Comparison of Central Dimmer Systems Based on ... - IEEE Xplore
IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 59, NO. 4, APRIL 2012
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Comparison of Central Dimmer Systems Based on Multiple-Tapped Autotransformer and High-Frequency Switching Converter Guillermo Velasco-Quesada, Member, IEEE, Manuel Román-Lumbreras, Member, IEEE, and Alfonso Conesa-Roca, Member, IEEE
Abstract—This paper compares two central dimmer system technologies used in street lighting. These dimmers are utilized in adaptive lighting systems based on high-intensity-discharge lamps and magnetic ballasts. The first technology is based on a multiple-tapped autotransformer which is commonly used for these types of installations. The second technology is based on a high-frequency switch converter (more specifically in a singlephase matrix converter topology) and represents a novelty for this type of application. Tests were conducted to determine the main features of both dimmer technologies, and the obtained results are presented. Index Terms—Adaptive lighting system, central dimmer system, street lighting.
I. I NTRODUCTION
S
TREET lighting is a public service which governments and municipalities must offer due to its important role of providing comfort and enhancing citizens’ security. In this regard, various studies show the effect that street lighting has on traffic accidents, crime, fear, and pedestrian street use after dark [1]–[3]. Increasing local business, promoting economic development, and aesthetic factors are also its functions [4]. The energy consumed by street lighting in the European Union (EU)-27 over the 2007 is estimated at 37 TWh, which accounts for 1.3% of the total electricity consumption, with an approximate cost of 2.5 billion euros [5]. This data place street lighting energy consumption between 45 kWh/cap (kilowatthour per capita and year) in countries such as Germany or The Netherlands and 85 kWh/cap in countries such as Slovenia or Spain, with 50 kWh/cap being the average energy consumption in the EU-27 [6]. Reduced street lighting energy consumption provides significant savings to owners, reduces taxes [7], decreases the burden over the electric system, and reduces greenhouse gas emissions. In this regard, new technologies can provide great potential for energy savings in street lighting systems. The replacement of Manuscript received September 17, 2010; revised November 29, 2010; accepted January 21, 2011. Date of publication February 7, 2011; date of current version November 1, 2011. The authors are with the Industrial Engineering College of Barcelona, Polytechnic University of Catalonia (EUETIB-UPC), 08036 Barcelona, Spain (e-mail: [email protected]; [email protected]; alfonso. [email protected]). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TIE.2011.2112321
existing street lighting by intelligent street lighting systems can reduce energy consumption by about 70% [8]. Based on its long life span (over 30 years), there is a large market for upgrading old street lighting technology. However, a strong adversity to improving their energy efficiency is based on a lack of simple and low-cost energy saving measures. Lamps in street lighting are mostly high-intensity-discharge (HID) lamps that need an appropriate ballast and optic system. In most cases, the implementation of an energy-efficient technology implies that the ballasts, or the complete luminary, need to be replaced [9]. This is the case of the street lighting systems based on high-brightness light-emitting diodes (LEDs). The high cost of this technology, along with some technical problems to be solved (directivity, luminous efficacy, or suitable current drive circuits), makes this a promising technology but in the medium or long term [10]–[13]. As a result, measures which are normally implemented consequences to increase street lighting energy efficiency are based on keeping the luminaries installed (usually HID lamps with magnetic ballasts) and using adaptive lighting systems instead of intelligent street lighting systems. Adaptive lighting is the most basic approach to the practical implementation of intelligent street lighting. This is because the concept adaptive lighting only describes the light performance on a road level [14]. Among other capabilities, a basic adaptive lighting system must adjust the illumination level of a particular street according to its time pattern of utilization. The illumination level must be higher at times of greater utilization and must fall gradually when its use decreases. This control of the illumination is realized by means of a device that, following an established hourly program, adjusts the lamp light output. A dimmer (also called a fader) is the device used for light brightness variation, and its operating principle is closely related to the utilized luminary technology. For example, dimmable LED drivers are described in [15] and [16], and in [17], a flicker-insensitive dimmer for incandescent lamps is described. Moreover, in [18]–[20], various dimmers for fluorescent lamps are described. When HID lamps are used, the dimmable capability can be achieved using both magnetic and electronic ballasts. In specialized literature, it is possible to find several studies oriented toward the following: HID lamps modeled for electronic ballast design [21], [22], the description of a variety of topologies
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TABLE I C OMPARISON OF E LECTRONIC AND M AGNETIC BALLAST S YSTEMS
used in electronic ballast design [23]–[29], and the comparison between dimmable electromagnetic and electronic ballast systems in order to determine their advantages and disadvantages [30], [31]. In the latter case, results show that dimmable street lighting systems based on high-performance (HP) magnetic ballasts have many more favorable features in terms of energy saving and environmental sustainability than the system based on HP electronic ballast. Table I summarizes the comparison of the two ballast technologies performed in [30] and [31]. As mentioned earlier, the utilization of a central dimmer system for HID lamps with magnetic ballasts appears as a practical solution to the problem of energy saving in street lighting systems. Important energy savings are obtained when the luminary voltage is stabilized and reduced because its power consumption is a square function of the applied voltage. Energy savings can be around 30% to 40% with respect to lighting systems that operate with constant voltage [32]. This paper discusses the comparison of two central dimmer systems, one based on autotransformers and the other based on high-frequency switching converter technology. The first one is currently manufactured and commercialized by the MIMAVEN Group under the denomination STALVIAL [33], and it is available in a single-phase version (from 3.3 to 40 kVA) and a three-phase version (from 10 to 120 kVA). The second one is a prototype developed at the Technical University of Catalonia by the company’s request and was previously described in [34]. The main objective of this development is to quantify the possible improvements that the innovative use of switching converters could provide for street lighting dimming applications. II. E XPERIMENTAL S ETUP Tests have been set up to evaluate and compare two dimmer technologies in a lighting network, and this section describes the different elements used to support them. A. Lamps A set of 25 Phillips lamps, referenced as HPL-N 400 W, is used as the load in the performed tests. Each lamp is a 400-W high-pressure mercury vapor and is driven by the magnetic
Fig. 1.
