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毕业设计论文-恒温箱温度控制系统的设计,毕业设计,论文,恒温箱,温度,控制系统,设计

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毕业设计（论文）中期检查表（指导教师）指导教师姓名：韦寿祺填表日期： 2016 年 04 月 21 日学生学号1200120304学生姓名孙卉题目名称恒温箱温控制系统的设计已完成内容1、 搜集并查阅文献，完成开题报告2、 完成外文翻译3、 完成主控电路板、系统供电电路板、加热驱动板的PCB图。制作出部分的硬件电路，经过测试，板子工作正常。4、 部分模型的建立 检查日期：2016年04月21日完成情况全部完成R按进度完成滞后进度安排存在困难1、 外文翻译准确度稍差，且排版存在问题。2、 程序编写的还不是很完善，未能达到预期的期望3、 在检测电压和检测电流的时候，选取的电压和电流互感器的时候参数难以确定。4、制作加热灯的晶闸管驱动电路的时候，因为未将弱电和强电布线过进，导致上电时产生爬电、电弧现象。5、对建模软件MATLAB的使用还不是很熟练，对一些专业知识理解的不够透彻，使PID参数的整定难度增加解决办法1、 多查阅资料，多请教英文专业的同学，排版时要更加细心。2、 多查阅相关资料，不断进行调试，知道达到预期效果。3、 查阅资料，和根据自己所买的加热器件的参数，确定电压互感器和电流互感器的变比等参数。4、将板子的布线进一步优化，将弱电和强电的先尽可能分开，在距离近的地方，在板子上打通孔，利用空气绝缘。5、多上网查询该软件的使用方法或询问会使用该软件的同学，多看书，及时了解该方面的专业知识，了解相关系统的原理及参数的整定。预期成绩优 秀良 好R中 等及 格不及格建议按照任务书提出的要求，查阅和收集了相关资料，并在此基础上撰写了开题报告。且自己查找外文文章并对其进行翻译。确定设计的总体思路，电路的设计，编写程序，完成了部分电路的制作与=调试。开始建立模型。表现良好，达到了中期检查的要求。 教师签名： 教务处实践教学科制表说明：1、本表由检查毕业设计的指导教师如实填写；2、此表要放入毕业设计（论文）档案袋中；3、各院(系)分类汇总后报教务处实践教学科备案。11223344DDCCBBAATitleNumberRevisionSizeA4Date:2016/6/1Sheet ofFile:E:.Sheet1.SchDocDrawn By:S1S212J1220VACF1250VAC/30ARV110D471C10.1uF,275VACT19VACD11N4007D21N4007D41N4007D51N4007C22200uF,25VC3100uF,25VC50.1uFInput3GND2Output1U1LM7805C4100uF,25VC60.1uFR7100KR6510D3GNDVDD_5V220VAC_L220VAC_NANODE1CATHODE2NC3MAIN TERM4NC5MAIN TERM6U2MOC3021213T2BT41800R11330RVDD_5VR13330RR17470R12J2ROAD1243U3PC817D61N4007D71N4007D91N4007D81N4007R1030K,2WR84.7KVDD_5VR1530K,2WQ12N3904R121KR16100KR94.7KVDD_5VGNDGNDGNDMCU_P32220VAC_L220VAC_NMCU_P33R1422K,2WC70.1uF,400V220VAC_N220VAC_LGND1VCC2VO3RS4RW5E6D07D18D29D310D411D512D613D714BLAVCC15BLKGND16LCD1LCD1602GNDGNDVDD_5VVDD_5VR1810KVDD_5VLCD_RSLCD_RWLCD_ENLCD_D0LCD_D1LCD_D2LCD_D3LCD_D4LCD_D5LCD_D6LCD_D7EA/VPP31XTAL119XTAL218RST9P3.7(RD)17P3.6(WR)16P3.2(INT0)12P3.3(INT1)13P3.4(T0)14P3.5(T1)15P1.01P1.12P1.23P1.34P1.45P1.56P1.67P1.78(AD0)P0.039(AD1)P0.138(AD2)P0.237(AD3)P0.336(AD4)P0.435(AD5)P0.534(AD6)P0.633(AD7)P0.732(A8)P2.021(A9)P2.122(A10)P2.223(A11)P2.324(A12)P2.425(A13)P2.526(A14)P2.627(A15)P2.728PSEN29ALE/PROG30(TXD)P3.111(RXD)P3.010GND20VCC40U5STC12C5A60S2MCU_RSTMCU_XTAL1MCU_XTAL2LCD_RSLCD_RWLCD_ENLCD_D0LCD_D1LCD_D2LCD_D3LCD_D4LCD_D5LCD_D6LCD_D7GNDVDD_5VVDD_5VR1910KR2010KR2110KVDD_5VS6C100.1uFR2210KGNDMCU_RSTVDD_5V12Y112MHzC1330pFC1430pFGNDMCU_XTAL1MCU_XTAL2S3S4S5GNDR110KR210KR310KR410KR510KVDD_5VLS1BUZZERQ22N3906R23100KGNDR241KVDD_5V VDD_5VGND1I-2I+3VCC4SCK5CS6SO7NC8U4MAX6675C80.1uFVDD_5VGNDGNDC90.1uFVDD_5V12J3MCU_P10MCU_P11MCU_P12MCU_P13MCU_P14MCU_P15MCU_P16MCU_P17MCU_P32MCU_P33MCU_P34MCU_P35MCU_P10MCU_P11MCU_P12MCU_P13MCU_P14MCU_P15MCU_P16MCU_P17MCU_P34C110.1uFVDD_5VGNDC120.1uFVDD_5VGND01. 按键电路02. 5VDC稳压电路03. 过零检测04. 加热负载驱动电路05. MCU控制系统06. LCD1602显示08. 蜂鸣器驱动07. 热电偶信号处理电路 光刻投影镜头多闭环温度控制系统 摘 要 图像质量是光学光刻工具的最重要指标之一，尤其易受温度、振动和投影镜头（PL）污染的影响。本地温度控制的传统方法更容易引入振动和污染，因此研发多闭环温度控制系统来控制 PL 内部温度，并隔离振动和污染的影响。一个新的远程间接温度控制（RITC）方案，提出了利用冷却水循环完成对 PL 的间接温度控制。嵌入温度控制单元（TCU）的加热器和冷却器用于控制冷却水的温度，并且，TCU 必须远离PL,以避免震动和污染的影响。一种包含一个内部级联控制结构（CCS）和一个外部并行串联控制结构（PCCS）的新型多闭环控制结构被用来防止大惯性，多重迟滞，和RITC 系统的多重干扰。一种非线性比例积分（PI）的算法应用，进一步提高收敛速度和控制过程的精度。 不同的控制回路和算法的对比实验被用来验证对控制性能的影响。结果表明，精度达到 0.006规格的多闭环温度控制系统收敛率快，鲁棒性强，自我适应能力好。该方法已成功地应用于光学光刻工具，制作了临近尺寸（CD）100 纳米的模型，其性能令人满意。 关键词关键词：投影镜头，远程间接温度串级控制结构，并行串连控制结构，非线性比例积分（PI）的算法 1 简 介 由于集成电路缩小，更小的临界尺寸（CD）要求，生产过程的控制越来越严格。作为最重要的制造工艺设备，先进的光学光刻工具需要更严格的微控制环境，如严格控制其温度、洁净度、气压、湿度等。温度波动，特别是导致图像失真和平面图像转变，成为了光学光刻工具对图像质量影响的一个关键因素。投影镜头(PL)内的温度精度要求一个光刻工具在接近 0.01制造一个小于 100 nm 的模型。另外需要 PL 内部温度收敛率快以降低光刻技术的所有权（CoD）的成本. 然而，实现这些目标是一个很大的挑战，因为加热器和冷却器控制温度要求操作远离 PL, 否则其性能将被它们的振动和污染所破坏。另一个原因是，PL 内部结构复杂，它包含数十个镜头，会导致几个小时惯性，所以 PL 内部的温度反应相当缓慢，并需要很长时间去调整适应。因此，一个新的结构和控制算法是 PL 内部温度控制的必要和重要部分。 许多温度控制结构已经被提出了。著名的经典方法之一是被广泛应用于简单或低精度温度控制系统的单闭环回路控制结构。当被控对象变得更加复杂或产生分布式干扰时，串级控制结构（CCS）的提出改善了精度和收敛率。预测前馈控制结构已被证明具有更好的滞后系统性能。另一种有效的方法，并行串级控制结构（PCCS） ，也开发了具有延迟分布式干扰的系统。但是上述使用方法，很难实现 PL 内部温度控制的 高精确度和快收敛率。 在此，本文提出了一种新的方法，即多闭环温度控制系统，含有一个内部 CCS 和一个外部 PCCS。本文大致分为四个部分。第一部分解释了一个远程间接温度控制方法的应用。第二部分是一个多闭环回路温度控制结构的分析。第三部分，一个双进双出非线性比例积分（PI）算法的提出用来提高控制过程的收敛速度和精度。在文章的最后一部分，对比实验验证了系统的有效性这种显示，最后，给出了结论。 2 远程间接温度控制方法 为了防止震动和污染影响 PL 的性能， 一个远程间接温度控制的方法被提出来控制PL 内部温度。不同于传统的直接加热和冷却控制对象的方法，它借助于冷却水和冷却套间的热交换使 PL 内部温度恒定。冷却水通过长距离管道由 TCU 输送至冷却外壳。TCU 由水箱、温度传感器、温度控制器、加热器、冷却器和泵组成。它用于调节冷却水的温度以达到需求值。 TCU 和光刻工具放置在不同的洁净室， 如图 1 所示。 理论上，这种方法属于开环结构。 除了 PL，其他光刻技术的部分，如晶圆阶段、标线的阶段、标线交接、晶圆移交等，都在操作时产生热量。TCU 中的冷却水还用于冷却光刻技术的其他部件。循环系统回收冷却水，节省最大能量，是很必要的。图 1 展示了包括 TCU、分离器、冷却套和管道的循环系统。