电力电子变压器具备电压变换、电气隔离和功率调节等功能，能够实现电网、储能和可再生能源等多种源荷的接入，是能源互联网背景下的关键能量互联设备。随着功率半导体技术的发展，电力电子变换器的功率变换潜力不断提升，如何进一步提高装置的实用性成为了电力电子变压器领域的重要课题。受到现有器件水平和功率变换方法的限制，电力电子变压器通常采用多级联和多级变换结构，大量的半导体开关和无源器件造成了装置体积庞大、效率低下的问题。本文面向电力电子变压器的多级功率变换结构，提出了一种基于H桥复用的新型拓扑及其功率变换方法，减少了电力电子变压器的变换级数，并对新型电力电子变压器的特性展开研究。首先，本文阐明了H桥分时复用方法的基本原理，给出了电力电子变压器控制策略和脉宽调制方法，分析了H桥分时复用时的电流特征，评估了工频调制功能和高频功率传输功能。与传统功率变换方法相比，分时复用方法有效地减少了电路中的功率器件数量。其次，针对分时复用所特有的工作模式切换问题，本文通过建立模型和数学推导给出了模式切换过程的开环和闭环控制方法，分析了死区时间对模式切换过程的影响，采取死区补偿的方式对过渡脉冲进行了修正。本文还研究了电路参数与H桥分时复用的关系，阐述了调制频率、高频支路LC 谐振频率和高频方波频率等关键参数对功率传输功能的影响，给出了电路参数选取的约束条件。最后，基于PLECS仿真工具和硬件实验平台，本文对所提出的分时复用功率传输功能进行了验证。本文针对分时复用方法所特有的间歇高频功率传输、状态切换脉冲电流和工频调制区间耦合问题，通过理论推导和实验测试的方式探究了特有问题对开关器件、高频变压器和高频功率传输的影响。最终，本文对基于分时复用H桥的电力电子变压器进行了仿真和实验，实验结果表明本文所提出的新型功率变换方法能够实现功率复合传输，简化电力电子变压器拓扑。
With the functions of voltage conversion, electrical isolation and power regulation, power electronic transformers are able to realize the access of various source loads such as power grids, energy storage and renewable energy. It’s the key energy interconnection equipment in the energy internet. With the development of power semiconductor technology, the power conversion potential of power electronic transformers is increasing. How to further improve the practicability of the apparatus has become an important issue in the field of power electronic transformers.Restricted by the level of existing devices and power conversion methods, power electronic transformers usually adopt multi-cascade and multi-level conversion structures. A large number of semiconductor switches and passive devices cause problems of bulky size and low efficiency. In this paper, a new topology based on time-sharing H-bridge and its power conversion method are proposed for the multi-stage power conversion structure of PET, which reduces the number of conversion stages of PET. The characteristics of power electronic transformers with the new power conversion method are studied.Firstly, this paper clarifies the basic principle of H-bridge time-sharing method, gives the power electronic transformer control strategy and pulse width modulation method, analyzes the current characteristics of H-bridge time-sharing, and evaluates the modulation function and power transfer function. Compared with the traditional power conversion method, the time-sharing method effectively reduces the number of semiconductor switches in the circuit.Secondly, for the operating mode switching problem, this paper gives the open-loop and closed-loop control methods of the mode switching process by establishing a model and mathematical derivation, analyzes the influence of dead time on the mode switching process, and adopts the dead time compensation method to correct the transition pulse. This paper also studies the relationship of circuit parameters and time-sharing method, expounds the influence of key parameters such as modulation frequency, resonant frequency and square wave frequency on the power transmission ability. Constraints on the selection of circuit parameters are given.Finally, based on the PLECS simulation tool and experimental platform, the proposed time-sharing method is verified. Aiming at the intermittent high-frequency power transmission, mode switching current pulses and modulation coupling problems unique to the time-sharing method, this paper explores the influences of these unique problems on switching devices, high-frequency transformers and high-frequency power transfer through theoretical derivation and experimental testing. At last the simulation and experiment results of the power electronic transformer based on the time-sharing H-bridge are carried out in this paper. The experimental results show that the new power conversion method can realize the power transmission and simplify the power electronic transformer topology.
