太阳能毕业设计外文翻译.doc

（一） What is Maximum Power Point Tracking (MPPT) and How Does it Work?
Photovoltaic (PV) generation is becoming increasingly important as a renewable source since it offers many advantages such as incurring no fuel costs, not being polluting, requiring little maintenance, and emitting no noise, among others. PV modules still have relatively low conversion efficiency; therefore, controlling maximum power point tracking (MPPT) for the solar array is essential in a PV system.
The amount of power generated by a PV depends on the operating voltage of the array. A PV’s maximum power point (MPP) varies with solar insulation and temperature. Its V-I and V-P characteristic curves specify a unique operating point at which maximum possible power is delivered. At the MPP, the PV operates at its highest efficiency. Therefore, many methods have been developed to determine MPPT.
Maximum Power Point Tracking, frequently referred to as MPPT, is an electronic system that operates the Photovoltaic (PV) modules in a manner that allows the modules to produce all the power they are capable of. MPPT is not a mechanical tracking system that “physically moves” the modules to make them point more directly at the sun. MPPT is a fully electronic system that varies the electrical operating point of the modules so that the modules are able to deliver maximum available power. Additional power harvested from the modules is then made available as increased battery charge current. MPPT can be used in conjunction with a mechanical tracking system, but the two systems are completely different.
To understand how MPPT works, let’s first consider the operation of a conventional (non-MPPT) charge controller. When a conventional controller is charging a discharged battery, it simply connects the modules directly to the battery. This forces the modules to operate at battery voltage, typically not the ideal operating voltage at which the modules are able to produce their maximum available power. The PV Module Power/Voltage/Current graph shows the traditional Current/Voltage curve for a typical 75W module at standard test conditions of 25°C cell temperature and 1000W/m2 of isolation. This graph also shows PV module power delivered vs module voltage. For the example shown, the conventional controller simply connects the module to the battery and therefore forces the module to operate at 12V. By forcing the 75W module to operate at 12V the conventional controller artificially limits power production to≈53W.
Rather than simply connecting the module to the battery, the patented MPPT system in a Solar Boost charge controller calculates the voltage at which the module is able to produce maximum power. In this example the maximum power voltage of the module (VMP) is 17V. The MPPT system then operates the modules at 17V to extract the full 75W, regardless of present battery voltage. A high efficiency DC-to-DC power converter converts the 17V module voltage at the controller input to battery voltage at the output. If the whole system wiring and all was 100% efficient, battery charge current in this example would be VMODULE ÷ VBATTERY x IMODULE, or 17V ÷12V x 4.45A = 6.30A. A charge current increase of 1.85A or 42% would be achieved by harvesting module power that would have been left behind by a conventional controller and turning it into useable charge current. But, nothing is 100% efficient and actual charge current increase will be somewhat lower as some power is lost in wiring, fuses, circuit breakers, and in the Solar Boost charge controller.
Actual charge current increase varies with operating conditions. As shown above, the greater the difference between PV module maximum power voltage VMP and battery voltage, the greater the charge current increase will be. Cooler PV module cell temperatures tend to produce higher VMP and therefore greater charge current increase. This is because VMP and available power increase as module cell temperature decreases as shown in the PV Module Temperature Performance graph. Modules with a 25°C VMP rating higher than 17V will also tend to produce more charge current increase because the difference between actual VMP and battery voltage will be greater. A highly discharged battery will also increase charge current since battery voltage is lower, and output to the battery during MPPT could be thought of as being “constant power”. What most people see in cool comfortable temperatures with typical battery conditions is a charge current increase of between 10 – 25%. Cooler temperatures and highly discharged batteries can produce increases in excess of 30%. Customers in cold climates have reported charge current increases in excess of 40%. What this means is that current increase tends to be greatest when it is needed most; in cooler conditions when days are short, sun is low on the horizon, and batteries may be more highly discharged. In conditions where extra power is not available (highly charged battery and hot PV modules) a Solar Boost charge controller will perform as a conventional PWM type controller.
WHY MPPT?
