Studies On Harmonic Impact And Placement Of Distributed Generation In Power Distribution System

With more and more DG used in distribution network, it's important for guaranteeing the reliable and optimal operation of grid and equipment by planning DG rationally and correctly assessing the influence of harmonic distortion after adding DG This paper studies the harmonic impact of DG, based on which, it optimizes the site and size of DG through improved multi-objective particle swarm optimization (MOPSO) algorithm.This paper classifies DG as the linear model and nonlinear model from the harmonic analysis perspective, and establishes their harmonic calculation model. In theory, the rule of THD (Total Harmonic Distortion) variety is deduced when two types of DG access to an ideal distribution network with the different site and size. The simulation of 21-bus chain distribution network shows the same result as the ideal system's using PCFLO software.Based on the above analysis, two optimal models of DG planning are proposed with considering the harmonic effct of DG:one is the single-objective optimization model for minimizing THD; the other is multi-objective optimization model considering active power loss and THD. The particle swarm algorithm is improved by linear adjustment of inertia weight and introducing an item in formula of updating particle's velocity to form a hybrid PSO model. Then MOPSO algorithm with bidirectional searching strategy is proposed mixed optimal solution and isolated point search. Combining the improved MOPSO algorithm with fundamental and harmonic power flow can solve DG optimization configuration of multi-objectives constraints and integer optimization. The simulation result of IEEE 33-bus distribution network proves that the improved back/forward sweep flow algorithm, decoupled harmonic power flow calculation, DG optimization configuration model and improved MOPSO algorithm are correct and suitable. Easonable planning of DG not only can effectively decrease THD and power loss of distribution network but raise the voltage level, which has high practical value.