A variable-frequency drive (VFD) is a power control device that uses frequency conversion technology and microelectronics to control an AC motor by changing the frequency of its power supply. A VFD mainly consists of a rectification unit (AC to DC), a filter, an inverter (DC to AC), a braking unit, a drive unit, a detection unit, and a microprocessor unit. The VFD adjusts the voltage and frequency of the output power supply 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, VFDs have many protection functions, such as overcurrent, overvoltage, and overload protection. With the continuous improvement of industrial automation, VFDs have been widely used.
Based on Xichi Electric's years of industry experience, frequency converters can be applied to 32 classic industry sectors, including: air conditioning loads, crusher loads, large kiln/calcining furnace loads, compressor loads, rolling mill loads, converter loads, hoist loads, roller conveyor loads, pump loads, cranes, dump truck loads, wire drawing machine loads, transport vehicle loads, elevator/elevated sightseeing vehicle loads, feeder loads, stacker/reclaimer loads, fan loads, mixer loads, spinning machine loads, and special power supply loads.
Below, we will analyze the specific applications in these industries:
1. Inverter applications in air conditioning loads
Office buildings, shopping malls, supermarkets, and factories all have central air conditioning systems, which consume a significant amount of electricity during the summer peak season. In hot weather, air conditioning accounts for over 40% of peak electricity consumption in Beijing, Shanghai, and Shenzhen. Therefore, using inverters to drive the chilled water pumps and fans in air conditioning systems is an excellent energy-saving technology. Currently, many companies nationwide specialize in air conditioning energy saving, with inverter speed control being their primary technology.
2. Frequency converters are used in crusher-type loads.
Crushers and ball mills are widely used in metallurgy, mining, and building materials industries, and frequency conversion has shown significant effects on these types of loads.
3. Frequency converters are used in large kilns and calcining furnaces.
Previously, most large industrial rotary kilns (converters) in metallurgy, building materials, and caustic soda industries used DC motors, commutator motors, slip-ring motors, cascade speed regulation, or medium-frequency generator speed regulation. However, due to the presence of slip rings or low efficiency of these methods, many units have adopted frequency converter control in recent years, with excellent results.
4. Variable frequency drives are used in compressor-type loads.
Compressors are also widely used loads. Low-pressure compressors are commonly used in various industrial sectors, while high-pressure, large-capacity compressors are widely used in steel (such as oxygen generators), mining, fertilizer, and ethylene industries. Utilizing variable frequency speed control brings advantages such as low starting current, energy savings, and optimized equipment lifespan.
5. Frequency converters are used in rolling mill loads.
In the metallurgical industry, large rolling mills used AC-AC frequency converters in the past, but in recent years they have adopted AC-DC-AC frequency converters. The AC conversion of rolling mills has become a trend, especially in light-load rolling mills. For example, the multi-stand aluminum rolling mill of Ningxia National Aluminum Products Factory uses a general-purpose frequency converter to meet the requirements of low-frequency load start-up, synchronous operation between stands, constant tension control, and simple and reliable operation.
6. Frequency converters are used in winch-type loads.
Variable frequency speed control (VFD) is used for winch-type loads, ensuring stability and reliability. Blast furnace winches in ironworks are the primary equipment for conveying raw materials in ironmaking. They require smooth starting and braking, uniform acceleration and deceleration, and high reliability. Previously, cascade, DC, or rotor resistance speed control methods were commonly used, resulting in low efficiency and poor reliability. Replacing these methods with AC VFDs achieves ideal results.
7. Frequency converters are used in converter-type loads.
For converter-type loads, using AC frequency converters to replace DC units is simple, reliable, and provides stable operation.
8. Frequency converters are used in roller conveyor loads.
Roller conveyor loads are mostly used in the steel and metallurgical industry. Using AC motor frequency conversion control can improve the reliability and stability of the equipment.
9. Variable frequency drives are used in pump loads.
Pumps are a wide range of loads, including water pumps, oil pumps, chemical pumps, mud pumps, sand pumps, etc., ranging from low-pressure small and medium-capacity pumps to high-pressure large-capacity pumps.
Many water pumps used by water companies, chemical pumps in the chemical and fertilizer industries, reciprocating pumps, and mud pumps in the non-ferrous metals industry have adopted variable frequency speed control, which has produced very good results.
10. Variable frequency drives are used in loads such as cranes and dump trucks.
Cranes and dump trucks, among other loads, require high torque and stable operation, frequent forward and reverse rotation, and high reliability. Variable frequency drives (VFDs) can meet these requirements for controlling cranes and dump trucks.
