风力发电对电力系统的影响毕业论文中英文资料对照外文翻译文献综(4)

power quality, short-circuit capacity, system reserve, frequency and protection. After that, corresponding countermeasures to handle these problems are recommended in order to accommodate wind power generation in power systems.

2. Development situation of wind power generation

From the report of the Global Wind Energy Council (GWEC), the countries with the highest total installed capacity are Germany (20 621 MW), Spain (11 615MW), the USA (11603MW), India(6270 MW) and Denmark (3 136 MW). Thirteen countries around the world can now be counted among those with over 1000 MW of wind capacity, with France and Canada reaching this threshold in 2006. Fig.1 shows the top 10 cumulative installed capacity of the world until December, 2006[2].

Fig. 1 Top 10 cumulative installed capacity of the world until December,2006

China started to develop wind power very late. It stepped into the stage of commercialized development and scale construction only in 1990s. Accumulated and newly added installed generating capacity over the years is shown in Fig.2.The single-unit capacity increased from 100 kW, 200 kW, and 300 kW to 600 kW, 750 kW, and 1500 kW step by step.

China doubled more than its total installed capacity by installing 1 347 MW of wind energy in 2006, a 70% increase from last year’s figure. This brings China up to 2 604 MW of capacity, making it the sixth largest market world wide. the Chinese market has grown substantially in 2006, and this growth is expected to continue and speed up. According to the list of approved projects and those under construction, more than 1 500 MW will be installed in 2007. The goal for wind power in China by the end of 2010 is 5000 MW[3].

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Fig. 2 Accumulative and newly-added installed capacity of wind power in China

3. Characteristics of wind power generation

From the point of view of wind energy, the most striking characteristic of the wind resource is its variability. The stochastic variation of wind farms outputs root mainly in fluctuation of the wind speeds and directions. The wind is highly variable, both geographically and temporally. Furthermore this variability persists over a very wide range of scales, both in space and time.

Fig. 3 Wind spectrum farm Brookhaven based on work by van der Hoven

The wind speed varies continuously as a function of time and height. The time scales of wind variations are presented in Fig.3 as a wind frequency spectrum[4]. The turbulent peak is caused by gusts in the sub second to minute range. The diurnal peak depends on daily wind speed variations and the synoptic peak depends on changing weather patterns, which typically vary daily to weekly but include also seasonal cycles.

From a power system perspective, the turbulent peak may affect the power quality of wind power generation. The influence of turbulences on power quality depends very much on the turbine technology applied. Variable-speed wind turbines, for instance, may absorb short-term power variations by the immediate storage of energy in the rotating masses of

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wind turbine drive trains. That means that the power output is smoother than strongly grid-coupled turbines, fixed-speed wind turbines. Diurnal and synoptic peaks, however, may affect the long-term balancing of power system, in which wind speed forecasts plays a significant role.

Another important issue is the long-term variations of the wind resources. The wind speed up to the height of the hub should be known to calculate the wind farm output. A number of measurements of wind speeds show that wind speeds are mostly mild in a year; their probabilities between 0 and 25m/s are considerable; most of the average annual wind speeds subject to the Wei bull distribution[5], as in formula(1).

错误！未找到引用源。 (1)

Where: v is average wind speed; k is shape parameter; c is scale parameter.

The relationship between the wind turbine output Pw and the wind speed up to the height of the hub v can be expressed approximately as the curve of wind turbine’s outputs vs. wind speed or a subsection function, as in formula (2).

错误！未找到引用

源。 (2)

Where: Pw is rated output of the wind turbine; v is wind speed up to the height of the hub; VCI is cut-in wind speed; VCO is cut-out wind speed; VR is rated wind speed. …… 此处隐藏：2245字，全部文档内容请下载后查看。喜欢就下载吧 ……