考虑群延迟和暂态时延的短窗低通滤波器设计

Design of short-window low-pass filter considering group delay and transient delay

为采用基于采样值和正弦信号模型的快速保护算法,并防止重采样环节的频率混叠,智能变电站的数字化保护需要数字低通滤波器配合。提出一种基于Tukey窗函数,并且同时考虑滤波器幅频特性和群延迟、暂态时延的低通滤波器设计方法。该方法首先确定窗函数时域宽度T_c和截止频率f_c,再根据采样频率f_s和固定不变的f_c,确定滤波器的长度N≤2 f_s/f_c,最后根据N和f_c得到完整的滤波器系数。通过理论分析、数字仿真和静态实验,研究了所设计滤波器的幅频特性、群延迟和暂态时延。对采用所设计滤波器的母线保护进行RTDS实验,通过对比表明,按所提方法设计的滤波器在群延迟和暂态时延性能上明显优于传统窗函数法设计的滤波器,降低了滤波器环节对保护速动性的影响。

The digital relays in smart substations need the assistance of low-pass digital filters in order to adopt fast algorithms based on sampling values and sine signal models and avoid the frequency aliasing during resampling. A design method of low-pass filter based on Tukey-window function is proposed,which simultaneously considers the amplitude-frequency characteristic,group delay and transient delay. Firstly,the time-domain width T_c and cutoff frequency f_c of window function are determined,then the filter length N is determined to be less than or equal to 2 f_s/f_c according to the sampling frequency f_s and the fixed f_c,finally the complete filter coefficients can be obtained by N and f_c. The amplitude-frequency characteristics,group delay and transient delay of the designed filter are studied through theoretical analysis,digital simulation and static experiment. The RTDS experiment of a busbar protection adopting the designed filter shows that the designed filter is obviously superior to the filter designed by the traditional window function method in the aspects of group delay and transient delay,and the designed filters can effectively reduce the influence of filters on the speed of protection.