F. Stögerer, J.W. Kolar, U. Drofenik:
"A Novel Concept for Transformer Volt Second Balancing of a VIENNA Rectifier III Based on Direct Magnetizing Current Meas";
Talk: IEEE Nordic Workshop on Power and Indusrial Electronics, Aalborg, Dänemark; 06-13-2000 - 06-16-2000; in: "Proceedings of the IEEE Nordic Workshop on Power and Indusrial Electronics", (2000), ISBN: 87-89179-29-3; 134 - 140.

For a VIENNA Rectifier III different turn-on and turn-off delay times of the power transistors and different on-state voltages of the valves would cause an unbalance of the positive and negative volt seconds applied to the high frequency transformer within a pulse period and/or result in transformer saturation without additional measures.
This paper proposes a novel concept for actively ensuring a symmetric magnetization with switching frequency of the transformer magnetic core of a VIENNA Rectifier III based on direct measurement of the magnetizing current. The magnetizing current is determined by subtraction of the transformer primary and the secondary currents being weighted according to the transformer turns ratio. The subtraction is realized by magnetic compensation employing a through-hole DC current transducer. A deviation from a symmetric magnetization within a pulse period is detected and used by a controller for closed-loop balancing of the volt seconds applied to the transformer primary in order to eliminate an existing asymmetry. The controller is designed based on sampled data system theory. The theoretical considerations and the controller dimensioning are verified by experimental results gained from a 8.5kW prototype of the VIENNA Rectifier III.