Dimmer based on multiple-tapped autotransformer.
Fig. 2.
Voltage regulation process for 185 and 220 Vrms as reference values.
ballast suggested by the manufacturer. Therefore, the total power of the load used is 10 kW.
B. Autotransformer-Based Dimmer In these kinds of dimmers, the voltage adjustment is implemented through several static ac controlled switches and one multiple-tapped autotransformer, as shown in Fig. 1. The control system activates the appropriate switch and selects the autotransformer tap according to the desired ac voltage value to apply to the magnetic ballast light system (MBLS) [35]. Fig. 2 shows the output voltage regulation process for two possible reference values: 185 and 220 Vrms . This figure shows, on the dashed line, the transformation ratio for the different taps (n) of the autotransformer. The transformation ratio value depends on the desired output voltage regulation ratio α and the selected output voltage hysteresis h (both as a per-unit ratio of the nominal input voltage). The expressions for determining the transformation ratio of each transformer tap are
RT (+n)
1−α = 1 + (α − h)
n RT (−n)
1+α = 1 − (α − h)
n (1)
VELASCO-QUESADA et al.: COMPARISON OF CENTRAL DIMMER SYSTEMS
Fig. 3.
Detail of the output voltage regulation process.
Fig. 4.
Dimmer based on autotransformer under test.
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is generated by the control unit according to the pattern of the voltage regulation programmed by the user. 3) Controller. The control unit manages the lamp ignition process and the system operation under voltage reduction mode. The ignition process has two different intervals: a) The first one corresponds to lamp preheating. The duration of this interval is 6 min, and the user can select the voltage applied to the MBLS from two possible values: 205 or 210 Vrms . The MBLS preheating is performed using a voltage lower than the nominal in order to reduce the start current value. b) The second time interval completes the MBLS warmup. The duration of this interval is 8 min, and the nominal voltage is applied to the MBLS. The user can set this nominal voltage value at 220 or 230 Vrms . The transition between the voltages corresponding to these two intervals is performed with a gradient of 6 volts per minute (Vrms /min). In accordance with what was previously mentioned, the lamps warm-up process takes approximately 16 min, which agrees with [36]. Once the ignition process is finished, the controller activates the dimming process. For this process, the user can program the sequence of the voltages applied to the lamps and the time of application of each one. The dimming voltage can be selected among the following values: 185, 190, 195, and 200 Vrms . Moreover, the transitions between voltages are also performed at a 6-Vrms /min gradient.
C. High-Frequency Switch Converter Dimmer where RT (−n) is the transformation ratio for reducing voltage taps, RT (+n) is the ratio for boosting voltage taps, and n is the number (in absolute value) of the tap under consideration. Fig. 3 details the regulation process. This figure shows the relationship between the evolution of the output voltage around the reference value (VRef ) and the value of the parameters α and h. It also shows the different switching points between two successive taps, depending on whether the input voltage is increasing or decreasing. The main objective is the prevention of multiple switching between taps when the input voltage value is near these thresholds. Finally, the dimmer tested is shown in Fig. 4 and corresponds to 15-kW single-phase equipment. This figure also shows its main parts. 1) Autotransformer. The autotransformer used has nine different outputs: two outputs for boosting voltage (n = {1, 2}), six outputs for reducing voltage (n = {−1, −2 . . . − 6}), and the output for the voltage equal to the input (n = 0). The difference of the voltage between two consecutive autotransformer outputs is around 6 Vrms when a nominal input voltage of 220 Vrms is applied. 2) AC switches and drivers. Each autotransformer output is connected to a MBLS through a controlled ac switch. These ac switches are based on two thyristors in antiparallel connection. The activation command of each switch
As described in [31], this dimmer is based on a single-phase matrix converter (MC), and it is characterized by the continuous regulation of the output voltage, with a theoretical margin of regulation between 0% and 100%. Moreover, it does not use an autotransformer. In accordance with the discussion in [34], the relationship between the input and output voltages of the dimmer is given by VO (t) = D · VIN (t).
(2)
Thus, if the value of the duty cycle (D) remains constant over a period, then the waveform shapes of the input and output voltages are equal and the rms value of the output voltage is proportional to the duty cycle value (D). The MC is a forced commutated ac–ac converter which uses an array of controlled bidirectional switches as the main power elements in order to create a variable output voltage system. It has no dc-link circuits and needs no large energy storage elements [37]. Fig. 5 shows the topology of this dimmer, which implies the input and output LC filters and two bidirectional switches, each one formed by two insulated-gate bipolar transistors (emitter connected) and their antiparallel connected diodes. The dimmer prototype under test is shown in Fig. 6. This dimmer corresponds to 15-kVA single-phase equipment and is
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Fig. 5. Dimmer based on high-frequency switch converter.
Fig. 7.
Output voltage reference used for test.
Fig. 8.
Output voltage of the dimmers under test.
Fig. 6. Prototype of dimmer based on switching converter.
managed by the same control unit used on the autotransformerbased dimmer. D. Data Acquisition System As a data acquisition and recording system, a WT1600 power meter from Yokogawa has been used. This instrument has been utilized for the acquisition and recording of voltages and currents at the input and output of the tested dimmers.
A. Output Voltage E. Input Voltage to Dimmers The input voltage applied to the dimmers under test is obtained from a voltage regulator system. This approach ensures a line voltage of 230 Vrms with relative independence of the utilized grid robustness. F. Dimming Pattern Utilized The dimming pattern utilized for performing the dimmer test can be seen in Fig. 7, which shows the stages of the lamp preheating (first 6 min at a 210-V operation), the lamp warmup (between 8 and 16 min with a 220-V operation), and the operation on voltage reduction mode (from 16 min to the end of the test at a 200-V operation). III. E XPERIMENTAL R ESULTS This section is devoted to show the different results obtained in the tests performed on both dimmers tested.
