Research On Speed-sensorless Direct Torque Control Of 3-phase Induction Motor Drives

In the last few years, the development of the technique of modern Electric Power and Electronics, Micro-processor, and Advanced Control provides very important pledge for high-performance control of motor. At the same time, with the development of the technique of production and the level of modern automation equipment, favorable stable-state and dynamic-state performance for the drive system of motor is wanted. The Direct Torque Control (DTC) technique and the Vector Control (VC) technique, which belong to high performance variable-frequency adjusting-speed technique in the AC drives, are both researched widely. Especially, DTC is very popular to the entire world because of its fast behavior, simple structure, and robustness. And DTC technology has successfully been applied in high-power ac drives. However, Bang-Bang control mode of classic DTC introduces extra electromagnetic torque chattering, stator flux ripples, and current harmonics, which has become its inherent disadvantages and confined the DTC technique to be applied widely. It is the best method to solve the above questions that a novel DTC theory is founded by synthesizing VC. Moreover, for high-performance speed close-loop system, the feedback of speed is wanted. Speed-sensorless technique is very important to reduce its cost and strengthen its reliability, and has become the focus of AC adjusting-speed field.So, this dissertation develops theoretic and application research on the problems of speed-sensorless DTC of induction motor. Its main works are followed as:1, For its inherent drawbacks of classic DTC, such as torque, flux, and current ripple, a novel DTC scheme is presented, in which a sliding mode variable structure control (SMVSC) method is applied to control electromagnetic torque and stator flux by using torque and flux errors. In order to preserve the system states near the sliding-mode surface and reduce the reaching distance, a time-variable integral sliding-mode surface is devised, which not only improves the system's robustness, but also guarantees good dynamic quality of the sliding-mode states. For its intrinsic chattering of SMVSC, this dissertation suggests a hybrid sliding-mode variable structure control (HSMVSC) method, in which VSC can smoothly transit to classic PI control by hysteresis comparator, taking advantage of the best features of linear control, smooth operation, and of VSC, quickness and robustness to perturbations, resulting in reducing the chattering.