A study on a new sensorless control method for an induction motor using a non-linear speed observer and hybrid V/f control method

Abstract

This paper proposes a new hybrid voltage per frequency(V/f) control method for induction motor sensorless speed control. Induction motors are durable and inexpensive, so they are used in many industrial fields, from small-capacity to large-capacity pumps and fans over 100kW. Conventional V/f scalar control is widely used in induction motor control because it is easy to use. However, since open-loop control is without a feedback component, the speed decreases due to slip as the load increases. In addition, performance deteriorates in the low-speed region due to the influence of stator resistance and slip. Furthermore, there is a disadvantage in that the loss is more significant at light loads. Therefore, this paper proposes a novel method to combine V/f patterns and compensate for V/f control with speed and torque estimated through a nonlinear speed observer and a magnetic flux observer. In considering the nonlinear dynamic characteristics of the induction motor, the gains of the nonlinear speed observer are selected as multiple points. Using a 75kW induction motor simulation and MATLAB/SIMULINK, we verified that the nonlinear speed observer could accurately estimate the actual speed. In addition, it confirmed that the hybrid V/f control performance was improved by compensating the estimated torque obtained by the magnetic flux observer to the V/f control.