从储水中抽出冷却水通过管道和分离器进入冷却套，最后通过合成器、管道和冷却器流回储水箱。 对冷却水循环系统的分析表明了影响 PL 内部温度的三个主要因素：干扰多，迟滞多，还有惯性大。干扰多，包括冷却水温度波动，PL 内部热量散失，PL 和外部介质之间的热交换。 冷却水温度波动是多种因素造成的， 其中包括 TCU 内部自励温度震荡造成的非线性加热冷却，管道和周围气体之间的热传递，以及光刻工具其他地方产生的热量。在这个循环系统中，冷却水温度波动达到 0.1是最差的情形。PL 内部热量散失有两个原因，一个是当激光穿过透镜时，内部辐射和导热交换，另一个是在镜 头和内部净化氮之间的导热和对流热交换。至于激光，它的散热量大概是 15W。PL与外部介质之间热交换来自两个方面，一方面来自 PL 与其相邻零件之间的相互热交换，另一方面来自 PL 外部箱体和周围空气的导热和对流热交换。但是，PL 和外部介质之间交换的热量由于其复杂性，故难以计算。迟滞多主要包括 TCU 加热和冷却 3秒迟滞，冷却水交换 3 分钟迟滞，还有 PL 和冷却套间热交换 10 分钟迟滞。此外，PL的复杂结构导致不平衡热交换，而由于其体积大导致惯性在和小体积物体相比时，温度波动较小。 上述分析表明，仅仅通过开环结构使 PL 内部温度控制精度高和收敛速度快是非常难以实现的。此外，在开环结构中还有很大的稳态误差。在以下部分中，我们将介绍一个提高 PL 内部温度控制的控制结构，并解释如何提高温度控制精度和收敛率。 3 多闭环控制结构 多闭环温度控制结构由一个内部 CCS 和一个外部 PCCS 组成。 3.1 串连控制结构 PL 温度控制的内部 CCS 如图 2 所示。有两个分别带有两个控制器的反馈回路。主要回路用来控制 PL 内部的温度(T1)。 TCU 水箱中的冷却水温度控制(Tw)形成了第二条回路. 分析这个系统的运作质量是很容易。如果 PL 内部温度偏离期望值(Ts), 嵌入主控制器中的控制算法会通过比较温度的测量值Tl和期望值Ts之间的偏差而计算一个新的冷却水温度设定值（Tt） 。然后，发送新的设定值 Tt给 TCU 的温度控制器。随后根据温度测量值 Tw和新的设定值 Tt间的偏差，TCU 中的控制算法计算加热器和冷却器的输入值， 并对 TCU 中水箱里的冷却水进行加热或者降温， 直到温度达到新的设定值。 PL 内部温度期望设定值通过一台机器连续地给出。 Ti 控制回路是一个慢控制回路。Tw控制回路是一个快速控制回路，能快速跟随主回路设定值 Tt。当一个新的设定值 Tt发送到 TCU，它需要几分钟时间去调整 TCU 水箱中的水温至设定值。二次回路具有很强的抗内部干扰的能力。此外，还可以减少对主回路非线性和迟滞的影响。 图 3 显示了关于上述描述串级控制系统的控制原理图。在下面的图表和方程式， Gt(s)表示加热器和冷却器传递函数,Gp(s)表示管道传递函数，Gl(s)表示 PL 传递函数。Gm(s) Gm(s)表示主控制回路传递函数，Gs(s)表示二次控制回路传递函数。Hm(s) 表示测量设备主回路传递函数， Hs(s)表示测量设备二次回路传递函数。 表示 TCU 水箱中冷却水迟滞， 表示通过管道的冷却水迟滞，表示 PL 内部热交换迟滞，Nt(s) 表示TCU外部扰动,Np(s)表示管道外扰动,Nc(s)表示PL外部扰动,Nn(s)表示PL内部扰动,Rl(s)表示 PL 内部输入温度，Rt(s)表示 TCU 水箱中冷却水的输入温度，C1(s)表示 PL 内的输出温度，Ct(s)表示 TCU 水箱中冷却水的输出温度。 二次回路中的输入输出函数如下所示： 根据二次回路的稳态，输出 Ct(s)近似等于输入 Rt(s)。因此，主回路的输入输出函数可表示如下： 在此 早期的研究表明，PL 的时间常数约为 4h。传递函数 G1(s）为 传递函数 Gp(s)为 对于简单的闭环系统CCS， 很容易消除它的稳态误差。 然而， 根据方程式(2)和 （3)，PL 里温度的收敛率从开始到稳态变慢，因为和的延迟。而且，很难获得PL里面 很精确的温度，因为和的扰动。在定态的状态之下，由于的作用，当瞬时温度变动超过冷却水温度0.1时，PL 里的温度变动超过 0.O 1。需要几个控制周期才达到下一个稳定状态。因此介绍PCCS来提高控制特性。 3.2 并行串联控制结构 图4是扩展的PCCS。这个图省略了操作系统，在系统的框中确定了主要组成环。与 CCS 相比较，也有两个控制环和两个控制器。一个是PL里温度的主环，另一个是结合处冷却水温度的副环。它们之间的不同是主控制对象和副控制对象之间是并行的。副控制对象的输出不是主控制对象的输入。在这个系统中，控制运算法则是主要的控制器根据和之间的偏差决定一个新的冷却水的最佳温度值。然后辅助的控制器中的控制运算法则依照和之间的偏差计算TCU的输入。控制环是一个慢的控制环。控制环是一个快速控制环，它过去一直快速的预测结合处的冷却水最佳温度值。当PL内的温度是想要的值时，结合处冷却水的温度就是最佳温度。这个最佳温度将会保存为一个常数。从扰动抑制的观点看，根据前馈控制相同的原则来控制辅助环。他们之间的不同是扰动必须是可测量的前馈结构，而PCCS可应用于不可测量的扰动。PCCS的另一个优点是它可加速主环的收敛率。 图 5 显示了上面提到的并行串联控制系统的详细原理图。在下面的图表和方程式中，代表结合处冷却水的传递函数，代表副控制器的传递函数。代表辅助环测量装置的传递函数，代表结合处冷却水的输入温度，代表结合处冷却水的输出温度。 副环的输入输出的传递函数如下： 在副环的稳定状态下，输出和输入近似相等。所以主环的输入和输出的传递函数可以简化为： 比较方程（2） （3）和（7） ，我们可以得出扰动和延迟时间常数从主环分离，只有扰动和延迟时间常数仍在主环内。所以辅助环获得了物理结构中互相延迟和互相扰动的分离，且隔离了主控制对象的非线性，互相延迟和互相扰动的影响。这种结构也控制器设计的困难。即使冷却水有温度的变动，他也能通过副控制器补偿。因此，PL 内的温度控制可具有高精度和快收敛率。 4 非线性比例积分算法 为了进一步提高系统的收敛率和精确度，一种具有非线性 PI 算法的二重输入和二重输出智能控制器被设计出来，如图六所示。PL 里的温度偏差和结合处冷却水的温度偏差都是控制器的输入端。控制器的输出端是 TCU 里面冷却水温度值和结合处最佳冷却水温度值。 控制器里嵌有智能算法。 它包括两级且根据理想的动态响应分为五个控制阶段。高级算法决定从我们先前介绍的五个阶段中选择10。非线性 PI 算法在低级算法中使用，它将在后面的段落中介绍。 考虑到温度控制系统的相互扰动特点，PI 算法代替了不同比例积分算法（PID） ，因为不同项目将引起高频率振动和增加系统稳定性误差。 图七显示了非线性 PI 算法的原理图，在接下来的图表和方程中，代表 TUC内冷却水的温度值，代表结合处最佳冷却水的温度值，代表 PI 控制法对的 影响，代表 PI 控制法对的影响，代表 PI 控制法对的影响，代表PI 控制法对的影响，和代表数据融合系数。 控制算法可以被描述如下： 其中 i=1，2，j=1，2，是基本不相关的增加的 PI 控制算法： 其中，代表比例系数，代表积分系数，代表取样结果，和分别代表在 k-1 和 k 时刻的控制输出，e（k-1）和 e（k）分别代表（k-1）和 k 时刻的信号偏差。 数据混合系数由已有的规则得出。详细规则如下： 其中代表由 PL 内温度的的稳态误差决定的偏差值，代表由 PL 内温度的暂态误差决定的扰动值，代表由结合处冷却水温度的稳态误差决定的偏差值，代表由结合处冷却水温度的暂态误差决定的扰动值。 根据已有的规则和控制过程的输入信息，可以获得十六种不同的算法。根据输入数据控制器可以灵活的选择任何一种算法。这不仅能提高算法的适应性和收缩率，还能增强系统的稳定性和反干扰能力。 5 实验验证控制结构与算法 如图 8 所示， 建立了一个实验平台来验证该方法的有效性， 其中包括一个仿制 PL，温度传感器，温度测量系统，TUC，工程计算机，隔热室，光源等。仿制的 PL 与实 际的 PL 具有相同的温度特性。隔热室模仿光刻表面隔离热的作用。用一个 20W 的白炽灯作为暴露光源。三个温度传感器具有高精度的负温度系数，的校准精度是用来检测 PL 内的温度，结合处冷却水的温度和热隔离室外环境的温度。温度测量系统由 1590 模型超温度计和一个具有分辨率的扫描器组成。TCU 配置了的精确度。工程计算机上具有智能算法。 用四个实验来检测控制系统和算法： （a）是用开环结构， （b）使用具有 PI 算法的CCS， （c）使用具有 PI 算法的 PCCS， （d）使用具有非线性 PI 算法的 PCCS。在这些试验中理想的 PL 温度是 22， 非线性 PI 算法的参数是：是 0.01，是 0.005，是 0.02，是 0.05。 实验结果如图 9 所示。图 9（a）展示了开环结构的温度曲线。正如图 9 所示，PL里的温度在21.75稳定且没有达到TCU设置的22.由于开环系统中存在三个大的稳定性误差，使用闭环系统是非常必要的。图 9（b）显示了使用闭环系统 CCS 在 20 小时后代到了稳定。图 9（c）显示了温度收敛比图 9（b）快，但 PL 内温度的精确度并没有得到很大的提高。图 9（d）显示了具有非线性 PI 算法的 PCCS 系统的温度曲线。它只用了 4.5 小时达到了稳定。即使外部温度在内摆动，PL 内的温度仍可以达到的稳定性。很明显新的方法大大的增加了收敛率，精确性和抗干扰能力。 6 结论 通过使用闭环交互系统可以提高光刻 PL 的温度控制准确性。 通过分析和实验揭示了具有 PI 算法的 PCCS 系统具有预测和滚动最优的能力。它在收敛率，控制精确性， 抗干扰能力方面比开环结构和闭环 CCS 更好。 它用于光学领域生产 100nm工具。经过简单的改进，它也可以控制其他的需要远程遥控的非直接温度控制，尤其是侵入液体的侵入式光刻等复杂对象的温度控制。 