Boiler level control system based on
ControlLogix5550 PLC
Abstract-This paper is a research design based on EFPTprocess control device. In the design, actual industry fieldhas been simulated and corresponding modeling has beencarried on for the boiler level system. Then the appropriatePID parameter has been sorted out and ControlLogia5550PLC has been used to control the entire boiler level system.
At last, a corresponding control interface has beenestablished and the boiler level has been under a safe andaccurate control
K eywords：EFPT，PID，Modeling，Boiler level;
1 Introduction
The task of the industrial boiler level control is to maintain a dynamic balance by controlling the water flow and evaporation, so that the drum level can bemaintained in the technological level, which is anecessity for ensuring safe operation and also one ofthe main indicators of the boiler's normal operation.Water level which is too high will affect the effect ofthe steam-water separation, but too low it is will breakring cycle or even cause boiler explosion. To ensure a safe and efficient production, the boiler level must bestrictly controlled in maintaining constant or changingonly according to a certain rule.
Using Logix5550 PLC with analogy I/O modules,launched by Rockwell Automation Company ascontrollers, and EFPT process control experimentaldevice as control object, this system have brought theboiler water level under an accurate control in a miniboiler system with sensors and actuators that used inindustrial production.
Fig. 1 Boiler level setting value adjustment system
2 System Overview
This system is composed of an EFPT processcontrol device, an inverter, a Logix5550 PLC and acomputer. EFPT process control device is a simulatedheating and water supply and drainage system for amicro-small boiler. It realizes process control in amini boiler system with sensors and actuators used inindustrial production. The actuator includes not onlymeasuring appliance, but also AC inverter, heatingcontroller, heater and so on. The system simulatesindustry scene through a mini-boiler heating, watersupply and drainage system, which is reliable andvisual.
In the design, boiler Level was selected as thecontrolled variable. The controlled object is composedof the water trough, the force pump, the boiler and thepipe-line valve. Micro Master 6SE9214-ODA40inverter is taken as the actuator and the boiler level iscontrolled by Logix5550. Configuration softwareRSView32 and touch screen PanelView1000 are combined to realize the real-time monitoring. In thedesign, a simple design of single-loop boiler liquidlevel value adjustment is selected for the study. Thecomposition of the system is shown in Fig. 1.
In the design, the inverter as an actuator directlyreceives PLC analogy I/O port output, and convertersinto frequency of inverter so as to drive the 3-phasemotor in
the lift pump, change the inlet, and adjust theboiler level to the dynamic balance at last. And theconfiguration software is used to design monitoringpicture to realize the computer and the touch screen tothe boiler level long-distance and the scenemonitoring.
[1]. Pump started, pid controller pressure transmitter to the control point to provide the pressure signal, when the pressure point is not equal to set value, pid controller by adjusting the inverter output frequency to change the pump speed to regulate the pipeline pressure constitutes a closed-loop feedback control system, water pressure regulator so that users timely, small fluctuations in results. And in the process control system designed to take full account of the principle of load balancing, to take "first-in-first out" strategy of lining up, the way the implementation of the rotating frequency to ensure that the basic balance of the water usage.
1 Frequency Control Constant Pressure Water Supply
Principle
Frequency Control Constant Pressure Water Supply System by the programmable logic controller (plc), converter (built-pid), pressure transmitter, low-voltage electrical and pump components, such as Figure
1. Map m1 ~ m3 for water pump motors, p1 ~ p3 for pumps, km1 ~ km6 for motor starting and stopping each of the AC contactor switch. Basic working principle of the system: by the plc a signal to the inverter to control the water cycle work, when the large volume of water consumed by the plc control of all water line installed in the outlet pipe of the pressure transmitter, pressure standard signals into dc 0 v ~ 10 v into the analog signal converter with pid regulator, pressure settings and pressure feedback values after the implementation of pid calculated values of the output of a frequency converter to set the value for the pump by the inverter to provide variable frequency electrical power to realize stepless speed regulation of electric pumps to regulate the exit of the water supply pipe network pressure, constant pressure water supply to achieve the purpose. Pressure feedback signal in order to ensure an accurate value, yet the value of feedback signal to set the filter time constant. The scope of the power converter, Figure 1 can increase the number of the motor to achieve "a multi-trailers," Optimization of the program.
