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1、Comparison of Photovoltaic Array Maximum PowerPoint Tracking Techniques光伏阵列最大功率点跟踪技术的比较Trishan Esram, Student Member, IEEE, and Patrick L. Chapman, Senior Member, IEEEAbstractThe many different techniques for maximum power point tracking of photovoltaic (PV) arrays are discussed. The techniques are
2、taken from the literature dating back to the earliest methods. It is shown that at least 19 distinct methods have been introduced in the literature, with many variations on implementation. This paper should serve as a convenient reference for future work in PV power generation.摘要：关于光伏阵列最大功率点跟踪的许多不同技
3、术的讨论，著作中的这些方法都可以追溯到最早的方法。结果表明至少有19种方法已经在著作中被介绍，有许多已经实现变形。本文应该对将来的光伏发电工作提供一个方便的参考。Index TermsMaximum power point tracking (MPPT), photovoltaic (PV).索引词最大功率点跟踪，光伏。I. INTRODUCTIONI简介TRACKING the maximum power point (MPP) of a photovoltaic (PV) array is usually an essential part of a PV system. As such,
4、 many MPP tracking (MPPT) methods have been developed and implemented. The methods vary in complexity, sensors required, convergence speed, cost, range of effectiveness, implementation hardware, popularity, and in other respects. They range from the almost obvious (but not necessarily ineffective) t
5、o the most creative (not necessarily most effective). In fact, so many methods have been developed that it has become difficult to adequately determine which method, newly proposed or existing, is most appropriate for a given PV system.跟踪光伏阵列的最大功率点通常是光伏系统的主要部分，鉴于此许多最大功率点跟踪方式已经被开发和实现。这些方法各不相同，如复杂程度、传
6、感器需要、收敛速度、花费、范围的有效性、硬件实现、普及程度以及其他方面。他们几乎涵盖了所有的从平淡无奇（但是不一定不起作用）到最具创造性（不一定都有效）。事实上，由于许多的方式已经被开发，在新提出的或是现存的方法中，对于给定的光伏系统准确的决定最适合方式的变的困难Given the large number of methods for MPPT, a survey of the methods would be very beneficial to researchers and practitioners in PV systems. Fig. 1 shows the total numb
7、er of MPPT papers from our bibliography per year since the earliest MPPT paper we found. The number of papers per year has grown considerably of the last decades and remains strong. However, recent papers have generally had shorter, more cursory literature reviews that largely summarize or repeat th
8、e literature reviews of previous work. This approach tends to repeat what seems to be conventional wisdom that there are only a handful of MPPT techniques, when in fact there are many. This is due to the sheer volume of MPPT literature to review, conflicting with the need for brevity.鉴于大量的方法来研究MPPT，
9、在光伏系统中采用调查的方法对研究人员和实践者都是非常有益的。图一给出了自从我们发现最早MPPT论文以来每年我们文献目录中MPPT论文的总数目，最近几十年论文的数量已有了长足的发展并且发展仍然很强劲。然而，最近的论文普遍较短，更多粗略的文学评论以致大量的总结或重复前人的总结工作。这种重复方式似乎是传统的智慧，以至于只有很少的MPPT技术，但事实上有很多。这是由于有大量的公开的MPPT文献回顾与简洁的需求相冲突。This survey is a single reference of the great majority of papers and techniques presented on
10、MPPT. We compiled over 90 papers pertaining to different MPPT methods published up to the date of submission of this manuscript. It is not our intention to establish a literal chronology of when various techniques were proposed, since the publication date is not necessarily indicative of when a meth
11、od was actually conceived. As is typical of review papers, we have elected not to reference patents. Papers referencing MPPT methods from previous papers without any modification or improvement have also been omitted. It is possible that one or more papers were unintentionally omitted. We apologize
12、if an important method or improvement was left out.这个调查参考了绝大多数提出MPPT的论文和技术。我们收集了超过90篇关于MPPT不同方法的论文的手稿提交的日期。我们的意图不是当不同的技术被提出时建立一个文字年代， 因为出版日期不能表明一种方法是什么时间构思的。作为典型的评论性文章，我们推选不涉及专利。如果论文中所涉及的MPP T的方法来自以前的论文而没有任何的修改和改善，则论文将被忽略。一篇或更多的论文被无意识的遗漏也是可能的，如果是一种重要的方法或改进被遗漏，我们表示歉意。Manuscript received September 24,
13、 2004; revised September 8, 2005. This work was supported by the National Science Foundation ECS-01-34208. Paper no. TEC-00276-2004. The authors are with the Grainger Center for Electric Machinery and Electromechanics, University of Illinois at Urbana-Champaign, Urbana, IL 61801- 2918 USA (e-mail: ;
