三相四线制电网部分调压调容无功补偿装置的设计
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任务书一、毕业设计（论文）的内容随着我国各种产业的迅速发展，现在电力系统的规模日益扩大，但电力系统的迅速发展也导致了新的矛盾和问题的日益突出，例如系统结构更加复杂，负载用电密度迅速增加，各种复杂、精密、对电能质量敏感的用电设备不断普及，同时用户对电网运行的可靠性和电能的质量要求也越来越高。而三相四线制电网具有三相负荷不平衡严重、负载变化频繁、负载功率因数低等缺点，这不利于电网的安全高效运行。无功补偿是维持电网电压稳定，维持电力系统安全运行的重要手段，而并联电容器是电网进行无功补偿的重要手段。常规的电容器补偿装置采用三相等容量的同时投切方式，容易造成某相过补偿，另一相却欠补偿的现象，而危及电网安全。另外，常规的电容器补偿装置实时性差、补偿精度低和投切过程冲击电流较大等缺点。本毕业设计就是应用电力电子技术，设计一个三相四线制电网部分调压调容无功补偿装置，具体的任务是：1、收集有电网无功补偿的文献资料，了解电网无功补偿的工作原理、控制要求等，重点学习掌握部分调压调容无功补偿系统的构成、运行参数、控制特点等，选择合适的控制方式，制定部分调压调容无功补偿系统的控制方案。2、建立部分调压调容无功补偿系统的数学模型，应用仿真软件进行仿真，分析系统稳态和动态的性能指标。3、完成部分调压调容无功补偿系统的硬件电路设计和相关控制软件程序的编写，绘制系统原理图，计算元器件参数，选择元器件型号。4、制作演示模拟样机，进行软硬件联调。二、毕业设计（论文）的要求与数据1、收集电网无功补偿电路的工作原理及控制方法的相关文献资料15篇以上，其中英文文献不少于2篇。2、部分调压调容电网无功补偿控制系统针对的是三相四线制电源电网，单个补偿电容容量为5kVar，每相为55调节精度等级。 3、选择单片机或PLC作为控制器。4、演示模拟样机仅模拟单相调压调容电网无功补偿部分，即单相220V电源，自行定义补偿电容值（全压补偿容量为100Var以内），分5档调节精度等级。3、 毕业设计（论文）应完成的工作1、完成二万字左右的毕业设计说明书，要求原理正确，数据详实，文理通顺，格式规范；毕业设计说明书的英文摘要要求300个单词以上，内容与中文摘要一致，语句通顺，无语法错误；附15篇以上参考文献，其中英文文献不少于2篇。2、独立完成与课题相关，不少于四万字符的英文资料翻译（附英文原文），要求译文语句通顺，符合汉语习惯，避免出现语法错误。3、根据毕业设计数据要求完成部分调压调容无功补偿控制系统的设计，包括硬件电路图、弱电的PCB板图、强电的接线图；软件的程序框图以及程序的编写；计算电路元器件参数并完成元器件的选型。4、阐述部分调压调容无功补偿装置运行注意事项及保护措施。5、建立部分调压调容无功补偿系统的数学模型，应用仿真软件进行仿真，分析系统稳态和动态的性能指标。6、制作演示模拟样机，进行软硬件联调。演示模拟样机仅模拟单相调压调容电网无功补偿部分，即单相220V电源，自行定义补偿电容值（全压补偿容量为100Var以内），分5档调节精度等级。模拟样机仅作为实验演示用，毕业论文需按工程实际参数设计。四、应收集的资料及主要参考文献1 韦寿祺，刘志杰，苏振源等.三相四线制电网部分调压调容无功补偿装置及方法P.中国专利:CN103490432A，2014-01-01. 2 韩学军.综合补偿三相不平衡负载的研究J.电网技术，2006(30):288-290.3 韩浩.用于380/220V三相四线制的功率因数调节装置P.中国专利:CN202997582U,2013-06-12.4 程顺足，郭西进，李素英.基于交流斩波装置的三相不平衡无功补偿方案J.工矿自动化，2013.39(01):74-77.5 Leszek,Czamecki.Power Related Phenomena in Three-phase Unbalanced Systems.IEEE Transactions on Power Delivery, 1995:1168-1176.6 Feifeng Ji,Muhammad Mansoor Khan, Chen Chen. Static Var Compensator Based on Rolling Synchronous Symmetrical Component Method for Unbalance Three-Phase System. IEEE,2005:621-622.五、试验、测试、试制加工所需主要仪器设备及条件计算机1台、示波器1台、万用表1台、电工工具1套、单片机开发系统1套或PLC1台，电气绘图软件1套，控制系统仿真软件1套。任务下达时间：2015年12月28日毕业设计开始与完成时间：2015年12月28日至2016年05月22日组织实施单位：电气工程及其自动化系教研室主任意见：签字：2015年12月30日院领导小组意见：签字：2015年12月31日开题报告1毕业设计的主要内容、重点和难点等主要内容：随着经济的发展和人民生活水平的提高，用户对供电质量的要求也越来越高，电压是标志电能质量的一个基本技术指标，它与无功功率密切相关。而无功补偿是维持电网电压稳定，电力系统运行的重要手段，常规的电容器补偿装置采用三相等容量的同时投切方式，而采用三相等容量的投切方式容易引入新的故障隐患，并且影响供电水平和质量，危及电网安全。电力系统运行的经济性与电能质量和无功功率有重大的关系。无功功率是电力系统一种不可缺少的功率。大量的感性负荷和电网中的无功功率损耗，要求系统提供足够的无功功率，否则电网电压将下降，电能质量得不到保证。同时，无功功率的不合理分配，也将造成线损增加，降低电力系统运行的经济性。对电网进行无功补偿可以减少线路损耗、改善电能质量，延长了电器寿命，提高了产品质量。主要研究内容如下：（1）查阅资料，研究已有电网无功补偿装置的构成，控制特点，选择合适的方法进行研究和设计；（2）建立无功补偿系统的数学模型并仿真分析稳态和动态指标；（3）研究通过分析确定无功补偿装置设计的方案；（4）完成硬件电路的设计和软件程序的编写。（5）验证方案可行性，制作样机并进行测试。重点：（1）了解三相四线制电源电网无功补偿的原理选择控制方案并实现5档精度调节。（2）建立数学模型，对选择的方案进行仿真系统的稳态和动态性能。（3）制造演示样机，让其实现5档调节精度等级。（4）控制方案程序的编写。难点：（1）如何设计功率因素检测电路精确检测实际的数值并符合单片机采集数据要求。（2）如何设计电容投切控制电路，使之对电网进行精确的补偿并对电网波动不大。（3）如何合理单片机程序，使功率因数检测电路精确反馈到单片机。2准备情况（查阅过的文献资料及调研情况、现有设备、实验条件等）已查阅的文献：1 韦寿祺，刘志杰，苏振源，陈叙，黎明，李雪娇，崔九喜. 三相四线制电网部分调压调容无功补偿装置及方法P.中国专利:CN103490432A,2014年01月01日. 2 韩学军.综合补偿三相不平衡负载的研究J.电网技术,2006年10月，第30卷，增刊：288-290.3 韩浩.用于380/220V三相四线制的功率因数调节装置P.中国专利:CN202997582U,2013年06月12日.4 廖培.不平衡负荷电流无功补偿的优化设计J.现代电力，2007年12月，第24卷，第6期：17-20.5 程顺足，郭西进，李素英.基于交流斩波装置的三相不平衡无功补偿方案J.工矿自动化，2013年1月，第39卷，第1期：74-77.6 单铁铭，杨仁刚.不平衡电流补偿方法研究J.电力自动化设备，2004年12月，第24卷，第12期：26-29.7 许苏跃.配电网三相不平衡全电容无功补偿的研究J.电器与能效管理技术，2015年，第20期.8 高晶晶，赵玉林.电网无功补偿技术现状及发展趋势J.