A Modified Full-Band Adjustable Bi-Quad Filter for Mechanical Resonance Suppression in Industrial Servo Drive Systems

As for mechanical resonance suppression, the online adjustable bi-quad filter is a powerful method and has been widely used in industrial applications. Compared with the notch filter, the bi-quad filter has one more parameter for notch depth design, which is more suitable for servo systems with nature damping coefficient and limited resonant gain. However, this classic method still has room for improvement. Usually, the adjustable bi-quad filter has two steps, including fast Fourier transformation (FFT) analysis, and filter tuning. In this paper, concerning these two steps mentioned above, two targeted modification strategies are proposed. Firstly, a single-phase MIT (SM/T) method is used to remove the certain noise cluster of the FFT result. Then, inspired by the discretization distortion correction of the notch filter, a similar method is designed to avoid that the bi-quad filter becomes inaccurate when the central notch frequency is close to the Nyquist frequency. In the end, the validity and effectiveness of aforementioned analysis and strategies are verified by experimental results.