【作者】 王杨；

【导师】 张千帆；

【作者基本信息】 哈尔滨工业大学 ， 电气工程（专业学位）， 2023， 硕士

【摘要】 传统化石能源因其日益缺少、环境污染严重、效率低下等问题,已经成为制约国民经济和社会发展的因素。因此,风光发电、电动汽车等新能源,新基建迎来了快速发展。在这些中高电压大功率电能变换和交流驱动的场景下,NPC三电平逆变器以其输出谐波少,开关应力低的优势已经慢慢淘汰传统的两电平逆变器。但NPC三电平逆变器也面临着中点电位波动和直流漂移的问题,导致输出波形失真和开关器件过压损坏。本文基于NPC三电平逆变器拓扑结构,重点研究抑制中点电位波动,控制中点电位平衡,使其在极低频率下(0.33～3Hz)输出电流的THD满足小于5%的要求。本文首先介绍了NPC三电平逆变电路的拓扑结构,深入分析了其工作原理,引入开关函数,建立了逆变器输出线电压、相电压和开关函数之间的数学模型。接着引入空间电压矢量,通过建立中点电位和中点电流的数学模型,分析了中点电位波动的根本原因,为之后控制中点电位平衡提供理论基础。其次,根据空间电压矢量对中点电流的影响,研究了基于空间矢量的调制算法,首先对传统空间矢量调制的最近三矢量法的基本原理和算法实现进行了具体分析,接着提出了加入冗余小矢量中点电位控制的SVPWM调制算法和虚拟空间矢量调制算法这两种抑制中点电位波动的方法,通过仿真验证了虚拟空间矢量调制算法对中点电位波动的抑制效果。之后,详细分析了传统单调制波载波调制的基本原理,以便清晰了解载波调制的特点,并推导了NPC三电平可以完全控制中点电位波动的条件。针对虚拟空间矢量调制算法流程繁杂,计算量大以及不具备控制中点电位直流漂移能力的问题,根据NPC三电平逆变器拓扑结构和载波调制特点,提出了双调制波载波调制算法和中点电位直流漂移控制算法。经仿真验证了两种算法的有效性,结果显示所提出的双调制波载波调制算法占用内存最小,核心程序运行时间最短,控制效果和虚拟空间矢量调制算法基本一致。最后,设计并制作了硬件在环仿真平台控制板,通过硬件在环测试验证了SVPWM调制算法、虚拟空间矢量调制算法、双调制波载波调制算法和中点电位直流漂移控制算法的正确性。并搭建NPC三电平逆变器实验平台,验证了双调制波载波调制算法的有效性。更多还原

【Abstract】 Traditional fossil energy has become a constraint to national economic and social development due to its increasing lack,serious environmental pollution and low efficiency.Therefore,new energy sources such as wind power generation,photovoltaic power generation,electric vehicles,etc.,and new infrastructures have ushered in rapid development.In these me dium and high voltage high-power electrical energy conversion and AC drive scenarios,NPC three-level inverters have slowly phased out traditional two-level inverters with their advantages of low output harmonics and low switching stress.However,NPC three-level inverters also face the problems of neutral potential fluctuation and DC drift,which lead to output waveform distortion and over-voltage damage to switching devices.In this paper,based on the NPC three-level topology,we focus on suppressing the neutral potential fluctuation and controlling the neutral potential balance so that the THD of the output current meets the requirement of less than 5% at very low frequency(0.33～3Hz).This paper first introduces the topology of the NPC three-level inverter circuit,analyzes its working principle in depth,introduces the switching function,and establishes the mathematical model between the inverter output line voltage,phase voltage and switching function.Then the space voltage vector is introduced,and the root cause of neutral potential fluctuation is analyzed by establishing the mathematical model of neutral potential and neutral current,which provides the theoretical basis for controlling the neutral potential balance afterwards.Secondly,according to the influence of space voltage vector on neutral current,the modulation algorithm based on space vector is studied.Firstly,the basic principle and algorithm implementation of the nearest three vector method of traditional space vector modulation are specifically analyzed,and then two methods of suppressing neutral potential fluctuation,SVPWM modulation algorithm with redundant small vector neutral potential control and virtual space vector modulation algorithm,are proposed,which are verified by T he suppression effect of the virtual space vector modulation algorithm on the neutral point potential fluctuation is verified by simulation.After that,the basic principle of traditional single modulation wave carrier modulation is analyzed in detail in order to clearly understand the characteristics of carrier modulation,and the conditions under which the NPC tri-level can completely control the neutral point potential fluctuation are derived.To address the problems that the virtual space vector modulat ion algorithm is complicated in process,computationally intensive and does not have the ability to control the DC drift of neutral point potential,the dual modulating wave carrier modulation algorithm and the DC drift control algorithm of neutral point p otential are proposed according to the topology and carrier modulation characteristics of NPC three-level inverter.The effectiveness of the two algorithms is verified by simulation.The results show that the proposed dual-modulated-wave carrier modulation algorithm occupies the least memory,the core program has the shortest running time,and the control effect is basically the same as that of the virtual space vector modulation algorithm.Finally,the hardware-in-the-loop simulation platform control board is designed and fabricated,and the correctness of SVPWM modulation algorithm,virtual space vector modulation algorithm,dual modulated wave carrier modulation algorithm and midpoint potential DC drift control algorithm are verified by hardware-in-the-loop testing.And the experimental platform of NPC three-level inverter is built to verify the effectiveness of dual modulated wave carrier modulation algorithm.更多还原