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Learn how to use the power supply correctly for the normal operation of mechanical equipment and power systems is very important.
First of all, in the selection of frequency converter, in accordance with the type of mechanical equipment, load characteristics and power, static speed accuracy and the requirements of the use of the environment, and then decide to choose what kind of control and how large capacity of the frequency converter is most appropriate.
The so-called rational use is to meet the actual process and production requirements of mechanical equipment and the use of occasions under the premise of realizing the best cost-effective application of variable frequency converter.
I.According to the load characteristics and power selection of appropriate control
With the rapid development of science and technology, the market now sells more and more types of frequency converter, and increasingly powerful, so the performance of the frequency converter has gradually become the determining factor of the advantages and disadvantages of the speed control performance, the use of frequency converter with a large capacity and the choice of what kind of control is also very important.
II.The load torque characteristics of mechanical equipment
People in practice often production machinery according to the different load torque characteristics, divided into three major types: constant torque load, constant power load and fluid load.
1、Constant torque load
In this type of load, the load torque TL is independent of the rotational speed n, any speed TL always remain constant or basically constant, the load power with the load speed increases linearly.
Friction loads such as conveyor belts, extruders and feeding mechanisms of mechanical equipment, as well as gravity loads such as hoists and elevators, are all constant torque loads.
When the variable frequency converter drags loads of constant torque nature, the output torque at low speed should be large enough and have enough overload capacity.
If it is necessary to run at low speed for a long period of time at a steady speed, the heat dissipation capacity of the standard cage-type asynchronous motor should be considered to avoid too high a temperature rise of the motor.
2、Constant power load
This type of load is characterized by demand torque TL and rotational speed n roughly inversely proportional to the product that is the power is approximately constant.
Metal cutting machine tool spindle and rolling mill, paper machine, film production line in the winding machine, unwinding machine, etc., all belong to the constant power load.
The constant power nature of the load is supposed to be with respect to a certain range of speed variations.
When the speed is very low, by the mechanical strength of the limitations, TL can not be increased indefinitely, at low speeds into a constant torque nature.
The constant power and constant torque zones of the load have a great influence on the selection of the drive scheme.
When the motor is in constant flux speed regulation, the maximum allowable output torque is unchanged, which belongs to constant torque speed regulation; while in weak magnetic speed regulation, the maximum allowable output torque is inversely proportional to the speed, which belongs to constant power speed regulation.
If the range of constant torque and constant power speed regulation of the motor is consistent with the range of constant torque and constant power of the load, i.e. the so-called “matching” situation, the capacity of the motor and the capacity of the frequency converter are minimized.
3、Fluid load
The torque of this type of load is proportional to the quadratic of the rotational speed, and the power is proportional to the cubic of the rotational speed.
Various fans, pumps and oil pumps are typical fluid loads. Fluid loads through the frequency converter speed control to adjust the air volume, flow, can greatly save power.
Because of the fluid loads at high speeds when the demand for power grows too fast, and the load speed of the third power is proportional to the rotational speed of the load, so this type of load should not be made to run over the frequency.
