SINGLE STAGE ELECTRONIC BALLAST FOR HID LAMPS Márcio Almeida Có and Márcio Brumatti
Domingos S. L. Simonetti and José Luiz F. Vieira
CEFETES - Federal Technologic Education Center of Espírito Santo Vitória – Brazil
[email protected] [email protected]
Electrical Engineering Department Federal University of Espírito Santo Vitória – Brazil
[email protected] the utility line voltage variation and the voltage lamp increasing during lamp lifetime.
Abstract— This paper presents a single power processing stage electronic ballast for HID lamps. A DC-DC buck converter that controls the current and the power of the lamp, a power factor pre-regulator based on discontinuous conduction mode boost converter and the inverter are combined in a dual fed full bridge BIBRED converter. It operates with a low frequency current driving the lamp. All signals of the power stages are provided by a dedicated microcontroller. A 70W prototype without acoustic resonance and no stroboscope effect was implemented.
At a glance, high frequency operation (dozens up to hundreds of kHz) seems to be the best choice for the electronic ballast inverter stage, due to the high frequency resistive behavior of discharge lamps. However, in the case of HID lamps, pressure waves effect into the tube, called acoustic resonance, can happen for these frequencies. This phenomenon perturbs the discharge path, causing: arc bowing and snaking, flicker, changing in the color temperature, and in the worst case, the arc can be extinguished. The acoustic resonance depends on the lamp tube geometry and dimensions, gas composition and thermodynamic conditions of the gas (temperature, pressure and density)[1, 6, 7].
Keywords- HID lamps; microcontroller; ballast.
I.
INTRODUCTION
The high intensity discharge (HID) lamps present features as high lighting efficiency, longer lifetime and good color rendering, which become them relevant in industrial light system. Due to the negative impedance characteristic of the lamp, a device to limit its current should be used; typically electromagnetic ballast is applied. However, it has high size and weight, low efficiency, poor power regulation, and presents high sensibility to voltage changes [1, 2, 3, 4]. Electronic ballast can overcome all these drawbacks.
Some solutions have been presented in the literature [1 – 12], using electronic ballast to drive the HID lamps without acoustic resonance. The low frequency operation driven the lamp with a square waveform seems to be a good solution due to its great simplicity, reliability and mainly due to the severe conditions of acoustic resonance that the low wattage HID lamps are submitted [4, 12, 13, 14].
The operation of the HID lamp can be described in three distinct phases: starting, warm-up and nominal power operation. An adequate high ignition voltage is needed to the electrical breakdown of the starting gases within the arc, after that the electrons collisions maintains rising the temperature of the arc tube, vaporizing the metal and increasing the pressure. At the end of this phase, that may last many seconds, a full high-pressure arc is established: the temperature and brightness have reached their equilibrium [1]. During the lamp lifetime, the final lamp voltage rises, that can increase the lamp power with lifetime reduction. This problem is particularly excessive in high-pressure sodium and metal halide lamps [2, 5].
Lamp power (P) and lamp current (I)
rated power
(P)
warm-up current
Inew lamp Iold lamp
For electronic ballasts, the desired lamp current (I) and lamp power (P) versus lamp voltage characteristics, is illustrated in Fig. 1, where all values should be considered as rms values. The current should be maintained constant at a high value during the warm-up, resulting in time reduction of this phase. When the lamp power reaches its rated value, the ballast control acts reducing the lamp current and maintaining constant the output power. This procedure compensates both,
( I)
Vnew lamp warm-up phase
Vold lamp
Lamp voltage (V)
rated power phase
Figure 1. Lamp current (I) vs. lamp voltage and the lamp power (P) vs. lamp voltage.
0-7803-7883-0/03/$17.00 © 2003 IEEE
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II.
shown in Fig.2.b. In this case the output power is controlled changing the duty cycle of S1 switch, and the voltage on the capacitor C0 can be controlled acting on the switching frequency.
LOW FREQUENCY SQUARE WAVE ELECTRONIC BALLASTS
A low frequency square wave electronic ballast can be implemented by using three power-processing stages, as is illustrated in Fig. 2.a. The input one, called power factor preregulator (PFP) stage, is used to obtain high power factor maintaining constant the DC bus voltage. The intermediate stage is a DC-DC buck converter, operating at high frequency to control the lamp current and power. The output stage is a low frequency square wave inverter that drives the lamp [4, 12, 13, 14].
