The Research On Load Balance Transformer And Power Quality Comprehensive Compensation System

Electric energy is of vital importance in the development of social economy and people’s daily life. Meanwhile, it’s a strong driving force to promote the flourish of national industry, the progress of science and the stability of society. In recent years, more and more large-power electronic devices are used in the power grid, which results in power quality problems and these problems become gradually critical. High power nonlinear loads will lead to voltage fluctuation and flicker and three-phase unbalance. It will also cause the matters of harmonic pollution and low power factor. The existence of these problems will not only influence the stability of the system, but also cause a huge waste of power. Therefore, applicating reasonable and effective methods to improve the power quality are essential to ensure the safe and economical operation of the system.A novel load balance transformer wiring scheme is proposed in this paper. This kind of transformers is based on zig-zag transformers, taking advantage of the principle of electromagnetic inductance between transformer core and windings to achieve the aim of load transfer. Thus, the current of transformer primary side becomes balanced. This scheme is of big significance in theoretical innovation. Starting from the wiring scheme of the transformer, its basic equation, constraint of the impedance in the transformer and winding structure arrangement are researched in this paper. At the same time, a systematic analysis of zero-sequence and negative-sequence unbalance in the asymmetric operation as well as the characteristics of load transfer is considered.Technical and economic indicators of the load balance transformer are discussed. The model of load balance transformer is built in Matlab simulation tool and the correctness of the design method is verified. Meanwhile, a model of unbalanced line loss coefficient is established to analyze how the load balance transformer affects the unbalanced line loss. The material utilization of the transformer is analyzed as well as the comparison between the power saving benefits which results from the decrease of line loss and the extra costs of manufacturing it. The results showed that the load balance transformer has a outstanding economical efficiency.Aiming at solving the power quality problems such as low power factor, three-phase unbalance and harmonic pollution, this paper proposes a power quality comprehensive compensation solutions and systems based on the load balance transformer. This solution combines the advantages of active power control devices and load balance transformers respectively. The current detection method and control strategy of the power quality comprehensive compensation solutions are researched, too. A variable ring width quasi-constant frequency hysteretic control method is proposed, which optimizes the traditional hysteretic loop comparator control method and decrease the fluctuation of switching frequency. The paper analysed how the characteristics of load transfer affects the design capacity of active power control devices.Finally, the proposed power quality comprehensive compensation system is stimulated in Matlab. Analysis is made in respect of the grid unbalance, harmonics and their unified governance effect. The results prove that the power quality comprehensive compensation system can restrain the unbalanced degree of the power grid and the harmonic pollution. At the same time,the system has the function of reactive compensation.In conclusion the various quality indicators of the power grid are improved under this circumstance.In addition, a comparison of offset current in the power quality comprehensive compensation system which based on different transformers is developed.The result showed that the load transfer characteristics of load balance transformer could reduce the design capacity of active power control devices.