随着光伏发电在电力系统中的渗透率日益增加，虽然有效地缓解了我国的能源问题，但光伏系统与电网运行之间的相互影响也越来越大。低电压穿越(Low Voltage Ride Through, LVRT)技术的应用有效协调了两者之间的关系，对于大规模光伏并网具有重要意义。由于光伏并网低电压穿越过程中存在多个非线性环节且控制要求高，现有控制方法存在动态响应与静态稳定能力不足的问题。因此，为满足光伏并网低电压穿越高性能高质量的要求，本文利用滑模非线性控制能力强与响应速度快的特点，提出了一种双幂次非奇异快速终端滑模(Double Powered-Nonsingular Fast Terminal Sliding Mode, DP-NFTSM)控制的光伏并网低电压穿越方法。本文主要工作如下：

本文根据光伏并网系统各模块数学模型基础上，推出系统内部之间的信号传输特性。在此基础上，分析了电网发生对称故障和不对称故障时，故障类型与光伏并网低电压穿越期间系统特性变化的规律。然后，以典型比例积分(Proportional Integral, PI)控制为例，分析在传统控制方法下，光伏并网低电压穿越中所存在的问题，结果表明：传统低电压穿越控制中仍存在系统响应速度慢、暂态性能差、谐波含量高与振荡严重等问题。

为了提高光伏并网低电压穿越能力，本文将双幂次趋近律与非奇异快速终端滑模面相结合，提出了一种DP-NFTSM控制方法，并将该方法与电网对称故障下的光伏并网低电压穿越模型相融合，设计出具有全局快速收敛的光伏并网低电压穿越控制器。基于实时数字模拟(Real Time Digital Simulation, RTDS)装置、功率放大器与动态电压恢复器(Dynamic Voltage Restorer, DVR)构建的有源配网低电压穿越实验系统，验证电网对称故障时，本文所提出的低电压穿越控制方法的有效性，与PI控制、积分滑模(Integral Sliding Mode, ISM)控制相比，该方法响应速度快、暂态特性好、抑制抖振能力强与电能质量高。

针对电网发生不对称故障时，光伏并网系统电压电流中同时存在正序与负序分量，导致并网电流发生畸变与有功、无功功率产生二倍频波动，进而对低电压穿越期间电网与光伏系统产生不良影响。为解决这些问题，本文先采用双三阶广义积分器(Double Three Order Generalized Integrator, DTOGI)实现不对称故障下光伏并网系统正负序信号的提取与电压跌落检测。再针对并网电流畸变与有功、无功功率二倍频波动的问题，通过分析光伏并网系统输出电流与功率特性的基础上，提出了分别抑制电流负序、有功二倍频与无功二倍频分量的三种不对称故障低压穿越控制目标，并将三种控制目标与DP-NFTSM控制相结合，设计出不对称故障下多目标的低电压穿越DP-NFTSM控制器。通过有源配网低电压穿越实验系统，验证本文所提三种控制目标的可行性与DP-NFTSM控制在不对称故障低电压穿越中的优越性。

With the increasing penetration rate of photovoltaic (PV) power generation in the power system, although it has effectively alleviated the energy problem in our country, the mutual influence between the PV system and the power grid operation is also increasing. The application of Low Voltage Ride Through (LVRT) technology effectively coordinates the relationship between the two, which is of great significance for large-scale PV grid-connection. Because there are many nonlinear links and high control requirements in the process of PV grid-connected LVRT, the existing control methods have insufficient dynamic response and static stability. Therefore, in order to meet the requirements of high performance of PV grid-connected LVRT, this thesis takes advantage of the characteristics of strong sliding mode nonlinear control ability and fast response speed. A LVRT method controlled by Double Powered-Nonsingular Fast Terminal Sliding Mode (DP-NFTSM) is proposed. The main work of this thesis is as follows:

Based on the mathematical models of various modules in PV grid-connected systems, this thesis deduces the signal transmission characteristics within the system. On this basis, the pattern of fault types and changes in system characteristics during the LVRT of PV grid-connected systems under symmetric and asymmetric grid faults is analyzed. Subsequently, taking the typical Proportional-Integral (PI) control as an example, this thesis analyzes the issues encountered in the LVRT of PV grid-connected systems under traditional control methods. The results indicate that traditional LVRT control still faces problems such as slow system response, poor transient performance, high harmonic content, and severe oscillations.

In order to improve the LVRT ability of PV grid-connected, a DP-NFTSM control method is proposed by combining the double power reaching law with the non-singular fast terminal sliding mode surface, and a PV grid-connected LVRT controller with global fast convergence is designed by combining the method with the PV grid-connected LVRT model under symmetrical faults. Based on an active distribution network experimental system constructed with Real-Time Digital Simulation (RTDS) equipment, a power amplifier, and a Dynamic Voltage Restorer (DVR), the effectiveness of the proposed LVRT control method during grid symmetric faults is verified. Compared with PI control and Integral Sliding Mode (ISM) control, the proposed method has fast response speed, good transient characteristics, strong buffeting suppression ability and high power quality.

When asymmetric faults occur in the power grid, positive and negative sequence components coexist in the voltage and current of the PV grid-connected system, leading to distortion of the grid-connected current and double-frequency fluctuations in active and reactive power, thereby affecting the grid and PV system during LVRT. To solve these problems, a Double Three Order Generalized Integrator (DTOGI) is used to extract positive and negative sequence signals and detect voltage drop in PV grid-connected systems under asymmetric faults. Based on the analysis of the output current and power characteristics of PV grid-connected system during asymmetric faults, three kinds of asymmetric fault LVRT control targets are proposed to suppress negative sequence current, active power double frequency and reactive power double frequency components respectively. By combining three control objectives with DP-NFTSM control, a multi-target LVRT DP-NFTSM controller under asymmetric faults is designed. The feasibility of the three control objectives proposed in this thesis and the superiority of DP-NFTSM control in asymmetric fault LVRT are verified by RTDS experimental platform.