JOURNAL OF ELECTRONIC SCIENCE AND TECHNOLOGY, VOL. 9, NO. 1, MARCH 2011 23 AbstractThe wind energy generation, utilization and its grid penetration in electrical grid are increasing world-wide. The wind generated power is always fluctuating due to its time varying nature and causing stability problem. This weak interconnection of wind generating source in the electrical network affects the power quality and reliability. The localized energy storages shall compensate the fluctuating power and support to strengthen the wind generator in the power system. In this paper, it is proposed to control the voltage source inverter (VSI) in current control mode with energy storage, that is, batteries across the dc bus. The generated wind power can be extracted under varying wind speed and stored in the batteries. This energy storage maintains the stiff voltage across the dc bus of the voltage source inverter. The proposed scheme enhances the stability and reliability of the power system and maintains unity power factor. It can also be operated in stand-alone mode in the power system. The power exchange across the wind generation and the load under dynamic situation is feasible while maintaining the power quality norms at the common point of coupling. It strengthens the weak grid in the power system. This control strategy is evaluated on the test system under dynamic condition by using simulation. The results are verified by comparing the performance of controllers. Index TermsBattery energy storage, power quality, wind energy generating system. 1. Introduction In the recent years, wind energy generation has been focused as a clean and inexhaustible energy and its penetration level has increased throughout the world. The growth rate of renewable investment in the power Manuscript received October 18, 2010; revised February 18, 2011. S. W. Mohod is with the Department of Electronic Engineering, Prof. Ram Meghe Institute of Technology & Research, Badnera-Amravati. Presently he is a research scholar with Visvesvaraya National Institute of Technology, Nagpur, India. ( E-mail: sharadmohod). M. V. Aware is with the Department of Electrical Engineering, Visvesvaraya National Institute of Technology, Nagpur, India (e-mail: mva_win ). Digital Object Identifier: 10.3969/j.issn.1674-862X.2011.01.005 generation is increasing world-wide. Germany has around 16% power from wind and Denmark 20%. US is planning to generate 20% power from wind. India is the fifth largest wind energy producing country, having gross wind power potential estimated as 45,195 MW and installed capacity 10,925 MW in 2009. However, the output power of wind generator is fluctuating and will affect operation of interconnected grid. The utility system cannot accept the new generation without the strict condition of voltage regulation due to real power fluctuation and reactive power generation/absorption. These require some measures to mitigate the output fluctuation so as to keep the power quality in the grid. There have been a number of studies done to evaluate and mitigate the impact of wind generating system on the grid. A few studies in the interconnected grid system are based on the form of hydrogen, capacitor, batteries storage, and superconducting magnetic energy storage1-5. In Japan, battery energy storage was used for mitigation of variations in wind farm output to stabilize the short fluctuations of output6. The bulk energy storage was proposed for managing wind power fluctuation which provides increasing requirement for reserve, enhance the wind power absorption, achieve the fuel cost savings, and reduce CO2 emissions7. The statistical approach was proposed for utilization of two batteries energy storage, in which wind power is used to charge one battery storage and the other is used to discharge the battery storage8. The control method for the state of charge of battery was proposed in 9. The static compensator and battery energy storage was proposed for fixed speed wind generator to improve the power quality and stability for the power system10,11. The penetration of wind generation into the power system will increase further due to the use of variable speed wind generation to accommodate the maximum power in the power system. Thus, it promotes wind generating system through battery energy storage in todays scenario. The battery storage provides a rapid response for either charging or discharging the battery thus it acts as a constant voltage source in the power system. The