A Robust MPPT Control Based on Double Ended Forward Converter Architecture

In this paper,a stand-alone photovoltaic(PV)system based on a Double Ended Forward Converter(DEFC)is presented.The proposed converter is specified for 48 V,100Wapplications as most of the equipment used in telecommunication and aircraft fall in this range.The literature has limited potential application of DEFCin PV systems.The research work deals with an in-depth study of DEFCand proposes an improvedDEFCfor PV applications with battery backup.Besides,a bi-directional dc-dc converter for the battery is integrated to track theMaximumPower Point(MPP)of the PV generator.The converter is examined under variable irradiance and load conditions,and the analytical analysis of boundary conditions are implemented.The converter’s architecture also ensures built-in I-V curve tracing for the identification of MPP of PV generator.It offers low voltage stresses across switches and avoids sinking power supply and core resetting circuits.The topology’s behavior is analyzed based onMPP achievement and maintaining output under different conditions of battery backup availability,environmental,and load conditions.The PV system architecture is designed and analyzed theoretically and verified with simulations on the PSIM software.

Evaluation of the Double Snap-Through Mechanism on the Wave Energy Converter’s Performance

Lower efficiencies induce higher energy costs and pose a barrier to wave energy devices'commercial applications.Therefore,the efficiency enhancement of wave energy converters has received much attention in recent decades.The reported research presents the double snap-through mechanism applied to a hemispheric point absorber type wave energy converter(WEC)to improve the energy absorption perfomance.The double snap-through mechanism comprises four oblique springs mounted in an X-configuration.This provides the WEC with different dynamic stability behaviors depending on the particular geometric and physical parameters employed.The efficiency of these different WEC behaviors(linear,bistable,and tristable)was initially evaluated under the action of regular waves.The results for bistable or tristable responses indicated significant improvements in the WEC's energy capture efficiency.Furthermore,the WEC frequency bandwidth was shown to be significantly enlarged when the tristable mode was in operation.However,the corresponding tristable trajectory showed intra-well behavior in the middle potential well,which induced a more severe low-energy absorption when a small wave amplitude acted on the WEC compared to when the bistable WEC was employed.Nevertheless,positive effects were observed when appropriate initial conditions were imposed.The results also showed that for bistable or tristable responses,a suitable spring stiffness may cause the buoy to oscillate in high energy modes.

A zero-voltage transition for three-phase double-PWM voltage-fed converter

In comparison with several zero-voltage transition （ZVT） inverter topologies, a double-PWM converter is presented using a simple ZVT topology. The rectifier and inverter of this double-PWM share a set of commutation circuit which can provide soft-switching for the power devices and the diodes. The commutation circuit consists of 1 auxiliary device, 6 resonant inductors, and 12 diodes. Its topology is simpler than the conventional auxiliary resonant converter, leading to low loss and easy control. The control strategy and resonant working modes are analyzed. Experimental results show good performance of the system.

Period-doubling bifurcation in two-stage power factor correction converters using the method of incremental harmonic balance and Floquet theory

In this paper, period-doubling bifurcation in a two-stage power factor correction converter is analyzed by using the method of incremental harmonic balance （IHB） and Floquet theory. A two-stage power factor correction converter typically employs a cascade configuration of a pre-regulator boost power factor correction converter with average current mode control to achieve a near unity power factor and a tightly regulated post-regulator DC-DC Buck converter with voltage feedback control to regulate the output voltage. Based on the assumption that the tightly regulated postregulator DC-DC Buck converter is represented as a constant power sink and some other assumptions, the simplified model of the two-stage power factor correction converter is derived and its approximate periodic solution is calculated by the method of IHB. And then, the stability of the system is investigated by using Floquet theory and the stable boundaries are presented on the selected parameter spaces. Finally, some experimental results are given to confirm the effectiveness of the theoretical analysis.

