An Improved Kalman Filtering Method And Its Application In Harmonics Measurement Of OCT

The power system is developing rapidly towards the direction of digitization,networking and intelligence.This trend requires the matched equipments that used to measure,monitor,control and protecte power system.Optical current transducer(OCT)has become a new research hotspot because of the superiority of measuring mechanism compared with traditional electromagnetic current transducer,which makes it has potential prospect in the field of measurement.However,OCT still has some problems need to be solved urgently if we want to apply it to practice.One problem is how to deal with the input signals featured with low signal-to-noise ratio and complex composition.This paper firstly introduces measuring principle and sensing mechanism of OCT,then analyzes the characteristics of signal,noise and the frequency characteristic in the sensing process.A linear Kalman filtering model for measuring the DC,fundamental current and harmonics in OCT is establish ed based on these theoretical analysis.However,it is found that this model is sensitive to the frequency of measured current in simulation.An improved Kalman filtering method is proposed to solve this problem.This method fistly measurs the frequency de pend on phase-locked loop that has the function of real-time frequency tracking.The improved method uses the tracking frequency and linear Kalman filtering model to measure steady state current.Finally,a program to measure the steady state current is wt itten based on the improved method in LabVIEW.Experimental platform is designed using the OCT,light source,photoelectric converter,optical fiber,data acquisition card.The simulation results done on LabVIEW and experimental results done on experimental platform show that this improved method can not only measure harmonics but also improve the SNR and the measurement accuracy.This improved method provides a new way for signal processing in OCT,especially for harmonics measurement.