In this paper, the stability problems of power systems with large power source are analyzed with viewpoint of energy balance. The phenomena are studied when the energy delivery are “blocked” by faults that occur on ...In this paper, the stability problems of power systems with large power source are analyzed with viewpoint of energy balance. The phenomena are studied when the energy delivery are “blocked” by faults that occur on some key transmission lines of a large power source within a power system, on the transmission lines between the interconnected power systems, or on some key buses. The cases are based on a practical power system and its interconnected systems.展开更多
In our paper we demonstrate that the filtration equation used by Gorban’ et al. for determining the maximum efficiency of plane propellers of about 30 percent for free fluids plays no role in describing the flows in ...In our paper we demonstrate that the filtration equation used by Gorban’ et al. for determining the maximum efficiency of plane propellers of about 30 percent for free fluids plays no role in describing the flows in the atmospheric boundary layer (ABL) because the ABL is mainly governed by turbulent motions. We also demonstrate that the stream tube model customarily applied to derive the Rankine-Froude theorem must be corrected in the sense of Glauert to provide an appropriate value for the axial velocity at the rotor area. Including this correction leads to the Betz-Joukowsky limit, the maximum efficiency of 59.3 percent. Thus, Gorban’ et al.’s 30% value may be valid in water, but it has to be discarded for the atmosphere. We also show that Joukowsky’s constant circulation model leads to values of the maximum efficiency which are higher than the Betz-Jow-kowsky limit if the tip speed ratio is very low. Some of these values, however, have to be rejected for physical reasons. Based on Glauert’s optimum actuator disk, and the results of the blade-element analysis by Okulov and Sørensen we also illustrate that the maximum efficiency of propeller-type wind turbines depends on tip-speed ratio and the number of blades.展开更多
The energy balance equations in the Classical Statistical Energy Analysis (CSEA) are modified by the equations of power flow among the thtee serial coupled oscinators. The modified equations include not only the direc...The energy balance equations in the Classical Statistical Energy Analysis (CSEA) are modified by the equations of power flow among the thtee serial coupled oscinators. The modified equations include not only the direct power flow, but also the indirect power flow. The parameters in the modified equations can be expressed by those in the classical equations when the accuracy of the predicted results is able to satisfy the needs for ellgineering.展开更多
During this decade,many countries have experienced natural and accidental disasters,such as typhoons,floods,earthquakes,and nuclear plant accidents,causing catastrophic damage to infrastructures.Since the end of 2019,...During this decade,many countries have experienced natural and accidental disasters,such as typhoons,floods,earthquakes,and nuclear plant accidents,causing catastrophic damage to infrastructures.Since the end of 2019,all countries of the world are struggling with the COVID-19 and pursuing countermeasures,including inoculation of vaccine,and changes in our lifestyle and social structures.All these experiences have made the residents in the affected regions keenly aware of the need for new infrastructures that are resilient and autonomous,so that vital lifelines are secured during calamities.A paradigm shift has been taking place toward reorganizing the energy social service management in many countries,including Japan,by effective use of sustainable energy and new supply schemes.However,such new power sources and supply schemes would affect the power grid through intermittency of power output and the deterioration of power quality and service.Therefore,new social infrastructures and novel management systems to supply energy and social service will be required.In this paper,user-friendly design,operation and control assist tools for resilient microgrids and autonomous communities are proposed and applied to the standard microgrid to verify its effectiveness and performance.展开更多
