What Is A Variable Frequency Motor？
Definition: Frequency conversion technology actually uses the principle of motor control to control the motor through the so-called frequency converter. The motor used for this type of control is called a variable frequency motor. Common frequency conversion motors include three-phase asynchronous motors, DC brushless motors, AC brushless motors, and switched reluctance motors. The speed regulation and control of the motor is one of the basic technologies of various industrial and agricultural machinery and office and people's livelihood electrical equipment. With the amazing development of power electronic technology and microelectronic technology, the AC speed regulation method using "special frequency conversion induction motor + frequency converter" is leading the field of speed regulation in its field of speed regulation with its excellent performance and economy. The change of speed regulation method. The gospel it brings to all walks of life lies in: greatly improving the degree of machine automation and production efficiency, saving energy, improving product qualification rate and product quality, correspondingly increasing the capacity of the power supply system, miniaturizing the equipment, and increasing comfort. Fast speed replaces traditional mechanical speed regulation and DC speed regulation scheme. Due to the particularity of the variable frequency power supply, and the system's requirements for high-speed or low-speed operation, dynamic response to speed, etc., it has put forward stringent requirements for the motor as the main body of power, which brings new topics in the electromagnetic, structure, and insulation aspects of the motor. .
Control principle: Usually the control strategy of variable frequency motors is constant torque control at base speed, constant power control above base speed, and field weakening control in ultra-high speed range. Base speed: Because the back electromotive force is generated when the motor is running, the size of the back electromotive force is usually proportional to the speed. Therefore, when the motor runs to a certain speed, since the magnitude of the back 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 base speed. At this time, the back electromotive force E of the motor is proportional to the rotation speed of the motor. And the output power of the motor is proportional to the product of the torque and speed of the motor, so at this time the motor power is proportional to the speed. Constant power control: When the motor exceeds the base speed, the back electromotive force of the motor is basically kept constant by adjusting the motor excitation current, thereby increasing the speed of the motor. At this time, the output power of the motor remains basically constant, but the motor torque decreases in inverse proportion to the speed. Field weakening control: when the motor speed exceeds a certain value, the excitation current is already quite small and can no longer be adjusted. At this time, the field weakening control stage is entered.
Application: Frequency conversion speed regulation has become the mainstream speed regulation scheme, which can be widely used in continuously variable transmission of all walks of life. Especially with the increasingly extensive application of frequency converters in the field of industrial control, the use of frequency conversion motors is also becoming more and more widespread. It can be said that due to the superiority of frequency conversion motors in frequency conversion control compared to ordinary motors, wherever we use frequency converters, we It is not difficult to see the figure of inverter motor.