【作者】 任碧莹；

【导师】 钟彦儒； 同向前；

【作者基本信息】 西安理工大学 ， 电力电子与电力传动， 2009， 博士

【摘要】 随着世界能源危机和环境污染日趋严重,光伏发电系统受到各国政府的高度重视。特别是户用式光伏发电系统,作为未来光伏应用中重要领域之一,应用前景十分广阔,成为当前国内外学者研究的热点。本文针对户用式单相光伏并网发电系统,在最大功率点跟踪算法、数字锁相环、并网电流控制和孤岛保护等控制策略方面分别进行了深入的理论分析和探讨。首先,针对光伏电池的电流-电压非线性特性及其受光照强度和电池温度影响的特点,在描述了光伏电池原理基础上,研究了光伏电池外特性机制和物理特性机制,分别建立了各自的仿真模型。根据仿真结果与实测数据的对比分析,验证了模型的正确性,为进一步研究最大功率点跟踪算法以及深入研究并网控制策略奠定了良好的基础。其次,深入研究了光伏阵列最大功率点跟踪问题。在详细介绍常规的最大功率点跟踪方法基础上,提出了一种新颖的间歇变步长搜索算法,包括定时变步长搜索和定时定占空比控制两个过程。在起动阶段或外界环境变化较大时,以较短定时时间间隔连续进行变步长跟踪搜索,确保快速达到最大功率点；在外界环境变化较小时,维持较长定时时间的最优定占空比控制。仿真与实验结果验证了该新方法不仅可以有效降低持续扰动而引起的功率波动,而且即使在外界条件变化时也能实现快速跟踪最大功率点。第三,深入探讨了一种数字锁相环的实现方法。在分析了三相并网锁相控制方法基础上,结合有限冲击响应(FIR)数字滤波器具有线性相移的特点,提出了基于有限冲击响应数字滤波器线性相移控制的单相数字锁相环方法。设计了有限冲击响应滤波器,构建了两相正交电压矢量信号,参照三相并网系统基于αβ静止坐标系到dq同步旋转坐标系的数字锁相环原理,采用同步采样技术确保滤波器系数恒定的方法,实现了基于虚拟两相直角坐标系的数字锁相环控制。该方法能够快速准确地实现锁相,而且不受谐波、电压频率和幅值波动等因素影响,并通过仿真和实验结果进行了验证。第四,针对传统的预测电流控制方法在滤波电感参数不匹配时可能出现的稳态相位差甚至系统不稳定问题,提出了一种用于预测电流控制的滤波电感参数在线估计方法。通过简化单相光伏并网发电系统的等效电路,建立了平均电感参数的在线估计方程。针对电感参数变化、逆变器输出电流幅值变化以及注入一定的谐波电流、电网电压幅值变化和注入一定幅值的谐波电压等各种情况,进行了仿真和实验研究,结果表明该方法有效地解决了滤波参数不匹配带来的问题。最后,深入研究了两种新型的孤岛检测方法。针对被动检测方法中的过/欠电压、过/欠频率检测法和主动检测法中常用的主动频率偏移法存在的孤岛检测盲区问题,分别提出了基于交替电流扰动法的孤岛检测方法和2N周期扰动法的孤岛检测方法。这两种方法都是打破了单纯依靠检测公共耦合点电压频率是否超出规定频率范围的判断准则,而是根据公共耦合点相邻周期间的电压频率差是否正负连续交替变化来有效地识别非检测区内的孤岛现象。为防止多台并网逆变器输出的扰动电流相互抵消而引起的无法识别孤岛现象,又提出了多台逆变器并网孤岛检测同步技术。仿真和实验结果验证了上述方法既能够识别各种条件下的孤岛现象,也可以解决非检测区问题,同时适用于多台逆变器并网运行。更多还原

【Abstract】 All over the world focus on the photovoltaic (PV) generation system seriously due to the worldwide energy crisis and worse and worse environment pollution. Especially, residential PV generation system will be one of the most important fields in the PV application in the near future and its foreground will be very wide, therefore, it becomes the research highlight for many scholars.In this thesis, the control strategies including the maximum power point tracking (MPPT), digital phase-locked loop (DPLL), grid-connected current control and islanding detection strategy have been analyzed in detail for the residential single-phase PV grid-connected generation system.Firstly, as for theⅠ-Ⅴnonlinearity characteristics of PV cells and the influence of irradiation intensity and temperature on PV cells, the outsideⅠ-Ⅴcharacteristics and physical characteristics are developed and their simulation models are built respectively on the basis of the working principle of PV cells. Compared the simulation results with experimental data of PV cells, the above models are proved to be right and it provides an excellent simulation platform to realize MPPT method and study the control strategy for the grid-connected generation system in depth.Secondly, the MPPT method of PV array is studied in detail. Based on the introduction of regular MPPT methods, the novel MPPT method based on intermittent step-varied search is proposed, it is composed of two control processes including step-varied timing search and constant duty ratio timing control. When the PV system starts up or the environment changes strongly, step-varied search is implemented at intervals of the shorter timing to track the maximum power point (MPP) quickly. When the environment changes slightly, the optimal constant duty ratio is utilized for a longer timing. The simulation and experimental results prove that this method can reduce the tracking power loss caused by the continuous perturbation, and track the MPP fast even under the quick environment change.Thirdly, a digital phase-locked loop (DPLL) method is developed. On the basis of description of the PLL method for the three-phase grid-connected system, a single-phase DPLL method based on the linear phase-shifted control of the finite impulse response (FIR) filter is proposed. The FIR filter is designed to construct two-phase quarter voltage vector signals. According to the DPLL principle by means of the transformation fromαβstationary reference to dq synchronously rotating reference for a three-phase system, and the synchronously sampling technique used to ensure the constant filter order, a DPLL based on a fictitious two-phase quarter coordinate transformation for a single-phase grid-connected power conversion system is implemented. The simulation and experimental results validate that this method can realize PLL quickly and it is not influenced by such conditions as voltage harmonics and the fluctuations of the voltage frequency and amplitude.Fourthly, an on-line estimated method of the filter inductance for the predictive current control is analyzed. The equivalent circuit for a single-phase PV grid-connected generation system is simplified, on-line estimated equation of the average filter inductance is given. Some conditions such as filter inductance change, magnitude change of output current and injected harmonic current, magnitude change of AC grid voltage and injected harmonic voltage are studied by the simulation and experiments, the results verify the method solves the problems which are the steady-state phase error and system instability in the conventional predictive current control system when the filter inductance changes.Lastly, two novel islanding detection methods are studied in depth. Owing to the islanding non-detection zone (NDZ) problem for over-/under-voltage protection (OVP/UVP) and over-/under-frequency protection (OFP/UFP) in passive detection methods and active frequency drift (AFD) in active detection methods, islanding detection methods based on the alternative current disturbance and the 2N period current disturbance are proposed, respectively. The proposed two methods depend on the voltage period error between the 2Nth and (2N+1)th period at the point of common coupling (PCC) changes alternately in the form of the positive and negative signs to identify the NDZ islanding phenomenon, they do not simply judge whether the voltage frequency at the PCC is beyond the presetting frequency range. In order to prevent the counteraction of current disturbance generated by some grid-connected inverters, the synchronous control strategy of islanding detection for the grid-connected inverters is proposed. The simulation and experimental results verify that two methods can not only identify the islanding very well, but also solve the NDZ problem, and some grid-connected inverters may operate synchronously.更多还原