Distributed Harmonic Mitigation And Stability Analysis Of Power Electronic Distribution Networks

With the large-scale integration of distributed energy and power electronic devices,as well as the rapid development of operation and detection equipment such as AC-DC energy converters,modern distribution networks are gradually exhibiting power electronic characteristics.Currently,harmonic pollution in distribution networks mainly manifests in two aspects.On the one hand,the large-scale integration of nonlinear devices leads to an increasingly severe level of harmonic pollution in distribution networks,presenting characteristics of high density,decentralization,and network-wide distribution.On the other hand,the equivalent inductance of transmission lines and power factor correction capacitors can easily form resonance circuits,and under harmonic excitation,multi-node resonance in power systems can occur,increasing the level of harmonic voltage and exacerbating node voltage distortion.To address the issue of harmonic governance in modern power electronic distribution networks,a distributed harmonic governance scheme based on voltage detection active power filters(VDAPF)is proposed,and the stability of the governance system is analyzed.The specific content is as follows:Firstly,the modal analysis method based on matrix decoupling technology was studied.The admittance matrix models of a three-node and a five-node test system were established.By analyzing the eigenvalues of the admittance matrix,the resonance frequency of the test system was detected.Combined with the left and right eigenvectors of the admittance matrix,the resonance participation factors were calculated to determine the resonance center of the test system,providing a theoretical basis for further eliminating resonance.Secondly,the working principles of current detection active filters and voltage detection active filters were studied,and a distributed harmonic mitigation strategy based on VDAPF was proposed.The thirteen-node distribution network was selected as the harmonic mitigation area,and the modal analysis method was used to analyze the harmonic resonance frequency and resonance characteristics of the distribution network,combined with participation factors to determine the installation position of VDAPF.A distributed harmonic mitigation optimization model for the distribution network was established,with the objective of minimizing the total modal voltage of all nodes in the network,considering the capacity constraint of VDAPF.An improved particle swarm optimization algorithm was used for optimization and solution,thereby achieving harmonic compensation and resonance suppression for the distribution network.Finally,based on the distributed harmonic mitigation system of the thirteen-node distribution network,the state space equations of VDAPF and network lines were derived.A complete small signal model of the distributed harmonic mitigation system was established,and the key parameters affecting the stability of the mitigation system were obtained based on the eigenvalues of its state matrix.The stable value range of the key parameters was determined by the root locus of the main eigenvalues of the state matrix.A simulation model of the distributed harmonic mitigation system was built to verify the correctness of the established small signal model.