3 speed control methods for AC motors

AC motors are machines used to achieve the mutual conversion of mechanical and electrical energy. Due to the great development of AC power systems, the AC motor has become the most commonly used motor. AC motors have no commutator, so their structure is simple, easy to manufacture, relatively strong, easy to make, high speed, high voltage, high current, and large capacity. AC motor power covers a wide range, from a few watts to hundreds of thousands of kilowatts and even millions of kilowatts.

AC motor speed control

With the development of power electronics technology, microelectronics technology, digital control technology, and control theory, the dynamic and static characteristics of the AC drive system can be fully comparable with those of the DC drive system. The AC drive system is widely used, and the use of the AC drive to replace the DC drive has gradually become a reality.

Due to the nature of the AC motor's nonlinear, multivariable, strong coupling, parameter time-varying, large disturbances in the complex object, its effective control has been a hot issue in domestic and foreign research. A variety of control strategies and methods have been proposed. Among them, classical linear control can't overcome the load, model parameters of a wide range of changes, and the impact of nonlinear factors, control performance is not high; vector control and direct torque control also have some problems. In recent years, with the theoretical development of modern control and intelligent control, advanced control algorithms have been applied to the control of AC motors and achieved certain results.

What are the three methods of AC motor speed regulation?

• Change the number of magnetic poles for speed control; the purpose is to control the synchronous speed of the magnetic field to control the rotor speed. The differential rate is unchanged, the differential loss is less, and for graded speed control, the use of occasions has restrictions.
• Change the rate of speed control, synchronous speed is unchanged and change the rotor return differential excitation current. The disadvantage is that it can't utilize the slip power of the motor, its power factor is low, and all the slip power is consumed in the form of heat energy. 3. Change the frequency speed control; the slip rate and slip power consumption are unchanged.

From the perspective of energy conversion, of the above three speed control methods, which change frequency speed control is the most efficient? Because of the frequency conversion speed control power and high efficiency, speed control accuracy is also quite high. And with its very hard mechanical characteristics and wide speed range, it is easy to realize that closed-loop automatic control is also the most energy-saving AC motor speed control method. It represents today's AC drive speed control level and is the main reason why frequency converters are used more and more widely.