Economical and reliable protection of DC-side shortcircuit faults has become a key technology for promoting the development of module multilevel converters based on the high voltage direct current grid(MMC-HVDC-Grid)....Economical and reliable protection of DC-side shortcircuit faults has become a key technology for promoting the development of module multilevel converters based on the high voltage direct current grid(MMC-HVDC-Grid).The fault current limiter(FCL)can effectively suppress the rapid development of the fault current and reduce the current breaking capacity of the circuit breaker.In this paper,a method based on transient energy flow(TEF)analysis is proposed to optimize the allocation of a resistive and inductive FCL in the MMC-HVDC-Grid.In the proposed method,the electromagnetic TEF is measured first,and then,the TEF suppression rate and suppression efficiency are defined as optimization objectives,and the installation location of the FCL and its impedance parameters as optimization variables.To test the proposed method,two-terminal and four-terminal bipolar MMC-HVDC-Grids with single-pole-to-ground DC faults are modeled in the PSCAD/EMTDC so that the TEF data can be acquired.The optimal FCLs’location and parameter values are determined through investigating the evolution paradigm of TEF along with changes of the FCL position and parameters.The results prove that the selected parameters can effectively slow down the DC fault current rising rate,thus reducing the requirements on tripping current of the DC breakers.展开更多
<p align="left" style="text-align:justify;"> <span style="font-family:;" "=""><span style="font-family:Verdana;">Tef [</span><i><...<p align="left" style="text-align:justify;"> <span style="font-family:;" "=""><span style="font-family:Verdana;">Tef [</span><i><span style="font-family:Verdana;">Eragrostis</span></i> <i><span style="font-family:Verdana;">tef</span></i><span style="font-family:Verdana;"> (Zucc.)Trotter]) is one of the most important cereal crops </span></span><span style="font-family:Verdana;">grown </span><span style="font-family:Verdana;">in Ethiopia. Tef production has been partly constrained by low yield and less stability of the genotypes under cultivation. Field experiments were carried out in Halaba, Loka Abaya, Bensa and Areka, South Ethiopia, from August to November, during 2016 and 2017 main cropping seasons, in order to estimate yield stability </span><span style="font-family:Verdana;">and the association between AMMI analysis and other stability parameters. Experiments were laid out in randomized complete block design with three replications</span><span style="font-family:;" "=""><span style="font-family:Verdana;"> using fourteen improved tef genotypes. Mean yield for Halaba, Loka Abaya2016, Loka Abaya2017, Bensa, Areka2016 and Areka2017 was 0.99, 0.45, 0.48, 1.50, 1.62 and 0.77 tons/ha, respectively. Genotypes A</span><span><span style="font-family:Verdana;">marach, Boset, Simada, and Tseday exhibited high mean yield of 1.09, 1.10, 1.07 and 1.07 tons/ha, respectively. AMMI stability value (ASV) ranged from 0.17 (genotype Lakech) to 1.40 (Amarach);yield stability index (YSI) from 7 (Lakech) to 25 (Quncho);and superiority measure (</span><i><span style="font-family:Verdana;">P</span><sub><span style="font-family:Verdana;">i</span></sub></i><span style="font-family:Verdana;">) from 0.015 (Boset) to 0.145 (Dega Tef). Rank correlation of yield with </span><i><span style="font-family:Verdana;">P</span><sub><span style="font-family:Verdana;">i</span></sub></i></span></span><span style="font-family:;" "=""> </span><span style="font-family:;" "=""><span style="font-family:Verdana;">(</span><i><span style="font-family:Verdana展开更多
Tef [Eragrostis tef (Zucc.) Trotter] is the major cereal crop in Ethiopia. Increasing tef yield requires improving soil phosphorus (P) supply and identifying P efficient varieties. An experiment was conducted at Wenag...Tef [Eragrostis tef (Zucc.) Trotter] is the major cereal crop in Ethiopia. Increasing tef yield requires improving soil phosphorus (P) supply and identifying P efficient varieties. An experiment was conducted at Wenago, Ethiopia, from May to August, 2011, during the main cropping season, to investigate the role of P supply in relation to grain yield, nutrient uptake (N, P, Ca and K) and P efficiency, and to investigate varietal differences for these parameters using four P rates (0, 3, 6 and 9 g/m2 P2O5) as main plots and three tef varieties (DZ-Cr-37, DZ-Cr-82, and DZ-Cr-255) as subplots in split-plot design with three replications. For respective 0, 3, 6 and 9 g/m2 P2O5, grain yield was 84, 203, 215 and 218 g/m2, total biomass 586, 897, 971 and 1016 g/m2, and harvest index 0.14, 0.23, 0.22 and 0.22. For respective variety DZ-Cr-37, DZ-Cr-82, and DZ-Cr-255, grain yield was 194, 182 and 163 g/m2, total biomass 810, 922 and 871 g/m2, and harvest index 0.24, 0.19 and 0.18. Total plant nutrients (g/m2) for respective 0, 3, 6 and 9 g/m2 P2O5 were N 3.92, 7.95, 9.49 and 10.80, P 0.57, 1.20, 1.49 and 1.66, calcium 0.16, 0.27, 0.38 and 0.45, and K 4.45, 7.96, 9.70 and 10.50. For respective 3, 6 and 9 g/m2 P2O5, P physiological efficiency (PE) was 224, 153 and 127, apparent recovery (AR) 0.49, 0.36 and 0.28, and agronomic efficiency (AE) 92, 50 and 35. For respective variety DZ-Cr-37, DZ-Cr-82 and DZ-Cr-255, PE was 248, 130 and 126, AR 0.28, 0.44 and 0.41, and AE 68, 57 and 51. The present experiment suggests that excess P supply beyond 3 g/m2 could result in low grain yield increase and low P recovery requiring soil P assessment prior to fertilizer application. Moreover, variety DZ-Cr-37 may be incorporated in the future breeding programs for P efficiency in tef.展开更多
Tef [Eragrostis tef (Zucc.)Trotter] is an ancient and major cereal crop in Ethiopia. Increasing tef grain yield partly requires developing cultivars that are adapted to drought stress environment. An experiment was ca...Tef [Eragrostis tef (Zucc.)Trotter] is an ancient and major cereal crop in Ethiopia. Increasing tef grain yield partly requires developing cultivars that are adapted to drought stress environment. An experiment was carried out using 18 tef genotypes grown during September to December, 2010, under two water supply environments (stress during grain filling period, and non-stress) to identify genetic variation, heritability and correlations of grain yield and yield related traits. Broad-sense heritability values under respective stress and non-stress environments were grain yield (g/m2) 0.80 and 0.89, total biomass (g/m2) 0.89 and 0.73, harvest index 0.69 and 0.79, panicle weight (g/plant) 0.93 and 0.92, and seed weight (g/plant) 0.96 and 0.86. The correlations of grain yield under respective stress and non-stress environments were total biomass rp = 0.64, rg = 0.70, and rp = 0.48, rg = 0.56, harvest index rp = 0.70, rg = 0.64, and rp = 0.87, rg = 0.90, panicle weight rp = 0.98, rg = 1.00, and rp = 0.96, rg = 1.00, and seed weight/plant rp = 0.98, rg = 1.00, and rp = 0.90, rg = 1.00. The present experiment showed that either grain yield per se, or seed weight/plant could be used to improve grain yield under stress and non-stress environments.展开更多
It is ordinarily common for forage production in southern Kyushu to adopt a double cropping system, composed of summer forage crops (e.g. maize and sorghum) cultivated from late March to early September, and winter gr...It is ordinarily common for forage production in southern Kyushu to adopt a double cropping system, composed of summer forage crops (e.g. maize and sorghum) cultivated from late March to early September, and winter grass crops (e.g. Italian ryegrass (IR) and oat) from mid-October to the following May. However, if high total digestible nutrient (TDN) production is aimed to introduce winter cereal crops (e.g. wheat and barley) as a replacement of IR, it is necessary to cultivate tropical grass, which has a rapid-growth potential with high crude protein (CP) concentration in a switching period between summer and winter crops. In this study, teff (Eragrostis tef) was tried to evaluate as a candidate crop in the switching period. Yield and quality of two types of triple forage cropping system were determined under maize-teff-barley and maize-teff-wheat in the first and second year, respectively. Compared with the normal year, summer temperature was higher and summer and winter precipitations were lower in the first year, while no climatic disorder was observed in the second year. Even though dry matter yield of teff was minimal in the present system due to weed damage, CP concentration was the highest among crops and TDN yields of the present cropping system tended to be higher in the second year with no drought stress than in the conventional maize-IR system in the region.展开更多
