主动防护接地MMC换流器方案及不对称能量极间交互机制研究

To meet the requirements of multi-energy interconnection system for flexibility and reliability of AC/DC distribution network, converters should be able to flexibly grounding operation and uninterrupted power transmission. In this project, the active protective grounding control of modular multilevel converter (MMC) and its operation mode conversion method are proposed. Drawing on the idea of DC pole decoupling control, the fault protection strategy based on AC side-to-ground voltage clamping and fault pole-to-ground (or pole-to-pole) voltage control will be studied. The restraint effect on DC fault current and overvoltage will be revealed, and the dynamic characteristics of active protective grounding MMC converter fault traversing. For the strong coupling characteristics of fault transient energy flow and transmission power flow, the decoupling method based on transmission loop reconstruction and power flow transfer will be explored. Then, a multi-level energy circulation adaptive control strategy will be discussed and an inter-polar synergistic mechanism for transient and steady-state energy interactions will be established. Through theoretical analysis, scheme design, simulation and experimental verification, the grounding DC pole configuration scheme and asymmetric operation control optimization method will be proposed. Expected research results of this topic would form a complete theory and method of active protection grounding MMC converter fault protection operation control, which provides theoretical support and scientific reference for AC/DC distribution network interconnection.

为适应多能源互联体系对交直流配网运行灵活性和可靠性的要求，配网换流器应具备灵活接地运行和不间断功率传输能力。鉴于此，本项目提出模块化多电平换流器（Modular Multilevel Converter, MMC）主动防护接地方案及其运行模式转换方法。借鉴直流极解耦控制的思想，研究基于交流阀侧对地钳位和故障极（或极间）电压控制的故障保护策略，解析其对直流侧故障电流和对地过电压的抑制作用，明确交流侧主动防护接地控制的故障穿越动力学。针对故障期间暂态能流和传输功率流的强耦合特性，探究基于传输回路重构和功率流转移的物理解耦方法，提出能量环流自适应控制策略，建立兼顾暂态/稳态能量交互的极间协同机制。通过理论分析、方案设计、仿真和实验验证，提出接地直流极配置与不对称运行控制优化方法。本课题预期研究成果将形成主动防护接地MMC换流器故障保护运行控制的理论与方法，为交直流配网互联提供理论支撑和科学参考。

柔性直流技术是能源互联网中骨干网架以及配电网和微电网的核心，直流故障保护与运行控制是实现交直流灵活组网与可靠运行的关键技术难点之一。本项目针对MMC换流器灵活接地控制和不对称运行等需求，从系统级运行方式与设备级控制技术两个层面，研究MMC换流器方案及不对称能量极间交互机理。采用理论分析、建模仿真、方案配置与参数优化、实时硬件在环仿真以及实验研究，提出适用于MMC换流器的主动防护接地方式和故障保护控制策略，有效抑制直流侧故障电流和对地过电压；建立换流器极间交互协同机制，解决极间故障时交直流功率传输中断的难。相关研究结果将有助于发展和丰富柔性直流系统方案与运行控制理论与方法，使交直流系统组网运行更加灵活和可靠。