Search

To solve the unit commitment (UC) problems with efficient mixed‐integer linear programming solvers, the quadratic cost functions (QCFs) of thermal units are always approximated to piecewise linear (PWL) functions. This study examines the accuracies of different approximation methods for piecewise linearizing the QCFs of units in UC problems. We use five piecewise linearization methods—evenly spaced PWL interpolation, evenly spaced PWL tangent, evenly spaced PWL–ɛmax/2 shifted interpolation, tighter PWL interpolation, and evenly spaced PWL least‐squares fit—to approximate the QCFs of units. The authors first perform a series of reproductivity studies to verify the program. Then, numerical tests are conducted using different methods on the systems with 10, 100, and 800 units. The results show that different approximation methods lead to considerable differences in operating costs and the tighter PWL interpolation, compared with the other methods, is preferred in terms of approximation accuracy. [ABSTRACT FROM AUTHOR]

In the studies of unit commitment or optimal power flow, to formulate a mixed-integer linear programming model that can be efficiently solved with commercial solvers, it is necessary to approximate the quadratic cost curves of thermal units as piecewise linear (PWL) functions. The conventional approach involves evenly spaced piecewise linear (ES-PWL) interpolation, which often results in relatively large approximation errors. In order to reduce the error, this paper proposes a more accurate PWL method for approximating the quadratic cost functions of thermal units. The method employs a linear least-squares fit instead of linear interpolation within each subinterval and introduces a one-terminal-constraint approach to ensure the continuity of the piecewise function. Subsequently, a straightforward equation is derived, applicable to the widely used ES-PWL interpolation, with the potential to enhance the accuracy of the approximation. Mathematical verification attests that the proposed method substantially diminishes the squared 2-norm error, less than 37.5% of the error associated with ES-PWL interpolation. Subsequent numerical investigations are carried out on a 10-unit system, the IEEE RTS-79, and a real industrial system. The findings validate that all the approximation errors of the proposed method are within 37.5% of the errors associated with the ES-PWL interpolation, meaning that a unit commitment solution that closely approximates the outcome of the quadratic function is obtained. The computational time is also acceptable. [ABSTRACT FROM AUTHOR]

In traditional unit commitment models, the ramping process of coal-fired generators is often represented by either a static average ramping rate or a once-changing rate model. However, this approach fails to accurately capture the actual ramping process of the unit, resulting in scheduling biases, particularly in systems with renewable energy sources. To address this issue, we propose a dynamic piecewise linear ramping (DPWLR) model that allows arbitrary multi-changes of ramping rates within a single period. We shift our focus from slope changes to time changes. By using a series of location indicator variables that satisfy the type 2 special ordered set, we locate the forward and backward time change limits and then determine the up and down power output limits of the units at each hour. We tested the intraperiod multiple-changing DPWLR model, as part of the unit commitment model, on different systems, including a 3-unit system, a 10-unit system, the IEEE RTS-79, and a 100-unit system. Comparative analysis demonstrates the functionality and superior performance of our proposed model. • A dynamic ramping model to simulate the unit's ramping process is proposed. • The model allows multiple ramping rate changes in one period. • The model uses location indicator variables to identify the ramping limits. • Some reproducibility studies on previous papers are carried out. • Comparison studies between the proposed model and the existing model are conducted. [ABSTRACT FROM AUTHOR]