MPPT loads solar panel that it operates at the maximum power point. MPPT is a DC-DC converter that uses high frequency switching and control algorithm. It is desired to design the circuit at high efficient, light weight, small size, and reliable for the event. Solar cells are dependent on environment conditions like temperature, sun light, and load voltage. While this parameters always changing daytime, solar cell or solar panel output characteristics vary also. Some hours photovoltaic system may give lower power than rated power of load. If solar panel is connected to battery by directly, a power loss occurs in the system since solar panel operating characteristic will change at some period of time up to environment conditions. This problem can be solved by using larger solar panels, but the solution is expensive. Instead of this, maximum power point tracker circuit is located between solar panel and battery.
INCREASE SOLAR CHARGING WITH AN MPPT POWER TRACKING CHARGE CONTROLLER
A new feature is showing up in charge controllers. It's called maximum power point tracking (MPPT). It extracts additional power from your PV array, under certain conditions. This article explains the process by a mechanical analogy, for people who do not understand basic electricity.The function of a MPPT is analogous to the transmission in a car. When the transmission is in the wrong gear, the wheels do not receive maximum power. That's because the engine is running either slower or faster than its ideal speed range. The purpose of the transmission is to couple the engine to the wheels, in a way that lets the engine run in a favorable speed range in spite of varying acceeration and terrain.
Let's compare a PV module to a car engine. Its voltage is analogous to engine speed. Its ideal voltage is that at which it can put out maximum power. This is called its maximum power point. (It's also called peak power voltage, abbreviated Vpp). Vpp varies with sunlight intensity and with solar cell temperature. The voltage of the battery is analogous to the speed of the car's wheels. It varies with battery state of charge, and with the loads on the system (any appliances and lights that may be on). For a 12V system, it varies from about 11 to 14.5V. In order to charge a battery (increase its voltage), the PV module must apply a voltage that is higher than that of the battery. If the PV module's Vpp is just slightly below the battery voltage, then the current drops nearly to zero (like an engine turning slower than the wheels). So, to play it safe, typical PV modules are made with a Vpp of around 17V when measured at a cell temperature of 25°C. They do that because it will drop to around 15V on a very hot day. However, on a very cold day, it can rise to 18V! What happens when the Vpp is much higher than the voltage of the battery? The module voltage is dragged down to a lower-than-ideal voltage. Traditional charge controllers transfer the PV current directly to the battery, giving you NO benefit from this added potential. Now, let's make one more analogy. The car's transmission varies the ratio between speed and torque. At low gear, the speed of the wheels is reduced and the torque is increased, right? Likewise, the MPPT varies the ratio between the voltage and current delivered to the battery, in order to deliver maximum power. If there is excess voltage available from the PV, then it converts that to additional current to the battery. Furthermore, it is like an automatic transmission. As the Vpp of the PV array varies with temperature and other conditions, it "tracks" this variance and adjusts the ratio accordingly. Thus it is called a Maximum Power Point Tracker.
What advantage does MPPT give in the real world? That depends on your array, your climate, and your seasonal load pattern. It gives you an effective current boost only when the Vpp is more than about 1V higher than the battery voltage. In hot weather, this may not be the case unless the batteries are low in charge. In cold weather however, the Vpp can rise to 18V. If your energy use is greatest in the winter (typical in most homes) and you have cold winter weather, then you can gain a substantial boost in energy when you need it the most!

中文翻译
什么是最大功率点跟踪(MPPT),它是又如何工作的?