Fig. 8 shows the output voltage of the two dimmers under test when the reference utilized for the output voltage is that shown in Fig. 7. This result shows that the dimmer based on a switching converter has a better regulation of the output voltage when compared with the autotransformer-based dimmer. The output voltage of the dimmer based on the switching converter practically coincides with the reference voltage, while the output voltage of the dimmer based on the multiple-tapped autotransformer follows the reference voltage as a staggered voltage. As a consequence, energy saving is not optimized. As mentioned earlier, the voltage difference between two consecutive autotransformer outputs is around 6 Vrms , which means that the maximum difference between the reference and the output voltage could be about ±3 Vrms (this is ±1.3% of the nominal voltage). In this sense, the capability to regulate the output voltage of both dimmers results in an increase of the lamp lifetime.
VELASCO-QUESADA et al.: COMPARISON OF CENTRAL DIMMER SYSTEMS
Fig. 9.
Output current of the dimmers under test.
Fig. 10. Output power of the dimmers under test.
B. Output Current Fig. 9 shows the output current of the two tested dimmers. The output currents of the two dimmers are very similar because they are imposed by the set of lamps used as a load. As a result, the overcurrent produced in the lamp preheating period can be observed. The value of this overcurrent can be between 1.5 and 2 times the nominal current of the lamps. C. Output Active Power and Efficiency Fig. 10 shows the output active power of the two dimmers tested. This result allows the estimation of the energy savings of about 20%, achieved by reducing the lamp voltage from 220 to 200 V (from approximately 10 kW at 220 V to 8 kW at 200 V). Fig. 11 shows the power efficiency of the dimmers under test and demonstrates the best efficiency of the autotransformerbased dimmer. In the nominal conditions of operation, its efficiency is 98.5%, compared to the 97.5% efficiency presented by the dimmer based on the switching converter. Furthermore, the efficiency of the autotransformer-based dimmer presents a small decrease when the dimmer operates on voltage reduction
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Fig. 11. Power efficiency of the dimmers under test.
Fig. 12. Input PF of the dimmers tested.
mode. This is not the case of the dimmer based on the switching converter as its efficiency drops one point (from 97.5% to 96.5%) when it operates on the voltage reduction mode. The high efficiency of the autotransformer-based dimmer is a direct result of the autotransformer’s high efficiency and the low value of the forward conduction losses in the used ac switches. As an example, a value of autotransformer efficiency quite close to 99.5% can be achieved when the difference between the output and input voltages is around 10% [38], [39]. In order to account for all possible losses in the system, the efficiency of both dimmers has been measured as the ratio between the output and input powers. D. Input PF Fig. 12 shows the input power factor (PF) of the two dimmers tested and shows the best behavior of the autotransformer-based dimmer when the lamps are heated. The two dimmers show a low PF during the lamp preheating, and this value increases while the lamps are warming. On the autotransformer-based dimmer, the maximum PF value (about 0.96) is achieved when the lamps have reached
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TABLE II C OMPARISON OF AUTOTRANSFORMER -BASED D IMMER AND MC-BASED D IMMER
Fig. 13. Top waveform: Output voltage (after LC output filter). Bottom waveform: Current through the inductor of LC output filter. Scales: Voltage of 200 V/div, current of 20 A/div, and time of 4 ms/div and 100 μs/div on detail.
their nominal operating temperature. This value is practically independent of the dimmer output voltage, even when the dimmer operates on voltage reduction mode. Similarly, the PF value of the dimmer based on the switching converter is independent of its output voltage level. Fig. 12 shows that the PF value is about 0.95 when the dimmer output voltage is 220 V (nominal voltage of the MBLS) and practically remains constant when the dimmer operates on voltage reduction mode. E. Output Filter Current Fig. 13 shows the dimmer output voltage and the current through the inductor of the LC output filter for the dimmer based on the switching converter when a 3-kW resistive load was used. The figure shows the ripple that appears on the current through the output filter inductor, with an amplitude of 20 A and a frequency of 13 kHz, equal to the switching converter switching frequency. This ripple, typical on switched power converters, represents another disadvantage of dimmers based on switching converters because the greater current harmonic distortion increases the probability of electromagnetic interference (EMI) emissions.
V. C ONCLUSION This paper has considered a comparative test between two technologies for central dimmer systems. The first is based on a multiple-tapped autotransformer, and the second is based on a single-phase MC topology. Both technologies can be used in adaptive lighting systems for street lighting based on HID lamps and magnetic ballasts. An operative test, using 10 kW of high-pressure mercury vapor lamps as the load, has been performed in order to evaluate the main features of the two central dimmer systems. In this regard, the output voltage, output current, output power, power efficiency, and PF have been compared. The results obtained allow us to conclude that the classical central dimmer systems based on autotransformers still offer better electrical performances if they are compared with the central dimmer systems based on high-frequency switching converters. ACKNOWLEDGMENT This work has been developed in collaboration with the MIMAVEN Group, a Spanish company with more than 30 years of experience developing and manufacturing electromagnetic components and power electronic systems.
IV. D ISCUSSION The experimental results, shown in the previous section, allow the determination of which aspects of each dimmer technology present a better behavior. In this regard, these results have been summarized in Table II. In view of these data, the conclusion is that the autotransformer-based dimmer technology appears to be the most favorable option for the adaptive lighting system design. This is the technology that offers the greatest efficiency both in nominal conditions and in voltage reduction mode, which has a higher PF when the dimmer operates in voltage reduction mode, and it is also the technology that has no EMI emission risk. The dimmer technology based on switching converters offers a continuous output voltage regulation, which is an interesting feature from the point of view of energy saving optimization and increasing lamp lifetime.
