Common variable frequency motors include: three-phase asynchronous motor, DC brushless motor, AC brushless motor and switched reluctance motor. The control strategy of common variable frequency motor is constant torque control at base speed, constant power control above base speed, super high speed. Range weak magnetic control. The base speed produces a back electromotive force when the motor is running, and the back electromotive force is usually proportional to the rotational speed. Therefore, when the motor runs to a certain speed, since the magnitude of the counter electromotive force is the same as the magnitude of the applied voltage, the speed at this time is called the base speed.
Constant torque control: The motor performs constant torque control at the base speed. At this time, the back electromotive force E of the motor is proportional to the rotational speed of the motor. In addition, the output power of the motor is proportional to the product of the torque and speed of the motor, so the motor power is proportional to the speed. Constant power control: When the motor exceeds the base speed, the motor's back-EMF is kept constant by adjusting the motor's excitation current to increase the motor's speed. At this point, the output power of the motor remains basically constant, but the motor torque decreases inversely proportional to the speed. Weak magnetic control: When the motor speed exceeds a certain value, the excitation current is already quite small, and basically can not be adjusted again.
At this time, the field weakening control is entered. The speed control and control of the motor is one of the basic technologies of various types of machinery and office and industrial and electrical equipment. With the amazing development of power electronics technology and microelectronic technology, the AC speed regulation method using “special frequency induction induction motor + frequency converter” is leading a place to replace the traditional one in the field of speed regulation with its excellent performance and economy. The change of the speed control mode is changed. The gospel that it brings to all walks of life is: to greatly improve the degree of mechanical automation and production efficiency, save energy, improve product qualification rate and product quality, improve power system capacity, miniaturize equipment, and increase comfort.
Fast speed replaces traditional mechanical speed control and DC speed control solutions. Due to the special nature of the variable frequency power supply and the system's demand for high-speed or low-speed operation and dynamic speed response, the demanding motor is a demanding requirement, which brings new problems in the electromagnetic, structural and insulation aspects of the motor. . The application of variable frequency speed control of frequency conversion motor has become the mainstream speed regulation scheme, which can be widely used in continuously variable transmission of various industries. Especially with the increasing application of frequency converters in the field of industrial control, the use of variable frequency motors is becoming more and more extensive. It can be said that because of the superiority of inverter motors in inverter control compared with ordinary motors, wherever inverters are used, It is not difficult to see the figure of the inverter motor.