A drive converter for light emitting diodes is presented, which is able to add the constant current operation mode and power factor correction without any control feedback or special control algorithm while obtaining very good performances regarding high efficiency, good reliability and most importantly, low cost. The converter is based on a half bridge resonant topology, controlled with a discrete self-oscillating drive circuit, with an output parallel resonant tank. The working principle is based on the inherent current source behaviour of these kinds of converters, allowing a high power factor and low harmonic distortions. One topology uses no electrolytic high or low voltage filtering capacitors, thus obtaining a longer working lifetime for the driver. In addition, a second topology with output non-electrolytic condenser filtering for higher performances in dimming applications is proposed.

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L e h r s t u h l f u r E r z e u g u n g u n d A n w e n d u n g e l e k t r isct-ier E r i e r y i e R u h r--U n i v e r s i ty B oc h u m , D -4 6 3 0 B o c k i CA r -r i , c3e r-rna n y Abstract -Control strategies for three-phase voltage dc-link PWM converters presented so far always use a portion of the available switching operations of the converter valves for control of the dc-link voltage. The new control strategies presented here use all allowed switching operations of the converter such that the converter has a line-friendly performance from point of view of the utilities or the consumer. In case of an ideal converter (switching frequency of the semiconductor devices is infinitely high, no losses) and a distortion-free supply network, the power factor becomes equal to unity under steady-state conditions and the dynamic characteristics of the control system are sufficient. In order to reach this "line-friendly" performance with an existing converter and to keep the expenditure for the line-side filter low. appropriate PWM at a high switching frequency ( > 10 kHz) is necessary. The theory of the control strategies and appropriate PWM are presented. Practical results obtained with an IGBT-converter illustrate the dynamic and steady-state performance of the new control system in both energy-flow directions. The new control strategies are most economically used in the medium power range ( 5 kW to 200 kW).