AC motor speed control principle and method
AC motor introduction
"AC motor" is a machine for converting mechanical energy and AC power. Due to the tremendous development of AC power systems, AC motors have become the most commonly used motors. Compared with DC motors, AC motors have no commutator (see commutation of DC motors), so they are simple in structure, easy to manufacture, and relatively robust. They are easy to make motors with 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, or even millions of kilowatts. In the early 1980s, the largest steam turbine generator had reached 1.5 million kilowatts. The AC motor was invented by the American Serbian scientist Nikola Tesla.
Motor principle
Description of single-phase capacitive motors: Single-phase motors have two windings, the start winding and the running winding. The two windings are spatially different by 90 degrees. A large-capacity capacitor is connected in series on the starting winding. When the running winding and the starting winding pass the single-phase alternating current, the current in the starting winding is advanced by 90 degrees from the current of the running winding due to the action of the capacitor, reaching the maximum first. value. Two identical pulsed magnetic fields are formed in time and space, so that a rotating magnetic field is generated in the air gap between the stator and the rotor. Under the action of the rotating magnetic field, an induced current is generated in the rotor of the motor, and the current interacts with the rotating magnetic field. The electromagnetic field torque causes the motor to rotate.
Practical application
In practical applications, AC motors are always associated with production machinery to form an electric drive system. Different production machines require different speeds. Even if the same production machine needs different speeds under different operating conditions, it is necessary to adjust the running speed of the drag system, that is, the AC motor speed is generated. AC motors, especially cage induction motors, have no mechanical reversing device, simple structure, reliable operation, convenient maintenance, low cost, and good energy saving effect, and are higher than DC motors in terms of single unit capacity and speed limit; Especially in harsh environments with high dust and explosion hazard, AC motors are more suitable. However, the speed regulation performance of the AC motor is not as good as that of the DC motor. For a long time, the AC motor can only operate at a constant speed. Solving the problem of speed regulation of AC motors has always been the subject of concern and research by electric drag workers. A brief history of development As early as the 1930s, many scholars proposed various AC speed control systems in an attempt to improve the speed regulation performance of AC motors.
