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    基于PLC的离心风机变频调速控制系统设计6.14毕业论文.doc

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    基于PLC的离心风机变频调速控制系统设计6.14毕业论文.doc

    目录1绪论···································································································12总体设计方案······················································································12.1控制系统的要求·············································································12.2系统构成及工作原理·······································································12.3变频调速节能分析··········································································22.4变频调速的依据·············································································32.5离心风机控制原理分析····································································33硬件设计·····························································································63.1温度传感器的选择··········································································63.2PLC的选择····················································································73.2.1FP0系列PLC的特点··································································73.2.2PLC控制系统设计流程·······························································73.3变频器的选择·················································································84软件设计···························································································114.1PLC程序设计···············································································114.1.1离心风机转换过程分析····························································144.1.2系统工作状态·········································································144.1.3状态转换过程的实现方法·························································154.2程序设计的梯形图········································································165系统可靠性设计·················································································166系统调试···························································································196.1软件系统的调试···········································································196.2硬件系统的调试···········································································196.3软硬件结合调试···········································································197结论·································································································19谢辞···································································································20参考文献······························································································20附录:程序清单····················································································2211绪论在工业生产、产品加工制造业中,风机设备主要用于锅炉的燃烧系统、其他设备的烘干系统、冷却系统、通风系统等场合,根据生产需要对炉膛压力、风速、风量、温度等指标进行控制和调节以适应工艺要求和运行工况。而最常用的控制手段则是调节风门、挡板开度的大小来调整受控对象。这样,不论生产的需求大小,风机都要全速运转,而运行工况的变化则使得能量以风门、挡板的节流损失的形式消耗掉了。在生产过程中,不仅控制精度受到限制,而且还造成大量的能源浪费和设备损耗。从而导致生产成本增加,设备使用寿命缩短,设备维护、维修费用高居不下。为此,需要采用多项措施实现对离心风机的自动控制,以使系统的各种性能达到合理的要求。近年来,出于节能的迫切需要和对产品质量不断提高的要求,加之采用PLC和变频器易操作、易维护、控制精度高,并可以实现高功能化等特点,采用基于PLC的变频器驱动方案开始逐步取代风门、挡板、阀门的控制方案。从而大大的降低生产成本,减少能量损耗和对环境的污染,为企业带来可观的经济效益和社会效益1。2总体设计方案2.1控制系统的要求控制系统的要求:(1)高可靠性,以适应工业现场十分恶劣和复杂的工作条件。(2)具有实时响应处理能力,以满足工业生产过程实时控制要求。(3)有丰富的可与工业现场信号相连接的工业接口,方便实现在线监控。(4)控制系统结构应能组配灵活,易于扩展。(5)有先进的系统环境和应用软件便于开发。(6)有自动/手动转换系统,保证在自动控制系统出现故障时,可以手动控制。(7)有可靠的报警系统,在风机电机过热,变频器出现故障时能及时发出报警信号。2.2系统构成及工作原理工业离心风机的工作要求是指在特定的工作环境中,风机输出的风量要随着外界条件的变化,保持在设定的参数值上。这样,既可满足工作要求,又不使电动机空转,而造成电能的浪费。为实现上述目标,本系统采用闭环控制的方式。工业现场的温度由温度传感器检测,变换成模拟输入反馈信号,经A/D转换后2与PLC中给定值比较,再经D/A转换变成模拟量输出信号,控制变频器调节风机转速,从而达到控制工厂车间温度的目的2。系统组成简图如图1所示。图1自动控制系统组成框图2.3变频调速节能分析变频调速应用于风机系统电机的自动控制中,其节能效果明显。由流体力学的基本定律可知:风机、泵类设备均属平方转矩负载,其转速n与流量Q,压力H以及轴功率P具有如下关系:Qn,Hn2,Pn3,即流量与转速成正比,压力与转速的平方成正比,轴功率与转速的立方成正比。图2给出了风机中风门调节和变频调速两种控制方式下风路的压力-风量(H-Q)关系及功率-风量(P-Q)关系。其中,曲线1是风机在额定转速下的H-Q曲线,曲线2是风机在某一较低速度下的H-Q曲线,曲线3是风门开度最大时的H-Q曲线,曲线4是风机在某一较小开度下的H-Q曲线。可以看出,当实际工况风量由Q1下降到Q2时,如果在风机以额定转速运转的条件下调节风门开度,则工况点沿曲线1由A点移到B点;如果在风门开度最大的条件下用变频器调节风机的转速,则工况点沿曲线3由A点移到C点。显然,B点与C点的风量相同,但C点的压力要比B点压力小得多。因此,风机在变频调速运行方式下,风机转速可大大降低,节能效果明显。曲线5为变频控制方式下的P-Q曲线,曲线6为风门调节方式下的P-Q曲线。可以看出,在相同的风量下,变频控制方式比风门调节方式能耗更小,二者之差可由下述经验公式(l)表示:30.40.6/(/)PQQeQQePe(l)其中Q为风机运行时实际风量。Qe为风门开度为最大,且电机运行在额定转速时的风量。Pe为风门开度为最大,且电机运行在额定转速时的功率。通过以上分析得出,采用转速进行调节风量,比起用挡板调节风量节省能源,风量调节幅度越大,节电效果越高。对我国风机现有的运行状况进行调查后得出,3其中大多数风机处于大马拉小车的状态,用挡板进行运行流量的调节,极大的浪费了电能,若采用调速方式运行,则可以大量节约电能,并能在1至2年内收回投资成本3。图2变频调速在风机中的节能分析2.4变频调速的依据变频调速技术的基本原理是根据电机转速与工作电源输入频率成正比的关系,如公式(2)所示:60(1)/nfsp(2)其中n表示电机转速;f为电动机工作电源频率;s为电机转差率;p为电机磁极对数。通过改变电动机工作电源频率达到改变电机转速的目的。交流电动机调速方法有三种,主要有:(1)变极对数调速,(2)变转差率调速,(3)变频调速,即改变电源的频率来改变电机的转速。这三种方法前两种有一定的局限性,而变频调速具有其他调速方法无可比拟的优势,变频调速的性能和经济指标己赶上直流调速系统。变频调速传动效率高,因变频调速属于电气调速,无中间机械设备,也就没有附加的转差损耗,属于低损耗的高效调速,而且其调速范围广,反应速度快,精度高,装置安全可靠,安装调试方便,容易实现闭环控制,能达到自动调节。另外,使用变频调速还具有高效节能的效果。目前,变频调速控制器作为一种新型的节能控制装置,已开始在各行各业逐渐得到推广和应用4。变频系统的主电路原理图如图3所示。2.5离心风机控制原理分析三台大容量的离心风机(1#,2#,3#)根据工作状态的不同,具有变频、工频

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