IMPROVEMENTS IN OR RELATING TO STABILITY AND POWER CONTROL IN MULTIPHASE AC NETWORKS

In the field of multi-phase AC networks there is a need for improved AC network voltage and power control, and overall power system stability. [0002] A method of determining actual first and second radius and phase angle values (rp, θρ, rn, θn) of a first time-domain symmetrical component v abc + of an AC voltage in a multi-phase AC network (10) comprises the steps of: (a) expressing a measured AC voltage (vabc) in the AC network (10) as at least a first time-domain symmetrical sequence component v abc + ; (b) equating the first time-domain symmetrical sequence component v abc + to a summation of first and second polar quantities, the first polar quantity having a first radius value (rp) and a first phase angle value (θp) and the second polar quantity having a second radius value (rn) and a second phase angle value (θn); and (c) calculating actual first radius and phase angle values (rp, θρ) by iteratively subtracting estimated second radius and phase angle values (r̂n, θ̂n) from the first time-domain symmetrical sequence component v abc + and calculating actual second radius and phase angle values (rn, θn) by iteratively subtracting estimate first radius and phase angle values (r̂p, θ̂p) from the first time-domain symmetrical sequence component v abc + , both while driving the difference between the estimated (r̂p, θ̂p, r̂n, θ̂n) and actual (rp, θp, rn, θn) values to zero.