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The cluster DC voltage balancing control adopting zero-sequence voltage injection is appropriate for the star-connected cascaded H-bridge STATCOM because no zero-sequence currents are generated in the three-phase three-wire system. However, as the zero-sequence voltage is expressed in trigonometric form, traditional control methods involve many complicated operations, such as the square-root, trigonometric operations, and inverse tangent operations. To simplify cluster voltage balancing control, this paper converts the zero-sequence voltage to the <tex>$dq$</tex> frame in a DC representation by introducing a virtually orthogonal variable, and the DC components of the zero-sequence voltage in the <tex>$dq$</tex> frame are regulated linearly by proportional integral regulators, rather than being calculated from uneven active powers in traditional controls. This removes all complicated operations. Finally, this paper presents simulation and experimental results for a <tex>$\mathbf{400}\ \mathbf{V}/ \pm \mathbf{7.5}$</tex> kvar star-connected STATCOM, in balanced and unbalanced scenarios, thereby verifying the effectiveness of the proposed control.