SELF-OSCILLATING ELECTRONIC BALLAST WITH LIGHTING INTENSITY CONTROL

Transcription

1 SELF-OSCILLATING ELECTRONIC BALLAST WITH LIGHTING INTENSITY CONTROL J. DE P. LOPES, M. F. DA SILVA, P. C. LUZ, V. BORIN, M. F. MENKE, F. E. BISOGNO, Á. R. SEIDEL AND R. N. DO PRADO Intelligence for Lighting Group (GEDRE), Federal University of Santa Maria Santa Maria, RS, , Brazil Abstract - This paper presents electronic ballast with dimming capability supplying a 32 W fluorescent lamp. The electronic ballast is a self-oscillating driving circuit with an additional circuit responsible for dimming the fluorescent lamp based on a signal from a lighting dependent resistor. This luminous sensor measures the luminous flu level and set the lamp power by the voltage gain variation of the resonant filter. Simulation and eperimental results of the electronic ballast are presented to demonstrate the feasibility of the proposed system. Keywords Electronic ballast, fluorescent lamps, self-oscillating, switching frequency. 1. Introduction The growing electric energy consumption worldwide, day by day, is stimulating research and development of energy efficiency technique. Considering that the artificial lighting systems represent a great amount of consumption (Hammer, 1985), the development in this field making possible saving energy to produce light. This will make a significant contribution on total electric energy consumption. This work propose a saving energy solution for lighting systems, using electronic ballast operating at high-frequency to supply fluorescent lamps. Some electric advantages can be observed in the use of high-frequencies electronic ballast comparing to electromagnetic one, like audible noise, flicker absence, and better lighting efficacy (lm/w). Moreover, electronic ballasts are lighter and smaller than electromagnetic ballasts. Self-oscillating electronic ballast (SOEB) has been used widely due to its simplicity. On the other hand its design has been reported in several papers due to its compleity (Chang, 2001; Seidel, 2003c; Seidel, 2007; Tao, 2001). These studies have shown that several applications were derived since SOEB behavior was understood as a nonlinear control system circuit (Dalla Costa, 2003; Seidel, 2003b). Thus, in this work is proposed one application involving the SOEB with dimming capability. The electronic ballast is formed by a self-oscillating driving circuit with an additional circuit that must control light intensity for the fluorescent lamp. The dimming capability is achieved by the switching frequency sweep that changes the resonant filter gain. The light intensity control is done through a lighting-dependent-resistor (LDR) that has a resistance proportional to the visual electromagnetic radiation spectrum applied. The LDR is responsible to measure the environment luminous flu level and set the luminous flu through the lamp power. The remainder of this paper is organized as follows; the proposed idea is shown in Section 2, the design synthesis and simulation results are shown in section 3 and 4, the eperimental results are presented in section 5 and the final considerations are presented in the last section. 2. Proposed Self-Oscillating Electronic Ballast The proposed system is an application of the traditional SOEB with switching frequency sweep that allows for regulating the fluorescent lamp light intensity based on a feedforward control. Electronic ballast with dimming capability was proposed in (Seidel, 2003a; Seidel, 2003b). However, the circuit and the design methodology were different. Figure 1(a) shows the proposed circuit that is based on the universal SOEB (Lopes, 2009). However, in this paper the additional circuit is used to dimming the fluorescent lamp. Thus, the proposed work consists in controlling the fluorescent lamp power by the electronic ballast switching frequency (fs) as the LDR resistance changes, since the lamp power decreases (increases) as fs increases (decreases) if it is considered the LCC resonant filter