单级光伏并网多逆变器系统并联交互影响分析

在弱电网条件下，多逆变器间、多逆变器与电网间的动态交互作用影响着电力系统的电能质量和稳定性，易引发谐波谐振等问题. 为了研究单级光伏并网多逆变器系统的谐波谐振特性，考虑光伏源与系统之间的交互作用，采用模态分析法对谐振问题进行了系统的分析与讨论. 首先，根据三相单级式光伏并网系统结构及控制策略，建立了多逆变器戴维南等效模型；其次，通过构建多逆变器系统节点导纳矩阵，应用了一种能够确定系统谐振频率、谐振中心以及各节点参与程度的模态分析方法，从逆变器台数、外界环境、输电距离3个方面研究了系统谐振特性与变化规律；最后，基于MATLAB/Simulink仿真平台，通过搭建三相单级式光伏并网多逆变器系统仿真模型，验证了模态分析法的正确性与有效性. 研究结果表明:当逆变器台数增加时，低频谐振频率呈降低趋势，依次为30、27、25次谐波，高频谐振频率为2 230 Hz保持不变；当外界环境温度降低时，低频谐振频率逐渐升高，依次为22、23、24次谐波，高频谐振频率固定约为2 225 Hz；当输电距离增长时，低频与高频谐振频率均逐渐降低且变得接近. 

Parallel Interaction Influence of Single-Stage Photovoltaic Grid-Connected Multi-Inverter System

Under the condition of weak grid, the dynamic interactions between multi-inverters and between multi-inverters and the grid affect the power quality and stability of the power system, which is likely to cause harmonic resonance. In order to study the harmonic resonance characteristics of the single-stage photovoltaic grid-connected multi-inverter system, the modal analysis method is used for systematical analysis and discussion on the resonance problem while the interaction between the photovoltaic generation and the system is considered. Firstly, according to the structure and control strategy of three-phase single-stage photovoltaic grid-connected system, the Thevenin equivalent model for the multi-inverter system is established. Secondly, a modal analysis method is applied, which can determine the system resonance frequency, resonance center and the participation degree of each node by constructing node admittance matrix of the multi-inverter system. The resonance characteristics and variation laws of the system are studied from three aspects: the number of inverters, external environment and transmission distance. Finally, with the use of MATLAB/Simulink simulation platform, the correctness and effectiveness of the modal analysis method are validated by a simulation model of a three-phase single-stage photovoltaic grid-connected multi-inverter system. The results show that when the number of inverters increases, the low resonance frequency tends to decrease, which is 30th, 27th, and 25th harmonics respectively, while the high resonance frequency remains unchanged at 2 230 Hz. When the ambient temperature decreases, the low resonance frequency increases gradually, which is 22th, 23th, and 24th harmonics respectively, and the high resonance frequency is stable at about 2 225 Hz. When the transmission distance increases, the low and high resonance frequencies gradually decrease and become close to each other.