Among the many approaches for studying the net primary productivity (NPP), a new method by using remote sensing was introduced in this paper. With spectral information source (the visible band, near infrared band and ...Among the many approaches for studying the net primary productivity (NPP), a new method by using remote sensing was introduced in this paper. With spectral information source (the visible band, near infrared band and thermal infrared band) of NOAA-AVHRR, we can get the relative index and parameters, which can be used for estimating NPP of terrestrial vegetation. By means of remote sensing, the estimation of biomass and NPP is mainly based on the models of light energy utilization. In other words, the biomass and NPP can be calculated from the relation among NPP, absorbed photosynthetical active radiation (APAR) and the rate (epsilon) of transformation of APAR to organic matter, thus: NPP = ( FPAR x PAR) x [epsilon * x sigma (T) x sigma (E) x sigma (S) x (1 - Y-m) x (1 - Y-g)]. Based upon remote sensing ( RS) and geographic information system (GIS), the NPP of terrestrial vegetation in China in every ten days was calculated, and the annual NPP was integrated. The result showed that the total NPP of terrestrial vegetation in China was 6.13 x 10(9) t C . a(-1) in 1990 and the maximum NPP was 1 812.9 g C/m(2). According to this result, the spatio-temporal distribution of NPP was analyzed. Comparing to the statistical models, the RS model, using area object other than point one, can better reflect the distribution of NPP, and match the geographic distribution of vegetation in China.展开更多
The approach to planning,design and operation of distribution networks have significantly changed due to the proliferation of distributed energy resources(DERs)together with load growth,energy storage technology advan...The approach to planning,design and operation of distribution networks have significantly changed due to the proliferation of distributed energy resources(DERs)together with load growth,energy storage technology advancements and increased consumer expectations.Planning of active distribution systems(ADS)has been a very hot topic in the 21st Century.A large number of studies have been done on ADS planning.This paper reviews the state of the art of current ADS planning.Firstly,the influences of DERs on the ADS planning are addressed.Secondly,the characteristics and objectives of ADS planning are summarized.Then,up to date planning model and some related research are highlighted in different areas such as forecasting load and distributed generation,mathematical model of ADS planning and solution algorithms.Finally,the paper explores some directions of future research on ADS planning including planning collaboratively with all elements combined in ADS,taking into account of joint planning in secondary system,coordinating goals among different layers,integrating detailed operation simulations and regular performance based reviews into planning,and developing advanced planning tools.展开更多
High penetration rates of renewable energy will bring stability problems for the future power grid.One of the critical issues is lack of inertia.In this paper,a synchronous motor-generator pair(MGP)system is proposed ...High penetration rates of renewable energy will bring stability problems for the future power grid.One of the critical issues is lack of inertia.In this paper,a synchronous motor-generator pair(MGP)system is proposed as a possible solution for renewable energy integration to enhance inertia and improve grid stability.First,feasibility studies of MGP on inertia,damping,efficiency,and cost are presented.Second,an analytical model is established based on its rotor angle relation.An active power control scheme based on voltage phase difference between renewable energy source and grid is then proposed,and state equations of MGP are derived for small signal stability.Next,two experiments are designed and implemented to verify stable operation and active power regulation of the MGP system.A single-machine infinite bus system is tested to investigate small signal stability and frequency response of MGP.The results show that the MGP system has a solid base in physics and is a feasible solution for providing enough inertia and improving small signal performance in the power grid with high penetration of renewable energy.The paper concludes with a discussion on future research directions to gain a better understanding of MGP.展开更多
文摘Among the many approaches for studying the net primary productivity (NPP), a new method by using remote sensing was introduced in this paper. With spectral information source (the visible band, near infrared band and thermal infrared band) of NOAA-AVHRR, we can get the relative index and parameters, which can be used for estimating NPP of terrestrial vegetation. By means of remote sensing, the estimation of biomass and NPP is mainly based on the models of light energy utilization. In other words, the biomass and NPP can be calculated from the relation among NPP, absorbed photosynthetical active radiation (APAR) and the rate (epsilon) of transformation of APAR to organic matter, thus: NPP = ( FPAR x PAR) x [epsilon * x sigma (T) x sigma (E) x sigma (S) x (1 - Y-m) x (1 - Y-g)]. Based upon remote sensing ( RS) and geographic information system (GIS), the NPP of terrestrial vegetation in China in every ten days was calculated, and the annual NPP was integrated. The result showed that the total NPP of terrestrial vegetation in China was 6.13 x 10(9) t C . a(-1) in 1990 and the maximum NPP was 1 812.9 g C/m(2). According to this result, the spatio-temporal distribution of NPP was analyzed. Comparing to the statistical models, the RS model, using area object other than point one, can better reflect the distribution of NPP, and match the geographic distribution of vegetation in China.
基金This work was supported by National High Technology Research and Development Program of China under Grant 2014AA051901(Key Technology Research and Demonstration for Active Distribution Grid).
文摘The approach to planning,design and operation of distribution networks have significantly changed due to the proliferation of distributed energy resources(DERs)together with load growth,energy storage technology advancements and increased consumer expectations.Planning of active distribution systems(ADS)has been a very hot topic in the 21st Century.A large number of studies have been done on ADS planning.This paper reviews the state of the art of current ADS planning.Firstly,the influences of DERs on the ADS planning are addressed.Secondly,the characteristics and objectives of ADS planning are summarized.Then,up to date planning model and some related research are highlighted in different areas such as forecasting load and distributed generation,mathematical model of ADS planning and solution algorithms.Finally,the paper explores some directions of future research on ADS planning including planning collaboratively with all elements combined in ADS,taking into account of joint planning in secondary system,coordinating goals among different layers,integrating detailed operation simulations and regular performance based reviews into planning,and developing advanced planning tools.
基金supported in part by the National Key Research and Development Program of China(2016YFB0101900).
文摘High penetration rates of renewable energy will bring stability problems for the future power grid.One of the critical issues is lack of inertia.In this paper,a synchronous motor-generator pair(MGP)system is proposed as a possible solution for renewable energy integration to enhance inertia and improve grid stability.First,feasibility studies of MGP on inertia,damping,efficiency,and cost are presented.Second,an analytical model is established based on its rotor angle relation.An active power control scheme based on voltage phase difference between renewable energy source and grid is then proposed,and state equations of MGP are derived for small signal stability.Next,two experiments are designed and implemented to verify stable operation and active power regulation of the MGP system.A single-machine infinite bus system is tested to investigate small signal stability and frequency response of MGP.The results show that the MGP system has a solid base in physics and is a feasible solution for providing enough inertia and improving small signal performance in the power grid with high penetration of renewable energy.The paper concludes with a discussion on future research directions to gain a better understanding of MGP.