A distributed VSG control method for a battery energy storage system with a cascaded H-bridge in a grid-connected mode

With the high penetration of renewable energy,new challenges,such as power fluctuation suppression and inertial support capability,have arisen in the power sector.Battery energy storage systems play an essential role in renewable energy integration.In this paper,a distributed virtual synchronous generator(VSG)control method for a battery energy storage system(BESS)with a cascaded H-bridge converter in a grid-connected mode is proposed.The VSG is developed without communication dependence,and state-of-charge(SOC)balancing control is achieved using the distributed average algorithm.Owing to the low varying speed of SOC,the bandwidth of the distributed communication networks is extremely slow,which decreases the cost.Therefore,the proposed method can simultaneously provide inertial support and accurate SOC balancing.The stability is also proved using root locus analysis.Finally,simulations under different conditions are carried out to verify the effectiveness of the proposed method.

Sizing of Converters Interfacing the Rotor of Wind Driven DFIG to the Power Grid

In this paper, the operation of the Double Fed Induction Generator (DFIG) in the range from synchronous speed down to sub-synchronous speeds is analyzed using the power-flow approach. The objective of this analysis is to determine a ceiling for the rating of the converter interfacing the rotor of the wind driven double fed induction generator (DFIG) to the grid. Sizing the converter is an important issue in determining the economic viability of using the DFIM as a generator at synchronous and sub-synchronous speeds in wind energy conversion systems. The size of the converter is proved to be less than 10% of the rated power of the DFIG, which is 40% to 67% lower than that estimated in previous publications.

Comparing the Quality of Power Generated from DFIG with Different Types of Rotor Converters

In this paper the quality of power generated from wind energy conversion system employing a double fed induction generator (DFIG) is investigated. The DFIG performance is tested with 3 types of converters interfacing the rotor with the grid. These are: the six-step thyristor inverter with diode rectifier, six-step IGBT inverter with diode rectifier, and 3-level IGBT-PWM inverter with diode rectifier. The harmonics in current and voltage, power factor value, and the transient behavior in each system are investigated and compared. Comparison is done at sub-and super-synchronous DFIG operational speed. In the system with lowest power quality passive filters or LC filter are added and improvement in system performance is recorded. From this study the optimum system from point of view of cost and control complexity is concluded.

Bioactive metabolites:The double-edged sword in your food

Food contains many different bioactive metabolites that interact with human metabolism.Many of these have health benefits,but in this issue of Cell,researchers show that the gut microbiome can convert a bioactive metabolite to metabolites that may elevate the risks of developing cardiovascular disease.

Dynamical Analysis of Nonlinear Bifurcation in Current-Controlled Boost Converter

Based on the bifurcation theory in nonlinear dynamics, this paper analyzes quantitatively period solution dynamic characteristic. In particular, the ones of period-1 and period-2 solutions are deeply studied. From locus of Jacobian matrix eigenvalue, we conclude that the bifurcations between period-1 and period-2 solutions are pitchfork bifurcations while the bifurcations between period-2 and period-3 solutions are border collision bifurcations. The double period bifurcation condition is verified from complex plane locus of eigenvalues, furthermore, the necessary condition occurred pitchfork bifurcation is obtained from the cause of border collision bifurcation.

双频DC-DC变换器的磁集成技术

双频Buck变换器由两个降压单元级联构成,具有动态响应快,开关损耗小等优势。然而不足的是磁件占据了整个系统的大部分体积与重量,降低了系统的功率密度。针对这一问题,提出一种三段式绕制磁集成技术,将磁件以解耦的方式集成在一副磁心中。该文首先建立集成磁件的磁路等效模型,通过抵消各绕组之间的耦合作用推导出解耦条件,并详细阐述了磁心的选取、匝数以及气隙的设计原则。其次,利用有限元仿真平台对所提集成磁件进行建模分析,与现有的集成方法相比,磁通密度分布更为均匀,磁心的利用率得到了有效提升。最后,搭建一台48 V/12 V、108 W的实验样机,体积和重量同分离磁件相比降低了31.2%和25.3%,提高了系统的功率密度,验证了该集成方法理论分析的正确性和可行性。