voltage gain feature (Wakabayashi, 2005). Figure 1(b) shows the equivalent gate driver circuit and its waveforms. The behavior of the SOEB is based on the resonant current feedback i s from the LCC resonant filter through a current transformer (CT), which includes L S1, L S2 and L P. The CT secondary side is connected to gate-source terminals of S 1 and S 2 with complementary polarity, which ensures S 1 turns on (off) and S 2 turns off (on). It is shown that when zener current i z crosses zero, the polarity over S 1 -S 2 gate-source changes. The i z current is the sum of i s and the CT magnetizing current i m as it is shown in the equivalent circuit. The f s is controlled through the series inductance L d and equivalent resistance R d provided by a bipolar transistor T SC. It is possible due to the insertion of a current path paralleled with i m and i s currents according points 1 and 2 in Figure 1(b). The rectifier bridge D 6 -D 9 allows flow the bidirectional i d current. Thus, the transistor T SC operates as a variable resistance which depends on T SC base current i b. The i b current controls i d and it is also controlled by means the voltage divider LDR+R 1 and R 2. The zener 3681

2 (a) Figure 1 - (a) Proposed system (b) Equivalent gate driver circuit and its waveforms (b) diode D ZC ensures the additional circuit operation. Then, D ZC conducts when the voltage through it reaches a defined value according to LDR+ R1 and R2. 3. Design Methodology The SOEB design should be developed in a proper strategy, following some steps: Step 1: The desired operation frequency range should be chosen considering the lamp power per frequency, based on the curve of the resonant output filter. Figure 2 shows this curve considering eperimental results obtained of an electronic ballast prototype. The minimum design frequency should be higher than output filter resonant frequency in order to ensure zero-voltage-switching (ZVS) in all frequency range. The resonant filter parameters and the selfoscillating driving design are based on (Bisogno, 2002; Seidel, 2007). Considering the curve behavior of Figure 2, the SOEB design frequency, f smin, is 40 khz for the nominal power of around 32 W. The maimum switching frequency chosen according Figure 2, f sma, is 51 khz that corresponds about 12 W lamp power. Step 2: The second step is to determine the environment light intensity in which the dimming should start to work. The LDR changing curve should be considered, as it is shown in Figure 3. Analyzing this variation curve, the dimming additional circuit should start to work if the environment light intensity is 100 Lu, that is equivalent to LDR resistance of 18 kω. If the light intensity of 500 Lu is measured, the dimming additional circuit has its maimum actuation, sweeping the operating switching frequency at 51 khz, related to LDR resistance of 5.8 kω. Step 3: L d dimming inductor should be design. The behavior of L d is illustrated in the block diagram of dimmable SOEB, as it is depicted in Figure 4(a). In order to obtain this block diagram, some simplifications were made. The bus voltage was considered constant. Besides that, the lamp was represented by an equivalent resistance and the intrinsic capacitances of the switches S 1, S 2 and its delay time were neglected. Based on these simplifications, the half-bridge converter and zener diodes output polarity can be represented by the hard limit nonlinearly shown in this figure multiplied through a gain K. Thus, a perturbation E/2 allows change the values of the half-bridge inverter that is 0 Figure 2 Resonant filter characteristic curve Figure 3 LDR Resistance Lu 3682