battery storage is effective when wind speed output fluctuations are high particularly at speed just below the normal operating speed. Hence, output smoothing strongly depends on battery storage capability. In this paper, the proposed system is efficient and Battery Energy Storage to Strengthen the Wind Generator in Integrated Power System Sharad W. Mohod and Mohan V. Aware JOURNAL OF ELECTRONIC SCIENCE AND TECHNOLOGY, VOL. 9, NO. 1, MARCH 2011 24 economical to strengthen the power system. In order to verify the effectiveness of the proposed system, current control mode of voltage source inverter is proposed with battery storage and wind generating system. The controller action is simulated in MATLAB/SIMULINK based on instantaneous modeling approach. The proposed control system with energy storage has the following objectives: Unity power factor at the common coupling bus; Reactive power support from wind generator and batteries to the load; Stand-alone operation in case of grid failure. The paper is organized as follows. Section 2 introduces the generalized weak grid system. Section 3 gives the system configuration to strengthen the power system. Section 4 presents the mathematical model. Section 5 describes the system performance and section 6 draws the conclusion. 2. Weak Generator in Weak Grid System The generalized wind generator interface system in the power system has voltages on each side. The connected bus of wind generator is a weak bus in the power system and it is connected to strong grid through the impedance Z, shown in Fig. 1. In the generalized power system, the three-phase power is transmitted as symmetrical as possible. The line-to-line voltage is 3 times larger than phase voltage and total three-phase power is constant. The voltage drop over the impedance can be written as - 123VVIZ= (1) where V1 and V2 are the root mean square (r.m.s) voltage, I is the r.m.s current and Z is the impedance of transmission line and transformer feeding to grid. At the point of common connection (PCC), wind farm and local load are also connected. The short circuit power SK in wind connection is given as 21KSVZ=. (2) GridV1V2Point of commonconnectionWind powerPQLL+LoadZPwQw Fig. 1. Generalized wind generator in the power system. The change in wind power production will cause changes in the current through the impedance Z. These current changes cause the changes in the voltage V2. In practice, connections with network having short circuit ratio less than 2.5 are to be avoided, as it gives rise to the voltage fluctuations and it is called as weak grid. The impedance ZRjX=+ is at the fundamental frequency. Generally the impedance in presence of harmonics becomes as ( )LZ hRjhX=+ (3) where h is the harmonic order, that is to say, the inductive reactance changes linearly with frequency. The combination of wind power production and load is represented as PjQ+, where P is the active power and Q is the reactive power. The reactive power is dependent on the phase shift between voltage and current, as shown in (4): 1tanQP=. (4) The reactive power in the wind has an impact on voltage V2. The impact is also dependent on local load and on the feeding grid impedance. Thus, it is necessary to strengthen the weak grid using the energy storage system in the wind energy generated power system. 3. System Configuration to Strengthen the System The proposed energy storage to strengthen the wind generating grid in the power system is configured on its operating principle and based on the control strategy for switching the inverter, as shown in Fig. 2. 3-phase 415 V,50 HzPoint of Common CouplingSourceBattery Energystorage=LoadVs,IsIbInverterAC-DCconverterInterfacingTransformerWind generatorPL,QLV ia,b,cV sa.b.cR,LRi, LiC Fig. 2. Scheme of energy storage to strengthen the wind generator. Point of common connection Wind powerPL+QL LoadPw Qw Z V2 V1Grid Vs, Is3-phase 415 V, 50 Hz point of common couplingsa, ,b cV R, LPL, QLLoadVia,b,c Ri, Li InverterBattery energy storageac-dc converter Interfacing transformerWind generatorSourceIb CMOHOD et al.: Battery Energy Storage to Strengthen the Wind Generator in Integrated Power System 253.1 Operating Principle In the proposed system, the magnitude of source current is determined by the instantaneous current among source, power converter and load. The battery is used as an energy storage element for the purpose of voltage regulation. The wind energy generating system is connected to the uncontrolled rectifier bridge whose output voltage is variable dc and connected to battery storage for charging. The battery can also be charged from grid in low demand in grid and can be used for peak demand. The error current is injected through current control voltage source inverter in the grid at the point of common coupling. 