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[7] P. George, “Centralized street lighting control and monitoring demonstration project—Final report,” DMD Assoc. Ltd., Woodinville, WA, May 2006. [8] Intelligent Energy Europe, Guide for Energy Efficient Street Lighting Installations, Eur. Comm.—EACI, 2007. [9] P. Van Tichelen, T. Geerken, B. Jansen, M. Vanden Bosch, V. Van Hoof, L. Vanhooydonck, and A. Vercalsteren, “Lot 9: Public street lighting—Final report,” Eur. Comm. DG TREN, Brussels, Belgium, Jan. 2007. [10] F. Li, D. Chen, X. Song, and Y. Chen, “LEDs: A promising energy-saving light source for road lighting,” in Proc. APPEEC, Mar. 2009, pp. 1–3. [11] C. Richardson, “Streetlighting requires large numbers of LEDs,” Bodo’s Power Syst., no. 7, pp. 30–32, Jul. 2010. [12] C. Richardson, “Streetlighting requires large numbers of LEDs,” Bodo’s Power Syst., no. 8, pp. 34–36, Aug. 2010. [13] X. Long, R. Liao, and J. Zhou, “Development of street lighting systembased novel high-brightness LED modules,” IET Optoelectron., vol. 3, no. 1, pp. 40–46, Feb. 2009. [14] Intelligent Energy Europe, Project Report. Intelligent Road and Street Lighting in Europe, Brussels, Belgium: European Comm.—EACI, 2008. [15] H.-J. Chiu, Y.-K. Lo, J.-T. Chen, S.-J. Cheng, C.-Y. Lin, and S.-C. Mou, “A high-efficiency dimmable LED driver for low-power lighting applications,” IEEE Trans. Ind. Electron., vol. 57, no. 2, pp. 735–743, Feb. 2010. [16] Z. Ye, F. Greenfeld, and Z. Liang, “Single-stage offline SEPIC converter with power factor correction to drive high brightness LEDs,” in Proc. 24th Annu. IEEE APEC, Feb. 2009, pp. 546–553. [17] C.-S. Wang, “Flicker-insensitive light dimmer for incandescent lamps,” IEEE Trans. Ind. Electron., vol. 55, no. 2, pp. 767–772, Feb. 2008. [18] G.-C. Hsieh, “Group-asymmetrical PWM control for dimmable fluorescent lamp ballast without striation and thermostat effect,” IEEE Trans. Power Electron., vol. 24, no. 5, pp. 1293–1303, May 2009. [19] J. C. W. Lam and P. K. Jain, “A dimmable electronic ballast with unity power factor based on a single-stage current-fed resonant inverter,” IEEE Trans. Power Electron., vol. 23, no. 6, pp. 3103–3115, Nov. 2008. [20] H.-L. Cheng and Y.-H. Huang, “Design and implementation of dimmable electronic ballast for fluorescent lamps based on power-dependent lamp model,” IEEE Trans. Plasma Sci., vol. 38, no. 7, pp. 1644–1650, Jul. 2010. [21] R. O. Sanchez, N. Vazquez, C. Hernandez, E. Rodriguez, S. Pinto, and M. Juarez, “Electric dynamic modeling of HID lamps for electronic ballast design,” IEEE Trans. Ind. Electron., vol. 57, no. 5, pp. 1655–1662, May 2010. [22] J. M. Alonso, M. A. Dalla-Costa, J. Cardesin, J. A. Martin-Ramos, and J. Garcia-Garcia, “Small-signal modeling of discharge lamps through step response and its application to low-frequency square-waveform electronic ballasts,” IEEE Trans. Power Electron., vol. 22, no. 3, pp. 744–752, May 2007. [23] R. Orletti, M. A. Co, D. S. L. Simonetti, and J. L. de Freitas Vieira, “HID lamp electronic ballast with reduced component number,” IEEE Trans. Ind. Electron., vol. 56, no. 3, pp. 718–725, Mar. 2009. [24] H.-J. Chiu, T.-H. Song, S.-J. Cheng, C.-H. Li, and Y.-K. Lo, “Design and implementation of a single-stage high-frequency HID lamp electronic ballast,” IEEE Trans. Ind. Electron., vol. 55, no. 2, pp. 674–683, Feb. 2008. [25] T. B. Marchesan, M. A. Dalla-Costa, J. M. Alonso, and R. N. do Prado, “Integrated zeta-flyback electronic ballast to supply high-intensity discharge lamps,” IEEE Trans. Ind. Electron., vol. 54, no. 5, pp. 2918–2921, Oct. 2007. [26] C. Branas, F. J. Azcondo, and R. Casanueva, “Phase-controlled quadruple LC P resonant inverter to drive 600-W HPS lamps,” IEEE Trans. Power Electron., vol. 22, no. 3, pp. 831–838, May 2007. [27] C. Ekkaravarodome, A. Nathakaranakule, and I. Boonyaroonate, “Singlestage electronic ballast using class-DE low-dv/dt current-source-driven rectifier for power-factor correction,” IEEE Trans. Ind. Electron., vol. 57, no. 10, pp. 3405–3414, Oct. 2010. [28] C.-S. Moo, C.-K. Huang, K.-H. Lee, and D.-J. Huang, “Repeatedly resonating ignition circuit for HID lamp electronic ballasts,” IEEE Trans. Ind. Electron., vol. 58, no. 1, pp. 244–249, Jan. 2011. [29] J.-C. Hsieh and J. Lin, “Novel single-stage self-oscillating dimmable electronic ballast with high power factor correction,” IEEE Trans. Ind. Electron., vol. 58, no. 1, pp. 250–262, Jan. 2011. [30] “Technical guide 5: High performance fluorescent lighting: The next steps—Including the cases for high-performance magnetic vs. high performance electronic ballasts,” Ecospecifier Technical Guides, 2008. [Online]. Available: http://www.ecospecifier.org [31] H. S.-H. Chung, N.-M. Ho, W. Yan, P. W. Tam, and S. Y. Hui, “Comparison of dimmable electromagnetic and electronic ballast systems—An
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assessment on energy efficiency and lifetime,” IEEE Trans. Ind. Electron., vol. 54, no. 6, pp. 3145–3154, Dec. 2007. W. Yan and S. Y. R. Hui, “Dimming characteristics of large-scale highintensity-discharge (HID) lamp lighting networks using to energy-saving power station system,” in Conf. Rec. IEEE IAS Annu. Meeting, 2006, vol. 3, pp. 1090–1098. “ESTALVIAL technical specifications,” MIMAVEN Group Documentation, 2008. [Online]. Available: http://www.mimaven.com M. Román, G. Velasco, and A. Conesa, “Matrix converter applied to energy saving for street lighting systems,” in Proc. 15th IEEE MELECON, Apr. 2010, pp. 527–531. H. S. H. Chung, N. M. Ho, S. Y. R. Hui, and W. Z. Mai, “Case study of a high-reliable dimmable road lighting system with intelligent remote control,” in Proc. 11th Eur. Conf. Power Electron. Appl., 2005, p. 10. J. Hollander, “High intensity discharge lamp dimming,” In-Lighten (COOPER Lighting Literature), no. 3, pp. 18–19. [Online]. Available: http://www.cooperlighting.com F. Bradaschia, M. C. Cavalcanti, F. Neves, and H. de Souz, “A modulation technique to reduce switching losses in matrix converters,” IEEE Trans. Ind. Electron., vol. 56, no. 4, pp. 1186–1195, Apr. 2009. D. P. Kothari and I. J. Nagrath, Basic Electrical Engineering, 2nd. New Delhi, India: Tata McGraw-Hill Publ. Co. Ltd., 2002. U. A. Bakshi and M. V. Bakshi, Electrical Machine—I, 1st ed. Pune, India: Tech. Publ., 2010.
