太阳能集热装置自动跟踪太阳方位角系统设计【自动化毕业论文开题报告外文翻译说明书】.zip
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自动化毕业论文开题报告外文翻译说明书
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太阳能集热装置自动跟踪太阳方位角系统设计【自动化毕业论文开题报告外文翻译说明书】.zip,自动化毕业论文开题报告外文翻译说明书
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Design and Implementation of a Sun Tracker with a Dual-AxisSingle Motor for an Optical Sensor-Based Photovoltaic SystemAbstract: The dual threats of energy depletion and global warming place the developmentof methods for harnessing renewable energy resources at the center of public interest. Solarenergy is one of the most promising renewable energy resources. Sun trackers cansubstantially improve the electricity production of a photovoltaic (PV) system. This paperproposes a novel design of a dual-axis solar tracking PV system which utilizes thefeedback control theory along with a four-quadrant light dependent resistor (LDR) sensorand simple electronic circuits to provide robust system performance. The proposed systemuses a unique dual-axis AC motor and a stand-alone PV inverter to accomplish solartracking. The control implementation is a technical innovation that is a simple and effectivedesign. In addition, a scaled-down laboratory prototype is constructed to verify thefeasibility of the scheme. The effectiveness of the Sun tracker is confirmed experimentally.To conclude, the results of this study may serve as valuable references for future solarenergy applications.Keywords: dual-axis Sun tracker; photovoltaic panel; feedback control theory; lightdependent resistor; stand-alone PV inverter; energy gain1.IntroductionWith the rapid increase in population and economic development, the problems of the energy crisisand global warming effects are today a cause for increasing concern. The utilization of renewableenergy resources is the key solution to these problems. Solar energy is one of the primary sources ofclean, abundant and inexhaustible energy, that not only provides alternative energy resources, but also improves environmental pollution.The most immediate and technologically attractive use of solar energy is through photo voltaic conversion. The physics of the PV cell (also called solar cell) is very similar to the classical p-n junction diode. The PV cell converts the sunlight directly into direct current (DC) electricity by the photovoltaic effect 1,2. A PV panel or module is a packaged interconnected assembly of PV cells. In order to maximize the power output from the PV panels, one needs to keep the panels in an optimum position perpendicular to the solar radiation during the day. As such, it is necessary to have it equipped with a Sun tracker. Compared to a fixed panel, a mobile PV panel driven by a Sun tracker may boost consistently the energy gain of the PV panel.Solar tracking is the most appropriate technology to enhance the electricity production of a PV system. To achieve a high degree of tracking accuracy, several approaches have been widely investigated. Generally, they can be classified as either open-loop tracking types based on solar movement mathematical models or closed-loop tracking types using sensor-based feedback controllers 35. In the open-loop tracking approach, a tracking formula or control algorithm is used.Referring to the literature 610, the azimuth and the elevation angles of the Sun were determined by solar movement models or algorithms at the given date, time and geographical information. The control algorithms were executed in a microprocessor controller 11,12. In the closed-loop tracking approach, various active sensor devices, such as charge couple devices (CCDs) 1315 or light dependent resistors (LDRs) 12,1619 were utilized to sense the Suns position and a feedback error signal was then generated to the control system to continuously receive the maximum solar radiation on the PV panel. This paper proposes an empirical research approach on this issue.Solar tracking approaches can be implemented by using single-axis schemes 12,1921, and dual-axis structures