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U. Drofenik, J.W. Kolar:
"Influence of the Current-Dependency of the Inductance of the Input Inductors of Three-Phase PWM Rectifier Systems on the";
Vortrag: IEEE Applied Power Electronics Conference, Tokyo Japan; 03.04.2000 - 07.04.2000; in: "Proceedings of the International Power electronics Conference", Vol.2 (2000), S. 1017 - 1022.

Abstract. Three-phase boost-type PWM rectifier systems with inductors connected in series on the AC side are characterized by a degree of freedom of the modulation scheme due to switching states being redundant concerning the input voltage formation. Therefore, there is a possibility of optimizing the modulation scheme of such converter systems, e.g., concerning the mains current ripple rms value. All optimized modulation schemes which have been proposed so far are based on the assumption of inductances that are linear, i.e. current-independent as given, e.g., for inductors with ferrite cores. However, aiming for lower weight and size of inductive components in recent years new magnetic materials, e.g., iron powder, have been introduced which show a pronounced dependency of the permeability on the magnetomotive force and/or result in a nonlinear behavior of the input inductors, i.e. in a dependency of the inductance on the actual current level.
This paper calculates the optimized modulation scheme for a three-phase six-switch PWM rectifier under consideration of the nonlinear behavior of the input inductors. It is shown that even for highly nonlinear behavior space vector modulation as used for linear inductors can be applied and results in a current harmonics rms value being close to the actual minimum. Furthermore, guidelines are given how to select the inductance of a nonlinear inductor in order to achieve an equal rms value of the input current ripple as in the case of a linear inductor. Finally, size, weight and losses of a linear and nonlinear inductor are compared for optimal modulation and equal ripple of the mains current.