Evaluation of fluctuating voltage topology with fuel cells and supercapacitors for automotive applications

To develop a single‐stage power conversion topology in which energy storage devices can be directly coupled, a fluctuating voltage topology is applied, leading to lower cost and more compactness with the absence of DC/DC converters. This paper investigates such a topology for automotive applications where fuel cells are directly connected to the DC bus of the inverter, resulting in fluctuating voltage across the DC bus. Further, a supercapacitor pack is also introduced to maintain the power capacity and voltage stability. The hybridization principle and practical application of such a topology are then discussed in the time domain and frequency domain. Furthermore, the transient power requirement is decomposed to design the size of fuel cells and supercapacitors. Simulation results from the modeling of the fuel cell‐supercapacitor powertrain demonstrate the feasibility and effectiveness of this topology. The supercapacitors can serve as a low‐pass filter for the fuel cells. In conclusion, the peak power requirement can be successfully achieved because of the lowered system impedance, and the fuel cells only need to supply the average power.     

A fuel cell powered autonomous surface vehicle: The Eco-SWAMP project

Autonomous surface vehicles are becoming consolidated robotic tools for marine, coastal and inland surveys. Autonomous surface vehicles are usually equipped with electronic instruments to perform remotely controlled or autonomous geo-morphological, biological, chemical, physical analyses and data collection. Actually, well-established solutions provide battery power but the research focuses on introducing a fuel cell to decrease the environmental impact meanwhile increasing the cruising range. In this paper, the design of the Eco-SWAMP, a fuel cell powered autonomous surface vehicle, is presented starting from its battery-powered version, the SWAMP prototype. The experimental power consumption profile of the SWAMP during four missions is analysed to define the primary energy sources ratings of the Eco-SWAMP. After a commercial choice of primary sources, power management algorithms are designed and compared in MATLAB/Simulink environment by simulation results. The proposed procedure can be easily applied to any autonomous marine vehicle.     

Elimination of drift-like errors in intelligent cyclic A/D converters

The paper presents a new method of elimination of influence of drift-like errors in so called intelligent cyclic A/D converters, in particular, errors caused by drifts (droops) of voltage at the output of sample-and-hold blocks. The method is based on application of the extended multi-dimensional algorithm, which estimates simultaneously values of the input sample and drift rate. Implementation of the extended algorithm in the intelligent cyclic A/D converters requires only insignificant changes in the digital part of the converter and does not increase their production costs. The motivations to these investigations resulted from practical realizations of the intelligent cyclic A/D converter in CMOS technology and difficulties in design of a precise sample-and-hold circuit. The results of selected simulation experiments related to analysis of influence of a droop rate on the final performance of the intelligent cyclic A/D converters employing the standard (one-dimensional) and extended algorithms are discussed and compared in the paper. The results of experiments show that application of the proposed solution enables efficient functioning of the converters even in the presence of relatively large drifts.     

Low‐Voltage‐Ride‐Through Performance of an HVDC Transmission System Using Two Modular Multilevel Double‐Star Chopper‐Cells Converters

This paper presents an intensive discussion on a long‐distance high‐voltage direct‐current (HVDC) transmission system that combines two modular multilevel cascade converters based on double‐star chopper cells (MMCC‐DSCC) with DC power cables. Hereinafter, a single MMCC‐DSCC is referred to as a DSCC converter or just as a DSCC for the sake of simplicity. The HVDC transmission system is required to provide low‐voltage‐ride‐through (LVRT) capability to enhance transmission system availability. This paper proposes a new LVRT method without any direct information exchange between the two DSCC converters. The validity of the method is verified, using simulated waveforms from the software package of “PSCAD/EMTDC” and experimental waveforms from a three‐phase 200‐V, 400‐Vdc, 10‐kW, 50‐Hz downscaled HVDC system with a set of 300‐meter‐long DC power cables.     