Tef is grown as<span> an</span><span> important domestic cereal in Ethiopia. Currently</span><span>,</span><span> global attention is given for it particularly as a </span&...Tef is grown as<span> an</span><span> important domestic cereal in Ethiopia. Currently</span><span>,</span><span> global attention is given for it particularly as a </span><span>“</span><span>health food</span><span>”</span><span> due to the absence of gluten and gluten like proteins in its grains. Regardless of its wider adaptation, productivity of tef is low in the country with the national average grain yield of 1.379 tons·ha</span><sup><span style="vertical-align:super;">-1</span></sup><span>. This is mainly because of low soil fertility and severe organic matter depletion intensified by low rate of chemical fertilizer application. This study was conducted to evaluate effects of balanced fertilizers on the yield, yield components of tef and to determine economic feasibility for tef production in Wolaita. The experiment was laid out in a randomized complete block design (RCBD) with sixteen treatments replicated three times. The treatments consist of factorial combinations of four rates of K (Potassium) (0, 25, 50, and 100 kg/ha) and four rates of NPSB (Nitrogen, Phosphorus, Sulfur and Boron) (0, 50, 100, 200 kg/ha) fertilizers. Fertilizer types such as urea (46-0-0), NPSB (18.9-37.7-6.95-0.1) and K (0-0-60) were used as a source of nutrients. The soil analysis result indicated that, most of the nutrients are below optimum level to support the potential crop production. This may be related with reduced farm management practices and continuous cropping with little or no fertilizers input. In this study</span><span>,</span><span> it was found that, the combined application of NPSB and K fertilizers had </span><span>a </span><span>significant effect on growth, yield and yield components of tef. Among the treatments studied, NPSB (100</span><span> </span><span>Kg/ha) and K (50</span><span> </span><span>Kg/ha) gave greater grain yield. Furthermore, this treatment enhanced growth and yield related parameters compared to the control treatment. Thus, it is conceivable to recommend each to attain greater grain yiel展开更多
Starting from normalized generators' equations of rotor motion with respect to the center of inertia of power systems, post-fault power system dynamic is analogized as a motion of a particle with 1.0 mass in an n-...Starting from normalized generators' equations of rotor motion with respect to the center of inertia of power systems, post-fault power system dynamic is analogized as a motion of a particle with 1.0 mass in an n-dimensional Euclidean space. A rotational coordinate axis is defined for the moving particle. Transient stability of a multi-machine power system is transformed into a simple one-dimensional motion of particle on the axis. Based upon the above new idea, a new concept transient energy function (NCTEF) is proposed for transient stability assessment of power systems. Case studies on the 10-generator New England power system verified the rationality of NCTEF.展开更多
This study investigated the agronomic characteristics of pot-cultured teff (Eragrostis tef) under soil moisture and fertilization treatments in southern Kyushu, Japan. In experiments examining the effects of soil mois...This study investigated the agronomic characteristics of pot-cultured teff (Eragrostis tef) under soil moisture and fertilization treatments in southern Kyushu, Japan. In experiments examining the effects of soil moisture and fertilization, growth of teff and Setaria (Setaria sphacelata) as a reference species was compared under six treatments combining two soil moisture regimes, control (C) and high moisture (H) treatment, and three fertilizer applications, chemical fertilizer with manure (CF + M), chemical fertilizer (CF) and doubled level of manure (DM). H treatment did not decrease dry matter yield in teff two months after transplanting, except when combined with CF + M, compared with a decreasing tendency in Setaria. Top and underground dry matter yields and harvest index in teff increased significantly (P -2);6.2 gN m-2 is the standard level in the USA. Dry matter yield in teff did not differ significantly (P > 0.05) at CF application levels above 6.2 gN m-2 two months after sowing, suggesting that the optimum CF level of teff in southern Kyushu was comparable with that in the USA, and that teff had potential as an early-harvest forage crop two months after planting to replace summer forage in paddy fields of this region.展开更多
基金supported by National Key R&D Program of China(2018YFB0904600)the grant supported by 111 project.
