基于PLC三相异步电动机变频设计中英文翻译.doc

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1、基于PLC三相异步电动机变频设计摘 要可编程逻辑控制器（PLC）技术应用于三相异步电动机的监测和控制系统的设计和实施，并且实现速度控制和保护的软硬件设计以及对异步电动机性能测试的结果。该可编程控制器可根据使用者设定的电机转速值关联、控制操作参数。可在正常和跳闸工况下监测异步电机系统。与一个常规V/f控制系统比较，由变换器驱动和由PLC控制的异步电动机的测试系统证明在调速方面有更高的准确性。PLC的控制效率高速增加到同步转速的95%。因此，PLC是电驱动工业控制的一个有效的工具。关键词：计算机控制系统；计算机监视系统；电驱动；异步电动机；可编程控制器1 简介近年来随着工业生产迅速地改变和信息技术

2、突飞猛进，一些传统大型电子装置必须长期被监测。工业系统中的控制设备例如通信接口等，逐渐进入网络信息时代，所有设备的控制也已经开始使用计算机进行。多数设备使用PLC连接到计算机，继而监测每个负载和耗电设备。因为价格低廉，容易安装和应用非常灵活，可编程逻辑控制器（PLC）广泛的应用在工业控制中。PLC通过它的输入和输出与外部设备进行互动。可编程逻辑控制器（PLC）的使用与电器应用相关联的电力电子学也被介绍到自动化生产中。这个用途提供了许多好处，例如，低电压启动，控制电机和其他设备的功率因数相同等。许多工厂在自动化过程中使用PLC以减少生产成本和增加质量和可靠性，其他的应用包括由于使用PLC而改进精

3、确度的计算机化数控机床（CNC）。要得到准确的工业电驱动系统，使用PLC连接大功率变换器、个人计算机和其他电设备是十分必要的。然而，这么做会使设备变得复杂，庞大和昂贵。三相异步电动机的功率因数控制器运用PLC，可以改进功率因数和在整体控制条件下保持电压频率比率恒定。为了调节三相脉冲宽度模块化变换器的电压和电流，矢量控制集成电路使用了复杂可编程逻辑阵列（CPLD）和整数算术。许多有关异步电机的应用不仅要求电机控制功能化，而且还要求其对模拟信号、数字信号、内部信号，跳闸信号、开/关/反向命令等具有可操作性；基于以上情况，在系统结构中就有必要加入控制单元（结合了可编程控制技术）。本文提出了一套基于P

4、LC的检测和控制系统应用于三相异步电机。对相应配置的软硬件的设计及功能进行了阐述。在异步电机上的试验结果表明，在变载荷恒速控制操作下，电机在功率，精确性方面有提高。该可编程控制器可根据使用者设定的电机转速值关联、控制操作参数，并且可在正常和跳闸工况下监测异步电机系统。2 PLC作为系统控制器可编程逻辑控制器是模块化的工业加固计算机，它通过输入/输出模块执行控制功能。PLC的模块化允许用户根据他的需要以最容易理解的方式将普通输入/输出模块和适当的控制器结合起来形成控制特殊系统。设计的控制器操作重复执行以下三个步骤：（1）从输入模块读取输入信息；（2）执行预先编好的程序；（3）将逻辑运算的结果输出

5、到输出模块，将过程中用到的输入和输出装置连接到PLC，然后将控制程序写入PLC的存储器。在应用中，PLC通过控制模拟量和数字量的输入和输出控制带各种负载的异步电动机恒速运行。并且，PLC持续地监测输入并根据程序的执行输出结果。本PLC控制系统中的各种特定类型的硬件模块（模块）直接接入一个专有总线：一个中央处理器单元(CPU)，电源单元、输入-输出模块和程序终端。这种模块化方法的优点是初始配置可根据今后的其他应用进行扩展，如多媒体计算机系统或计算机连接。3 异步电动机的控制系统在开发项目的软件需求分析阶段生成该软件模型，在设计阶段完善和美化该模型。在这个阶段要做出实施决定，例如不同的软件模块之间

