WO2010054454A2

WO2010054454A2 - Electronic ballast for metal vapor lamps using integration techniques for power factor correction and acoustic resonance elimination

Info

Publication number: WO2010054454A2
Application number: PCT/BR2009/000370
Authority: WO
Inventors: Arnaldo José PERIN; André Luiz FUERBACK
Original assignee: Ufsc- Universidade Federal De Santa Catarina
Priority date: 2008-11-13
Filing date: 2009-11-03
Publication date: 2010-05-20
Also published as: BRPI0805183A2; WO2010054454A3

Abstract

Electronic ballast for metal vapor lamps using integration techniques for power factor correction and acoustic resonance elimination describes high frequency electronic converters used with high intensity discharge metal vapor or metal halide lamps. Integration techniques are used to obtain a high power factor and to reduce the output power oscillation in order to eliminate the acoustic resonance phenomenon. Two controlled switches are used, which integrate the half-bridge voltage-source inverter function to supply the lamp and the power factor correction function. The integration of these functions is obtained by using two passive filtering structures (using inductors and capacitors). The output filtering elements are responsible for limiting the current supplied to the lamp and its harmonic content. The input filtering elements make it possible to achieve an input current with low harmonic content when charging the dc-link capacitors. Furthermore, if designed properly, the input filter capacitors in conjunction with the line impedance operate as a filter to reduce the harmonic current of the ballast's input current even further.

Description

ELECTRONIC BALLAST FOR METAL VAPOR LAMPS USING INTEGRATION TECHNIQUES FOR POWER FACTOR CORRECTION AND ACOUSTIC

RESONANCE ELIMINATION

Field of the Invention

The present invention relates to electronic converters operating at high frequency for high-intensity discharge metal vapor or metal halide lamps using integrated techniques to obtain high input power factor and a power supply to reduce oscillations in the output power and eliminate the occurrence of the acoustic resonance phenomenon.

Background of the Invention

The behavior of discharge lamps, such as metal vapor lamps, is unstable due to their negative incremental impedance. Therefore, in order to operate properly, elements are required to limit the current through the lamp. Such devices are called ballasts. When a voltage source is used to supply these lamps, it is a common practice to use electromagnetic devices as a series element. The advantages of this technique include low cost and robustness. However, the weight and volume along with problems such as light flickering and audible noise make this technique unattractive, especially when low power lamps are used, where it is desirable to integrate the power supply and the lamp.

By using structures that inject high frequency currents into the lamp it is possible to improve upon the undesirable characteristics of the electromagnetic ballasts; however, high power factor operation does not occur. For this reason, a technique to reduce the harmonic distortion of the current drawn from the supply is required. The proposed structure (FIGURE 1) uses two approaches. The first, based upon the boost converter operating in discontinuous conduction mode, is used to reduce the amplitude of the input current harmonics around the multiples of the supply frequency. The second technique uses interleaving to reduce the harmonic content of the input current at the switching frequency and its multiples.

By conditioning the energy of the source to control the current through the lamp by using electronic structures, one can, for example, increase the frequency of the current and, consequently, reduce the filtering elements (FIGURE 2). This is because the volume and, therefore, the weight are tied to this variable.

The most worrisome factor when using electronic ballasts to supply metal vapor lamps, is related to the spectral content of the power applied to the lamp. This is because temperature and pressure fluctuations inside the discharge tube of the lamp are considered responsible for generating standing or resonant waves. These standing waves can cause fluctuations in the luminous flux and even extinguish the arc, a phenomenon known as acoustic resonance. Studies on metal vapor lamps have shown that, although the frequencies at which these oscillations occur are predictable, they vary drastically among the different types of lamps due to differences in geometry and composition of the discharge gas elements, which can be even more obvious among lamps of different manufacturers. This makes it difficult to use single-stage ballasts, based on, for example, the charge pump concept, which normally supply the discharge lamp with high frequency sinusoidal currents.

The charge pump concept is presented in publications Qian, J. and Lee, F. C. in January, 2000, in the IEEE Transactions on Power Electronics, Volume 15, number 1, pp.121 - 129, under the title: "Charge Pump Power - Factor - Correction Technologies. Part I: Concept and Principle" and Qian, J. and Lee, F. C. in January, 2000, in the IEEE Transactions on Power Electronics, Vol.15, no.l, pp.130 - 139, under the title: "Charge Pump Power - Factor - Correction Technologies. Part II: Ballast Applications". This concept is used in the design of electronic ballasts for fluorescent lamps.

The frequency spread at the acoustic resonant frequency can be observed within a range that extends from a few kHz to hundreds of kHz, with limited occurrence of the phenomenon above 100 kHz. Despite this fact, there are ballasts that use the spectral spreading technique to generate high frequency currents and in structures operating at frequencies above 500 kHz, where no acoustic resonance is excited in the metal vapor lamps. Approaches such as these face difficulties including highly complex modulation and control structures and increased power losses in the controllable switches, resulting from the extremely high switching frequencies being used.

