Economic Load Dispatching Control Research Articles

A Study on Influence of Ramp Event of Aggregated Power Output of Photovoltaic Power Generation on Electric Power System Frequency

SUMMARYThis paper examines the influence of aggregated power output fluctuation of photovoltaic power generation system (PVS) on the power system frequency focusing on ramp events of aggregated PVS power output. A numerical simulation model of economic load dispatching control (EDC) and load frequency control (LFC) is used together with a PVS power output forecasting model and a unit commitment (UC) scheduling model developed in our preceding study. As a result, in the case of ramp event with long duration and high ramp rate, the frequency violation occurs when the power output of controllable generators with high load‐following capability reaches to upper/lower limit even if the power output of low load‐following capability generators is still available. If the load dispatching scheme is tentatively changed from the conventional EDC using an equal incremental fuel cost rule to, for example, a dispatching policy based on the capacity without the consideration of fuel cost, the aggregated load‐following capability can be kept, avoiding the frequency violation.

Numerical definitions of wind power output fluctuations for power system operations

Because of unpredictable fluctuations in wind power output caused by sudden changes in weather conditions, operations that balance supply and demand in power systems will gradually become more difficult with the massive deployment of wind power generation. Therefore, it is necessary to quantitatively evaluate wind power output fluctuations in a way that corresponds to frequency controls in power system operations. In this study, we analyzed data for the fluctuations of actual wind power output at 20 wind farms, as designated by three basic definitions: the changes in time-averaged values, the maximum power-fluctuation range within a time window, and the deviations from a centered moving average value. The results indicated relevant differences between the definitions and demonstrated the importance of percentile analysis. We proposed a novel quantitative definition of the output fluctuations associated with the frequency controls of power systems: primary turbine-governor control, secondary load-frequency control, and tertiary economic load-dispatch control. Using these definitions to quantify fluctuations demonstrates how each smoothing technique can contribute to reducing the reserve capacity necessary for frequency control in the power system operations. Our proposed definitions for dividing the frequency ranges of the fluctuations were confirmed as a convenient and practical method for quantitatively evaluating the fluctuations and determining the reserve capacity required for stable power system operations.

太陽光発電合計出力のランプ変動が系統周波数に与える影響に関する一検討

This paper examines the influence of aggregated power output fluctuation of photovoltaic power generation system (PVS) on the power system frequency, focusing on ramp-events of aggregated PVS power output. A numerical simulation model of economic load dispatching control (EDC) and load- frequency control (LFC) is used together with a PVS power output forecasting model and a unit commitment (UC) scheduling model developed in our preceding study. As a result, in the case of ramp event with long duration and high ramp rate, the frequency violation occurs when the power output of controllable generators with high load following capability reaches to upper/lower limit even if the power output of low load following capability generators is still available. If the load dispatching scheme is tentatively changed from the conventional EDC using an equal incremental fuel cost rule to, for example, a dispatching policy based on the capacity without the consideration of fuel cost, the aggregated load-following capability can be kept, avoiding the frequency violation.

電力系統における需給解析・シミュレーションの動向について

The stable electric power supply requires to maintain the system frequency within a specified band by matching the supply and demand constantly with the help of Economic load Dispatching Control (EDC) or Load Frequency Control (LFC). On the other hand, recently the penetration of renewable energy sources (RESs) such as photovoltaic generations (PVs) and wind turbines (WTs) are rapidly increasing due to the introduction of feed-in tariff (FIT) and growing environmental awareness. However, the output power generated by these RESs depends on the climatic conditions, and as such the output may not always be available when required. As a result, it would be more difficult to ensure the stable power supply by balancing the supply and demand in view of the uncertain outputs of RESs at all the time. In order to grasp the influences and to verify the effectiveness of countermeasures for various issues such as the frequency deviation caused by a large penetration of RESs, the analysis and simulation technologies for the electric power supply and demand control are becoming more important. Hence in this paper, the recent trends of these technologies are reviewed.

Evaluation of Power Surpluses and Shortfalls Due to Error in Forecasting of Photovoltaic Generation Output

SUMMARYThe 2011 Tohoku earthquake had a great impact on Japanese energy policy. It is expected that nuclear power plants will be phased out and a large amount of generation from renewable energy sources will be installed. Attention is particularly focused on photovoltaic (PV) generation, technology in which Japan is superior, and a high price is set in the feed‐in tariff policy, which started in 2012. However, large integration of PV into power grids may cause imbalances between power supply and demand. It will be indispensable to use PV power generation forecasts in economic‐load dispatching control (EDC), so that the economics and reliability of power systems networks can be maintained. Thus, in the previous study, we proposed an EDC method with unit commitment (UC) based on the results provided by a day‐ahead PV forecast. In this study, we evaluate the frequency and trend of shortfalls and surpluses of power due to error in forecasting PV power generation by numerical simulations using the power system model of the Kanto area in Japan. The results showed that shortfalls or surplus power occur not only due to overestimations or underestimations of PV power, but also due to the operating conditions of the power systems.

A Very Short-Term Load Forecasting Method for Economic Load Dispatching Control

This paper proposes a very short-term load forecasting technique in order to make Economic Load Dispatching Control (EDC) more effective. The controllable periodic term of EDC is made clear through power spectrum analysis of actual load and actual EDC outputs of the Kansai Electric Power Company. A real-time predictor is designed based on this result, and it can decrease the EDC error at almost the same level as the actual AR (Area Requirement: final error after EDC and LFC) through the year. In addition, it can be seen from the generation simulation by using this predictor that we can decrease the fuel cost and LFC margin.