互补储能系统的优化建模与控制策略

针对单一蓄电池储能系统功率密度低和超级电容储能系统能量密度低的问题,结合二者的特性,提出一种互补储能控制策略,从而充分发挥它们的优势。最后通过数学建模和仿真,结果表明互补储能系统在抑制可再生能源发电系统功率波动上具有明显的优势。     

考虑超级电容SOC的混合储能系统功率分配策略

为解决超级电容能量密度小、在运行过程中荷电状态(state of charge, SOC)容易越限的问题,对传统低通滤波法进行改进,提出考虑超级电容SOC的功率分配策略。该方法依据超级电容的SOC划分5个不同的工作区域,并以超级电容的SOC作为变量,在不同工作区域同滤波时间常数建立相应的函数关系,之后根据SOC的变化动态调整滤波时间常数,实现蓄电池和超级电容之间功率的合理分配,保证超级电容SOC维持在合理范围内。最后,在Matlab/Simulink中搭建相关模型并仿真验证所提方案的正确性和有效性。仿真结果表明,同传统低通滤波法相比,该方法可在平抑功率波动的同时,根据超级电容的SOC合理分配超级电容和蓄电池的功率需求,使超级电容的SOC自行恢复,防止其过充过放,提高了直流微电网系统运行的经济性和稳定性。     

双源纯电动汽车能量管理策略研究

针对双源纯电动汽车运行中超级电容与蓄电池联合供电的能量分配问题,本文引入基于模糊控制的能量管理策略。通过将整车需求功率、蓄电池及超级电容SOC(荷电状态,State of Charge)作为模糊控制器的输入,蓄电池功率分配系数作为输出,对能量控制系统进行建模仿真。通过Simulink的仿真结果表明,该模糊控制器能够较好地分配能量,满足实车运行中的功率需求,减少大电流对蓄电池的冲击,提高蓄电池的循环利用次数,有利于汽车长时间稳定运行。     

双向LLC谐振型直流变换器设计与控制

针对直流配电网中连接超级电容的LLC谐振直流变换器,利用双向LLC直流变换器电压稳态增益,设计变换器谐振回路的参数。运用等效电路模型法对双向LLC直流变换器进行小信号建模,分析设计变换器的闭环PI控制器,据此控制超级电容的充放电功率,维持系统母线电压稳定。最后,对所设计的LLC直流变换器在Matlab/Simulink里进行仿真分析,并通过实验样机进行实验验证,通过仿真和实验结果证实了该文所采用的理论分析与设计方法的正确性和可靠性。     

基于超级电容储能的可变速驱动抵御扰动研究

提出基于超级电容储能的变频调速装置（ASD）抵御电网电能质量扰动的实用方案。超级电容模块接在直流母线上，在系统发生短时供电中断或电压暂降时，由超级电容储能供给负载有功支持。研制了具有抵御电能质量扰动的15kVA ASD实验室样机。数字仿真及物理实验验证了所提拓扑结构和控制策略消除电能质量扰动对ASD影响的正确性及有效性。     

超级电容储能的高性能集成三端口变换器设计及仿真模拟

作为当今主要的电化学储能元件之一,超级电容因其功率密度高、工作条件限制少等优点具有广阔的发展前景.为了更好地发挥超级电容的优越特性、降低系统的成本,本工作提出一种适用于超级电容储能的集成三端口变换器.超级电容储能端口通过双向Cuk变换器与输入端口连接,既能满足超级电容宽电压工作特性带来的升降压要求,还能获得连续、纹波小...     

光伏直流微电网超级电容储能控制策略研究

光伏直流微电网有离网和并网两种工作模式。离网模式下,由于负荷及分布式电源功率变化,导致母线电压波动;并网模式下,微电网输入功率变动以及非线性负载产生的低次谐波会使并网电流脉动,影响电能质量。文章提出了基于超级电容的储能控制方案,利用超级电容的快速充放电特性,离网运行时在传统双闭环控制方案中加入电压的功率微分控制,稳定直流母线电压的波动;并网模式时提出一种并网电流脉动补偿控制方案,降低并网电流的脉动,提高电能质量。最后,仿真建模验证了所提控制方案能有效解决直流母线电压波动及并网电流脉动的问题。     

基于SOC的混合储能风电功率平抑方法

近年来风电等可再生能源的装机容量越来越大,鉴于风电的输出功率随机性特别强且波动性十分大,在混合储能风电平抑系统的基础上引进滞环控制,提出了一种基于超级电容端电压的能量管理方法。该方法通过在低通滤波算法中引进滞环控制,可将风电功率的波动幅度严格控制在滞环宽度之内;同时根据监控超级电容端电压判断电池的荷电状态(SOC),防止超级电容频繁过度地充电和放电,有利于延长储能装置的工作寿命,最后通过仿真试验,验证了该方法的有效性。     