Joining the DC-DC buck converter with the inverter, another topology can be obtained [12, 14], as shown in Fig. 2.c. To drive the lamp with low frequency square wave current and still control its value, the switches S1 and S3 operate at low frequency complementary mode and the switches S2 and S4 operate at high frequency PWM mode. The simplest electronic ballast can be obtained combining the three stages, forming a single power processing stage, as shown in Fig. 2.d. The dual fed full bridge BIBRED converter [17] is able to obtain high power factor at its input, controlling a square wave low frequency output current. The bridge’s switches are commanded as the same way of the DC-AC stepdown topology, and by changing the PWM frequency like in the BIBRED converter the DC bus voltage can be controlled. This solution applied for HID electronic ballast will be described in the next section.
However, three power-processing stages demand more components, that increase the overall cost and reduce the electronic system reliability [15]. There are some alternatives to simplify the overall converter, which consist in combining the power stages described above. A first alternative, the PFP and DC-DC buck converter are mixed, forming the BIBRED (Boost Integrated with Buck Rectifier / Energy storage / Dc-dc converter) converter [16], as
DC-DC buck converter
Power factor preregulator L boost
low frequency inverter
BIBRED Lboost
L buck C0
Lig2
lamp
Inverter Lbuck L ig2
C0
lamp
S1
Control
Igniter L ig1
Control
Igniter L ig1
(b) (a) Dual fed BIBRED inverter DC-AC step-down converter PFP
Lboost
Cp
L boost C0
S1
Lbuck
L ig2
Lbuck
lamp
L ig2
S3 lamp
Igniter
C0 S4
S2
S4
S2
Control
S3
Cp S1
Igniter
Control
L ig1
L ig1
(d)
(c)
Figure 2. The square wave low frequency lamp current electronic ballasts: a) with three power-processing stages, b) using a BIBRED converter, c) using a DCAC step-down converter, d) using a dual-fed full bridge BIBRED converter
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III.
a1 stage: During this stage S1 and S4 are ON, so the Lbuck current increases linearly through C0 -S1 - S4. The Lboost current increases linearly through Vin - Db2 - S4 modulated by the input voltage.
THE SINGLE STAGE HID ELECTRONIC BALLAST OPERATION
The Fig.3 shows the complete power stage circuit of the proposed electronic ballast. The input rectifier, the dual fed full bridge BIBRED and the igniter circuit forms it.
b1 stage: S4 is turned off. The Lbuck current decreases linearly through S1-DS3 and Lboost current decreases linearly through Db1 - DS1 - C0 until it becomes null.
The dual fed full bridge BIBRED converter is able to obtain high input power factor, controlling a square wave low frequency output current. It can be done by an appropriate bridge signal command: the switches S1 and S3 operating at low frequency complementary mode and the switches S2 and S4 operating at high frequency PWM mode. Using a high value of C0 capacitor, this topology can integrate an input boost converter with an output step-down inverter [5].
c1 stage: During this stage iLboost = 0 and the Lbuck current still decreases through S1-DS3 until start a new high frequency switching period. These stages repeat until the switches S1 and S4 are turned off. After the dead time, S2 and S3 switches start to operate and the lamp current inverts resulting in the a2, b2 and c2 stages, which are similar to a1, b1 and c1. A dedicated device performs the control signals of all structure (using high performance RISC CPU microcontroller PIC16F873, from Microchip). The control tasks of this device should be resumed as shown in Fig. 5 and described below:
The input inductance (Lboost) is designed to operate in discontinuous conduction, so that ensures the high input power factor. The output inductance (Lbuck) is placed in series to the lamp and its value has to be as small as possible to ensure fast polarity changes of the lamp current. A capacitor filter is still needed to reduce the lamp ripple current, preventing the acoustic resonance [3].
Ignition sequence: The ignition pulses occur only if the lamp is off, regarding to a sequence of short time interval ignition trial (less than 0.5 second) followed by a long time of interrupted interval (up to 10 seconds). During the trial interval the lower switches of the bridge work with a limited maximum duty cycle and the igniter switch is maintained on after the ignition pulse. These facts help to maintain the DC bus voltage in accepted level if the lamp do not star-up, due to the power consumption on Rig. During the interrupted interval the duty cycle of S2 and S4 switches is forced to be zero to stop C0 charge.
