有源箝位三电平光伏并网逆变器LVRT技术研究

发布时间：2019-04-16 16:54

【摘要】：随着光伏产业的不断升级,现今市场光伏逆变器的容量不断增大,光伏发电的占比逐渐增加,其安全性和可靠性受到越来越多的关注。其中,光伏逆变器的低电压穿越(LVRT)能力是考察一台机器好坏的重要性能指标,三相锁相环的精度以及并网和低电压穿越控制算法的好坏将直接影响到逆变器能否按照要求完成穿越任务。本文以实际项目为背景,针对传统三相锁相环在精度和抗干扰能力方面的不足,提出了一种改进的控制方法,并依托有源箝位三电平逆变器拓扑和低压穿越实验,验证提出理论的可靠性。论文采用有源箝位三电平电路作为逆变器主拓扑,分析了它的换流路径和调制策略。针对三电平逆变器固有的中点电位不平衡问题设计了一种控制方法,研究了不同开关矢量对中点电位的影响程度,利用注入零序参考电流控制中点电位的波动,并通过仿真验证算法的有效性。分析了基于同步坐标系锁相环(SRF-PLL)和基于双广义二阶积分器锁相环(DSOGI-PLL)的结构特点和应用环境,针对工程中常用的DSOGI-PLL锁相环在电网频率发生波动时易出现锁相精度降低的问题提出了一种改进方法,通过固定角频率输入和输出幅值补偿提升输出正交信号精度,减小频率波动。最后通过仿真比较了电网在各类跌落状态下三种锁相环的输出特性。基于逆变器的数学模型分别讨论了光伏逆变器在电网稳态和故障状态下的并网控制策略。按照逆变器低压穿越要求设计了一种基于无功功率支撑的穿越策略,在电压跌落时根据跌落深度设置不同的参考电流,详细分析了穿越过程中的控制逻辑,最后通过仿真对理论分析进行验证。搭建了1 MW实验平台,设计了样机主拓扑器件参数、部分硬件电路和软件流程图。在不同的工况下对光伏逆变器的输入输出特性和低压穿越能力进行了测试,分析了实验结果,验证了所提理论的有效性。
[Abstract]:With the continuous upgrading of PV industry, the capacity of PV inverter is increasing and the proportion of PV power generation is increasing, so the safety and reliability of PV inverter have been paid more and more attention. Among them, the low voltage traversing (LVRT) capability of photovoltaic inverter is an important performance index to investigate the quality of a machine. The accuracy of the three-phase-locked loop and the grid-connected and low-voltage traversal control algorithms will directly affect whether the inverter can complete the traversing task according to the requirements. In this paper, an improved control method is proposed to improve the accuracy and anti-jamming ability of the traditional three-phase-locked loop, which is based on the active clamp three-level inverter topology and the low-voltage traversal experiment, which is based on the actual project and the traditional three-phase-locked loop. The reliability of the proposed theory is verified. The active clamped three-level circuit is used as the main topology of the inverter, and its commutation path and modulation strategy are analyzed. Aiming at the inherent midpoint potential imbalance problem of three-level inverter, a control method is designed. The influence of different switching vectors on the midpoint potential is studied, and the fluctuation of the midpoint potential is controlled by injecting zero sequence reference current. The validity of the algorithm is verified by simulation. The structure characteristics and application environment of phase-locked loop (SRF-PLL) based on synchronous coordinate system and phase-locked loop (DSOGI-PLL) based on double generalized second-order integrator are analyzed. An improved method is proposed to improve the accuracy of DSOGI-PLL phase locked loop when the frequency fluctuates in the power network. The accuracy of the output orthogonal signal is improved by compensation of the input and output amplitude of the fixed angle frequency, and the accuracy of the output orthogonal signal is improved by using the fixed angle frequency input and output amplitude compensation. Reduce the frequency fluctuation. Finally, the output characteristics of three kinds of PLL under various sags are compared by simulation. Based on the mathematical model of inverter, the grid-connected control strategy of photovoltaic inverter under steady-state and fault-state is discussed respectively. According to the requirements of inverter low voltage traversal, a traversal strategy based on reactive power support is designed. When voltage sags, different reference currents are set according to the depth of sag, and the control logic in the process of traversing is analyzed in detail. Finally, the theoretical analysis is verified by simulation. The experiment platform of 1 MW is built, and the parameters of the main topology device, some hardware circuits and software flowchart of the prototype are designed. The input-output characteristics and low-voltage traversal ability of photovoltaic inverter are tested under different operating conditions, and the experimental results are analyzed to verify the effectiveness of the proposed theory.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM464

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