6、的连接，横跨多个处理器的软件划分，分配输入和输出到输入/输出接口等等。PLC的软件设计在书写时必须遵循简单和直观的原则。PLC是不断发展的，系统技术的进步同样将影响PLC软件要求的发展。因此PLC设计软件一定是可维护和可扩展的。以下配置可以从这个设定得到。（1） 匀速操作的闭环控制系统，并配置速度反馈。异步电机靠一个逆变器驱动可变负载，PLC控制逆变器的输出；（2） 改变速度和频率操作的开环控制系统。异步电动机根据控制模式驱动可变负载，PLC在启动后可以作为一个恒定的变频器；（3） 调节速度的标准。异步电动机靠恒定电压，恒定频率标准的三相供电来驱动可变负载。通过取消速度反馈开环的配置（2）可以

7、从闭环配置（1）得到。另一方面，如果整个控制系统被绕过，操作（3）发生。PLC的编程是基于输入设备的逻辑要求，程序的实施主要是逻辑算法，而不是数值计算的算法。大多编程的操作是基于直接的“开”和“关”两种状态，并且这些两种状态分别对应于“true或false” （逻辑形式） 或“ 1或0” （二进制形式）。因此，PLC使用模拟装置提供一个灵活的编程，替代以中继电路为基础的控制系统。本编程采用梯形图的编程方法。PLC系统提供了一个可以在主机电脑终端上运行的软件工具设计环境，在电脑上可以进行梯形图的开发，验证，测试和诊断。首先，用梯形图编辑高级程序；然后，梯形图转换成二进制指令代码，以便它们可以存储

8、在随机存取存储器（ RAM ）或可擦除可编程只读存储器（EPROM）。每个指令被解码后由CPU执行。CPU的功能是控制内存和I / O设备的操作，并根据程序进行数据处理。每个PLC的输入和输出连接点上都分配一个用于识别的I / O位地址。输入，输出和内存中数据的直接代表PLC内存的三个区域，即PLC内存的三个区域为：输入印象寄存器（I），输出印象寄存器（Q）以及内部寄存器（M）。所有存储单元直接地使用%I、%Q和%M作为参考。PLC程序采用循环扫描主程序的循环方式，例如定期检查所作的输入变量。程序循环的开始是扫描系统的输入并且将它们的状态存到固定的存储区（输入印象寄存器I）。然后PLC从上到下

9、一步一步执行梯形图程序，边扫描程序边进行各种各样的梯形图逻辑指令以确定输出状态。更新输出状态并将数据储存在固定的存储区（输出印象寄存器Q）。在程序扫描的结尾在寄存器中的输出值置位或复位PLC的物理输出端。本设计中的PLC，一个周期或扫瞄时间是0.18 ms/K （对于1000条指令）和以1000条指令为最大程序容量。开放系统包括一个主机（个人计算机）以及通过RS232端口连接的目标PLC。主机提供软件环境用来执行文件编辑，存贮、打印和监视程序操作。在PLC中运行程序开发过程包括：使用程序编辑器绘制出源梯形图程序，将源程序转化成能在PLC的微处理器中执行的二进制工程代码，最后通过串行通信端口将工

10、程代码从个人计算机下载到PLC。PLC系统可以在线控制机器同时监控数据使其正确操作。4 结论以上方案的成功实验结果表明，PLC可应用于异步电动机的自动化控制系统中。事实证明用PLC控制和变频器驱动的异步电动机监控系统，在恒速变负荷运行中的调速精度较高。基于PLC软件控制的效率可以达到同步转速的96 ，这是令人满意的。相对于使用变频器反馈到异步电动机的开环配置，用PLC的效率会更高。具体说来，在高速和多负载的情况下，与一个标准网络供给异步电动机相比，PLC控制系统的效率会高出10-12，尽管速度控制使用方法较简单。同时，这个系统提出：l 速度随着负载转矩而不断变化；l 充足的扭矩可使电机工作在一

11、个更宽的速度范围；l 方案具有高精度的闭环速度控制；l 具有更高的效率；l 提供过载保护。因此，在工业电力驱动的应用中，PLC被证明是一种多功能和高效率的控制工具。DESIGN AND IMPLEMENTATION OF PLC-BASED MONITORING CONTROL SYSTEM FOR THREE-PHASE ONDUCTION MOTORS FED BY PWM INVERTERYASAR BIRBIR, H.SELCUK NOGAY Abstract：This paper presents a design and implementation of a monitoring