for higher accuracy systems 1618,2227. In general, the single-axis tracker with one degree of freedom follows the Suns movement from the east to west during a day while a dual-axis tracker also follows the elevation angle of the Sun. In recent years, there has been a growing volume of research concerned with dual-axis solar tracking systems. However, in the existing research, most of them used two stepper motors 22,23 or two DC motors 16,17,24,25 to perform dual-axis solar tracking. With two tracking motors designs, two motors were mounted on perpendicular axes, and even aligned them in certain directions. In some cases, both motors could not move at the same time 5.Furthermore, such systems always involve complex tracking strategies using microprocessor chips as a control platform. In this work, employing a dual-axis with only single tracking motor, an attempt has been made to develop and implement a simple and efficient control scheme. The two axes of the Sun tracker were allowed to move simultaneously within their respective ranges. Utilizing conventional electronic circuits, no programming or computer interface was needed. Moreover, the proposed system used a stand-alone PV inverter to drive motor and provide power supply. The system was self-contained and autonomous. Experiment results have demonstrated the feasibility of the tracking PV system and verified the advantages of the proposed control implementation.The remainder of the article is organized in the following manner: Section 2 describes the tracking strategies of the developed closed-loop solar tracking system in which a sensor-based feedback controller is used. The detailed architecture of the Sun tracker hardware is proposed in Section 3. In Section 4, a scaled-down laboratory prototype is built and tested. Finally, the main conclusions of this work are drawn in Section 5.2. Developed Closed-Loop Solar Tracking SystemThe block diagram of the developed closed-loop solar tracking system is illustrated in Figure 1, describing the composition and interconnection of the system. For the closed-loop tracking approach, the solar tracking problem is how to cause the PV panel location (output) to follow the sunlight location (input) as closely as possible. The sensor-based feedback controller consists of the LDR sensor, differential amplifier, and comparator. In the tracking operation, the LDR sensor measures the sunlight intensity as a reference input signal. The unbalance in voltages generated by the LDR sensor is amplified and then generates a feedback error voltage. The error voltage is proportional to the difference between the sunlight location and the PV panel location. At this time the comparator compares the error voltage with a specified threshold (tolerance). If the comparator output goes high state, the motor driver and a relay are activated so as to rotate the dual-axis (azimuth and elevation)tracking motor and bring the PV panel to face the Sun. Accordingly, the feedback controller performs the vital functions: PV panel and sunlight are constantly monitored and send a differential control signal to drive the PV panel until the error voltage is less than a pre-specified threshold value. Figure 1. Block diagram of the solar tracking system. The system tracks the Sun autonomously in azimuth and elevation angles. The whole working algorithms are summed up in the flowcharts shown in Figures 2 and 3. The sunlight intensity from four different directions is measured by the LDR-based sensing circuit. The voltages vE, vW, vS and vN are defined as the sensing voltages produced by the east, west, south, and north LDRs respectively. In an attempt to draw maximum power from the PV panel, the azimuth and elevation tracking processes can simultaneously proceed until the PV panel is aligned orthogonally to the sunlight. The tracker installation is not restricted to the geographical location.Figure 2. Flowchart of tracking algorithm for azimuth control.Figure 3. Flowchart of tracking algorithm for elevation