Digital Simulation of Modified Solar Based LED Driver for Street Light Application

Transcription

1 Digital Simulation of Modified Solar Based LED Driver for Street Light Application Abstract In this paper, a novel design of integrated double buck boost converter with PI filter is proposed for power LED Street light. This circuit consists of only one switch three inductors and three capacitors and this can provide very high power factor with increased efficiency. In this paper the film capacitors used in order to reduce the size of the filter capacitor. The open loop simulation was done to analyze the output of the converter and the closed loop simulation was done in order to compare the behavior of circuit under open loop and closed loop while disturbance occur. Index Terms IDBB-Integrated Double Buck boost Converter, LED- Light Emitting Diode, Continuous Conduction mode CCM, Discontinuous Conduction Mode- DCM. N.Manimaran 1, S.A.Elankurisil 2, K.R.Devabalaji 3 I. INTRODUCTION Nowadays the energy-inefficient incandescent lamps and mercury-based tubular and compact fluorescent lamps are replacing as LED lamps. Due to the high efficiency of the LEDs with maximum illumination, the utilization is 85%-90% of the input power into light energy, whereas the fluorescent lamps will produce only 77%.[2]-[4] On the other hand global warming and increasing power demand etc. are may be fulfilled by LEDs by implementing enhanced control technique (light dimming and preheating of filaments if possible). The recombination of electrons and holes can cause either photons (light) or phonons (heat). So the junction temperature of the LEDs increasing leads to the degradation of the luminous flux of LEDs [4]. The main drawback of these LEDs is they needs constant voltage as input and they need current limiter before the input of the LED. An integrated double buck boost converter is proposed to supply power-led lamps from the Solar power, providing high power factor, low LED current ripple, and high efficiency. The operation of the converter is equivalent to two buck boost converters in cascade, in which the controlled switch is shared by the two stages. Thus, the proposed converter includes two inductors, two capacitors, three diodes, and one ground-referenced controlled switch, featuring affordable low cost and good reliability for this kind of applications. In Section II basis of LED is presented,. In Section III Modified IDBB converter is presented and In Section IV, Simulation Circuit Diagrams is presented. Fig. 1: Efficacy versus junction temperature of LED. Structure of LED II. LED Fig 2 LED A light emitting diode is nothing but PN junction diode. Carriers inject in the forward biased, and then they emits incoherent light. Let us consider the pn + junction. The depletion region mainly concentrates on p-side, so there is a potential barrier from E c on n side to the E c on the p side is named as built-in voltage. This potential barrier prevents the excess free electrons on the n + side from diffusing into p side. 1

2 INDIRECT RECOMBINATION: In the indirect band gap materials, the minimum energy in the conduction band is shifted by a k-vector relative to the valence band. The k-vector difference represents a difference in momentum. Due to this difference in momentum, the probability of direct electron hole recombination is less. In these materials, additional dopants (impurities) are added which form very shallow donor states. These donor states capture the free electrons locally; which provide the necessary momentum shift for recombination. FIG. 3:P-N+ JUNCTION UNDER UNBIASED AND BIASED CONDITIONS The recombination can be classified into the following two kinds Direct recombination Indirect recombination DIRECT RECOMBINATION: In direct band gap materials, the minimum energy of the conduction band lies directly above the maximum energy of the valence band in momentum space energy. In this material, free electrons at the bottom of the conduction band can recombine directly with free holes at the top of the valence band, as the momentum of the two particles is the same. This transition from conduction band to valence band involves photon emission (takes care of the principle of energy conservation). This is known as direct recombination. Direct recombination occurs spontaneously. GaAs is an example of a direct band-gap material. LED Structure: Fig. 5: Indirect Recombination The LED structure plays a crucial role in emitting light from the LED surface. The LEDs are structured to ensure most of the recombination s which take place on the surface by the following ways. By increasing the doping concentration of the substrate, so that additional free minority charge carriers electrons move to the top, recombine and emit light at the surface. By increasing the diffusion length L = Dτ, where D is the diffusion coefficient and τ is the carrier life time. But when increased beyond a critical length there is a chance of re-absorption of the photons into the device. The LED has to be structured so that the photons generated from the device are emitted without being reabsorbed. One solution is to make a thin p layer on the top, enough to create a depletion layer. Following picture shows the layered structure. There are different ways to structure the dome for efficient emitting LEDs are made on an n-type substrate, with an electrode attached to the p-type layer and it is deposited on its surface. P-type substrates occur as well. Fig. 4: Direct Recombination 2