东北农业大学学报，2004年10月，第35卷，第5期：639-644.9 Fei feng Ji, Muhammad Mansoor Khan, Chen Chen. Static Var Compensator Based on Rolling Synchronous Symmetrical Component Method for Unbalance Three-Phase System. IEEE,2005:621-622.10 Leszek S. Czamecki. Power Related Phenomena in Three-phase Unbalanced Systems. IEEE Transactions on Power Delivery, 1995,Vol.10(3),pp.1168-1176.调研情况：（1）三相四线制电网部分调压调容无功补偿研究概况随着经济和科学技术的发展，对电能质量的要求也随之提高。配电网三相不平衡造成了电网系统诸多电能质量不达标的问题，影响良好的生活秩序。电力系统三相不平衡主要是由于系统三相元件或负荷不对称所致，由此产生的不平衡电流对系统影响很大：造成变压器损耗增加，影响出力；电动机效率降低；影响发电机的安全和正常运行；线路损耗增加； 三相电压不对称，不平衡电流分解出来的负序和零序电流对计量仪表的精度也会产生影响。（2）国内外的发展趋势早期的无功补偿装置为同步调相机和并联电容器。同步调相机可以理解为专门产生无功功率的同步电机，但是属于旋转设备，运行中的损耗和噪声都比较大，运行维护复杂，成本高，此外，响应速度慢，难以满足快速动态补偿的要求。并联电容经济方便，但是阻抗不稳定，也不能实现动态补偿。随着电力电子器件的发展，无功补偿控制器在其性能和功能上也出现不同的发展阶段。无功补偿已由基于SCR的静止无功补偿器、晶闸管控制串联电容补偿器发展到基于GTO的静止无功发生器静止同步串联补偿器、统一潮流控制器可转换静止补偿器等。在当今电力系统中，一方面，用户中存在着大量无功功率频繁变化的设备，如轧钢机、电弧炉、电气化铁道等，同时大功率变流、变频等传动装置也将对电网产生大的无功功率冲击；另一方面，现代工业的发展对供电的可靠性和供电质量提出了更高的要求，计算机，机器人，自动化生产线等行业对系统电压稳定性均有较高要求。因此，迫切需要对系统的无功功率进行快速、动态的无功补偿。按电网无功功率补偿方式可分为串联补偿和并联补偿。并联补偿方式又可分为电容器组补偿，调电感补偿，调相机补偿的移相补偿等。本设计我们将采用并联电容器补偿，主要应用单片机技术，实现对低压电力系统的监控，完成功率因数的测量，并根据所得数据进行电容组的投切，以实现对电力系统的补偿。现有设备：计算机1台、电气绘图软件1套，控制系统仿真软件1套。试验条件：示波器1台、万用表1台、电工工具1套、单片机开发系统1套或PLC1台。3、实施方案、进度实施计划及预期提交的毕业设计资料实施方案：本课题有三个主要问题需要解决，分别是补偿装置整体设计、各部分电路的设计和仿真、补偿装置程序和实物设计制作。其中，整体设计可以通过查阅相关资料和借鉴工业成品来解决；各部分电路设计和仿真主要通过所学知识和查阅相关资料吸取总结已有经验，对各部分电路的功能进行仿真和分析；软件程序的设计和实物的制作与调试可以根据所学知识进行，对于该过程中所遇到的问题可以通过查阅相关资料，和同学讨论，询问指导老师，到实验室进行试验等手段解决。具体如下：（1）硬件设计本系统包括以下几部分：以单片机AT89S51为核心，周围电路包括显示电路、电压检测电路、电流检测电路、功率因素检测电路。AT89S51是一种带4K字节闪烁可编程可擦除只读存储器的低电压，高性能CMOS8位微处理器。系统组成如图1所示：AT89S51电流检测电路功率因素检测电压检测电路LED显示V、W相电容投切控制电路图1 系统组成（2）软件设计由主程序、显示电路、电压检测电路、电流检测电路、功率因素检测电路等各部分子程序组成。先确定某一相为控制对象，然后从线路上采集所需要的数据，单片机通过对数据进行的分析后确定其功率因数。接下来判断该相的功率因数是否大于0.95如果大于0.95不进行补偿，如果小于0.95再进行补偿。主程序框图如图2所示：开始确定某相为控制对象采集测试数据查表计算功率因素值显示功率因素功率因素小于0.9？查表计算投切电容容量投切电容返回NY图2 程序框图进度实施计划：序号时间工作内容12015.12.28-2016.01.04查找外文翻译资料。22016.01.05-2016.01.11查找毕业设计需要的参考文献和相关资料。32016.01.12-2016.01.18熟悉任务书内容，无功补偿的工作原理、控制要求。42016.02.29-2016.03.06根据原理以及各部分的内容撰写开题报告。52016.03.07-2016.03.13方案设计，查找资料。62016.03.14-2016.03.20画出原理框架图，提交硬件原理草图一份。72016.03.21-2016.03.27方案论证。82016.03.28-2016.04.04硬件设计布局。92016.04.05-2016.04.11对原理图进行仿真。102016.04.12-2016.04.18绘制PCB图。112016.04.19-2016.04.25器件选型，电路板的制作。122016.04.26-2016.05.02软件编程并与硬件进行联调。132016.05.03-2016.05.09对系统建立模型，并用仿真软件进行仿真。142016.05.10-2016.05.16毕业设计（论文）的撰写。152016.05.17-2016.05.22毕业设计（论文）的撰写。162016.05.23-2016.05.30完成毕业设计，提交论文预期提交的毕业设计资料：1、撰写两万字以上的毕业设计说明书（兼附15篇以上的参考文献）；在毕业设计说明书中应包括300500个单词的英文摘要及关键词；2、完成与课题相关英文资料的翻译（约四万英文字符，附英文全文）；3、完成三相四线制电网部分调压调容无功补偿装置的研究和实现方案；4、设计出系统的硬件和完成相应软件程序设计，给出必需的硬件实现原理图；5、根据课题任务与要求，完成可供掩饰的功能样机。指导教师意见指导教师（签字）： 2016年 3 月 1 日开题小组意见开题小组组长（签字）：2016年 3 月 1 日 院（系、部）意见主管院长（系、部主任）签字： 2016年3月1日- 6 -Design and Practice of an Elevator Control System Based on PLC Xiaoling Yang1, 2, Qunxiong Zhu1, Hong Xu1 1 College of Information Science &Technology, Beijing University of Chemical Technology, Beijing 100029, China 2 Automation College of Beijing Union University,Beijing,100101, China yxl_lmy , zhuqx, Abstract This paper describes the development of 2 nine-storey elevators control system for a residential building. The control system adopts PLC as controller, and uses a parallel connection dispatching rule based on minimum waiting time to run 2 elevators in parallel mode. The paper gives the basic structure, control principle and realization method of the PLC control system in detail. It also presents the ladder diagram of the key aspects of the system. The system has simple peripheral circuit and the operation result showed that it enhanced the reliability and performance of the elevators. 