1、PDF外文：http:/ Electromagnetic Analysis & Applications, 2009, 2: 114-117 doi:10.4236/jemaa.2009.12018 Published Online June 2009 (www.SciRP.org/journal/jemaa) Air Compressor Control System for Energy Saving in Locomotive Service Plant Wenyu Mo Department of Control Science of Engineering, Hu
2、azhong University of Science and Technology, Wuhan, China. Email: M Received January 2nd, 2009； revised March 12th, 2009； accepted March 20th, 2009. ABSTRACT The actuality and disadvantages of traditional high power asynchronism motor drive air compressor in locomotive service plant are discus
3、sed. In order to reduce the energy consumption and obtain safe running, a variable frequency control method to the motor is supplied. A PLC with touch screen is used for monitoring the status of the compressor and its control system. It also presents energy consumption analysis caused by the variabl
4、e frequency control method in a locomotive service plant. Keywords: Variable Frequency, Air Compressor, Locomotive Service Plant 1. Introduction Air compressor is a key equipment to provide air power, which is driven by asynchronism motor. Air compressor is operated by adjusting rotation speed
5、 of the motor. In general, the output air pressure in pipeline of the air tank is acted as controlling object in the system. The air pressure in the pipeline is controlled to be fluctuate in a certain range. Its upper limit (0.7MPa) is under the rating pressure of the pipeline, and its lower l
6、imit (0.4MPa) is above the rating pressure of the equipment using the compressive air. Usually, there are two ways to control the air pressure in the pipeline to content this demand. The first method is starting up and stopping the motor continually for adjusting air pressure in pipeline. When
7、 the air pressure is under the upper limit, the air compressor operates until the air pressure goes up to the upper limit, then the motor stops running. But the air pressure will be lowered with air leak or air consuming equipment operating. When the air pressure goes down to the lower limit, the mo
8、tor begins to work and air compressor operates again. This method is simple and low cost, but it is suitable for small power motor because the motor will be started up continually. The second method is using pressure valve to limit air pressure in the pipeline. When the pressure goes up to the
9、 upper limit pressure, the valve will close entrance of the air compressor, then the compressor is in idle state. In this case, the compressor is still driven in operation by the motor, but it does not export compressive air, so the air pressure will not go up further. When the pressure goes down to
10、 the lower limit, the valve will be open again, and then the compressor exports compressive air and the air pressure will be up again. The variable air pressure is same as that of the first method. In this case, motor is running continuously, which can be used for high power motor. In locomoti
11、ve serve plant, the second method is widely used for control the air pressure from air compressor because of high power motor being used, which rating power is about 100KW. Although the motor is in running operation, its starting up should be controlled. Traditionally, there are two ways to fulfill
12、the starting up, which are linking series resistor in the rotor loop and converting Y-connection of the starter loop . However, there are still some disadvantages in these two ways as follows. 1) The air pressure in pipeline fluctuates greatly between the upper and lower limits. 2) The c
13、ontinual upload and download of air compressor causes voltage fluctuation in electrical power supply. 3) The air compressor is in full speed rotation all the time, which may lead to mechanical failure and temperature rise. 4) The air compressor and the air pressure valve in their operations ca
14、use a great noise pollution. 5) The driving motor of air compressor is inefficient and energy consumptive and cause low power factor. So, it is necessary to change the traditional control method of the air compressor operation for energy saving, less pollution and low failure possibility
15、. 2. Variable Frequency Control of AirCompressor Motor 2.1 System Principle With the rapid development of power electronics technology, transducer is widely used in adjusting speed of AC asynchrony motor 2. So, a transducer is designed as an executor in the air compressor control system to adjust ou
16、tput air pressure. In order to control the air pressure in the pipeline, the motors rotation speed should be in control. However, the motor disables to change its rotation speed itself, the only method is to adjust its frequency to change the rotation speed. So, a transducer used to control the moto
17、rs rotation speed, then, the flux from air compressor can be adjusted. The system schematic diagram is shown in Figure 2. After comparing enactment pressure signal with feedback pressure signal, a pressure signal error is obtained, which is used for calculation of PID arithmetic and then converted t
18、he error signal to a control value to adjust frequency of AC power supply. Then the asynchronies motor will drive air compressor to an appropriate rotation speed with variable frequency power supply to eliminate the pressure error and ensure a constant air pressure. The air pressure adjusted by PID
19、arithmetic in the pipeline is shown in Figure 3. In general, a transducer has an inner PID control unit. 0: negative effects, when > 0, transducer output frequency raises； < 0, frequency declines. 1: positive effects, when > 0, transducer output frequency declines； , < 0, frequency
20、 raises. When the pressure detected by pressure sensor is higher than the enactment pressure, PID regulator output signal declines and the transducer output frequency falls down, then the air compressor rotation speed reduces and the output air pressure declines； when the detected pressure is
21、lower than the enactment pressure, PID regulator output signal raises and the transducer output frequency increases, then the air compressor rotation speed increases and the output air pressure increases. The system controls the air pressure automatically through the above method. In Figure ,
22、a transducer of YASKAMA 616PC5 forms the air pressure feedback control system. On the transducer, FS, FV, FI and FC are ports of pressure enactment and feedback input signal. The FS provides power supply (+15V). An input voltage, which deter-mines frequency of AC power supply from the transducer, is
23、 linked to the FV port from a resistor (4.7K). A feed-back voltage of air pressure in the air tank detected by a remote pressure gauge is linked to FI port. These two signals are compared in the transducer and an error can be calculated, by which PID arithmetic is used for calculating control variab
24、le. The transducer has selfeducated ability, i.e. PID parameters can be adjusted automatically in terms of actual pressure change characteristic in the transducer. S1, S3, S4 and SC are ports for several control functions. When K1 is closed, the transducer operates normally. If there is a failure ou
25、tside the transducer, K2 will be closed, and the transducer will stop operation. In thiscase, a signal can be detected in S3 port to protect the whole system. However, if there is a failure in the transducer, MA and MC ports will be connected in it, by which control system (PLC) can stop the whole s
26、ystem operation. When the failure is removed, control system makes K3 close, a signal inputs to the S4 port, which can reset the transducer. M1 and M2 ports output running state signal. Three-phrase AC power supply are linked to R, S, and T ports on the transducer. Then, the variable frequency AC po
27、wer supply can be exported from U, V, and W ports. A PLC acts as a control unit in the system, from which switches K1, K2 and K3 can output relative signals. Signals from ports M1, M2, MA and MC on the transducer can also be input to the PLC. 2.2 Existing Problems and Solutions Using the transducer would generate harmonic wave. The external input industrial frequency power supply AC (380V/50Hz) is rectified into DC by threephrase bridge. Finally, it is
