Analysis of Light Load Efficiency Characteristics of a Dual Active Bridge Converter Using Wide Band-Gap Devices

In this paper, the zero voltage switching (ZVS) region of a dual active bridge (DAB) converter with wide band-gap (WBG) power semiconductor device is analyzed. The ZVS region of a DAB converter varies depending on output power and voltage ratio. The DAB converters operate with hard switching at light loads, it is difficult to achieve high efficiency. Fortunately, WBG power semiconductor devices have excellent hard switching characteristics and can increase efficiency compared to silicon (Si) devices. In particular, WBG devices can achieve ZVS at low load currents due to their low parasitic output capacitance (Co,tr) characteristics. Therefore, in this paper, the ZVS operating resion is analyzed based on the characteristics of Si, silicon carbide (SiC) and gallium nitride (GaN). Power semiconductor devices. WBG devices with low Co,tr operate at ZVS at lower load currents compared to Si devices. To verify this, experiments are conducted and the results are analyzed using a 3 kW DAB converter. For Si devices, ZVS is achieved above 1.4 kW. For WBG devices, ZVS is achieved at 700 W. Due to the ZVS conditions depending on the switching device, the DAB converter using Si devices achieves a power conversion efficiency of 91% at 1.1 kW output. On the other hand, in the case of WBG devices, power conversion efficiency of more than 98% is achieved under 11 kW conditions. In conclusion, it is confirmed that the WBG device operates in ZVS at a lower load compared to the Si device, which is advantageous in increasing light load efficiency.

Modeling and Current Programmed Control of a Bidirectional Full Bridge DC-DC Converter

Modelling of bidirectional full bridge DC-DC converter as one of the most applicable converters has received significant attention. Mathematical modelling reduces the simulation time in comparison with detailed circuit response;moreover it is convenient for controller design purpose. Due to simple and effective methodology, average state space is the most common method among the modelling methods. In this paper a bidirectional full bridge converter is modelled by average state space and for each mode of operations a controller is designed. Attained mathematical model results are in a close agreement with detailed circuit simulation.

A Flux DC Bias Suppression Scheme of Single-stage Full-bridge PFC Converters Based on Dead Zone Adjustment

由于单级桥式功率因数校正（power factor correction,PFC）AC/DC变换技术电路的特点,导致高频变压器存在偏磁现象,影响了系统正常工作。传统方式通过增加变压器气隙或使用隔直电容来防止变压器出现偏磁,但是该类方案影响了系统性能,并增加了电路的复杂程度。结合有源钳位单级PFC变换器工作特点,提出一种基于死区调节的偏磁抑制策略,通过改变系统的开关时序,能够有效抑制偏磁,具有不增加主电路复杂程度、不影响系统性能、数字控制和模拟控制都能够实现等优点。在提出抑制策略的基础上,设计实现电路,给出死区设计方法及影响规律,最后进行实验研究。理论分析及实验结果表明,该策略能够在不影响系统性能的基础上,有效抑制单级桥式PFC变换器的高频变压器偏磁。

Improved Full Bridge Converter with Low Peak Voltage on Rectifier Diodes

To suppress peak voltage on rectifier diodes in a full bridge( FB) converter,the mechanism of peak voltage was analyzed and an improved FB converter was proposed. One reason for peak voltage is the resonance of the transformer's leakage inductance and the rectifier diodes' junction capacitances. The other reason is that the fast reverse recovery current of the rectifier diodes flows through the transformer's leakage inductance. An H bridge composed of four diodes,an auxiliary inductance, and a clamping winding were adopted in the proposed converter,and peak voltage was suppressed by varying the equivalent inductance, principally in different operating modes. Experimental results demonstrate that the peak voltage of rectifier diodes decreases by 43%,the auxiliary circuit does not lead to additional loss, and the rising rate, resonant frequency,and amplitude of the rectifier diodes' voltage decrease.Peak voltage and electromagnetic interference( EMI) of rectifier diodes are suppressed.

Design and performance of an EMI filter to reduce conducted EMI in an isolated full bridge buck converter power supply

EMI Filter Design and Performance for isolated full bridge buck converter is developed in this paper. In order to design a high performance EMI filter, many issues need to be considered beforehand. Some important issues including accurate model of converter components, parasitic elements, its effect on EMI noise and impedance mismatch are included in this paper. A numerical prediction of EMI/EMC has the potential to evaluate EMI performances at the design stage and before prototyping. It can also help reduce the post-prototype EMC cost by minimizing late redesign and modifications of a design implementation. Saber simulator is used to analyze the EMI noises and EMI filter’s performance. Conducted EMI noise measurement and EMI filter design of isolated full bridge buck converter has been achieved while successfully satisfying the FCC class B limits in the frequency range from 150 kHz to 30 MHz. Simulation results are compared with experimental data and the effectiveness of the EMI simulation approach is demonstrated.