Abstract Although the integration of large–scale clean wind power will have a positive impact on the environment deterioration and reduce the fossil fuel depletion, it also creates challenges for power system operations. Considering that some countries, such as China, hold a geographical advantage of adjacent distributions of wind and coal resources, i.e., the windy areas are located/close to the areas with vast coal reserves, one feasible plan of both utilizing the large–scale wind power and alleviating the operation burden of power systems is to build bundled wind–thermal generation systems (BWTGSs). This paper first gives the optimal BWTGSs (investment) planning method, in which the cost changing rules, the candidate scheme formation, and long–term wind–thermal coordinated generation scheduling simulation are introduced. Then based on different compensation purposes or requirements, four transmission power modes, i.e., constant transmission power mode, thermal–generation–smoothed transmission power mode, transmission power mode considering load pattern of receiving system, and sectioned transmission power mode, are proposed. Finally, numerical studies are conducted. Planning results show that the generator schemes, total costs, and clean energy proportions differ when adopting different transmission modes, and the sectioned transmission power mode is the most desirable mode with the lowest total planning cost and the highest clean energy proportion. Highlights • An optimal model for bundled wind–thermal generation system planning is presented. • Four transmission power (TP) modes for bundled generation system are proposed. • Optimal planning results for different TP modes are calculated and compared. • Sectioned TP mode leads to the lowest total cost and highest clean energy proportion. [ABSTRACT FROM AUTHOR]

The increasing penetration of intermittent wind power affects the secure operation of power systems and leads to a requirement of robust and economic generation scheduling. This paper presents an optimal day–ahead wind–thermal generation scheduling method that considers the statistical and predicted features of wind speeds. In this method, the statistical analysis of historical wind data, which represents the local wind regime, is first implemented. Then, according to the statistical results and the predicted wind power, the spinning reserve requirements for the scheduling period are calculated. Based on the calculated spinning reserve requirements, the wind–thermal generation scheduling is finally conducted. To validate the program, a verified study is performed on a test system. Then, numerical studies to demonstrate the effectiveness of the proposed method are conducted. [ABSTRACT FROM AUTHOR]

Integration of large-scale wind power is very challenging for cost-effective and secure operations of power systems. The development of bundled wind–thermal generation and transmission system is viewed as a promising means to cope with the challenges. This paper presents a method to optimize the planning of bundled wind–thermal generation and transmission system. A comprehensive optimization planning model is formulated by taking the unit generation cost as the objective function and using the compensating capacity of thermal generating units and the rated capacity of converter station as the constraints. The proposed model takes into account the fuel cost of thermal generating units, the capital costs and maintenance costs of wind turbine generators, thermal generating units, converter stations, transmission lines, and the losses of the system. The simulated annealing algorithm is used as the solver of the model. Case studies are conducted to demonstrate the effectiveness of this proposed method. [ABSTRACT FROM AUTHOR]

Integration of large-scale wind power creates challenges for power system operations. One of the effective ways of dealing with these challenges is to build thermal power plants to form bundled wind–thermal generation system (BWTGS), i.e., using thermal power to alleviate the fluctuation of wind power. This paper presents a method for optimal capacity and type planning of BWTGS with the given wind farms. Branch-descending technique (BDT) is used to generate candidate schemes of thermal generating units by analyzing the rules of total cost changing with the reduction of the number of thermal generating units. The optimal scheme of BWTGS can be obtained by simulating a long-term operation process of BWTGS and comparing the total costs of all schemes. Techniques to accelerate computation, such as combining redundant states in dynamic programming (DP) algorithm and the saving-branch-cost technique in BDT, are developed to reduce the computational complexity. The major advantage of the proposed method is that it can be used to obtain not only the optimal capacity of thermal generating units, but also the optimal type and number of thermal generating units. Case studies are conducted to demonstrate the effectiveness of this proposed method. [ABSTRACT FROM AUTHOR]

Abstract: All eight stereoisomers of saxagliptin have been synthesized and evaluated for their inhibitory activity against DPP-IV. It was unambiguously confirmed that the configuration of saxagliptin was critical to potent inhibition of DPP-IV. Docking study was performed to elucidate the configuration–activity relationship of saxagliptin stereoisomers. Tyr662 and Tyr470 have been suggested as the key residues of DPP-IV interacting with the inhibitors. This work provides valuable information for further inhibitor design against DPP-IV. [Copyright &y& Elsevier]