Guillermo Velasco-Quesada (S’04–M’09) was born in Barcelona, Spain. He received the Technical Engineering in Electronics degree, the Electronics degree, and the Ph.D. degree from the Polytechnic University of Catalonia (UPC), Barcelona, in 1990, 2002, and 2008, respectively. Since 1992, he has been an Associate Professor with the Electronics Engineering Department, Industrial Engineering College of Barcelona, UPC (EUETIB-UPC), where he teaches analog and power electronics. He is also a Researcher with the Energy Processing and Integrated Circuits Group and the Power Electronics Research Center of the UPC. His main research interest includes the analysis, modeling, and control of power systems for renewable energy applications and gridconnected photovoltaic systems based on reconfigurable topologies. Dr. Velasco-Quesada is a member of the IEEE Industrial Electronics Society and the IEEE Power Electronics Society.
Manuel Román-Lumbreras (M’09) was born in Gallur, Spain. He received the Industrial Engineering degree and the Ph.D. degree from the Polytechnic University of Catalonia (UPC), Barcelona, Spain, in 1975 and 2006, respectively. He is currently with the Industrial Engineering College of Barcelona, UPC (EUETIB-UPC), where he was an Assistant Professor from 1977 to 2000 and has been an Associate Professor in the Electronics Engineering Department since 2001. Furthermore, from 1965 to 2000, he worked in the industry, where he was focused on the area of electrical energy production, railway power traction systems, ac and dc motor drives, electric power quality, and power converters for uninterruptible power supplies and active power filters. His actual research interests include power electronics, electric power network quality, converters for renewable energy systems, and digital control of power converters. Dr. Román-Lumbreras is a member of the IEEE Industrial Electronics Society and the IEEE Power Electronics Society.
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Alfonso Conesa-Roca (M’10) was born in Barcelona, Spain. He received the Electronics degree and the Ph.D. degree from the Polytechnic University of Catalonia (UPC), Barcelona, in 1998 and 2006, respectively. He is currently an Associate Professor with the Electronics Engineering Department, Industrial Engineering College of Barcelona, UPC (EUETIBUPC). His current research interests include switching mode power supplies, power architectures, resonant conversion, and photovoltaic applications. Dr. Conesa-Roca is a member of the IEEE Sensors Council.
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Comparison of Central Dimmer Systems Based on Multiple-Tapped Autotransformer and High-Frequency Switching Converter Guillermo Velasco-Quesada, Member, IEEE, Manuel Román-Lumbreras, Member, IEEE, and Alfonso Conesa-Roca, Member, IEEE
Abstract—This paper compares two central dimmer system technologies used in street lighting. These dimmers are utilized in adaptive lighting systems based on high-intensity-discharge lamps and magnetic ballasts. The first technology is based on a multiple-tapped autotransformer which is commonly used for these types of installations. The second technology is based on a high-frequency switch converter (more specifically in a singlephase matrix converter topology) and represents a novelty for this type of application. Tests were conducted to determine the main features of both dimmer technologies, and the obtained results are presented. Index Terms—Adaptive lighting system, central dimmer system, street lighting.