Application research on ZVZCS full-bridge converter technique

Based on ZVZCS （zero voltage zero current switching） full bridge converter technique, a novel inverter welding power supply is designed, in which the secondary side of the transformer adopts passive clamping circuit to reduce voltage stress of rectifying components. This supply can realize power switches ZVS （zero voltage switching ） or ZCS （zero current switching） within a very wide range of load; Only through setting up blocking capacitor in the primary side of transformer, the power transformer＇s bias in the full-bridge converter is suppressed and the primary current can be reset easily. In addition, how to calculate the blocking capacitor and its influence to power supply performance are also subjects discussed in this paper.

The Implementation of a High Efficiency Full-Bridge Converter

A high efficiency full-bridge converter is investigated and implemented in this paper. The measured data result from the other converter implemented by IC UCC3895 is to compare with that of the previous converter. This full-bridge converter proposed and implemented converter can obtain about 96% power efficiency in conversion procedure when compared with that of 90%, which were ever published by the conventional techniques. Apart from, the L-C resonance circuits were developed and embedded into the popular PWM (pulse width modulation) power converter, which is referred as the soft-switching, so as to down sizing the volume of the IC which can totally reduces the power losses caused in the duration of a semi-con- ductor switching.

An Improved Modulation Strategy for Single-phase Three-level Neutral-point-clamped Converter in Critical Conduction Mode

Two-level totem-pole power factor correction(PFC)converters in critical conduction mode(CRM)suffer from the wide regulation range of switching frequency.Besides,in highfrequency applications,the number of switching times increases,resulting in significant switching losses.To solve these issues,this paper proposes an improved modulation strategy for the single-phase three-level neutral-point-clamped(NPC)converter in CRM with PFC.By optimizing the discharging strategy and switching state sequence,the switching frequency and its variation range have been efficiently reduced.The detailed performance analysis is also presented regarding the switching frequency,the average switching times,and the effect of voltage gain.A 2 k W prototype is built to verify the effectiveness of the proposed modulation strategy and analysis results.Compared with the totem-pole PFC converter,the switching frequency regulation range of the three-level PFC converter is reduced by 36.48%and the average switching times is reduced by 45.10%.The experimental result also shows a 1.2%higher efficiency for the three-level PFC converter in the full load range.

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.

A Qualitative Assessment of a Modified Multilevel Converter Topology M2LeC for Lightweight Low-Cost Electric Propulsion

A Cascade H Bridge (CHB) is evaluated for both electric vehicle motor traction control and off-vehicle charging against the Power ElectronicsUK Automotive Challenge for cost and mass for the year 2035. By combining the power electronics with batteries using low-voltage MOSFET transistors in a series cascade arrangement the cost and mass targets could be met 12 years earlier (in 2023 and 20 times lighter if an application specific integrated circuit (ASIC) is used. A 200 kW peak reference car was used to evaluate cost and mass benefits using four different topologies of power electronics. Vehicle installation is shown to be simplified as only passive cooling is required removing the need for liquid cooling systems and the arrangement is inherently safe;no high voltages are present when the vehicle is stationary. The inherently higher efficiency of CHB increases vehicle range. The converter with integrated batteries can also behave as an integrated on-board battery charger delivering additional off-vehicle benefits by removing the need for costly external chargers.

两桥臂交叉解耦不平衡控制策略研究

由于非不平衡控制策略中没有考虑线电压和相电流的相角差,造成三相电网的有功、无功电流无法完全补偿。为了解决这一问题,根据电压电流相角差,推导出单相补偿器中无功参考补偿电流与负载电流的关系,提出一种两桥臂交叉解耦不平衡控制策略,利用多变量滤波器和交叉解耦双复系数滤波器优化锁相环,精确锁定三相不平衡电网的电压频率和相位,对2个单相背靠背变换器的无功电流分别控制,进而利用两桥臂变换器补偿三相不平衡无功。实验结果验证了所提两桥臂交叉解耦不平衡控制策略,可抑制三相有功不平衡及补偿三相不平衡无功,将三相电流的不平衡度从150.0%降低至2.6%,三相电网功率因数从0.257提升至0.997,减少了三相无功补偿器的开关管个数。

基于移相控制统一模型的双有源桥DC-DC变换器基波环流优化控制策略

为充分利用双有源桥DC-DC变换器的容量,减小无功功率,提升工作效率,提出一种基于变换器移相控制统一模型的基波环流优化控制策略。通过引入基波移相比对变换器的所有移相控制方式进行统一描述,并采用傅里叶分解法建立全桥交流电压及电感电流的统一模型。该统一模型降低了多控制变量下变换器多模态分析的复杂性,适用于不同移相控制的所有工作模式,具有普适性。基于频域分析法和功率因数角,构建变换器传输功率及无功功率的统一数学模型。在此基础上,提出考虑无功基波分量的环流优化控制策略,并对传导损耗进行建模与分析。该策略简单有效,能够很好地减小变换器无功功率和改善系统效率,更有利于工程实际的应用。搭建了实验平台,对比了所提基波环流优化控制策略与传统移相控制方式下变换器的功率因数及变换效率,仿真和实验结果验证了理论分析的正确性和所提控制策略的可行性。

