Function and application of frequency converters
The function of frequency converter
1. Variable frequency energy saving
The energy-saving effect of frequency converters is mainly reflected in the application of fans and pumps. After adopting frequency conversion speed regulation for fan and pump loads, the power saving rate is 20% to 60%. This is because the actual power consumption of fan and pump loads is basically proportional to the cube of the speed. When the average flow rate required by the user is small, using frequency conversion speed regulation to reduce the speed of fans and pumps results in a very significant energy saving effect. Traditional fans and pumps use baffles and valves for flow regulation, with the motor speed remaining basically constant, resulting in little change in power consumption. Statistics show that fan and pump motors account for 31% of the national electricity consumption and 50% of industrial electricity consumption. Using frequency conversion speed regulation devices on such loads is of great significance. Currently, successful applications include constant pressure water supply, various types of fans, central air conditioning, and hydraulic pumps.
2. Application in automation systems
Because frequency converters have built-in 32-bit or 16-bit microprocessors, they possess various arithmetic logic operations and intelligent control functions, with an output frequency accuracy of 0.1%~0.01%, and are equipped with comprehensive detection and protection mechanisms. Therefore, they are widely used in automation systems. Examples include: winding, stretching, metering, and guiding in the chemical fiber industry; flat glass annealing furnaces, glass kiln stirring, edge-drawing machines, and bottle-making machines in the glass industry; automatic feeding and batching systems for electric arc furnaces; and intelligent control of elevators. Frequency converters are also used in CNC machine tool control, automobile production lines, papermaking, and elevators to improve process efficiency and product quality.
3. Applications in improving technological level and product quality
Variable frequency drives (VFDs) are also widely used in the control of various mechanical equipment such as conveyors, cranes, extruders, and machine tools. They can improve process levels and product quality, reduce equipment impact and noise, and extend equipment lifespan. Adopting VFD speed control simplifies mechanical systems, making operation and control more convenient. In some cases, it can even alter existing process specifications, thereby improving the overall functionality of the equipment. For example, in textiles and many other industries, the temperature inside a setting machine is regulated by changing the amount of hot air supplied. Hot air is typically supplied using a circulating fan, and since the fan speed is constant, the amount of hot air supplied can only be adjusted using a damper. If the damper malfunctions or is improperly adjusted, the setting machine will become uncontrollable, affecting the quality of the finished product. High-speed startup of the circulating fan causes severe wear between the drive belt and bearings, making the drive belt a consumable item. With VFD speed control, temperature regulation can be achieved automatically by adjusting the fan speed, solving the product quality problem. Furthermore, VFDs can easily enable low-frequency, low-speed fan startup, reducing wear between the drive belt and bearings, extending equipment lifespan, and saving up to 40% in energy.
4. Achieve soft start for the motor
Hard starting of a motor not only severely impacts the power grid but also places excessive demands on its capacity. The large current and vibration generated during startup cause significant damage to baffles and valves, severely shortening the lifespan of equipment and pipelines. However, by using a frequency converter, its soft-start function allows the starting current to change from zero, with the maximum value never exceeding the rated current. This reduces the impact on the power grid and the demand on power supply capacity, extends the lifespan of equipment and valves, and also saves on equipment maintenance costs.
Working principle of frequency converter
A frequency converter mainly consists of rectification (AC to DC), filtering, inversion (DC to AC), braking unit, drive unit, detection unit, and microprocessor unit. The frequency converter adjusts the output voltage and frequency by switching its internal IGBTs, providing the required power voltage according to the actual needs of the motor, thereby achieving energy saving and speed regulation. In addition, the frequency converter has many protection functions, such as overcurrent, overvoltage, and overload protection. With the continuous improvement of industrial automation, frequency converters have been widely used.
The main circuit is the power conversion section that provides voltage and frequency adjustable power to the asynchronous motor. The main circuit of a frequency converter can be broadly divided into two categories: voltage-source converters, which convert DC power from a voltage source to AC power, and current-source converters, which convert DC power from a current source to AC power, and inductors, which filter the DC circuit. It consists of three parts: a rectifier that converts the mains frequency power to DC power, and a smoothing circuit that absorbs voltage ripples generated in the converter and inverter.
