三电平光伏并网逆变器的控制

发布时间：2018-04-09 11:57

本文选题：并网逆变器　切入点：三电平　出处：《华南理工大学》2014年硕士论文

【摘要】：与传统的两电平并网逆变器相比，三电平并网逆变器的开关器件承受电压低、输出电流谐波含量少、开关频率低和电磁干扰小，在高压、大功率场合得到了广泛应用。然而，三电平并网逆变器开关器件和控制目标较多，控制较复杂，为了提高光伏并网逆变器性能和效率，需要对三电平并网逆变器的控制系统进行合理设计。为此本文对三电平光伏并网逆变器的控制技术进行研究，本文的主要研究内容如下： 1、对比分析了传统三电平逆变器拓扑的优缺点，给出了一种T型三电平逆变器拓扑，与二极管钳位型相比，该拓扑具有成本低、功耗小且能平衡所有开关损耗的优点，基于此拓扑建立了三电平光伏并网逆变器的数学模型，为系统的控制设计打下基础。 2、对三电平光伏并网逆变器的控制技术进行了分析，选择对模型预测控制技术进行深入研究，该控制技术相比于传统的控制技术控制灵活，通过调整目标函数的权重因子即可实现对三电平光伏并网逆变器综合性能的优化，且无需调制器，直接根据目标函数选择最优的开关状态，在电流跟踪性能和中点电位平衡控制方面具有较快的响应速度。在分析模型预测控制基本原理的基础上，建立了三电平光伏并网逆变器的离散预测模型和目标函数，并对传统模型预测控制技术存在的延时、计算量大的问题，，给出解决方案。 3、分析了电网不平衡时三电平并网逆变器的基本问题，给出了基于模型预测控制的抑制并网电流负序分量的不平衡控制技术，针对不平衡电网下需要检测电网电压正负序分量和传统锁相环无法快速准确地锁定电网电压相位的问题，给出了基于解耦的双同步坐标系的正负序分离方法和锁相方法，该方法可以在不平衡电网下快速准确地检测电网电压正负序分量并锁定电网电压相位。 4、基于Matlab/Simulink搭建了系统仿真模型，对三电平光伏并网逆变器的模型预测控制效果进行了仿真分析，仿真结果表明本文设计的模型预测控制器能够很好地跟踪参考电流，控制中点电位平衡，且在不平衡电网下控制输出电流平衡，动态和稳态性能较好。 5、在仿真分析的基础上，设计了三电平光伏并网逆变器的硬件和软件系统，搭建了30kW三电平光伏并网逆变器实验电路，通过实验验证了模型预测控制技术的有效性。实验结果表明本文设计的模型预测控制器能够很好地控制并网电流和中点电位平衡，且并网电流THD较小，系统功率因数较高，符合系统设计要求。
[Abstract]:Compared with the traditional two-level grid-connected inverter, the three-level grid-connected inverter is widely used in high-voltage and high-power applications because of its lower voltage, less harmonic output current, lower switching frequency and less electromagnetic interference.However, there are many switching devices and control targets for the three-level grid-connected inverter and the control is more complex. In order to improve the performance and efficiency of the photovoltaic grid-connected inverter, it is necessary to design the control system of the three-level grid-connected inverter reasonably.Therefore, the control technology of three-level photovoltaic grid-connected inverter is studied in this paper. The main contents of this paper are as follows:1. The advantages and disadvantages of the traditional three-level inverter topology are analyzed, and a T type three-level inverter topology is presented. Compared with the diode clamping type, the topology has the advantages of low cost, low power consumption and balance of all switching losses.Based on this topology, the mathematical model of the three-level photovoltaic grid-connected inverter is established, which lays a foundation for the control design of the system.2. The control technology of three-level photovoltaic grid-connected inverter is analyzed, and the model predictive control technology is deeply studied. The control technology is more flexible than the traditional control technology.By adjusting the weight factor of the objective function, the comprehensive performance of the three-level photovoltaic grid-connected inverter can be optimized, and the optimal switching state can be selected directly according to the objective function without modulator.It has fast response speed in current tracking performance and midpoint potential balance control.On the basis of analyzing the basic principle of model predictive control, the discrete prediction model and objective function of three-level photovoltaic grid-connected inverter are established.3. The basic problems of three-level grid-connected inverter in unbalanced power network are analyzed, and the unbalanced control technology based on model predictive control is presented to suppress the negative sequence component of grid-connected current.In order to solve the problem that it is necessary to detect the positive and negative sequence components of power network voltage and the traditional phase-locked loop can not lock the voltage phase quickly and accurately under unbalanced power grid, a method of separating positive and negative sequence and phase lock based on decoupled double synchronous coordinate system is presented.This method can quickly and accurately detect the positive and negative sequence components and lock the voltage phase in unbalanced power systems.4. The system simulation model based on Matlab/Simulink is built, and the model predictive control effect of three-level photovoltaic grid-connected inverter is simulated and analyzed. The simulation results show that the model predictive controller designed in this paper can track the reference current well.The dynamic and steady performance of the output current balance is better than that of the control of the neutral point potential balance and the output current balance under the unbalanced power network.
【学位授予单位】：华南理工大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM464;TM615

【参考文献】