Research On Global Cooperative Harmonic Mitigation On The Grid Side Of Power Electronic Active Distribution Network

With the large-scale penetration of distributed generation including converters and power electronic equipment into distribution network,as well as the rapid development and application of power control equipment such as AC-DC power grid converters and power electronic transformers,the modern distribution network presents a significant electric power electronic trend.The high-density access of a large number of power electronic equipment makes the harmonic pollution of power grid more and more serious.The harmonic emission of a single power electronic device in the power electronic distribution network is relatively limited,which can be regarded as micro-harmonic source.However,the superposition of a large number of micro-harmonic sources cannot be ignored.Therefore,the harmonic pollution of modern distribution network is characterized by high density,decentralization and full network.Aiming at the problem of high-density access to harmonic sources caused by electricity electronization of modern distribution network,a harmonic distributed global optimal mitigation scheme based on VDAPF is proposed,and the harmonics distributed collaborative mitigation strategy is realized by combining global optimization with local control.The details are as follows:The harmonic equivalent modeling method of Markov Chain(MC)time series based on Non-intrusive load monitoring(NILM)data was studied.The classification strategy of decentralized harmonic source equipment and the harmonic Norton equivalent model of typical harmonic source are established.Electricity of MC simulation equipment for the user that has state and obtain NILM technology equipment start-stop state identification data,load access number sequence characteristics of dynamic change model is established,and the equipment start-stop time-series model in harmonic Norton equivalent circuit,resulting in area of harmonic equipment group to the higher harmonic emission behavior model of grid nodes.The realization principle of VDAPF is studied,and the local operation control characteristics of VDAPF reflecting the relationship between mitigation intensity and harmonic voltage are established.Based on the analysis of the relationship between the harmonic voltage of the controlled node and the sensitivity of the control node,a harmonic partitioning algorithm based on the VDAPF access point is constructed.According to the needs of power grid subdivision mitigation and combined with the analysis of subdivision harmonic sensitivity,a method for selecting characteristic parameters of local operation control of VDAPF based on subdivision sensitivity is proposed to realize local online mitigation,which can effectively adapt to time-varying pollution.This paper proposes a global distributed mitigation strategy based on VDAPF,and establishes a multi-time scale distributed collaborative mitigation method combining global optimization of long time scale with local operation characteristic parameter setting of short time scale.In the long time scale,a distributed VDAPF operating point optimization configuration model aiming at the optimal voltage distortion index of all nodes in the whole network is established to realize the global optimization of the harmonic long time scale.On this basis,aiming at the time-varying of harmonics in distribution network,a short-time scale rolling optimization model based on model predictive control principle is established to correct the mitigation deviation caused by harmonic prediction error on long time scale,and to realize the effective suppression of random harmonic disturbance by mitigation decision.Through the combination of global optimization of long time scale and online rolling optimization of short time scale,the distributed and coordinated optimization of multi-time scale of the whole network is realized.Finally,a data-driven dynamic power quality observation node selection strategy is proposed to solve the problem that the high dimension of optimization nodes in the whole network is not conducive to global equilibrium optimization.By extracting the important characteristic points of the observed data of voltage harmonic signals of each node in the distribution network,the array sequence with the same time dimension is constructed by using the cross-interpolation optimization algorithm.The correlation between the data of each node is calculated by the grey correlation analysis method.According to the correlation degree between the voltage signal data of each node,several node clusters of the distribution network are aggregated into a leading harmonic control observation node,and the global harmonic control is carried out according to the leading observation node.By analyzing the mitigation effect of the leading observation nodes,the rationality of the selection method of observation nodes is verified,which is more convenient for global harmonic balance mitigation.