The benefits brought to electric power systems by reactive power static compensation are well known. Further benefits can arise when an independent active power compensation and a reactive one are carried out together, especially if the electronic apparatus can be controlled rapidly. Independent and rapid control of both active and reactive power can be achieved by convertors with biparametric regulation, whose behaviour is strongly influenced by their AC power system interactions and which can work in nonideal conditions such as those arising from voltage harmonics and unbalances. The authors present mathematical models of convertors with biparametric regulation with a view to carrying out a complete analysis in steady-state nonideal conditions; the models are developed so that they are applicable for studies both at fundamental and at harmonic frequencies. Numerical applications to convertors connected to a superconducting coil for energy storage are also discussed.