11. Frequency converters are used in loads such as wire drawing machines.
The wire drawing machine for producing steel wire requires high-speed, continuous production. The steel wire strength is 200 kg/mm², and the speed control system requires high precision, high stability, and synchronization.
12. Variable frequency drives are used in transport vehicle loads.
Variable frequency technology (VFD) has proven highly effective in coal mine loading vehicles and steel mill molten steel transport vehicles. It allows for rapid start-up and shutdown, strong overload capacity, and flexible forward and reverse rotation, ensuring a level coal surface and accurate weight (neither overloading nor underloading). It essentially eliminates the need for manual operation, thereby improving raw coal production efficiency and saving energy.
13. Variable frequency drives are used in loads such as elevators, elevated walkways, and sightseeing vehicles.
Because elevators are passenger-carrying vehicles, their drive systems require high reliability, and they frequently accelerate, decelerate, and reverse. Improving the dynamic characteristics and reliability of elevators increases the safety, comfort, and efficiency of passengers. In the past, elevator speed control was mostly DC, but in recent years it has gradually shifted to AC motor variable frequency speed control, a trend observed in both Japan and Germany. Many elevator manufacturers in my country are rushing to equip their elevators with variable frequency speed control. For example, Shanghai Mitsubishi, Guangzhou Hitachi, Qingdao Fuji, and Tianjin Otis all use AC variable frequency speed control. Many previously manufactured elevators have also undergone variable frequency retrofitting.
14. Frequency converters are used in feeder-type loads.
In industries such as metallurgy, power, coal, and chemicals, there are numerous feeders. Whether it's a disc feeder or a vibrating feeder, the effects of frequency conversion speed regulation are very significant. The disc feeder on the sulfuric acid production line of Jilin Chemical Company's dye plant originally used slip-ring speed regulation, resulting in low-frequency torque, frequent malfunctions, and frequent jamming. After adopting frequency conversion speed regulation, because it's an asynchronous machine, it boasts high reliability and energy savings. More importantly, the closed-loop system with the temperature transmitter ensures accurate material delivery, preventing excessive oxidant delivery and overheating that could cause accidents, thus ensuring orderly production.
15. Variable frequency drives (VFDs) are used in stacker-reclaimer type loads.
Stacker-reclaimers are the main equipment for material stacking and reclaiming in coal yards, docks, and mines. Their main functions are stacking and reclaiming materials. They achieve automatic stacking and semi-automatic reclaiming, improving equipment reliability. The equipment operates smoothly without impact or shaking. The reclaiming process uses a rotation speed regulation according to the 1/cosφ law, which improves the efficiency of bucket wheel rotation and the uniformity of coal conveying by belt conveyor, making them very popular with workers.
16. Variable frequency drives are used in fan-type loads.
Fan-type loads are widely used equipment in industries such as steel mills, power plants, non-ferrous metals, mining, chemicals, textiles, chemical fibers, cement, and papermaking. Most systems adjust airflow by regulating the opening of dampers, which wastes a significant amount of electricity. Using variable frequency speed control (VFDs) can save energy, reduce mechanical wear, and extend equipment lifespan.
17. Variable frequency drives are used in mixer-type loads.
There are many mixers in the chemical and pharmaceutical industries. Using frequency conversion speed regulation instead of other speed regulation methods has many advantages.
18. Frequency converters are used in spinning machine-type loads.
The spinning process is complex, involving multiple stations and requiring tension control, and in some cases, position control. Variable frequency speed regulation (VFD) provides excellent performance in this area.
19. Frequency converters are used in special power supply loads.
Many power supplies, such as experimental power supplies and aircraft traction power supplies (400Hz), can be supplied by frequency converters. The advantages are low investment, quick results, small size, and simple operation.
20. Frequency converters are used in papermaking machine loads.
In my country's papermaking industry, paper machines requiring high precision often employ SCR DC speed control, while some use slip ring motors or commutator motors. However, the presence of slip rings and carbon brushes results in low reliability and precision, leading to outdated papermaking machinery with typical speeds around 200 m/min, far below the 2000 m/min of foreign machines. Therefore, the adoption of frequency conversion in papermaking machinery is an inevitable trend.
21. Variable frequency drives are used in loads such as washing and ironing equipment.
Larger hotels typically use mechanical speed control or variable speed control for their washing machines and ironing equipment, which only offer one or a few speeds and are not ideal for fabrics that require repeated washing and ironing. Adopting variable frequency speed control significantly improves the efficiency of washing machines.
22. Frequency converters are used in loads such as musical fountains.
The musical fountain, which attracts many tourists, controls the height and volume of water using frequency conversion.
