Frequency Converter: Basics and Advantages
Frequency converter is a device widely used for the control of electric motors. Wikipedia defines it most accurately as a device that regulates the rotational speed of an asynchronous motor, thereby reducing the power consumption.
The structure of the converter involves converting incoming alternating voltage into an intermediate direct voltage using a rectifier or inverter bridge. The frequency converter acts to convert single-phase direct current into three-phase alternating current, which is used in asynchronous electric motors. Such devices provide better power factor, lower harmonic distortions, and reduced sensitivity to the sequence of input phases compared to traditional phase-controlled converters.
As the incoming alternating voltage is converted into direct current, the devices can operate with both single-phase and three-phase input voltage. However, when using single-phase power, limitations must be considered, as only part of the rectifier may connect to the load.
Key Aspects of Frequency Converter Operation
The main function of the frequency converter is to regulate the rotational speed of the electric motor. This device is free from contactors that can burn out, and the power factor correction function is built into modern models. In certain cases, the use of single-phase voltage is permitted.
The converter also has a built-in power failure protection system. This includes:
- phase interruption;
- phase recognition;
- protection against excessively high or low voltage.
When using an electric drive connected to a motor coupled with a centrifugal pump, the laws of similarity of pumps apply, which define the relationship between rotational speed, power, and head.
Hydraulic Similarity Laws
These laws state that with a constant size of the pump impeller, if the speed of motion changes:
- The flow rate of water is proportional to the rotational speed of the shaft.
- The hydrostatic head is proportional to the square of the shaft speed.
- The required power is proportional to the cube of the shaft rotational speed.
The advantages of these laws in water supply lie in the fact that the same pump and one working wheel can be used to create different heads and flow rates. At the same time, the pump speed remains at the maximum efficient level, and electrical energy is consumed rationally, in the amount necessary for doing work, without additional costs for valve control.