Robust pole location with experimental validation for three-phase grid-connected converters

This paper provides design and experimental validation of robust current controllers for three-phase grid-connected converters. The main objectives here are: (i) to show that a simple polytopic model can be used for designing robust controllers for predominately inductive grids; (ii) to help in the choice of the control design parameter, based on a trade-off between an upper bound of the transient settling times and the control gain sizes. Linear matrix inequality based conditions are used to design the robust control gains with lower numerical complexity than similar conditions on literature. It is shown that small values the radius of pole location lead to better bounds for the transient responses, at the price of higher control gains. Good tracking of references for the grid currents is also illustrated in practice, allowing the closed-loop system to inject active and reactive power into the grid. Simulation and experimental results prove that the system connected to the grid can provide three-phase currents complying with requirements of an important international standard.     

基于自然坐标与功率前馈的三相电压型PWM变流器控制

针对三相电压型PWM变流器控制系统,提出一种自然坐标与负载功率前馈控制方法。根据p-q理论在自然坐标下的表征,引入瞬时有功电压和瞬时无功电压的概念。从而基于电网电压定向的矢量控制策略引入PWM变流器的自然坐标控制方法,省去了电网相位检测和坐标系变换,降低控制复杂度。针对PWM变流器矢量控制下直流侧负载(包括有源负载和无源负载)功率波动对直流侧电压产生较大冲击和波动问题,基于功率平衡和p-q理论推导了负载扰动点到三相交流电流指令的前馈通道增益矩阵,提高PWM变流器直流侧稳压控制的鲁棒性。RCP实验证明所提方法的正确性和可行性。     

A new arrangement of Z‐source AC–AC converter and its closed‐loop control system

In this study, a Z‐source alternating current‐to‐alternating current (AC–AC) converter with a specific topology, which can provide both buck and boost modes, is investigated. This converter, which can be implemented easily, utilizes only two switches with complemented commands. A comparison between the Z‐source AC–AC converter and a conventional thyristor voltage controlled one is presented here, and it shows that in the most areas, the Z‐source converter provides a faster response and lower total harmonic distortion of the output currents than the conventional one. Moreover, the Z‐source converter is also extended to the multiphase systems. In addition, a new arrangement of this converter is proposed here to remove the isolated single‐phase sources. Furthermore, an open‐loop method is proposed for soft‐starting applications. Finally, a closed‐loop control system is also suggested for a three‐phase Z‐source converter to soft start and control the speed of an induction motor. Computer simulations show the validity and effectiveness of the proposed schemes. Copyright © 2014 John Wiley & Sons, Ltd.     

改进的STATCOM相内直流电容电压平衡控制策略

在三角形接线方式下,分析级联H桥变流器静止同步补偿器(STATCOM)直流侧电容电压稳态数学模型,重点研究电压内环对直流侧电容电压控制的影响。同时,分析不加电压内环与传统电压内环的控制策略。在此基础上,提出利用变流侧电流反馈来叠加误差信号,以实现每个H桥调制波微小的移相,省去了锁相环,算法简单易行。仿真实验证明:在STATCOM补偿无功与谐波电流时,该策略都能使各H桥直流侧电容电压达到很好的平衡,稳态误差小。最后,搭建了电压660V、容量300kvar的试验样机进行补偿特性分析,试验结果表明该策略的正确性与有效性。     

并联换流器高压直流输电系统控制策略

随着中国高压直流输电技术的发展,在直流工程分期建设和融冰方式运行方面,并联换流器结构受到越来越多的关注。文中详细分析了并联结构的四端直流输电系统特点,提出了整流站定直流电流控制、逆变站定直流电压控制且附加直流电流平衡控制功能的多端直流系统协调配合方式。该方式不仅最大程度地保持了双并联直流系统的相对独立性,简化了多端直流系统控制策略的设计,而且可以实现并联换流器间功率的灵活分配。由于换流器的并联和解并联是系统运行的关键技术,文中提出了详细的第二换流器解锁及第一换流器闭锁控制策略,并基于PSCAD/EMTDC搭建了四端并联直流系统的详细控制策略模型,验证了所提控制策略的有效性。