3 (a) (b) Figure 4 (a) Complete block diagram of the proposed system (b) and reduced block diagram or E (bus voltage). The block G F (s) represents the transfer function of resonant filter and the fluorescent lamp from the voltage V ab to resonant current I L. The block G M (s) represents the transfer function of the magnetizing inductance L m from the gate-source voltage to the magnetizing current I M. The only difference between the block diagram shown in Figure 4(a) and the block diagram of the traditional SOEB is the block G SC (s). This block represents the transfer function of the additional circuit shown in (1). G s SC( ) Ld. s 1 + R d (1) Considering the simplifications above, the block diagram of Figure 4(a) can be reduced to the block diagram shown in Figure 4(b). In order to determine the behavior of the system and the main equations, the describing function method and the etended Nyquist stability criterion are used (Seidel, 2007). The inductance L d allows increase f S since it allows the bidirectional current i d flows through the bipolar transistor changing i Z current. At low input voltage there is not current flowing through T SC so the additional circuit is turned off. Thus, L d is determined for the highest switching frequency, 51 khz. The additional circuit is turned on when the voltage over R 2 reaches the zener conduction voltage plus the transistor base-emitter voltage what happens for 100 Lu. Thus, employing the design methodology shown in (Seidel, 2003b) L d é determined solving (2). 1 Ld( ω) 1 ω KF ( ω) Lm. ω (2) Where: a1/r.c p, b((1/c s.l)+(1/cp.l)), c1/r.c p.c s.l, KE/2V Z,nn p /n s, K. n ωac+ ω ( b a ) ω KF( ω) L c + ω ( b 2 ac) + ω ( a 2 b) + ω np is the turns number of the CT primary side, and ns is the turns number of the CT secondary side. Inductor L d is determined considering the R d minimum value, in this case R d 0, in the first approimation. It is considered for the maimum switching frequency when LDR has the minimum value of resistance. So, i b and i c currents are maimum and V ce is minimum, which means that it is equal a low R d value (V ce /i c ), considering the transistor characteristic curves. Step 4: Determine R 1 and R 2 resistors. These resistors are determined considering the additional circuit turns on and the additional circuit maimum influence in the SOEB. Considering the T SC characteristic curve and the additional circuit influence in the SOEB, R 1 and R 2 can be determined solving (3) and (4). R R (3) R R (4) Table 1 shows the main components of the proposed system. In Table 2 is resumed the design methodology shown in this section. 4. Simulation Results This section presents the simulation results of the proposed system. Figures 5 and 6 show the waveforms for the maimum and minimum switching frequency. Figure 5(a) shows the lamp voltage and current for the maimum LDR resistance. The measured lamp power is about 31 W for 40 khz electronic ballast switching frequency f s. Figure 5(b) shows the lamp voltage and current for the minimum LDR resistance. The lamp power presents in this case about 13 W and f s increases to 53 khz. Figures 6(a) and (b) show the voltage and current over switch S 1 for the maimum and minimum LDR resistance, respectively. Through these waveforms it can be seen that ZVS operation is C S C P L L P, L S1,L S2 D Z1 -D Z4 S 1, S 2 T SC D ZC Table 1. Main Components of the Proposed System Resonant filter parameters Polypropylene Capacitor 150 nf/250vac Polypropylene Capacitor 8.2 nf/600vac Inductor, 2.1 mh EE-25 IP6 THORNTON Self-oscillating circuit 34.5 µh/ 342 µh NT 15/9/8 THORNTON Zener diode C12ST/0.5W MOSFET IRF740 Additional circuit Bipolar transistor 2N2222 Zener diode 12V/0.5W L d Dimming inductor 315 µh R 1 Resistor 50 kω/ 1/8W R kω/ 1/8W 3683

