A case of negative interaction is reported between the AC and DC voltage co
ntrol of a STATCOM installed in a power system. A technique to design a dec
oupled multivariable sampled regulator for multi-input multi-output systems
is applied-for the co-ordinated control-of STATCOM AC and DC voltage, so a
s to overcome a potential negative interaction. A comprehensive demonstrati
on is presented by an example power system installed with a STATCOM.