文摘Economical and reliable protection of DC-side shortcircuit faults has become a key technology for promoting the development of module multilevel converters based on the high voltage direct current grid(MMC-HVDC-Grid).The fault current limiter(FCL)can effectively suppress the rapid development of the fault current and reduce the current breaking capacity of the circuit breaker.In this paper,a method based on transient energy flow(TEF)analysis is proposed to optimize the allocation of a resistive and inductive FCL in the MMC-HVDC-Grid.In the proposed method,the electromagnetic TEF is measured first,and then,the TEF suppression rate and suppression efficiency are defined as optimization objectives,and the installation location of the FCL and its impedance parameters as optimization variables.To test the proposed method,two-terminal and four-terminal bipolar MMC-HVDC-Grids with single-pole-to-ground DC faults are modeled in the PSCAD/EMTDC so that the TEF data can be acquired.The optimal FCLs’location and parameter values are determined through investigating the evolution paradigm of TEF along with changes of the FCL position and parameters.The results prove that the selected parameters can effectively slow down the DC fault current rising rate,thus reducing the requirements on tripping current of the DC breakers.
文摘<p align="left" style="text-align:justify;"> <span style="font-family:;" "=""><span style="font-family:Verdana;">Tef [</span><i><span style="font-family:Verdana;">Eragrostis</span></i> <i><span style="font-family:Verdana;">tef</span></i><span style="font-family:Verdana;"> (Zucc.)Trotter]) is one of the most important cereal crops </span></span><span style="font-family:Verdana;">grown </span><span style="font-family:Verdana;">in Ethiopia. Tef production has been partly constrained by low yield and less stability of the genotypes under cultivation. Field experiments were carried out in Halaba, Loka Abaya, Bensa and Areka, South Ethiopia, from August to November, during 2016 and 2017 main cropping seasons, in order to estimate yield stability </span><span style="font-family:Verdana;">and the association between AMMI analysis and other stability parameters. Experiments were laid out in randomized complete block design with three replications</span><span style="font-family:;" "=""><span style="font-family:Verdana;"> using fourteen improved tef genotypes. Mean yield for Halaba, Loka Abaya2016, Loka Abaya2017, Bensa, Areka2016 and Areka2017 was 0.99, 0.45, 0.48, 1.50, 1.62 and 0.77 tons/ha, respectively. Genotypes A</span><span><span style="font-family:Verdana;">marach, Boset, Simada, and Tseday exhibited high mean yield of 1.09, 1.10, 1.07 and 1.07 tons/ha, respectively. AMMI stability value (ASV) ranged from 0.17 (genotype Lakech) to 1.40 (Amarach);yield stability index (YSI) from 7 (Lakech) to 25 (Quncho);and superiority measure (</span><i><span style="font-family:Verdana;">P</span><sub><span style="font-family:Verdana;">i</span></sub></i><span style="font-family:Verdana;">) from 0.015 (Boset) to 0.145 (Dega Tef). Rank correlation of yield with </span><i><span style="font-family:Verdana;">P</span><sub><span style="font-family:Verdana;">i</span></sub></i></span></span><span style="font-family:;" "=""> </span><span style="font-family:;" "=""><span style="font-family:Verdana;">(</span><i><span style="font-family:Verdana
