A high-flexibility DC load for fuel cell and solar arrays power sources based on DC–DC converters

In this paper, a flexible DC load to test and evaluate current–voltage characteristics of fuel cells stacks and photovoltaic modules based on DC–DC converters is proposed. The load features are simple structure, scalability, low cost, and its possibility to emulate an arbitrary load profile. The measure of the desired characteristics of fuel cells and photovoltaic modules further includes high speed of response and high fidelity. A comparison between conventional methods and the proposed one is also provided. Experimental results show the usefulness of the DC load proposed.     

Nonlinear stability analysis and a new design methodology for a PEM fuel cell fed DC–DC boost converter

The dynamical behaviour of a fuel cell feeding a boost converter is studied in this paper. A nonlinear model of the combined system is derived including the effect of the switching action of the converter. Using Filippov's theory, it is possible to analytically study the bifurcation patterns of the system and to demonstrate that the system loses stability through a period doubling bifurcation. To overcome this instability, we inject a high frequency sinusoidal signal into the system that forces the system to remain stable while at the same time retaining its basic slow scale properties (like the steady state error). This controller is simple to implement and does not require any special hardware. The stability analysis and new controller design method presented in this paper allow for the re-design of the converter to stabilize circuit operation with a substantially reduced inductor size, reducing the size and cost of the converter while maintaining its average currents and voltages and other circuit steady-state behaviour characteristics. The results are confirmed by using numerical and analytical tools.     

太阳能发电系统的DC／DC电路单元

描述了太阳能发电系统ＤＣ／ＤＣ电路单元主回路的线路结构,并简述了驱动电路的控制原理。     

光伏发电系统的新型DC/DC变换器设计

针对传统全桥DC/DC变换器存在的硬开关损耗和因开关管开关特性不一致使变压器原边磁芯单向饱和问题,设计了一种用于光伏发电系统中的移相ZVS全桥DC/DC变换器,控制电路采用基于芯片UC3875的双环反馈方案,驱动电路由专用驱动集成芯片IR2110S构成.不仅实现了开关管的软开关控制、降低开关损耗、提高系统效率,还可解决偏磁问题,使变压器的磁通密度工作接近于饱和点.实验样机的研制验证了设计的可靠性.     

Comparison of solar hydrogen storage systems with and without power-electronic DC–DC-converters

For long-time-storage problems of electrical energy, hydrogen-storage-systems have some significant advantages. In photovoltaic systems, especially in island-applications, they can help to solve the seasonal storage problem with solar energy and a not correlated energy demand. In summer the surplus of photovoltaic energy is used to produce hydrogen-gas by water electrolysis. In winter the hydrogen is converted back to electricity with a fuel-cell at high efficiency. This usually needs extensive system technology and therefore it is only useful for complex photovoltaic systems.One problem in such hydrogen plants is efficiency and cost of the power electronic devices. Therefore, there exist some ideas and concepts in order to eliminate most of the converter-technology by a direct coupling of the electrochemical devices on the same DC-bus-bar without equalising the different operating-points by converters. The train of thought are backed up by simulations especially with regards to efficiency and the results which are shown seem to be a glimmer of hope. But what about the costs and the possibility for realisation in real hydrogen plants? The aim of this paper is to consider the mentioned aspects by surveying especially those hydrogen plants, which, from our point of view, may become technological maturity at first. The results of these investigations are then corroborated through a data analysis of the existing power-plant PHOEBUS of the AG-Solar in Jülich, Germany.     

直流微电网系统的DC/DC变换器控制系统设计

全桥DC/DC变换器由于具有高功率密度、高效率、高变压比及电气隔离的特点,成为直流微电网系统中重要的电力电子接口。而移相全桥DC/DC变换器具有高阶时变非线性的特点,具体应用时较难建立其精确的数学模型,这影响了传统PID控制性能,因此设计了模糊自整定控制器。通过对峰值电流模式下变换器的小信号建模,在传统PI控制的基础上,给出了基于模糊理论的PI参数在线自整定方法。同时,利用Matlab仿真工具给出了模糊控制器的设计方法,并通过DSP对其进行软硬件实现。仿真和试验结果表明,模糊自整定控制与常规PI控制相比,提高了系统的抗扰动能力,改善了系统的动态性能,从而提高了整个微电网系统的可靠性。     

