Sensorless Direct Torque Control Of High Speed PMSM

With more and more advanced requirements of social actual production requirements, the varieties of motor are gradually increasing and the control technologies of modern motor are also upgrading unceasingly. High speed permanent magnet synchronous motor (PMSM) drives are of interest as direct drives for high speed milling machines, compressors and pumps, yielding a high output power with smaller machine size. The high speed PMSM has the advantages such as high efficiency, low torque ripple, low noise, and excellent control performance. The direct torque control (DTC) technique, which is a kind of high performance variable-frequency adjusting-speed technique in the AC drives, is studied widely after the vector control (VC) technique. DTC for PMSM has the advantages of simple structure, fast torque response, good robustness etc. However, there are many problems with the conventional DTC, such as large ripple of current, flux and torque, variable switching frequency, difficulty to accurately control at very low speed. Meanwhile, using the speed sensor deteriorates system reliability and increases the cost of the system. The sensorless control is particularly desirable for the high speed PMSM drives because it is difficult to mount complex sensors on the high speed shaft. To solve all above problems, a new sensorless variable structure sliding mode ( VSS) DTC strategy for high speed PMSM is proposed.Firstly, based on the state of the art review of DTC, the theory of coordinate transformation in motor control and mathematical model of PMSM are introduced, and at the same time, the principles of the basic DTC and voltage space vector pulse width modulation (SVPWM) are introduced. Secondly, the theory of VSS control and the methodology of speed estimation are presented. According to above theories, to solve the problem of the torque in the DTC system, a sensorless VSS-DTC strategy for high speed PMSM is proposed. The simulation model of system is built by the means of MATLAB/SIMULINK. The proposed system is compared with the basic DTC. The simulation results prove the feasibility and advantages of this scheme.At last, the DTC system of high speed PMSM is designed. The hardware design of the control system includes the main circuit, drive circuit and current sample circuits and so on. The software is designed in assemble language based on TMS320LF2407 DSP. It has realized functions of the stator current sampling, observing stator flax and the output of switching signal, etc.