一类三电平伪图腾柱无桥PFC变换器

针对传统二极管钳位型三电平整流器在单相电源前级功率校正(power factor correction,PFC)电路应用场景下全控开关器件数量多的问题,该文基于3种传统无桥PFC电路进行三电平电路拓扑设计,提出一类三电平伪图腾柱PFC电路(single-phase three-level pseudo totem-pole PFC circuit,STPT-PFC),该类三电平PFC具有双电感支路桥臂,两者相互配合工作为输入电流提供路径,在正负半周两电感支路桥臂工作于不同模态可有效降低分别流过两电感的电流;基于该类PFC的一个代表性电路,从工作电流路径过程、关键波形和调制脉冲分配等方面对其进行工作原理分析,并对其它电路进行电路特性总结,推导桥臂对地电压电平特性与开关脉冲分配的数学关系式。另外,该类STPT-PFC共有5种结构,结合该类STPT-PFC结构特点,提出统一区间判断条件的双层载波调制技术,该类STPT-PFC具有相同开关器件不同拓扑结构可采用同一调制方案的特点,便于该类调制技术移植。最后,基于STPT-PFC-I电路设计1台额定功率1 kW、直流输出电压400 V的实验样机,从稳态及动态两方面进行实验分析,实验结果验证所提出一类三电平伪图腾柱PFC电路的可行性和三电平统一双层调制方法的有效性。

基于双模式变频移相调制的单级式双有源桥型DC-AC变换器

针对单级式双有源桥(DAB)型DC-AC变换器关断电流较大和软开关范围有限的问题,该文提出一种双模式变频移相调制策略。首先,对DAB变换器的单移相(SPS)调制和扩展移相(EPS)调制进行时域分析,得到其功率传输特性;然后,分析变换器的关断电流与软开关条件,得到移相比和开关频率约束方程;在此基础上,分析双模式间的移相比边界条件,提出变换器运行模式的切换机制,从而在实现变换器单级功率变换的同时,保证全范围软开关并降低低压侧的关断电流;最后,通过仿真和实验验证了所提调制策略的有效性与可行性。

基于预估-校正算法的分数阶Boost变换器倍周期分岔研究

基于电感电容本质是分数阶的事实,对分数阶Boost变换器的非线性动力学特性进行了深入研究。采用分数阶微积分的预估-校正算法,建立了Boost变换器的预估-校正模型,在此基础上得到了以参考电流、输入电压以及电容电感阶数为分岔参数的分岔图,研究了变换器的倍周期分岔和混沌行为,同时与整数阶Boost变换器的非线性动力学行为进行了比较。研究结果表明,在一定的工作条件下,随着变换器某些电路参数的变化,分数阶Boost变换器会出现分岔和混沌等非线性现象;在相同电路参数的条件下,整数阶和分数阶变换器的稳定参数域之间存在差异,与整数阶变换器相比,分数阶变换器的参数稳定区域更小,更真实地反映了Boost变换器的非线性动力学特性。

DAB储能变换器双闭环模型预测控制与PI补偿控制策略研究

针对直流微电网中分布式电源输入输出功率不稳定造成的直流母线电压波动问题,鉴于双有源桥(DAB)储能变换器具有能量双向流动的特点,提出一种基于内模原理的双闭环模型预测控制策略。在分析DAB变换器扩展移相调制原理与特性基础上,重点研究电压外环和电流内环的模型预测控制策略。针对模型预测控制性能依赖电路参数准确度问题,分别从电路主要参数失配对功率传输和直流母线稳压的影响两个角度出发,深入分析模型参数敏感度。最终设置直流母线电压稳态误差灵敏度区,在误差灵敏度区外仅采用双闭环模型预测控制以保证系统的动态响应性能,在误差灵敏度区内采用双闭环模型预测控制和PI补偿控制以消除系统稳态误差。搭建实验平台进行实验验证,结果表明:在系统受到扰动时,DAB储能变换器可实现快速地充放电对系统进行补偿,混合控制策略可快速保持母线电压的稳定,实现系统功率均衡,增强系统抗扰能力。

基于双重移相的双向变换器优化控制策略

为解决双向DC-DC变换器(dual active bridge,DAB)采用单移相(single-phase-shift,SPS)控制产生的回流功率较高及动态性能较差的问题,提出一种采用双重移相(dual-phase-shift,DPS)控制下的最小回流功率算法与直接功率控制相结合的方法。首先对DPS控制下的基本原理及回流功率特性进行分析,并建立回流功率与移相比之间的数学关系,从而推导出各分段条件下回流功率在各阶段最小化的方案。其次在保证对变换器回流功率最小化的同时提出结合直接功率法来显著提高变换器的动态性能。最后通过MATLAB/Simulink中建立的仿真验证了上述控制策略的有效性。