1. Introduction With the development of architecture technology, the building is taller and taller and elevators become important vertical transportation vehicles in high-rise buildings. They are responsible to transport passengers, living, working or visiting in the building, comfortable and efficiently to their destinations. So the elevator control system is essential in the smooth and safe operation of each elevator. It tells the elevator in what order to stop at floors, when to open or close the door and if there is a safety-critical issue. The traditional electrical control system of elevators is a relay-controlled system. It has the disadvantages such as complicated circuits, high fault ratio and poor dependability; and greatly affects the elevators running quality. Therefore, entrusted by an enterprise, we have improved electrical control system of a relay-controlled elevator in a residential building by using PLC. The result showed that the reformed system is reliable in operation and easy for maintenance. This paper introduces the basic structure, control principle and realization method of the elevator PLC control system in detail. 2. System structure The purpose of the elevator control system is to manage movement of an elevator in response to users requests. It is mainly composed of 2 parts: 2.1. Electric power driving system The electric power driving system includes: the elevator car, the traction motor, door motor, brake mechanism and relevant switch circuits. Here we adopted a new type of LC series AC contactors to replace the old ones, and used PLCs contacts to substitute the plenty of intermediate relays. The circuits of traction motor are reserved. Thus the original control cabinets disadvantages, such as big volume and high noise are overcome efficiently. 2.2. Signal control system The elevators control signals are mostly realized by PLC. The input signals are: operation modes, operation control signals, car-calls, hall-calls, safety/protect signals, door open/close signal and leveling signal, etc. All control functions of the elevator system are realized by PLC program, such as registration, display and elimination of hall-calls or car-calls, position judgment of elevator car, choose layer and direction selection of the elevator, etc. The PLC signal control system diagram of elevator is showed in Figure 1. Figure 1 PLC signal control system diagram 2.3. Requirements The goal of the development of the control system is to control 2 elevators in a 9-storey residential building. For each elevator, there is a sensor located at every floor. We can use these sensors to locate the current 2008 Workshop on Power Electronics and Intelligent Transportation System978-0-7695-3342-1/08 $25.00 2008 IEEEDOI 10.1109/PEITS.2008.4494position of the elevator car. The elevator car door can be opened and closed by a door motor. There are 2 sensors on the door that can inform the control system about the doors position. There is another sensor on the door can detect objects when the door is closing. The elevator cars up or down movement is controlled by a traction motor. Every floor, except the first and the top floor, has a pair of direction lamps indicating that the elevator is moving up or down. Every floor, has a seven segment LED to display the current location of the elevator car. The first step for the development of the elevator control is to define the basic requirements. Informally, the elevators behavior is defined as follows. (1) Running with a single elevator