多重化双向DC/DC变换器电流增广控制研究

针对光储分布式发电系统中多重化双向DC/DC变换器结构,提出一种基于输入-输出线性化的增广电流控制方法。首先建立双向DC/DC变换器仿射非线性模型并分析其内动态方程,确定以电感电流为输出的状态空间描述;然后利用非线性变换将输入-输出线性化并引入增广电流反馈机制,根据二阶经典控制系统,设计控制器参数。最后经数字仿真验证该文提出的控制方法可准确、快速、强鲁棒性地跟踪功率指令,消除稳态误差对电网和负荷的不良影响,多重化结构与错相调制有效减小电感电流以及储能充放电电流纹波。     

稀疏采样下DC/DC输出波形时域参数计算方法

分析了纹波频谱及稀疏采样下频域计算方法的误差,设计了一种基于时域指数函数的计算方法,并提出了采样点在分段中的辨识方法,实现了稀疏采样下电流电压较高精度的计算,为直流系统电能计量及保护测控装置中的电流电压计算提供了一种参考方案。最后,以Buck DC/DC输出电能计量为例,比较分析了本方法与基于频域的电度计量方法的精确度;结果表明,在相同的采样率下,本算法相对误差和绝对误差都较小。     

直流模块式光伏发电系统前级DC/DC变换研究

针对传统集中式光伏发电系统结构存在的问题,介绍了直流模块式光伏发电结构,并利用反激变换器作为直流模块式光伏发电系统的前级直流模块,采用变步长的滞环比较法实现光伏电池的最大功率跟踪控制,采用带有输入电压前馈控制的电压闭环控制策略实现直流母线的稳压控制。试验结果表明,该方案可行。     

含双倍压DCM结构的高增益DC/DC变换器

为了增加直流变换器的电压增益,减少开关管的电压应力,将耦合电感倍压单元与二极管-电容(Diode capacitor multiplier,DCM)单元进行组合,提出一种双倍压DCM结构,将该结构引入含输出二极管的非隔离变换器中,不仅能提升该类变换器的电压增益,有效降低器件的电压应力,同时利用结构中的二极管-电容支路作为无源钳位支路吸收漏感能量,提高变换器的效率。并以含双倍压DCM结构的Sepic变换器为例进行了工作模态和工作性能的分析,推导了电感电流临界的工作状态,与同类型变换器进行了对比分析,充分证明了该类变换器具有高增益、低应力的优势。最后,搭建了一个60W的试验样机,验证了上述理论的正确性。     

直流微网DC/DC变换器的虚拟直流电机控制策略研究

直流微网是小惯性系统,负荷频繁投切和新能源出力波动等因素都会影响母线电压的稳定。在直流微网系统中,往往通过储能单元维持系统功率平衡和母线电压稳定。针对储能端口双向DC/DC变换器,提出一种简化的虚拟直流电机控制方法,以增强系统的惯性和阻尼;建立虚拟直流电机控制的小信号模型,分析控制策略的稳定性和动态特性;对于动态响应初期母线电压的冲击性变化,提出输出电流前馈的小信号模型补偿方法,进一步平滑母线电压的动态过程;最后通过仿真分析验证了所提控制策略的正确性和有效性。     

DC/DC单管谐振式变换器在光伏电热水器中的应用

针对光伏电热水器DC/DC变换器存在磁芯利用率低、控制困难、成本高、可靠性低等问题,文章设计了一种单管谐振式DC/DC变换器,在建模、分析的基础上,提出了改变开关频率实现最大功率点跟踪(MPPT)的控制方法;对变换器主电路中器件的关键参数进行了设计,制作了实验样机,通过实验验证了所提出的单管谐振式DC/DC变换器供电的可行性。     

新型燃料电池汽车用交错式结构DC/DC系统研究

为解决电动汽车中氢燃料电池输出纹波大的问题,提出了将交错式直流电压(DC/DC)变换器引入氢燃料电池汽车动力系统的改进方案.以三相交错式Boost变换器为基础拓扑,在输入端加入滤波电感和π型缓冲电路,构造了综合考量的燃料电池输出和DC/DC变换器输入的新型交错式DC/DC变换器结构.结合输入输出双重控制策略,搭建了新型...     