The wind power potential in Interior Alaska is evaluated from a micrometeorological perspective. Based on the local balance equation of momentum and the equation of continuity we derive the local balance equation of k...The wind power potential in Interior Alaska is evaluated from a micrometeorological perspective. Based on the local balance equation of momentum and the equation of continuity we derive the local balance equation of kinetic energy for macroscopic and turbulent systems, and in a further step, Bernoulli’s equation and integral equations that customarily serve as the key equations in momentum theory and blade-element analysis, where the Lanchester-Betz-Joukowsky limit, Glauert’s optimum actuator disk, and the results of the blade-element analysis by Okulov and Sorensen are exemplarily illustrated. The wind power potential at three different sites in Interior Alaska (Delta Junction, Eva Creek, and Poker Flat) is assessed by considering the results of wind field predictions for the winter period from October 1, 2008, to April 1, 2009 provided by the Weather Research and Forecasting (WRF) model to avoid time-consuming and expensive tall-tower observations in Interior Alaska which is characterized by a relatively low degree of infrastructure outside of the city of Fairbanks. To predict the average power output we use the Weibull distributions derived from the predicted wind fields for these three different sites and the power curves of five different propeller-type wind turbines with rated powers ranging from 2 MW to 2.5 MW. These power curves are represented by general logistic functions. The predicted power capacity for the Eva Creek site is compared with that of the Eva Creek wind farm established in 2012. The results of our predictions for the winter period 2008/2009 are nearly 20 percent lower than those of the Eva Creek wind farm for the period from January to September 2013.展开更多
为延长电池储能系统的整体寿命,需保持储能系统中各单元的荷电状态(state of charge,SOC)均衡。为此,提出一种基于二阶一致性算法的改进下垂控制策略,通过指数函数嵌套变化系数,实现不同容量储能单元快速SOC均衡。在SOC均衡的基础上设...为延长电池储能系统的整体寿命,需保持储能系统中各单元的荷电状态(state of charge,SOC)均衡。为此,提出一种基于二阶一致性算法的改进下垂控制策略,通过指数函数嵌套变化系数,实现不同容量储能单元快速SOC均衡。在SOC均衡的基础上设计二次控制策略,在一定通信时延下实现频率、电压恢复和有功、无功功率合理分配。最后,以4台储能单元组成的电池储能系统为算例进行仿真,验证了所提控制策略的有效性,SOC能够快速收敛达到均衡状态,频率、电压能够恢复到额定值,有功、无功功率能够按照相应下垂系数比例进行分配。展开更多
直流微电网处于孤岛运行状态时需要储能来维持整个系统的功率平衡与电压稳定,而分布式接入的储能单元由于负荷功率分配不合理等会出现荷电状态(state of charge,SOC)不一致问题。为了实现不同储能单元SOC之间的快速均衡,提出了一种基于...直流微电网处于孤岛运行状态时需要储能来维持整个系统的功率平衡与电压稳定,而分布式接入的储能单元由于负荷功率分配不合理等会出现荷电状态(state of charge,SOC)不一致问题。为了实现不同储能单元SOC之间的快速均衡,提出了一种基于自适应下垂控制的多储能SOC均衡策略。在所提策略中,储能单元的下垂系数通过反正切函数与SOC建立联系,下垂系数可随SOC在允许范围内自适应地变化,以达到合理分配功率、均衡多储能SOC的目的。此外,为了加快均衡速率,引入放大因子,并建立采用所提控制策略的直流微电网小信号模型,对放大因子对系统稳定性的影响进行了分析。最后,搭建了光储直流微电网硬件在环仿真(hardware-in-the-loop simulation,HILS)实验平台,实验结果验证了所提控制策略在快速均衡多储能SOC方面的有效性。展开更多
文摘In this paper, the stability problems of power systems with large power source are analyzed with viewpoint of energy balance. The phenomena are studied when the energy delivery are “blocked” by faults that occur on some key transmission lines of a large power source within a power system, on the transmission lines between the interconnected power systems, or on some key buses. The cases are based on a practical power system and its interconnected systems.
文摘In our paper we demonstrate that the filtration equation used by Gorban’ et al. for determining the maximum efficiency of plane propellers of about 30 percent for free fluids plays no role in describing the flows in the atmospheric boundary layer (ABL) because the ABL is mainly governed by turbulent motions. We also demonstrate that the stream tube model customarily applied to derive the Rankine-Froude theorem must be corrected in the sense of Glauert to provide an appropriate value for the axial velocity at the rotor area. Including this correction leads to the Betz-Joukowsky limit, the maximum efficiency of 59.3 percent. Thus, Gorban’ et al.’s 30% value may be valid in water, but it has to be discarded for the atmosphere. We also show that Joukowsky’s constant circulation model leads to values of the maximum efficiency which are higher than the Betz-Jow-kowsky limit if the tip speed ratio is very low. Some of these values, however, have to be rejected for physical reasons. Based on Glauert’s optimum actuator disk, and the results of the blade-element analysis by Okulov and Sørensen we also illustrate that the maximum efficiency of propeller-type wind turbines depends on tip-speed ratio and the number of blades.
文摘The energy balance equations in the Classical Statistical Energy Analysis (CSEA) are modified by the equations of power flow among the thtee serial coupled oscinators. The modified equations include not only the direct power flow, but also the indirect power flow. The parameters in the modified equations can be expressed by those in the classical equations when the accuracy of the predicted results is able to satisfy the needs for ellgineering.