3 Establishing Mathematics model for the charged object
One of the main tasks of establishing controlsystem mathematical model is to determine themathematical model of the controlled object.Generally, there are two kinds of basic methods forestablishing process control mathematical model:mechanism analysis and experimental method.However, for controlled
object whose structure andinternal process is very complex, it is very difficult todetermine the object just by its own internal physicalprocess and to solve out the differential equationssystematically. Besides, considering the nonlinearfactor, mechanism analysis used some approximationand hypothesis for mathematical deduction. Althoughthese approximation and assumptions have practicalbasis, but not fully reflect actual situation, and evencause incalculable effects.
Therefore, in this design, the experimental methodis chosen to establish a mathematical model forcontrolled object. This kind of modeling is based onthe input and output in the actual production process,that is to say, establishing mathematical model for thecontrolled object through process identification andparameter estimation. In this design, step responsecurve method is used to identify mathematical modelsof the process. A 20Hz step disturbance input signal isapplied to the charged object, and the response curveof the output that changes with time can be mapped.After the analysis, the transfer function of thecontrolled object can be defined. In the process ofexperiment, the object was conducted several https://www.doczj.com/doc/eb17447205.html,ing RSLogix5000 trend monitoring function curve,more than 10 charged object step response curve havebeen recorded. To all the parameters for average, steady time: ts≈821.525s, steady value: h(∞)=58.5, peak time: tp=394.4s overshoot: a%}29%. Accordingto the theoretical analysis, the controlled object is themost likely second-order object.
However, the difference is very apparent betweenthe ideal second-order controlled object step responsecurve and the actual curves. So the ideal curve can'tresponse to its actual characteristics. It is inferred thatthe controlled object may be the second-ordercontrolled object that includes zero. The try and errormethod and MATLAB simulation tools are used to geta curve whose parameters are close to the average dynamic parameters of the controlled object's response curve. It is shown in Fig. 2.
Some adjustments can be made according to thefollowing rules:
1) When the zero is closer to the imaginary axis,settling time will be longer and the overshoot will bebigger and peak time will be smaller. With the zeroclosing to the imaginary axis, the effect is moreobvious.
2) The effect which the closed loop dominant apiceshave on dynamic performance is increasing the peaktime, reducing the overshoot and adjusting time.Nonparametric model is used to describe thecontrolled object. In other words, step response curvewhich approximately describe the controlled object isused because of the controlled object's complexity anduncertainty.
To a constant water supply, landing in the water pressure to increase the inverter
output frequency, when the maximum frequency converter and a constant pressure pump can not meet the requirements, while running the pump frequency to switch to the running frequency, At the same time need to start a second frequency or third pump until the water supply to meet the requirements. Need to determine criteria for the launch of a new water pump is the inverter output frequency is set to reach the upper limit. In order to determine the frequency of the inverter limits the accuracy of least squares by chance should be the frequency of the frequency of fluctuations in the ceiling from the situation. Inverter control motor pumps are activated each time the soft-start, and requires the use of water pumps must turn to serve as a continuous variable frequency pump operation shall not exceed 3 h, each time when the need to launch a new water pump, the pump will run from the existing removal of the inverter, and replace the power-frequency operation, reset the inverter and run the pump for a new start. Three pumps to control the duty cycle is the use of pump No. 1 way to achieve (to 3 in the plus 1 equal to zero), or combined with the total number of pump pump pump rotation to achieve its work.
4 The installation of controllerparameter
4.1 The selection of control algorithm
After establishing the approximate mathematicalmodel of the controlled object, a complete feedbackcontrol system can be formed to improve theperformance of the open-loop control system. PID isan ideal control law in that integral is introducedbasing on the proportion, which can eliminate theresidual error, plus the derivative action, which canalso improve the stability of the system. According tothe characteristics of the controlled object andlaboratory conditions, a single-loop feedback controlloop for the controlled object is established, and PIDalgorithm is used to realize boiler level control. Theschematic diagram of level control is shown in Fig.
