Principle of UC-VFD Series

The variable frequency drive (VFD) air compressor takes the user-end system pressure as the control object, constitutes the closed-loop control system with frequency converter, pressure sensor, and VFD motor. The VFD working pressure may set directly through the operation panel, the sensor detects the system pressure and converts into 4 ~ 20mA current signal to feedback to the controller. The controller compares the PID calculation with the working pressure under system frequency conversion setting, thus controlling the output frequency of the converter, and changes the speed of the motor to ensure the accurate matching between the output and the air demand of the user to accomplish the goal of constant pressure air supply and energy saving.

Product Features

·       Adopt international brand variable frequency drive for the VFD motor;

·       Advanced full frequency conversion structure and system;

·       Advanced vector control technology;

·       Frequency conversion soft start, less impact on the power grid, more reliable operation, longer life;

·       High-efficiency energy-saving reduces about 30% ~ 50% energy consumption;

·       Constant pressure air supply, pressure fluctuation can be stable within ±0.01Mpa, effectively improve the quality of air source;

·       The noise level is lower, about 3 to 7 decibels lower than that of a conventional compressor.

High-Efficiency Energy-Saving Air End

·       United air end highly recognized by the air compression industry with its sophisticated design and precision manufacturing.

·       With adopting large diameter and the balanced length-diameter ratio of the screw rotors, the optimized design based on the new 4th generation rotor moulded line subjected to higher-efficiency, so that the contact surface, contact line, leak triangle and hydrodynamic characteristics of rotors could reach the optimal performance, further improved the volume efficiency. This screw rotor then has high adiabatic efficiency and low power consumption.

·       By using imported large-sized heavy-duty bearing and unique bearing layout, at the same time of ensuring the bearing rigidity, the bearing capacity is much improved, service life lengthened, and its high reliability could keep even under the extreme condition.

·       The lip type shaft seal of the spiral groove fits with the shaft sleeve made of high-grade bearing steel, ensuring the wear resistance of the shaft seal and shaft sleeve. The shaft seal has a pumping function with high reliability and leakage resistance.

Cabinet Structure Design

The cabinet structure divided into cooling and heating chambers which means better heat dissipation. All the functional components located in the cooling chamber to extend service life.

The rational layout design obtained national patent which integrating the electrical mechanism, making it easy to operate and could install without foundation on the site. Inside, the cooling and heating chambers do not affect each other and expand the internal space of the cabinet. The optimized internal air circulation ensures comprehensive cooling of all functional components, extending their service lives. On the outside, the closed type removable cabinet with built-in high-quality fire retardant and sound insulation sponges reduces noises effectively.

This structure design not only meets the environmental protection requirements but also easy to service.

Vulnerable Part

High-Efficiency Particulate Air (HEPA) Filtration:

Heavy-duty air filtration system powered by Donaldson USA, with filtration accuracy up to 99.9% for particles greater than 3μm. Suitable for all kinds of heavy dust environments.

Oil Filter:

Donaldson oil filters, high grade of clean filtration, effectively protect the safe operation of the air end bearing, extend the service life of the air end.

Oil and Air Separation System:

Euro design efficient oil and air separation core, glass fibre filter material, long life, more efficient, no need for frequent replacement. The aggregate separation core and the oil return device work together, recover and recycle the lubricating oil effectively, avoiding oil over-spraying, and ensuring the oil content of the compressor exhaust ≤2ppm.

All New Temperature Control and Oil Filter Combination Valves

This patent awarding design integrates the temperature control and oil filter valves which makes the internal piping connection more concise, and fewer leakage points that reduce the occurrence rate of fault. More importantly, it further decreases the pressure drop, achieve more energy-saving and avoid obstacles like tube vibration fracture and leakage in the separated installation of the oil filter base and temperature control value.

