This paper deals with the design of observers for a class of continuous time nonlinear multi-input multi-output systems with nonlinear outputs. Geometric tools are used to transform the original system into an appropriate observer canonical form. Furthermore, a pole placement technique is used to obtain a desired transient response of resulting error dynamics. The observer design is presented for two cases. In both cases, it is shown that the observer gain can be obtained from the solution of a Riccati equation. An illustrative example of state estimation in induction motors is presented to explain the proposed observer design. The performance of the method is also verified by numerical simulations.
High frequency signal injection techniques are widely used to extract rotor position information from low speed to stand still. Accuracy of estimated rotor position is decreased when stator winding resistance is neglected. Position estimation error also results in output Torque reduction. Parasitic resistance of stator winding causes significant position estimation error and Torque reduction, if not compensated. Signal injection techniques developed in the literature does not provide detailed analysis and compensation methods to improve rotor position estimation of PMS Motors, where stator winding resistance cannot be neglected. This work analyzes the stator winding resistance effect on position estimation accuracy and proposes novel compensation technique to reduce the position estimation error and torque reduction introduced by stator winding resistance. Prototype hardware of a self-sensing PMSM drive is developed. The effectiveness of the proposed method is verified with the MATLAB/Simulink simulations and experimental results on a prototype self-sensing PMSM drive.
Induction motor speed control is an area of research that has been in prominence for some time now. Recent advances in this field have made it possible to replace the DC motor by induction machines, even in applications that demand a fast dynamic response. Many industrial applications demand speed sensorless operations, due to various reasons. It is also required to strictly maintain the speed of the motor within certain permissible tolerance, irrespective of the load changes that occur in the system. Unless prior knowledge of the load characteristics is known, it is very dincult to compensate for the same. Direct Torque Control (DTC) of induction motor is a popular method because of the resulting fast dynamic response of the motor, lower sensitivity to motor parameter variations and relatively low switching harmonics in the inverter. However, the present DTC approach is unsuitable for highperformunce applications because of the need of a speed sensor for increased accuracy, the absence of any error decay mechanism, and the requirement of prior knowledge of the load or disturbance characteristics. In this paper, a nonlinear observer is designed for the stator jlux, speed, and load torque estimation that will take care of the above limitations. The estimated values along with other measured states are used for the closed loop speed sensorless control operation of the induction motor. Simulations are done and the results discussed.
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