Air compressor is a kind of equipment that uses motor to compress gas in compression chamber and make the compressed gas have a certain pressure. As a basic industrial equipment, air compressors are widely used in almost all industrial industries, such as metallurgy, machinery manufacturing, mining, electric power, textile, petrochemical, light textile and so on. Air compressors account for 15% of the power consumption of large industrial equipment (fans, water pumps, boilers, etc.). Due to the structural principle, most air compressors have obvious technical weaknesses. When the output pressure is greater than a certain value, the load relief valve is automatically opened to make the asynchronous motor idle, seriously wasting energy; The asynchronous motor is easy to start and stop frequently, which affects the service life of the motor. The power frequency starting current of the air compressor is large, which has a great impact on the power grid, large motor bearing wear and large amount of equipment maintenance; Poor working conditions and loud noise; The degree of automation is low. The adjustment of output pressure is realized by manually adjusting the opening of the valve. The adjustment speed is slow, fluctuating, unstable and low precision.
The frequency conversion electrical system is composed of a KE300 frequency converter, pressure sensor and other peripheral components.
(1) KE300 adopts open-loop vector control to meet the requirements of high and low frequency torque output;
(2) The system adopts PID control. The whole control process is as follows: gas demand ↑ - pipeline air pressure ↓ - difference between pressure setting value and feedback value ↑ - PID output ↑ - frequency converter output frequency ↑ - air compressor motor speed ↑ - air supply flow ↑ - pipeline air pressure tends to be stable.
(3) The pressure sensor provides 0-10V (or 4-20mA) signal as PID setting value, which is connected from the analog input AI of KE300.
(4) The start and stop signals are given by the central control system. KE300 can provide the analog output signal through the analog output terminal AO and connect it to the central control system to observe the pressure fluctuation in real time. At the same time, it can provide fault alarm signal through relay output.
(5) Power frequency bypass can be considered to ensure production continuity.
The terminal wiring diagram that can be referred to is shown in the figure below:
三相交流电源--three-phase alternating-current supply；瞬间短路保护电路--Momentary short circuit can protect the circuit；直流电抗器--direct current reactor；正转--rotate forward；停机--halt；压力传感--pressure sensing；频率给定--frequency settings；跳线--jumper；模拟量输出--analog output；故障告警输出--Fault Alarm Output
(1) Active power saving: when the rotating speed of the air compressor is reduced, active power saving (the significance of active power saving is that it can directly save electricity expenses and reduce production costs.) is obviously effective.
(2) Improve the power factor at the network side and save reactive power significantly. The significance of reactive power saving lies in reducing the line loss of workshop power supply bus and the secondary current of workshop distribution transformer. The saved reactive current can be transferred to the newly installed equipment in the power grid, so as to solve the problem of capacity increase of workshop distribution transformer after adding new equipment. At the same time, the reduction of reactive current can reduce the operating temperature rise of power transformer, so as to prolong the service life of power transformer
(3) Smooth heavy start. KE300 series frequency converter has good low-frequency response and large power margin, which can fully meet the torque demand during low-frequency operation. Therefore, it is fully applicable to "heavy load start".
(4) Extend mechanical life. The reduction of air compressor speed reduces the running wear of air compressor pump, which has the effect of prolonging the service life of air compressor; At the same time, the leakage of air compressor oil circuit is greatly reduced, reducing the pressure on environmental pollution
(5) The low rise and fall of oil temperature is a good solution to the predicament of reducing the working pressure of air compressor in high temperature environment in summer.
(6) Reduce noise. It can significantly improve the on-site operation environment and provide effective means for environmental noise pollution control in occupational health management.
(7) Superior soft start and soft stop characteristics. The start-up and stop time of KE300 frequency converter is arbitrarily adjustable (0 ~ 10min), that is, the acceleration at start-up and the deceleration at stop are arbitrarily adjustable. At the same time, in order to start smoothly, it can also match its S-type acceleration and deceleration time, so as to minimize the impact during the start-up and stop of air compressor, which is difficult to be achieved by other driving equipment.
In order to ensure the normality of the oil circuit of the air compressor, the lower limit frequency of the frequency converter is generally limited to more than 20Hz.