The uncertainty in wind power affects the generation scheduling (unit commitment) of coal-dominated power systems. A reasonable spinning reserve is required to handle this uncertainty. In this study, a method that considers the unique local wind regime into the calculation of spinning reserve requirements and makes the unit commitment more local-adaptive is presented. First, a virtual wind power transfer matrix which displays the probabilities of wind power transferring from one value to another by using the historical wind speed data is formulated. Second, the spinning reserve requirements of the wind-thermal power system are calculated according to the virtual wind power transfer matrix. Finally, the day-ahead unit commitment is conducted based on the spinning reserve calculation. The main advantage of using historical virtual wind power data, instead of historical wind speed data, is the acquisition of real wind power transfer probabilities, which avoids the distortion caused by the nonlinear conversion between wind power and wind speed. Application and comparison studies to demonstrate the effectiveness and cost benefits are performed on two systems. Sensitivity analyses of different parameters used in the method are also investigated. [Display omitted] • A modified wind-thermal unit commitment model is proposed. • Wind power transfer matrix is formed to include the local wind characteristics. • Additional spinning reserve is calculated using the wind power transfer matrix. • Comparison study is conducted. • More realistic result with lower operating cost can be obtained. [ABSTRACT FROM AUTHOR]

• A flexibility enhancement pre-selection strategy based on network flexibility balance degree and line outage distribution factor is proposed. • The available flexibility index (AFI) is proposed to quantify the supply of system flexibility. • An optimization model of power system flexibility enhancement method based on pre-selection of structure adjustment strategy is proposed. The flexibility enhancement method of power system usually focuses on node flexible resource, without considering the transmission process. It may result in some flexible resources not being transferred, thus affecting the accuracy and effectiveness of the flexibility enhancement. In this paper, a flexibility enhancement optimization model based on pre-selection method of structure adjustment strategy is proposed, which can improve system flexibility with guaranteed availability of flexible resources. Firstly, the flexibility enhancement pre-selection method based on power system topology adjustment mathematical formulation is proposed to select the lines suitable for topology adjustment. Secondly, a flexibility enhancement optimization model considering economy and available flexibility is developed, which takes the maximum available flexibility index as the objective function and ensures the system flexible and economical by cost-floating constraint. The available flexibility deviation constraint corrects the system flexibility supply to guarantee the accuracy of available flexibility. Finally, the effectiveness of the proposed method is investigated through the case study on modified IEEE 24-bus and IEEE 118-bus system. [ABSTRACT FROM AUTHOR]

Antidiabetic agents simultaneously inhibiting hepatic glucose production and stimulating hepatic glucose consumption could apply a better control over hyperglycemia. A series of oleanolic acid derivatives with bulky substituents at C-3 position were designed and synthesized in order to search for this kind of agents. All of the compounds were evaluated biologically in vitro using glycogen phosphorylase and HepG2 cells. The results indicated that several derivatives exhibited moderate-to-good inhibitory activities against glycogen phosphorylase. Compound 8g showed the best inhibition with an IC50 value of 5.4 μ m. Moreover, most of the derivatives were found to increase the glucose consumption in HepG2 cells in a dose-dependent manner. The possible binding mode of compound 8g with glycogen phosphorylase was also explored by docking study. 8g was found to have hydrogen bonding interactions with Arg193, Arg310, and Arg60 of the allosteric site. [ABSTRACT FROM AUTHOR]

Abstract: To explore the molecular mechanisms of oleanolic acid, two novel photoaffinity probes were synthesized based on the structure–activity relationship reported previously. Their potency were evaluated in an enzyme inhibition assay against rabbit muscle glycogen phosphorylase a (RMGPa), a known target protein of oleanolic acid. The inhibitory activity of probe 2 was only about two-fold less potent than the mother compound oleanolic acid. The photoaffinity labeling experiments were also performed and two proteins were specifically tagged by probe 2. The results suggest that the synthesized probes could be used as powerful tools to isolate and identify the target proteins of oleanolic acid. [Copyright &y& Elsevier]