基于有源功率解耦的三相AC/DC型电力电子变压器研究

Nowadays the schemes to acquire DC traction power supply for urban rail transportation include widely applied multi-pulse diode rectifier, and the PWM rectifier which can achieve desired power quality. However, both schemes bulky line-frequency transformers are needed, which greatly decrease the power density of the system and have negative efficiency on saving limited urban rail space. By adopting power electronic transformer (PET), the weight and volume of transformer can be greatly reduced, but the introduced low-frequency pulsating-power greatly increases the capacity of passive elements. To address the aforementioned problems, this study proposes a power channel based on power electronic transformer (PC-PET) as well as active power decoupling. Firstly, the characteristic and possibility of elimination of the pulsating-power in conventional PETs are analyzed. Multi-winding transformers are adopted to build up power channels among the cascaded chains, which provides physical path for the pulsating-power. Secondly, power decoupling method based on dynamic phase-shift control is proposed. By this method, the second-order ripple powers in three phases can be counteracted without flowing into DC link, therefore the storage capacity of passive elements can be reduced. At last, the advantage of proposed scheme compared with existing methods will be analyzed. The project introduces improvements in the circuit topology and control scheme of PET, attempts to promote the application of PET in traction power supply and presents promising prospect in realizing smart traction power supply system.

目前在城轨直流牵引供电中，应用广泛的多脉波不控整流方案，以及具有良好供电质量的PWM整流方案，都需要体积庞大的工频变压器，不利于提高功率密度。采用高频化的电力电子变压器（PET）可显著降低变压器体积、重量，但在变换器内引入低频脉动功率而极大增加了无源储能元件容量。为解决上述问题，本项目提出基于功率通道的有源功率解耦电力电子变压器（PC-PET）方案：首先分析目前主流PET中的低频脉动功率形成的根本原因及消除的理论可行性，采用多绕组变压器在三相级联链间开辟功率通道，为脉动功率提供互相抵消的物理途径；其次采用基于动态移相控制的有源功率解耦策略，使三相脉动功率无需进入直流电容而直接抵消，降低对无源存储容量的需求；最后对所提出的PC-PET方案与现有的牵引供电方案进行比较分析。本项目将为PET的拓扑结构、控制策略提供新的研究思路，拓展PET的应用领域，有利于城轨牵引供电系统的小型化、轻量化和智能化

本项目研究对象为三相AC/DC型电力电子变压器（PET），可广泛应用于三相交流电网与直流电网之间的电力电子接口，替代传统的工频变压器+高频整流器的方案，在体积、损耗、成本等方面均有显著潜力。模块化的AC-DC型PET通常采用级联H桥连接到高/中压交流电网，其交流侧每相引入低频的二次脉动功率，极大增加了模块内储能电容的容量，不利于提升功率密度。针对该问题，本项目提出基于功率通道的电力电子变压器（PC-PET）及其有源功率解耦策略：首先，在三相低频脉动功率分布特性理论分析的基础上，采用四绕组变压器在三相级联高频链间开辟功率通道，为脉动功率提供互相抵消的物理途径；其次提出动态移相有源功率解耦策略结合功率均衡控制，使平衡的三相脉动功率不进入模块内的直流电容，而在功率通道内通过磁链耦合抵消，降低了储能元件体积，提高功率密度；最后提出针对PC-PET中四有源桥（QAB）的变频LLC谐振控制，结合功率解耦实现软开关，进一步降低系统损耗，提升效率。本项目为PET的拓扑结构、控制策略提供新的研究思路，有利于直流配网中能源路由器的小型化、轻量化和智能化，具有广阔的研究和应用前景。