3.2 Control Strategy of the System The control strategy to strengthen the wind generating system is shown in Fig. 3. In the implementation of control strategy into the grid system, a dc link is required to interface the wind energy generating system into the grid through a power converter. The induction generator output is first converted through a rectifier. The dc voltage at which the battery energy storage system (BESS) is connected with reference values and errors is fed into proportional-integral controller. The output of proportional-integral controller is multiplied by a reference sine wave generator. Hence, the desired reference current *RefI can be obtained. The practical current is detected by current sensor and subtracted from the desired reference current so that the error is sent to the hysteresis current mode controller to generate the switching pattern. Thus, this control strategy acts as an instantaneous feedback current control method of pulse width modulation (PWM) for switching the inverter in grid system as shown in Fig. 4. Fig. 3. Control strategy of the system. Fig. 4. Instantaneous feedback control of PWM. The current controlled mode of inverter operation is presented as iaiasaia()()iiidiR iLvvLdt= + (5) ibibsbib()()iiidiR iLvvLdt= + (6) icicscic()()iiidiR iLvvLdt= + (7) dciaibic()ABcdvi Si Si SCdt=+ (8) where iav, ibv, and icv are the inverter voltages, sav, sbv, and scv are voltages at PCC, and iia, iib, and iic are inverter currents. Switching signals are obtained by comparing reference currents *sai, *sbi, and *sci with the actual currents sai, sbi,sci of source. The current errors ai, bi, and ci are applied to the hysteresis controllers that produce the correct signal to switch the power electronics switches ON and OFF until the current exceeds or falls below the tolerance limit. In this technique, a separate comparator is used to drive the inverter. The conduction state of a three-leg inverter is represented by three logic variable switching functions SA, SB, and SC. The characteristics of the switching function as SA=(ai) of a hysteresis controller for phase A of the inverter. The characteristics constitute a hysteresis loop that can be described as 0, if 21, if 2aAaihSih (9) where h denotes the width of the loop, and SA=0 and AS=1 indicate the state of switches. Due to this switching function, the inverter injects the current into the grid in such a way that the source current is harmonic free. The injected current will cancel out the reactive and harmonic part of the load current and thus improve the power factor. To accomplish these goals, the grid voltages are sensed and synchronized in generating the current command for the inverter. For a balanced three-phase source, voltage is written at the grid as sasbscsin()sin(120 )sin(120 ).abcvVtvVtvVt=+? (10) Therefore, the reference current for the comparison must be derived from the source (grid) voltage. These currents can be expressed as VDC(Ref) BESS PI controller X multiplierIsa ia SASASwitching signal Isa(actual) Sine-wave generator Source voltage detector VDC(actual) 0 0.004 0.008 0.012 0.016 0.020Time (s) 6420246 I (Amps) Reference current Hysteresis bands Actual current JOURNAL OF ELECTRONIC SCIENCE AND TECHNOLOGY, VOL. 9, NO. 1, MARCH 2011 26 sasbscsin()sin(120 )sin(240 )iItiItiIt=? (11) where I is proportional to the magnitude of the filtered source voltage of phase a. This ensures that the source current is controlled to be sinusoidal irrespective of whether the source voltage is unbalanced or not. The wind generating system with battery energy storage system is the best suited since it rapidly injects or absorbs the reactive power to stabilize the grid. It also controls the distribution and transmission system at a very fast rate. 4. Mathematical Model of Wind Generating System with Battery The mathematical model of wind generating system is described as follows. 