Online humidification diagnosis of a PEMFC using a static DC–DC converter

This paper deals with the online checking of the humidification of a Proton Exchange Membrane Fuel Cell (PEMFC). Indeed, drying or flooding can decrease the performance of the PEMFC and even lead to its destruction. An online humidification diagnosis can allow a real-time control. A good indicator of the membrane humidification state is its internal resistance. As known, the membrane ionic conductivity increases with the membrane water content. This resistance can be calculated at high frequency by dividing the voltage variation by the current variation. The proposed scheme makes use of measurements of current and voltage ripples coming from the association of a static DC–DC converter and the fuel cell. The experiment thus consists in computing the internal resistance in wet and dry conditions.     

多模直流模块式光伏发电系统前级DC/DC变换器研究

对DC/DC变换器进行了分析,以半桥变换器为研究内容,讨论了多模直流模块式光伏发电系统的结构及性能;并介绍了变换器的运行控制,包括MPPT控制、恒压控制、恒功率控制;最后进行了理论分析与仿真验证,得到结论:隔离型电流馈电半桥变换器能够较好地实现高电压增益和高效率,在进行控制仿真时,选用的扰动观察法能够很好地观测输出功率,从而得到预期的效果,验证了变换器的可行性。     

一种适用于BESS的交错并联双向DC/DC变换器

针对现有电池储能系统(BESS)双向DC/DC变换器(BDC)电压增益低和开关器件电压应力高等特点,提出一种适用于BESS的两相交错并联BDC。该储能系统(ESS)能有效结合Z源网络和交错并联结构的优势特性。详细分析了该ESS的工作原理、Boost和Buck模式,并推导出2种工作模式下的电压变化比。同时对该ESS两相交错并联BDC的带逻辑判断单元的载波移相控制策略进行了详细介绍。在Matlab/Simulink中搭建仿真实验模型,验证了该ESS各工作模式下的主要工作波形。仿真实验结果表明该系统具有电压增益高、开关器件电压应力低和各相电感之间能实现自动均流等优点。     

一种适用于BESS的交错并联双向DC/DC变换器

针对现有电池储能系统(BESS)双向DC/DC变换器(BDC)电压增益低和开关器件电压应力高等特点,提出一种适用于BESS的两相交错并联BDC。该储能系统(ESS)能有效结合Z源网络和交错并联结构的优势特性。详细分析了该ESS的工作原理、Boost和Buck模式,并推导出2种工作模式下的电压变化比。同时对该ESS两相交错并联BDC的带逻辑判断单元的载波移相控制策略进行了详细介绍。在Matlab/Simulink中搭建仿真实验模型,验证了该ESS各工作模式下的主要工作波形。仿真实验结果表明该系统具有电压增益高、开关器件电压应力低和各相电感之间能实现自动均流等优点。     

单Buck/Boost集成三端口双向DC/DC变换器研究

将双向Buck/Boost电路与DAB集成在一起构成三端口双向DC/DC变换器,Buck/Boost电路和DAB在原边共用功率开关管。DAB的移相角控制变压器两侧的能量双向流动,从而控制输出侧电压,而双向Buck/Boost电路的占空比用来控制前级母线电压,该端口可接入光伏等新能源,前级全桥单元采用交错并联PWM方式可自动实现变压器原边伏秒平衡。该文分析系统稳态特性及软开关特性,在前级母线电压宽范围幅值变化的情况下,所有的功率开关可在宽范围内实现软开关,最后通过实验样机进行方案验证。     

大容量储能系统三电平双向DC/DC变换器的研制与仿真

设计了一种适用于大容量储能系统的三电平双向DC/DC变换器,其拓扑采用可承受大电压的高频隔离双半桥三电平结构。介绍了三电平双向DC/DC变换器的工作原理和开关器件应力情况,分析了在单移相调制策略下的工作特性以及功率特性和软开关条件,并设计了闭环控制系统。通过仿真实验表明,该变换器具有开关管电压应力小,适用于大电压大功率场合;开关管工作在高频软开关条件下,功率密度高;输出电压稳态无差等特点,可满足大容量储能系统的工作要求。