The igniter circuit uses an appropriated ratio between the coupled inductances Lig1 and Lig2, ensuring the high voltage ignition pulses to start up the lamp. These pulses are obtained when the Sig is turned on, through the Cig and Lig1 resonance. The Fig. 4 shows the main waveforms of the circuit. This converter has three typical operation stages that happen in the positive (a1, b1, c1) and in the negative (a2, b2, c2) lamp current half cycles as described below:
Dbp
D1
D2
iLboost
Db2
S1
Cp
DS1 iLbuck
Lf Cf
D4
C0
Lbuck S2
S1-S4, Sig command
DS2
Rl1a
Rl1b
Rl2a
Rl2b
Microcontrolled based command and measure circuit
Figure 3. The proposed electronic ballast circuit
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Rig
DS3
Lig2
Lboost Db1
D3
S3
S4
DS4
RB1 RB2
Dig Sig
Cig Lig1
Lamp current and power control: After the start-up and during the warm-up phase the lamp current is kept constant at a pre-established value through a digital PI control acting over the duty cycle of S2 and S4 switches. When the lamp reaches the nominal power the reference current is constantly calculated taking in account the lamp voltage to ensure the fixed rated power. To avoid over current and unstable function during the operation the PI controller gain is changed in a schedule way.
IV.
EXPERIMENTAL RESULTS
A prototype of the single stage topology has been implemented, and some results will be showed below. The electronic ballast specifications are:
DC bus voltage control: A digital PI control, acting over the switching frequency maintains the DC bus voltage constant independent of lamp voltage or utility line voltage variations. This controlled voltage guarantee the discontinuous conduction mode in Lboost, providing high power factor.
•
RMS AC mains voltage: 220V, 60Hz;
•
DC bus voltage: 430V;
•
Output power: 70W (High pressure sodium lamp)
•
Inverter switching frequency: 150Hz;
•
PWM rated switching frequency: 40kHz;
The Fig. 6 shows the gate commands of S1-S4 switches. S1
The Fig. 7 shows the input voltage and current, which present THD = 25% and power factor of 0,97. The Fig. 8 shows the square wave lamp voltage and lamp current. This behavior ensures a free acoustic resonance operation.
S2
S3
The Fig. 9 shows the lamp current (dashed line) and the lamp power (completed line) versus lamp voltage. This characteristic confirms that the ballast works with a fixed current during the warm-up phase and constant power during lamp lifetime. The lamp voltage increasing was obtained involving the lamp with an aluminum paper, so its temperature increases like during lamp lifetime.
S4
iLbuck, i lamp
The Fig. 10 and 11 show the switching frequency changes imposed by the control to maintain the DC bus voltage constant for input voltage and lamp voltage variation respectively. The frequency was limited at minimum value of 36 kHz to guarantee a ripple current in the lamp less than 5%. This is the reason for the DC bus voltage changes in both figures.
i Lboost
a2 b2 c2
a1 b1 c1
Finally the Fig. 12 shows the proposed ballast efficiency curve.
Figure 4. The main waveforms of the proposed electronic ballast.
e(k)
ton(k)
PI Controller
PWM module
Vgs1-4
v Co (t)
Dual fed BIBRED inverter + Lamp
vlamp(t)
Ts(k) ignition pulse
PI Controller
igniter
e(k) controller gain and limits adjustment
_
Σ
+ Vco ref
Vco(k)
Σ
_
Ilamp(k)
Vgsig
Ilamp(k)
Iref
+
Ilamp(t)
reference current calculation and adaptative mechanism
Vlamp(k)
Vco(k)
A/D
A/D
A/D
Figure 6. Gate commands
Figure 5. Block diagram of control
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55
DC bus voltage(V)
frequency (kHz)
440 430
50 420 45
410 400
40
390 35 380 30
370 201
210
220
229
237
RMS input voltage (V)
Figure 10. Switching frequency and DC bus voltage for input voltage variation.
Figure 7. Input voltage and current
DC bus voltage (V) 450
frequency (KHz) 60
400 350
50
300 40 250 30
200 150
20
100 10
50
0
0 70
85
94
102
110
lamp voltage (V)
Figure 11. Switching frequency and DC bus voltage for lamp voltage variation.
Figure 8. Lamp voltage (top trace) and lamp current (bottom trace).
lamp power (W)
1
lamp current (A)
80
1,4
0,95
70
1,2
0,9
60
efficiency
1
50
0,8
40 0,6
30 20 10 0 50
75 90 lamp voltage (V)
0,8 0,75
0,4
0,7
0,2
0,65
0 25
0,85
0,6
105
75
85
95
105
lamp voltage (V)
Figure 9. Lamp power and lamp current versus lamp voltage.
