一种新型四电平嵌套中点钳位的多相H桥变频器悬浮电容电压平衡控制优化研究

The Nested Neutral Point Clamped(NNPC) converter is a new multi-level converter with simple topology, wide output voltage range (2.4kV~7.2kV), no power device series and common DC bus, which is very suitable for dc 10kV high power density applications. However，the flying capacitor voltage in converter fluctuates greatly when operates at low frequencies, and there is no comprehensive solution currently. Based on the China's second-generation integrated power system with dc 10kV/dozens of MWs propulsion demand, the project takes the four-level NNPC multi-phase H-bridge inverter as the research object. Several important performance factors such as minimum pulse width limit, full range speed regulation under extreme conditions and common mode voltage suppression, are comprehensively considered. The optimal control strategy of flying capacitance voltage balance of NNPC multi-phase H-bridge inverter was studied. The main research contents include：(1)Flying capacitor voltage balance control with considering minimum pulse width limit; (2) Considering the extreme working conditions and the closed loop control of the inverter drive motor in full speed range, the flying capacitor voltage balance control and its stability domain are solved; (3) Flying capacitor voltage balance control with considering multi-targets such as common-mode voltage suppression and output harmonics; Finally, semi-physical simulation and small prototype experiments are carried out to verify the effectiveness of the algorithm.

嵌套中点钳位（NNPC）变换器是一种拓扑结构简单、输出电压范围宽（2.4kV~7.2kV）、无功率器件串联、共直流母线的新型多电平变换器，非常适合于直流10kV高功率密度场合应用，然而该拓扑在低频运行时，存在悬浮电容电压波动大问题，目前还没周全的解决方案。本项目拟结合我国二代综合电力系统直流10kV/数十兆瓦级推进需求，以NNPC四电平多相H桥变频器为研究对象，综合考虑最小脉宽限制、极端工况全范围调速、共模电压抑制等多个重要性能指标，对NNPC多套多相H桥变频器悬浮电容电压平衡控制策略展开优化研究。主要研究内容包括：(1)考虑最小脉宽限制的悬浮电容电压平衡控制及波动机理分析；(2)考虑极端工况、全转速范围内变频器驱动电机闭环控制下的悬浮电容电压平衡控制及其稳定域求解；(3)考虑共模电压抑制、输出谐波等多目标下的悬浮电容电压平衡控制；最后进行半实物仿真和小样机实验，验证算法的有效性。

嵌套中点钳位（NNPC）变换器是一种拓扑结构简单、输出电压范围宽（2.4kV~7.2kV）、无功率器件串联、共直流母线的新型多电平变换器，非常适合于直流10kV高功率密度场合应用，然而该拓扑在低频运行时，存在悬浮电容电压波动大问题，目前还没周全的解决方案。本项目拟结合我国二代综合电力系统直流10kV/数十兆瓦级推进需求，以NNPC四电平多相H桥变频器为研究对象，综合考虑最小脉宽限制、死区消除、共模电压抑制等多个重要性能指标，对NNPC多套多相H桥变频器悬浮电容电压平衡控制策略展开优化研究。主要完成的研究内容包括：(1)悬浮电容电压平衡控制及波动机理分析；(2)考虑死区消除的悬浮电容电压平衡控制；(3)考虑共模电压抑制的悬浮电容电压平衡控制；（5）搭建了控制器在回路实时仿真平台，试制了15kW/5相H桥四电平原理样机，在上述基础上，完成了四电平拓扑电容平衡控制策略及关键技术实验验证。