Temperature Control Valve

Powered by AMOT of the UK

Accurately controls the oil return temperature at 65°C. If the oil return temperature too high, the oil film will damage and results in oil deteriorate, cooling and sealing degrade, also easily to carbon deposit; if the oil temperature is too low, the water will separate from the air, and the oil will emulsify and deteriorate, affecting the service life of the air end. Therefore, the temperature control value is the critical assurance of stable operation of our compressor.

EPC Intelligent Control System

UNITED Compressors equipped with an Electronic Pressure Controller (EPC) to guarantee the automatic intelligent operation of the machine. Through examing of exhaust pressure, temperature and other sensor data, the inlet valve controls the exhaust pressure between the upper and lower limits of the preset pressure to output stable pressure. When compressor idling too long, the system will automatically shut down and restart when the air supply is requested, not only outputting constant pressure but also reaching the energy saving. Meanwhile, the system may rapidly diagnose all field faults during the operating process, furthest ensuring the reliable operation of the compressor and extending the service life.

Local Control

·       The display language available in English and Chinese, soft-touch buttons, and the menu operation is intuitive, rapid and convenient.

·       User may preset and control the delay time of star-delta switching, starting, loading, shutdown, overpressure and others during the operation.

·       Allow user to view and manage field faults.

·       User may store and search history faults through classified types and occurrence times.

·       Internal calendar with accurate timing and allow adjustment.

·       User may accumulate and store the operating time, loading time, unloading time, and filter service time.

·       User may check all preset parameters and cumulative time at any time during operation.

·       User may modify and store parameters to preset when required.

Linkage Control

User may set 1 compressor as the central unit and others as the auxiliary or standby units (maximum 16 units) to constitute the linkage control of many compressors, assuring the economic and stable air supply, and may automatically adjust the start/stop sequence of each compressor by employing EPC and balance the accumulated working time of each compressor.

Remote Control

The distributed control system (DCS) remotely controls the startup, shutdown, fault output and early warning signal through passive dry contacts.

Master Computer Control

·       The master computer remotely interlock-controls two units or more of compressors, collects and displays field signals, coordinates control and computer operation. Through the setting of master computer parameters, the user may obtain the comprehensive management of the compressor units at any time, to receive stable compressed air within the set pressure range.

·       Acquire and display much field data

·       Vivid graphical interfaces

·       Monitoring the operating status of equipment

·       Records essential data to the database

·       Automatically generate data history report for later analysis

·       Setting of operating parameters of the compressor controller

·       Trend curves of pressure, temperature and other parameters

·       Real-time and history alarm

·       The operating is permissions secured. Require password to essential operations.

·       Single compressor unit test

·       Maintenance or replacement reminder of vulnerable compressor parts

* UNITED COMPRESSOR provides a variety of PLC system centralized control schemes according to the actual needs of users, effectuates man-machine interface through IPC, LCD and configuration software, and communicates with DCS in the user system to remote monitoring, which has the advantages of multi unites control and strong independent development ability.

Variable Frequency Speed Regulation Technology & Ideal Energy Saving Effect

Using UNITED Variable Frequency Speed Regulation Screw Air Compressor, you do not need to worry about complicated electrical installation and programming. The compressor unit is constructed entirely before leaving the factory; it will immediately work when the power source is connected. The pressure change of the air system is continuously detected, and the rotation speed is adjusted accurately using powerful EPC, keeping the outlet air consistent with the demand of the user system at all times. The response time of EPC calculation is at the millisecond level, and the correction to speed completes within 3ms to accurately control the outlet air pressure within 0.1bar. Our built-in filter assures safe and reliable operation of the frequency converter. During the use process, you do not need to trouble about problems such as "harmonic wave" and "radio frequency interference". The dedicated  Automatic Energy Optimization  (AEO) function guarantees the frequency converter provide the minimum power to the motor accurately according to the actual load. It could save up to 10% power and reduces the compressor noises.

