Robust stability of the current control system to parameter errors in sensorless control based on maximum torque control frame

In this paper, the stability of the current control system in a sensorless method based on the maximum torque control frame (MTCF) which we have proposed is described. First, the closed-loop transfer function of the current control system considering position errors on the MTCF is derived. Next, the influence of the position estimation error on parameter errors in the steady state is examined. Since the parameter (L_qm) which is used in estimation of the MTCF is less affected by magnetic saturation than the conventional parameter L_q, the position estimation error in the proposed method can be suppressed to a far greater degree compared to that in the conventional method, even if the parameter L_q changes as a result of magnetic saturation. The pole assignment on the position estimation error, which is caused by parameter errors, is then investigated. The pole assignment in the proposed method changes only slightly when a position estimation error exists. As a result, the proposed method is more stable than conventional methods in the presence of parameter errors.