There are many types of production machinery, different performance and process requirements, and different torque characteristics. Therefore, before applying the inverter, first understand the nature of the load on the motor, that is, the load characteristics, and then select the inverter and the motor. There are three types of loads: constant torque load, fan pump type load and constant power load. Different types of inverters should be selected for different load types.
(1) Constant torque load Constant torque load is divided into friction type load and position energy type load.
The starting torque of the friction type load generally requires about 150% of the rated torque, and the braking torque generally requires about 100% of the rated torque, so the frequency converter should choose to have constant torque characteristics, and both the starting and braking torques Larger inverter with large overload capacity and overload time.
The position energy can generally achieve a large starting torque and energy feedback function, which can realize the forward and reverse rotation quickly. The inverter should select the inverter with four quadrant operation capability.
(2), fan pump type load negative pump type wind load is a typical square torque load, the load is very small at low speed, and proportional to the square of the speed, the combination of general-purpose inverter and standard motor is most suitable. This type of load does not require high performance of the inverter, only economical and reliable, so choose a frequency converter with U/f=const control mode. If the inverter output frequency is increased above the power frequency, the power increases sharply, sometimes exceeding the capacity of the motor inverter, causing the motor to overheat or fail to operate. Therefore, for this type of load torque, do not easily increase the frequency above the power frequency.
(3) Constant power load Constant power load refers to the load whose torque is inversely proportional to the speed, but the power remains constant, such as coiler and machine tool. When using the inverter with constant power characteristics, pay attention to the problem: the output voltage of the inverter is fixed value control within the frequency range above the power frequency, so the torque generated by the motor is constant power, using standard motor and universal frequency conversion. There is no problem with the combination of the devices. In the frequency range below the power frequency, U/f constant value control, the torque generated by the motor and the load torque are opposite, and the combination of the standard motor and the general frequency converter is difficult to adapt, so it is specially designed.
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