Electronic Ballast Platform - EBP

In this paper will be reported the implementation of a flexible platform to study electronic ballasts systems. The platform is a microcontrolled and FPGA-based system and was developed to generate command signals to the half bridge inverter. A specific hardware using FPGA was developed to generate the switches signals command. This hardware is responsible for the autonomous frequency (FM) and pulse width (PW), setting free the microcontroller for others applications. This platform may be programmed using a personal computer which give us a high level of flexibility, allowing the study of different ballasts topologies, power filters, new control and dimmer techniques, as well as, acoustic resonance effect on high intensity discharge (HID) lamps. Finally, experimental results will be presented for a 250 W high-pressure sodium (HPS) lamp electronic ballast, however this platform may be used for any kind of discharge lamps. Introduction Nowadays, an important topic of awareness is the importance of environment preservation. In this direction, important efforts have been made in the diverse areas of knowledge. In electrical engineering field, this phenomenon has reflected in searching for alternatives energy systems, for a higher efficiency on available resources utilization, for losses reduction in equipments and for an increase of electric energy quality from who supplies to who consumes. In the last few years the market was flooded by a great number of electronic ballasts for fluorescent lamps operating in high frequency, in special for the compact fluorescent lamps. Its utilization was widely stimulated by Brazilian media for energy economy, due the fact that luminous efficiency increases with the frequency for this kind of lamp. Brazil faced a serious energy crisis in 2001. Many corrective actions were taken to mitigate this serious problem. One of them was the energy rationing which consisted in overtaxing or even cutting energy supply from consumers which exceeds the prefixed energy quotes. Also many electric energy concessionaires had distributed gratuitously this type of lamp for residential consumers, showing the importance of illumination’s segment inside the global energy consumption, estimated to be about thirty percent of total consumption. Because of these, innumerable research groups around the world, like [1], [2], [3] and [4], have dedicated their efforts to the development of new topologies and new control techniques for different kinds of lamps. Most of magnetic ballast manufacturers had to develop electronic ballasts for discharge lamps to guarantee their survival in business because the consumers started to demand this type of product. Also it simplifies the production line, which has expressive physical reduction and productivity increase in relation the line that produces the conventional ballasts. Now, the challenges for industries are the reduction of production costs, the reduction of converter size, substantial improvement of energy quality consumed by ballasts, unitary power factor and null harmonic distortion. Here in Brazil, the development of electronic ballasts for HID lamps is being made by a few groups of researchers. However in a close future, these ballasts will be in the production lines of main national manufacturers. The porpoise of this paper is to report the development of an electronic ballast platform, that allows the study and development of ballasts for HID lamps. There are many kind of high-pressure lamps; however, this work will focus only high-pressure sodium lamps (HPS), widely used in public illumination. The HPS lamps radiate energy on a great part of the visible spectrum [5]. These lamps provide a reasonable color reproduction (it has IRC 23 color reproduction index). They are available up to 130 lm/W of luminous efficiency and temperature color of 2100 K, approximately. The HPS lamps, as any other HID lamps, need ballast to operate correctly. The Ballast is an auxiliary equipment linked between the power line and the discharge lamp. The Ballast has two main functions: guarantees the ignition of the lamp through the application of a high voltage pulse between the lamp electrodes and limits the current that will circulate through it. The lamp would be quickly destroyed without current limitation, due the negative resistance characteristic of the lamp, as can be observed in Figure 1. The HPS lamps have many particularities when they operate in high frequency, such as: ƒ Can be modeled by a resistance in steady state; ƒ Can have controlled luminous intensity; ƒ The spectrum color reproduction can be modified; ƒ Presents the acoustic resonance phenomenon, which can result in the arc extinguishing until the lamp destruction; Lamp Current Positive Resistence