New approaches with sensorless drives

In this article, we investigate a means of extricating the position information involved in terminal voltages and currents to estimate the rotor position of a PM synchronous motor. One way to extract the position information is to construct the state observer based on the motor model including electrical and mechanical equations. Then, the stability of the observer is an important issue in providing accurate position information for the motor drive system. In order to stabilize the system, the gains of the observer have to be optimized. However, these schemes have some difficulties in determining the optimum gains of the observer under any operating condition because the electrical equations are nonlinear in such motor models. We present a new approach for constructing the observer to extract precise information from the rotor position, and its speed from the technical quantities. First, to overcome the aforementioned problem, we propose the control inputs that can eliminate the nonlinear term in the electrical equations and realize the linearization of the motor model. This permits use of linear control strategies to determine the characteristics of the system. Second, we perform the rotor-speed estimation by using the reduced-order observer based on the linearized model. Third, the rotor position is calculated by using the estimated rotor speed and then corrected by the d-axis current error. Thus, we realize the stable drive of the motor without position sensors by measuring only two line currents. Finally, the validity of the proposed control scheme is confirmed by experiments.