3.
Open the outlet valve to a certain degree, andmake the hydraulic discharge invariable. Comparingthe process variables of the water level in feedbackwith the given volume, the deviation can be obtained.PID instruction does PID operation on the deviation,and the results is a control variable, so the frequencyof the inverter can be changed to control the rotatespeed of the pump. If the liquid level is on the highside, the results make the control variable smaller, and
reduce the rate of inflow, make liquid level lower; ifthe level is on the low side, the results make thecontrol variable larger, and increase the rate of inflow,make liquid level higher.
4.2 The Parameter Tuning of PID
Because the transfer function of the controlledobject includes a zero second-order link, thecomputation work load is quite big regardless of usingthe root-locus method or the frequency characteristiclaw among theory methods when tuning PIDparameter. And the process mathematical model canonly reflect dynamic parameter approximately, so thereliability of the parameter value which is obtained bythe theoretical calculation is not very accurate and itwill be adjusted constantly in the scene. Therefore,engineering parameter tuning is chosen to seek thePID parameter in the design. The common method ofengineering tuning are
dynamic characteristicparameters, the stable boundary law, the decay curvelaw and field experience settingmethod, etc. In theprocess of PID parameters, the 4:1 decay curve law is
adopted. The steps are:
1) In the closed system, regulator's integral timeis set the largest (Ti≈∞) and differential time Td is setzero (Td=0). The proportion is taken the great valueto perform the given value perturbation experimentrepeatedly, and the proportion is reduced graduallyuntil the record curve presents up to 4:1 weaken. Thenthe proportion is called 4:1 weaken proportion s s
and the distances between two neighboring waveridge's are called 4:1 damped cycle Ts. In theexperiment, the level quantitative test is set for the200mm, and then the system response curve isobtained and reorganized 4:1 decay curve (thick red line is shown in Fig. 4
'Thus measuring: δs≈8，Ts≈2.2;
2) According to the following formula, eachparameter of the regulators is
δ=0.8, δs≈6.4;
Ti=0.3, Ts≈6.6;
Td=0.1, Ts≈2.2
3) According to these results, regulator parametersare set. Then the dynamic process of system isobserved and the parameters are made adjustment todetermine the optimum parameters.
5 Monitoring Design
Frequency according to the principle of constant pressure water supply system the design water level control system of the water tower block diagram shown in Figure 2, the city water network eq with the water level controller to control the injection valve yv1, as long as the water level below the high water mark, then to the pool water automatically. Pool of high / low water level signal directly to the plc, as a high / low level alarm. In order to ensure continuity of supply, the water level of the smaller distance between the upper and lower limits. Domestic water and fire water pump three shared [3], usually yv2 solenoid valve in a state of loss, the closure of the fire pipe network, when a fire occurs, the solenoid valve was yv2 electricity, water distribution network with the closure of life, three water pumps for fire use, and maintain high-pressure fire water value. After the lifting of the fire, three use domestic water pump replaced and the cycle of operation, to maintain constant low water value. Each pump motor can run frequency, and frequency can be run. When the small volume of water consumed, a water pump under the control of the converter stable operation of large quantities of water to the pump when running at full speed there is no guarantee that the pressure on network stability, plc pressure given the lower limit of the inverter signal and high-speed signal at the same time plc was detected, plc automatically work in the original state of the pump frequency into frequency operation, in order to maintain the continuity of pressure at the same time use the next pump put into operation after start-up converter in order to increase the supply pipe network pressure of water to ensure stability; if running two pumps can not meet the requirements of the pressure, the frequency of work will be followed by a state into the pump-frequency operation, and then pump into a variable frequency operation; when the water consumption reduction, the first performance inverter has been working effectively at the lowest speed signals, when the pressure signal, such as the ceiling is still there, plc will be the first first run of the pump frequency to quit in order to reduce the volume of water supplied, when the two signals when there are still, plc and then quit second frequency of the pump to run until a constant pressure water supply pump with frequency converter. All pump motors start from a stop to and from the start to stop by the inverter to control to achieve soft-start with set, to
avoid the start of high-current impact to the pump motor to extend the life of the motor. At the same time, the use of variable frequency operation of the system pumps water cycle in order to "first to open the first gate" of the order of related pumps, so that both the water supply system to ensure back-up water pumps, water pumps and the system have the same running time as effective in preventing back-up pump death occurred not long-term phenomenon of rust and improve the comprehensive utilization rate of equipment, reducing maintenance costs.
