Unattended air compressor variable frequency constant voltage monitoring system

In the automation transformation of a coal mine air compressor in Jincheng, Shanxi, a set of variable frequency constant voltage monitoring system with various sensors, transmitters and actuators was designed with PLC as the core. The system continuously adjusts according to the change of wind power demand, ensures constant pressure gas supply, saves energy, protects equipment, and realizes scientific management of equipment.

1 Equipment Overview There are 4 SA200A air compressors in a coal mine in Jincheng, Shanxi. The single displacement is 30.0m3/min and the exhaust pressure is 1.0MPa. Water cooling is adopted. The air compressor is driven by a three-phase asynchronous motor with a rated power of 210 kW and a voltage of 10 kV. The compressed air users of the whole mine mainly include 4 anchor bolts and eye-mounting machines, 3 concrete jets, 10 wind coal drills and 5 sets of bolt-on eye-mounting machines. The number of wind power users in the system is numerous, and the demand for gas is extremely unstable.

2 Monitoring program The basic purpose of the air compressor monitoring system is to ensure the stability of the gas supply pressure and meet the gas demand at all times; to obtain the equipment operating parameters, * Xuzhou Engineering College Jiangsu Province large-scale engineering equipment testing and control key construction. The monitoring system has an automatic control function, which can record the historical data of the equipment operation, and has an over-limit alarm and protection mechanism.

According to the relevant requirements of the coal mine safety regulations and the unattended air compressor variable frequency constant voltage monitoring system of the control system - Luo Huiqing, and other actual needs, determine the relevant temperature, power and pressure as the main system parameters, using temperature, electricity, The pressure sensor collects and converts it into a PLC standard input signal of 0~5V or 4~20mA through the transmitter, and transmits the signal by using a shielded cable.

The temperature parameters mainly include the temperature of the intake and exhaust, the temperature of the cooling water, and the temperature of the lubrication system. Engineering thermodynamics theory has proven that the compressor has the least amount of cyclic work under isothermal compression conditions. However, it is impossible to achieve isothermal compression in actual working conditions. To achieve energy saving, it is necessary to ensure that the compression process is close to isothermal compression. The system prepares the control program in the PLC by collecting the intake and exhaust temperature and the cooling water temperature of each stage of each compressor. Once the cooling effect is deviated, the flow of the cooling water is adjusted to keep the compression process close to isothermal. The temperature of the lubrication system is collected to ensure that the lubrication system works normally and avoid lubrication failure. Once the lubrication fault occurs, an alarm is issued through the sound and light alarm device.

The electrical parameters mainly reflect the basic operating state of the air compressor, and the relevant electrical parameters participate in the preparation of the program to avoid some misoperations.

The pressure parameters mainly include the suction and exhaust pressure of the air compressor, the pressure of the gas storage tank, and the pressure of the cooling water pipeline. The target pressure of the gas storage tank is adjusted according to the wind power demand. When the demand for compressed gas is large, the gas storage pressure of the gas storage tank is set to a large value, and the gas tank pressure setting value is followed by controlling the number of air compressor operating units and the frequency converter. When the compressed gas demand is relatively small, it is set to a smaller gas storage pressure value. However, the system requires that the pressure of the gas storage tank should not exceed 0.84 MPa. When the limit is exceeded, an alarm is issued and the number of inverters and machine running units is adjusted. The purpose of collecting the cooling water line pressure is to ensure that the cooling system is constantly water.

3 variable frequency constant voltage control In the whole monitoring system, the most important control functions are: frequency conversion regulation and constant voltage control.

The Siemens MM440 series inverter is introduced in the monitoring system, which makes the pressure of the gas storage tank continuously adjusted and avoids the start and stop of high frequency equipment. The inverter itself has a parameter setting panel, which can be manually input related parameters, or parameters can be given to the inverter through the PLC.

The traditional frequency conversion condition is to manually input a frequency given parameter to the inverter. However, the air compressor system has a large hysteresis, and the demand for mine wind power is extremely unstable. This frequency conversion adjustment obviously cannot meet the requirements of automation. For this system, a smart PID controller is used to design a digital fuzzy PID controller that combines the fuzzy reasoning mechanism with the traditional PID. This fuzzy PID controller not only has the intelligence of fuzzy inference anthropomorphic control, but also has the reliability and stability of PID. It analyzes and calculates the given pressure value and actual pressure value of the gas storage tank, and obtains the frequency reference value of the frequency converter through the PID algorithm with parameter online setting function, and transmits it to the frequency converter in the form of 0~5V voltage. . The structure of the fuzzy PID controller is as shown.