Generally, an elevator has three operation states: normal mode, fire-protection mode and maintenance mode. The maintenance mode has the highest priority. Only the maintenance mode is canceled can the other operation modes be implemented. The next is fire-protection mode, the elevator must return to the bottom floor or base station immediately when the fire switch acts. The elevator should turn to normal operation mode when the fire switch is reset. Under normal operation mode, the control systems basic task is to command each elevator to move up or down, to stop or start and to open and close the door. But is has some constraints as follows: Each elevator has a set of 9 buttons on the car control panel, one for each floor. These buttons illuminate when they are pressed and cause the elevator to visit the corresponding floor. The illumination is canceled when the corresponding floor is visited by the elevator. Each floor, except the first and the top floor, has two buttons on the floor control panel, one to request an up- elevator, one to request a down-elevator. These buttons illuminate when they are pressed. The illumination is canceled when an elevator visits the floor, then moves in the desired direction. The buttons on the car control panel or the floor control panel are used to control the elevators motion. The elevator cannot pass a floor if a passenger wants to get off there. The elevator cannot stop at a floor unless someone wants to get off there. The elevator cannot change direction until it has served all onboard passengers traveling in the current direction, and a hall call cannot be served by a car going in the reverse direction. If an elevator has no requests, it remains at its current floor with its doors closed. (2) Parallel running with two elevators In this situation, there are two elevators to serve the building simultaneously. It runs at 7am to 9am and 5pm to 7pm every day. When an elevator reaches a level, it will test if the stop is required or not. It will stop at this level when the stop is required. At the same time, to balance the number of stops, the operation of two elevators will follow a certain dispatching principle. An elevator doesnt stop at a floor if another car is already stopping, or has been stopped there. The normal operation of elevators is implemented by cooperation of its electric power driving system and logic control system. 3. Software design Due to the random nature of call time, call locations and the destination of passengers, the elevator control system is a typical real-time, random logic control system. Here we adopted collective selective control method with siemens PLC S7-200 CPU226 and its extension modules. There are 46 input points and 46 output points in the system. The I/O points are showed in Table1 and Table 2. Table 1 Input points description address 1-8 floor up hall-call I0.0-I0.7 2-9 floor down hall-call I1.0-I1.7 1-9 floor car-call I2.0-I2.7, I3.0 1-9 arrival sensor I3.1-I3.7, I4.0-I4.1 door open button I4.2 door close button I4.3 door close location switch I4.4 door open location switch I4.5 up leveling sensor I4.6 down leveling sensor I4.7 fire switch I5.0 driver operation switch I5.1 touch panel switch of car door I5.2 overload I5.3 Forced speed changing switch I5.4 full load I5.5 Table 2 Output points description address 1-8 floor up hall-call lamp Q0.0-Q0.7 2-9 floor down hall-call lamp Q1.0-Q1.7 1-9 floor car-call lamp Q2.0-Q2.7, Q3.0 up moving lamp Q3.1 down moving