Figure 12. Ballast efficiency curve
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[6] H. Peng, S. Ratanapanachote, P. Enjeti, L. Laskai and I. Pitel, “Evaluation of Acoustic Resonance in Metal Halid (MH) Lamp And An Approach to Detect Its Occurrence”, in Proc. IEEE Industry Application Society Annual Meeting – IAS, 1997, pp. 2276 – 2283. [7] S. Wada, A. Okada and S. Morii, “Study of HID Lamp with Reduced Acoustic Resonance’s”, Journal of the Illuminating Engineering Society, vol.10, No. 1, pp.162-175, Winter 1987 [8] J. M. Alonso, C. Blanco, E. Lopez, A. J. Calleja, M. Rico, “Analysis, Design, and Optimization of the LCC Resonant Inverter as a HighIntensity Discharge Lamp Ballast”, IEEE Transaction on Power Electronics, Vol. 13, No. 3, May 1998, pp. 573 - 585. [9] S. Ben-Yaakov and M. Gulko, “Design and Performance of an Electronic Ballast for high-pressure Sodium (HPS) Lamps”, in Proc. Applied Power Electronics Conference – APEC, 1995, pp. 665 – 669. [10] P. Enjeti, L. Laskai and I. Pitel, “ A Unity Power Factor Electronic Ballast for Metal Halide Lamps”, in Proc. Applied Power Electronics Conference – APEC, 1994, pp. 31 – 37. [11] P. Van Tichelen, D. Weyen, G. Meynen, “Test Result from High Intensity Discharge Lamps With Current Supplied at 50 Hz, 400 Hz and Modulated between 15 and 35 kHz”, in Proc. IEEE Industry Application Society Annual Meeting – IAS, 1996, pp. 2225 – 2230. [12] H. Nishimura, H. Nagase, K. Uchihashi, T. Shiomi and M. Fukuhara, “A New Electronic Ballast for HID Lamps”, Journal of the Illuminating Engineering Society, Summer 1988, pp.70-76, [13] T. Yamauchi and T. Shiomi, “ A Novel Charge Pump Power Factor Correction Electronic Ballast For High Intensity Discharge Lamps” in Proc. IEEE Power Electronics Specialists Conference 1998, pp. 17611767. [14] M. Shen and Z. Quian and F. Z. Peng, “A Novel Two-Stage Acoustic Resonance Free Electronic Ballast For HID Lamps”, in Proc. IEEE Industry Application Society Annual Meeting – IAS, 2002. [15] M. Brumatti, C. Z. Resende, D. S. L. Simonetti and J. L. F. Vieira, “Self-Oscillating High Power Factor Electronic Ballast with Coupled Inductors”, XIII CBA, pp. 1951-1956, 2000. [16] M. T. Madigan, R. W. Erickson and E. H. Ismail, “Integrated HighQuality Rectifier-Regulators”. IEEE Transaction on Industrial Electronics, Vol. 46, No. 4, August 1999, pp. 749 -758. [17] M. A. Johnston and R. W. Erickson, “Reduction Of Voltage Stress In The Full Bridge BIBRED By Duty Ratio And Phase Shift Control”, in Proc. IEEE, 1994.
V. CONCLUSIONS A simple electronic ballast for HID lamps operating with low frequency square wave current in the lamp can be implemented using a single power processing stage, and the dual fed full bridge BIBRED inverter revealed to be a good choice in this role. The lamp current and the DC link voltage are controlled by a dedicate microcontroller. The use of a microcontroller becomes simple the circuitry and the control task, allowing to compensate the increase of the voltage lamp during its lifetime and the utility line variation by adjusting the high switching frequency. Besides that, the ballast operates with high power factor, the low frequency current assures the operation free of acoustic resonance and the controlled current permits to reduce the warm-up time. The single stage demand less components, that reduces the overall cost and increases the electronic system reliability and efficiency. REFERENCES [1]
[2] [3]
[4]
[5]
R. Redl and J. D. Paul, “A New High Frequency and High-Efficiency Electronic Ballast for HID Lamps: Topology, Analysis, Design, and Experimental Results”, in Applied Power Electronics Conference – APEC, 1999. B-R. Lin and Y-C. Hsieh, “Dimming Control for High Intensity Discharge Lamp with Power Factor Correction”, In Proc. EPE 1999. H. Ohguchi, M. H. Ohsato, T. Shimizu, G. Kimura, H. Takagi, “A High-Frequency Electronic Ballast for HID Lamps Based on a / 4 – Long Distributed Constant Line”, IEEE Transaction on Power Electronics, Vol. 13, No. 6, November 1998, pp. 1023 - 1029. M. A. Có, C. Z. Resende, D. S. L. Simonetti and J. L. F. Vieira, “Microcontrolled Electronic Gear For Low Wattage Metal Halide (Mh) And High-Pressure Sodium (Hps) Lamps” in Proc. IEEE Industry Application Society Annual Meeting – IAS, 2002. M. Gulko, D. Medini, S. Ben-Yaakov, “Inductor-Controlled CurrentSourcing Resonant Inverter and its Application as a High Pressure Discharge Lamp Driver”, in Proc. Applied Power Electronics Conference – APEC, 1994, pp. 434 – 440
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