大规模风电集中并网已经成为中国风电送出的主要模式,但由于电网的薄弱和无功补偿配合的不足,电网的损耗问题较为突出。针对电压降低和无功流动对损耗的附加作用,依据多无功补偿的调节特性,提出一种两阶段协调控制方法,将缓慢离散的电...大规模风电集中并网已经成为中国风电送出的主要模式,但由于电网的薄弱和无功补偿配合的不足,电网的损耗问题较为突出。针对电压降低和无功流动对损耗的附加作用,依据多无功补偿的调节特性,提出一种两阶段协调控制方法,将缓慢离散的电容器、电抗器在长时间尺度安排,将快速连续的静止无功补偿器(Static Var Compensator,SVC)、静止无功发生器(Static Var Generator,SVG)在短时间尺度安排,通过多无功补偿的分解协调,逐步实现降损的控制目标。以我国某大规模风电集中接入电网进行仿真计算,所提控制策略能够取得一定的降损效果。展开更多
Spatial scaling for net primary productivity （NPP） refers to the transferring process of establishing quantitative correlation between simulated NPP derived from data at different spatial resolutions. How to transfe...Spatial scaling for net primary productivity （NPP） refers to the transferring process of establishing quantitative correlation between simulated NPP derived from data at different spatial resolutions. How to transfer NPP at one scale by the algorithm with smaller error to at another is the urgent problem. Nonlinearity and effects from land cover type are two main problems in NPP scaling. In this paper, the contextural approach based on mixed pixels and support vector machine （SVM） algorithm are used to make the scaling model from the fine resolution （TM） to the coarse resolution （MODIS）. Spatial scaling from NPP retrieved from fine resolution data to NPP derived from coarse resolution images is performed, and the correction of scale effect to NPP retrieved from coarse resolution data of MODIS is accomplished. The result shows that the correlation between Rj_coereted of the correction factor for scale effect and 1-Fmiddle dessity grassland estimated by SVM regression model is higher （R2=0.81）. Before the correction for scale effect, the correlation between NPPMODIS and NPPTM is lower （R2=0.69; RMSE=3.47）, while the correlation between NPPTM and corrected NPPMODIS_corrected is higher （R2=0.84; RMSE= 1.87）. Therefore, NPP corrected for scale effect has been greatly improved in both correlation and error.展开更多
In this research paper,we have presented variable area type capacitive sensor signal conditioning system for angular displacement measurement and for this purpose we have used timer LM555 based astable multivibrator a...In this research paper,we have presented variable area type capacitive sensor signal conditioning system for angular displacement measurement and for this purpose we have used timer LM555 based astable multivibrator and universal frequency to digital converter (UFDC). Due to variation in angular displacement in the variable area type capacitor which is connected in the timer based astable circuit,capacitance changes which in turn changes the time period of the timer circuit output. The time period of the timer output waveform is linear with the capacitance and hence linear with angular displacement. The timer output is further processed with UFDC for the measurement. The experimental results show that the time period is linear with the angular displacement in the range of 0- 180° and the uncertainty we should associate it with this average time period value is the standard deviation of the mean,often called the standard error (SE),which is ± 0.023 μs. Because of the simplicity,this measurement system can be used in both electronic and industrial instrumentation.展开更多
文摘大规模风电集中并网已经成为中国风电送出的主要模式,但由于电网的薄弱和无功补偿配合的不足,电网的损耗问题较为突出。针对电压降低和无功流动对损耗的附加作用,依据多无功补偿的调节特性,提出一种两阶段协调控制方法,将缓慢离散的电容器、电抗器在长时间尺度安排,将快速连续的静止无功补偿器(Static Var Compensator,SVC)、静止无功发生器(Static Var Generator,SVG)在短时间尺度安排,通过多无功补偿的分解协调,逐步实现降损的控制目标。以我国某大规模风电集中接入电网进行仿真计算,所提控制策略能够取得一定的降损效果。
基金Foundation： Chinese Liaoning Province Education Bureau General Science Research Project （No. L2010226） Chinese Education Ministry Humanities and Social Sciences Key Research Base Project （No.08JJD790142）+1 种基金 Chinese Liaoning Province Education Bureau Innovation Team Project （No. 2007T095） Chinese Special Funds for Major State Basic Research Project （No. 2007CB714406）.
文摘Spatial scaling for net primary productivity （NPP） refers to the transferring process of establishing quantitative correlation between simulated NPP derived from data at different spatial resolutions. How to transfer NPP at one scale by the algorithm with smaller error to at another is the urgent problem. Nonlinearity and effects from land cover type are two main problems in NPP scaling. In this paper, the contextural approach based on mixed pixels and support vector machine （SVM） algorithm are used to make the scaling model from the fine resolution （TM） to the coarse resolution （MODIS）. Spatial scaling from NPP retrieved from fine resolution data to NPP derived from coarse resolution images is performed, and the correction of scale effect to NPP retrieved from coarse resolution data of MODIS is accomplished. The result shows that the correlation between Rj_coereted of the correction factor for scale effect and 1-Fmiddle dessity grassland estimated by SVM regression model is higher （R2=0.81）. Before the correction for scale effect, the correlation between NPPMODIS and NPPTM is lower （R2=0.69; RMSE=3.47）, while the correlation between NPPTM and corrected NPPMODIS_corrected is higher （R2=0.84; RMSE= 1.87）. Therefore, NPP corrected for scale effect has been greatly improved in both correlation and error.
文摘In this research paper,we have presented variable area type capacitive sensor signal conditioning system for angular displacement measurement and for this purpose we have used timer LM555 based astable multivibrator and universal frequency to digital converter (UFDC). Due to variation in angular displacement in the variable area type capacitor which is connected in the timer based astable circuit,capacitance changes which in turn changes the time period of the timer circuit output. The time period of the timer output waveform is linear with the capacitance and hence linear with angular displacement. The timer output is further processed with UFDC for the measurement. The experimental results show that the time period is linear with the angular displacement in the range of 0- 180° and the uncertainty we should associate it with this average time period value is the standard deviation of the mean,often called the standard error (SE),which is ± 0.023 μs. Because of the simplicity,this measurement system can be used in both electronic and industrial instrumentation.