Starting and Operation

The figure shows the comparison among several starting modes. It observed that the frequency inverter slowly accelerates starting and is steadier than soft starting and avoiding the peak current. After starting to the rated pressure, the frequency inverter performs step-less speed regulation and tracks air output through pressure detection, then outputs the required air volume with the pressure unchanged, completely eradicating the energy waste of loading and unloading of the fixed speed compressor.

Constant Pressure Power Saving

The figure shows the comparison of working pressure between the standard compressor and variable frequency speed regulation compressor. It observed that the standard compressor frequently loads and unloads between the minimum required pressure and 1.5bar higher, which wastes 10.5% more energy on producing the 1.5bar pressure than the frequency-controlled pressure that stabled at the minimum required pressure (Every 1 bar pressure increased consumes 7% more power). Additionally, during unloading, the zero-air standby consumes 45% more no-load energy. Therefore, the constant pressure air supply not only saves energy but also extend the unit's service life while loading and unloading as well as eliminates the unfavourable factors that affect user's production from unstable pressure.

As an example, the compressor with annual energy consumption of 250KW (the used air volume is 50%), the operating time is 6,000h/year.

Compare the volume adjustment with standard compressors; the VFD compressors may reduce power consumption by 42%, saving energy of about 570,000kWh annually.  (A suitably sized air storage tank must install to increase the energy-saving effect.)

Cost Comparison

Modularised Vector Frequency Inverter

UNITED UC-VFD series compressors carry with new generation modularized high-performance frequency inverter which is custom-made by international OEM under the requirements of UNITED. The development, design and manufacturing follow the principles of complete matching of UNITED compressors; the R&D and production of compressor characteristics, hardware, software, power module, printed circuit board and accessories assure reliable quality. The frequency inverter has the function to automatically matching with a motor, to read and check parameters of the motor real-time to ensure the best matching between the frequency inverter and motor.

·       The motor is disconnected from the load when the frequency inverter is initially set. The frequency inverter can automatically unload motor.

·       Immune to the fluctuations in the power system, if the input voltage is -10%, the frequency inverter will automatically compensate the output voltage to the rated voltage of the motor.

·       One frequency inverter may drive multiple standard compressors to linkage control.

·       The optimized fault protection effectuates the all-around protection from the frequency inverter to the motor.

·       Small torque fluctuation, fast speed compensation, strong load impact resistance and equipped with an internal electric reactor.

·       The multi-speed and built-in PLC functions automatically control multi-frequency logics.

·       Stable output frequency, strong immunity from interference; certified tests at various laboratories.

Personalized function:

·       Starting torque: 0.5HZ/150% (SVC).

·       Speed regulation range: The energy-saving effect is significant at 1:100.

·       The SFV, constant speed precision, may up to +/-0.5%.

·       Overload capacity: 60s at 150% rated current and 1s at 180% rated current.

·       Allowing live check on peripheral equipment when power is on, such as grounding and short circuit.

UNITED VFD screw compressors may accurately change the speed of the motor according to the volume change of the used air, under the principle of stable exhaust air pressure; the compressor outputs air volume at the required level and consumes the energy that only needed for outputting required compressed air to reach the purpose of energy-saving. The future saved energy cost shall greatly exceed the value of the compressor.

Technical Parameters

Patent Protection

By continually investing in R&D, the product development and new technology application pace accelerated. At present, UNITED has registered near 100 national patents covering the critical technology and integrated layout of compressor and integration improvement of parts. These patents address a range of compressor problems, such as internal temperature rise and maintenance difficulties under different operating conditions. Through the unique design and integration, the equipment can better meet the use requirements and services, in line with environmental protection requirements, fully demonstrated the excellent quality of products.

Quality Assurance

In 2003, UNITED Compressor was accredited with ISO9001 Quality Management System and ISO14001 Environmental Management System Certificates. The company strictly follows the quality requirement of Crosby’s “doing it right the first time”, persists in the working standard of “zero defect”, regards the “It is immoral to produce a defective product” as the criteria of measuring the quality. UNITED devotes itself to the continuous improvement of products all the time.