基于稳态功率修正的混合储能新型控制策略研究

超级电容在响应系统功率波动时,荷电状态与额定值相比会产生一定偏移。针对该问题,文章在直流母线电压变化率进入稳定状态后,提出了在蓄电池电流内环增加与超级电容实际荷电状态有关的扰动项,改变蓄电池及超级电容的参考电流,实现稳态下蓄电池对超级电容的功率修正,最终使超级电容的荷电状态自动恢复至额定值。将所提的基于稳态功率修正的混合储能控制策略应用于直流微网并进行仿真,结果表明,该策略能够增强混合储能可靠性,减少超级电容配置容量,提高微网的稳定性和经济性。     

基于半桥变换器与次序耦合变压器的超级电容均压

针对于超级电容串联储能系统中单体电压不均衡的问题,本文介绍了一种基于半桥变换器和首尾次序耦合变压器的均压电路。利用次序耦合绕组可以减小因变压器单元漏感误差而引起的超级电容单体电压不均衡。该电路结构简单,还可以均衡超级电容器的电压,恒定开关频率和占空比,不需要反馈控制环节。通过分析半桥变换器每个工作模态,建立了输出电压方程,推导了串联超级电容电压均衡方程。根据电路特性,分析了变压器匝比设计方程及实现软开关变压器原边漏感要求。仿真及实验结果表明此均压电路具有均压速度快且均压效果好的特点。     

Improved dynamic performance of hybrid PEM fuel cells and ultracapacitors for portable applications

Transient power demand fluctuations and maintaining high energy density are important for many portable devices. Small fuel cells are potentially good candidates as alternative energy sources for portable applications. Hybrid power sources have some inherent properties which may be effectively utilized to improve the efficiency and dynamic response of the system. In this paper, an improved dynamic model considering the characteristics of the temperature and equivalent internal resistance is presented for proton exchange membrane (PEM) fuel cells. The dynamic behavior of a system with hybrid PEM fuel cells and an ultracapacitor bank is simulated. The hybrid PEM fuel cell/ultracapacitor bank system is used for powering a portable device (such as a laptop computer). The power requirement of a laptop computer varies significantly under different operation conditions. The analytical models of the hybrid system with PEM fuel cells and an ultracapacitor bank are designed and simulated by developing a detailed simulation software using Matlab, Simulink and SimPowerSystems Blockset for portable applications.     

Optimal battery/ultracapacitor storage combination

A simple, global model for the optimal combination of ultracapacitor and battery for electrical energy storage is developed. The goal for this hybrid storage technology is to reduce the system life-cycle cost by making use of an ultracapacitor’s claimed long cycling-life in order to supplement relatively cheap, but cycle-limited battery storage. The model is built up of two independent sub-models that allow flexibility in the relative proportion of system energy storage. An analysis performed in this paper indicates that ultracapacitor/battery storage systems may be cost effective for high-cycle applications.     

Multiple model predictive control for a hybrid proton exchange membrane fuel cell system

This paper presents a hierarchical predictive control strategy to optimize both power utilization and oxygen control simultaneously for a hybrid proton exchange membrane fuel cell/ultracapacitor system. The control employs fuzzy clustering-based modeling, constrained model predictive control, and adaptive switching among multiple models. The strategy has three major advantages. First, by employing multiple piecewise linear models of the nonlinear system, we are able to use linear models in the model predictive control, which significantly simplifies implementation and can handle multiple constraints. Second, the control algorithm is able to perform global optimization for both the power allocation and oxygen control. As a result, we can achieve the optimization from the entire system viewpoint, and a good tradeoff between transient performance of the fuel cell and the ultracapacitor can be obtained. Third, models of the hybrid system are identified using real-world data from the hybrid fuel cell system, and models are updated online. Therefore, the modeling mismatch is minimized and high control accuracy is achieved. Study results demonstrate that the control strategy is able to appropriately split power between fuel cell and ultracapacitor, avoid oxygen starvation, and so enhance the transient performance and extend the operating life of the hybrid system.     

Modelling of the thermal behaviour of an ultracapacitor for a 42-V automotive electrical system

A three-dimensional modelling approach is used to study the effects of operating and ambient conditions on the thermal behaviour of a NESSCAP 2.7 V/3500 F ultracapacitor cell for a 42-V automotive electrical system. The rate of heat generation of the ultracapacitor during charge and discharge is measured with a calorimeter. The transient temperature distribution of the ultracapacitor during cycling is obtained by using the finite element method with an implicit predictor-multicorrector algorithm. The results show that the temperature of the ultracapacitor cell increases during the first 50 cycles after which it reaches a periodic steady-state value that increases with increasing ambient temperature.     

An ultracapacitor circuit for reducing sulfation in lead acid batteries for Mild Hybrid Electric Vehicles

The nickel metal hydride (NiMH) batteries used in most hybrid electric vehicles (HEVs) provide satisfactory performance, but are quite expensive. In spite of their lower energy density, lead acid batteries would be much more economical except they are prone to sulfation in HEV applications. However, sulfation can be greatly reduced by a circuit that uses an ultracapacitor in conjunction with the battery. The resulting system will provide much cheaper energy storage if ultracapacitor prices can be reduced to levels predicted by some manufacturers.     

