NPC型三电平半桥并网逆变器研究

发布时间：2018-01-10 22:07

本文关键词：NPC型三电平半桥并网逆变器研究　出处：《南京航空航天大学》2014年硕士论文　论文类型：学位论文

【摘要】：太阳能是目前利用比较广泛的新能源之一，光伏发电的容量及规模在不断地扩大。中点箝位(Neutral Point Clamped, NPC)型三电平半桥拓扑由于结构及控制相对简单，在高压大容量光伏并网逆变系统中应用广泛。本文主要研究单相NPC型三电平半桥逆变器的开关器件损耗分布、直流侧电容均压控制策略及其光伏并网逆变技术，其中，直流侧电容均压控制是需要解决的首要问题。本文详细分析了3种衍生NPC型三电平半桥拓扑(三电平有源NPC (Three-levelActive NPC,3L-ANPC)，三电平层叠NPC (Three-level Stacked NPC,3L-SNPC)，三电平有源层叠NPC(Three-level Active and Stacked NPC,3L-ASNPC))的零电平续流路径的特点，分别总结了4种SPWM调制策略。在此基础上，研究了各调制策略对NPC型拓扑开关器件损耗分布的影响，与传统3L-NPC拓扑相比，衍生NPC型拓扑结构及其SPWM调制策略的变化不仅可以改善开关器件损耗分布的均衡程度，而且开关器件的总损耗基本不变。根据各拓扑开关器件损耗分布的特点可得：传统3L-NPC拓扑适用于中小功率场合；3L-ANPC拓扑不易调节开关器件的损耗；3L-SNPC拓扑易于改善开关器件的损耗分布，适用于大功率场合；3L-ASNPC拓扑结构复杂，无明显优势。本文从频域和时域角度详细分析了3L-NPC拓扑直流侧电容电压的自平衡特性，即当存在电容压差时，电容电流中将产生相应的直流分量来消除电容压差，该直流分量主要来源于桥臂输出电流的直流分量及开关频率附近的偶次谐波分量。根据自平衡特性，本文总结了两类均压控制思想：A)直接或间接地对电容压差进行闭环控制，消除引起电容电压不均衡的因素；B)采用恰当的调节器或控制结构，以保证闭环控制时3L-NPC依然具有自平衡特性。其中，B类均压控制策略无需检测电容电压，可简化系统控制，降低系统成本。本文搭建了5kW NPC型三电平半桥逆变器的统一实验平台，该平台采用LCL滤波器以及基于电容电流比例反馈的双电流闭环并网控制策略。通过Saber软件仿真及对统一实验平台的实验研究，分别验证了4种SPWM调制策略及A类和B类均压控制策略的可行性；通过对比各NPC型拓扑的并网效率，验证了NPC型拓扑结构及SPWM调制策略的变化对系统的总体效率基本没有影响，，与理论分析相吻合。
[Abstract]:Solar energy is one of the new energy sources which is widely used at present. The capacity and scale of photovoltaic power generation is expanding continuously. Neutral Point Clamped is clamped at the midpoint. NPC-type three-level half-bridge topology is relatively simple because of its structure and control. It is widely used in high voltage and large capacity photovoltaic grid-connected inverter system. This paper mainly studies the switching device loss distribution of single-phase NPC three-level half-bridge inverter. DC side capacitor voltage equalizing control strategy and photovoltaic grid-connected inverter technology, among which, DC side capacitance voltage sharing control is the most important problem to be solved. In this paper, three kinds of derived NPC three-level active NPC3L-ANPCs (three-level active NPC-NPC-3L-ANPCs) are analyzed in detail. Three-level Stacked NPC-3L-SNPC). The characteristics of zero-level continuation paths of three-level active cascading NPC(Three-level Active and Stacked NPC-3L-ASNPCs. Four kinds of SPWM modulation strategies are summarized respectively. On this basis, the effects of each modulation strategy on the loss distribution of NPC topology switching devices are studied, compared with the traditional 3L-NPC topology. The variation of derivative NPC topology and its SPWM modulation strategy can not only improve the loss distribution equalization of switching devices. According to the characteristics of the loss distribution of each topology switch device, the traditional 3L-NPC topology is suitable for medium and small power situations; 3L-ANPC topology is not easy to adjust the loss of switch devices; 3L-SNPC topology is easy to improve the loss distribution of switching devices and is suitable for high-power applications. The topological structure of 3 L-ASNPC is complex and has no obvious advantage. In this paper, the self-balancing characteristics of DC side capacitor voltage of 3L-NPC topology are analyzed in detail in frequency domain and time domain, that is, when there is capacitance voltage difference. A corresponding DC component will be produced in the capacitor current to eliminate the capacitance voltage difference. The DC component is mainly derived from the DC component of the output current of the bridge arm and the even harmonic component near the switching frequency. In this paper, two kinds of equalizing voltage control ideas: 1 A) are summarized to control the capacitance voltage difference directly or indirectly, to eliminate the factors that cause the capacitance voltage imbalance. B) A proper regulator or control structure is adopted to ensure that 3L-NPC still has self-balancing characteristics in closed-loop control. Class B voltage equalization control strategy does not need to detect capacitance voltage, so it can simplify the system control. Reduce system cost. In this paper, a unified experimental platform of 5kW NPC three-level half-bridge inverter is built. The platform adopts LCL filter and double-current closed-loop grid-connected control strategy based on capacitive current proportional feedback. The simulation of Saber software and the experimental research on the unified experimental platform are carried out. The feasibility of four SPWM modulation strategies and the A and B voltage sharing control strategies are verified respectively. By comparing the grid connection efficiency of each NPC topology, it is verified that the variation of NPC topology and SPWM modulation strategy has no effect on the overall efficiency of the system, which is consistent with the theoretical analysis.
【学位授予单位】：南京航空航天大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM464

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