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Design of DC side voltage rated value is a very important issue for the development of static var generators (SVG), but so far is lack of discussion in a quantitative manner from previous publications. In this paper, an extensive analysis on the influence of DC side voltage to the performance of SVG is carried out, and a specification of the DC side voltage rated value is presented. First, through equivalent circuit analysis and analytical expressions, a required lowest value of DC side voltage for full compensation (a unity total power factor) is obtained for both leading compensation and lagging compensation, where SVG is providing leading reactive current and lagging reactive current respectively. For the situation of DC voltage smaller than the above-obtained lowest value, there are two basic options for the SVG PWM control. One is to keep the linear modulation of PWM but loose the compensation capability to a unity power factor, for which case the quantitative relationship between the DC voltage and the total power factor after compensation is detailed. The other is to keep the unity power factor compensation capability through over modulation of PWM control, for which case the amount of lower order harmonics generated by SVG is also elaborated in the paper. Based on these analysis, the specification of DC voltage rated value for SVG is quite straight forward. Both simulation investigations and hardware experimental results are finally provided to verify the analysis and specification.