4.1 Wind Energy Generating System The induction generator having been used is wind turbine generating system, because it has advantages of generating the power from variable speed prime mover, being suitable for high speed operation, maintenance, lower cost comparing with other machines of identical rating, and the voltage and frequency being controlled by grid. The output power of this wind turbine system is presented as 3wind12PAV= (12) where (kgm3) is the air density and A (m2) is the area swept out by turbine blade. It is not possible to extract all kinetic energy of wind, thus it extracts a fraction of power in wind, called power coefficient Cp of the wind turbine, and it is given as mechwindpPC P= (13) where Pmech is the mechanical power of wind turbine in Nm, and 160.5917pC = (14) which is also known as Betzs limit. This coefficient can be expressed as a function of tip speed ratio and pitch angle . It is a highly nonlinear function having power function of and . If the mechanical torque Tmech is applied, it is convenient to calculate Pmech from generating system, where is the turbine rotational speed. mechmechturbineTP=. (15) Therefore, mechturbinewind(, )PfV= (16) 23mechwind12pPR VC= (17) where Vwind is the wind speed in m/s. VdcEbCVdcRectifiedfrom windgeneratorIbRbIdc(rect)Idc(inv) Fig. 5. dc link for battery storage and wind generator. 4.2 dc Link for Battery and Wind Generator In the inverter, the capacitor is used as the intermediate element, which decouples the wind generating system and grid system shown in Fig. 3. The use of capacitor is more efficient and less expensive than inductor and it is modeled as dcdc(rect)dc(inv)bdCVIIIdt= (18) where C is circuit capacitance, Vdc is rectifier voltage, Idc(rect) is rectified dc-side current, and Idc(inv) is inverter dc-side current, as shown in Fig. 5. The battery storage is connected to dc-link grid and is represented by a voltage source Eb connected in series with an internal resistance Rb. The internal voltage varies with the charge status of the battery. The terminal voltage Vdc is given as dcbbbVEI R= (19) where Ib represents the battery current. It is necessary to keep adequate dc-link level to meet the inverter voltage: dcinv2 2VVM (20) where Vinv is line-to-neutral r.m.s voltage of inverter, switching frequency is 2 kHz, inverter output frequency is 50 Hz, and M .is modulation index (0.9). Thus the dc link is designed for 800 V. The dc-link capacitance is calculated as cpposICf V= (21) where fs is the switching frequency, Vcpp is the peak-peak value of voltage across the capacitor, and Io is the output current of inverter. 4.3 Model of Battery In the analysis of the system with batteries storage, the mathematical model of battery is dependent on the system studies. The numbers of battery models are available as far as the terminal behavior is concerned12. The approximate short-term model having source Eb connected in series with an internal resistance Rb is used for the study. The response time of battery is dependent on its electrical parameters. In practice the lead acid batteries are generally used. For electrical energy storage applications, a large number of VdcIdc(inv) Idc(rect)Ib Eb CRb Vdc Rectified from wind generatorMOHOD et al.: Battery Energy Storage to Strengthen the Wind Generator in Integrated Power System 27cells are connected in series in order to produce the required operating voltages as design for dc link. 4.4 Voltage Source Inverter In the voltage source inverter, each switch of converter is represented as a binary switch. The value of this resistance is infinite if the switch is OFF and zero if it is ON. The inverter output phase voltage equations can be written and modeled as ANdcBNCN 2111 21311 2ABCVSVVSSV=. (22) where VAN, VBN, and VCN are the phase voltages of inverter. The switching functions for the inverter are derived from a hysteresis type of controller. The SA, SB, and SC are the switching functions and Vdc is the battery voltage13-17. 5. System Performance The scheme of a wind generator with battery energy storage for extraction of wind energy is shown in Fig. 2 and it is simulated in MATLAB/SIMULINK with power system block set. The SIMULINK model library includes the models of converter, induction generator, load, etc. It has been constructed for simulation. The simulation parameters for the given system are listed in Table 1. 