I. What are the main uses of a 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.
Specifically, frequency converters include, but are not limited to, the following uses:
1. Air conditioning load
Office buildings, shopping malls, some 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 more than 40% of peak electricity consumption in Beijing, Shanghai, and Shenzhen.
Therefore, using variable frequency drives to power the chilled water pumps and fans in air conditioning systems is an excellent energy-saving technology. Currently, many companies across the country specialize in air conditioning energy saving, with variable frequency speed control being their primary technology.
2. Crusher type load
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. Large kilns and calcining furnaces
Previously, most large industrial rotary kilns (converters) in metallurgy, building materials, caustic soda and other industries used DC, commutator motors, slip differential motors, cascade speed regulation or medium frequency unit speed regulation.
Because these speed control methods either have slip rings or are inefficient, in recent years, many organizations have adopted frequency converter control 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 is used for winch-type loads, ensuring stability and reliability. Blast furnace winches in ironworks are the primary equipment for conveying raw materials for ironmaking. They require smooth starting and braking, uniform acceleration and deceleration, and high reliability.
Traditional speed control methods often employ cascade, DC, or rotor series resistance methods, which are inefficient and unreliable. Replacing these methods with AC frequency converters can achieve ideal results.
II. Inverter Fault Diagnosis and Repair
(I) Types of Faults and Causes of Faults
1. Types of faults
Faults can be categorized into power supply faults, internal faults, and load faults.
Power supply failure: Due to a fault in the power grid to which the frequency converter is connected.
Internal fault: A fault in the frequency converter itself.
Load failure: The motor malfunctions, such as phase loss, overload, short circuit, etc.
2. Cause of the malfunction
There are two types of causes for the failure: external and internal.
External causes: Faults caused by external factors to the frequency converter, such as operational errors, incorrect parameter settings, external interference, etc.
Internal causes: Faults caused by internal factors of the frequency converter, such as short circuits, component damage, poor contact of connectors, etc.
(II) Inverter Fault Diagnosis and Repair
Fault diagnosis can be aided by some instruments and frequency converters.
1. Fault Diagnosis Process
① Check the fault symptoms and indications of the frequency converter, as well as the changes in the external environment when the fault occurred.
②Analyze the causes of the malfunction.
③ Open the equipment to inspect the damaged areas and analyze the feasibility of repair and restoration.
④ Analyze the circuit's working principle from the working location of the damaged component to find the cause of the damage.
⑤ Find a suitable replacement component.
⑥ After eliminating all causes of the fault, power on the device and conduct the experiment. When doing this step, all external conditions must be met and the fault must not be allowed to worsen.
