A New Topology Pattern for AC-DC Mixed Microgrid

In order to realize the modular design of the microgrid, this paper proposed a new modular topology for the AC-DC mixed microgrid. In that topology, the AC microgrid unit and the DC microgrid unit were packaged together by the back-to-back converter. The battery-supercapacitor hybrid energy storage system was connected to the DC bus of back-to-back converter. By the reasonable design on the battery-supercapacitor hybrid system, the energy storage system could supply the rapid power and energy support for the microgrid spontaneously. The mathematical model and the control algorithm of that microgrid topology were studied. By the simulation analysis, it can be concluded that AC-DC mixed modular microgrid topology could operate steadily on both the grid-connected mode and the isolated mode. Furthermore, we can conclude by the simulation that the designed modular microgrid could operate uninterrupted when the microgrid topology switched from the grid-connected mode to the isolated mode. The seamless switching became the natural property for the modular microgrid. As a result, the modular microgrid topology can be considered as a usual power/load module to realize the friendly power interaction with the power grid.

Field Investigation and Comparison Analysis of Low-Grade Heat Pump Technologies in Building Space Heating Projects

The building sector contributes a large ratio of final energy consumption,and improving building energy efficiency is expected to play a significant role in mitigating its carbon dioxide emission.Herein,we collected the on-site measurement data to investigate the techno-economic performances of different heat pump types that exist in building space heating projects in Qingdao,China.An in-depth analysis revealed the temperature variations of measured low-grade heat sources over the whole heating supply period,and urban sewage water shows high stable heat energy quality compared with seawater and geothermal heat resources.Operational behaviors including cycling inlet and outlet temperature of the selected heat pumps were illustrated,and analysis evaluated detailed effects of operational parameters on energy efficiency performances.Then the relationship between COPs distributions of heat pumps and operational conditions was examined further,and the positive effect of the rising temperature of heat sources on energy efficiency improvement of heat pump is highlighted when the heating supply temperature is higher.Furthermore,we analyzed the economic and carbon emission performance of the heat pump system,and results show that electricity price plays a vital role in the lifespan energy cost saving potential,and the heat pump could serve as a promising approach in reducing CO_(2) related to the building space heating.Finally,we recommended suggestions for improving the overall energy efficiency and cost competitiveness of decentralized heat pump systems for building space heating.

Modeling and SOC estimation of lithium iron phosphate battery considering capacity loss

Modeling and state of charge(SOC)estimation of Lithium cells are crucial techniques of the lithium battery management system.The modeling is extremely complicated as the operating status of lithium battery is affected by temperature,current,cycle number,discharge depth and other factors.This paper studies the modeling of lithium iron phosphate battery based on the Thevenin’s equivalent circuit and a method to identify the open circuit voltage,resistance and capacitance in the model is proposed.To improve the accuracy of the lithium battery model,a capacity estimation algorithm considering the capacity loss during the battery’s life cycle.In addition,this paper solves the SOC estimation issue of the lithium battery caused by the uncertain noise using the extended Kalman filtering(EKF)algorithm.A simulation model of actual lithium batteries is designed in Matlab/Simulink and the simulation results verify the accuracy of the model under different operating modes.