Three-phase asynchronous AC motor speed control method
Third, cascade speed control method
Cascade speed regulation refers to the winding motor in the rotor loop into the adjustable additional potential to change the motor slip, to speed control purposes. Most of the slip power is absorbed by the additional potential in series, and the additional device is used to return the absorbed slip power to the grid or to convert the energy. According to the slip power absorption and utilization, cascade speed can be divided into motor cascade speed, mechanical cascade speed control and thyristor cascade speed form, the use of thyristor cascade speed, which features:
Can be transferred in the speed of the process of slip loss back to the grid or production machinery, the higher efficiency;
Device capacity and speed range is proportional to the investment province, for the speed range of 70% -90% of the rated speed of production machinery;
Speed ??control device failure can switch to full speed operation, to avoid shutdown;
Thyristor cascade speed power factor is low, the greater the impact of harmonics.
This method is suitable for use in wind turbines, water pumps and rolling mills, mine hoists, extruders.
Second, the frequency control method
Frequency control is to change the frequency of the motor stator power supply, thus changing its synchronous speed control method. Frequency converter system can be divided into AC - DC - AC inverter and AC - AC inverter two categories, most of the current domestic use - cross - frequency converter. Its characteristics:
High efficiency, no additional loss during the speed control process;
Wide range of applications, can be used for cage type asynchronous motor;
Speed ??range, the characteristics of hard, high precision;
Complex technology, high cost, maintenance and repair difficult.
This method is suitable for applications requiring high precision and better speed performance.
First, variable pole alignment speed method
This method is to change the way to change the stator winding red way to change the cage motor stator pole to achieve the purpose of speed, the characteristics are as follows:
With a hard mechanical properties, good stability;
No slip loss, high efficiency;
Wiring is simple, easy to control, low prices;
A level of speed, large difference, can not get smooth speed;
Can be used with the regulator speed, electromagnetic slip clutch used to obtain a more efficient smooth speed control characteristics.
This method is suitable for production machinery that does not need stepless speed regulation, such as metal cutting machine tools, lifts, lifting equipment, fans, pumps and so on.