文摘Tef [Eragrostis tef (Zucc.) Trotter] is the major cereal crop in Ethiopia. Increasing tef yield requires improving soil phosphorus (P) supply and identifying P efficient varieties. An experiment was conducted at Wenago, Ethiopia, from May to August, 2011, during the main cropping season, to investigate the role of P supply in relation to grain yield, nutrient uptake (N, P, Ca and K) and P efficiency, and to investigate varietal differences for these parameters using four P rates (0, 3, 6 and 9 g/m2 P2O5) as main plots and three tef varieties (DZ-Cr-37, DZ-Cr-82, and DZ-Cr-255) as subplots in split-plot design with three replications. For respective 0, 3, 6 and 9 g/m2 P2O5, grain yield was 84, 203, 215 and 218 g/m2, total biomass 586, 897, 971 and 1016 g/m2, and harvest index 0.14, 0.23, 0.22 and 0.22. For respective variety DZ-Cr-37, DZ-Cr-82, and DZ-Cr-255, grain yield was 194, 182 and 163 g/m2, total biomass 810, 922 and 871 g/m2, and harvest index 0.24, 0.19 and 0.18. Total plant nutrients (g/m2) for respective 0, 3, 6 and 9 g/m2 P2O5 were N 3.92, 7.95, 9.49 and 10.80, P 0.57, 1.20, 1.49 and 1.66, calcium 0.16, 0.27, 0.38 and 0.45, and K 4.45, 7.96, 9.70 and 10.50. For respective 3, 6 and 9 g/m2 P2O5, P physiological efficiency (PE) was 224, 153 and 127, apparent recovery (AR) 0.49, 0.36 and 0.28, and agronomic efficiency (AE) 92, 50 and 35. For respective variety DZ-Cr-37, DZ-Cr-82 and DZ-Cr-255, PE was 248, 130 and 126, AR 0.28, 0.44 and 0.41, and AE 68, 57 and 51. The present experiment suggests that excess P supply beyond 3 g/m2 could result in low grain yield increase and low P recovery requiring soil P assessment prior to fertilizer application. Moreover, variety DZ-Cr-37 may be incorporated in the future breeding programs for P efficiency in tef.
文摘Tef [Eragrostis tef (Zucc.)Trotter] is an ancient and major cereal crop in Ethiopia. Increasing tef grain yield partly requires developing cultivars that are adapted to drought stress environment. An experiment was carried out using 18 tef genotypes grown during September to December, 2010, under two water supply environments (stress during grain filling period, and non-stress) to identify genetic variation, heritability and correlations of grain yield and yield related traits. Broad-sense heritability values under respective stress and non-stress environments were grain yield (g/m2) 0.80 and 0.89, total biomass (g/m2) 0.89 and 0.73, harvest index 0.69 and 0.79, panicle weight (g/plant) 0.93 and 0.92, and seed weight (g/plant) 0.96 and 0.86. The correlations of grain yield under respective stress and non-stress environments were total biomass rp = 0.64, rg = 0.70, and rp = 0.48, rg = 0.56, harvest index rp = 0.70, rg = 0.64, and rp = 0.87, rg = 0.90, panicle weight rp = 0.98, rg = 1.00, and rp = 0.96, rg = 1.00, and seed weight/plant rp = 0.98, rg = 1.00, and rp = 0.90, rg = 1.00. The present experiment showed that either grain yield per se, or seed weight/plant could be used to improve grain yield under stress and non-stress environments.
