A frequency converter (FC) is an electrical device used to control asynchronous motors. With its help, you can smoothly change the torque and rotation speed of the electric motor spindle. Due to the smooth regulation of the characteristics of the electric motor, its service life increases, the service interval is extended, and power consumption is reduced.
PEs regulate the rotation speed of the shafts of asynchronous motors according to one of two principles:
- scalar control . It is carried out according to a linear scheme, when the frequency and current are proportional to each other;
- vector control, which allows you to achieve a given torque at any spindle speed. Smooth adjustment of the rotation speed reduces the load on the mechanisms and increases the accuracy of their movement.
Areas of application
At Emplekt you can buy a frequency converter for controlling motors of systems such as:
- ventilation equipment. Due to the ability to regulate the ventilation performance, the efficiency of the system increases, the noise level during its operation decreases;
- heating systems. The ability to automate the operation of exhaust and injection fans of boiler equipment makes it possible to ensure complete combustion of energy carriers in the boiler. This increases the thermal power of the boiler room, reduces fuel costs;
- electric motors of machine tools. The use of motors with adjustable torque in machines makes it possible to avoid the use of gearboxes. This reduces the cost of the machine, simplifies its design, and increases reliability;
- lifting mechanisms - span, cantilever, portal cranes, winches, hoists, mounting blocks. In equipment for this purpose, the engine operates with overloads, in frequent starts and stops. The use of a frequency converter in its control system makes it possible to provide maximum torque when starting to lift the load. Due to this, the load moves more smoothly, without swinging on slings and hanging chains. This eliminates the risk of cargo damage and personnel injury when working with lifting mechanisms;
- belt, plate, scraper, overhead conveyors, conveyor belts, rolling mills. Due to the smooth movement of conveyor assembly equipment, the possibility of damage to workpieces and semi-finished products is eliminated. This increases the quality of the finished product and eliminates the appearance of defects. In addition, the service life of conveyor mechanisms increases, industrial emergencies are eliminated;
- pumping equipment in water supply and wastewater systems. The inclusion of frequency converters in the control circuit of pump electric motors allows you to reduce the number of valves, taps, gate valves on the water supply line, and extend the period of its trouble-free operation.
The operating principle of a frequency converter
The electric current, when passing through the state of emergency, undergoes the following transformations:
- in the rectifier, the alternating current turns into direct current when passing through the diode bridge;
- in the voltage filter, capacitors smooth out the ripples of the direct current current;
- the current with a filtered carrier frequency of the original variable frequency is converted into an alternating pulse current with a rectangular voltage diagram;
- the output voltage is integrated, as a result of which its graph takes the form of a sine wave. A pure sine wave is necessary to reduce the load on the electric motor being put into operation.
The inclusion of a frequency generator in the control circuit of the electric motor can be carried out according to two schemes:
- star. The outputs of the motor windings are connected to a common bus;
- triangle when the windings are connected in series.
The advantage of the “star” circuit is the ability to smoothly adjust the speed. But this prevents the electric power plant from reaching full power. When connected using the “triangle” method, the electric motor operates at full power. The disadvantage of this method is large starting currents.
When choosing a method for connecting the emergency control, you need to take into account the power developed by the motor in different operating modes. Control and control devices must have a power reserve. Otherwise, prolonged operation of the system under overload can lead to failure of its components.
