Stator Resistance Variation On The Speed Sensorless Direct Torque Control System

Speed identification is the core of the speed sensorless direct torque control system. Regardless of the type of speed identification method, the stator resistance is an important parameter of the stator flux observation and speed identification. In the process of operation, the motor stator resistance would change under the influence of the factors such as the temperature rise, skin effect and frequency effect. It will inevitably reduce the precision of flux observation and speed identification. Therefore, the influence of the stator resistance uncertainty to speed sensorless direct torque control system has become the hotspot research in recent years.AnalyzedΓasynchronous motors equivalent circuit mathematical model, established the state equation of induction motor with the stator and the rotor flux for state variables, and proved the observability. On this basis, this paper analyzed the stator resistance uncertainty influence to the three basic stator flux estimation schemes and electromagnetic torque of speed sensorless direct torque control system, pointed out that the necessity study of the impact of the stator resistance uncertainty speed sensorless direct torque control system. According to the uncertainty of the stator resistance, proposed a stator resistance identification scheme which based on adaptive flux observer and another scheme which based on stator resistance robust observer.In the stator resistance identification scheme that based on adaptive flux observer, a new Lyapunov function was constructed, the identification rate of speed and stator resistance was deduced. On the basis of methods which analysis poles and LMI, using iterative LMI method, then the adaptive observer gain matrix was obtained, and the stability of the observer was guaranteed. Through the simulation research, by contrast, the method of poles configuration according to different motor parameter, may lead to instability. Also verified the stator resistance identification method that based on adaptive flux observer can improve the precision of the speed identification at a certain extent.The designed method of the stator resistance robust observer in the stator resistance uncertain circumstances converged estimated error to the bounded area. Using Lyapunov stability theory, this paper deduced the rotor speed identification method and the nonlinear inequalities which ensured the stability of the observer, using robust theory, the nonlinear inequalities transformed into linear matrix inequality, then the observer gain matrices which ensured the stability of observer. Through the simulation research, compared to the stator resistance identification scheme, this scheme can eliminate or inhibit the stator resistance uncertainty influence to speed identification at a certain extent. But relative to the stator resistance and speed double identification scheme, the stator resistance robust observer scheme has the smaller amount of calculation and real-time easily satisfied, which has more advantage on the engineering requirement.