I. I NTRODUCTION
S
TREET lighting is a public service which governments and municipalities must offer due to its important role of providing comfort and enhancing citizens’ security. In this regard, various studies show the effect that street lighting has on traffic accidents, crime, fear, and pedestrian street use after dark [1]–[3]. Increasing local business, promoting economic development, and aesthetic factors are also its functions [4]. The energy consumed by street lighting in the European Union (EU)-27 over the 2007 is estimated at 37 TWh, which accounts for 1.3% of the total electricity consumption, with an approximate cost of 2.5 billion euros [5]. This data place street lighting energy consumption between 45 kWh/cap (kilowatthour per capita and year) in countries such as Germany or The Netherlands and 85 kWh/cap in countries such as Slovenia or Spain, with 50 kWh/cap being the average energy consumption in the EU-27 [6]. Reduced street lighting energy consumption provides significant savings to owners, reduces taxes [7], decreases the burden over the electric system, and reduces greenhouse gas emissions. In this regard, new technologies can provide great potential for energy savings in street lighting systems. The replacement of Manuscript received September 17, 2010; revised November 29, 2010; accepted January 21, 2011. Date of publication February 7, 2011; date of current version November 1, 2011. The authors are with the Industrial Engineering College of Barcelona, Polytechnic University of Catalonia (EUETIB-UPC), 08036 Barcelona, Spain (e-mail: [email protected]; [email protected]; alfonso. [email protected]). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TIE.2011.2112321
existing street lighting by intelligent street lighting systems can reduce energy consumption by about 70% [8]. Based on its long life span (over 30 years), there is a large market for upgrading old street lighting technology. However, a strong adversity to improving their energy efficiency is based on a lack of simple and low-cost energy saving measures. Lamps in street lighting are mostly high-intensity-discharge (HID) lamps that need an appropriate ballast and optic system. In most cases, the implementation of an energy-efficient technology implies that the ballasts, or the complete luminary, need to be replaced [9]. This is the case of the street lighting systems based on high-brightness light-emitting diodes (LEDs). The high cost of this technology, along with some technical problems to be solved (directivity, luminous efficacy, or suitable current drive circuits), makes this a promising technology but in the medium or long term [10]–[13]. As a result, measures which are normally implemented consequences to increase street lighting energy efficiency are based on keeping the luminaries installed (usually HID lamps with magnetic ballasts) and using adaptive lighting systems instead of intelligent street lighting systems. Adaptive lighting is the most basic approach to the practical implementation of intelligent street lighting. This is because the concept adaptive lighting only describes the light performance on a road level [14]. Among other capabilities, a basic adaptive lighting system must adjust the illumination level of a particular street according to its time pattern of utilization. The illumination level must be higher at times of greater utilization and must fall gradually when its use decreases. This control of the illumination is realized by means of a device that, following an established hourly program, adjusts the lamp light output. A dimmer (also called a fader) is the device used for light brightness variation, and its operating principle is closely related to the utilized luminary technology. For example, dimmable LED drivers are described in [15] and [16], and in [17], a flicker-insensitive dimmer for incandescent lamps is described. Moreover, in [18]–[20], various dimmers for fluorescent lamps are described. When HID lamps are used, the dimmable capability can be achieved using both magnetic and electronic ballasts. In specialized literature, it is possible to find several studies oriented toward the following: HID lamps modeled for electronic ballast design [21], [22], the description of a variety of topologies
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TABLE I C OMPARISON OF E LECTRONIC AND M AGNETIC BALLAST S YSTEMS
used in electronic ballast design [23]–[29], and the comparison between dimmable electromagnetic and electronic ballast systems in order to determine their advantages and disadvantages [30], [31]. In the latter case, results show that dimmable street lighting systems based on high-performance (HP) magnetic ballasts have many more favorable features in terms of energy saving and environmental sustainability than the system based on HP electronic ballast. Table I summarizes the comparison of the two ballast technologies performed in [30] and [31]. As mentioned earlier, the utilization of a central dimmer system for HID lamps with magnetic ballasts appears as a practical solution to the problem of energy saving in street lighting systems. Important energy savings are obtained when the luminary voltage is stabilized and reduced because its power consumption is a square function of the applied voltage. Energy savings can be around 30% to 40% with respect to lighting systems that operate with constant voltage [32]. This paper discusses the comparison of two central dimmer systems, one based on autotransformers and the other based on high-frequency switching converter technology. The first one is currently manufactured and commercialized by the MIMAVEN Group under the denomination STALVIAL [33], and it is available in a single-phase version (from 3.3 to 40 kVA) and a three-phase version (from 10 to 120 kVA). The second one is a prototype developed at the Technical University of Catalonia by the company’s request and was previously described in [34]. The main objective of this development is to quantify the possible improvements that the innovative use of switching converters could provide for street lighting dimming applications. II. E XPERIMENTAL S ETUP Tests have been set up to evaluate and compare two dimmer technologies in a lighting network, and this section describes the different elements used to support them. A. Lamps A set of 25 Phillips lamps, referenced as HPL-N 400 W, is used as the load in the performed tests. Each lamp is a 400-W high-pressure mercury vapor and is driven by the magnetic
Fig. 1.
Dimmer based on multiple-tapped autotransformer.
Fig. 2.
Voltage regulation process for 185 and 220 Vrms as reference values.
ballast suggested by the manufacturer. Therefore, the total power of the load used is 10 kW.
B. Autotransformer-Based Dimmer In these kinds of dimmers, the voltage adjustment is implemented through several static ac controlled switches and one multiple-tapped autotransformer, as shown in Fig. 1. The control system activates the appropriate switch and selects the autotransformer tap according to the desired ac voltage value to apply to the magnetic ballast light system (MBLS) [35]. Fig. 2 shows the output voltage regulation process for two possible reference values: 185 and 220 Vrms . This figure shows, on the dashed line, the transformation ratio for the different taps (n) of the autotransformer. The transformation ratio value depends on the desired output voltage regulation ratio α and the selected output voltage hysteresis h (both as a per-unit ratio of the nominal input voltage). The expressions for determining the transformation ratio of each transformer tap are
RT (+n)
1−α = 1 + (α − h)
n RT (−n)
1+α = 1 − (α − h)
n (1)
VELASCO-QUESADA et al.: COMPARISON OF CENTRAL DIMMER SYSTEMS
Fig. 3.
Detail of the output voltage regulation process.
Fig. 4.
Dimmer based on autotransformer under test.
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is generated by the control unit according to the pattern of the voltage regulation programmed by the user. 3) Controller. The control unit manages the lamp ignition process and the system operation under voltage reduction mode. The ignition process has two different intervals: a) The first one corresponds to lamp preheating. The duration of this interval is 6 min, and the user can select the voltage applied to the MBLS from two possible values: 205 or 210 Vrms . The MBLS preheating is performed using a voltage lower than the nominal in order to reduce the start current value. b) The second time interval completes the MBLS warmup. The duration of this interval is 8 min, and the nominal voltage is applied to the MBLS. The user can set this nominal voltage value at 220 or 230 Vrms . The transition between the voltages corresponding to these two intervals is performed with a gradient of 6 volts per minute (Vrms /min). In accordance with what was previously mentioned, the lamps warm-up process takes approximately 16 min, which agrees with [36]. Once the ignition process is finished, the controller activates the dimming process. For this process, the user can program the sequence of the voltages applied to the lamps and the time of application of each one. The dimming voltage can be selected among the following values: 185, 190, 195, and 200 Vrms . Moreover, the transitions between voltages are also performed at a 6-Vrms /min gradient.
