Application of cubic spline interpolation in var compensator with thyristor controlled reactor

Var compensator with thyristor controlled reactor is usually used to adjust power factor and three-phase unbalanced degree in the power system. The inductive reactive power of compensator is controlled by the conduction angle of the thyristor, but it is difficult to get accurate conduction angle since the relationship between inductive reactive power and conduction angle is nonlinear. In order to get accurate conduction angle corresponding to required inductive reactive power, this paper uses cubic spline interpolation algorithm to fit the nonlinear function of two adjacent sample data. Each sample data includes conduction angle and reactor amplification coefficient, and the reactor amplification coefficient is independent variable. A cubic function is established to fit the nonlinear function between conduction angle and reactor amplification coefficient. The cubic function value is the conduction angle corresponding to the input amplification coefficient. The more sample data are used, the more accurate conduction angles are calculated. At last, it uses the proposed method to calculate the conduction angle with the amplification coefficient in range [20], [30], and the results show that the conduction angles are accurate enough to use in practice.