弱电网条件下并网变流器控制策略的研究

发布时间：2018-07-04 09:04

本文选题：弱电网 + 并网变流器　；参考：《北京交通大学》2015年硕士论文

【摘要】：随着可再生能源的普及,分布式发电系统成为研究热点,而并网变流器是实现电网与分布式发电系统之间能量交换的纽带。传统的变流器在设计时是将电网视为理想的电压源,但在分布式发电系统中,理想的电网模型将不再适用。实际的电网会因线路传输阻抗、变压器漏感等而呈现出弱电网特性。并网变流器与电网之间形成了一个交互系统,变流器与电网之间的交互作用可能会对并网系统的稳定性产生影响。本文主要研究弱电网条件下并网变流器的控制策略,具体分析了电网和变流器间阻抗交互作用对并网系统稳定性产生的影响,并选取了适用于弱电网条件下并网变流器的锁相环方法。首先,对基于阻抗的稳定性判据进行了说明,以此作为分析并网交互系统稳定性的理论基础。分别对采用L和LCL型滤波器的并网变流器输出阻抗进行了建模,由于LCL型滤波器会给并网变流器系统引入额外的谐振峰继而使并网系统不稳定,本文采用在电容支路串联阻尼电阻的无源阻尼方法来抑制LCL谐振峰,增加阻尼以使系统稳定。论文在频域下定量分析了并网变流器与弱电网之间由于阻抗交互作用所产生的谐波谐振问题。理论分析表明,在电网阻抗和变流器阻抗幅值相等处的频率附近易产生一定程度的谐波谐振,相比于L滤波型变流器,LCL滤波型变流器更容易与弱电网发生谐波谐振。在时域下进行的仿真验证了理论分析的正确性。其次,本文选取了基于二阶广义积分器的锁相环方法来进行锁相,通过仿真验证了该锁相环方法在不同电网条件下锁相的有效性和准确性,说明该方法是适用于本文中弱电网条件下三相并网变流器系统的。最后,搭建了三相并网变流器的实验平台,对弱电网条件下并网变流器系统的稳定性分析结果进行了实验验证,给出了采用不同滤波器时不同电网条件下的并网电流波形和谐波分析结果,验证了本文中理论分析和仿真结果的正确性。
[Abstract]:With the popularization of renewable energy, distributed generation system has become a hot research topic, and grid-connected converter is the link to realize the energy exchange between grid and distributed generation system. The traditional converter is designed as the ideal voltage source, but in the distributed generation system, the ideal power network model will no longer be applicable. The actual power network will show weak network characteristics due to transmission impedance and leakage inductance of transformer. An interactive system is formed between the grid-connected converter and the grid. The interaction between the converter and the grid may affect the stability of the grid-connected system. This paper mainly studies the control strategy of grid-connected converter under the condition of weak electric network, and analyzes the influence of impedance interaction between power grid and converter on the stability of grid-connected system. A phase locked loop (PLL) method suitable for grid-connected converters with weak electric grids is also selected. First, the stability criterion based on impedance is explained, which is used as the theoretical basis for analyzing the stability of grid-connected interactive systems. The output impedance of grid-connected converter using L and LCL filters is modeled respectively. Because the LCL filter will introduce extra resonance peak to the grid-connected converter system, it will make the grid-connected system unstable. In this paper, the passive damping method is used to suppress the LCL resonance peak and increase the damping to make the system stable. In this paper, the harmonic resonance between grid-connected converter and weak grid is analyzed quantitatively in frequency domain because of the interaction of impedance. Theoretical analysis shows that harmonic resonance is easy to occur near the frequency where the impedance amplitude is equal to the impedance of the converter. Compared with the L-filter converter, the LCL filter converter is more likely to produce harmonic resonance with the weak current network. The simulation in time domain verifies the correctness of the theoretical analysis. Secondly, the phase-locked loop method based on the second-order generalized integrator is selected, and the validity and accuracy of the phase-locked loop method under different power grid conditions are verified by simulation. It is shown that this method is suitable for the three-phase grid-connected converter system under the condition of weak current network in this paper. Finally, the experimental platform of the three-phase grid-connected converter is built, and the stability analysis results of the grid-connected converter system under the condition of weak grid are verified experimentally. The results of current waveform and harmonic analysis under different power network conditions with different filters are given, and the correctness of the theoretical analysis and simulation results in this paper is verified.
【学位授予单位】：北京交通大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TM46

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