Harmonics Analysis Under SVC Unbalance Compensation

With the rapid development of modern industry, the growing number of unbalanced load in the power system is bigger and bigger. Electrified railway, electric arc furnaces, and other typical unbalanced load will cause a three-phase system voltage, current imbalance, so here comes to the need of compensation. Static reactive power compensation device SVC can not only compensate reactive power but also for three-phase unbalanced compensating reactive. But as a nonlinear element SVC will generate harmonics when it is used in compensation for the three-phase unbalanced system, and the harmonics are different from which are generated when used in compensation for the three-phase balanced system. So it is important with further research analysis of SVC when making unbalanced compensation.This paper first introduces the basic concepts of the three-phase unbalanced system, disadvantages and the importance of compensation. Secondly, the basic principle of the use of SVC compensation for unbalanced system is given in the second chapter. Then analysis harmonics generated in the SVC for unbalanced system and design harmonic filter. Finally, on the basis of theoretical analysis, SVC can fully balance system of three-phase unbalanced load, and reactive power compensation by founding simulation models using Matlab/Simulink tool.This article analyzes harmonic currents in two conditions of balance compensation and imbalance compensation comparatively. More specifically, it analyzes3,5,7harmonic currents respectively in these two compensations based on Fourier Transform Principle, and then come to the principle of zero sequence harmonic currents, negative sequence harmonic currents, the positive sequence harmonic currents from balance compensation and imbalance compensation.In balance compensation,3rd harmonic as the representative of the zero sequence harmonic currents in three-phase offset each other and will not flow into the power grid, But in the imbalance compensation, they will not offset each other. Similarly, three-phase amplitude and phase in5th harmonic as the representative of the negative sequence harmonic currents and7th harmonic as the representative of the positive sequence of the harmonic currents both change a lot in balance compensation and imbalance compensation.