4 XVIII Congresso Brasileiro de Automática / 12 a 16 Setembro 2010, Bonito-MS. Table 2. Design Strategy Data for the SOEB Luminous Intensity Resonant filter (L,CS, CP) Self-oscillating gate driver (Lm, LS1, LS2) Inductance Ld (Rd0) R1, R2 100 Lu Switching Frequency 500 Lu 40 khz 51 khz Figure 5. - Lamp voltage and current (a) LDR maimum resistance. (b) LDR minimum resistance Figure 6.- S1 voltage and current - (a) LDR maimum resistance. (b) LDR minimum resistance ensured for both conditions. Thus, the simulation results show the feasibility of the proposed system Eperimental Results Conclusion This paper presented a Self-Oscillating Electronic Ballast with Dimmable Lighting Intensity Regulation using the self-oscillating driving circuit with feedforward control. The proposed system is based on the traditional SOEB with an additional circuit which allows for variable the luminous flu and save about 30% of the energy consumption for fluorescent lamp applications. Presented Simulation and Eperimental results demonstrate the performance and feasibility of the proposed solution. The proposed electronic ballast is simple and has a reduced number of components. The system maintain the SOEB main characteristics which are simplicity and low cost. In this section the eperimental results are presented of the proposed system. Figure 7 shows the prototype that has been built and tested. Figures 8 and 9 show the waveforms for the lamp voltage and current and S1 voltage and current, respectively. Figure 8(a) shows the lamp voltage and current for the highest LDR resistance. The measured lamp power in this case is about 31 W for khz electronic ballast switching frequency. In Figure 8(b) is shown the lamp voltage and current for the lowest LDR resistance. The lamp power presents about 12 W and fs increases to khz. Figures 9(a) and (b) show the voltage and current over switch S1 for the maimum and minimum LDR resistance, respectively. Through these waveforms it can be seen that ZVS operation is ensured for both conditions. Thus, the switching frequency and lamp power has shown the designed behavior. Figure 7 Photograph of the prototype 3684

5 Figure 8 - Lamp voltage and current (a) LDR maimum resistance. (b) LDR minimum resistance Figure 9. - S 1 voltage and current (a) LDR maimum resistance. (b) LDR minimum resistance Acknowledgment The authors gratefully thank the support to this work provided by THORNTON INPEC and National Council for Scientific and Technological Development (CNPq - P /2008-6). References Bisogno, F. E; Seidel, A. R; Holsbach, R; Prado, R. N (2002). Resonant Filter Applications in Electronic Ballast. IEEE Industry Applications Society Annual Meeting, Vol.2, pp Chang, C; Bruning, G. W (2001). Self-oscillating Electronic Ballast Analysis Via Relay Systems Approach. IEEE Transactions on Industry Applications, Vol.27, No. 1, pp Dalla Costa, M. A; Seidel, A. R; Bisogno, F. E; Prado, R. N (2002). Self-Oscillating Dimmable Electronic Ballast to Supply Two Independent Lamps. IEEE Industry Applications Conference, Vol2. pp Hammer E. E; Mcgowan, T. K (1985). Characteristics of Various F40 Fluorescent Systems at 60 Hz and High Frequency. IEEE Transaction on Industrial Applications, Vol.21, No. 1, pp Lopes, J. de P.; Silva, M. F; Pinto, R. A; Prado, R. N; Seidel, A. R (2009). Universal Input Voltage Self-Oscillating Electronic Ballast with Feedforward Control. IEEE Industry Applications Society Annual Meeting, V.4, pp Seidel, A. R; Bisogno, F. E; Pappis, D.; Prado, R. N (2003a). Automatic Luminous Control for Self- Oscillating Electronic Ballast. IEEE Industry Applications Society Annual Meeting Vol.2, pp Seidel, A. R; Bisogno, F. E; Prado, R. N; Pinheiro, H. (2003b). Self-Oscilating Dimmable Electronic Ballast. IEEE Transactions on Industrial Eletronics, Vol50, No 6, pp Seidel, A. R; Pappis, D; Bisogno, F. E; Prado, R. N (2003c). Simple Valley-Fill Self-Oscillating Electronic Ballast with Low Crest Factor Using Pulse-Frequency-Modulation. IEEE Industry Applications Conference, Vol.2, pp Seidel, A. R; Bisogno, F. E; Prado, R. N (2007). A Design Methodology for a Self-Oscillating Electronic Ballast. IEEE Transactions on Industry applications, Vol.43, No. 6, pp Tao. F; Zhao, Q; Lee, F. C; Onish, N (2001). Self- Oscilating Eletronic Ballast with Dimming Control. IEEE Power Electronics Specialist Conference, Vol.4, pp Wakabayashi, F. T; Canesin, C. A (2005). An improved Design Procedure for LCC Resonant Filter of Dimmable Electronic Ballasts for Fluorescent Lamps, Based on Lamp Model. IEEE Transactions on Power Electronics, Vol. 20, No. 5, pp