为更精确的分析多逆变器并网系统中存在的串联和并联谐振现象，提出在单台逆变器小信号模型的基础上考虑输电电缆及风机输出功率的影响。首先，风电场常通过电缆与大电网相连，而电缆存在较大的对地电容，其对系统谐振的影响不容忽略，提出基于电缆的等值模型分析电缆电容对系统谐振的影响。其次，不同的风机输出功率会在电网中产生不同的阻尼效果，提出根据风机输出功率和公共连接点(point of common coupling,PCC)处负荷水平的大小确定负荷等效阻抗，进而分析风机输出功率对谐振点阻抗幅值的影响；最后，通过仿真验证理论分析的准确性。
英文摘要:
In order to analyze the series and parallel harmonic resonances in multiple inverters grid-connected system more accurately, the factors of transmission cable and wind output power were considered based on the small-signal model of an inverter. The wind farm is connected to the power grid through a system of cables, which of the influence on harmonic resonances can't be ignored because of the much large capacitance of cables to earth. A cable equivalent model was proposed to analyze the effect of the cable capacitance on resonances. Then due to different wind output power would generate different damping effect, an equivalent mpedance computing method was proposed according to the magnitude of wind output power and the load level at point of common coupling (PCC). And then the change of impedance amplitude at resonance points was received. Finally, simulation results were presented to verify the correctness of the harmonic resonance analysis method.
