Study On Multi-objective Optimization Control Of Low-voltage Reactive Power Compensation

As the rapid development of electric power system of our country, reactive power has increasingly became one of the most important factors which impact of the quality of grid power. As the increases of inductive load capacity from users, there is an urgent requirement to reactive power compensation to improve system power factors, voltage quality and reduce line lose, however, the use of shunt capacitors for reactive power compensation may affect harmonics in power grid because of the unsuitable choice of compensation capacity. This paper conducted a study on the low harmonic content in the reactive power compensation and harmonic amplification and proposed multi-objective optimization method on choosing compensation capacity. This method can effectively reduce the amplification effect from reactive power compensation on harmonic.Firstly, it introduced the development history and related principles of reactive power compensation and harmonic suppression, and discussed the relationship among terminal voltage, power factor and compensation capacity. After the establishment of the reactive power compensation model which with harmonic source we found that the utilization of a series reactor to suppress harmonic will produce good results but it will cause additional equipment investment on purchasing reactors, maintenance costs and power loss on the operation of the reactor; If series reactor is unsuitable for compensation capacity that will amplify the effect of a second harmonic, so that total harmonic distortion becomes large which will burn capacitors and other electrical equipment. To resolve this problem, this paper use the multi-objective control method to choose the capacity of reactive power compensation and base on multi-objective optimization model, take the harmonic distortion as the Constraints. Through Weighted average to get the evaluation function with the highest power factor and minimum harmonic distortion weighted by the weighting coefficients and finally we could obtain the optimal compensation capacity by using the evaluation function as the switching control volume. MATLAB simulation showed that it optimized the power factor which is compensated and harmonic distortion rate when this method is used in the low-voltage power grid which with less harmonic content to chose compensation capacity.Finally, based on data of Fushun Special Steel it made MATLAB simulation on harmonic effects which measured for the existing reactive power compensation system. Through comparing and analyzing compensating harmonic changes and equipment costs, we found that multi-objective optimal control can not only improve system power factor, reduce reactive power compensation effect on harmonic amplification but also can lower investment on equipment as well as power loss on the operation of the reactor.