12、 and control system for the three-phase induction motor based on programmable logic controller (PLC) technology. Also, the implementation of the hardware and software for speed control and protection with the results obtained from tests on induction motor performance is provided. The PLC correlates

13、the operational parameters to the speed requested by the user and monitors the system during normal operation and under trip conditions. Tests of the induction motor system driven by inverter and controlled by PLC prove a higher accuracy in speed regulation as compared to a conventional V/f control

14、system. The efficiency of PLC control is increased at high speeds up to 95% of the synchronous speed. Thus, PLC proves themselves as a very versatile and effective tool in industrial control of electric drives.KEY WORDS computer-controlled systems, computerized monitoring, electric drives, induction

15、 motors, programmable logic controllers (PLC).1. IntroductionWith the rapidly changes on industries and information technologies in recent years, some traditional bulk electronic appliances have to be monitored for a long time. All of their control devices such as communication interfaces gradually

16、enter the Intemet information era. The control of all equipment has been performed through the use of computers. Most equipment uses PLC to connect with computers to monitor each load and electricity consuming devices. Programmable Logic Controllers (PLC) are widely used in industrial control becaus

17、e they are inexpensive, easy to install and very flexible in applications. A PLC interacts with the external world through its inputs and outputs. Since technology for motion control of electric drives became available, the use of programmable logic controllers (PLC) with power electronics in electr

18、ic machines applications has been introduced in the manufacturing automation.This use offers advantages such as lower voltage drop when turned on and the ability to control motors and other equipment with a virtually unity power factor.Many factories use PLC in automation processes to diminish produ

19、ction cost and to increase quality and reliability. Other applications include machine tools with improved precision computerized numerical control (CNC) due to the use of PLC. To obtain accurate industrial electric drive systems, it is necessary to use PLC interfaced with power converters, personal

20、 computers, and other electric equipment. Nevertheless, this makes the equipment more sophisticated, complex, and expensive.A power factor controller for a three-phase induction motor utilizes PLC to improve the power factor and to keep its voltage to frequency ratio constant under the whole control

21、 conditions.The vector control integrated circuit uses a complex programmable logic device (CPLD) and integer arithmetic for the voltage or current regulation of three-phase pulse-width modulation (PWM) inverters. Many applications of induction motors require besides the motor control functionality,

22、 the handling of several specific analog and digital I/O signals, home signals, trip signals, on/off/reverse commands. In such cases, a control unit involving a PLC must be added to the system structure. This paper presents a PLC-based monitoring and control system for a three-phase induction motor.

23、 It describes the design and implementation of the configured hardware and software. The test results obtained on induction motor performance show improved efficiency and increased accuracy in variable-load constant-speed-controlled operation. Thus, the PLC correlates and controls the operational pa

24、rameters to the speed set point requested by the user and monitors the induction motor system during normal operation and under trip conditions.2. PLC as a System Controller Programmable logic controllers are modular, industrially hardened computers which perform control functions through modular in

25、put and output (I/O) modules.The modularity of PLC allows the user to combine generic I/O modules with a suitable controller to form a control system specific to his is most simply understood needs. The operation of a controller by envisioning that it repeatedly performs three steps: a) Reads inputs

26、 from input modules b) Solves preprogrammed control logic c) Generates outputs to output modules based on the control logic solutions. Input devices and output devices of the process are connected to the PLC and the control program is entered into the PLC memory .In our application, it controls thro

27、ugh analog and digital inputs and outputs the varying load-constant speed operation of an induction motor. Also, the PLC continuously monitors the inputs and activates the outputs according to the control program. This PLC system is of modular type composed of specific hardware building blocks (modu

28、les), which plug directly into a proprietary bus: a central processor unit (CPU), a power supply unit, input-output modules I/O and a program terminal. Such a modular approach has the advantage that the initial configuration can be expanded for other future applications such as multi machine systems

29、 or computer linking.3. Control System of Induction MotorThe software models generated in the Software Requirements Analysis phase of the development project are refined and embellished in the design phase of the project.This phase involves making implementation decisions such as the interfacing bet

