双向LLC变换器低压侧零环流的边沿偏移型变导通时间调制

doi:10.19595/j.cnki.1000-6753.tces.251200

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摘要

凭借高效高功率密度等优点,双向LLC变换器已成为48 V户用光伏储能系统等低压大电流应用场景的理想方案。然而,传统的调制面临非对称的谐振腔导致的正反向稳态特性不一致、难以双向平滑切换以及谐振腔环流大等问题。为此,本文提出了边沿偏移型变导通时间（ESVOT）调制。随后,本文对变换器各工作模式进行了模态分析、软开关特性分析以及稳态特性分析。分析表明,所提ESVOT调制不仅实现了变压器低压侧零环流、全范围软开关,还获得了双向运行时完全对称的增益特性。在此基础上,提出了一种基于二维查找表的双向控制策略。该策略利用前馈控制器实时调控开关频率、外移相角和低压侧开关器件导通时间的前馈值,同时通过开关频率实现传输功率的闭环控制,实现了双向平滑切换。最后,通过一台2.5 kW的样机,对所提出的ESVOT调制及双向控制策略的有效性进行了实验验证。

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关键词 ：双向LLC变换器, 调制策略, 控制策略, 零环流

Abstract：

The bidirectional LLC converter, valued for its high efficiency and power density, is a prime candidate for low-voltage, high-current applications such as battery optimizers. Traditional modulation, however, is hampered by asymmetrical gain characteristics, difficult bidirectional switching, and significant circulating currents.
To address these problems, this chapter proposes the edge-shifted variable on-time (ESVOT) modulation. This new modulation introduces two additional control degrees of freedom—a phase-shift angle and the on-time of the low-voltage side (LV-side) switches—to optimize the LV-side circulating current and ensure perfectly symmetrical forward and reverse operating characteristics.
Since the ESVOT modulation complicates the converter's operating modes, the conventional fundamental harmonic analysis (FHA) method is no longer adequate for accurately modeling its steady-state characteristics. Therefore, to precisely calculate the phase-shift angle and LV-side switch on-time required to achieve zero circulating current under various load and gain conditions, this paper employs exact time-domain analysis (ETDA) for the steady-state analysis. Based on the characteristics of the resonant tank waveforms, eight operating patterns are identified. The mode analysis and a soft-switching characteristic evaluation are then conducted for each pattern. Among these, four patterns are selected as feasible operating patterns due to their excellent soft-switching performance and their ability to achieve zero circulating current on the LV-side. The ETDA is also used to derive the steady-state voltage gain characteristics and the boundary conditions for each pattern. Building on this analysis, a bidirectional control scheme that integrates the ESVOT modulation with a two-dimensional look-up table (2D-LUT) is developed. This scheme utilizes a 2D-LUT-based feedforward controller to provide the feedforward values for the switching frequency, phase-shift angle, and LV-side switch on-time, thereby ensuring zero circulating current on the transformer's LV-side in the steady state. Concurrently, a closed-loop controller adjusts the switching frequency to regulate the power.
The proposed ESVOT modulation and bidirectional control scheme has been validated on a 2.5 kW prototype. The 2D-LUT based feedforward controller requires a minimum of just 10 kB of memory, offering advantages such as simple implementation and low hardware requirements. Dynamic experimental results demonstrate that the prototype can complete smooth and rapid transitions between forward and reverse operation within 8 ms. Furthermore, steady-state experimental results indicate that, compared to the conventional modulation, the ESVOT modulation successfully eliminates the circulating current on the transformer's LV-side. This boosts the prototype's efficiency under forward and reverse light-load conditions by up to 5.8% and 4.5%, respectively. Finally, the prototype achieved a peak efficiency of 98.67% and a power density of 46 W/in³, while also exhibiting perfectly symmetrical forward and reverse operating characteristics.

Key words： Bidirectional LLC converter modulation control scheme zero circulating current

收稿日期: 2025-07-08

PACS:

TM46

通讯作者: 段善旭男,1970年生,教授,博士生导师,主要研究方向为新能源及分布式发电技术、无线电力传输及船用电能变换与控制。E-mail：duanshanxu@hust.edu.cn

作者简介: 李勇男,1998年生,博士研究生,研究方向为高效高密度隔离型DC/DC变换器的拓扑与控制;磁集成矩阵变压器的优化设计。E-mail：yong_li@hust.edu.cn

引用本文:

李勇, 包浚炀, 刘邦银, 段善旭. 双向LLC变换器低压侧零环流的边沿偏移型变导通时间调制[J]. 电工技术学报, 0, (): 20251200-20251200. Li Yong, Bao Junyang, Liu Bangyin, Duan Shanxu. Edge-Shifted Variable On-Time Modulation for Bidirectional LLC Converter with Zero Circulating Current on the Low-Voltage Side. Transactions of China Electrotechnical Society, 0, (): 20251200-20251200.

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