Broken rotor bar impact on sensorless control of induction machine

Purpose - The Purpose of this paper is analysis of the sensorless control system of induction machine with broken rotor for diagnostic purposes. Increasing popularity of sensorless controlled variable speed drives requires research in area of reliability, range of stable operation, fault symptoms and application of diagnosis methods. Design/methodology/approach - T transformation used for conversion of instantaneous rotor currents electrical circuit representation to space vector components is investigated to apply with closed-loop modeling algorithm. Evaluation of the algorithm is based on analysis of asymmetry influence to the orthogonal and zero components of space vector representation. Multiscalar model of the machine and selected structures of state observers are used for sensorless control system synthesis. Proposed method of frequency characteristics calculation is used for state observers analysis in open-loop operation. Findings - New algorithm of applying the T transformation allows for closed-loop and sensorless control system simulation with asymmetric machine due to broken rotor. Compensating effect of the closed-loop control system with speed measurements and diagnosis information in control system variables are identified. Proposed frequency analysis of state observers is presented and applied. Variables with amplified characteristic frequency components related to rotor asymmetry are compared for selected structures of state observers and with closed-loop and open-loop operation. Method of improving the sensorless system stability is proposed. Practical implications - In closed-loop and sensorless control system rotor fault can be diagnosed by using PI output controllers variables. Compensating effect of mechanical variables sets limitation to specified diagnosis methods. Rotor asymmetry affects sensorless control system stability depending on estimator structure. Originality/value - This paper concentrates upon sensorless control system operation with machine asymmetry and indicates rotor fault symptoms.