高效双变压器 LLC 转换器：宽输入电压范围应用的优化设计

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本文是一篇关于高效率LLC（Boosting LLC）变换器的设计论文，发表于2013年4月的《电气与电子工程 Transactions on Power Electronics》期刊。LLC变换器是一种在电力电子领域广泛应用的拓扑结构，主要用于实现高效率的电压转换，特别适合宽输入电压范围的应用场景。作者Haibing Hu、Xiang Fang、Frank Chen和Z.John Shen、Issa Batarseh等人提出了一种创新的修改版LLC变换器，其特点是采用了两个串联的变压器，这使得变换器能够覆盖四倍于最小输入电压的操作范围。论文的核心内容集中在优化这种新型LLC变换器的设计上。为了实现更高的效率，研究者开发了一种数值方法，基于LLC变换器的稳态方程，通过分析磁化电流来最小化损耗。他们特别关注了磁化电感，因为较大的磁化电感有助于减小磁化电流，从而降低导通损耗和核心损耗。设计目标是找到最大磁化电感，以实现最佳的效率和性能。论文还提供了一个优化过程和一个具体的250瓦、210伏输出功率的原型设计实例。设计过程中，作者构建了一个输入电压范围从25伏到100伏的实验平台，用来验证所发展的数值模型和优化方法的有效性。实验数据中的dc增益与理论计算的结果高度吻合，这表明了新提出的LLC变换器设计方案的成功。这篇论文为宽输入电压范围的LLC变换器设计提供了实用的优化策略和技术支持，对于从事电源系统设计的工程师来说，具有很高的参考价值，能够帮助他们提升电源系统的效率和适应性。通过深入理解文中提出的理论模型和优化技术，设计师可以更好地应对各种工作环境中电源转换的需求。

1948 IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 28, NO. 4, APRIL 2013

Fig. 4. Different operation conﬁgurations. (a) Conﬁguration 1. (b) Conﬁgura-

tion 2. (c) Conﬁguration 3. (d) Conﬁguration 4.

structure will change to half-bridge structure, which will fur-

ther double the dc gain. In summary, there are four operation

conﬁgurations in this proposed topology illustrated as follows.

Conﬁguration 1: As shown in Fig. 4(a), transformer T2is

disabled by turning ON the bidirectional switch and rectiﬁer 2

is blocked. In this case, the converter operates as a conventional

LLC converter.

Conﬁguration 2: As shown in Fig. 4(b), the bidirectional

switch is OFF and two transformers operate in series at the

primary side and in parallel at the secondary side. In this manner,

the total magnetizing inductance is the sum of two transformers’

magnetizing inductance, L

m 1

m 2

Conﬁguration 3: As shown in Fig. 4(c), the full bridge is

changed to half-bridge operation by switching OFF S3 and keep-

ing S4 always ON. Meanwhile, transformer T2 is disabled by the

bidirectional switch. In this manner, the dc gain will be halved

compared to that in Conﬁguration 1.

Conﬁguration 4: As shown in Fig. 4(d), the converter operates

in half bridge and transformer 2 is enabled by turning OFF the

bidirectional switch. Similar to Conﬁguration 3, the dc gain is

half of that in Conﬁguration 2.

III. DC G

AIN ANALYSIS

A. Current DC Gain Analysis

Obtaining the accurate dc gain will help guiding the design

of LLC converters. However, as the characteristics of LLC con-

verters are complicated by the nonlinear relationship between

output voltage with excitations (input voltage and switching

frequency) and load, obtaining a mathematical expression of

the accurate dc gain becomes almost impossible. To simplify

the analysis of the characteristics of LLC converters, FHA has

been developed, where the voltages and currents are assumed

to be sinusoidal waveforms, thereby permitting the traditional

ac circuit analysis to be employed, and thus the approximated

dc gain in mathematical expression can be easily derived [15].

However, the inaccuracy in dc gain of the FHA technique may

mislead the design, since the dc gain in FHA is much lower than

that in real circuits, especially when the switching frequency

deviates far away from the resonant point. It clearly indicates

that the design based on FHA leads to setting the magnetizing

inductance lower than necessary to meet the desired dc gain

range, thus resulting in higher magnetizing current and higher

conduction losses. Although there are several other techniques,

such as describing function, Fourier series expansion, etc., to

improve the dc gain accuracy [16]–[25], they still cannot give

an accurate dc gain due to some approximations assumed in

these techniques. In an efﬁciency-oriented design, an accurate

dc gain is necessary in choosing the right magnetizing induc-

tance to reduce the magnetizing current while meeting the dc

gain range.

B. Numerical DC Gain Calculation

It is straightforward to obtain accurate dc gain character-

istics by using simulation tools, such as Pspice, Saber, and

Psim. However, applying this method to a recursive optimization

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