Derivation of zero-sequence circulating current and the compensation of delta-connected static var generators for unbalanced load

Cascaded static var generators (SVG) with delta-configuration is discussed for a compensation of reactive, negative-sequence and harmonic currents. According to phasor analysis of negative-sequence current compensation, the role of zero-sequence circulating current for power balance is analysed. According to power analysis, the analytical expressions of zero-sequence circulating current and 2nd frequency ripples of dc-link voltages are derived. On the basis of this, the phase-current reference detection and the simplified control method of SVG for negative-sequence current compensation are proposed, which is concise and can achieve power balance of three-phase clusters by superimposing a zero-sequence circulating current without additional controllers. Finally, the simulation and experimental results have effectively verified the proposed method.