Sensorless Direct Torque Control For PMSM

Permanent magnet synchronous motor (PMSM) has been widely used in high performance drive applications for its advantages, such as high power density, high efficiency, reliability and suitability to environment. Usually it is necessary to achieve control good performance of PMSM that the information of rotor position and speed must be obtained by mechanical sensors, exactly. However, using mechanical sensors are caused some problems, unavoidable, for example system stability and high cost. Therefore, sensorless control technologies are gradually taken some attentions and became one of hot areas of research.Firstly, in this thesis, mathematical model of PMSM and the schemes of direct torque control (DTC) are introduced. Based on these, the way of combination control with Space Vector Pulse Width Modulation (SVPWM) and DTC, is discussed. In order to improving the operation efficiency, minimum stator current control scheme is used. The validity and feasibility of the adopted control scheme have been tested by simulation and experimentation. The results show this control method lay the foundation for sensorless control schemes.Secondly, a fourth order sliding mode observer of SPMSM is designed for achieving the information of rotor speed, of which state variables are stator currents and rotor electromotive force, respectively. The sliding mode plane is gained by Current error equations and the self-adaptive rules of sliding gain are confirmed by Lyapunov theory. When the system works in sliding mode status, the voltage self-adaptive equations can be obtain by principle of equivalent control. Based on the voltage error equations, the speed self-adaptive rules can be obtained under the condition which is keeping the voltage error equations stabilization, at the same time rotor position angle can be obtained by electromotive forces, as well as the torque and flux can be calculated by current equations.Finally, some simulations and experimentations are adopted to prove the validity and feasibility of designed sliding mode observer. The results show this control method can exactly obtain the rotor speed, as well as retain good dynamic and steady state performance under mechanical sensors...