Phasor measurement unit (PMU) can provide high precision measurements to improve the observability of smart distribution network. Considering the imbalance of supply and demand caused by a large number of buses but limit investment cost, a model of PMUs placement which takes the limited number of PMUs as the constraint is proposed. The objective function maximizes network measurement redundancy while maximizing the number of observable buses. The model considers the influence of various topologies and improves the observability further by taking zero injection bus (ZIB), injection measurement and power flow measurement into consideration. A customized genetic algorithm (CGA) is proposed to solve the model. All individuals become feasible solutions by performing customized crossover and mutation operations. Finally, a method for determining the order of PMUs placement based on the optimal solution is given. The method is tested on IEEE standard bus systems. The results indicate the feasibility and effectiveness of the proposed method.
Energy efficiency investments have become strategically important for the European Union. In particular, energy efficient renovation and investment in its existing building stock have become a major challenge. Creation of a high-performance building should be carried out according to a holistic and integrated design process, which considers all three aspects of sustainability. The aim of this work is to suggest a mathematical model that considers the weight of each sustainability aspect, to support housing owners in decisions regarding the optimal sustainable renovation alternative. Multi-criteria decision making (MCDM) concerns structuring and solving multiple-criteria decision problems. MCDM has become popular in energy planning as it enables the decision maker to give attention to all the criteria available and make the appropriate decision as per the priority of criteria. In this study, an example explains the suggested numerical system for comparing different renovation alternatives. The suggested method will facilitate the decision making process in renovation projects and allows housing owners to choose the best renovation method according to their companies policies and preferences.
With the advancement of market-oriented reform and the development of microgrid technology, the interconnected microgrids will play an important role in industrial parks, development zones and other scenarios. This paper establishes an operating mode structure of interconnected microgrids in the market environment and proposes a two-layer optimal operation strategy for interconnected microgrid. In the lower layer, the interconnected microgrids system aims at minimizing the total purchase cost of the system and optimize the clearing power price and the power allocation of microgrids, considering the voltage and power flow constraints of the system. In the upper layer，the microgrid operators optimize the bidding strategy with maximum profit, consider feedback from inner optimization. The genetic algorithm and mixed integer programming solver of Cplex is used to solve the model. The case study verifies the effectiveness of the proposed method in different scenarios.
In order to satisfy high torque output and high speed driving demand, electric vehicles need a gearbox to adjust the gear ratio. The shift schedule is popular in gear shift research. The most widely used schedule, the two-parameter shift schedule, ignores the influence of dynamic conditions, resulting in that it is hard to suit the road and it causes energy waste. In this paper, a strategy based on model predictive control is proposed. A Recurrent neural network is used to predict velocity sequences in the 5-second horizon. Dynamic programming is adopted to construct a benchmark strategy and also to act as the rolling optimization part of the MPC shift schedule. Simulation results show that this shift strategy can reduce the shift frequency while saving energy consumption.
Recently, metal foam (MF) flow field has exhibited its superiority on mass transfer and potentials on promoting the power density of PEM fuel cells. In this study, the geometry of MF is reconstructed through three-dimensional X-ray computational tomography. The single- and two-phase flow simulations are then carried out. It is found that the pores in MF are relatively inhomogeneous, which has rarely been considered in previous numerical studies. Moreover, the convective flow, water retention and water split up are the unique mass transfer characteristics observed. In addition, the contact angle of MF ligaments shows a dramatic influence on the water management.
The event-driven optimal (EDO) control has recently been proposed for central air-conditioning (AC) systems for operation improvement. In EDO control, optimization actions are driven by pre-defined events. However, there is lack of a systematic approach to defining events in existing studies of EDO control. To address this limitation, this paper proposes a systematic method to define events for the EDO control of AC systems. Events are defined from the perspective of guaranteeing high optimization necessity. The event definition method is illustrated through a case study of an AC system.
The effects of side chain (SC) length of perfluorosulfonic acid (PFSA) polymers on the structure of PEM fuel cell catalyst layer (CL) have been studied using molecular dynamics simulation. Two possible transport paths of reactant molecules towards platinum (Pt) surface are inferred based on the visualization of CL configurations. And the sandwich-like structure of CL is observed. Moreover, the results show that the short PFSA SCs will lead to the high accessibility of sulfonate acid groups, water molecules and hydronium ions to Pt particles, which can improve the transport of protons to Pt particles. Additionally, this paper has also found that PFSA SC length has little effect on the migration of hydronium ions.
This paper presents an experiment study on the composition effect on droplet combustion of ABE mixture fuel. The ratios of ethanol and butanol in ABE are varied. Experimental results show that the micro-explosion characteristics of the two ABE/kerosene droplets are different, which is obviously reflected by (D/D0) 2 curves. Increasing proportion of ethanol will lead to more intense micro-explosion. The process of nucleation in droplets in the early stage of micro-explosion is recorded to investigate the underlying physics. These experimental results show that besides the boiling point difference of ethanol and butanol, ethanol will tend to cause more intense micro-explosion due to insoluble in kerosene than butanol under the same conditions.
The spray characteristics of a fuel injection is highly dependent on the fluid transport properties. Different from gasoline and diesel, some biofuels behave as a non-Newtonian fluid whose viscous properties are a function of shear rate. The spray performance of these fuels still remains unclear, which will further impact the air-fuel mixture and combustion properties. In this paper, direct numerical simulation (DNS) coupled volume of fluids (VOF) method is adopted to investigate the near field spray characteristics of cylinder power-law fuel jets. Liquid jet evolution process which transforms from liquid column to droplet parcels has been detected. The evolution differences which include liquid column shapes, penetration lengths and surface wavelengths have been considered. The breakup differences of the liquid column deformation degrees, ligament types and droplet sizes have been analyzed. Compared to Newtonian and shear-thickening fluids, shear-thinning fuels have a better atomization effect with a smaller droplet size and a larger penetration length.
Based on the dynamic load of the client and the dynamic output power of the generator, this paper establishes the economic efficiency evaluation model of the distributed photovoltaic-energy storage hybrid system (DPV-ES), quantitatively analyzes the system by the carbon trading income, and considers the depreciation tax-deduction benefit and residual net income in the model. In the empirical case, this paper studies the cost, benefit, net present value (NPV), and payback period (PBP), and conducts sensitivity analysis for six types of policy variables. At the same time, the Multi-factors influence on the economic benefits of the system is studied. According to the empirical results, the corresponding policy recommendations are given for users and governments.