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Power Electronics for Lighting

Faculty: Simone Buso, Giorgio Spiazzi

Introduction

Lighting is one of the traditional areas of power electronics application. The electronic ballasts for fluorescent, compact fluorescent, high pressure lamps have dominated the scene for a relatively long time. More recently, the development of line fed drivers for high-brightness-light-emitting-diode (HBLED) based lamps has become a major area of interest for industrial manufacturers and academic researchers worldwide. The interest is motivated by the high expectations regarding the technology of power LEDs. These light sources are expected to replace, in the near future, the currently dominant solutions for domestic general lighting, i.e. halogen and fluorescent lamps. It is generally recognized that one of the key requirements for a pervasive diffusion of the technology, besides the obvious reduction of the LED cost, is the minimization of the driver’s volume. This seems to be recommendable in order to avoid what is already happening with compact fluorescent lamps (CFLs), whose market penetration is limited, among other factors, by the bulky design of the electronic ballast. The driver’s volume reduction calls for, in the first place, the identification of simple (i.e. characterized by a reduced component count) converter topologies, capable of very high frequency operation, in the several hundred kHz or, possibly, MHz range, as required to reduce the reactive components’ volume to the minimum. At the same time, the lamp thermal management and the converter’s efficiency issues need to be properly addressed, so as to guarantee the minimization of the stress suffered by the light emitting devices and the consequent maximization of the lamp expected lifetime. 

Research goals

The Power Electronics Group is active in this line of research, with particular reference to the investigation of AC/DC converters for line-fed HBLED based lamps, capable of operating at high switching frequency. Indeed, the target reduction of  circuit volume occupation poses different technological challenges. The magnetic component design is a key factor and needs to be optimized so as to make the inevitable stray inductances capable of playing an active role in the power conversione process (which is possible in resonant converters topologies). In turn, this calls for modelling and implementation techniques capable of guaranteeing adequate repeatability of  transformer parameters. As far as the solid state components are concerned, suitable custom integrated circuits need to be developed, including most of the control circuit and possibly the drivers for power switches.

Research areas

The areas covered by the research program are both system level and circuit level:

  • Investigation of the tradeoff between input current harmonics and LED current crest factor and conversion efficiency (filter caps minimization)
  • Evaluation of the possibility to operate at high frequency with a reasonable efficiency (magnetic component minimization)
  • Study of the magnetic component (transformer) and how its physical dimension scales with the operating frequency
  • Analysis of the correlation between  transformer  leakage and magnetizing inductance at high frequency so as to find the best winding arrangement

Line-fed LED lamp driver based on an Asymmetrical Half-Bridge Flyback Topology. No electrolytic capacitors are employed. Physical dimensions 2.1 x 4.2 x 1.4 cm.
 

Publications

  • S. Buso, G. Spiazzi, F. Sichirollo, "Study of the Asymmetrical Half-Bridge Flyback Converter as an Effective Line-Fed Solid-State Lamp Driver," IEEE Trans. Ind. Electron., Vol. 61, no. 12, pp. 6730-6738, Dec. 2014
  • F. Sichirollo, J. M. Alonso, G. Spiazzi, "Use of Current Controlled Mutual Inductor to Limit Recycling Current in the AHB-Flyback Converter," 38th Annual Conference of the IEEE Industrial Electronics Society (IECON), Montréal, 2012, pp. 4593-4598.
  • F. Sichirollo, S. Buso, G. Spiazzi, "A High Efficiency and High Power Factor Offline Converter for Solid State Street Lighting Applications," IEEE Energy Conversion Congress and Exposition (ECCE), North Carolina, 2012, pp. 1188-1195.
  • S. Buso, G. Spiazzi, M. Meneghini, G. Meneghesso, “Performance Degradation of High Brightness Light Emitting Diodes under DC and Pulsed Bias”, invited paper, IEEE Transactions on Device and Materials Reliability, Vol. 8, No. 2, June 2008, pp. 312-322.
  • S. Buso, G. Spiazzi, “Non Iterative Design Procedure of LCC-based Electronic Ballasts for Fluorescent Lamps Including Dimming Operation”, 2009 IEEE Energy Conversion Congress and Exposition, San Jose, California, USA, September 20-24, 2009, pp. 2065-2072.
  • S. Buso, G. Spiazzi, “A triple output driver for line-fed HBled lamps” 10th Brazilian Power Electronics Conference, Bonito (MS), Brazil, September 27-October 1, 2009, pp. 571-577.