高频双频Buck变换器平面集成磁件优化设计

针对目前开关器件和磁性元件性能不足导致双频Buck变换器的效率和功率密度低的问题,研究了一种高效高功率密度的双频Buck变换器。变换器将工作在连续导通(CCM)模式,采用解耦合的平面集成电感器完成系统磁元件的集成,结合磁件的集成方法、有限的PCB层数和变换器的特性给出双频Buck变换器的参数,然后,提出了一种双频Buck变换器平面磁件的设计方法,并完成系统磁元件的优化设计。最后,基于第3代半导体SiC器件以及平面集成磁件,设计了额定功率200 W、开关频率400 kHz的双频Buck变换器。结果表明:该变换器峰值效率将达到96.1%,功率密度为46.1 W/in^(3)(1 in=25.4 mm),验证了双频Buck变换器设计方法的正确性和有效性。

基于反激变换器的电池充电系统设计

以具有结构简单、电气隔离等优点的反激变换器为电池充电电源,分析反激变换器电路的连续和断续模式工作原理,通过设计电压电流双闭环控制方法,实现电池的恒流充电模式和恒电压充电模式,也可实现两种充电模式的切换。实验结果证明了反激变换器的连续工作模式和断续工作模式的正确性,验证了应用于电池充电电源的可行性和有效性,切换时间小于1 ms,电压波动小于1 V。

基于MATLAB的功率因数可控的AC-DC变换电路研究

为解决谐波信号过多可能会导致电网的传输效率降低的问题,对功率因数可控的AC-DC变换电路进行了研究.基于Boost型单级有源功率因数校正变换器,控制电路中采用了外电压环和内电流环双闭环控制系统,利用滞环电流控制提高交流端功率因数,电压环稳定输出电压.采取小信号分析法,建立小信号模型并设计了控制电路.通过MATLAB仿真实验可得,双环控制的功率因数校正电路能够实现高功率因数,同时能够稳定输出电压.

基于高频振荡的变流器杂散电感多参数提取方法

针对变流器不同位置杂散电感准确获取困难的问题,提出一种基于LC高频振荡原理的杂散电感多参数提取方法,充分利用变流器自身结构,通过3个现场实验主动构建不同的谐振电路,并根据它们的振荡频率计算变流器不同位置的杂散电感。首先阐述了高频振荡法的基本原理,建立了不同谐振实验的等值电路模型。然后,以1700 V/450 A IGBT变流器系统为例,通过仿真与实验进行了可行性与有效性验证。最后,通过实验与传统双脉冲法进行了对比分析。研究表明:所提出的方法可有效提取变流器内不同位置的杂散电感参数,与双脉冲法提取开关杂散电感结果基本一致,精度可达纳亨级。

MMC器件损耗分布与电容电压纹波综合优化方法

逆变工况下,半桥子模块下部绝缘栅双极晶体管(insulated gate bipolar transistor,IGBT)(简称T_(2)管)损耗占比较大,减小其损耗有利于提升设备运行可靠性。同时,抑制电容电压纹波有利于减小电容需求及提高功率密度。然而,现有优化控制策略未关注损耗分布优化及电容电压纹波间的矛盾,难以兼顾设备运行可靠性及功率密度。为此,文中提出兼顾减小T_(2)管损耗及抑制电容电压纹波的综合优化方法。首先,通过分析电荷量对器件损耗及电容电压纹波的影响路径,阐述减小T_(2)管的通态损耗与抑制电容电压纹波间的内在矛盾。接着,通过引入罚函数,建立计及T_(2)管损耗及电容电压纹波的综合目标函数。然后,以主动旁路策略为例,通过分析二倍频环流与三次谐波电压注入对T_(2)管损耗和电容电压纹波的影响规律,提出基于二倍频环流及三次谐波电压注入的综合优化方法。最后,在MATLAB/Simulink及PLECS中搭建仿真模型进行验证。仿真结果表明:该综合优化方法兼顾了T_(2)管损耗与电容电压纹波优化,一定程度上增加了设备可靠性与设备的功率密度。