抑制电网背景谐波的变流器导纳重塑方法

Admittance Reshaping Method of Converter for Suppressing Background Harmonic of Grid

电网电压中的背景谐波作用在并网变流器上产生谐波电流,而并网变流器的频率耦合特性还会映射出新的谐波电流成分。为抑制电网背景谐波对并网电流的影响,文中提出改善并网电流质量的导纳重塑方法。首先,为了消除变流器的频率耦合特性,减少并网电流谐波成分,构造出内、外环导纳重塑因子的一般形式,将并网变流器重塑为dq坐标系下的对称系统;然后,从减少谐波含量出发,对导纳重塑因子进行合适选择,通过降低变流器导纳值来改善并网电流质量,实现消除变流器频率耦合特性的同时抑制电网背景谐波的目的;此外,变流器序导纳模值减小,使得其与电网阻抗构成的回路比曲线更难在幅相平面包围(-1,0)点,有益于并网系统的稳定。仿真和实验均验证了所提导纳重塑方法的可行性和有效性。

The background harmonic in grid voltage will produce harmonic current on grid-connected converter,and the frequency coupling characteristics of grid-connected converter will map new harmonic current components.In order to restrain the influence of background harmonics on grid connected current,this paper proposes an admittance remodeling method to improve the quality of grid connected current.First,the general form of the inner and outer loop admittance reshaping factors is constructed,and the grid connected converter is reconstructed into a symmetrical system in dq coordinate system to eliminate the frequency coupling characteristics of the converter and reduce the harmonic components of the grid connected current.Then,from the perspective of reducing harmonic content,the admittance remodeling factor is appropriately selected to improve the grid connected current quality by reducing the admittance value of the converter,which can eliminate the frequency coupling characteristics of the converter and suppress the background harmonics of the power grid.Furthermore,the decrease in the sequence admittance modulus of the converter makes it more difficult for the loop ratio curve formed by the converter and the grid impedance to surround(-1,0)point in the amplitude and phase plane,which is beneficial to the stability of the grid connected system.Simulation and experiment verify the feasibility and effectiveness of the proposed admittance remodeling method in improving the quality of the grid-connected current.