3 FILM CAPACITORS: Fig. 6: (a)p-layer grown epitaxial on an n + substrate (b) First n + is epitaxial grown and then p region is formed by dopant diffusion into the epitaxial layer. LED efficiency: A very important metric of LED is the external quantum efficiency ηext. It quantifies the efficiency of the conversion of electrical energy into emitted optical energy. It is defined as the light output divided by the electrical input power. It is also defined as the product of Internal radioactive efficiency and Extraction efficiency. η ex t = P out (optical) / IV For indirect band gap semiconductors ηext is generally less than 1%, whereas for a direct band gap material it could be substantial. η in t = rate of radiation recombination/ Total recombination The internal efficiency is a function of the quality of the material and the structure and composition of the layer. Advantages: The size of the LED is very small. It can be used for frequent on-off cycling, unlike fluorescent lamps that burn out quickly when cycled frequently. The efficiency of LED is high when compared to other light. LED does not contain mercury as in fluorescent and other lamps. LED can easily dim by using PWM or reducing the forward current. The life time of LED is high when compared to other lamps. Applications: LED has a lot of applications. Following are few examples. Devices, medical applications, clothing, toys Remote Controls (TVs, VCRs) Lighting Indicators and signs Optoisolators and optocouplers CONSTRUCTION OF CAPACITORS CELLS Film capacitors are built up by two electrodes (the capacitor plates) with plastic dielectric material in-between. The type of electrode used determines whether the capacitor is a metalized film or film/foil type. In metalized types, the very thin electrode is evaporated on the plastic dielectric material. The thin metalized electrodes have a thickness of approximately 10 nm to 50 nm. The electrodes of film/foil capacitors have discrete metal foils with thicknesses of approximately 5 μm to 10 μm. Metalized capacitors have a self-healing behaviour as an intrinsic characteristic. Self-healing is the ability to recover after a dielectric breakdown. Due to their construction, very thick electrodes, film/foil capacitors can carry higher currents than metalized types, but are much larger in volume. These capacitors cannot recover after a breakdown. Therefore In some constructions double side metalized plastic film is used as electrode to replace the foil. The plastic material has only the function of carrier: the self-healing properties are maintained and the current carrying capability is increased a lot in comparison with single metalized types. Depending on the AC voltage in the application, single or series constructions are used. In a series construction two or more sections are placed internally in series in one capacitor. Single section capacitors are normally used for products with an AC rating up to 300 Vac. Series constructions are used for higher voltages. The end connection of the capacitor cell to the outside circuit is realized by metal sprayed end connections wherein lead wires or tabs are welded. ENCAPSULATION Finally the capacitor cells can be protected for severe environmental conditions or to withstand passive flammability. Encapsulation with epoxy materials in plastic boxes is commonly used for fixed outline dimensions. Epoxy dipped capacitors have a more rounded and easy to handle shape. All these encapsulations are flame retardant materials fulfilling the UL 94 classification system. Axial types are typically of the wrapped end construction. An extra wrapped film and epoxy at the end connections protects the cell. III. MODIFIED IDBB CONVERTER This IDBB converter acts as two buck-boost converter in series. The input of the buck-boost converter is made by Li,D 1,C, and S. similarly the output is L 1,D 2,D 3,Co,ans S.The reversing polarity produced by the first converter in the capacitor C B is corrected by the second converter, given a positive output voltage with respect to ground. It will make the circuit simple for the measurement of the load current in the closed loop operation and it leads to reducing sensing circuit and cost. 3

4 OUTPUT AND BUS VOLTAGES Fig.7 : Block Diagram of Circuit Diagram With R being the static equivalent resistance of the LED load, which can be obtained by the ratio between the dc values of LED voltage (V LED ) and current (I LED ) at each operating point. The sum of both voltages does not depend on the duty cycle, being only proportional to the line peak voltage, as given by the following: Where V b is Fig. 8: modified IDBB converter. If the inductor is operated in the discontinuous conduction mode (DCM), the average current in the line is proportional to the line voltage and it leads to provide nearly unity power factor. In order to achieve bus voltage C b independent of the duty cycle and output power. we have to operate the circuit in the discontinuous conduction mode. But it leads to drawback of requiring a higher value of output capacitance to have a low current ripple through the load. The output inductance is operated in the CCM in order to obtain reduced value for output capacitance. Since the current ripple is lower in this operation. The second stage is operated in CCM with duty cycle < 0.5 which reduces the low-frequency ripple voltage. D limit can be obtained from the voltage conversion ratio in the DCM CCM boundary. As long as the actual duty cycle is lower than the limit value the input stage will operate in DCM. IV. SIMULATION RESULTS LINE CURRENT AND INPUT POWER: The input current i g corresponds to the current through the inductance L i during the time interval 0 DT S, where D is the transistor duty cycle and T S is the transistor switching period. Thus, the value of the input current averaged at line frequency can be calculated as follows Since the output stage corresponds to a buck boost converter operating in CCM, the bus voltage V B can be calculated by using the voltage conversion ratio for this converter. Fig. 9: proposed system circuit diagram 4