23. Frequency converters are used in mechanical loads such as grinding machines.
Grinding machine spindles rotate at very high speeds, requiring high-frequency power supplies, such as 200Hz, 400Hz, or even 800Hz. Previously, spindle motors were mostly powered by medium-frequency generator sets. These generator sets were large, inefficient, noisy, and had poor precision.
24. Frequency converters are used in cigarette machine-type loads.
In the past, the cigarette rolling machines imported by the cigarette industry, whether Moline 8 or Moline 0, were not continuously variable speed (CVT) machines. Therefore, the main challenge in the cigarette industry was to solve the problems of CVT and reliability. The technology was simple, the frequency converters were easy to use, and the results were significant.
25. Frequency converters are used in vibration-damping and noise-reducing loads.
Many loads, such as large air compressors and medium-frequency units, generate significant noise and vibration. Variable frequency technology can reduce vibration and noise levels, bringing them within acceptable limits.
26. Frequency converters are used in dyeing and printing machine loads.
Most dyeing and printing machinery consists of multi-unit equipment. The process requires each unit to operate synchronously at the same linear speed and maintain constant tension; otherwise, quality problems such as fabric breakage, tangling, uneven color, insufficient color saturation, and excessive shrinkage will occur. Previously, dyeing and printing machinery, whether using a shared power supply or a separate power supply, employed DC speed control systems.
Due to the inherent drawbacks of DC power, the printing and dyeing industry has gradually adopted AC frequency conversion technology. Rotary screen printing machines consist of a fabric feeding unit, a printing unit, a drying oven guide belt unit, and a fabric unloading unit, making them one of the most complex speed control systems in printing and dyeing. They employ frequency conversion speed regulation to form a speed chain control, offering good synchronization performance, high precision, and high reliability.
27. Frequency converters are used in injection molding machine loads.
Injection molding machines are key pieces of equipment in plastic processing and molding, and are numerous and consume a lot of electricity. Past energy-saving methods often involved converting delta (△) type speed control to Y (Y) type speed control, but the effect was generally limited. Using variable frequency speed control (VFD) without changing the original structure of the injection molding machine, by controlling the pressure or flow rate of several processes of the oil pump (such as mold clamping, mold closing, injection, holding pressure, demolding, and ejection), can save 20% to 52% of electricity. This effectively replaces the previous proportional valve throttling speed control method, significantly reducing energy consumption. Many injection molding plants in the Pearl River Delta have implemented VFD retrofits. When retrofitting injection molding machines, attention should be paid to accelerating mold closing, otherwise output will decrease. Also, be aware of harmonic interference at the input and output ends.
28. Variable frequency drives are used in environmental protection loads such as wastewater treatment.
Environmental protection is receiving increasing attention because it relates to the environment upon which humanity depends for survival. As a result, clean energy and green cities have emerged. Variable frequency drives (VFDs) can be used for three types of environmentally friendly loads: industrial wastewater treatment, waste-to-energy plants, and industrial smoke, exhaust, and dust control.
29. Variable frequency drives (VFDs) are used in production lines in industries such as glass, ceramics, pharmaceuticals, beverages, food, and packaging to handle loads.
Variable frequency speed control has been successfully implemented in production lines for glass, ceramics, pharmaceuticals, beverages, food, and packaging.
30. Variable frequency drives (VFDs) are used in loads on offshore oil production platforms.
For oil drilling, AC motor frequency conversion speed regulation is far superior to DC speed regulation, especially in windy, sandy, and dusty environments, because AC motors are more reliable. Offshore oil drilling platforms require frequency conversion speed regulation devices.
31. Variable frequency drives are used in submersible electric pump loads.
Submersible electric pump (SAP) is a method of oilfield production. SSPs typically operate in wells below 1800m and mostly use full-pressure start-up at industrial frequency and constant-speed operation, which has the following drawbacks:
☆ Excessive starting current will damage the motor insulation.
☆ This generates impact torque, damaging the pump structure;
☆A sudden surge in pump suction can easily draw in sand, causing the pump to jam. Furthermore, the lack of a pressure stabilization system and significant fluctuations in the downhole fluid level can lead to unstable voltage and current, causing over-excitation and under-excitation of the submersible motor, resulting in malfunctions.
32. Frequency converters are used in polyester chip loads.
Polyester chips are one of the main products of the petrochemical industry. Due to the high precision of variable frequency speed control, its ease of control across multiple control points, stable and reliable operation, and the ability to improve product quality, variable frequency speed control brings significant benefits to enterprises. Many companies adopt variable frequency speed control technology when expanding their operations.
