According to different control methods, the inverter can be divided into 3 types: variable frequency variable voltage (U / f) control, vector control (VC) and direct torque control.
1. Frequency conversion control (U / f)
U / f control is the control of the frequency-to-frequency ratio. Its basic feature is to control the voltage and frequency of the inverter output at the same time, and obtain the required torque characteristics by keeping the U / f constant. This method of low cost control, used for less precision universal drive.
2. Vector Control (VC)
According to the dynamic mathematical model of AC motor, the stator current of AC motor is decomposed into current component and torque component current of magnetic field by coordinate transformation method, and separately controlled, ie the control mode of DC motor imitates the magnetic field and torque of motor respectively To control, you must also control the motor stator current amplitude and phase, it can be said that the control current vector, so this control is called vector control. AC motors provide dynamic performance similar to DC speed control systems.
Vector control makes high performance induction motors possible. Not only can the vector inverter be comparable to a DC motor in the speed range, but also to directly control the variation of the asynchronous motor torque, it has been widely used in many fields requiring precision or quick control.
3. Direct torque control
Direct torque control by controlling the motor instantaneous input voltage to control the motor stator flux instantaneous rotation speed, change its instantaneous rotor slip, so as to achieve the purpose of direct control of the motor output.