高电缆化率下谐波源谐波发射水平评估方法

Harmonic Emissions Evaluation for Harmonic Sources Under High Cable Rate

城市电网高电缆化率加剧了谐波污染,对于谐波电压含量较高的母线,有必要评估系统侧与用户侧的谐波发射水平。现有方法大多基于系统侧谐波阻抗远小于用户侧阻抗且背景谐波相对稳定这两点假设。但电缆对地电容较大,易引发感容耦合,增大系统侧谐波阻抗。此外,高电力电子化率也加剧了背景谐波波动,传统方法所需的两个假设不再成立。为此,对该领域所流行的FastICA算法进行改良,首先提出一种基于稀疏成分分析与综合负熵最大化的筛选机制,在该筛选机制引导下搜索与真实谐波源吻合的局部信号,然后通过该局部信号计算两侧谐波阻抗,并评估谐波发射水平。当两侧谐波阻抗幅值接近且背景谐波波动较大时,所提方法均具有较高精度。仿真与实际案例验证了所提算法的有效性。

Due to the high cable ratio of city grid,the harmonic pollution is aggravated. For the buses with high harmonic voltage content,it is necessary to evaluate the harmonic emission level of the utility side and customer side. Most of the existing evaluation methods are based on two assumptions:1)the harmonic impedance of the utility side is far smaller than that of the customer side;2)the background harmonic is relatively stable. However,the capacitance to earth of the cable is large,which is easy to cause inductance-capacitance coupling and increase the harmonic impedance of the utility side. In addition,the high power electronization rate of city grid also aggravates the fluctuation of background harmonics,thus,the two assumptions required by traditional evaluation methods are no longer tenable. To solve these problems,the FastICA algorithm,a popular method in this researching field,was improved. First,a screening mechanism based on sparse component analysis(SCA)and comprehensive negative entropy maximization was introduced to search the local signal which is highly similar to original harmonic source. Then,the harmonic impedance and harmonic emission level of two sides can be calculated through this local signal. The proposed method is effective even when the harmonic impedance amplitudes of both sides are close and the fluctuation of background harmonic is large. Simulation and engineering cases verified the validity of the proposed algorithm.