Analysis of Voltage Distortion and Comparison of Two Simple Voltage Compensation Methods for Sensorless Control of Induction Motor

Many algorithms of induction motor sensorless control need accurate knowledge of the stator voltage vector. However, the machine is in most cases supplied by a two-level voltage-source inverter; therefore, the voltage is distorted by the inserted dead-time and also by nonlinearities of the semiconductor switches. This paper analyzes a distortion caused by the dead-time and delayed IGBT switching in terms of distorting voltage vector. An offline measurement is performed to obtain the inverter model. Then, an analysis of two simple volt-seconds-based compensation methods (compensation of the reference voltage vector and duty cycle, respectively) on the accuracy of the speed estimation of a sensorless field-oriented control based on the rotor flux model reference adaptive system is performed. The analyzed methods use either the full inverter model implemented as a look-up table or its trapezoidal approximation. Outline on computational complexity and discussion on finding optimal coefficients for the trapezoidal model are given, too.