Development of integrated fuel cell hybrid power source for electric forklift

A hybrid drivetrain comprising a 16 kW polymer electrolyte membrane fuel cell system, ultracapacitor modules and a lead-acid battery was constructed and experimentally tested in a real counterweight forklift application. A scaled-down version of the hybrid system was assembled and tested in a controlled laboratory environment using a controllable resistive load. The control loops were operating in an in-house developed embedded system. The software is designed for building generic control applications, and the source code has been released as open source and made available on the internet. The hybrid drivetrain supplied the required 50 kW peak power in a typical forklift work cycle consisting of both loaded and unloaded driving, and lifting of a 2.4 tonne load. Load variations seen by the fuel cell were a fraction of the total current drawn by the forklift, with the average fuel cell power being 55% of nominal rating. A simple fuel cell hybrid model was also developed to further study the effects of energy storage dimensioning. Simulation results indicate that while a battery alone significantly reduces the load variations of the fuel cell, an ultracapacitor reduces them even further. Furthermore, a relatively small ultracapacitor is enough to achieve most of the potential benefit.     

Load-Following Strategies for Evolution of Solid Oxide Fuel Cells Into Model Citizens of the Grid

Proper converter design can allow solid oxide fuel cells operated as distributed generators to mutually benefit both the load and the electric utility during steady-state conditions, but dynamic load variations still present challenges. Unlike standard synchronous generators, fuel cells lack rotating inertia and their output power ramp rate is limited by design. Two strategies are herein investigated to mitigate the impact of a large load perturbation on the electric utility grid: 1) external use of ultracapacitor electrical storage connected through a dc–dc converter and 2) internal reduction of steady-state fuel utilization in the fuel cell to enable faster response to output power perturbations. Both strategies successfully eliminate the impact of a load perturbation on the utility grid. The external ultracapacitor strategy requires more capital investment while the internal fuel utilization strategy requires higher fuel use. This success implies that there is substantial flexibility for designing load-following fuel cell systems that are model citizens.      

Dynamic performance of an in-rack proton exchange membrane fuel cell battery system to power servers

To improve the reliability and the energy efficiency of data centers, as well as to reduce infrastructure costs and environmental impacts, we experimentally evaluated in-rack powering of servers with a hybrid 12 kW Proton Exchange Membrane Fuel Cell (PEMFC) and battery system. The steady state and the transient performance of the PEMFC and battery in response to dynamic AC loads and real server loads have been evaluated and characterized. The PEMFC system responds quickly and reproducibly to load changes directly from the server rack. Peak efficiency of 55.2% in a single server rack can be achieved. The effect of fuel cell coolant temperature on the hybrid system transient behavior is also captured and evaluated. The observed PEMFC transient responses obtained from the experiments were used to design the size of the energy storage component for the hybrid system. Simulations and analysis of various types of energy storage devices for the hybrid system were carried out. To provide power to meet the most significant transient demand, energy storage capacity greater than 0.3 kWh is required for all battery types, while only 0.053 kWh capacity is required for the ultracapacitor. During charging, the ultracapacitor uses the shortest amount of time to recover to the original SOC, while the charging duration for the lead acid battery is twice as long as that of the ultracapacitor.     

Portable PEM fuel cell‐ultracapacitor system: Model and experimental verification

This paper presents a comparative study between a model of portable direct hydrogen‐fed proton exchange membrane fuel cell‐ultracapacitor (PEMFC‐UC) power source and experimental results obtained from an actual PEMFC‐UC system in the authors' laboratory. In the proposed system the UC is directly connected to the PEMFC output terminals. The UC is used to supply the power mismatch during the sudden load variations when the load is higher than the PEMFC maximum capacity. The model is then used to estimate the output voltage and study the transient response of the PEMFC‐UC system when subjected to rapid changes in the load. To validate the model, laboratory experiments are carried out using a 100 W commercially available PEMFC and an UC. The model results are verified against the experimental data using three statistical indices to measure the variations, unbiasedness, and accuracy. The indices indicate a maximum difference of 1.06%, which shows a close agreement between the voltage and power responses of the proposed model and the actual PEMFC‐UC system. Copyright © 2009 John Wiley & Sons, Ltd.     

Analysis of generalized parallel-series ultracapacitor shift circuits for energy storage systems

Ultracapacitors have numerous advantages including a remarkably high energy density as compared to conventional capacitors, long life cycle, temperature stability, and require no maintenance, which make them a good candidate to replace batteries as energy storage devices in renewable energy applications. However, ultracapacitors, just like conventional capacitors, inevitably suffer from constant voltage drop during discharging, which may limit their energy utilization, increase the voltage ripple of the DC bus across which the capacitors are connected and consequently increase the VA stresses of the subsequent converter stage. To alleviate the above limitations, parallel-series ultracapacitor shift circuits are employed to improve the energy utilization and minimize the DC bus voltage ripple. Two generalized parallel-series ultracapacitor shift circuits are presented and analyzed, and some design considerations and optimization methods are discussed.