| The renewable energy has got a significant attention and considerable development,because of the increasing depletion of conventional energy and aggravated environment pollution.Wind energy is currently considered as the largest scale commercial development potential renewable energy,which is non-hydro energy resource,but its inherent unsteady characteristics,which are discontinuity,instability,and uncontrollability,have led the wind power difficult to predict,schedule,and control,severely restricting the large-scale development of the wind power and utilization of the wind.Energy storage technology can realize the space-time translation,which is an effective means to stabilize wind power fluctuations and improve the power quality.Compressed air energy storage is a novel energy storage technology in recent years,which has attracted extensive attention because of its longer lifecycle,larger capacity lower cost and less contaminating to environment.However,compared to batteries and other energy storage technologies,the cycle efficiency of compressed air storage is still low,and market share in the energy storage has been not high.The essential reasons:on the one hand,due to its complex structure and energy conversion mechanism of compressed air energy storage,which has caused a variety of laws coexist and interact,it is leading to its analysis and modeling difficulties in its precise control and optimization;on the other hand,the compressed air energy storage is different from batteries and other traditional energy storage,its storage efficiency is dramatically affected by operating conditions,while the current energy management strategies of energy storage system are lack of considerations about the inherent characteristics of the energy storage system,leading to operate in the inefficient zone for a long time,and reducing the cost effective of compressed air energy storage.In response to resolve these problems,this paper has proposed efficiency optimization of the compressed air energy storage system,and cooperative control and energy optimization respectively of the compressed air storage system integrating into the wind power system to carry out theory analysis and critical technology research.The main contents and innovations are as follows:(1)The energy conversion mechanism is complex in the compressed air energy storage system,meanwhile,the many a device parameters and some varying and unmeasurable parameters are in the compression\expansion device,moreover,it is difficult to model and modeling accuracy is not high,as a result it is difficult to optimize its precise control.This paper adopts a hybrid modeling method based on the mechanism analysis and data-driven binding to analyze and determine the relationship between input and output parameters,according to the energy conservation and mass conversation,then to establish differential equations.Then it has choose parameters,such as intake pressure,temperature,and rotate speed as input parameters,which are easy to measure and control,and the exhaust flow,exhaust temperature and the torque are taken as output parameters.Finally,it builds the mathematical model according to the measured experimental data,which is utilized to identify and estimate the coefficients in the differential equation.This technique not only reserves the system internal mechanism instinct,but it selects observation and control system variables to simplify the model,which greatly reduces the complexity of the system model.The comparison between model calculations and experimental results has illustrated that the flow,torque,exhaust gas temperature of hybrid model are consistent with the experimental results in the normal operating range of compressed air energy storage system,whose error is less than 10%,indicating that the proposed hybrid modeling can ensure the model accuracy taking into account the usefulness of model engineering controls.(2)At present,the research rarely involves in the compressed air energy system efficiency in variable conditions,however,the efficiency is closely related to its operation conditions.Especially for the micro compressed air storage system,it is often utilized in distributed energy supply system to stabilize power fluctuations,whose input power and output power fluctuate widely as the outside world parameters(such as wind,light output power and load demands,etc.)vary,it takes a long time to operate away from the rated design conditions.This paper realizes the quantitative test of leakage,friction,heat and other factors during the compression or expansion process,which has an impact on the efficiency,analyses its internal coupling relationship with the operating conditions(input and output power,speed,etc.)of the energy storage system.On this basis,it proposes perturb and observer maximum efficiency control strategy of the compressed air storage system,combining with the model calculation.Experimental results has illustrated that proposed control strategies can realize that compressed air energy storage system is always maintained at maximum efficiency point in the whole operation rang,effectively improving efficiency and adaptability of compressed air energy storage system in complex and changeful conditions,which is the foundation of the structure optimization of compressed air energy storage system and energy optimization of wind power system integrating with compressed air energy storage system.(3)As to the short battery life and secondary pollution of the small off-grid wind power generation energy storage system,this paper adopts hybrid energy storage off-grid wind power generation system integrating compressed air energy storage with a bit batteries.Taking into account of the operation characteristics of compressed air energy storage systems and energy fluctuations of the wind power system,it has proposed energy storage control strategies,which are to resolve the slow dynamic response of compressed air energy storage system and discharge loss increase caused by the frequently high-power discharge of batteries,based on the short-term loading forecasting to overcome the slow response of compressed sir energy storage system,improving the system stability and battery life-cycle.As the compressed air energy storage efficiency changing with the operation conditions,this paper has integrated the compressed air energy storage efficiency and battery life-cycle into the energy optimization objectives of wind power system,and proposed multi-objective energy optimization strategies considering compressed air energy storage efficiency and battery life-cycle.By coordinating compressed air energy storage and battery output,it can avoid the compressed air energy storage system working in inefficient area.(4)As fluctuations in wind power have obvious multi-time scale characteristics,the single compressed air energy system is difficult to meet its requirements.In this paper,it has established multi-compound composite energy storage system including compressed air energy storage,batteries and super capacitor based on the magnitude-frequency characteristics analysis of wind power system.The hybrid system makes full use of the large capacity and low cost of compressed air energy storage,the high energy density of batteries,and high power density of capacitors,as a result,the simulation results has shown that the hybrid system has a significant cost advantage.This paper has proposed full life-cycle cost conversion method of the energy storage system,which sets up the unified evaluation criteria of the energy storage cost,life-cycle and maintenance,providing an objective evaluation standard for the capacity disposition of the composite energy storage system.It also has proposed a multi-time scale energy management strategy of the composite energy storage system based on empirical mode decomposition,which realizes the transformation of the composite energy storage power disposition from "qualitative" to "quantitative",according to the time scales of the wind power fluctuations to allocate power for different equipment.The simulation example reveals that,compared to traditional energy management strategy based on the filtering method,the proposed method effectively avoids the impact on the smoothing effect and storage capacity disposition because of the time constants of filters,founding a theoretical basis for energy distribution among different storage media.(5)Finally,this paper has designed and built the experimental platform of the compressed air energy storage wind power system based on the scroll machine to verify the proposed control strategies.By comparing power changes of the composite energy storage device using power load forecasting or not,it verifies that the proposed energy management strategies based on load forecasting can schedule the output of the compressed air energy storage in advance,reducing the power fluctuation of batteries.The multi-objective optimization scheduling experiment of the composite energy storage system has shown that the compressed air energy storage are higher than 40%throughout the experiment range,to verify the effectiveness of the energy management strategies.The experimental results of the composite energy storage system proposed,in this paper,illustrate that energy storage cost is only 47%of the traditional battery energy storage system herein the same operation condition,which has obvious advantages.In this paper,experimental achievements not only have verified the effectiveness of the proposed control strategies,while also have accumulated technical experience for promoting the engineering application of the compressed air energy storage system. |
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