Abstract

In this paper, an active support control strategy based on the third-order model of synchronous generator is proposed for battery energy storage system in renewable energy systems. The control strategy converts grid-connected inverters of energy storage system into synchronous voltage sources with excitation and speed control systems, which provides necessary inertia and damping characteristics for grid-connected renewable energy sources. The difference coefficient σbattery% of the BESS is defined by the power-frequency proportional coefficient Km and the damping coefficient D. By setting the difference coefficient σbattery%, it is possible to control the frequency modulation depth of the BESS to participate in the primary frequency response of renewable power generation system. The output power for primary frequency response of the synchronous generator is reduced, and the steady frequency deviation of the system after primary frequency modulation can be reduced. Therefore, the frequency stability of the renewable energy systems for power generation are improved.

Abstract

The relationship between air temperature and energy consumption at the city level has been investigated to better understand the impact of the climate change on energy demands. Temperature rising caused by the climate change has been shown to lead to the increase of building energy demands. Buildings also contribute to climate change by radiating heat from building surfaces. In this respect, this study aims to evaluate the potential impact of building rooftop and façade surface temperatures on household energy consumption. We developed a method that combines multiple scale observations, including an Internet of things (IoT) sensor network and remote sensing, to estimate the relationship between surface temperatures and energy consumption. The results will contribute to managing building energy uses based on the better understanding of micro-scale temperature effects in urban area.

Abstract

A computational fluid dynamic (CFD) model has been developed for the fuel reactor of a chemical looping gasification (CLG) system with biomass as fuel and natural hematite as oxygen carrier (OC). By coupling the fluid dynamics and the chemical kinetics, the multiphase continuum model is able to describe the motion of gas and solid phases and the heterogeneous reactions between them, which take place in a bubbling fluidized bed reactor. The simulated average concentrations of five gas species fit the experimental data provided in the literature quite well, with a deviation for each gas component lower than 2%. This verified model is then applied to investigate the effects of various gasifying agents on the compositions of syngas. The results show that the biomass CLG performance is significantly improved in the presence of CO2/H2O and their mixture. Furthermore, synergistic effect of CO2/H2O mixture can be observed based on the evolution of char mass within the reactor.

Abstract

In smart grid, smart meter (SM) samples the energy consumption of users at high frequency. By analyzing measurement data, users’ behavior patterns can be identified, which threatens consumers’ privacy. This paper studies the protection of SM privacy by solar power generation system and rechargeable battery (RB). Solar energy provides alternative power other than power grids for users. RB provides energy storage. Under the constraints of RB physical conditions and solar radiation, a “privacy-cost dual optimization model” is proposed to minimize the weighted sum of privacy leakage and power consumption costs. In order to solve the optimization problem, we propose a new optimization algorithm. The simulation results show the effectiveness of the algorithm. The effects of different target curves on privacy protection are studied.

Abstract

An oval-tube structure is used as the new generation aero-engine recuperator, which has a wide range of application prospects in aerospace, marine and other important industrial fields. The heat transfer performance of this structure directly determines the energy efficiency of the aero engine. However, the enhanced heat transfer mechanism of oval-tube recuperator is not clear due to the lack of internal flow field information. Based on the standard k-ε model, shell-side heat transfer and resistance performance are conducted by using commercial CFD software FLUENT. The influences of structural parameters and tube arrangement on heat transfer and resistance performance are further studied. Then the mechanism on heat transfer augmentation is discussed according to the fluid flow characteristics and the field coordination principle. The results show that the standard k-ε and periodicity model is feasible and accurate to simulate the fluid flow on shell side of oval-tube recuperator. The heat transfer and resistance performance increase with the ratio of major and minor axes and longitudinal spacing of oval-tube. With the increase of horizontal and longitudinal spacing of oval-tube, the performance increases at first and then decreases. The maximum velocity appears at the minor axis, and the minimum value of fluid temperature, velocity and pressure appears at the major axis. The amplitude of field synergy angle is small in the inlet section, but the fluctuation amplitude in the recuperator is large.