光伏发电作为可再生能源变得日益重要，它有许多有点，如不需燃料、没有污染、需要很少的维护费用、没有噪声等等。光电模块的转换效率依然很低，所以控制光伏阵列的最大功率点跟踪成为光伏系统的要点。
光伏系统产生的能量取决于阵列的开路电压。PV 的最大功率点（MPP）随光照强度和和温度变化。它的 V-I 和 V-P 特性曲线表示了一个特定的工作点，在这个点上可以提供最大功率。在最大功率点上，光伏系统工作具有最高效率。所以许多方法被用来确定最大功率跟踪。
最大功率点跟踪，经常被称为 MPPT，是一个使光电(PV)模块工作在一种特定运作模式的电子系统，这种运作模式能够让模块产生它们所能够产生的最大电力。 MPPT 不是一种移动模组本身来使它们更直接面对太阳的机械跟踪系统。 MPPT是完全的电子系统,它通过改变模组的电特性工作点，让模块能够提供最大可用电力。从模块得到的额外电力将以电池充电电流的形式得到利用。MPPT 可与机械跟踪系统配合使用,但这两个系统完全不同。
为了了解 MPPT 使如何工作的，我们先了解一下常规的(非 MPPT)充电控制器是如何工作的。当一个 常规控制器在为用完的蓄电池充电的时候，它只是简单的将光伏模组与电池直接相连。这就促使模组工作在蓄电池的电压上，而这个电压通常不是能够让光电组件产生最大可用电能的理想工作电压。光电模块的功率/电压/电流图显示了典型的传统75W的光伏模块在25°C电池温度和1000w/m2日照强度的标准测试条件下的电流/电压曲线。这个图表也显示了光电组件电压变化时功率的变化. 如例子所示，传统的控制器只是简单的将光电模块和电池相连，这就促使模块工作在 12V 电压。由于 75W 的模块被钳制在 12V 电压下工作，传统的控制器人为的限制了产生的电能大约在 53W 左右。
与简单地连接光电模块与电池不同的是，在光电 Boost 充电控制器中使用的专利 MPPT 系统计算模块能够产生最大电能的工作电压。这个例子中模块产生最大功率时的电压（VMP）是 17V。 MPPT 系统将使模块工作在 17V 的电压下来充分获得 75W 的电能，而不管目前电池的电压。一个高效率的 DC/DC 电力转换器转换在控制器输入端的 17V 模块电压为输出端电池的电压。 如果整个系统布线全部是100%的效率,在目前这个例子中电池电流为 VMODULE ÷ VBATTERY x IMODULE 或17V ÷12V x 4.45A = 6.30A。通过收获那些本来会被传统控制器浪费的电能并将它转化为可用的充电电流， 将增加 1.85A 的充电电流或达到 42%的增量。 但是,没有什么是 100%的效率， 由于部分电力损失在线路、 保险丝、 电路断路器和 Boost太阳能充电控制器上面，所以电流增量通常都会低一些。
有用充电电流增量随工作条件的变化而变化。如上所述,光电组件最大功率点电压（VMP）与电池电压的差异越大，充电电流增加的也就越大。降低光伏电池单元的温度倾向于产生更高的最大功率点电压（VMP） ，也就更大的充电电流增量。 这是因为， 随着光伏电池单元的温度降低最大功率点电压和可用电能将增加，如光电组件温度特性曲线所示， 模块 25°C 时的最大功率点电压高于 17V 也同样能够产生更大的充电电流，因为此时实际的最大功率点电压将比蓄电池电压更高。 一个完全用完的蓄电池也将增加充电电流， 因为电池电压更低同时通过 MPPT输出到蓄电池的电能可以认为时连续的。在适当的低温条件和典型电池条件下，人们可以看到充电电流将增加 10 – 25%。更低的温度和更完全使用的蓄电池将使充电电流增幅超过 40%。寒冷气候下的客户报道说充电电流甚至超过了 40%的增幅。这是意味着最需要的时候，充电电流增加的最大。在寒冷环境下，白天很短暂，太阳离地平线低,蓄电池将被更完全的放电。在那些没有可以利用的额外能量（满充的蓄电池和高温光电组件）的条件下，Boost 光电充电控制器将替代传统的 PWM 型控制器。
为什么要最大功率点跟踪（MPPT）?