The strategy being explored in the proposed structure bases itself on the reduction of lamp power pulsations by using square-wave current (FIGURE 3-a). This is because, according to research published by Moskowitz, W. P. and Olsen, J. in July, 2004, in the 10^th International Science and Technology Symposium on Light Sources, in Toulouse - France, under the title: "Measuring Ripple Generated by an HID Ballast" and Olsen, J. and Moskowitz, W. P. in October, 2005, in the 40^th Annual IAS Meeting - Industry Applications Conference, Volume 3, pp. 1581 - 1587, under the title: "Detrimental Effect of a Small Amount of Ripple in a Metal Halide System", oscillations in power or in lamp current are responsible not only for exciting acoustic resonance but also for reducing the lamp life.

Supplying the metal vapor lamps with constant power is becoming the most promising alternative since it does not require complex control strategies. However, synthesizing single-stage structures with high enough current inversion rates, as not to cause fluctuations in power dissipation (FIGURE 3-b) is one of the challenges in using this technique.

Due to its simplicity, another advantage of the proposed structure is the possibility of using the same topological structure for different types of metal vapor lamps by just modifying a few power-processing elements, such as capacitors and inductors, to adjust them to the different power levels of the lamp. Simple alterations to the configuration of the structure's electrical components (Figure 16) originate topological variations (to the configuration of Figure 1) with equivalent electrical characteristics. In other words, a ballast that is capable of drawing current with low harmonic content from the supply and providing the lamp with a low frequency square current.

As said before the same structure can be used to supply other types of discharge lamps, such as, for example, high-pressure sodium vapor lamps. Since the output current of the ballast is square, resonance does not occur in this type of lamp either when using this ballast. Due to its simplicity and low cost, this structure becomes a direct competitor of structures that supply the lamps with sinusoidal waveforms and employ complex methods in order to avoid acoustic resonance.

Description of the Drawings

To complete the description of the invention and with the objective of facilitating the comprehension of its characteristics, a series of figures of illustrative but not limiting character are presented:

Figure 1 presents one of the topological configurations of the proposed invention. For the sake of simplicity, elements and additional circuits, such as specific drive circuits, sensing devices, and control structures, are omitted from the figure. The symbolic representation of controlled switches Si and S₂ demonstrates that any semiconductor technology can be used as long as it is able to meet the necessary physical requirements for the proper operation of the converter.

Figure 2 illustrates some output filter structures commonly used in high frequency electronic ballasts. The use of such a structure, in general, results in a reduction of the lamp's voltage and/or current harmonic content. These structures are also explored for generating high voltages to ignite one or more lamps.

Figure 3 presents the principles used in the power supply of the lamp in order to eliminate the acoustic resonance effect. Figure 3 (a) illustrates the desired ideal characteristic for applying this technique, i.e., inverting the lamp current with an infinite derivative in order to prevent distortions in the power dissipated by the arc. Figure 3(b) presents the effect created at the same power level in a real world scenario, i.e., when the inversion rate of the lamp current is finite, which generates a "ripple" in the power of the lamp.

Figure 4 presents a structure that is the root of the proposed work and is cited here as Prior Art - Ac/dc converter. When originally presented, this topology was not intended to be directly applied to the area of the proposed invention. Inductors L_F i and L_F2 in conjunction with capacitors C_FI and C_F2 are used to increase the power factor at the source.

Another work, which is relevant to the evolution of the proposed invention, is illustrated in Figure 5 and is referred to as Prior Art - Electronic ballast for a fluorescent lamp with a power factor correction stage filter on the dc side. In the analysis, the converter is presented in its structural configuration to demonstrate the technical feasibility of the invention and previous studies developed in areas common to the invention.

Figure 6 is also cited as part of the invention's conception and origin and is presented as Prior Art - Electronic ballast for a fluorescent lamp with a power factor correction stage filter on the ac side.

Figure 7 illustrates the inverter's current inversion strategy as well as the analysis interval for the converter (proposed ballast). Due to the intrinsic electrical decoupling between the different stages, it is important to note that the invention is capable of generating currents at frequencies that are different from or equal to the frequency of the source.

Figure 8 illustrates the first stage of operation and the waveforms of the proposed invention for time intervals comparable to the duration of the switching period, which is much shorter than the time intervals shown in Figure 7. For the sake of simplicity, the output capacitors, C_B i and C_B2, are replaced by dc voltage sources and the current source characteristic of inductor Lβ_ai is used to replace the output structure with an ideal current source. The notation "Gs_n(t)" used in this figure refers to the drive signals of switches Si and S₂ (Gs i and Gs₂).