Electrical control system main circuit see Figure 3. AC contactor km1, km3, km5 were three pump motor control m1, m2, m3 frequency operation; AC contactor km2, km4, km6 respectively control m1, m2, m3 of Frequency operation; fr1, fr2, fr3 thermal relay for protection of the three pump motor overload; qs1, qs2, qs3, qs4 respectively, and three pump motor inverter main circuit isolation switch; fu1 ~ fu3 mainly The fuse circuit. The system works in manual mode, plc alarm detection only by the artificial adoption of panel buttons and switches From water pumps to stop and switch; the system works in automatic mode, all controlled by the plc completed report to the police.
RSView32 software and PanelBuilder32software of Rockwell Automation Company arerespectively used to design monitor screen tocomplete such function as animating display,parameter setting, report output, the current curvedisplay and history curve display and so on. And makethe computer and touch screen achieve the remote andon-site control to the boiler liquid level. The picture screen of system monitor is shown in Fig.5
The main work of realizing configuration is toestablish level control objects and make animatingdisplay scenes. Controlled objects include inlettingwater flow, exporting water flow and the numericalobject of the boiler level. When animation connectionis established, the basic graphic elements andanimation component library are called in the userwindow to construct configuration diagram. Graphicobjects and data objects defined by the state are set inthe state of the corresponding attribute and animationconnection is defined. Having finished the design of
the developing system, you can switch to run mode tocarry on the real-time monitoring to the controlsystem and test configuration.
6 Conclusions
This paper has introduced the composition andrunning of EFPT process control system based onControlLogix5550 PLC control, the mathematicalmodel establishing of controlled object and theparameter tuning of PID. The use of configurationsoftware extends the communication function.Through experimental
testing, the control curve'sovershoot is small and the transition time is short, sothe control effect is quite ideal. This device beingreliable and intuitive is suitable for scientific researchand teaching, and has important application value inthe actual industrial production. the design of the towers the water level control system uses a programmable logic controller, inverter based on changes in water pressure transmitter through the pid to realize stepless speed variable frequency drive pump motor in the water changes to maintain constant water pressure meet the water requirements, so as to achieve the purpose of constant pressure water supply. In the process control system designed to take full account of the principle of load balancing, to take "first-in-first out" strategy of lining up, the way the implementation of the rotating frequency to ensure that the basic balance of the water usage. Frequency Constant Pressure Water Supply to change the supply of the previous quantitative methods to achieve "DAMA" principle, constant pressure water supply frequency mode thus saving energy, easy to operate, high degree of automation.
基于ControlLogix5550 PLC的锅炉水位控制
系统
摘要本文是基于EFPT过程控制设备的研究设计。实际工业领域的设计，已经模拟和相应的建模beencarried锅炉水位系统。然后适当的PID参数已整理出ControlLogix5550PLC已被用来控制整个锅炉水位系统。最后，相应的控制界面建立好了，锅炉水位也已在安全和精确控制下
关键词：EFPT，PID控制，建模，锅炉水平;
1引言
工业锅炉水位控制的任务是维持一个动态的平衡，通过控制水的流量和蒸发，使汽包水位保持在技术水平，这是确保锅炉安全运行的必要条件和主要指标之一。锅炉水位太高会影响汽水分离的效果，但太低了，也会破坏循环周期，