High Efficiency DC-DC Converters Including a Performed Recovering Leakage Energy Switch

Abstract

In this paper we studied the possibility to use high voltage DC bus to facilitate the energy transport in the smart grids, especially oriented to renewable energies. Recent studies [1] show that it is necessary to increase the output voltage in order to minimize transport losses on high distances. That is possible if we use electronic systems able to convert with a high efficiency the low voltage delivered by the local generators constituted by the Pv panels, the wind generators and other ones systems in various power ranges, and providing a high output voltage. In our study we expect to reach a voltage up to 5kV and more. The facilities offered by the DC bus are essentially in a very easy full synchronization and the possibility of communication supported by the power lines as in a PLC mode. So, as a consequence, it is important to improve the DC-DC converters to reach more than 5kV DC at the output. The main difficulty encountered when the goal is to increase the voltage in a smart DC-DC converter, is the small volume usable of those converter, the low cost, and of course the higher efficiency as possible. High voltage elevation implies the use of specific transformers (THT transformers) with a high voltage isolation performance, and a specific coils configuration to avoid spark discharges. The use of high voltage transformers ineluctably implies lower coupling coefficient between the coils, and undesirable superposed oscillations in the primary and secondary currents and voltages. More over the low coupling factor implies an increasing of the internal energy stored in the leakage inductors, that must recycled in order to keep a good efficiency. Previous studies [2] show the interest of using light structure converters based on one driven switch as the basically step-up boost. Some improvements [3] allow an expanding range working, and more specifically in the high value Vout /Vin of the converter ratio. We demonstrate in this paper that it is possible to use low coupled coils transformers to insure a perfect control and management of the energy without worrying about the leakage non-transferable energies stored in the various distributed inductors.