多端口电力电子变压器(power electronic transformer, PET)将逐步应用于未来配电网中。一方面，要具备优越的动态响应特性，以快速调节系统潮流、提高系统稳定性；另一方面，应能在电网故障时平滑切换运行模式，以利于提高可靠性和系统的自愈性。然而，共高频母线PET(high-frequency-bus-based PET, HFB-PET)的特殊结构决定了其内部瞬时能量存在强耦合，多端口多级联特性又使得其与外部“源-网-荷-储”的组合控制灵活而复杂，传统分布式发电系统的解决方案应用于基于HFB-PET的交直流混联系统存在明显局限性。本文立足于以上问题，依次以电网连接正常、电网电压短暂跌落以及电网故障三种场景，从多时间尺度角度研究HFB-PET的协同控制规律和方法，以改善其动态性能和运行可靠性。首先，揭示HFB-PET模块、端口以及电网间的功率/电流耦合规律，提出一种解耦与协同控制策略。包括中压交流(medium-voltage AC, MVAC)端口多形态的多维解耦控制方法、模块化多有源桥(modular multi-active bridge, MMAB)的功率交叉解耦策略、以及端口内部模块间的功率均衡策略。通过同步解耦模块、端口及电网间的功率/电流，使三者相互协同工作，提升HFB-PET的动态响应特性。然后，针对MVAC电网电压短暂跌落的场景，提出一种多端口大时间尺度协同作用下的低电压穿越(low-voltage ride-through, LVRT)控制方法。包括LVRT协同控制方案、基于功率坐标系的LVRT模式分类方法、电网电压跌落深度检测算法、以及LVRT过渡期的有功给定路径优化策略。所提LVRT控制方法无需更改端口工作模式，无需直接调节外部新能源的有功出力，使PET在“发电”和“用电”状态下同时具备LVRT能力，发展针对多端口PET的LVRT新范式。进一步地，针对MVAC电网故障的场景，提出一种多端口小时间尺度协同作用下的并/离网控制策略。包括基于线性自抗扰的MMAB动态解耦策略，基于功率预平衡和相移比基准更新的MMAB松弛端口切换策略，基于端口协同和双积分退饱和的孤岛检测过渡过程控制方法，以及全功率范围内孤岛检测和判断方法。通过对切换过程瞬态行为的分析与优化控制，抑制LC振荡，改善控制鲁棒性和动态性能，实现工作模式的平滑过渡，提升HFB-PET的运行可靠性。最后，从工业样机的设计、研制、示范运行三个方面对兆瓦级四端口HFB-PET的工程实现进行研究。

Multi-port power electronic transformer (PET) will be gradually applied in the future distribution grid. On the one hand, it must have excellent dynamic response characteristics to quickly adjust the power flow and improve the stability of the power system. On the other hand, it should be able to smoothly switch the port operation mode when the external power grid fails, so as to improve its reliability and the self-healing of the power system. However, the special structure of high-frequency-bus-based PET (HFB-PET) determines the strong coupling of its internal instantaneous energy, and the multi-port and multi-cascade characteristics make its combination relationship with external “source, grid, load or storage” more complicated. So the application of the traditional distributed energy resource system solution to the HFB-PET-based AC-DC hybrid system will bring obvious limitations. Based on the above problems, this paper studies the coordinated control laws and methods of the HFB-PET from the perspective of multiple time scales in order to improve its dynamic performance and operational reliability in three scenarios: normal grid connection, short-term grid voltage drop, and grid failure.Firstly, the law of power/current coupling between modules, ports and power grid in the HFB-PET is revealed, and a decoupling and coordinated control strategy is proposed. It includes the multi-mode multi-dimensional decoupling control method of the medium-voltage AC (MVAC) port, the power cross decoupling strategy of the modular multi-active bridge (MMAB), and the power balance strategy between the internal modules in each port. By synchronously decoupling the power/current between the module, the port and the grid, they can work in harmony with each other to improve the dynamic response characteristics of the HFB-PET.Secondly, a low-voltage ride-through (LVRT) control method is proposed for the scenario of MVAC grid voltage drop, including LVRT coordinated control scheme, LVRT mode classification method based on the power frame, grid voltage sag depth detection algorithm, and active power given path optimization strategy during the LVRT transition period. The proposed LVRT control method does not need to change the working mode of the port, and does not need to directly adjust the active power output of the external energy source. The PET has the LVRT capability in the "power generation" or the "power consumption" state, and a new LVRT paradigm for multi-port PET is developed. Furthermore, for the scenario of MVAC grid failure, a grid-connection/islanding control strategy is proposed, including MMAB dynamic decoupling strategy based on the technology of linear active disturbance rejection, MMAB slack port switching strategy based on power pre-balance and phase-shift-ratio benchmark update, island detection transition process control method based on port coordination and double integral desaturation, and full power in-scope island detection method. Through the analysis and optimization control of the transient behavior of the switching process, the LC oscillation is suppressed, the control robustness and dynamic performance are improved, the smooth transition of the working mode is realized, and the operation reliability of the HFB-PET is improved. Finally, the engineering realization of a megawatt four-port HFB-PET is studied from three aspects: design, development and demonstration operation of the industrial prototype.