光伏、风能等新能源系统发电存在间歇性，需要双向DC/DC变换器连接储能系统来维持母线电压稳定，其中双向CLLLC谐振变换器因具有良好的软开关特性，双向运行的一致性得到广泛应用。但其现有参数设计方法过多借鉴LLC现成结论，忽略变换器重载时失去电压增益随频率变化的单调性，同时传统变频控制下降压能力弱且效率不高，为此，本文围绕双向CLLLC谐振变换器的参数优化设计方法和控制策略进行深入研究。

首先对变换器变频控制的工作原理进行详细分析，采用基波分析法建立数学模型，得到变换器的等效电路，从而对变换器的电压增益特性以及阻抗特性进行研究。在此基础上，综合考虑变换器的软开关约束条件、电压增益特性及其单调性、变换器的效率，深入分析品质因数Q和电感系数k对变换器性能的影响，进而提出了一套系统的参数优化设计方案，并以储能系统为背景，对变换器主电路参数进行设计并对功率器件进行选型，同时分析了实际电路中原副边谐振参数存在差异对变换器性能的影响。其次，针对变频控制降压能力不足且降压时开关损耗较大的问题，研究了变频-移相混合控制策略，并分析混合控制策略的实现方法和切换点。同时，提出了一种基于移相控制的改进软启动策略，优化了软启动波形，让变换器输出电压可以平稳快速地建立，减小了启动阶段的冲击电流。此外，针对储能系统中能量流动双向快速、平滑切换的需求，采用了电流与滞环电压判断相结合的换向判断方式，并运用所提出的软启动策略对变换器双向切换瞬态进行控制。最后，根据所研究的控制策略对双向CLLLC谐振变换器控制系统的软硬件进行设计，梳理了数字控制流程，并详细分析闭环调节方法。

根据所提参数设计方法与控制策略，对变换器进行仿真分析并研制了一台1kW的样机进行实验验证。实验结果表明：变换器具有良好的软开关特性，双向电压增益满足要求，混合控制策略提高了变换器的降压能力与工作效率，软启动过程冲击电流较小。验证了本文参数优化设计方法的正确性和控制策略的可行性。

The intermittent power generation of photovoltaic, wind energy and other new energy systems requires bidirectional DC/DC converters to connect to the energy storage system to maintain the voltage stability of the bus, among which bidirectional CLLLC resonant converters are widely used because of their good soft switching characteristics and bidirectional operation consistency. However, the existing parameter design methods draw too much from the existing conclusions of LLC, ignoring the monotonicity of the voltage gain changing with frequency when the converter is overloaded, and the traditional frequency conversion control has weak voltage reduction ability and low efficiency. Therefore, this paper conducts in-depth research on the parameter optimization design method and control strategy of the bidirectional CLLLC resonant converter.

Firstly, the working principle of inverter control is analyzed in detail, and the equivalent circuit of the converter is obtained by using fundamental wave analysis method. On this basis, the influence of quality factor Q and inductance factor k on the performance of the converter is deeply analyzed by considering the soft switching constraints, voltage gain characteristics and monotonicity of the converter, and the efficiency of the converter. Then, a set of system parameter optimization design scheme is proposed, and the main circuit parameters of the converter are designed and the power components are selected with the energy storage system as the background. At the same time, the influence of the difference of the resonant parameters on the converter performance is analyzed. Secondly, aiming at the problem of insufficient voltage reduction capability and large switching loss during voltage reduction, the variable-phase shift hybrid control strategy is studied, and the implementation method and switching point of the hybrid control strategy are analyzed. At the same time, an improved soft start strategy based on phase shift control is proposed to optimize the soft start waveform, so that the output voltage of the converter can be established smoothly and quickly, and the impulse current in the start stage can be reduced. In addition, to meet the need of fast and smooth bidirectional switching of energy flow in the energy storage system, the commutation judgment method combining current and hysteresis voltage judgment is adopted, and the proposed soft start strategy is used to control the bidirectional switching transients of the converter. Finally, according to the studied control strategy, the hardware and software of the bidirectional CLLLC resonant converter control system are designed, the digital control flow is sorted out, and the closed-loop adjustment method is analyzed in detail.

According to the proposed parameter design method and control strategy, the converter is simulated and analyzed, and a 1kW prototype is developed for experimental verification. The experimental results show that the converter has good soft switching characteristics, the bidirectional voltage gain meets the requirements, the hybrid control strategy improves the voltage reduction capability and working efficiency of the converter, and the impulse current in the soft start process is small. The correctness of the parameter optimization design method and the feasibility of the control strategy are verified.

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