14、 ).Digital Object Identifier 10.1109/TEC.2006.874230Fig.1. Total number of MPPT papers per year, since 1968.This manuscript steps through a wide variety of methods with a brief discussion and categorization of each. We have avoided discussing slight modifications of existing methods as distinct meth
15、ods. For example, a method may have been first presented in context of a boost converter, but later on shown with a boost buck converter, otherwise with minimal change. The manuscript concludes with a discussion on the different methods based on their implementation, the sensors required, their abil
16、ity to detect multiple local maxima, their costs, and applications they suit. A table that summarizes the major characteristics of the methods is also provided.这份手稿通过各种各样的方式进行简要的讨论和分类，我们讨论将稍加修改已经存在的方法作为独特的方法认为无效。例如，一种方法第一次已经在boost升压电路中提出，但之后又在升降压变换电路中提出，除此之外，几乎没有变化。手稿以实现不同方式结束，根据他们的实现、所需要的传感器、检测最大值的
17、能力、成本和适合的应用程序。我们提供了一个总结主要方法特征的表格。II. PROBLEM OVERVIEWII.问题概述Fig. 2 shows the characteristic power curve for a PV array. The problem considered by MPPT techniques is to automatically find the voltage VMPP or current IMPP at which a PV array should operate to obtain the maximum power output PMPP under
18、 a given temperature and irradiance. It is noted that under partial shading conditions, in some cases it is possible to have multiple local maxima, but overall there is still only one true MPP. Most techniques respond to changes in both irradiance and temperature, but some are specifically more usef
19、ul if temperature is approximately constant. Most techniques would automatically respond to changes in the array due to aging, though some are open-loop and would require periodic fine-tuning. In our context, the array will typically be connected to a power converter that can vary the current coming
20、 from the PV array.图二给出了光伏阵列的功率曲线。MPPT技术所要考虑的问题是自动的发现光伏阵列中电压最大功率点或电流最大功率点，使该光伏阵列在给定的温度和光照下得到最大功率输出。有人指出，在局部遮挡的情况下，有些时候他可能有多个极大值，但总体来说他只有一个真正的最大功率点。大部分技术应对温度和光照强度的变换，但是假如温度接近稳定一些特别的方法将更加有用。大部分技术能自动的对阵列中由老化引起的变化做出响应，尽管一些是开环控制需要周期性的微调。本文中，阵列和变流器相连，该变流器可以改变电流来自光伏阵列。III. MPPT TECHNIQUESIII.MPPT技术We intro
21、duce the different MPPT techniques below in an arbitrary order. 我们以任意顺序介绍不同的MPPT技术。A. Hill Climbing/P&OAmong all the papers we gathered, much focus has been on hill climbing 18, and perturb and observe (P&O) 925 methods. Hill climbing involves a perturbation in the duty ratio of the power converter,
22、 and P&O a perturbation in the operating voltage of the PV array. In the case of a PV array connected to a power converter, perturbing the duty ratio of power converter perturbs the PV array current and consequently perturbs the PV array voltage. Hill climbing and P&O methods are different ways to e
23、nvision the same fundamental method.A 爬坡/扰动与观察在我们收集的所有论文中， 大多数集中在爬坡方式1-8,和扰动与观察方式9-25。在变流器的一个工作周期内爬坡方式包含一个扰动，而扰动与观察方式是包含光伏阵列工作电压的一个扰动。就光伏阵列与变流器相连而说，变流器工作周期的扰动扰乱光伏阵列的电流，进而影响光伏阵列的电压。爬坡方式和扰动与观察方式是两种不同的方式来设想相同的基本模型。From Fig. 2, it can be seen that incrementing (decrementing) the voltage increases (decre
24、ases) the power when operating on the left of the MPP and decreases (increases) the power when on the right of the MPP. Therefore, if there is an increase in power, the subsequent perturbation should be kept the same to reach the MPP and if there is a decrease in power, the perturbation should be re
25、versed. This algorithm is summarized in Table I. In 24, it is shown that the algorithm also works when instantaneous (instead of average) PV array voltage and current are used, as long as sampling occurs only once in each switching cycle.Fig. 2. Characteristic PV array power curve.TABLE ISUMMARY OF
26、HILL CLIMBING AND P&O ALGORITHM从图二可以看出，随着电压的增长（下降）当作用于最大功率点左侧时功率增长（下降），当作用与最大功率点右侧时功率下降（增长）。因此，如果功率增长，则随之而来的扰动将保持相同达到最大功率点；如果功率下降，扰动就会相反。这种算法的总结在表I。在24中，给出当使用瞬时（而不是平均值）光伏阵列电压和电流时这种算法仍然使用， 只要在一个开关周期内采样一次即可。图 2.光伏阵列功率曲线表 I爬坡算法和扰动与观察方法摘要The process is repeated periodically until the MPP is reached. The
