Research On Collaborative Optimal Allocation Of Distributed Mitigation Devices For Harmonic And Voltage In Distribution Networks

With the large-scale grid connection of distribution generation(DG)and the application of many nonlinear,impulsive and power electronic loads,the power quality(PQ)problem in the distribution networks is deteriorating seriously,and the PQ pollution is more decentralized and grid-wide.Meanwhile,the modern devices to mitigate PQ pollution presents the characteristics of diverse types,multiple functions,cross functions,and coexistence of special and unspecialized,which provides a new opportunity for PQ pollution mitigation.Thus,in this thesis,an optimization allocation strategy is proposed,which can mitigate the decentralized gird-wide PQ pollution in the distribution networks through the collaborative allocation of various distributed harmonic and voltage mitigation devices.The specific research contents are as follows:According to the local characteristic of PQ,a comprehensive partition method for mitigation of harmonic and voltage is proposed to solve the problem that the harmonic and voltage devation pollution are becoming more decentralized and gird-wide in distribution networks.Considering the harmonic and voltage deviation indexes at same time,a partitioning model for PQ mitigation is constructed based on the sensitivity indexes of harmonic and reactive power.A partioning method based on community discovery algorithm is proposed for different situations that DG grid connected inverter(GCIN)does not participate in PQ mitigation,participates in reactive power compensation,as well as harmonic mitigation and reactive power compensation at same time.Combined with the function characteristics of devices,methods for selecting regional dominant mitigation nodes are given based on the sensitivity indexes of harmonic and reactive power,and based on the comprehensive voltage sensitivity index.The methods provide a basis for the candidate locations selection of voltage detection active power filter(VDAPF)and static var generator(SVG)in the subsequent collaborative optimal allocation model for the distributed mitigation devices.Considering that VDAPF can mitigate harmonic and compensate reactive power,and there is an intersection with SVG in the compensation function,a collaborative optimal allocation strategy of VDAPF and SVG is provided for comprehensive mitigation of harmonic and voltage.Taking the minimum cost of devices as the objective,the collaborative optimal allocation model of VDAPF and SVG is constructed.On the basis of the two methods proposed for selecting dominant mitigation nodes,two allocations can be obtained.In order to determine the optimal allocation in different PQ pollution scenarios,an integrated evaluation index based on economy and PQ mitigation effect is defined.An example is analyzed to verify the controllability of the dominant mitigation nodes selected in each region.The performance of two collaborative allocations is analyzed in different pollution scenarios,and compared with the traditional allocation strategy to verify the rationality and effectiveness of the proposed allocation strategy.Considering the ability of the GCIN remaining capacity for PQ mitigation in distribution networks,a multi-objective collaborative optimal allocation strategy of VDAPF and SVG is stuidied with considering the harmonic and voltage mitigation of the GCIN.Uncertainties of PQ pollution distribution and device mitigation capacity are characterized with a series of deterministic operation scenarios constructed by multi-scenario analysis technique in the progress of PQ mitigation.An allocation strategy for harmonic and voltage mitigation capacity is proposed to make full use of the remaining capacity of GCIN.The dominant mitigation nodes are selected for all regions in different operation scenarios.Taking into accuont the economy and PQ mitigation effect,a multi-objective collaborative optimal allocation model of VDAPF and SVG is established.Furthermore,Pareto solution set of the optimal allocation is obtained by the normalized normal constraint method.An example is analyzed to verify the rationality and effectiveness of the proposed strategy by comparing it with traditional allocation strategy,and with the collaborative allocation strategy without considering PQ mitigation of GCIN.Based on the ability of the GCIN remaining capacity for reactive power compensation in distribution networks,a bi-level collaborative optimal allocation strategy of VDAPF and SVG is proposed with considering DG active power curtailment.Taking the minimum annual investment cost as the upper planning objective and the optimal PQ operation level as the lower one,a bi-level optimization model of distributed mitigation devices is established to obtained the optimal allocation of VDAPF and SVG,as well as the active power curtailment of DG.An example is analyzed to verify the rationality and effectiveness of the proposed allocation strategy by comparing it with the collaborative allocation strategy without considering DG and with considering reactive power compensation of GCIN remaining capacity.