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.     

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.     

FC/UC hybridization for dynamic loads with a novel double input DC–DC converter topology

Due to the fact that the environmental issues have become more serious recently, interest in renewable energy systems, such as, fuel-cells (FCs) has increased steadfastly. Among many types of FCs, proton exchange membrane FC (PEMFC) is one of the most promising power sources due to its advantages, such as, low operation temperature, high power density and low emission. However, using sole PEMFC for dynamic loads may not be feasible to satisfy the peak demand changes. Therefore, hybridizing PEMFC and an energy storage system (ESS) decreases the FC cost and improves its performance and life. Ultra-capacitor (UC) is the most powerful candidate to hybridize with PEMFC for dynamic loads. The DC–DC converter is the key enabling technology for hybridization of PEMFC and UC. Generally, the efficiency and performance of hybridization is largely limited by the converter topology employed for the mentioned hybridization. Integrating each source (PEMFC and UC) with a DC–DC converter is not feasible in terms of cost, performance, and control. Due to the above mentioned reasons, an attractive converter topology which can combine PEMFC and UC is strongly required. In this regard, the objective of this study is to design and simulate a novel double input DC–DC converter based on current additivity concept, in order to combine two different types of energy systems (PEMFCs and UCs).     

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.     

Highly efficient maximum power point tracking using DC–DC coupled inductor single-ended primary inductance converter for photovoltaic power systems

Solar photovoltaics (PVs) have nonlinear voltage–current characteristics, with a distinct maximum power point (MPP) depending on factors such as solar irradiance and operating temperature. To extract maximum power from the PV array at any environmental condition, DC–DC converters are usually used as MPP trackers. This paper presents the performance analysis of a coupled inductor single-ended primary inductance converter for maximum power point tracking (MPPT) in a PV system. A detailed model of the system has been designed and developed in MATLAB/Simulink. The performance evaluation has been conducted on the basis of stability, current ripple reduction and efficiency at different operating conditions. Simulation results show considerable ripple reduction in the input and output currents of the converter. Both the MPPT and converter efficiencies are significantly improved. The obtained simulation results validate the effectiveness and suitability of the converter model in MPPT and show reasonable agreement with the theoretical analysis.     

Design and analysis of a high frequency DC–DC converters for fuel cell and super-capacitor used in electrical vehicle

This work focuses on the application of the high frequency DC–DC converters used in electric vehicles. Two converters are necessary. The first converter is interposed between the fuel cell and the DC–AC inverter. It is unidirectional. The second one is used as interface between the ultra-capacitor and the DC–AC inverter. It allows the bidirectional of the power transfer. Each converter is composed of two full bridges, LC resonant filter and two planar transformers. The use of high frequency transformer allows to minimize the size and weight of the converter, produce a higher voltage in secondary side from input voltage (fuel cell or super-capacitor) and isolate the full bridges. The control strategy of the converters is the phase shift. The converters have been designed, realised and controlled by an FPGA board. To demonstrate the converters feasibility, two converters are implemented and tested. The switching frequency of two converters is 20 kHz. The first converter has a 24-V input and 200 V/1.2 kW output. But, the second converter has a 12.5-V input and 100 V/400 W output.     

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.     

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.     

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。     

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。     

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。     

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。     

Corrosion resistant quaternary Al–Cr–Mo–N coating on type 316L stainless steel bipolar plates for proton exchange membrane fuel cells

Insufficient corrosion resistance, electrical conductivity and wettability of bipolar plates are some of the important issues affecting the performance of hydrogen fuel cells. To address these issues, an amorphous Al–Cr–Mo–N coating is deposited on type 316L stainless steel using direct current (DC) magnetron sputtering. The electrochemical corrosion behaviour is investigated under simulated fuel cell anode (H₂-purging) and cathode (air-purging) environment consisting of 0.5 M H₂SO₄ + 2 ppm NaF at 70 ± 2 °C. The corrosion current density is reduced to 0.02 μA cm⁻² comparable to the commercially used Ta/TaN coatings. The polarization resistance increases by two orders of magnitude and the interfacial contact resistance (ICR) reduces significantly due to the application of the coating. Further, the coating shows better water management due to high hydrophobicity than the bare stainless steel.     

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...