lamp Q3.2 Seven segment LED display of elevators position Q3.3-Q3.7 Q4.0-4.1 door opening Q4.2 door closing Q4.3 up moving Q4.4 down moving Q4.5 full load lamp Q4.6 high speed operation Q4.7 low speed operation Q5.0 acceleration of starting Q5.1 deceleration of braking Q5.2-Q5.4 alarm beeper Q5.5 About software designing, we adopt the modularized method to write ladder diagram programs. The information transmission between modules is achieved by intermediate register bit of PLC. 95The whole program is mainly composed of 10 modules: hall-call registration and display module, car-call registration and display module, the signal combination module, the hall-call cancel module, the elevator-location display module, the floor selection module, the moving direction control module, the door open/close module, the maintenance operation module and the dispatching module under parallel running mode. The design of the typical modules is described as follows: 3.1. Hall-call registration and display There are two kinds of calls in an elevator: hall-call and car-call. When someone presses a button on the floor control panel, the signal will be registered and the corresponding lamp will illuminate. This is called hall-call registration. When a passenger presses a button in the elevator car, the signal will be registered and with the corresponding lamp illuminated. This is called car-call registration. Figure2 shows the ladder diagram of up hall-calls registration and display. The self-lock principle is used to guarantee the calls continuous display. Figure 2 up hall-call registration and display 3.2. The collective selection of the calls Here the collective selection control rules are used. As showed in Figure3, M5.1-M5.7, M6.0 and M6.1 are auxiliary relays in PLC. They denote the stopping request signal of 1st to 9th floor respectively. The auxiliary relay M6.2 denotes the elevator drivers operation signal. When there is a call in a certain floor, the stopping signal of corresponding floor will output. When the elevator is operated by the driver, the hall-calls will not be served. And the elevator cannot pass a floor at which a passenger wishes to alight. 3.3. The cancellation of the calls The program of this module can make the elevator response the hall-calls which have the same direction as the cars current direction, and when a hall-call is served, its registration will be canceled. The ladder diagram of up hall-calls cancellation is showed in Figure4. Figure 3 The combination of the calls Figure 4 The cancellation of up calls In Figure4, the auxiliary relay M4.0 is the up moving flag of the elevator. When the current direction of the elevator is up, M4.0s contacts are closed; on the contrary, when the current direction of the elevator is down, M4.0s contacts are opened. M0.1 to M0.7 denotes the car-calls stopping request signal of floor 2 to floor 8 respectively. This program has two functions: (1) Make the elevator response the normal down hall-calls when it is moving down, and when a down hall-call is served, its registration is canceled. (2) When the elevator is moving up, the corresponding floors down hall-call it passing by is not served and the registration is remained. 96The cancellation of down hall-calls is reversed with up hall-calls. 