Vector Control Of Doubly Fed Motor Without Speed Sensor Based On Rotor Current Direction

For wind machines and pump load widely used in industry, the more desirable speed adjustment strategy is doubly fed regulation in order to save energy. The system has many advantages such as cheaply productive price, low harmonic pollution, high reliability and good speed adjusting behavior. As to doubly fed adjustment system, it will own excellent dynamic and static behavior if vector control is used. But if the system includes speed and position sensor, it will cause the increment of cost, descend of reliability, complication of structure and limitation of application area. As to traditional doubly fed adjustment vector control system, if rotor current vector fixing strategy is used, the system has large "blind area" at the synchronization speed. This dissertation is directed to solve these problems. The contributions done are as follows:According to the mathematical model of doubly fed motor and the theory of vector control, a unit power factor of rotor control scheme is proposed. In the doubly fed adjustment system, in order to control magnetic torque of motor this scheme is designed by controlling the reverse direction between rotor voltage and current to keep the vertical direction between rotor current and flux. It is known from theoretical analysis that for partly decoupling this scheme is only effective under sub-synchronization speed, but not control the system and obtain steady state since speed adjustment system can't adjust the magnitude of rotor flux under sup-synchronization. Simulations for these two conditions prove validity of theoretical analysis.On the basis of this scheme, a new speed adjustment strategy about vector control of doubly fed motor based on rotor current vector fixing is given. It introduces the closed-loop of stator excitation current to the system, which increases two adjustment channels: speed and excitation adjustment. This strategy has many advantages: solving the problems that the system is unsteady under super-synchronization; improving power factor of stator (it is unity relative to that of rotor); no rotor position sensor and no initial position measurement, easily building up doubly fed speed adjustment system with speed sensorless because adjusting speed is taken in the rotor coordinate and rotor current vector fixing is implemented.At last, the simulating analysis and experimental research for the second scheme are implemented by development system based on MCS196KC chip. The steady running of the control system is realized. The simulation and experiment results prove its stability and feasibility.