【作者】 李娜；

【导师】 王要强；

【作者基本信息】 郑州大学 ， 电气工程， 2022， 硕士

【摘要】 随着社会经济的发展,能源短缺与环境污染日益严峻,大力发展清洁可再生能源已成为我国能源发展战略的重要组成部分。光伏发电具有稳定性高、清洁环保等优势,近年来已成为新能源发电中不可或缺的一部分。逆变器是光伏发电系统中的重要组成,其性能影响整个系统的运行。其中,多电平逆变器由于能够提供高质量的交流输出,在直流电转化为交流电方面有其独特优势,在光伏发电系统中被广泛研究。为改善传统多电平逆变器结构复杂、升压困难等问题,结合光伏发电系统的需求,本文提出一系列可模块化扩展的升压型开关电容多电平逆变器拓扑并对其详细分析。论文主要研究内容包括:(1)为改善传统多电平逆变器功率器件数量较多及升压困难等问题,提出一种混合升压型开关电容多电平逆变器。所提逆变器通过分压电容与开关电容的配合工作,能够以单电源输入和较少数量的功率器件实现2倍升压增益和九电平交流电压输出;电容与直流电源周期性充放电,可在没有辅助电路的情况下实现电容电压自平衡;在该拓扑模块化扩展结构中,电容逐级充电的工作方式使得半周期内的输出电平数及升压增益随开关电容单元的增加呈幂次方扩展。(2)为进一步提高逆变器的升压增益,使其适用于产生低压直流电源的可再生能源系统,提出一种M型高增益开关电容多电平逆变器。利用电容的储能技术并以串联形式组合电容和直流电源,该逆变器可实现3倍升压增益和七电平交流输出电压;所提拓扑的M型升压单元具有切换输出极性的能力,使得逆变器可在没有后端H桥电路的情况下生成双极性输出电压,可有效降低开关器件的最大电压应力;此外,所提拓扑具有模块化扩展能力,升压增益和输出电平数目随着M型升压单元的增加而显著提高。(3)为改进上述逆变器中开关器件的电压应力随拓扑扩展而不断提高的问题,提出一种交叉型低应力开关电容多电平逆变器及其级联H桥扩展结构。该逆变器通过控制电容与直流电源的等值充放电,在实现电容电压自平衡和多电平输出的同时,还可将开关器件的承受的电压应力均限制在输入电源电压以内。该拓扑可通过级联H桥单元提高升压增益和输出电平数,随着级联H桥单元的增加,扩展结构中开关管的电压应力始终维持在较低水平,实际应用价值较高。本文详细分析了所提逆变器的工作原理、参数选取、模块化扩展结构并与其他拓扑对比分析。在此基础上进行了仿真和实验验证,结果表明逆变器在各种工作环境下都具有良好的性能,在光伏逆变系统中具有较好的应用前景。更多还原

【Abstract】 With the development of society and economy,environmental pollution and depletion of traditional energy have become increasingly prominent.Vigorously developing clean and renewable energy has become an important part of our country’s energy development strategy.Photovoltaic power generation has the advantages of high stability,cleanness and environmental protection,and has become an indispensable part of new energy power generation in recent years.The inverter is an important component in the photovoltaic power generation system,and its execution impacts the functioning of the entire system.Among them,multilevel inverters have unique advantages in converting direct current into alternating current because they can provide high-quality alternating current output,and have been widely studied in photovoltaic power generation systems.To improve the complex circuit structure and difficulty in voltage stup-up of traditional multilevel inverters,combined with the needs of photovoltaic power generation systems,a series of switched capacitor multilevel inverter topologies with boost capability and modular extension were proposed and analyzed in detail.The main research contents of the thesis include:(1)To improve the problems of large number of power devices and difficulty in boosting of traditional multilevel inverters,a hybrid boost switched capacitor multilevel inverter is proposed.The proposed inverter can achieve double boost gain and nine-level AC voltage output with a single power supply input and a small number of power devices through the cooperation of the voltage dividing capacitor and the switched capacitor.The capacitor and the DC power supply are periodically charged and discharged,so that the inverter can achieve self-voltage balance of the capacitors without auxiliary circuits.In this topology modular expansion structure,the working mode of capacitor charging step by step makes the output levels in a half working cycle and output voltage gain expand exponentially with the increase of switched capacitor units.(2)To further improve the output voltage gain of the inverter and make it suitable for renewable energy systems that generate low-voltage DC power,an M-type high-gain switched capacitor multilevel inverter is proposed.Using capacitor energy storage technology and combining capacitor and DC power in series,the inverter can achieve 3 times boost gain and seven-level AC output voltage.The M-type boost unit of the proposed topology has the ability to switch the output polarity,thus the inverter can generate bipolar output voltage without the back-end H-bridge,which reduces the voltage stress of the switches effectively.In addition,the proposed topology has modular scalability,which makes the voltage gain and the output levels increase significantly with the increase of M-type boost units.(3)To improve the above-mentioned problem that the voltage stress of switching devices in the inverter increases with topology expansion,a cross-type switched capacitor multilevel inverter with low voltage stress and its cascaded H-bridge expansion structure are proposed.By controlling the equivalent charging and discharging between the capacitor and the input power supply,the inverter can realize self-voltage balance of the capacitor and multilevel output,and at the same time limit the voltage stress of the switches within the input power supply voltage.This topology can increase the boost gain and the output levels by cascading H-bridge units.With the increase of cascaded H-bridge units,the voltage stress of the switches in the extended structure is always maintained at a low level,which makes the practical application value high.This thesis analyzes the working principle,parameter selection,modular expansion structure of the proposed inverters in detail and compares them with other topologies.On this basis,simulation and experimental verification are carried out.The results show that the inverters have good performance under both steady-state and dynamic conditions,and have a good application prospect in photovoltaic power generation systems.更多还原