Development of Concentric-Winding Type Three-Phase Variable Inductor

A variable inductor, which consists of only magnetic core and primary dc and secondary ac windings, can control effective inductance of the secondary ac winding by the primary dc current due to the magnetic saturation effect. Hence, the variable inductor can be applied as a VAR compensator for voltage regulation in electric power systems. In a previous paper, a novel concentric-winding type three-phase variable inductor was proposed, in which the primary dc and secondary ac windings are concentrically wound on the same leg. It was indicated by a numerical analysis that the proposed variable inductor has good controllability and low distortion current. This paper presents the experimental results of a 4 kVA concentric-winding type three phase variable inductor. Furthermore, to prove the advantage of the proposed variable inductor, copper and iron losses, leakage flux, and reactive power per weight are compared with those of the previous variable inductor. It is demonstrated that the copper loss of the proposed variable inductor is improved by 40%, the leakage flux is reduced by half, and the weight can be reduced by 40% in comparison with the previous variable inductor.