并联三相PWM变换器不平衡运行条件下电流控制

发布时间：2018-05-09 13:11

本文选题：三相PWM变换器 + 不平衡　；参考：《哈尔滨工业大学》2014年硕士论文

【摘要】：在光伏发电系统中，变换器模块并联是提高功率等级，增加并网容量的有效途径。随着光伏并网容量的不断增加，新的并网规则对系统的可靠性有了更高的要求。在光伏并网系统中，并网滤波器以电感为主。实际使用的三相滤波电感之间往往存在一定的差异，对变换器输出电流和并联系统模块间的环流都会产生影响。而实际电网时常出现的不平衡现象也会影响光伏系统的正常运行。为此，本文主要研究了变换器并联系统不平衡运行条件下的控制策略。本文首先在同步旋转坐标系下建立了电感不平衡条件下变换器数学模型，在此基础上分析了电感不平衡对变换器输出电流的影响；从排除电感不平衡影响的角度出发，在传统PI电流控制方法的基础上，提出了一种电流解耦控制策略，并将其动态性能与不平衡条件下正负序双同步旋转坐标系方法(DSRF)和正序同步旋转坐标系下的PIR方法进行了分析和对比。研究表明，电感不平衡会导致变换器的输出电流不平衡，而为了消除这一不利影响所提的的电流解耦控制策略能够有效解决电感不平衡带来的不利影响，保证变换器的输出电流平衡；相比于DSRF方法和PIR方法，所提的解耦控制方法在输出电流变化时，具有更快的动态响应。变换器并联控制是本文研究的重点。模块直接并联会带来环流问题，环流会使变换器的输出电流畸变，影响并联系统的均流效果，降低变换器的电能转换效率。三相平衡时，零序环流是环流的主要成分。因此，本文先是根据正序同步旋转坐标系下所建立的并联系统的数学模型分析了电感不平衡对零序环流的影响，在传统PI环流抑制方法的基础上，提出了一种前馈控制策略。研究表明，三相电感不平衡时，传统PI方法的环流抑制效果会变差，而本文所提的前馈控制方法能够有效解决电感不平衡条件下并联系统的环流问题，获得良好的电流控制效果。实际电网普遍存在不平衡波动。电网和电感不平衡均容易导致变换器的输出电流不平衡甚至畸变，影响并联系统的正常运行。为此，本文利用对称分量法分析了电网和电感不平衡对环流成分的影响，，并提出了并联系统在电网或电感不平衡运行条件下的协调控制方案。研究表明，电网和电感不平衡条件下模块间会产生负序环流，导致变换器输出电流不平衡和畸变，影响并联模块均流效果。本文所提协调控制方案能够有效解决电网和电感不平衡带来的不利影响，保证并联系统不平衡条件下的可靠运行。
[Abstract]:In photovoltaic power generation system, parallel converter module is an effective way to improve power level and increase grid-connected capacity. With the increasing of photovoltaic grid-connected capacity, the new grid-connected rules have higher requirements for the reliability of the system. In photovoltaic grid-connected systems, grid-connected filters are mainly inductors. The actual use of three-phase filter inductors often has some differences, which will have an impact on the output current of the converter and the circulation between the modules of the parallel system. The unbalanced phenomena often occur in the actual power grid will also affect the normal operation of photovoltaic systems. Therefore, this paper mainly studies the control strategy under the condition of unbalanced operation of the converter parallel system. In this paper, the mathematical model of the converter under the condition of inductance unbalance is established in the synchronous rotating coordinate system, and the influence of the inductance imbalance on the output current of the converter is analyzed. Based on the traditional Pi current control method, a current decoupling control strategy is proposed. Its dynamic performance is analyzed and compared with the positive and negative order double synchronous rotation coordinate system (DSRF) and the positive sequence synchronous rotation coordinate system (PIR) under unbalanced conditions. The results show that the unbalanced inductance will lead to the unbalanced output current of the converter, and the current decoupling control strategy proposed in order to eliminate this adverse effect can effectively solve the adverse effects caused by the unbalance of the inductance. Compared with the DSRF method and the PIR method, the proposed decoupling control method has a faster dynamic response when the output current changes. Parallel control of converters is the focus of this paper. The direct parallel connection of the modules will bring the circulation problem, which will make the output current distortion of the converter, affect the current-sharing effect of the parallel system, and reduce the power conversion efficiency of the converter. In three-phase equilibrium, the zero sequence circulation is the main component of the circulation. In this paper, the influence of inductance imbalance on zero-sequence circulation is analyzed based on the mathematical model of parallel system in positive sequence synchronous rotating coordinate system. A feedforward control strategy is proposed based on the traditional Pi loop suppression method. The results show that when the inductance is unbalanced, the conventional Pi method can reduce the circulation, and the feedforward control method proposed in this paper can effectively solve the circulation problem of the parallel system under the condition of the unbalanced inductance. Good current control effect is obtained. Unbalanced fluctuations are common in the actual power grid. The imbalance of power grid and inductor can easily lead to unbalanced or even distorted output current of the converter, which affects the normal operation of the parallel system. In this paper, the influence of the unbalanced network and inductor on the circulation composition is analyzed by using the symmetric component method, and the coordinated control scheme of the parallel system under the condition of the unbalanced operation of the power grid or inductor is proposed. It is shown that the negative sequence circulation will occur between the modules under the condition of unbalanced power grid and inductance, which will lead to the unbalanced output current and distortion of the converter, which will affect the current-sharing effect of the parallel modules. The coordinated control scheme proposed in this paper can effectively solve the adverse effects caused by the imbalance of the power grid and inductor and ensure the reliable operation of the parallel system under unbalanced conditions.
【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】：2014
【分类号】：TM615;TM46

【共引文献】