基于“仿真—半实物仿真—实物”三阶段开发流程的DAB变换器实验探索与研究

该文以双有源桥DC-DC变换器为对象,详细分析了变换器在三重移相调制下的两种数学模型,又基于这两种数学模型提出了对应的电感电流优化控制策略,搭建了包含MATLAB/Simulink仿真平台、StarSim半实物仿真平台和实物平台的三阶段实验平台,在平台中通过实验验证了优化控制策略的可行性和有效性。所设计的三阶段开发流程能够加深学生对电力电子领域相关知识的理解,逐步提升学生的理论分析能力、仿真验证能力和实践操作能力。

一种可实现双向故障闭锁的双极Y型模块化多电平直流变换器

直流电网互联通常采用隔离型高压大功率直流变换器,但其存在体积大、成本高及传输效率较低等问题。该文提出一种双极Y型模块化多电平DC/DC变换器,其避免使用中间变压器,实现直流功率双向传输,并且可以有效闭锁双向直流故障。首先分析了变换器拓扑结构及故障闭锁工作原理,并根据桥臂内电势等效原理建立了数学模型。基于变换器臂间、相间能量平衡约束,在闭环控制的基础上引入桥臂电流补偿控制,提升变换器暂态性能。最后,在Matlab/Simulink搭建了采用模块化多电平DC/DC变换器(modularmultilevelDC/DCconverter,DC-MMC)的直流输电系统仿真模型,通过对端口电流、桥臂电流及桥臂电容电压等动态指标的分析,验证了所提DC-MMC双向功率传输控制及双向故障闭锁能力的可行性和有效性。

基于回流功率优化的直流微网DC-DC变流器超螺旋滑模控制

针对直流微网系统中双有源桥直流变换器在系统发生扰动时动态特性差及在单移相调制下变换器效率不高等问题,该文在扩展移相调制下提出一种结合回流功率优化的超螺旋滑模控制策略。首先,分析双有源全桥(dual-active-bridge,DAB)变换器在扩展移相调制下两种模式的传输功率、回流功率数学模型及软开关特性,并以传输功率数学模型为基础建立DAB变换器的降阶模型。其次,以回流功率作为目标函数,以传输功率和软开关特性作为约束条件,通过Karush-Kuhn-Tucker(KKT)条件法寻找最优移相比组合;利用DAB变换器降阶模型设计超螺旋滑模控制中的等效部分,采用超螺旋算法作为切换部分,这两部分与内移相比D1共同作用生成外移相比D2,用于调节变换器的输出电压。最后进行了仿真及实验验证,实验结果表明:在负载投切、输入电压突变、参考电压改变时变换器具有良好的动态性能,同时能有效地减小回流功率。

基于双向半桥LLC谐振变换器的退役电池组均衡方法

退役电池在储能应用过程中,由于其较大的不一致性问题会导致退役电池组出现过充或过放现象,从而限制电池组整体的容量甚至引起热失控,造成安全隐患。针对以上问题,设计一种基于双向半桥LLC谐振变换器的有源均衡电路。该均衡电路通过开关阵列与隔离型双向半桥LLC谐振变换器的相互配合,能够实现单体电池与电池组整体之间的能量传递,使退役电池组中各单体电池达到能量平衡。另外,为进一步提高均衡器的均衡速度及精度,提出一种联合电压与荷电状态(SOC)共同作为均衡变量的多状态均衡控制策略。依据电池组当前不同的能量状态,在电池组静置、充电及放电3种不同状态下,分别采用不同的均衡变量以及对应的均衡策略,从而实现电池组的快速均衡。最后,通过搭建小型的均衡实验样机对6节串联电池进行均衡实验,实验结果表明,所提均衡方法具有较快的均衡速度及较好的均衡效果。

基于三相桥光储一体系统的建模与控制

为解决光伏发电具有波动性且伴有“弃光”现象的问题,提出了一种基于三相桥的光储一体转换器拓扑结构及相关控制策略。该结构能够实现光伏电源、蓄电池、负载之间的功率流动,并具有LLC谐振变换器的软开关性质、高效率、输入电压范围适应性更宽、高功率密度等优点。在控制策略方面,采用带有复合反馈的电导增量法来实现最大功率点跟踪;为实现双向DC-DC变换器共用电感和直流母线电压稳定,采用双频率控制方法确定电感,并实现电压外环电流内环双闭环控制;为保证输出负载电压稳定,LLC谐振转换器采用电压闭环的调频控制。最后,搭建了光储一体系统仿真模型与实验平台,仿真与实验结果表明:提出的新型光储一体系统结构简单,可以稳定运行且易于实现。