| Nowadays,with the rapid development of power electronics technology,more and more new nonlinear loads are emerging in urban low-voltage distribution networks.The accompanying harmonic pollution problem has caused serious negative impacts on the safety,stability,and efficient operation of the distribution network.As an important power equipment in the distribution network,transformers may experience vibration,noise,overheating,and other phenomena if they work in harsh conditions with high harmonic content for a long time,resulting in additional losses,reduced service life,and affecting the safe operation of the distribution network.Different from traditional filtering technologies,the emerging inductive filtering technology in recent years has improved the electromagnetic environment of transformers by transforming them,suppressing the harmonics generated on the load side during the transmission process of the transformer,improving the power quality of the power grid system,and improving the electromagnetic environment of the transformer.This thesis focuses on the research of distribution transformers and their filtering systems based on inductive filtering technology,and deeply explores their characteristics and performance advantages under different operating states.The main work and achievements are as follows:(1)By comparing with traditional distribution transformer filtering system,the harmonic suppression performance of the new distribution transformer inductive filtering system is analyzed,and its advantages in application in low-voltage distribution networks are verified.The filtering effect of traditional passive filtering system for distribution transformer is easily affected by system impedance.Even with the use of active filtering technology,the negative impact of harmonics on distribution transformer cannot be avoided.The filtering performance of the new distribution transformer inductive filtering system is less affected by the impedance of the power grid system,and can suppress harmonics on the load side of the distribution transformer,reducing the negative impact of harmonics on the transformer.The simulation comparative analysis based on MATLAB/Simulink shows that the new distribution transformer inductive filtering system has better harmonic suppression performance than traditional distribution transformer filtering system,and the system can still effectively suppress harmonics for abnormal operating conditions where the transformer is saturated under three-phase unbalanced loads.(2)A implementation scheme of active inductive filtering suitable for abnormal operation of low-voltage distribution network has been proposed,and its performance advantages in detuning and transformer saturation have been explored.In response to the applicability issues of inductive filtering technology based on passive filtering devices in applications such as unclear load harmonic characteristics,as well as inherent defects such as device aging,original design errors,and environmental impacts,a topology structure and solution for an active inductive filtering system around the new distribution transformer are proposed.The circuit equivalent model and filtering characteristics analysis of the system indicate that a reasonable harmonic damping coefficient can optimize the harmonic suppression characteristics of the filtering system.Simulation analysis shows that active inductive filtering system for new distribution transformers can effectively control harmonic currents in the detuning state and 3rd and9 th harmonic currents caused by transformer saturation state,maintaining good filtering performance.(3)Conducted field circuit coupling simulation and prototype experiments on a30 k VA new distribution transformer system.The field circuit coupling simulation analysis based on ANSYS/Maxwell shows that the new distribution transformer inductive filtering system improves the internal electromagnetic environment of the distribution transformer while avoiding the invasion of harmonics generated on the load side into the grid side.The prototype of the new distribution transformer inductive filtering system can effectively suppress harmonics under three-phase balanced and unbalanced loads,and has the function of compensating reactive power,improving the power quality of the power grid.There are 66 figures,12 tables,and 85 references in this thesis. |