C. High-Frequency Switch Converter Dimmer where RT (−n) is the transformation ratio for reducing voltage taps, RT (+n) is the ratio for boosting voltage taps, and n is the number (in absolute value) of the tap under consideration. Fig. 3 details the regulation process. This figure shows the relationship between the evolution of the output voltage around the reference value (VRef ) and the value of the parameters α and h. It also shows the different switching points between two successive taps, depending on whether the input voltage is increasing or decreasing. The main objective is the prevention of multiple switching between taps when the input voltage value is near these thresholds. Finally, the dimmer tested is shown in Fig. 4 and corresponds to 15-kW single-phase equipment. This figure also shows its main parts. 1) Autotransformer. The autotransformer used has nine different outputs: two outputs for boosting voltage (n = {1, 2}), six outputs for reducing voltage (n = {−1, −2 . . . − 6}), and the output for the voltage equal to the input (n = 0). The difference of the voltage between two consecutive autotransformer outputs is around 6 Vrms when a nominal input voltage of 220 Vrms is applied. 2) AC switches and drivers. Each autotransformer output is connected to a MBLS through a controlled ac switch. These ac switches are based on two thyristors in antiparallel connection. The activation command of each switch
As described in [31], this dimmer is based on a single-phase matrix converter (MC), and it is characterized by the continuous regulation of the output voltage, with a theoretical margin of regulation between 0% and 100%. Moreover, it does not use an autotransformer. In accordance with the discussion in [34], the relationship between the input and output voltages of the dimmer is given by VO (t) = D · VIN (t).
(2)
Thus, if the value of the duty cycle (D) remains constant over a period, then the waveform shapes of the input and output voltages are equal and the rms value of the output voltage is proportional to the duty cycle value (D). The MC is a forced commutated ac–ac converter which uses an array of controlled bidirectional switches as the main power elements in order to create a variable output voltage system. It has no dc-link circuits and needs no large energy storage elements [37]. Fig. 5 shows the topology of this dimmer, which implies the input and output LC filters and two bidirectional switches, each one formed by two insulated-gate bipolar transistors (emitter connected) and their antiparallel connected diodes. The dimmer prototype under test is shown in Fig. 6. This dimmer corresponds to 15-kVA single-phase equipment and is
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Fig. 5. Dimmer based on high-frequency switch converter.
Fig. 7.
Output voltage reference used for test.
Fig. 8.
Output voltage of the dimmers under test.
Fig. 6. Prototype of dimmer based on switching converter.
managed by the same control unit used on the autotransformerbased dimmer. D. Data Acquisition System As a data acquisition and recording system, a WT1600 power meter from Yokogawa has been used. This instrument has been utilized for the acquisition and recording of voltages and currents at the input and output of the tested dimmers.
A. Output Voltage E. Input Voltage to Dimmers The input voltage applied to the dimmers under test is obtained from a voltage regulator system. This approach ensures a line voltage of 230 Vrms with relative independence of the utilized grid robustness. F. Dimming Pattern Utilized The dimming pattern utilized for performing the dimmer test can be seen in Fig. 7, which shows the stages of the lamp preheating (first 6 min at a 210-V operation), the lamp warmup (between 8 and 16 min with a 220-V operation), and the operation on voltage reduction mode (from 16 min to the end of the test at a 200-V operation). III. E XPERIMENTAL R ESULTS This section is devoted to show the different results obtained in the tests performed on both dimmers tested.
Fig. 8 shows the output voltage of the two dimmers under test when the reference utilized for the output voltage is that shown in Fig. 7. This result shows that the dimmer based on a switching converter has a better regulation of the output voltage when compared with the autotransformer-based dimmer. The output voltage of the dimmer based on the switching converter practically coincides with the reference voltage, while the output voltage of the dimmer based on the multiple-tapped autotransformer follows the reference voltage as a staggered voltage. As a consequence, energy saving is not optimized. As mentioned earlier, the voltage difference between two consecutive autotransformer outputs is around 6 Vrms , which means that the maximum difference between the reference and the output voltage could be about ±3 Vrms (this is ±1.3% of the nominal voltage). In this sense, the capability to regulate the output voltage of both dimmers results in an increase of the lamp lifetime.
VELASCO-QUESADA et al.: COMPARISON OF CENTRAL DIMMER SYSTEMS
Fig. 9.
Output current of the dimmers under test.
Fig. 10. Output power of the dimmers under test.
B. Output Current Fig. 9 shows the output current of the two tested dimmers. The output currents of the two dimmers are very similar because they are imposed by the set of lamps used as a load. As a result, the overcurrent produced in the lamp preheating period can be observed. The value of this overcurrent can be between 1.5 and 2 times the nominal current of the lamps. C. Output Active Power and Efficiency Fig. 10 shows the output active power of the two dimmers tested. This result allows the estimation of the energy savings of about 20%, achieved by reducing the lamp voltage from 220 to 200 V (from approximately 10 kW at 220 V to 8 kW at 200 V). Fig. 11 shows the power efficiency of the dimmers under test and demonstrates the best efficiency of the autotransformerbased dimmer. In the nominal conditions of operation, its efficiency is 98.5%, compared to the 97.5% efficiency presented by the dimmer based on the switching converter. Furthermore, the efficiency of the autotransformer-based dimmer presents a small decrease when the dimmer operates on voltage reduction
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Fig. 11. Power efficiency of the dimmers under test.