文摘During this decade,many countries have experienced natural and accidental disasters,such as typhoons,floods,earthquakes,and nuclear plant accidents,causing catastrophic damage to infrastructures.Since the end of 2019,all countries of the world are struggling with the COVID-19 and pursuing countermeasures,including inoculation of vaccine,and changes in our lifestyle and social structures.All these experiences have made the residents in the affected regions keenly aware of the need for new infrastructures that are resilient and autonomous,so that vital lifelines are secured during calamities.A paradigm shift has been taking place toward reorganizing the energy social service management in many countries,including Japan,by effective use of sustainable energy and new supply schemes.However,such new power sources and supply schemes would affect the power grid through intermittency of power output and the deterioration of power quality and service.Therefore,new social infrastructures and novel management systems to supply energy and social service will be required.In this paper,user-friendly design,operation and control assist tools for resilient microgrids and autonomous communities are proposed and applied to the standard microgrid to verify its effectiveness and performance.
基金the National Science Foundation for funding the project work of Megan Hinzman and Samuel Smock in summer 2011Hannah K.Ross and John Cooney in summer 2012 through the Research Experience for Undergraduates(REU)Program,grant number AGS1005265the Alaska Department of Labor for funding Dr.Gary Sellhorst’s project work
文摘The wind power potential in Interior Alaska is evaluated from a micrometeorological perspective. Based on the local balance equation of momentum and the equation of continuity we derive the local balance equation of kinetic energy for macroscopic and turbulent systems, and in a further step, Bernoulli’s equation and integral equations that customarily serve as the key equations in momentum theory and blade-element analysis, where the Lanchester-Betz-Joukowsky limit, Glauert’s optimum actuator disk, and the results of the blade-element analysis by Okulov and Sorensen are exemplarily illustrated. The wind power potential at three different sites in Interior Alaska (Delta Junction, Eva Creek, and Poker Flat) is assessed by considering the results of wind field predictions for the winter period from October 1, 2008, to April 1, 2009 provided by the Weather Research and Forecasting (WRF) model to avoid time-consuming and expensive tall-tower observations in Interior Alaska which is characterized by a relatively low degree of infrastructure outside of the city of Fairbanks. To predict the average power output we use the Weibull distributions derived from the predicted wind fields for these three different sites and the power curves of five different propeller-type wind turbines with rated powers ranging from 2 MW to 2.5 MW. These power curves are represented by general logistic functions. The predicted power capacity for the Eva Creek site is compared with that of the Eva Creek wind farm established in 2012. The results of our predictions for the winter period 2008/2009 are nearly 20 percent lower than those of the Eva Creek wind farm for the period from January to September 2013.
文摘为延长电池储能系统的整体寿命,需保持储能系统中各单元的荷电状态(state of charge,SOC)均衡。为此,提出一种基于二阶一致性算法的改进下垂控制策略,通过指数函数嵌套变化系数,实现不同容量储能单元快速SOC均衡。在SOC均衡的基础上设计二次控制策略,在一定通信时延下实现频率、电压恢复和有功、无功功率合理分配。最后,以4台储能单元组成的电池储能系统为算例进行仿真,验证了所提控制策略的有效性,SOC能够快速收敛达到均衡状态,频率、电压能够恢复到额定值,有功、无功功率能够按照相应下垂系数比例进行分配。
文摘直流微电网处于孤岛运行状态时需要储能来维持整个系统的功率平衡与电压稳定,而分布式接入的储能单元由于负荷功率分配不合理等会出现荷电状态(state of charge,SOC)不一致问题。为了实现不同储能单元SOC之间的快速均衡,提出了一种基于自适应下垂控制的多储能SOC均衡策略。在所提策略中,储能单元的下垂系数通过反正切函数与SOC建立联系,下垂系数可随SOC在允许范围内自适应地变化,以达到合理分配功率、均衡多储能SOC的目的。此外,为了加快均衡速率,引入放大因子,并建立采用所提控制策略的直流微电网小信号模型,对放大因子对系统稳定性的影响进行了分析。最后,搭建了光储直流微电网硬件在环仿真(hardware-in-the-loop simulation,HILS)实验平台,实验结果验证了所提控制策略在快速均衡多储能SOC方面的有效性。