30、ween different software modules, the break down of software across multiple processors, assigning inputs and outputs to I/O cards, etc. PLC software, once written must be easy and intuitive to follow. PLCs are an integrated part of the domain system,advances in the technology of the system will effe

31、ct the requirements of the PLC software. PLC software must therefore be maintainable and extensible.The block diagram of the experimental system is illustrated. The following configurations can be obtained from this setup.a) A closed-loop control system for constant speed operation, configured with

32、speed feedback. The induction motor drives a variable load, is fed by an inverter and the PLC controls the inverter output. b) An open-loop control system for variable speed and variable frequency operation. The induction motor drives a variable load and is fed by control mode. The PLC is an inverte

33、r in constant in activated. c) The standard variable speed operation. The induction motor drives a variable load and is fed by a constant voltage-constant frequency standard three-phase supply. The open-loop configuration b) can be obtained from the closed-loop configuration a) by removing the speed

34、 feedback. On the other hand, operation c) results if the entire control system is bypassed.PLCs programming is based on the logic demands of input devices and the programs implemented are predominantly logical rather than numerical computational algorithms. Most of the programmed operations work on

35、 a straightforward two-state “on or off” basis and these alternate possibilities correspond to “true or false” (logical form) and“ 1 or 0” (binary form),respectively. Thus, PLCs offer a flexible programmable alternative to electrical circuit relay-based control systems built using analog devices.The

36、 programming method used is the ladder diagram method. The PLC system provides a design environment in the form of software tools running on a host computer terminal which allows ladder diagrams to be developed, verified, tested, and diagnosed. First, the high-level program is written in ladder diag

37、rams. Then, the ladder diagram is converted into binary instruction codes so that they can be stored in random-access memory (RAM) or erasable programmable read-only memory (EPROM). Each successive instruction is decoded and executed by the CPU. The function of the CPU is to control the operation of

38、 memory and I/O devices and to process data according to the program. Each input and output connection point on a PLC has an address used to identify the I/O bit. The method for the direct representation of data associated with the inputs, outputs, and memory is based on the fact that the PLC memory

39、 is organized into three regions: input image memory (I), output image memory (Q), and internal memory (M). Any memory location is referenced directly using %I, %Q, and %M.The PLC program uses a cyclic scan in the main program loop such that periodic checks are made to the input variables.The progra

40、m loop starts by scanning the inputs to the system and storing their states in fixed memory locations (input image memory I). The ladder program is then executed rung-by-rung. Scanning the program and solving the logic of the various ladder rungs determine the output states. The updated output state

41、s are stored in fixed memory locations (output image memory Q).The output values held in memory are then used to set and reset the physical outputs of the PLC simultaneously at the end of the program scan. For the given PLC, the time taken to complete one cycle or the scan time is 0, 18 ms/K (for 10

42、00 steps) and with a maximum program capacity of 1000 steps. The development system comprises a host computer (PC) connected via an RS232 port to the target PLC. The host computer provides the software environment to perform file editing, storage, printing, and program operation monitoring. The proc

43、ess of developing the program to run on the PLC consists of: using an editor to draw the source ladder program, converting the source program to binary object code which will run on the PLC s microprocessor and downloading the object code from the PC to the PLC system via the serial communication po

44、rt. The PLC system is online when it is in active control of the machine and monitors any data to check for correct operation.4. Conclusion Successful experimental results were obtained from the previously described scheme indicating that the PLC can be used in automated systems with an induction mo

45、tor. The monitoring control system of the induction motor driven by inverter and controlled by PLC proves its high accuracy in speed regulation at constant-speed-variable-load operation. The effectiveness of the PLC-based control software is satisfactory up to 96% of the synchronous speed. The obtai

46、ned efficiency by using PLC control is increased as compared to the open-loop configuration of the induction motor fed by an inverter. Specifically, at high speeds and loads, the efficiency of PLC-controlled system is increased up to 1012% as compared to the configuration of the induction motor supp

47、lied from a standard network. Despite the simplicity of the speed control method used, this system presents: n constant speed for changes in load torque; n full torque available over a wider speed range; n very good accuracy in closed-loop speed control scheme; n higher efficiency; n overload protection. Thus, the PLC proved to be a versatile and efficient control tool in industrial electric drives applications. 10