Fig. 12. Input PF of the dimmers tested.
mode. This is not the case of the dimmer based on the switching converter as its efficiency drops one point (from 97.5% to 96.5%) when it operates on the voltage reduction mode. The high efficiency of the autotransformer-based dimmer is a direct result of the autotransformer’s high efficiency and the low value of the forward conduction losses in the used ac switches. As an example, a value of autotransformer efficiency quite close to 99.5% can be achieved when the difference between the output and input voltages is around 10% [38], [39]. In order to account for all possible losses in the system, the efficiency of both dimmers has been measured as the ratio between the output and input powers. D. Input PF Fig. 12 shows the input power factor (PF) of the two dimmers tested and shows the best behavior of the autotransformer-based dimmer when the lamps are heated. The two dimmers show a low PF during the lamp preheating, and this value increases while the lamps are warming. On the autotransformer-based dimmer, the maximum PF value (about 0.96) is achieved when the lamps have reached
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TABLE II C OMPARISON OF AUTOTRANSFORMER -BASED D IMMER AND MC-BASED D IMMER
Fig. 13. Top waveform: Output voltage (after LC output filter). Bottom waveform: Current through the inductor of LC output filter. Scales: Voltage of 200 V/div, current of 20 A/div, and time of 4 ms/div and 100 μs/div on detail.
their nominal operating temperature. This value is practically independent of the dimmer output voltage, even when the dimmer operates on voltage reduction mode. Similarly, the PF value of the dimmer based on the switching converter is independent of its output voltage level. Fig. 12 shows that the PF value is about 0.95 when the dimmer output voltage is 220 V (nominal voltage of the MBLS) and practically remains constant when the dimmer operates on voltage reduction mode. E. Output Filter Current Fig. 13 shows the dimmer output voltage and the current through the inductor of the LC output filter for the dimmer based on the switching converter when a 3-kW resistive load was used. The figure shows the ripple that appears on the current through the output filter inductor, with an amplitude of 20 A and a frequency of 13 kHz, equal to the switching converter switching frequency. This ripple, typical on switched power converters, represents another disadvantage of dimmers based on switching converters because the greater current harmonic distortion increases the probability of electromagnetic interference (EMI) emissions.
V. C ONCLUSION This paper has considered a comparative test between two technologies for central dimmer systems. The first is based on a multiple-tapped autotransformer, and the second is based on a single-phase MC topology. Both technologies can be used in adaptive lighting systems for street lighting based on HID lamps and magnetic ballasts. An operative test, using 10 kW of high-pressure mercury vapor lamps as the load, has been performed in order to evaluate the main features of the two central dimmer systems. In this regard, the output voltage, output current, output power, power efficiency, and PF have been compared. The results obtained allow us to conclude that the classical central dimmer systems based on autotransformers still offer better electrical performances if they are compared with the central dimmer systems based on high-frequency switching converters. ACKNOWLEDGMENT This work has been developed in collaboration with the MIMAVEN Group, a Spanish company with more than 30 years of experience developing and manufacturing electromagnetic components and power electronic systems.
IV. D ISCUSSION The experimental results, shown in the previous section, allow the determination of which aspects of each dimmer technology present a better behavior. In this regard, these results have been summarized in Table II. In view of these data, the conclusion is that the autotransformer-based dimmer technology appears to be the most favorable option for the adaptive lighting system design. This is the technology that offers the greatest efficiency both in nominal conditions and in voltage reduction mode, which has a higher PF when the dimmer operates in voltage reduction mode, and it is also the technology that has no EMI emission risk. The dimmer technology based on switching converters offers a continuous output voltage regulation, which is an interesting feature from the point of view of energy saving optimization and increasing lamp lifetime.
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Guillermo Velasco-Quesada (S’04–M’09) was born in Barcelona, Spain. He received the Technical Engineering in Electronics degree, the Electronics degree, and the Ph.D. degree from the Polytechnic University of Catalonia (UPC), Barcelona, in 1990, 2002, and 2008, respectively. Since 1992, he has been an Associate Professor with the Electronics Engineering Department, Industrial Engineering College of Barcelona, UPC (EUETIB-UPC), where he teaches analog and power electronics. He is also a Researcher with the Energy Processing and Integrated Circuits Group and the Power Electronics Research Center of the UPC. His main research interest includes the analysis, modeling, and control of power systems for renewable energy applications and gridconnected photovoltaic systems based on reconfigurable topologies. Dr. Velasco-Quesada is a member of the IEEE Industrial Electronics Society and the IEEE Power Electronics Society.
Manuel Román-Lumbreras (M’09) was born in Gallur, Spain. He received the Industrial Engineering degree and the Ph.D. degree from the Polytechnic University of Catalonia (UPC), Barcelona, Spain, in 1975 and 2006, respectively. He is currently with the Industrial Engineering College of Barcelona, UPC (EUETIB-UPC), where he was an Assistant Professor from 1977 to 2000 and has been an Associate Professor in the Electronics Engineering Department since 2001. Furthermore, from 1965 to 2000, he worked in the industry, where he was focused on the area of electrical energy production, railway power traction systems, ac and dc motor drives, electric power quality, and power converters for uninterruptible power supplies and active power filters. His actual research interests include power electronics, electric power network quality, converters for renewable energy systems, and digital control of power converters. Dr. Román-Lumbreras is a member of the IEEE Industrial Electronics Society and the IEEE Power Electronics Society.
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Alfonso Conesa-Roca (M’10) was born in Barcelona, Spain. He received the Electronics degree and the Ph.D. degree from the Polytechnic University of Catalonia (UPC), Barcelona, in 1998 and 2006, respectively. He is currently an Associate Professor with the Electronics Engineering Department, Industrial Engineering College of Barcelona, UPC (EUETIBUPC). His current research interests include switching mode power supplies, power architectures, resonant conversion, and photovoltaic applications. Dr. Conesa-Roca is a member of the IEEE Sensors Council.
