Research On Load Harmonic Current Detection Method In Background Harmonic Voltage Environment

In recent years,the widespread use of various types of power electronic equipment increases the harmonic current on the user side,but also leads to the occurrence of system harmonic voltage on the power supply side of the distribution network,which affects the efficient and stable operation of the distribution network.In the background harmonic voltage environment,harmonic control of lower distribution network has become one of the hotspots in the field of power quality research.Accurate detection of harmonic current is the premise of harmonic pollution control and the key link of harmonic analysis.Therefore,it is of great significance to study the harmonic current detection method suitable for the background harmonic voltage environment.In the background harmonic voltage environment,the harmonic current at the common electrical connection point is formed by the coupling of the background harmonic voltage and the harmonic current generated by the nonlinear load.The existing harmonic current detection method does not consider the harmonic current at the common connection point.In order to solve the problem of current coupling phenomenon,the paper starts from the characteristics of harmonic current at the public electrical connection point of the distribution network,and deeply analyzes the coupling mechanism of the background harmonic voltage and the load harmonic current and the influence on the existing harmonic current detection methods.A background harmonic active current detection method based on the DIN40110-2 standard is proposed.Taking the background harmonic voltage as the benchmark,according to the principle that the active power consumption of the load before and after the equivalent is unchanged,reflects background harmonic voltage distortion degree of harmonic active current is detected by defining the harmonic equivalent conductance,realizes decoupling of harmonic current at the common electrical connection point.Aiming at the problem that the harmonic reactive current generated by reflecting the background harmonic voltage at the common electrical connection is not detected,this paper uses the Hilbert transform to perform accurate 90-degree phase shift for each frequency component of the voltage.A background harmonic reactive current detection method based on Hilbert transform is proposed,this method realizes the phase shift of the background harmonic voltage,realizes the detection of the background harmonic reactive current by defining the lumped harmonic reactive power and harmonic equivalent susceptance,and extract the harmonic reactive current that reflects the distortion degree of the background harmonic voltage.Aiming at the problems of unsatisfactory harmonic control effect and non-compliance with harmonic control principles in existing harmonic current detection methods,on the basis of the above background harmonic active current and background harmonic reactive current,an improved load harmonic current is proposed.The detection method realizes the purpose of separating the harmonic current only representing the emission of the user load from the test current of the common electrical connection point.The load harmonic current decomposed by the improved load harmonic current detection method is not affected by the background harmonic voltage,which can reduce the compensation current and compensation capacity of the active filter,and improve the parallel type active filter to the distribution network harmonics governance effect.The simulation model of the distribution network is established,and the correctness of the proposed detection method is verified by comparing the method in this paper with the traditional method in the background harmonic voltage environment.Taking the measured data of enterprise harmonic current as an example,the validity of the proposed detection method in the background harmonic voltage environment is further verified.