control.3. Sun Tracker Hardware DesignFigure 4 presents one of the hardware circuits of the proposed Sun tracker for azimuth tracking. The entire system has two hardware circuits with both of azimuth direction and elevation direction to drive the dual-axis AC motor. The developed Sun tracker is comprised of three modules, which are the LDR-based sensing circuit, comparator and a motor driver with a relay.Figure 4. Complete control circuit diagram of the Sun tracker for azimuth tracking.3.1. LDR-Based Sensing CircuitTo track the sunlight, it is necessary to sense the position of the Sun and for that an electro-optical sensor is needed. The proposed Sun tracker uses the electro-optical sensor for self-calibration. A LDR or photoresistor is a variable resistor whose electrical resistance depends on the intensity of the light falling on it. The LDR resistance decreases with incident light intensity increasing. As seen in the first part of Figure 4, the LDR sensor is a part of the voltage divider circuit in order to give an output voltage.3.1.1. Solar Sensing DeviceThe paper creates a Sun tracker using LDRs with a cylindrical shade as a Sun sensor. Figure 5 shows the designed solar sensing device, which comprises a four-quadrant LDR sensor and a cylinder mounted on a wood-block. The solar sensing device is attached to the PV panel. The East/West LDR and the South/North LDR are respectively used in the detection of azimuth motion and elevation motion of the PV panel. The design of the light sensor is based on the use of the shadow. If the PV panel is not perpendicular to the sunlight, the shadow of the cylinder will cover one or two LDRs and this causes different light intensity to be received by the sensing device.Figure 5. Solar sensing device with a four-quadrant LDR sensor.3.1.2. Creating Feedback Error VoltageThe simple electronic circuit for creating error voltage is presented in the first part of Figure 4. It can be seen that the output voltage of the voltage divider will be lower when the corresponding LDR is shadowed. If one sensor is lighted and the other is shadowed, the differential amplifier amplifies the difference voltage between them. The feedback error voltage can be expressed as: （1）which can be rearranged as follows: （2）If the west LDR is shaded,3.2. ComparatorThe main function of the comparator is to act as a switch to turn on the relay and rotate the motor. A comparator is essentially an operational amplifier (op-amp) operated in an open-loop configuration, which converts a time-varying analog signal into a binary output. As depicted in the second part of Figure 4, the comparator is designed to compare the error voltage with two threshold values. The threshold value is defined as the input voltage at which the output changes states. As shown in Figure 4, there are two threshold values which are given as:The output of the comparator is a high saturated state VH or a low saturated state VL. The saturated output voltages VH and VL may be closed to the supply voltages +VCC and VCC, respectively. The comparator outputs are then expressed as follows:The voltage transfer characteristics of the comparator with ideal op-amps are shown in Figure 6. It is noted that the sensitivity for the tracking system is dominated by the threshold values, which are adjusted by the variable resistor R4 according to the tracking accuracy. As R4 decreases, the tracking accuracy increases. However, the system tracking response will become increasingly oscillatory.Figure 6. Voltage transfer characteristics of the open-loop comparator.3.3. Motor Driver with a Relay As seen in the last part of Figure 4, it is observed that the designed motor driver with a relay consists of two Darlington pairs that provide increased current gain and actuate the relay. If the west LDR is shaded, a feedback error voltage vEW is generated. When vEW VTh1 VTh2, the comparator outputs vPE and vPW go high and low saturated voltages respectively. The transistors Q1 and Q2 will therefore conduct and Q3 and Q4 are in the cutoff state. Referring to Figure 4, transistors Q1 and Q2 operate in the forward-active mode, and the input current or the base current of Q1 is: where VBE is the forward-biased base-emitter voltage of the bipolar transistor. Therefore, the output current can be written as: The parameters 1 and 2 are the common-emitter current gain of the bipolar transistors. The relay is activated by the output current and normally-open contact a1 closes. In this case, thetracking motor rotates clockwise in the azimuth direction and thus the PV panel moves eastward to face the Sun. More specifically, the Sun tracker attempts to adjust the PV panel such that all thevoltages produced by LDRs are nearly equal and balance. As a result, the PV panel is almost perpendicular to the sunlight and has a high energy generation. 5.Conclusions The paper has presented a novel and a simple control implementation of a Sun tracker that employed a single dual-axis AC motor to follow the Sun and used a stand-alone PV inverter to power the entire system. The proposed one-motor design was simple and self-contained, and did not require programming and a computer interface. A laboratory prototype has been successfully built and tested to verify the effectiveness of the control implementation. Experiment results indicated that the developed system increased the energy gain up to 28.31% for a partly cloudy day. The proposed methodology is an innovation so far. It achieves the following attractive features: (1) a simple and cost-effective control implementation, (2) a stand-alone PV inverter to power the entire system, (3) ability to move the two axes simultaneously within their respective ranges, (4) ability to adjust the tracking accuracy, and (5) applicable to moving platforms with the Sun tracker. Theempirical findings lead us to believe that the research work may provide some contributions to the development of solar energy applications.基于单电机的光学传感器的光电系统，设计与实现双轴太阳跟踪器摘要：能源耗竭和全球气候变暖是地方发展的双重威胁，解决方法的公共利益中心是利用可再生的能源资源。太阳能源是一种最有前途的可再生能源。太阳跟踪器可以大幅度提高电力生产。本文提出了一种新颖的利用的双轴太阳跟踪光伏系统的设计反馈控制理论以及四象限光电阻(LDR)传感器和简单的电子电路提供强健的系统性能。拟议的系统采用独特的双轴交流电机和一个独立的光伏逆变器完成太阳能跟踪。 控制执行是一种简单而有效的技术创新设计。此外构造了一个按比例缩小的实验室原型来验证该计划的可行性。实验证实了太阳跟踪器的有效性。 最后，本研究结果可以作为未来太阳能应用的参考。关键词：双轴太阳跟踪器；太阳能光伏板；反馈控制理论的光依赖电阻器；独立光伏逆变器；能量增益 1、介绍随着人口和经济的发展，能源危机的问题的快速增加和全球变暖影响今天是一个令人日益感到关切。可再生能源资源的利用是解决这些问题的关键。太阳能是的主要来源之一清洁、 丰富和取之不尽，用之不竭的能源，这不仅提供了可替代能源资源，但也提高了环境污染。最直接的和技术上有吸引力地利用太阳能是通过光伏转换。（也称为太阳能电池） 在 PV 电池的物理是非常类似于经典的 p n结型二极管。光伏电池将阳光直接转化为直流电 （DC） 电力由光伏效应 1，2。光伏面板或模块是光伏电池封装互连的大会。在为了最大限度地从太阳能电池板，一个需要保留小组在最佳的输出功率位置垂直于白天的太阳辐射。因此，就必须有它的装备与太阳跟踪器。相对于固定效应的面板，由太阳跟踪器驱动手机光伏面板可能刺激一贯的能量增益的光伏面板。太阳能跟踪是最合适的技术，以提高电力生产的光伏系统。要实现较高程度的跟踪精度，几种方法已广泛进行了研究。一般来说，可以列为要么基于太阳能的开环跟踪类型运动数学模型或使用传感器基于反馈的闭环跟踪类型控制器 3 5。在开环跟踪方法，跟踪公式或控制算法。谈到文学 6-10，方位角和俯仰角，太阳角测定太阳运动的轨迹模型或在给定的日期、 时间和地理信息的算法。的控制算法在微处理器控制器 11，12 被处死。在闭环跟踪各种活动传感器设备，例如电荷耦合器件 (Ccd) 13-15 或光的方法依赖电阻器 （异地） 12,16-19 被用于感受太阳的位置及反馈错误信号然后生成控制系统要不断收到的最大的太阳能辐射在光伏面板。本文提出了在这个问题上的实证研究方法。太阳能跟踪方法可以通过使用单轴式方案 12,19-21，和双轴结构的高精度系统 16 18,22 27。一般来说，与单轴跟踪系统单自由度跟随太阳的运动从东到西白天时双轴跟踪也跟随太阳的仰角。近年来，已越来越多研究关注的双轴太阳跟踪系统的容量。然而，在现有的研究中，其中绝大多数用两个步进电机 22,23 或 16,17,24,25 两个直流电动机来执行双轴太阳能跟踪。有两个跟踪电机的设计，两个电机装在垂直轴上，甚至在某些方向对齐它们。在某些情况下，两台发动机都在同一时间 5 不能动弹了。此外，这类系统总是涉及使用微处理器芯片作为控制平台的复杂跟踪策略。在这项工作，只有单一的跟踪电动机，采用双轴企图取得了制定和实施一种简单而有效的控制方案。两轴间的阳光跟踪被允许在他们各自的范围内同时移动。利用常规电子线路，需要没有编程或计算机的接口。此外，拟议的制度使用独立的光伏逆变器驱动电机，并提供电源。该系统是独立和自主。实验结果证明跟踪的可行性光伏发电系统并验证了提出的控制实现的优点。2、 开发闭环太阳能跟踪系统发达国家的闭环太阳能跟踪系统的框图如图 1 所示描述组成和系统的互连。闭环跟踪的方法，太阳能跟踪问题是如何使光伏面板位置 （输出），跟随阳光（输入） 尽可能地接近的位置。基于传感器的反馈控制器包含 LDR传感器、 差分放大器和比较器。在跟踪操作中，低剂量辐射传感器测量阳光作为参考输入信号的强度。低剂量辐射传感器所产生的电压不平衡被放大，然后生成反馈误差电压。误差电压成正比阳光位置与光伏面板位置之间的差异。在这时间的比较将与指定的阈值 （公差） 误差电压进行比较。如果比较器输出变为高电平状态、 电机驱动和继电器被激活，旋转双轴 （方位角和俯仰角）跟踪电机和光伏面板给孙因此，反馈控制器执行的脸重要功能： 光伏面板和阳光不断地进行监测并发送微分控制信号来驱动光伏面板，直到误差电压小于预先指定的阈值。 图 1.太阳能跟踪系统框图。系统会跟踪太阳高度自主的方位角和俯仰角角。整个工作图 2 和图 3 所示的流程图中，总结了算法。四个阳光的强度LDR 基于传感电路测量不同的方向。电压 vE、 大众、 vS 和 vN 是定义为传感电压产生的东、 西、 南、 北异地分别。在尝试从光伏面板、 方位角和仰角跟踪过程可以得出最大功率同时继续进行直到光伏面板垂直对齐在阳光下。追踪器安装并不局限于地理位置。 图 2.跟踪方位控制算法的流程图。 图 3.跟踪高程控制
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