A photovoltaic array is environmentally friendly and a source of unlimited energy generation.However,it is presently a costlier energy generation system than other non-renewable energy sources.The main reasons are sea...A photovoltaic array is environmentally friendly and a source of unlimited energy generation.However,it is presently a costlier energy generation system than other non-renewable energy sources.The main reasons are seasonal variations and continuously changing weather conditions,which affect the amount of solar energy received by the solar panels.In addition,the non-linear characteristics of the voltage and current outputs along with the operating environment temperature and variation in the solar radiation decrease the energy conversion capability of the photovoltaic arrays.To address this problem,the global maxima of the PV arrays can be tracked using a maximum power point tracking algorithm(MPPT)and the operating point of the photovoltaic system can be forced to its optimum value.This technique increases the efficiency of the photovoltaic array and minimizes the cost of the system by reducing the number of solar modules required to obtain the desired power.However,the tracking algorithms are not equally effective in all areas of application.Therefore,selecting the correct MPPT is very critical.This paper presents a detailed review and comparison of the MPPT techniques for photovoltaic systems,with consideration of the following key parameters:photovoltaic array dependence,type of system(analog or digital),need for periodic tuning,convergence speed,complexity of the system,global maxima,implemented capacity,and sensed parameter(s).In addition,based on real meteorological data(irradiance and temperature at a site located in Addis Ababa,Ethiopia),a simulation is performed to evaluate the performance of tracking algorithms suitable for the application being studied.Finally,the study clearly validates the considerable energy saving achieved by using these algorithms.展开更多
For many decades, Ethiopia had been using a meter gauge railway from Addis Ababa to the red sea port of Djibouti. Currently, the century old railway is completely replaced by a brand new standard gauge electrified rai...For many decades, Ethiopia had been using a meter gauge railway from Addis Ababa to the red sea port of Djibouti. Currently, the century old railway is completely replaced by a brand new standard gauge electrified railway line aiming to connect the country to the global market by guaranteeing a unified access to different regions of the country. In order to meet modern railway standards, a 1 x 25 kV catenary system is adopted in Ethio-Djibouti railway line corridor. In this paper, an alternative and a more superior 2 x 25 kV traction power supply system is presented. The modeling and analysis of the 2 x 25 kV traction supply system including the traction load, the substation power transformer, the autotransformer(AT), the catenary line impedance, etc., are performed. In addition, in order to validate the benefits of the proposed system, a comparative analysis of the two types of traction power supply arrangement has been conducted using MATLAB simulation. The analysis focuses on evaluating the voltage profiles of both power supply configurations on the basis of BS EN 50163:2004 international standard.展开更多
基金supported by the following project of the Addis Ababa Institute of Technology,African Railway Center of Excellence,and World Bank group:“A research on integration of renewable and Alternative Energy Sources into Ethiopian Railway System.”(AAITRS-GSR-7767-18).
文摘A photovoltaic array is environmentally friendly and a source of unlimited energy generation.However,it is presently a costlier energy generation system than other non-renewable energy sources.The main reasons are seasonal variations and continuously changing weather conditions,which affect the amount of solar energy received by the solar panels.In addition,the non-linear characteristics of the voltage and current outputs along with the operating environment temperature and variation in the solar radiation decrease the energy conversion capability of the photovoltaic arrays.To address this problem,the global maxima of the PV arrays can be tracked using a maximum power point tracking algorithm(MPPT)and the operating point of the photovoltaic system can be forced to its optimum value.This technique increases the efficiency of the photovoltaic array and minimizes the cost of the system by reducing the number of solar modules required to obtain the desired power.However,the tracking algorithms are not equally effective in all areas of application.Therefore,selecting the correct MPPT is very critical.This paper presents a detailed review and comparison of the MPPT techniques for photovoltaic systems,with consideration of the following key parameters:photovoltaic array dependence,type of system(analog or digital),need for periodic tuning,convergence speed,complexity of the system,global maxima,implemented capacity,and sensed parameter(s).In addition,based on real meteorological data(irradiance and temperature at a site located in Addis Ababa,Ethiopia),a simulation is performed to evaluate the performance of tracking algorithms suitable for the application being studied.Finally,the study clearly validates the considerable energy saving achieved by using these algorithms.
文摘For many decades, Ethiopia had been using a meter gauge railway from Addis Ababa to the red sea port of Djibouti. Currently, the century old railway is completely replaced by a brand new standard gauge electrified railway line aiming to connect the country to the global market by guaranteeing a unified access to different regions of the country. In order to meet modern railway standards, a 1 x 25 kV catenary system is adopted in Ethio-Djibouti railway line corridor. In this paper, an alternative and a more superior 2 x 25 kV traction power supply system is presented. The modeling and analysis of the 2 x 25 kV traction supply system including the traction load, the substation power transformer, the autotransformer(AT), the catenary line impedance, etc., are performed. In addition, in order to validate the benefits of the proposed system, a comparative analysis of the two types of traction power supply arrangement has been conducted using MATLAB simulation. The analysis focuses on evaluating the voltage profiles of both power supply configurations on the basis of BS EN 50163:2004 international standard.