27、 system then oscillates about the MPP. The oscillation can be minimized by reducing the perturbation step size. However, a smaller perturbation size slows down the MPPT. A solution to this conflicting situation is to have a variable perturbation size that gets smaller towards the MPP as shown in 8,
28、12, 15, and 22. In 24, fuzzy logic control is used to optimize the magnitude of the next perturbation. In 20, a two-stage algorithm is proposed that offers faster tracking in the first stage and finer tracking in the second stage. On the other hand, 21 bypasses the first stage by using a nonlinear e
29、quation to estimate an initial operating point close to the MPP. 此过程要反复进行，直到达到最大功率点。然后系统在最大功率点附近震荡。在一定程度上可以通过减小扰动步长来减小振动。然而一个幅值小的扰动可以降低达到最大功率点的速度。这种矛盾的一种解决办法是有一个大小可变的扰动以更小的步长向最大功率点移动，在81215和22中给出，其中在24中，模糊逻辑控制使下一个扰动量达到最优。在20中提出两步运算法则，第一步采用快速跟踪，第二步采用最有追踪。另一方面，21通过运用非线性方程估计最初的工作点接近最大功率点来避开第一步。Hill cli
30、mbing and P&O methods can fail under rapidly changing atmospheric conditions as illustrated in Fig. 3. Starting from an operating point A, if atmospheric conditions stay approximately constant, a perturbation V in the PV voltage V will bring the operating point to B and the perturbation will be reve
31、rsed due to a decrease in power. However, if the irradiance increases and shifts the power curve from P1 to P2 within one sampling period, the operating point will move from A to C. This represents an increase in power and the perturbation is kept the same. Consequently, the operating point diverges
32、 from the MPP and will keep diverging if the irradiance steadily increases. To ensure that the MPP is tracked even under sudden changes in irradiance, 18 uses a three-point weight comparison P&O method that compares the actual power point to two preceding ones before a decision is made about the per
33、turbation sign. In 22, the sampling rate is optimized, while in 24, simply a high sampling rate is used. In 8, toggling has been done between the traditional hill climbing algorithm and a modified adaptive hill climbing mechanism to prevent deviation from the MPP.Fig. 3. Divergence of hill climbing/
34、P&O from MPP as shown in 9.爬坡方式和扰动与观察方式在快速变化的大气环境中不起作用，如图3.从工作点A开始，如果大气条件保持基本不变，光伏阵列电压V的扰动V将工作点变为B，同时由于功率的下降干扰将被反相。可是，如果光照强度增加使一个周期内的功率曲线由P1变为 P2，工作点将由A点移至C点。这表示功率的增长和扰动保持相同。因此，如果光照强度稳定的增加，工作点就会偏离最大功率点并且保持这种偏离状态。为了保证光强突然变化时最大功率点仍然能够被追踪，18应用三点比较P&O重要法，该方法是在扰动信号确定之前将先前的两个点和真实的功率点作比较。在22中，采样频率是最优的，而在24
35、中仅仅采用高频率的采样信号。在8中，将传统的爬坡模式算法和改进的自适应的机制相结合，以防止与最大功率点的偏差。图 3. 9中给出的爬坡和P&O模式最大功率点的差异D. Fractional Short-Circuit CurrentFractional results from the fact that, under varying atmospheric conditions, is approximately linearly related to the of the PV array as shown in 40, 42, and 4548 （6）where is a proport
36、ionality constant. Just like in the fractional technique, has to be determined according to the PV array in use. The constant is generally found to be between 0.78 and 0.92.D.定电流跟踪法定电流跟踪法源于这个事实，在多变的大气条件下，光伏阵列的与近似的呈线性关系，在论文40，42，4548 给出 （6）其中为正比例常数。正如定电压跟踪技术中，由使用的光伏阵列确定。常数一般在0.78-0.92间取值。Measuring du
37、ring operation is problematic. An additional switch usually has to be added to the power converter to periodically short the PV array so that can be measured using a current sensor. This increases the number of components and cost. In 48, a boost converter is used, where the switch in the converter
38、itself can be used to short the PV array. 在运行期间测量是有问题的。因此，在变流器上附加一个开关周期性的短接光伏阵列通过电流传感器实现对的测量。这就增加了元器件的数量和成本。在48中，运用一个升压变换器，变换器上的开关可以用来短接光伏阵列。Power output is not only reduced when finding but also because the MPP is never perfectly matched as suggested by (6). In 46, a way of compensating is proposed
39、 such that the MPP is better tracked while atmospheric conditions change. To guarantee proper MPPT in the presence of multiple local maxima, 45 periodically sweeps the PV array voltage from open-circuit to short-circuit to update. Most of the PV systems using fractional in the literature use a DSP.
