单相级联多电平光伏并网逆变器的控制研究

发布时间：2019-03-22 18:33

【摘要】：级联多电平逆变器输出电压波形为正弦式阶梯波,含有的谐波量很低,降低了对电压滤波的要求,这大大减小了所应用系统的体积,而且其本身具有很强的抗干扰能力,因此其在光伏发电的领域有着不可估量的发展前景。本论文对基于混合级联七电平逆变器的光伏并网系统进行研究,重点研究了逆变器的调制方法,分析了基于载波水平移相和载波垂直移相调制技术,并在此基础上设计了变载波频率调制方法,仿真验证了变载波频率调制方法在混合级联七电平逆变器上应用的可行性。首先,本文对光伏并网逆变器的拓扑结构及存在的实际问题进行阐述,并分析了多电平逆变器的拓扑结构,重点研究了单相级联和混合级联七电平逆变器,比较了二者的拓扑结构,输出电压特性,最终选定单相混合级联七电平逆变器作为本文的研究对象。其次,针对混合级联七电平并网逆变器,其主要调制方法包括阶梯波EPWM调制法和多载波SPWM调制法。本文针对这两种不同方法的实现过程及在系统中应用的优缺点进行分析。并提出三角载波频率可变的,且相邻载波相位相反的变载波频率调制策略,仿真验证了该调制方法可实现七电平输出电压,并避免逆变器功率倒送现象的发生。再次,本文分析了基于混合级联七电平逆变器的并网光伏系统控制策略。对光伏电池的输出特性、独立MPPT控制进行仿真,并重点分析了电流内环、电压外环的控制策略。在采用控制器上,比较电流内环采用PI或准PR控制器对电网系统性能影响并利用Matlab仿真验证。最后,对上述光伏系统的设计方案进行了阐述,硬件设计主要包含采样电路设计、PWM脉冲设计、锁相设计。软件设计主要包括主程序与中断程序。
[Abstract]:The output voltage waveform of cascaded multilevel inverter is sine ladder wave, which contains very low harmonic wave and reduces the requirement of voltage filtering, which greatly reduces the volume of the applied system and has strong anti-interference capability. Therefore, it has an inestimable development prospect in the field of photovoltaic power generation. In this paper, the photovoltaic grid-connected system based on hybrid cascade seven-level inverter is studied, the modulation method of the inverter is mainly studied, and the technology of carrier horizontal phase shift and carrier vertical phase shift modulation are analyzed. On the basis of this, the variable carrier frequency modulation method is designed, and the feasibility of the variable carrier frequency modulation method in hybrid cascade seven-level inverter is verified by simulation. Firstly, the topology and practical problems of photovoltaic grid-connected inverter are described. The topology of multi-level inverter is analyzed, and the single-phase cascade seven-level inverter and hybrid cascade seven-level inverter are mainly studied. After comparing their topology and output voltage characteristics, the single-phase hybrid cascade seven-level inverter is selected as the research object of this paper. Secondly, for hybrid cascade seven-level grid-connected inverter, the main modulation methods include step-wave EPWM modulation and multicarrier SPWM modulation. This paper analyzes the implementation process of these two different methods and the advantages and disadvantages of their application in the system. A variable carrier frequency modulation strategy with variable trigonometric carrier frequency and opposite adjacent carrier phase is proposed. The simulation results show that this modulation method can achieve seven-level output voltage and avoid the occurrence of inverter power reversal. Thirdly, the control strategy of grid-connected photovoltaic system based on hybrid cascade seven-level inverter is analyzed. The output characteristics of photovoltaic cells and independent MPPT control are simulated, and the control strategies of current inner loop and voltage outer loop are analyzed. On the controller, the influence of PI or quasi-PR controller on the performance of power system is compared and verified by Matlab simulation. Finally, the design scheme of the above photovoltaic system is described. The hardware design mainly includes sampling circuit design, PWM pulse design and phase locked design. Software design mainly includes main program and interrupt program.
【学位授予单位】：天津大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM464;TM615

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