The correct selection of the inverter is very important for the normal operation of the control system. When selecting a Inverter, it is important to fully understand the load characteristics of the Frequency Inverter driven. In practice, production machinery is often divided into three types: constant power load and fan, constant torque load, pump load.
1. Constant torque load
The load torque TL is independent of the speed n, at which the TL is always constant or basically constant. For example, mixers, conveyorbelts, extruders and other frictional loads, as well as cranes, hoists and other energy loads are constant torque loads. When the inverter drags a load of constant torque, the torque at low speed is large enough and has sufficient overload capacity. If you need to operate at low speeds, you should consider the thermal capacity of standard asynchronous motors to avoid excessive temperature rise of the motor.
2. Power load Machine spindles and paper machines, rolling mills, plastic film production lines in the roll-extracting machine, rolling machine and other requirements of the torque, generally inversely proportional to the speed, this is called constant power load. The constant power nature of the load should be in terms of a certain range of speed changes. When the speed is very low, the TL cannot always increase due to mechanical strength, and it is not possible to change to the constant torque at low speeds. The constant power area of the load and the constant torque zone have a great influence on the choice of transmission scheme. The maximum allowable output torque is unchanged when the motor is constantmagnetic flux, which belongs to the constant torque speed, while at the weak magnetic speed, the maximum allowable output torque is inversely proportional to the speed, which belongs to the constant power speed regulation. If the range of constant torque and constant power speed of the motor is consistent with the constant torque and constant power range of the load, that is, in the case of so-called "matching", the capacity of the motor and the capacity of the inverter are minimal.
3. Square turn load In various fans, pumps, oil pumps, with the rotation of the impeller, air or liquid in a certain speed range produced resistance is roughly proportional to the speed of 2 squares. As the speed decreases, the torque decreases by 2 times of the speed. The power required for this load is proportional to the speed of 3 times.
When the required air volume, flow reduction, the use of inverter through the speed control way to adjust the air volume, flow, can greatly save electricity.
Because the power required for high-speed drives increases too fast with the speed, in full proportional to the three aspects of the speed, it is not usually necessary to overload the fans and pumps. Proper selection is critical to the proper operation of the control system. The load characteristics of the drive driven must be fully understood when selecting the drive. In practice, production machinery is often divided into three types: constant torque load, constant power load and fan, water pump load.