40、In 48, a simple current feedback control loop is used instead 功率输出的降低的原因不仅仅由于寻找而且从提出的公式（6）中可以看到，MPP从来没有很好地匹配。在46中，提出一种补偿的方法以至于在大气环境变化时最大功率点能很好地被跟踪。在存在多个局部最大点时为了保证完全的最大功率跟踪,45周期性的快速改变开路到短路的电压来更新。文献中大多数运用部分的光伏系统应用DSP。在48中用一个简单的电流控制回路来代替。E. Fuzzy Logic ControlMicrocontrollers have made using fuzzy logi
41、c control 4958 popular for MPPT over the last decade. As mentioned in 57, fuzzy logic controllers have the advantages of working with imprecise inputs, not needing an accurate mathematical model, and handling nonlinearityE模糊逻辑控制 在过去的十年间，微控制器使模糊控制49-58在最大功率跟踪方面应用变得流行。如57，模糊控制在处理不确定输入和非线性问题方面处于有利条件，而他
42、不需要一个精确地数学模型。Fuzzy logic control generally consists of three stages: fuzzification, rule base table lookup, and defuzzification. During fuzzification, numerical input variables are converted into linguistic variables based on a membership function similar to Fig. 5. In this case, five fuzzy levels a
43、re used: NB (negative big), NS (negative small), ZE (zero), PS (positive small), and PB (positive big). In 54 and 55, seven fuzzy levels are used, probably for more accuracy. In Fig. 5, a and b are based on the range of values of the numerical variable. The membership function is sometimes made less
44、 symmetric to give more importance to specific fuzzy levels as in 49, 53, 57, and 58.Fig. 5. Membership function for inputs and output of fuzzy logic controller模糊控制一般包括三个阶段：模糊化、查找规则库表、去模糊化。在模糊化过程中，数字输入变量被转化成基于隶属度函数的语言变量，如图5.如此看来就有五个模糊子集：NB（负方向大的偏差）、NS（负方向小的偏差）、ZE（零）、PS（正方向小的偏差）、PB（正方向大的偏差）。在54和55中，应
45、用了七个模糊子集，可能更精确。在图5中，a和b的值决定于变量值的范围。隶属度函数有时候是不对称的来更加重视特殊的模糊子集，像49、53、57、58。图5 输入的隶属度函数和输出的模糊控制The inputs to a MPPT fuzzy logic controller are usually an errorand a change in error. The user has the flexibility of choosing how to computeand. Sincevanishes at the MPP, 58 uses the approximation （7）And (
46、8)MPPT模糊控制器的输入通常是一个错误和错误变化。用户可以灵活的选择如何计算和。鉴于在最大功率点为零，58应用近似值： （7）和 (8)Equivalently, (4) is very often used. Once and are calculated and converted to the linguistic variables, the fuzzy logic controller output, which is typically a change in duty ratio of the power converter, can be looked up in a ru
47、le base table such as Table II 50.TABLE IIFUZZY RULE BASE TABLE AS SHOWN IN 50相同的，公式（4）经常用，一旦和被计算出来和转化为语言变量，模糊控制器输出，该输出是典型的一个变流器占空比的变化且能在规则库表中被查出，如表II50.表II50中给出的模糊规则库表The linguistic variables assigned tofor the different combinations of and are based on the power converter being used and also on th
48、e knowledge of the user. Table II is based on a boost converter. If, for example, the operating point is far to the left of the MPP (Fig. 2), that is is PB, and is ZE, then we want to largely increase the duty ratio, that is should be PB to reach the MPP.分配给作为和不同的组合的语言变量以所使用的变流器和用户的知识为基础。表II是以升压变换器为基础。如果，举个例子，工作点在距离最大功率点左边很远的地方（图2），就是 就是PB， 是 ZE，然后我们想增大工作周期，即应该是PB来达到最大功率点。In the defuzzification stage, the fuzzy logic controller output is conv