The instability of the fuzzy PID controller's full mine wind power demand makes the gas pressure of the gas storage tank change frequently, and sometimes the underpressure is under pressure. The fuzzy PID calculation can automatically determine the optimal given frequency of the frequency converter, that is, when storing When the positive pressure deviation value of the gas tank is large, the controller transmits a large voltage signal to the frequency converter, and when the negative deviation is large, a smaller signal is given.

Before the automatic reformation of the air compressor of the mine, the constant pressure maintenance of the air compressor of the mine mainly relies on frequent start and stop of the motor to adjust the supply air pressure. Once the gas storage tank is over-pressurized or under-pressure, the number of compressors is increased or decreased. At the same time, supplemented by exhaust valve adjustment. Repeatedly alternating, on the one hand, the supply pressure is not continuously adjusted, resulting in waste of energy, and on the other hand, it accelerates the aging of equipment, and some air compressors operate for a long time, and some are idle for a long time.

To this end, the monitoring system adopts the method of combining frequency conversion adjustment and start-stop equipment, and establishes the equipment standby mechanism according to the historical data of each air compressor operation, realizing the continuous constant pressure regulation of the gas storage tank.

The system first starts the air compressor with frequency conversion, and calculates the optimal frequency of the inverter through the intelligent PID. When the frequency given by the fuzzy PID is greater than 48 Hz, it means that the operation of an air compressor can not meet the wind power demand, the system will The air compressor is adjusted to the power frequency operation, and the air compressor is started by the frequency conversion. The optimum frequency of the 2 air compressor is also calculated from the fuzzy PID, and the subsequent air compressor is operated accordingly. When the wind power demand is reduced, the compressor can be turned off one by one.

Other controls are mainly for overrun and fault protection. The parameters that may exceed the limit are mainly the tank pressure, the cooling water temperature, and the lubricating oil temperature. The possible faults mainly include cooling water cut-off and lubrication cut-off. When the above situation occurs in the system, the PLC will issue corresponding control commands, and the actuator will make corresponding switch opening and closing actions according to the instructions to protect the device.

4 software design using Step-7 software to write design PLC program. According to the specific characteristics of the operation of the air compressor, the system uses the sequential control method to develop related procedures. Independent sub-functions are programmed in FC or FB, mainly including fuzzy PID function block FB, analog acquisition function FB, and start-stop program FC of each air compressor. The main control program is written in OB35, the relevant data is stored in the DB block, and the data is exchanged with the host computer via Ethernet. The flow of the PLC main control program is as shown.

In August, coal mine machinery based on MCGS software and PLC's main drainage control system Sheng Jun (Pingdingshan Industrial Vocational Technical College, Henan Pingdingshan 467001) system can improve the automation level of downhole pump control, reduce manual input, and ensure the safety production of underground coal mines. The underground drainage system is an indispensable system in coal mine production. Its main task is to quickly send underground water to the surface. Therefore, the drainage system is an important guarantee for achieving underground safety production. It has become a hidden danger of water-permeable accidents in the key project of Henan Province (082102230031), so the reliability of underground mine drainage system is particularly important. At present, the power consumption of the drainage system is generally about 20% of the entire coal mine. While ensuring the stability and reliability of the drainage system, it is also important to study the economical drainage system with low power consumption and high efficiency.

1 Insufficient main control program flow chart interface of traditional main drainage system WinCC is the configuration software of Siemens. It has rich configuration functions and can design friendly and intuitive human-machine interface. The development of the system monitoring interface makes full use of the modules such as bar graphs and trend curves of WinCC. In the script of WinCC, the air compressor "standby mechanism" program is written in C language, and WinCC exchanges data with the PLC via the Ethernet communication protocol.

5 Conclusion The air compressor constant voltage monitoring system with the mature S7-300PLC as the core realizes stable and reliable variable frequency constant voltage regulation and system overrun and fault protection. The monitoring system has a remote communication and data exchange interface based on 0PC, which can serve the whole mine automation. The monitoring system is reasonable in design, simple and reliable, and has low operating cost. It effectively realizes the energy saving and consumption reduction of the air compressor, and has the value of popularization and application.