A Single Stage SEPIC PFC Converter for LED Street ... - IEEE Xplore

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single-stage LED lamp driver for street li based on SEPIC PFC converter topo continuous conduction mode (CCM). T achieved high efficiency and high power.
2010 IEEE International Conference on Power and Energy (PECon2010), Nov 29 - Dec 1, 2010, Kuala Lumpur, Malaysia

A Single Stage SEPIC PFC Converterr for LED Streett Lighting Applicationss Mokhtar Ali*, Mohaamed Orabi*, Mahrous E. Ahmed*, Abdelali El-A Aroudi** *APEARC, South Valley University, Aswan 81542, [email protected] ** UniversitatRoovira i Virgili, Tarragona, Spain, [email protected] street lighting as shown in Figg 1. The number of LEDs required for the streetlight is caalculated based on multiples of the light flux produced by a single LED [6].Typically the operating current of the higgh brightness white (HBW) LED ranges from 200 mA to 700mA. The typical drive voltage is about 2.5V to 4V. Fiigure 2 shows the current – voltage characteristics of a coommercial high brightness LED. The LED brightness is stronggly dependent on its current so an efficient driver is needed to regulate the LED current. In general lighting appplications the LED lamps have to operate from universaal AC input so an AC/DC converter is needed to drive the t LED lamp. The driver must comply with European IEC 61000-3-2-2000 mandatory regulations in terms of harmonic content and power factor correction (PFC C). A power factor of at least0.9 is needed. The converrter efficiency is one from the prime concerns due to thhe huge amount of power consumed by lighting sources.The driver must also have low cost and low component coount.

Abstract—Light Emitting Diodes (LEDs)) with their current performances have been proved to be the most suitable solution for street lighting applications. Nowadays, a topic of interest in this context is the design foor electronic driver in order to take the advantage of LE EDs performances. However, requirements such as high pow wer factor, long life time, accurate current control and high efficiency pose challenges to the design of LED driver ciircuits. Single-stage power factor correction (PFC) topologies are preferred here for their advantages of lower cost and near unity power C stage will surely factor, while adding a separated PFC increase the cost. This paper presents a high efficiency single-stage LED lamp driver for street liighting applications based on SEPIC PFC converter topoology operating in continuous conduction mode (CCM). This T converter has achieved high efficiency and high power factor all over the operating range with low total harmonicc distortion (THD). Simulation results are provided to demonstrate the T a laboratory effectiveness of the proposed driver. Then, prototype is built to verify the feasibilitty of the proposed LED lamp driver. Keywords—LEDs; power factor correction; street lighting; SEPIC.

I.

INTRODUCTIION

Developing efficient lighting system ms is an essential task today due to the huge amount of ennergy consumed by lighting sources as they represent approoximately 20 % of electrical energy consumed in the world w [1].With the advancement of lighting materials annd manufacturing process, a new lighting source, that is i high brightness Light Emitting Diodes (LEDs), are noow attracting more and more attention from both academy and a industry [2-3]. LEDs have no glass components or fillaments that made them with extremely long life time annd robustness. The life time of LEDs is more than 10 times that of the compact fluorescent lamp (CFL). They are a also insensitive to vibration or movement. LED lampps have relatively high efficacy compared with othercolorred light sources as there is no need for colored filters.Alsoo, the output light efficiency of power LEDs has increasedd over 100 lumens /watt. Moreover, LED lamps do not have any harmful emissions such as Ultra-Violet (UV) or Infra-Red (IR) output.They can be dimmed smoothly from f full output to off. LED lamps have a modular constrruction and do not need to an external reflector [4-5]. Because the illumination producedd by a LED is relatively weak, it is necessary to inccrease the flux by incorporating strings of LEDs of seeries and parallel combinations into a module array in ordder to use them for

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Fig. 1 LED module array used u in street lighting.

Fig. 2I-V curve of commerccial HB LEDs at 40° C.

