It has always been said that economical frequency converters can save electricity, and more people will accept it. Does it really save electricity?

When using frequency converters, we often have the following misunderstandings:

Misunderstanding: Using economical frequency converters can save electricity

Some claim that economical frequency converters are a power-saving control product, giving people the impression that as long as economical frequency converters are used, electricity can be saved.

In fact, economical frequency converters can save electricity because they can accelerate the motor. If economical frequency converters are power-saving control products, then all speed control devices can also be said to be power-saving control products. The efficiency and power factor of economical frequency converters are only slightly higher than other speed control devices.

Can economical frequency converters save electricity? This depends on the speed control characteristics of its load.

For loads such as centrifugal fans and centrifugal pumps, torque is proportional to the square of the speed, and power is proportional to the cube of the speed. It is important to understand that as long as the valve is used to control the flow and is not working at full load, it can be operated at variable speed.

When the speed drops to 80%, the power is only 51.2%. From these, it can be seen that the power saving effect of the application of economical frequency converters in this type of load is very obvious. For Roots blower loads, the torque is independent of the speed, that is, constant torque load. If the air volume is adjusted by releasing excess air volume with a bleed valve, power saving can also be achieved. When the speed drops to 80%, the power is 80%. Compared with the application in centrifugal fans and centrifugal pumps, the energy saving effect is much smaller. For constant power loads, the power is independent of speed. The constant power load of the cement plant, such as the batching belt scale, slows down the belt speed when the material layer is thicker under certain set flow conditions; when the material layer is thinner, the belt speed increases. The application of economical frequency converters in this type of load does not save power.

Compared with the DC speed control system, the DC motor has higher efficiency and power factor than the AC motor. The efficiency of the digital DC speed regulator is comparable to that of the economical frequency converter, and even the efficiency of the digital DC speed regulator is slightly higher than that of the economical frequency converter.

In this way, we can conclude that the claim that using AC asynchronous motors and economical frequency converters is more energy-efficient than using DC motors and DC speed regulators is not true in theory and practice.