Recent research on fractional-order cascaded H-bridge multilevel static compensator (FCHM-STATCOM) indicates that it has better performance than the traditional cascaded H-bridge multilevel static compensator (CHM-STATCOM). The existing FCHM-STATCOM control system lacks some special control links for dealing with unbalanced operative situations, which is demanded by power systems. This paper improves the existing FCHM-STATCOM control system to satisfy the demand for power systems, creating the potential for it to be applied in the electrical industry. The improvement of the FCHM-STATCOM control system is based on traditional CHM-STATCOM control systems, introducing special control loops for unbalanced operative situations. The improved FCHM-STATCOM control system constructed in this paper consists of an outer control loop that can apply special strategies for different control objectives, two inner control loops, respectively, for positive- and negative-sequence currents, and an inter-phase balancing control loop for balancing its arm operation. At the end of this paper, the results of digital simulations verify the FCHM-STATCOM complete control system’s capacity to regulate its negative-sequence currents and balance its arm operation to deal with unbalanced operative situations. Moreover, based on different strategies, the control system shows effectiveness in eliminating power oscillations and current balancing.

The Unbalanced Control Research of Fractional-Order Cascaded H-Bridge Multilevel STATCOM