Method Research On Harmonic Current Detection Of Shunt Active Power Filter

With the widespread application of new energy generation represented by wind power and photovoltaic,a large number of converters are connected to the distribution network,which not only generates integer harmonics,but also introduces subsynchronous harmonics and supersynchronous harmonics.At the same time,random changes in wind speed and light will cause voltage fluctuations on the DC side of the converter,making the amplitude of subsynchronous harmonics and supersynchronous harmonics change over time and show non-stationary characteristics,which need to be compensated for.Active power filters are the main device for harmonic compensation of harmonics in low-voltage distribution networks,and the accuracy of harmonic current detection is one of the key factors determining the compensation effect of active power filters.Therefore,it is of great significance to study a method that can simultaneously detect integer harmonics,subsynchronous harmonics and supersynchronous harmonic currents to improve the harmonic compensation effect.In view of the shortcomings of shunt active power filters that cannot effectively detect subsynchronous and supersynchronous harmonic currents,this paper deeply analyzes the harmonic current detection method based on the instantaneous reactive power theory,and clarifies that the low-pass filter’s gentle decay characteristics and its lack of good dynamic regulation are the fundamental reasons for the poor detection of harmonic currents.In order to solve the problem of low-pass filters’ gentle attenuation characteristics,which leads to the lack of accuracy in detecting subsynchronous and supersynchronous harmonic currents by existing harmonic current detection methods.Based on the steep attenuation characteristics of self-tuning filter near the fundamental frequency,this paper proposes a harmonic current detection method based on self-tuning filter to achieve accurate detection of integer harmonic currents while improving the detection accuracy of subsynchronous and supersynchronous harmonic currents.To solve the problem that low adaptivity of harmonic current detection methods in non-stationary subsynchronous and supersynchronous harmonic environments,this paper proposes an improved adaptive filtering algorithm for hyperbolic sinusoidal functions on the basis of the harmonic current detection method based on self-tuning filter.The method establishes the function relationship between the step parameter and the harmonic current,realizes the dynamic adjustment of the step parameter and improves adaptiveness of harmonic current detection methods to non-stationary harmonics that vary with time.In this paper,a simulation model of a distribution network containing a grid-connected photovoltaic power generation system is built,in which the current consists of integer harmonics,subsynchronous harmonics,supersynchronous harmonics and fundamental components,and the performance of this method is tested comprehensively by setting the subsynchronous harmonics and supersynchronous harmonics in steady state and non-steady state time-varying situations respectively.The harmonic distortion rate and harmonic current content rate are used to quantify and evaluate the effectiveness of this method in detecting harmonic currents,and to verify the effectiveness and applicability of the improved harmonic current detection method proposed in this paper.