Figure 9 presents the topological configuration of the proposed invention during the second operating stage as well as the idealized waveforms of a few select circuit elements.

Figure 10 illustrates the topological configuration of the proposed invention during the third operating stage as well as the idealized waveforms of a few select circuit elements.

Figure 11 illustrates the topological configuration of the proposed invention during the fourth operating stage as well as the idealized waveforms of a few select circuit elements. The fourth operating stage is considered to be the last one, since the stages concerning the switch commutations are neglected.

Figure 12 presents a block diagram describing the control strategy used in the analysis of the ballast.

Figure 13 shows the harmonic spectrum of the input current, in accordance with standard IEC 61000-3-2 Class C, of a hypothetical ballast design for a 70 W high intensity discharge metal halide lamp (HID - MH).

Figure 14 illustrates the current drawn from the hypothetical power supply of a 70 W HID - MH lamp. Both the actual current and its instantaneous average can be found in the figure, demonstrating both continuous conduction mode operation and the current's reduced distortion.

Figure 15 presents the ballast input and output currents to depict the employed synchronism.

Figure 16 presents a possible topological variation of the base structure depicted in Figure 1. With this simplification, the number of elements in the ballast can be reduced even further. However, the current of the power supply is in discontinuous mode. Detailed Description of the Invention

The innovation is in the integration of the aforementioned concepts (an inversion stage with a power factor correction stage using the charge pump technique), where some of the elements of the structure have multiple functions within the ballast, such as the elements of the output LC filter, which are also used as the ignition circuit. Furthermore, by integrating the stages, a simpler and more compact topology was achieved.

A structure with two controlled switches (Sj and S₂ in FIGURE 1) is used so that, when operating, they integrate the half-bridge voltage-source inverter, to provide current to the lamp, with the power factor correction capability. The integration of functions is achieved with the help of two filtering structures, based on passive elements (inductors and capacitors), and the frequency inverter, which can be either a half- or full-bridge structure. The output elements are responsible for limiting the current supplied to the lamp and its spectral content. The input elements are responsible for ensuring that the current of the power supply has low harmonic content (harmonics) when charging the bus capacitors. Furthermore, if properly designed, the capacitors used in the LLCC input filter (L_Fj, L_F2, C_FI, and C_F2 in FIGURE 1), in conjunction with the line impedance, behave as an LC filter to reduce the spectral content of the ballast's input current even further.

This type of approach, which seeks to compress and reduce the number of components in order to reduce the cost of supplying square-wave currents, is sought after across the globe. Typical examples include publications such as those presented by Yang, Y. et αl., in 2005, presented at the 20^th annual IEEE conference - APEC and included in the conference proceedings of APEC2005, Volume 2, pp. 1048 - 1052, under the title "A novel single-stage low-frequency square-wave electronic ballast for low-wattage HID lamps" and Dalla Costa, M. A. et αl., in 2007, in the 42^nd annual IEEE conference - IAS and included in the proceeding of the Industry Applications Conference 2007, pp. 484 - 489, under the title "Generalized Analysis and Comparison of High-Power-Factor Integrated Topologies to Supply Metal Halide Lamps with Low Frequency Square Waveform". Note that, in order to obtain the results presented in these publications, auxiliary circuits were needed to ignite the lamp, a problem that does not pose a challenge for the proposed topology. Furthermore, in these publications, the switches required to invert the current's direction through the lamp can be considered a second stage.

The topology of an ac/dc converter with integrated inversion and power factor correction stages is illustrated in FIGURE 4, with a voltage-supplied load. FIGURE 5 presents an evolution of this topology, which has been used to supply fluorescent lamps. Such structures can be considered as part of the evolution of the proposed ballast. The power factor correction structure is based on one of the topologies (FIGURE 6) proposed in the Doctoral Thesis of de Nascimento, C. B. under the supervision of Perin, A. J., in 2005, entitled "Estruturas de Reatores Eletrόnicos com Elevado Fator de Potencia" (Structures of High Power Factor Electronic Ballasts), and is also used to supply fluorescent lamps with a high frequency sinusoidal waveform.

The topology of this invention (FIGURE 1) eliminates the series dc blocking capacitor C_c (FIGURE 5) or C_d (FIGURE 6), in order to supply constant current, I_L, during the entire T_R/2 interval (FIGURE 7). Due to the decoupling provided by the current source characteristic of the output filter (since Lβ_ai is much larger than Lp i and L_F2), the voltages across bus capacitors C_B i and C_B2 oscillate linearly around Vβ/2. This oscillation is not perceived by the total voltage, Vβ(t). This characteristic gives the structure freedom to operate with other inversions periods, i.e. not just T_R, without affecting the input current.