3.4. Elevators direction The elevator may be moving up or down, depending on the combination of hall-calls and car-calls. The following ladder diagram in Fig.5 illustrates that the elevator will move up. Figure 5 Up moving of the elevator Figure5 shows that when the calls corresponding floor is higher than the elevators current location, the elevator will go up. Here the auxiliary relay M4.0 is used as the up-moving flag. When the elevator is moving up, the up-moving lamp is illuminated, so the M4.0 is connected on. When the elevator arrives the top floor, the up-moving lamp is off and the timer starts. After 0.2s, the M4.0 is disconnected, the up-moving display is off. Here we used M4.0 to replace Q3.1 which can ensure the cancellations reliability. 3.5. Elevators floor-stopping Figure6 shows the ladder diagram of the elevators floor-stopping function. As showed in Figure6, M6.4 is the flag of floor-stopping signal. M6.6 is the floor-stopping signal sent by the driver. M7.0 is the fire signal sent by the fire switch. And M6.7 is the forced speed changing signal. When either of these contacts act, the system should send out the floor-stopping signal. 4. Minimum waiting time algorithm In traffic of elevator systems, there are two types of control task usually. The one is the basic control function to command each elevator to move up or down, to stop or start and to open and close the door. The other is the control of a group of elevators. The main requirements of a group control system in serving both, car and hall calls, should be: to provide even service to every floor in a building; to minimize the time spent by passengers waiting for service; to minimize the time spent by passengers to move from one floor to another; to serve as many passengers as possible in a given time1. Figure 6 The elevators floor-stopping There are many dispatching algorithms for elevators group control. Such as Nearest-neighbor Algorithm2, which the elevator always serve the closet request next; Zoning Algorithm3 which by analyzing the traffic of elevator system with unequal floor and population demand to dispatch the elevator; and Odd-even rule, which an elevator only serves the odd floor and the other only serves the even floor. The Nearest-neighbor Algorithm minimizes the length of the elevators empty move to the next request. it usually has very small average waiting times, but individual waiting times can become quite large2. The Zoning Algorithm usually used in buildings which has heavy traffic situations, such as the office building at lunch time. Compared to the office building and shopping mall, the traffic flow of residential buildings is relatively low 97and even in every floor. Secondly, people usually think of elevators as purely functional objects and the experience of riding an elevator is time waited for most of them. Furthermore, there exist immense problems when attempting to satisfy all requirements. Considering all of the reasons above, we adopted the “minimum waiting time” algorithm to realize the 2 elevators parallel running4. 4.1. Evaluation function The goal of the “minimum waiting time” algorithm is to predict the each elevators response time according to all calls, and select the elevator which has the shortest response time to serve. When there is a call, the system calculates out the function values of each elevator according the evaluation function showed in (1) and (2): J(*)=MinJ(1),J(2),J(n) (1) J(i)=Tr(i)+KTd(i)+KTo(i) i=1,2,.,n (2) J(i) is the evaluation index of each elevator; Tr(i) denotes the time of the elevator directly moving to the destination corresponding the latest call from its current floor; To(i) denotes the additional