集成非均衡直流源的多电平变流器及其关键控制问题研究

DC sources, for instance, PV modules and storage batteries, when modularized and centrally connected to high voltage grid by multilevel converters, boasts with advantages as low harmonics, low cost, high efficiency and high reliability. Independently controlled voltage and power of sub-modules also avoid power mismatch of series connected PV modules and state of charge (SOC) mismatch of series connected storage batteries. To this end, the project will focus on the issues of unbalanced level voltage operation and unbalanced cell power control of multilevel converters. The study will be performed in the following procedures: Firstly, topology demand analysis will be conducted to provide multilevel topologies suitable for the integration of unbalanced DC sources; Secondly, multilevel modulation strategies for cells with time-varying unbalanced voltage will be developed to eliminate the influence of unbalanced voltage levels on fundamental component of output AC voltage; Thirdly, the power flow models will be established for the selected multilevel topologies, which are supposed to reveal the internal mechanism of power flow, and the unbalanced power control schemes will be proposed; Finally, their applications into PV and energy storage systems will be explored, and an objective evaluation of research results by means of experiments and simulations will be conducted from the perspective of their efficiency, reliability, extensibility, power quality and control complexity. This research project is to enhance the traditional multilevel technology, which will then be qualified for unbalanced level operation and unbalanced level power control, and its results are supposed to broaden the operating range of multilevel converters and strengthen their control performance.

将光伏组件、储能电池等直流源模块化，并以多电平形式集中并入中高压电网，具有低谐波、低成本、高效率和高可靠性等优点。对子模块电压和功率进行独立控制，还能解决直接串联带来的光伏组件功率失配和储能电池荷电状态（SOC）失配问题。为此，本项目将围绕多电平各电平单元的非均衡电压运行和非均衡功率控制问题展开研究：首先，进行拓扑需求分析，给出适用于集成非均衡直流源的多电平拓扑；然后，研究各电平电压非均衡时变条件下的多电平调制策略，消除非均衡电平对输出交流电压基波的影响；第三，建立所选多电平拓扑的功率流动模型，揭示功率流动内在机理，提出非均衡功率控制方案；最后，探索光伏与储能应用，根据仿真和实验结果，从成本、效率、可靠性、扩展性、波形质量、控制复杂度等方面对研究成果进行客观评价。本项目的研究是传统多电平技术在非均衡电平运行和非均衡功率控制上的深化，成果也可用于加强多电平变流装置的运行范围和控制性能。

将光伏组件、储能电池等直流源模块化，并以多电平形式集中并入中高压电网，具有低谐波、低成本、高效率和高可靠性等优点。对子模块电压和功率进行独立控制，还能解决直接串联带来的光伏组件功率失配和储能电池荷电状态（SOC）失配问题。为此，本项目围绕多电平各电平单元的非均衡电压运行和非均衡功率控制问题展开了研究：首先，建立了集成非均衡直流源的多电平基本单元模型，指出非均衡控制多电平技术的3 大拓扑需求：非均衡电压下正常的交流基波输出、较强的非均衡功率控制能力以及模块扩展性。接着，引入电平电压非均衡度参数δ，按开关周期伏秒积平衡原理给出了零序注入和调制波分解两种非均衡补偿策略，能够保证在非均衡模块电压下输出交流电压无基波偏移，仿真和实验结果验证了补偿的正确性。然后，建立了集成非均衡电流源下多电平变流器的非均衡电流控制模型，提出了基于零序注入和基于调制波分解的两种非均衡电流控制方法，并给出了控制极限。其中，基于零序注入的非均衡电流控制在光伏与储能上具有良好应用前景。最后，基于零序注入非均衡电流控制方法，提出了一种尽可能消除串联光伏组件失配功率损失的光伏应用方案。仿真和实验结果表明，该控制方法能够在非均衡光照较小时完全消除失配功率损失，在非均衡光照较大时极大降低失配功率损失。