MPPT 附加在太阳能电池板上使它工作在最大功率点上。MPPT 是一个利用高频开关和控制算法的 DC/DC 变换器。它要求将电路设计得高效率、重量轻、体积小、高可靠性。太阳能电池单元依赖环境条件比如温度条件，光照强度，负载电压。而这些参数在白天总是变化的，太阳能电池、太阳能电池板输出特性也各不相同。某些小时内光电系统可能产生的功率低于额定负载功率。如果将太阳能电池板直接连接到电池，系统会产生功耗，因为在某些时段太阳能电池板的运行特性将随环境条件的改变而改变。这个问题可以通过使用较大的太阳能板来解决，但解决方案较昂贵。基于此，在太阳能电池板和电池之间加设电池最大功率点跟踪电路。
利用 MPPT 功率跟踪充电控制器增加光伏充电电能。
充电控制器又出现了新的特点。它被称为最大功率点跟踪(MPPT)。它在一定条件下从你的光伏阵列摄取额外的电能。 本文为那些根本不懂电的人对这一过程做了机械类比。MPPT 的功能类似于汽车的传动装置，当传动装置运转在错误的档位，车轮得不到最大的动力。那是因为发动机运行速度低于或高于理想转速范围。传动装置的作用是连接引擎和车轮使引擎不管在任何速度，任何地形都运行在一个最佳的转速范围。 让我们把光电组件和汽车发动机做下比较。它的电压类似于引擎速度。理想的电压是指在这一电压点能够输出最大功率， 这就是所谓的最大功率点 (也被称作峰值功率电压,简称 VPP)。VPP 随阳光强度和太阳能电池温度变化，蓄电池的电压类似汽车车轮的速度，它会随电池充电状况,以及系统负载（任何电器和灯泡等等）而变化。一个 12V 系统，则由约 11 至 14.5V 之间变化。为了对电池充电(增加它的电压)，光电组件必须提供高于电池电压的充电电压。如果光电组件的 VPP 只是仅仅略低于电池电压,则电流也下降到近乎为零(如发动机转得比车轮慢)。所以,为了这方面的安全,典型的光电组件的 VPP 在 25℃光电池单元温度时测量大约 17v 左右。 他们这样做是因为这将减少到约 15V 在炎热的时候。 然而,在一个非常寒冷的日子,它可以上升到18V!在VPP远远高于电池电压的情况下会发生什么样的事呢？ 模块电压拉低到低于理想的电压。传统的充电控制器直接将光伏电池阵列的电流直接给蓄电池，让你得不到任何多余的好处。现在，让我们再作比喻，汽车的传动装置改变汽车传输速度及扭矩比例，低挡时，车轮的速度降低，扭矩加大，对不对？同样，MPPT 改变送往电池的电压和电流的比例，以提供最大功率。如果来自光电模块的电压超过现有的，它则将其转换成更大的电流送往电池。此外，它像一个自动传动装置一样。当光伏阵列的 VPP 随温度和其他一些条件变化的时候，它将跟踪这一变化来调整比例，因此被称为最大功率点跟踪。
在现实世界 MPPT 有什么好处？这取决于你的光伏阵列，你的气候，和你的季节性负荷特点。它为你提供有效的涌流，只有当 VPP 超过电池电压约 1V 的时候。在炎热的天气，情况可能并非如此，除非电池欠充电。然而在寒冷天气，VPP可以升到 18v。如果你能源利用最大的时候是冬季(最典型的家庭)，有寒冷的冬天，那么在你最需要能量的时候你可以得到可靠的能源供应！

（二） Enengy or Solar Enegry
Energy means the power which does work and drives machines. All living things (including humans) rely on the sun as a source of energy. Coal, petroleum, and natural gas are energy sources available today because organisms in the past captured unlight energy and stored it in the complex organic molecules that made up their bodies, which were then compressed and concentrated. With the development of society, alarge of energy sources have been used,such as coal, petroleum, natural gas,geothermal energy, nuclear fission power, nuclear fusion power, solar energy, and Hydrogen gas. however, under the circumstances, the quantity of energy source is limited. unlimited usage of energy source results in energy crisis.
At present, most of the energy consumed by humans is produced from fossi fuels. The greatest recoverable fossil is in the form of coal and lignite. Although world coal resources are enomous and potentially can fill energy needs for a century or two, their utilization is limited by environmental disruption from mining and emissions of carbon dioxide and sulfur dioxide. These would become intolerable long before coal resources were exhausted. Only a small percentage of coal and lignite has been utilized to date, whereas much of the recoverable petroleum and natural gas has already been consumed. Petroleum has several characteristics that make it superior to coal as a source of energy. Its extraction causes less environmental damage than does coal mining. It is a more concentrated source of energy than coal, and it burns with less pollution, and it can be moved easily through pipes. These characteristics make it an ideal fuel for automobiles.
Since first commercial oil well in 1859, somewhat more than 100 million barrels of oil have been produced in the United States, most of it in recent years. In 1990 world petroleum consumption was at a rate of about 65 million barrels per day. Projected use of petroleum and natural gas indicates rapid depletion. Alaskan oil can help the petroleum supply only temporarily. Peak world petroleum resources production will be reached within a few years.
Since the first "energy crisis" of 1973-1974, some concrete actions have even taken place. However, the several-fold increase in crude oil prices since 1973 has extacted a toll. In the U.S. and other industrialized nations, the economy has been plagued by inflation, recession, unempl