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 the power supply to the motor. With the continuous improvement of industrial automation, VFDs have found widespread application.
1. Air conditioning load category:
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. 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. Load of 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. Compressor-type loads:
Compressors are also a widely used type of load. 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. The use of variable frequency speed control brings advantages such as low starting current, energy saving, and optimized equipment lifespan.
5. 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. Hoist-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. Converter-type loads:
For converter-type loads, using AC frequency converters to replace DC units is simple, reliable, and provides stable operation.
8. 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. Pump loads:
Pumps are widely used and numerous, including water pumps, oil pumps, chemical pumps, slurry pumps, sand pumps, etc., ranging from low-pressure small-to-medium capacity pumps to high-pressure large-capacity pumps. Many water pumps used by water companies, chemical pumps and reciprocating pumps used in the chemical and fertilizer industries, and slurry pumps used in the non-ferrous metals industry have adopted variable frequency speed control, all of which have produced excellent results.
10. Loads from 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. Loads for 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. Load of transport vehicles:
Variable frequency technology 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. Load capacity of elevators, elevated sightseeing vehicles, etc.
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. 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. 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. 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.
