Several Speed Regulation Methods forThree-phase Asynchronous Motor
Several Speed Regulation Methods for Three-phase Asynchronous Motor
1. Pole-changing logarithmic speed regulation method
This speed regulation method is to change the stator pole pairs of the cage motor by changing the red connection method of the stator winding to achieve the purpose of speed regulation. The characteristics are as follows:
It has harder mechanical properties and good stability;
No slip loss, high efficiency;
Simple wiring, convenient control, low price;
Step-by-step speed regulation, with a large difference in level, and cannot obtain smooth speed regulation;
It can be used in conjunction with pressure and speed regulation and electromagnetic slip clutch to obtain smooth speed regulation characteristics with higher efficiency.
2. Frequency conversion speed regulation method
Frequency conversion speed regulation is a speed regulation method that changes the frequency of the motor's stator power supply, thereby changing its synchronous speed. The main equipment of the variable frequency speed regulation system is the inverter that provides variable frequency power. The inverter can be divided into two categories: AC-DC-AC inverter and AC-AC inverter. At present, most of the domestic AC-DC-AC inverters are used. Its characteristics:
High efficiency, no additional loss during speed regulation;
Wide range of applications, can be used for cage asynchronous motors;
Large speed range, hard characteristics and high precision;
The technology is complicated, the cost is high, and the maintenance and repair are difficult.
This method is suitable for occasions requiring high precision and good speed regulation performance.
3.Winding motor rotor series resistance speed regulation method
The rotor of the wound asynchronous motor is connected in series with additional resistance, which increases the slip rate of the motor, and the motor runs at a lower speed. The larger the resistance connected in series, the lower the speed of the motor. This method has simple equipment and convenient control, but the slip power is consumed in the resistance in the form of heat. It is a step-by-step speed regulation with softer mechanical characteristics.
4.The stator voltage and speed regulation method
When the stator voltage of the motor is changed, a set of different mechanical characteristic curves can be obtained to obtain different speeds. Since the torque of the motor is proportional to the square of the voltage, the maximum torque drops a lot, and its speed regulation range is small, making it difficult to apply general cage motors. In order to expand the range of speed regulation, a cage motor with a large rotor resistance value should be used for voltage regulation and speed regulation, such as a torque motor for voltage regulation and speed regulation, or a frequency sensitive resistor in series with a wound motor. In order to expand the range of stable operation, feedback control should be used when the speed is above 2:1 to achieve the purpose of automatically adjusting the speed.
The main device of voltage regulation and speed regulation is a power supply that can provide voltage changes. At present, the commonly used voltage regulation methods include series saturable reactor, autotransformer, and thyristor voltage regulation. The thyristor voltage regulation method is the best. The characteristics of voltage regulation and speed regulation: simple voltage regulation and speed regulation circuit, easy to realize automatic control;
In the process of voltage regulation, the slip power is consumed in the rotor resistance in the form of heat, and the efficiency is low.
Pressure regulation and speed regulation are generally applicable to production machinery below 100KW.