【作者】 刘飞；

【导师】 段善旭；

【作者基本信息】 华中科技大学 ， 电气工程， 2008， 博士

【摘要】 鉴于光伏发电在全球电力能源结构中的战略地位,太阳能完全具备成为未来主要供应能源的潜力,因此光伏并网发电技术成为了重要的研究方向。本文以三相光伏并网发电系统的控制策略为研究对象,深入分析其工作原理并建立数学模型,针对光伏阵列的最大功率点跟踪方法、单级式和两级式并网发电系统的控制策略以及并网滤波器的设计原理等问题进行全面系统的研究。首先,本文根据太阳能电池的电气特性以及光伏阵列在不同的光照强度和环境温度下的输出特性,分别对目前几种经典的定步长和变步长的最大功率跟踪(MPPT)方法进行理论分析,并结合DC/DC推挽电路的实验台架上进行实验验证;此外分析了光伏系统启动时的由于采样误差而造成对实际功率计算产生严重偏差的影响,在此基础上提出了采用恒压法(CVT)启动的方法来改善系统的启动特性,通过实验验证了其改善后的启动性能。由于单级式三相光伏并网发电系统中存在光照强度突然减弱而引起的直流母线下降甚至崩溃的问题,在常规的扰动观测法的基础上提出了一种改进方案,通过在单级式三相光伏并网发电系统中验证了该方案的可行性。其次,分析了三相光伏并网逆变器的工作原理和拓扑结构,建立三相光伏并网逆变器的状态空间数学模型。基于三相光伏并网逆变器控制策略的研究现状,以并网滤波器为切入点研究采用不同滤波器的三相光伏并网逆变器的控制方案,尤其是重点研究基于LCL滤波器的三相并网光伏逆变器的控制策略。同时总结L型、LC型滤波器的设计原理,并且分析了在并网逆变器控制为电流源并网时采用LCL型滤波器的优势,针对目前国内外LCL型滤波器的设计方法,分析几种设计方法的优缺点,提出了在尽量节约总的电感磁心材料的前提下,设计出滤波效果最优的LCL型滤波器的参数值,同时还保证LCL型滤波器的谐振频率不能太小,以免成为制约电流控制器设计时的因素,并给出设计实例。然后,通过分析dq坐标系下采用LCL型滤波器的三相并网逆变器的数学模型,可以看出由于采用了LCL型滤波器,d轴和q轴上的控制变量之间具有强耦合作用。如果通过状态反馈解耦控制会使控制系统设计起来非常复杂,于是本文基于αβ坐标系采用了基于并网电流外环电容电流内环电流的双环控制策略,并提出了一套合理的控制器参数设计方法,针对PI控制器在静止坐标系下跟踪正弦指令不能完全实现零稳态误差的问题,引入PR谐振控制器,通过仿真和实验详细地对比分析相同参数下PI控制器与PR控制器的性能。为了满足IEEE Std 929-2000标准以及国内关于光伏系统并网技术要求中对并网电流波形畸变的规定,考虑LCL谐振峰抑制问题,提出了基于状态反馈极点配置与重复控制相结合的控制策略,利用LCL型滤波器的电感电流和电容电压的反馈量,将系统的闭环极点配置在所希望的位置,从而获得满意的动态特性,另外利用重复控制改善状态反馈控制的稳态性能,提高波形质量,使系统兼具良好的动态、静态性能,能满足光伏并网控制的性能要求,并在三相光伏并网逆变器的实验台架上分别采用以上提出的两种并网控制方案实现并网运行,同时进行并网电流控制策略的实验验证。最后,深入分析两级式三相并网光伏发电系统的运行特点以及两级变换器之间的配合问题,总结了两种不同的控制策略,并结合理论研究,在DC/DC推挽试验系统和三相光伏并网试验系统的基础上搭建两级式三相并网光伏发电系统仿真模型,并重点进行控制策略的仿真研究。更多还原

【Abstract】 Due to the important status of solar power in the global power energy system, solar resource has the potential to be the main alternative energy source to replace traditional ones in the future. Therefore PV grid-connected generating technology becomes an important research field. This thesis focuses on control strategies in three-phase grid- connected PV systems, which includes modeling of three-phase grid-connected PV systems, maximum power point tracking(MPPT) methods for PV arrays, grid-connected control of single-stage and two-stage PV system and filter design method.Firstly, the electrical characteristic and output characteristic of solar cell act a vital role in solar research, especially in MPPT research. This thesis presents theoretical analysis and experimental results based on a DC/DC push-pull topology of constant step-size and variable step-size MPPT methods. Furthermore the serious power loss caused by sampling error in the starting stage is analyzed, and an improved strategy is proposed that constant voltage tracking method is adopted when PV system startup. Avoiding the collapse of the DC bus voltage of the single-stage three-phase system when the irradiation changes greatly, an improved method based on the traditional P&O method is proposed. And the viability of this method is verified by experiments on the one-stage three-phase platform.Then the topology and principle of three-phase PV grid-connected inverter are analyzed and the mathematical model of the system is established. Based on the contemporary research of grid-connected control strategies, this thesis analyzes different methods by categorizing them according to different grid-connected filters. Summarize the design principles of L and LC filter, this thesis gives out the advantages of LCL filter when treating the system as a current source. Comparing several design methods of LCL filter, an optimal method is used to give out the parameters of the filter while ensure the less use of inductance magnetic materials, good performance in filtering and high resonant frequency. And a design sample is also given.By analyzing model of grid-connected inverter with LCL filter under dq axis, it is obvious that the control variables of have strong coupling under dq coordinate. It is very complicated to decoupling, so a two-loop control strategy underαβcoordinate is adopted which chooses the capacitor current as the inner control variable and grid-connected current as the outer loop variable. Moreover, a designing method is given to get the parameters of the two-loop controller. In order to cover the static error of the PI controller under stationary coordinate, PR controller is adopted. The performances of PI and PR controller with the same parameters are compared through experiments and simulation.In order to satisfy the IEEE Std 929-2000 standard and the requirements of the grid-connected system in China, a hybrid controller incorporating repetitive control and state feedback pole-assignment control is proposed. Utilizing the feedback of inductance current and capacitor voltage, the system poles can be assigned as wish to achieve good dynamic performance. Besides, the repetitive controller is adopted to improve the static performance which can modify the quality of the grid-connected current to accord with the grid-connected requirement. The two mentioned control strategies are realized based on the three-phase PV grid-connected system. The experimental results prove the availability of the two strategies.Finally analyzing the operation characteristic of two-stage grid-connected PV system, as well as the co-ordination problem between the two converters, two different control strategies are analyzed. The experimental platform is based on the combination of the DC/DC push-pull converter and the three-phase inverter. The availability of the control strategy is verified by simulation.更多还原