Abstract

To minimize the impacts of climate change, it is increasingly clear that global CO2 emissions should be eliminated by 2050 (IPCC, 2018) and that advanced cities for carbon neutrality should have net zero emissions by 2040. However, the precise pathways by which they can reach such ambitious goals, have not been identified. As the costs of photovoltaics (PV), batteries, and electric vehicles (EV2) likely keep falling, they will play key roles for deep decarbonization. Here, we conduct a technoeconomic analysis of a city-scale energy system with PV, batteries, and EVs for the city of Kyoto, Japan. We find that aggressive EV adoption could help PV penetration in the city with substantially lower costs than just deploying PV and batteries alone. CO2 emissions from vehicle and electricity usages from the city could be reduced by 70- 80% in 2030 if 60% of current cars are replaced by EVs, at the same time reducing the costs by 40-50%.

Abstract

Due to the integration of distributed photovoltaic (PV) and access of electronic devices, power systems are suffering from serious voltage problems, and therefore they require greater flexibility. By using appropriate methods, a PV cluster can autonomously regulate reactive power output in a distributed manner to improve voltage profile. In this paper, a distributed Newton-based reactive power control method to realize distributed voltage control for high penetration of PV generation is introduced, which can fast respond to voltage mismatch and address the robustness issues of (de-)centralized approaches against communication delay and noises. The proposed distributed control scheme for PV clusters can coordinate PV to provide voltage regulation in a more efficient, reliable and flexible way than existing decentralized methods.

Abstract

In this paper, liquid-separation is attempted to plate condenser to improve the condensation of plate heat exchangers. Liquid-separation plate condenser (LPC) with two paths, three paths and four paths are proposed. The model exhibits good accuracy in predicting heat transfer coefficients (HTC). LPCs show superior performance to conventional plate condenser (CPC). There exists optimum configuration for each LPC, and they are selected for further study. It is found that the more paths LPC has, the higher HTC and heat load (Q) it would be. LPC with three paths and path length ratio (PLR) of 4:3:3 is recommended.

Abstract

The safety issues of lithium-ion batteries, i.e. thermal runaway, have attracted abroad attention and become more critical with the increase of battery energy density. In this study, the thermal runaway behaviors of high-energy-density lithium-ion batteries with nickel-rich cathode are investigated considering the effects of cathode morphology and state of health. The results show that the safety behaviors of batteries with single crystal cathode is almost same as that with the poly crystal cathode. However, after cycling, the battery with single crystal showed worsen thermal stability after cycling at 45oC, as the onset temperature of thermal runaway decrease, while the battery with poly crystal cathode exhibited opposite changes.

Abstract

The deep borehole heat exchanges (DBHEs) use a coaxial tube to obtain deep geothermal energy, avoiding the problem of groundwater corrosion and recharge, which have great application value. In this paper, a heat transfer model of a DBHE with a depth of 2000m and an outer diameter of 177.8mm is established by Fluent. The effects of various inlet temperature (5~20℃), inlet velocity (0.5~1m/s), thermal conductivity of rock (2.5~3.5W/(m·℃)) and geothermal gradient (0.035~0.045℃/m) on the heat transfer performance in a heating season are studied. The results show that the heat transfer performance of DBHEs decays with time. The rock temperature field is basically invariant outside the radius of 15m. Decreasing the inlet temperature, increasing the inlet velocity, increasing the thermal conductivity of the rock, and increasing the geothermal gradient can increase the heat extraction rate of DBHEs. Under the condition of constant geometric parameters, for every increase of 0.005℃/m in geothermal gradient, the heat extraction rate of the DBHE studied increases by an average of 22.76kW, and for every increase of 0.5W/(m·℃) in the thermal conductivity of the rock, it increases by an average of 26.44kW.