5.1 Steady State and Dynamic State Performance The load is considered as a nonlinear load for the simulation of the system. The performance of the system is observed for the power quality improvement as well as to support the load, when source is not available. The inverter is switched on at 0.2 s. The source current Is, load current IL, and inverter injected current Iinv are measured with and without inverter controller in the circuit and also at stand-alone mode of operation. The current supplied from Table 1: System parameters the source is made sinusoidal and harmonics-free as soon as the controller is in the system, which is shown in Fig. 6 (a). The load current in the system is shown in Fig. 6 (b). The injected current supplied from the inverter is shown in Fig. 6 (c). During the interval, the load current will be the addition of source current and inverter current. The grid failure is observed at time t=0.6 s and source voltage is not available, thus inverter will support for the load and will utilize the battery energy storage system from wind generator as a stand-alone mode. Fig. 6. Measured current: (a) source current, (b) load current, and (c) inverter-injected current. Fig. 7. dc Link performance: (a) dc-link voltage (b) rectified current of wind generator, (c) current supplied by battery, and (d) charging-discharging of dc-link capacitor. System parameters Specifications Source voltage 3-phase, 415 V, 50 Hz Source and line inductance 0.5 mH Wind generator parameter (induction generator) 150 kW, 415 V, 50 Hz, P=4, Rs = 0.01 , Rr = 0.015 , Ls=0.06H, Lr=0.06H, Ave. wind velocity: 5m/s dc-link parameter dc Link-800V, C= 5F. Rectifier-bridge parameter Snubber resistance R=100 , Ron=0.01 , C=1 F Inverter-parameter-IGBT- device, three arm bridge type Rated: 1200 V Forward current:50 A Gate voltage: +/20 V T-On delay: 70 ns T-Off delay: 400 ns Power dissipation: 300 W Battery storage dc: 800 V Interfacing transformer Rating-1 MVA,Y-Y type , 415/800 V, 50 Hz Load parameter 3-phase 415 V, nonlinear load _controller-OFFPower Quality modestand-alone-mode(a)00.70.8000(b)0000 300 50 600 8000controller-OFF(c)0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8Time (s) (a) 10050050100Isource (A) 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8Time (s) (b) 1000100Iload (A) 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8Time (s) (c) Iinv (A) 1000100(a)(b)(c)(d)controller-OFF0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8Time (s) (a) 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8Time (s) (b) 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8Time (s) (c) 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8Time (s) (d) 850800750Vdc (V) Idc-WG (A) 40200150100500Ibattery (A) 50050Icap (A) JOURNAL OF ELECTRONIC SCIENCE AND TECHNOLOGY, VOL. 9, NO. 1, MARCH 2011 28 5.2 dc Link Performance The wind energy generator is operated to generate the power and supplied to the uncontrolled rectifier to interface in the dc link. The output of variable speed induction generators are speed dependent and it is necessary to convert the output into dc voltage. The dc-link voltage is shown in Fig. 7 (a). To transfer the real power from the wind generator into the load, the generated power is fed to rectifier for charging the batteries. The control strategy will maintain the constant dc voltage across the dc link. The rectified current from wind generator is shown in Fig. 7 (b) and the current supplied from battery storage is shown in Fig. 7 (c). The charging and discharging of dc-link capacitor are shown in Fig. 7 (d). The depth of discharge is not considered in the simulation. 