AC motor seed control by terminal voltage refers to the technology of speed regulation by changing the stator voltage of induction motor.This is a kind of speed regulation by regulating slip rate.Adjusting the speed of a motor is to change its electromagnetic torque. Wheninduction motor When the stator and rotor circuit parameters are constant, the electromagnetic torque of the induction motor is proportional to the square of the stator voltage at a certain speed.Adjusting the stator voltage will change the electromagnetic torque, which can change the motor speed under a certain load torque.
Chinese name
AC voltage regulation and speed regulation
Foreign name
AC motor seed control by terminal voltage
Discipline
power engineering
Field
energy
Scope
Power system
Role
Speed regulation by changing stator voltage of induction motor
AC motor seed control by terminal voltageVoltageRealize speed regulation technology.This is a kind of speed regulation by regulating slip rate.Adjusting the speed of a motor is to change its electromagnetic torque. Wheninduction motor When the stator and rotor circuit parameters are constant, the electromagnetic torque of the induction motor is proportional to the square of the stator voltage at a certain speed.Adjusting the stator voltage will change the electromagnetic torque, which can change the motor speed under a certain load torque.When the stator voltage decreases, the speed of the motor will decrease, otherwise, the speed of the motor will increase[1]。
AC speed regulation mode
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According to the principle of voltage regulation and speed regulation, it can not only increase the stator voltage for speed regulation, but also reduce the voltage for speed regulation.However, as the increase of voltage will saturate the magnetic circuit of the motor, resulting in a sharp increase of no-load current and a decrease of load capacity, in fact, only the voltage can be reduced for speed regulation.The speed decreases due to the voltage drop, and the rotor circuitInduced electromotive forceWill increase, and the rotor current will also increase, which may cause overcurrent.If the rotor resistance is large, it can limit the rotor current and improve the power factor of the motor. Therefore, the special structure that can prevent high current at low speed must be adoptedCage induction motor, or adoptWound rotor induction motor。With the increase of rotor circuit resistance, a wide speed regulation range can be obtained under the load of constant speed. However, because the mechanical characteristics of induction motor are too soft to meet the requirements of static error rate, speed negative feedback shall be adoptedClosed loop control systemTo achieve smooth and wide range speed regulation[1]。
Effect of AC voltage regulation and speed regulation
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The effect of AC voltage regulation and speed regulation is obtained by increasing the loss on the rotor, so it is also called energy consuming speed regulation mode.When the load is fan and water pump, the load will also become smaller when the speed decreases, which is beneficial to reduce the heating of the motor. At the same time, it has a wide speed regulation range, so this speed regulation is more appropriate for the load of fan and water pump that is square with the speed.For constant torque load, it is better to adopt pole changing voltage regulating speed regulation[2]。
Control of AC voltage regulation and speed regulation system
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AC voltage regulation and speed regulation system can be controlled by autotransformer or saturated reactor, or controlled by thyristor.As the transformer or reactor is relatively bulky, with large loss, inconvenient for automatic regulation and slow dynamic response (above 0.1s), it has been replaced by thyristor AC voltage regulator.The typical main circuit of thyristor AC voltage regulator is listed in Table 1 (the basic circuit in Table 1 only draws the stator circuit). The first three circuits are symmetrical voltage regulating circuits, and the last three are asymmetrical circuits. Their characteristics and applications are also listed in Table 1.In order to realize reversible operation, electromagnetic contactor can be used to control the forward and reverse rotation. Although the device is simple, it is equipped with contact switching, and has poor rapidity and reliability. It is only applicable to small and medium capacity motors with infrequent forward and reverse rotation.If two groups of thyristor elements are connected in reverse phase sequence to achieve contactless switching, it can be applied to systems requiring frequent positive and negative rotation and fast braking.Thyristor AC voltage regulating circuit has the advantages of compact structure, portability, low cost, fast dynamic response, etc. It has been widely used in occasions with medium and small capacity and low requirements for performance indicators, such as low-speed elevators, lifting appliances, fans, pumps and other loads, and can also be used as a soft starter of induction motors without current impact[3]。
