Research On Governance Method And Experiment Of Unbalanced Three-phase Current Based On Optimal Injection Flow

Nowadays, there is a great deal of unbalanced three-phase load in medium andlower voltage distribution system of China, which leads to the long-time unbalancedoperation of distribution transformer. Unbalanced current caused by this seriouslyaffects the safety and economic operation of power system and causes a huge powerloss. Currently existing methods usually use susceptance compensation theory to governunbalanced three-phase current, but the efficiency of equipment is limited because ofhigh demand for compensation, which results from that the control target is set to ensurethat the system’s power factor be improved to1and unbalance factor be reduced to0.Furthermore, the way that compensation equipment governs unbalanced three-phasecurrent is switching control, and the equipment’s service life and loss are closely relatedto its operation times. However, those methods haven’t taken the limit of operationtimes into consideration, which leads to high cost and low govern effect. Aiming at thedisadvantages of susceptance compensation theory, this thesis will do research ongovernance method of unbalanced three-phase current from the perspective of inversemethod, the concrete research content is as follows:①Propose a governance method of unbalanced three-phase current based onoptimal injection flow, innovatively introduced injection flow to the governance ofunbalanced three-phase current. Construct the objective function which can representpower quality parameters in need of governance, inversely find susceptancecompensation capacity needed with network analysis and mathematical method. Inconsideration of inconvenience of using inductance compensation, make furtheroptimization on governance method of unbalanced three-phase current based on optimalinjection flow, do governance with full capacitance method by introducing constraintsof power factor and overcompensation and taking use of inductive reactive power fromload in the premise of govern effect, so that the inductance compensation will beavoided;②Make simulation experiment on governance method of unbalanced three-phasecurrent based on optimal injection flow with data collected from distributiontransformer. The results shows that governance method of unbalanced three-phasecurrent based on optimal injection flow improves the current distribution ofcompensation susceptance effectively and avoids the disadvantage of high demand for compensation. In additional, the govern effect of full capacitance govern method ofunbalanced three-phase current based on optimal injection flow is better than effect ofmethod based on susceptance compensation theory and the possibility of seriousovercompensation is avoided;③Take the service life and loss of compensation equipment into consideration,form the all-day optimal governance strategy of unbalanced three-phase current on thebasis of governance method of unbalanced three-phase current based on optimalinjection flow, confirm the optimal operation time and duration of compensationequipment by static equivalent integration of compensation capacity of each period andoptimization of capacity configuration according to all-day load curve to furtherimprove the power quality and lower the loss of distribution transformer;④Make lab experiment on governance method of unbalanced three-phase currentbased on optimal injection flow with laboratory experimental platform; rewrite thealgorithm program of unbalanced current’s governance and the control program ofcompensation unit. The result proves that the govern effect on each distributiontransformer’s power quality parameter taken by governance method of unbalancedthree-phase current based on optimal injection flow proposed in this thesis has beensignificantly improved compared to govern effect taken by governance method based onsusceptance compensation theory and the governance method of unbalanced three-phasecurrent based on optimal injection flow has better convergence and optimalperformance.