acceleration and deceleration time of a floor-stop of the elevator; Td(i) denotes the average time of the passenger boarding and alighting the elevator; and K is the sum of hall-calls and car-calls. But when a hall-call and a car call corresponds the same floor, the K is only calculated one time. 4.2. Calculation of minimum waiting time In equation (2), K is a certain value, To and Td can be obtained by means of statistics. Tr = T*L, where T denotes the average time of the elevator passing by one floor; L denotes the desired floors of the elevator from current floor to the hall-call floor. In order to calculate the L value, we defined the 2 elevators are A and B respectively; YA,YB denotes the current floor of elevator A and B respectively. H is the corresponding key value when a hall-call button is pressed, and H=floor number of the hall-call. We defined 4 tables for the PLC realization: up hall-call registration table, down hall-call registration table, car-call registration table of A and car-call registration table of B. When a certain call button is pressed, its floor value is recorded in corresponding table. Here we take elevator A as an example. First, define the variable MA, MB and MW. Where MA, MB denotes the extreme value of car-calls with same direction of A or Bs movement respectively. When elevator A is up-moving, set MA is equal to the maximum value in car-call registration table A; when elevator A is down-moving, set MA is equal to the minimum value in car-call registration table A. MW denotes the extreme value of hall-calls with same direction of As movement. When elevator A is up-moving and up-hall-call valueYA, set MW=0; otherwise, set MW is equal to the minimum value in up-hall-call registration table A. When elevator A is down-moving and up-hall-call valueYA, set MW=0; otherwise, set MW is equal to the maximum value in down-hall-call registration table A . Thus, we can determine the L value according to YA, H, MA and MW. There are 3 situations: (1) When the hall-calls direction is opposite to elevator As movement: L=|YA-MA|+|MA-H| (3) (2) When the hall-calls direction is same as elevator As movement and it is in the front of elevator A: L=|YA-H| (4) (3) When the hall-calls direction is same as the elevator As movement and it is in the back of elevator A: L=|YA-MA |+|MA-MW|+|H-MW| (5) So the i-th floors minimum waiting time can be calculated by (6) as follows: Time(i)=TL(i)+KTd(i)+KTo(i) i=1,2,.,n (6) When the calls change during the operation of elevators, the system calculates the minimum waiting time of each elevator. Then it allocates the current call to the elevator which has small value. When the each elevator has the same value, then the current call is prior to elevator A. When an elevator is wrong or not in service, the system can exit the dispatching algorithm and turns to a single elevator running mode. 4.3. Algorithm realization Compared with single elevator running mode, the parallel running mode is mainly different at the processing method about hall-calls. The former uses collective selective control method, and the latter uses dispatch rule combined with collective selective control method. Here the system is to control a 9-storey building, so we choose two Siemens S7-200 PLCs(CPU226) and its Extensive Modules to control the single elevator respectively. And by using PPI Protocol to realize the communication between 2 PLCs. The PPI Protocol adopts m
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