Method of Frequency Control for Alternating Current Electric Motors
One of the effective methods of controlling the operating modes of alternating current electric motors is frequency control. Instead of supplying standard alternating voltage from the network directly to the motor, the electrical energy first undergoes a conversion procedure. During this process, several key parameters change, namely:
- amplitude of voltage and current;
- frequency of voltage and current;
- phase angle difference;
- magnetic flux vector in the rotor and stator windings.
This conversion process is implemented using a special device commonly referred to as a frequency converter.
Structure of the Frequency Converter
The main structural blocks of the frequency converter are the rectifier and inverter blocks. In the rectifier block, standard alternating voltage is converted into direct voltage. Then in the inverter block, this direct voltage is converted back into alternating voltage with specified and adjustable parameters.
The operation of both blocks is regulated by auxiliary circuits and elements. Control information can come from various external devices, such as sensors, control panels, or even from other frequency converters. In addition, the parameters of the output voltage can be adjusted by internal blocks, such as a built-in clock, microprocessor, and protection systems.
Monitoring and Controlling Output Parameters
This allows for monitoring and regulating the output parameters both in automatic and manual modes, depending on the requirements of the specific situation. It is also possible to conduct automatic accounting and store changes in the characteristics of the output voltage.
The output voltage from the converter is supplied to the windings of the electric motor, allowing for the adjustment of how the motor operates, including the speed of the shaft and the torque.
Advantages of Frequency Control
- reduction of electricity costs, and in some cases – energy recovery;
- control of many parameters of the technological process, such as pressure, humidity, and temperature;
- reduction of the likelihood of accidents and breakdowns;
- increased accuracy of mechanism operation;
- simplification of the management of the entire system;
- reduction of repair and maintenance costs;
- shortening downtime.
The inclusion of frequency conversion significantly reduces the mutual influence between the power supply network and the electrical drive circuits, thereby decreasing the risk of malfunctions in the operation of devices.
Automation and Safety
Additionally, the use of frequency converters allows for achieving a high level of automation, reducing the impact of the human factor on technological equipment. This decreases personnel costs and can completely eliminate the need for human presence in hazardous technological areas.
Due to the advantages mentioned, frequency control is becoming increasingly popular and accessible for large enterprises and private individuals.