文摘It is ordinarily common for forage production in southern Kyushu to adopt a double cropping system, composed of summer forage crops (e.g. maize and sorghum) cultivated from late March to early September, and winter grass crops (e.g. Italian ryegrass (IR) and oat) from mid-October to the following May. However, if high total digestible nutrient (TDN) production is aimed to introduce winter cereal crops (e.g. wheat and barley) as a replacement of IR, it is necessary to cultivate tropical grass, which has a rapid-growth potential with high crude protein (CP) concentration in a switching period between summer and winter crops. In this study, teff (Eragrostis tef) was tried to evaluate as a candidate crop in the switching period. Yield and quality of two types of triple forage cropping system were determined under maize-teff-barley and maize-teff-wheat in the first and second year, respectively. Compared with the normal year, summer temperature was higher and summer and winter precipitations were lower in the first year, while no climatic disorder was observed in the second year. Even though dry matter yield of teff was minimal in the present system due to weed damage, CP concentration was the highest among crops and TDN yields of the present cropping system tended to be higher in the second year with no drought stress than in the conventional maize-IR system in the region.
文摘Tef is grown as<span> an</span><span> important domestic cereal in Ethiopia. Currently</span><span>,</span><span> global attention is given for it particularly as a </span><span>“</span><span>health food</span><span>”</span><span> due to the absence of gluten and gluten like proteins in its grains. Regardless of its wider adaptation, productivity of tef is low in the country with the national average grain yield of 1.379 tons·ha</span><sup><span style="vertical-align:super;">-1</span></sup><span>. This is mainly because of low soil fertility and severe organic matter depletion intensified by low rate of chemical fertilizer application. This study was conducted to evaluate effects of balanced fertilizers on the yield, yield components of tef and to determine economic feasibility for tef production in Wolaita. The experiment was laid out in a randomized complete block design (RCBD) with sixteen treatments replicated three times. The treatments consist of factorial combinations of four rates of K (Potassium) (0, 25, 50, and 100 kg/ha) and four rates of NPSB (Nitrogen, Phosphorus, Sulfur and Boron) (0, 50, 100, 200 kg/ha) fertilizers. Fertilizer types such as urea (46-0-0), NPSB (18.9-37.7-6.95-0.1) and K (0-0-60) were used as a source of nutrients. The soil analysis result indicated that, most of the nutrients are below optimum level to support the potential crop production. This may be related with reduced farm management practices and continuous cropping with little or no fertilizers input. In this study</span><span>,</span><span> it was found that, the combined application of NPSB and K fertilizers had </span><span>a </span><span>significant effect on growth, yield and yield components of tef. Among the treatments studied, NPSB (100</span><span> </span><span>Kg/ha) and K (50</span><span> </span><span>Kg/ha) gave greater grain yield. Furthermore, this treatment enhanced growth and yield related parameters compared to the control treatment. Thus, it is conceivable to recommend each to attain greater grain yiel
文摘Starting from normalized generators' equations of rotor motion with respect to the center of inertia of power systems, post-fault power system dynamic is analogized as a motion of a particle with 1.0 mass in an n-dimensional Euclidean space. A rotational coordinate axis is defined for the moving particle. Transient stability of a multi-machine power system is transformed into a simple one-dimensional motion of particle on the axis. Based upon the above new idea, a new concept transient energy function (NCTEF) is proposed for transient stability assessment of power systems. Case studies on the 10-generator New England power system verified the rationality of NCTEF.
文摘This study investigated the agronomic characteristics of pot-cultured teff (Eragrostis tef) under soil moisture and fertilization treatments in southern Kyushu, Japan. In experiments examining the effects of soil moisture and fertilization, growth of teff and Setaria (Setaria sphacelata) as a reference species was compared under six treatments combining two soil moisture regimes, control (C) and high moisture (H) treatment, and three fertilizer applications, chemical fertilizer with manure (CF + M), chemical fertilizer (CF) and doubled level of manure (DM). H treatment did not decrease dry matter yield in teff two months after transplanting, except when combined with CF + M, compared with a decreasing tendency in Setaria. Top and underground dry matter yields and harvest index in teff increased significantly (P -2);6.2 gN m-2 is the standard level in the USA. Dry matter yield in teff did not differ significantly (P > 0.05) at CF application levels above 6.2 gN m-2 two months after sowing, suggesting that the optimum CF level of teff in southern Kyushu was comparable with that in the USA, and that teff had potential as an early-harvest forage crop two months after planting to replace summer forage in paddy fields of this region.
