High performance ac speed regulation system

V/f constant, speed open-loop control of general frequency control system and the slip frequency speed closed loop control system, basically solved the problem of asynchronous
motor smooth speed. However, when the production machinery on the speed regulation system of dynamic and static performance put forward higher requirements, the above system or
than dc speed regulation system of lower. The reason is that, the system control law of asynchronous motor from steady-state equivalent circuit and steady state torque formula
is deduced steady-state value control, not considering the transition process, system in stability, starting and low speed torque dynamic response of performance is not
satisfactory.
Considering the asynchronous motor is a multi-variable, strong coupling, nonlinear time-varying parameter system, it is difficult to
rotating joints directly through applied signal accurately
control electromagnetic torque, but if rotor flux this rotating space vector for reference coordinates, use from static coordinate system to the rotating coordinate system
between the transformation, can put in the stator current excitation current component and torque component of current into scalar independent, control respectively. So, through
the transformation of coordinates reconstruction of motor model can be equivalent to
rotary union a dc motor, which can be as fast as dc motor torque and flux control is vector control.
And vector control is different, direct torque control reject decoupling thoughts, cancelled rotating coordinate transformation, simply by detecting motor stator voltage and
current, with the aid of instantaneous space vector theory calculation motor flux linkage and torque, and according to the given value compared with the income difference,
realize the flux and torque direct control.
Although vector control and direct torque control, the performance of the ac adjustable speed system has greatly improved, but there are many fields to be study:
(1) flux accurate estimate or observation
(2) the speed sensorless control method
(3) motor parameters online identification
(4) is extremely low speed including zero speed of motor control
(5) voltage reconstruction and dead zone compensation strategy
(6) of multilevel inverter high-performance control strategy
Six looking
In ac speed regulating the research and manufacture process, hardware design and assembly account for a considerable proportion. Motor manufacturing and speed control device
manufacturing needs a large number of skilled workers, the quality of personnel have certain requirements. And foreign relevant industry labor costs are relatively high, in the
recent ten years, ac speed control manufacturing are likely to developing countries transfer. For the Chinese, this is also an opportunity, if we take the chance, reuse itself
market advantage, it is possible to form ac adjustable speed system in our country manufacturing center, make our country industry to fiber optic rotary joint a new level. Note that the developed
countries in the high technology fields are won't give up easily, they pay much attention to the core technology and software protection and security, therefore, it is necessary
to increase the field of scientific research and development efforts.