17 July 2014
Dr Petre Teodosescu from the Technical University of Cluj-Napoca, Romania, talks to us about the research interests behind the paper ‘Resonant LED driver with inherent constant current and power factor correction’.
The research field that I am passionate about is soft switching and/or high frequency electronic converters for renewable energy, lighting, motor drive and automotive applications. During my PhD studies, the power factor and energy quality aspects of compact fluorescent lamps were my main research domains. In the search for high performance lighting technology, my research interest also incorporated the new trend of light emitting diodes and their use in general lighting applications. In seeing how LED applications can take advantage of soft switching converters, the opportunity to use high frequency converters in other applications has become more and more intriguing and exciting.
During the past few years, the semiconductor industry, focused on the development of lighting LEDs, has produced remarkable advances in terms of luminous efficiency, thermal management, lifespan and, most importantly, drastically reducing production costs. In view of this, the electronics behind LED lighting systems needs to keep up and produce a driver with compatible performance. One of the biggest challenges is the driver's shorter lifespan. Features like high power density, dimmability or high power factor, in the appropriate cost context, are still limiting use of the combined LED and driver as a general lighting solution.
The lifespan problem of the driver is mainly based on the thermal management and passive component technology, within which, the use of electrolytic capacitor technology is a big issue. Intensive research has tried to limit the use of an input high voltage electrolytic capacitor through power factor correctors, but electrolytic capacitors are still used at the output and the problem remains. Other approaches use film or ceramic capacitors, known for their long lifespan, solving this reliability issue, but another problem arises from this - high cost.
We propose two ways of using an electronic circuit to address the cost problem to obtain a good option for incandescent lamp replacement, having the same advantages, in addition to the performance obtained by the use of LEDs. The low cost is obtained by using just discrete components, no special control loop and, in one topology, no capacitive filtering. Besides the low cost, the circuit is characterised by good power factor and high efficiency.
In our Letter we are trying to see things from a different perspective; do we actually need the capacitive storage? We believe that by taking the right precautions in terms of output light quality aspects, the use of capacitive filtering can be limited or, in some cases, eliminated. This can all be obtained because of the high performances of LEDs in terms of high speeds in switching and energy transformation. Compared to other solutions, the LED driver proposed for general artificial lighting has no special current control loop, constant current behaviour and high power factor obtained inherently by the use of a parallel LC resonant converter.
More research is needed to fully validate the “no capacitive filtering LED driver” but if this shows good results in terms of reliability, not just for the driver itself but also regarding the LED semiconductor performances, the idea could be used not only in LED lamps but part of the idea could be used in applications like low cost active power factor correctors.
With the help of power converters, the idea of high power factor and grid energy quality management has been a strong focus in our research group. This, combined with the intriguing idea of having an appropriate incandescent lamp replacement, is the subject of a project to find the right power factor correction for low power applications. I am also now working on a high frequency, high power density converter for renewable energy and motor drive applications. The power electronics used in the automotive industry is gaining more importance in my vision. The development of high frequency and high power density converters represents my general research approach and I believe that, combined with the necessity of high efficiency, at low cost, in a smaller package is a way forward for sustainable power electronics development.
This interview is based on the letter 'Resonant LED driver with inherent constant current and power factor correction' (new window)
A PDF version (new window) of this interview is also available
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