Research On Harmonic Source Location Method For Distribution Network With Photovoltaic

With the continuous development of new energy,a large number of photovoltaic are connected to the power grid,and the installed capacity of photovoltaic is increasing,which also makes the harmonic problem of the power grid more complex.The harmonic generated by photovoltaic and various power electronic devices worsens the power quality of the distribution network,and brings huge economic losses to the distribution network and related users.Based on the harmonic information obtained by the measurement device,the research on the location method of harmonic source in the distribution network with photovoltaic is not only helpful to judge the source of harmonic pollution,but also conducive to the reasonable division of harmonic responsibility,and take corresponding reward and punishment measures to effectively control harmonic pollution.For this reason,this paper carried out the research on the harmonic source location method for the distribution network with photovoltaic.Firstly,according to the actual situation,in view of the global observability of the system,some nodes of the system have been installed with measuring devices but need to be optimally configured again,the number of measuring devices is limited and the number of important nodes is required to be observable,and on the basis of the installed part of measuring devices but more important nodes are required to be observable and the number of new devices is limited.In these four cases,different optimal configuration schemes of measuring devices are proposed,which reduce the number of measuring devices.In the proposed scheme,factors such as whether the node is connected with photovoltaic and the correlation between nodes are considered comprehensively,and the importance of each node is judged by weighting,so as to ensure the maximum observability of harmonics of photovoltaic and other important users and distribution network.Secondly,considering that there are few measuring devices in the distributed photovoltaic distribution network,the system may not be globally observable,and the photovoltaic harmonics have the characteristics of fluctuation with the change of light intensity,based on the multi-point harmonic measurement information,a harmonic source location method based on the orthogonal matching tracking algorithm is proposed.According to the known measurement and measurement matrix,the harmonic state equation of the under determined system is solved based on the orthogonal matching tracking algorithm in the compressed sensing theory,and the harmonic current injected into the node is estimated,which realizes the harmonic source location when the system is not globally observable.Compared with other methods,the simulation results show that the proposed method can effectively locate the harmonic source when the number and position of harmonic sources are changed,the measurement error is considered,and only the information of harmonic amplitude is available.Furthermore,the fluctuation characteristics of the estimated harmonic current and fundamental current can be combined with the change of light intensity to judge whether the harmonic source is photovoltaic.Finally,based on the single point harmonic measurement information of photovoltaic parallel network,an evaluation method of harmonic emission level considering the harmonic impedance of photovoltaic side and the harmonic voltage fluctuation of system side is proposed.According to the parameters of photovoltaic inverter and filter and the parameters of line harmonic impedance,the harmonic impedance of photovoltaic side is estimated.Based on the logistic regression,the data pairs of harmonic voltage and harmonic current at the photovoltaic grid-connected point are classified,and the data pairs with basically the same harmonic voltage at the system side are screened out,then the harmonic impedance of the system side is estimated by partial least square method.The influence of harmonic voltage fluctuation is reduced.Based on the estimation of harmonic impedance of photovoltaic side and system side,the level of harmonic emission is evaluated.