5 Closed loop circuit diagram Fig. 13: output Current of proposed system Fig. 10: closed loop circuit diagram Fig. 14: Output power of proposed system Fig. 11: output Voltage of Existing method Fig. 15: output Voltage of proposed method Fig. 12: Output power Existing system 5

6 Closed loop Fig. 16: Input voltage Fig. 17: output current Fig. 18: output voltage The simulation results of the existing circuit and waveform diagram are shown in (Figures 10,11) and proposed circuit and waveform are shown in (Figures 12,13,14) are presented and analyzed in the above Diagrams, the proposed system output voltage, can be increased with reduced ripple and output current, power also is increased. V. CONCLUSION A novel design of an IDBB converter has been investigated in this work in order to implement an improved high-factor offline power increasing the converter mean time between failures. The simulation results can show that the proposed converter can give high PF with more reduced output ripple, good efficiency, and low cost. This circuit can be able to implement for street light application. The LED efficiency increases for lower current values. Nevertheless, since the converter is formed by two stages integrated in a single one, its dynamics response can be made quite fast. For these reasons, and taking into account that, at this moment, galvanic isolation is not required by the standards, and the converter was designed without isolation. Nevertheless, it can be achieved very easily by simply including a secondary winding coupled to the output inductor. In this manner, the second stage will behave as a fly back converter instead of a buck boost converter. The operation of the converter will be exactly the same, having just an extra design parameter given by the winding turn ratio. REFERENCE [1 ] J. Marcos Alonso, Juan Viña, David Gacio Vaquero, Gilberto Martínez, and René Osorio, Analysis and Design of the Integrated Double Buck Boost Converter as a High-Power-Factor Driver for Power-LED Lamps, IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 59, NO. 4, APRIL 2012 [2 ] D. Gacio, J. M. Alonso, J. Garcia, L. Campa, M. Crespo, and M. Rico- Secades, High frequency PWMdimming technique for high power factor converters in LED lighting, in Proc. 25th Annu. IEEE APEC, Feb , 2010, pp [3 ] J. Garcia, A. J. Calleja, E. L. Corominas, D. Gacio, and J. Ribas, Electronic driver without electrolytic capacitor for dimming high brightness LEDs, in Proc. 35th Annu. IEEE IECON, Nov. 3 5, 2009, pp [4 ] Z. Bo, Y. Xu, X. Ming, C. Qiaoliang, and W. Zhaoan, Design of boost-flyback single-stage PFC converter for LED power supply without electrolytic capacitor for energy-storage, in Proc. 6th IEEE IPEMC, May 17 20, 2009, pp [5 ] K. I. Hwu, Y. T. Yau, and L.-L. Lee, Powering LED using high-efficiency SR flyback converter, in Proc. 24th Annu. IEEE APEC, Feb , 2009, pp [6 ] C. C. Chen, C. Y. Wu, Y. M. Chen, and T. F. Wu, Sequential color LED backlight driving system for LCD panels, IEEE Trans. Power Electron., vol. 22, no. 3, pp , May [7 ] K. Zhou, J. G. Zhang, S. Yuvarajan, and D. F. Weng, Quasi-active power factor correction circuit for HBLED driver, IEEE Trans. Power Electron., vol. 23, no. 3, pp , May [8 ] Luxeon LXK2 white LED datasheet, (2006). DS51, in [Online]. Available: [Online]. Available: [9 ] Y. Gu and N. Narendran, A non-contact method for determining junction temperature of phosphor-converted white LEDs, in Proc. SPIE 5187, 3rd Int. Conf. Solid State Lighting, 2004, vol. 5187, pp [10 ] C. C. Lee and J. Park, Temperature measurement of visible light-emitting diodes using nematic liquid crystal thermography with laser illumination, IEEE Photon. Technol. Lett., vol. 16, no. 7, pp , Jul

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