Sunwoele VFD (Variable-frequency Drive) energy-saving retrofit application on air compressors

Air compressors are widely used in many sectors of China's national economy and national defense construction, especially in textile, chemical, power and other industrial fields, and have become indispensable key equipment, and are the core equipment in the process flow of many industrial sectors. Sufficient air supply pressure for the compressed air required for automatic production is the key to a smooth production process. An instantaneous pressure drop will affect product quality. With the maturity of frequency conversion technology, VFD (Variable-frequency Drive) is more and more widely used in the field of electric transmission. The diversity of its control methods, perfect motor protection function and its unique advantages are unparalleled in the field of industrial control at present.

1. Working principle of screw air compressor

The working process of the screw air compressor is divided into four processes: suction, sealing and conveying, compression and exhaust. When the screw rotates in the casing, the tooth grooves of the screw and the casing mesh with each other, the air is sucked in from the air inlet, and the oil is also sucked in at the same time, and the sucked oil and gas are sealed and transported to the exhaust port due to the rotation of the meshing surface of the tooth groove; During the process, the tooth groove meshing gap gradually becomes smaller, and the oil and gas are compressed; when the tooth groove meshing surface rotates to the exhaust port of the shell, the higher pressure oil-gas mixture is discharged from the body.

2. Compressed air supply system composition and air compressor control principle

Composition of compressed air supply system:

The compressed air supply system of a factory is generally composed of an air compressor, a cold dryer, a filter, an air storage tank, pipelines, valves and gas equipment.

The control principle of the air compressor:

In the air compressor control system of the factory, the pressure relay installed on the back-end pipeline is generally used to control the operation of the air compressor.

OK. When the air compressor is started, the loading valve is in the non-working state, the loading cylinder does not move, the air inlet of the air compressor head is closed, and the motor starts without load. After the air compressor starts running, if the back-end equipment consumes a lot of air, the pressure of the compressed air in the air storage tank and the back-end pipeline does not reach the upper pressure limit

value, the controller operates the loading valve, opens the air inlet, the motor runs under load, and continuously generates compressed gas to the rear-end pipeline. If the back-end gas equipment stops using gas, the pressure of the compressed gas in the back-end pipeline and the gas storage tank will gradually increase. When the pressure reaches the set value of the upper limit, the pressure controller will send an unloading signal, and the loading valve will stop working. Off, the motor runs without load.

Three, screw air compressor frequency conversion transformation

Comparison of power frequency operation and variable frequency operation of air compressors:

The motor power of the air compressor is generally relatively large, and the starting method is mostly no-load (unloading) star-delta starting, and the loading and unloading methods are both instantaneous. This makes the air compressor have a large starting current when it is started, and it has a large mechanical impact on the equipment when it is loaded and unloaded; it not only causes fluctuations in the power supply voltage, but also causes large fluctuations in the compressed air source; at the same time, this mode of operation It will also accelerate the wear and tear of the equipment and reduce the service life of the equipment. Since the driving motor of the general air compressor cannot adjust the speed itself, it cannot directly use the change of pressure or flow to achieve the matching of output power by reducing the speed. No-load operation, a huge waste of electric energy.

The frequency conversion transformation of the air compressor can enable the motor to achieve soft start and soft stop, reduce the start-up impact, and extend the service life of the equipment; at the same time, because the motor operating frequency is variable, the air compressor can automatically adjust the motor speed according to the size of the air consumption. The frequent loading and unloading of the motor is reduced, thereby greatly reducing the operating power of the motor, so that the air pressure of the air supply system remains constant, and the purpose of energy saving can be achieved.

4. Design principles of frequency conversion transformation scheme

According to the problems existing in the original working conditions and combined with the requirements of the production process, the system after the frequency conversion transformation of the air compressor should meet the following requirements:

·The frequency conversion operation of the motor keeps the outlet pressure of the gas storage tank stable, and the pressure fluctuation range cannot exceed ±0.02Mpa.

·The system should have two control loops of frequency conversion and power frequency.

·According to the working condition requirements of the air compressor, the system should ensure that the motor has constant torque operation characteristics.

·In order to prevent the non-sine wave from interfering with the air compressor controller, the VFD (Variable-frequency Drive) input should have effective measures to suppress electromagnetic interference.

·In the case of small electricity consumption, when the VFD (Variable-frequency Drive) is running at low frequency, it should be ensured that the temperature of the motor winding and the noise of the motor do not exceed the allowable range

around.

According to the production process requirements, after the frequency conversion transformation, the air supply pressure of the compressed air supply system should be appropriately reduced, and the original high-pressure variable flow air supply should be changed to

Frequency conversion, constant pressure and variable flow gas supply mode.

5. Selection of VFD (Variable-frequency Drive)

According to the above principles, choose Chengdu Sunwoele HSF600 series general-purpose VFD (Variable-frequency Drive), equipped with industrial frequency conversion switching device, and only need to add a pressure transmitter to form a closed-loop control system. The air pressure signal fed back by the sensor is directly sent to the input port of the PID regulator that comes with the VFD (Variable-frequency Drive), and the pressure setting can be set using the keyboard of the VFD (Variable-frequency Drive), so that the system can meet the above working conditions Require.

HSF600 VFD (Variable-frequency Drive) features:

Adopt 32-bit motor control special microprocessor, high-precision frequency output

·Novel power accumulation function, more intuitive and convenient to observe the energy-saving effect.

·Built-in RS-485 interface, can be controlled by computer network. Multi-signal input, built-in simple PLC, more convenient automatic control.

·Carrier frequency is adjustable, silent operation.

·Variety of control methods, strong versatility.

·Built-in PID adjustment function, simple closed-loop control, low-speed rated torque output, stable operation.

·The keyboard is easy to operate, and relevant parameters can be adjusted and set online during operation.

·Low frequency torque output 180%. Low frequency operation characteristics are good.

The maximum output frequency is 600HZ, which can control high-speed motors

All-round detection and protection functions (overvoltage, undervoltage, overload) restart after momentary power failure,

Protection functions such as acceleration, deceleration, and stall prevention during rotation

·Stop from deceleration to natural stop, automatic return, DC braking

A variety of VFD (Variable-frequency Drive) operating status parameters are displayed, and the control signal and load operating status are clear at a glance. We will try our best to maintain the integrity of the main circuit and control circuit of the original equipment during the frequency conversion transformation, and will not change its circuit; It is convenient to change back to the original control mode, which ensures that the air compressor can operate under both frequency conversion and power frequency conditions.

Wiring schematic diagram: