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1、专业好文档基于基于 MPPT 的智能太阳能充电系统研究的智能太阳能充电系统研究 作者：卢琳 殳国华等1 引 言太阳能是一种清洁高效的可再生能源。在阳光充足的白天，屋顶的光伏电池将太阳能转化成电能，供人们在夜晚使用。据专家预测，到 2040 年，全球的光伏发电量将占世界总发电量的 26，2050 年后将成为世界能源的支柱。2 最大功率点跟踪最大功点跟踪(Maximum Power Point Tracking，简称 MPPT)系统是一种通过调节电气模块的工作状态，使光伏板能够输出更多电能的电气系统。图 1 示出光伏电池输出功率 Pb 与输出电压 ub 和输出电流 ib 的关系。图中A 为普通控制
2、器使光伏电池工作在 12V，仅输出 53W 时的功率点(一般功率点)；B 为 MPPT 控制器使光伏电池始终工作在最大功率点，从而 输出高达 75W 时的功率点(最大功率点)。最大功率点主要受环境温度和太阳光强的影响。在太阳光强不变的情况下，随着温度的升高，光伏电池的开路电压降低，最大输出功率随之降低。当温度不变，太阳光强增加时，光伏电池的开路电压基本不变短路电流大幅增加，最大输出功率大幅增加。图 2 示出线性系统电路图。专业好文档首先，计算消耗在 R1 上的功率为：然后，式(1)两边对 R1 求导可得： 由式(2)可得，当 r=R1 时，dP1dR1=0，此时 P1 取最大值。 由于光伏电池
3、系统受到光强、温度、太阳光入射角等多种因素的影响，其输出电压 ub、输出电流 ib 和内阻 r 也处于不停变化之中。只有使用 DCDC 变换器实现负载的动态变化，才能保证光伏电池始终输出最大功率。MPPT 需要及时准确地采样蓄电池当前的充电电压和充电电流。两者相乘得到当前的充电功率，与前一时刻的充电功率相比较，调节 PWM 的占空比，从而使光伏电池始终工作在最大功率点。图 3 示出具体的控制策略。3 MPPT 的硬件设计专业好文档由于光伏电池的输出特性呈非线性，且变化幅度较大，所以使用单端反激式变换器。该变换器由升降压变换器加隔离变压器推演而来，能够简单高效地提供直流输出，广泛用于功率 100
4、W 左右的小型开关电源中。控制器工作于电流断续模式。图 4 示出 MPPT 的硬件设计原理。其中，微控制器采用 MC68HC08SR12 微处理器，使用 AD 模块采样电源的输出电流和输出电压，继而调节 PWM 占空比，最终实现光伏电池的最大功率输出。MPPT 控制策略的效果好坏直接取决于电压和电流的采样是否精确。图 5 示出电压采样电路。它采用光耦 PC817 和三端稳压管 TLA31 相配合。TLA3l 是一种可编程稳压管，当变压器的次级输出电压 uout 变化时，光耦的输出电压随之变化，AD 会采样到当前的充电电压图 6 示出电流采样电路。由它对采样电阻 Rsam 两端的电压进行采样，并
5、使用差分式运算放大器放大输出到MCU 的 AD 采样端，从而得到主电路中的电流值。由于信号需要精确采样，并且与电源隔离，因此使用线性光耦 HCNR200。另外，单片机及周边电路的用电可直接通过蓄电池隔离变压得到，系统无须外部电源供电，十分方便。专业好文档4 软件分析由于太阳光强和环境温度的变化是一个缓慢的过程，故参数采样无须高实时性，每隔几秒钟采样一次即可满足要求。产生中断的时间间隔是可以调整的，初期较短，可以迅速逼近最大功率点；后期较长，防止系统在最大功率点附近振荡。为防止系统误判断，每次控制比较，均进行 3 次，当 3 次的结果一致时，才实施相应的控制策略，否则重新采样比较，这样便最大限度
6、地保证了系统的正常运行。图 7 示出实现 MPPT 的软件流程。由于单片机与开关电源一起工作，相互间的电磁干扰较大，而 AD 采样要求精确。故需要使用软件数字滤波。这里采用均值滤波，即通过多次采样求平均值的方法，以达到去除干扰的目的。蓄电池采用循环充电方式。以 12V 蓄电池为例，在充电电压达到 14.7V 最高限制电压后保持该电压继续充24 小时达到饱和。最大充电电流不允许超过额定容量的 25(如容量为 100A 时的蓄电池，最大充电电流为专业好文档25A)。采用保险丝实现硬件电路的过流保护。图 8 示出软件保护示意图。5 实验结果与展望表 1 给出了系统的主要组成部分及性能指标。图 9 反
7、映了 2005 年 12 月 20 日早上 9 点到下午 4 点的功率P，MPPT 充电器的充电情况及最大功率点的变化情况。12 月 20 日的天气变化较快，时而有阳光，时而多云，时而阴沉。最高 MPPT 可达到 50W，最小只有 5W 左右，这反映出太阳能电源输出功率的多变性。经测试，该 MPPT 充电系统反映出了太阳能电源输出功率的多变性，并可以快速跟踪最大功率点，这对光伏系统的稳定高效工作起到了至关重要的作用。努力提高系统的效率和可靠性，进一步改进 MPPT 算法，则是下一步研究的重点。专业好文档专业好文档Editors note: Judson Jones is a meteorolo
8、gist, journalist and photographer. He has freelanced with CNN for four years, covering severe weather from tornadoes to typhoons. Follow him on Twitter: jnjonesjr (CNN) - I will always wonder what it was like to huddle around a shortwave radio and through the crackling static from space hear the fai
9、nt beeps of the worlds first satellite - Sputnik. I also missed watching Neil Armstrong step foot on the moon and the first space shuttle take off for the stars. Those events were way before my time. As a kid, I was fascinated with what goes on in the sky, and when NASA pulled the plug on the shuttl
10、e program I was heartbroken. Yet the privatized space race has renewed my childhood dreams to reach for the stars. As a meteorologist, Ive still seen many important weather and space events, but right now, if you were sitting next to me, youd hear my foot tapping rapidly under my desk. Im anxious fo
11、r the next one: a space capsule hanging from a crane in the New Mexico desert. Its like the set for a George Lucas movie floating to the edge of space. You and I will have the chance to watch a man take a leap into an unimaginable free fall from the edge of space - live.The (lack of) air up there Wa
12、tch man jump from 96,000 feet Tuesday, I sat at work glued to the live stream of the Red Bull Stratos Mission. I watched the balloons positioned at different altitudes in the sky to test the winds, knowing that if they would just line up in a vertical straight line “we“ would be go for launch. I fee
13、l this mission was created for me because I am also a journalist and a photographer, but above all I live for taking a leap of faith - the feeling of pushing the envelope into uncharted territory. The guy who is going to do this, Felix Baumgartner, must have that same feeling, at a level I will neve
14、r reach. However, it did not stop me from feeling his pain when a gust of swirling wind kicked up and twisted the partially filled balloon that would take him to the upper end of our atmosphere. As soon as the 40-acre balloon, with skin no thicker than a dry cleaning bag, scraped the ground I knew i
15、t was over.专业好文档How claustrophobia almost grounded supersonic skydiver With each twist, you could see the wrinkles of disappointment on the face of the current record holder and “capcom“ (capsule communications), Col. Joe Kittinger. He hung his head low in mission control as he told Baumgartner the
16、disappointing news: Mission aborted. The supersonic descent could happen as early as Sunday. The weather plays an important role in this mission. Starting at the ground, conditions have to be very calm - winds less than 2 mph, with no precipitation or humidity and limited cloud cover. The balloon, with capsule attached, will move through the lower level of the atmosphere (the troposphere) where our day-to-day weather lives. It will climb higher
