correct most of the nonideal characteristics, including an origin in the R/D converter. However, these methods require much labor and time, an excessive computation burden, and a hardware. In [9], this method introduces the gain-phase-offset-correction method only by a low computing effort. The method proposed in [10] was only presented to integrate the ideal rotor position to get the magnitude of the position error according to the distorted rotor position due to the amplitude imbalance, without considering the variation of the rotor speed and bandwidth of the closed current control loop. In [11], this method is just introduced to reduce the torque ripple caused by the amplitude imbalance. This method needs an additional position sensor which has no distorted position information in order to reduce the torque ripple. However, both effects of the amplitude imbalance and the imperfect quadrature must simultaneously be taken into account for the accurate vector control of the permanent magnet synchronous motor (PMSM) using a resolver.
Schematic diagrams of the (a) resolver and (b) tracking loop of an R/D converter with ideal resolver signals.
