Study On The Theory Of Induction Motors Speed Control Based On Motional Electromotive Force (MEMF)

Induction motor, the so-called workhorse of industry, is one kind of important and complex electromechanical energy converter. The principle of electromechanical energy conversion is the basic principle of electromechanical energy converter and an important tool for rotating electrical machine analysis. Based on the principle of electromechanical energy conversion and reference frame transformation theory, the speed control methods for induction motor are studied from viewpoints of motional electromotive force (MEMF) and magnetic field in this dissertation. The main contributions are summarized as follows.The power balance of induction motor in arbitrary reference frame is analyzed. The physical meaning and characteristic of reference frame power are illustrated in detail. It is verified that the "workless forces" in passivity-based control of induction motor is due to reference frame transformation and the physical meaning of "workless forces" is given.The viewpoint of control of MEMF in variable-frequency induction motor drive is presented. It is proved that rotor field orientation decouples not only flux linkage and torque but also transformer electromotive force (TEMF) and MEMF in rotor. The control of torque and speed in variable-frequency induction motor drive can achieve by control of rotor MEMF.The universal field-oriented model of induction motor based on control of MEMF is proposed. The universal current vector controller for vector-controlled induction motors based on control of MEMF is presented. The simulation results show that the proposed methods are simple in control and have good dynamic performance.The universal voltage vector controller for vector-controlled induction motors based on control of MEMF is proposed. The voltage vector controllers for rotor field-oriented control and stator field-oriented control based on control of MEMF are proposed respectively. The simulation results show that the proposed methods havenot only good dynamic performance but also simple control structure for stator field-oriented control.The viewpoint of control of magnetic field in motor speed control is presented. The inherent relationship and difference between the conventional vector control, the field acceleration method, the direct torque control and the field-oriented control based control of MEMF are analyzed. The results show that the field-oriented method is an effective method of field control, but not the only method.The model of doubly fed motor based on stator current vector oriented reference frame is proposed. The flux estimator, which can calculate rotor flux, stator flux and air gap flux with independent on the stator resistance and rotor resistance, is presented based on stator current vector orientation. The simulation results show that the proposed flux estimator is robust to the stator and rotor resistance parameters.