5.3 Wind Generator Performance The induction generator is connected with turbine and transfer of power is made through the dc link. The wind turbine is operated at a wind speed of 5 m/s. The generated voltage and current is shown in Fig. 8 (a) and (b), respectively. The proportional-integral type controller is used in the control system and its response is very fast. It corrects the errors between measured variable and a desired set value. The Kp determines reaction to the current error and Ki determines the reaction to the sum of recent errors. The PI controller used to increase the overshoot and the changes in the settling time eliminates the steady-state errors in the system. The transfer function for the simulation is considered as 10( )0.0081G ss=+. (23) The performance of controller is shown in Fig. 9, which is used to stabilize the voltage in the distributed network. The source current is maintained in-phase with the source voltage. This indicates the unity power factor at the point of common coupling which satisfies the power quality norms. The results of in-phase source current and source voltage are shown in Fig. 10. Fig. 8. Generated voltage and current of wind energy generator: (a) three-phase voltage and (b) three-phase current. Fig. 9. Controller performance. The current waveform before and after the operation are analyzed for power quality measure. The Fourier analysis of the waveform is expressed without the controller in the system. The total harmonic distortion (THD) of the source current signal is shown in Fig. 11 (a) and the measured THD and its harmonic order is shown in Fig. 11 (b). The power quality improvement is observed at point of common coupling when the controller is in an ON condition. The inverter is placed in the operation and source current waveform is shown in Fig. 12 (a), with its fast Fourier transformation (FFT) in Fig. 12 (b). It is shown that the THD has been improved considerably and within the norms of the standard. The comparative performance with and without inverter controller and international electro- technical standard is presented in Table 2. Fig. 10. Source current and source voltage at PCC. Fig. 11. Current waveform and its FFT without the controller: (a) source current and (b) FFT of source current. 00.700.511.522.533.54Time(s)g a in0 0.1 0.2 0.3 0.4 0.5 0.6 0.7Time (s) 4.03.53.02.52.01.51.00.50Gain (a)(b)0.60 0.65 0.70 0.75 0.80 0.85 0.90Time (s) (a) 100001000V (V) I (A) 500500.60 0.65 0.70 0.75 0.80 0.85 0.90Time (s) (b) sourceV_I Inv.-OFFInv.ONVoltagecurrent0.36 0.37 0.38 0.39 0.40 0.41 0.42 0.43 0.44Time (s) 4002000200400Voltage & Current (a) 0.100 0.105 0.110 0.115 0.120 Time (s) (a) FFT window: 1 of 50 cycles of selected signal10050050100Isource (A) (b) 2 0 2 4 6 8 10 12Harmonic order (b) Fundamental (50 Hz)=64.96, THD=22.91%100806040200Mag (% of fundamental) MOHOD et al.: Battery Energy Storage to Strengthen the Wind Generator in Integrated Power System 29 Fig. 12. Current waveform and its FFT with the controller: (a) source current and (b) FFT of source current. Table 2: Performance of controller Harmonics order in source current F 3 5 7 9 11 THDWithout controller 64.9 0.1 22 10 0.1 8 22.9With controller 44.2 0.2 0.6 0.2 0.1 0.351.29With international electro-technical standard 3 The energy storage scheme for strengthening the wind generator in the power system not only has power quality improvement but also supports real and reactive power to the load. 6. Conclusions The paper proposes wind energy extraction scheme with batteries energy storage system with interface of current controlled mode for exchange of real and reactive power support to the load. The Hysteresis current controller is used to generate the switching signals for the inverter in such a way that it will inject the current into the distributed system. The scheme maintains unity power factor and also harmonic free source current at the point of common connection in distributed network. The exchange of the wind power is regulated across the dc bus having energy storage and is made available under the steady state condition. This also allows the real power flow during the instantaneous demand of the load. The suggested control system is suited for rapid injection or absorption of reactive/real power flow in the power system. The battery energy storage system provides rapid responses, enhances the performance under the fluctuation of wind turbine output, and improves the voltage stability of the system. This scheme provides a choice to select the most economical real power for the load amongst the available wind, battery, and conventional resources and the system supports to strengthen the power system with power quality norms. Acknowledgment Authors thanks for the facilities provided by Dept. of Electrical Engineering, Visvesvaraya National Institute of Technology, Nagpur, India. References 1 Z. Yang, C. Shen, L. Zhang, M. L. Crow, and S. 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