It is also required to operate at wide input voltage variations that are usually ranges from 90V to 230V rms. The control loop not only performs power factor correction but also regulates the lamp current. The AC/DC converters are categorized into two types: two stages and single stage topologies. The two stage PFC converters consist of two separate stages.The first stage is to make power factor correction and the second stage is to make the load regulations. They give the benefits of reaching unity power factor and providing fast output dynamics but they increase the size of the drive and therefore the cost. The LED lamp drivers presented in [7] and [8] are examples for the two stages systems. Single stage topologies are the most suitable converters as they have only one active switch, high efficiency, power factor near unity, one control loop and smaller size than that of the two stages topologies and therefore lower cost [9]. Among the single stage topologies the flyback and SEPIC are the most attractive solutions. Flyback converter is one of the frequently used topologies for low-power low-cost AC/DC conversions for lighting applications as shown in Fig 3. It has the advantages of isolation between input and output, high efficiency and low total harmonic distortion (THD) but a propersnubber circuit is needed to suppress the ringing caused by the leakage inductance of the transformer. Thecomponents' voltage stresses are very highe.g. the switch voltage stress is (Vin + N Vo ), where Vin is the input voltage, Vo is the output voltage and N is the flyback transformer turns ratio[10-12]. The SEPIC converter shown in Fig 4 has the best power factor correction and lowercomponents' voltage stresses than flyback converter e.g. the switch voltage stress is (Vin + Vo )and also does not have the leakage ring effect as in flyback converter. The introduced driver circuits for LEDs application have been divided based on their power level. For most low power applications (indoor lighting), discontinuous conduction mode (DCM) operation is applied where unity power factor can be obtained directly as introduced for SEPIC converter in [13-14]. On the other hand, for higher power applications (street lighting) continuous conduction mode (CCM) operation is the preferred to achieve high efficiency. Therefore, this paper presents a high-efficiency singlestage LED lamp driver for street lighting applications. The proposed driver is based on the SEPIC converter operating in CCM. This converter has achieved high efficiency and near unity power factor all over the operating range with low THD. Section II shows the SEPIC LED lamp driver circuit and its modes of operation. In section III the power stage design calculations are presented and section IV illustrates the control loop design. Simulation and experimental results to verify the feasibility of the proposed driver are presented in V.Finally, some concluding remarks are presented in the last section.

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II. MODES OF OPERATION AND STEADY STATE ANALYSIS

The SEPIC converter combines the best features of the boost and flyback topologies, making it especially advantageous in high power factor applications. The SEPIC converter consists of two inductors, two capacitors, one switch and a diode as shown in Fig 4. The voltage after the diode bridge rectifier is the rectified AC input voltage. The current sensing resistance Rs is put in series with the LED module. The SEPIC converter can be operated in DCM or in CCM. Operating in DCM, the current ofinductor L1 has three stages of operation. The first stage is during period t1 in which switchQ1 is on and diode D1 is off.The second stage is during period t2in which switchQ1 is off and diode D1 is on.The third stage is during period t3 in which switchQ1 is off and diode D1is off. Figure 5 shows the inductor L1 current during this mode of operation. The converter behaves as a ‘resistor emulator’ where the line current exactly follows the line voltage and provides a high power factor with a simple control technique with only one feedback loop and the automatic current shaping at constant switching frequency and duty cycle but the ripple content is high so the THD is large and requires an input EMI filter. It also suffers from high current stresses on devices. The second approach to achieve PFC is CCM operation which uses current control technique.Operating in CCM, the current of inductor L1 has two stages of operation. The first stage is during period t1 in which switchQ1 is on and diode D1 is off.The second stage is during period t2 in which switchQ1 is off and diode D1 is on.The inductor L1 current during this mode is shown in fig 6. As compared to voltage follower approach, it has low ripple and low current stresses but its controller has two loops and needs sensing of other variables in addition to the LED current [15-16]. However, for street lighting applications, CCM is the best choice as DCM imposes very high current stresses on devices. As mentioned above, operating in CCM has two stages of operation a) SwitchQ1 is on and diode D1is off b) SwitchQ1 is off and diodeD1is on. The converter circuits during these two stages are shown in Fig. 7 and Fig. 8, respectively.

Fig. 3Flyback converter for driving LEDlamps.

C1is small and must ensure that the voltage over C1is equal to the rectified input voltage.

Assuming that the switching frequency ( ) of the converter is much higher than the utility frequency ( ) so the input voltage can be assumed constant during switching cycle and C1is properly selected which means that the voltage of C1is equal to the rectified input voltage as in DC-DC SEPIC converter.

1 .

whereωL