1.3 Frequency Variation Speed Controlled Mode
The alternating frequency conversion velocity modulation technique obtained the rapid development in 20th century. This is related with some crucial technical which gain unprecedented progress, they are Motor vector control technique, Direct torque control technique, PWM technique, Entire numerical control technique and self-setting technique which based on microcomputer and large scale integrated circuit, and so on.
1) Vector Control Technique
Vector transformation control technique is a one kind of new control thought and control theory which posed by SIEMENS CO.本文来自辣~文\论|文/网，
毕业论文 www.751com.cn 加7位QQ324'9114找源文 component and the torque component solution lotus root by rotor magnetic field direction detection, and vector transformation, achieved the goal that separately control the motor flux linkage and the electric current, as a result, obtain finely static, dynamic performance. Until now, the vector control technique has obtained the considerable development, and also obtained the widespread application.
2) Vector Control Without Velocity Generator Technique
Vector control without velocity generator technique abolish the problems that the environment compatibility、install and maintenance bring on, reduce the cost, enhance the system reliability, at the same time, union vector control, has the fine performance of vector control. The speed estimate method in vector control technique without velocity generator, besides basis mathematical model computation electric motor rotational speed, at present the more applied are the model to refer auto-adapted method and expands the Kalman filtering law. In addition, entire Uygur rotor magnetic flux sight, tooth overtone electric potential, such as this theory and so on, also appearance in the vector control without velocity generator technique. Since 1983 proposed the vector control without velocity generator technique control strategy, receives the academic circles and the industrial field continuously highly focused all the time. Hitachi company and Sichuan electrical machinery and so on had published the research results separately in 1987, and had promoted the product one after another. At present, vector control without velocity generator technique in frequency converter controlling in the velocity modulation scope is about 1:50, some individual merchant has 1:75 or even higher product.
3) Direct Torque Control Technique
In1985, Germany's M. Depen-block proposes the direct torque control technique（DTC） for the first time，The direct torque control technique analyzes the motor mathematical model directly under the stator coordinate system. Uses the stator magnetic field direction detection but not to need the solution lotus root electric current，directly control the electric motor flux linkage and torque, enable the torque to obtain the fast response, in order to obtain the highly effective control performance.
Direct torque control technique is another kind of new、high performance alternating frequency conversion velocity modulation technique after vector control technique in the nearly 10 years, this kind of control technique is insensitive to the electrical machinery parameter, not influence by the rotor parameter, easy and feasible, it has the broad development and the application prospect.
4) PWM (pulse width modulation) Control Technique
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