Research On Energy Storage Subsystem Applied For Distributed Energy System

Along with the sustained, rapid and steady development of national economy, energy consumption in China also increases significantly. Recently, traditional extensive economic development mode is facing bottleneck problems about energy consumption, in details, i.e., low energy use efficiency, overmany pollutant emissions and greenhouse gases emissions, unreasonable energy structure, etc. Therefore, the government has proposed comprehensive energy policies, the basic contents of which are "giving priority to conservation, relying on domestic resources, encouraging diverse development, protecting the environment, promoting scientific and technologic innovation, deepening reform, expanding international cooperation, and improving the people’s livelihood". Actually, as one of the advanced energy supply systems, distributed energy supply system (DESS) is one of the available solutions to the abovementioned problems, as well as, is the critical reinforcement of the large-scale one because of its graded use of energy. Additionally, energy storage subsystem (ESS) is the key part as the load balance equipment and backup power resource. Also, ESS is necessary for the safety and reliability of DESS operation. Hence, more research on those related technologies will be crucial for maintaining national core competitiveness, improvement of energy utilization efficiency, and the reformation of energy structure.Energy storage technology (EES) is introduced in building distributed energy system (BDES) as a key part of distributed energy system. EES should be a resolution of the problems such as electricity generation instability, high system failure rate. The detailed contents are as follows:(1) Research based on the electricity load data of some office building, back propagation (BP) artificial neural networks (ANN) and energy storage size computation model show that:ANN can work efficiently for the case of DESS with EES, in another word,87.5%of predicted load data is within the acceptable relative error; electricity demand and ESS size can be determined based the ESS size determination model with the given peak load shifting and ESS technology characters. They are of certain directive significance to rational size determination and investment of DESS.(2)Simulation modeling by Matlab-Simulink is on the basis of system mathematical modeling of each part of HAES, as well as the theory analysis of PID control, conventional fuzzy control, and variable-universe fuzzy control. With the need of constant power output, simulation results in terms of the control characters reveal that variable-universe fuzzy control with smaller over shoot and shorter adjusting time is obviously better than PID control.(3)According to the different cases for the pressure from9MPa to18MPa and the hydraulic motor/pump rotation speed beween100revolutions per minute (r/min) and800r/min after the Hydraulic-air energy storage (HAES) experiment test platform is built, the results show that the system cycle efficiency gets the best when the discharge speed is400r/min and100r/min for the charging. When the speeds for charging and discharging are100r/min and200r/min, respectively, the HAES system cycle efficiency increases with the pressure additions for the pressure from9MPa to12MPa; and the one fluctuates between50.72%and48.98%for the pressure from12MPa to18MPa; also, volumetric efficiency varying with hydraulic motor/pump speed and the accumulator pressure is the key factor of HAES system cycle efficiency.(4)Based on the economic and social benefits analysis model, the analysis results for HAES illustrate that the critical cost per kW or kWh are of important directive significance to rational HAES investment, and it is done through the critical cost computation along with the critical economic indexes considering the factors of different subsidization rates of grid assistant service and initial investment, different peak load shifting, and current or future economic conditions; the quantitative analysis of the energy saving and gas emission reductions benefits show the underlying benefits in environment protection of HAES, and it can be a reference method for other cases studying in energy saving and gas emission reductions.