Due to the adopted power supply technique, this topology presents a low lamp current crest factor, which is an uncommon trait in charge-pump topologies. Another important characteristic is the simplification of the elements in the sensing and control circuits, since they can be referenced to the mid-point formed by capacitors C_B i and C_B2 (FIGURE 12). Furthermore, with the proper adjustment of elements L_F and C_F, this topology can operate with zero voltage switching at both turn-on and turn-off of Si and S₂, during the intervals in which the current through the complementary inductor is greater than the current through the lamp, that is, during the intervals in which iu(t) > ϊLa(t) in the positive semi-cycle of i_La(t) and, analogously, during the intervals in which i_L1(t) > ϊ_La(t) in the negative semi-cycle.

It can be clearly observed that this new topology (FIGURE 1) substantially reduces the number of components, allowing greater compactness, which translates into low investments in the mechanical coupling structure of the ballast to the fixture. This makes power factor correction possible in low power metal vapor lamps, where low cost, weight, and volume are extremely important.

The operating principle of the circuit is the same for both the positive and negative semi-cycles of the current through the lamp. In order to simplify the operating stages, period T_R is made to be the same as that of the source. Thus, symmetry of the stages is also obtained for the positive and negative semi-cycles of the mains. It will be presented only half of the stages of a switching period, those that occur during the positive semi- cycle of the mains (FIGURE 7).

During the description of the operating stages and the derivation of the equations, a few simplifications were made to analyze the circuit: the voltage ripple of voltage Vβ(t) (voltage across C_B i and C_B2) will be neglected; the voltage across the terminals of the source, V_in(t), will be considered constant during one switching period; the input current will be considered constant during the entire switching period; the current through filtering inductor Lβ_ai is considered constant during period T_R; all components will be considered ideal; the switching stages of switches Si and S₂ will not be represented because they do not affect the static characteristics of the converter.

At the time immediately preceding the beginning of the first stage (FIGURE 8), between instants to and tj, diodes D₂ and D_B4 were conducting. At to, switch S₁ is turned on and S₂ is off. At this time D_B1 starts conducting, which causes the rise of the current through Lp _l, the fall of the current through Lp₂ and, as a consequence, the polarity change of the currents through capacitors C_FI and Cp₂. During this interval part of the energy stored in L_F2, during the previous stage, is transferred to bus capacitors C_B1 and C_B2. Since voltage Vj_n(t) is constant during the switching period, the voltages across capacitors C_FI and C_F2, and, therefore, the voltage across L_F1 and L_F2, vary according to an second order undamped response. The first stage ends exactly when the current through Lp₂ reaches zero, resulting in D_B4 turning off naturally.

During the second stage (FIGURE 9), between instants t, and t₂ (FIGURE 9), Si remains on. Since the voltages across capacitors C_FI and CF₂ cannot vary instantaneously, being restricted to V_in(t) = V_CFi(t) + V_CF2(t), the voltage across C_F2 continues to rise. The current through Lp i continues to flow in the same direction, which decreases the voltage across the terminals of C_FI . This stage ends when switch Si is turned off.

In the third stage (FIGURE 10), between instants 0 and tø, diode D₂ starts to conduct due to the direction of the current through the load. During this stage, part of the energy stored in inductor L_FI is transferred to capacitors C_BI and C_B2- Since the sum of the voltages across C_FI and Cp₂ is equal to V_1n, the voltage across Cp i starts to increase as C_F2 discharges, delivering its stored energy to L_F2- AS the current through L_F2 increases, a change in the polarity of the current through the switch branch is possible. If this happens, the current naturally commutates from D₂ to S₂, thus giving way to the subsequent topological changes. This stage ends when the current through L_{F I} reaches zero and D_BI naturally turns off. In the fourth stage of operation (FIGURE 11), between instants t₃ and ^, the current through inductor Lp₂ continues to rise while capacitor C_F2 discharges. Since the current through L_FI is zero, the current through capacitor C_BI also goes to zero. Therefore, the load current circulates entirely through C_B2- This stage ends when switch S₂ is turned off. After the switching interval, Si is turned on, which restarts the operating cycle of the structure.

The mathematical analysis is carried out by observing the operating stages, which describe the idealized behavior of the ballast. From this analysis, it is possible to define the main parameters of the proposed ballast. It can be observed from the description of the operating stages that it is impossible to predict the behavior of the voltages across and currents through filter elements L_FI, L_F2, C_FI, and C_F2- However, by specifying operating conditions, such as Vp/Vβ tends to unity and fj/ff (Table 1) is much greater than one, one can simplify the equations that describe the voltages across and currents through these elements (Table 1).

Therefore, it is possible to obtain a set of simplified equations, from which the equations for the design of the inductive (1) and capacitive (2) elements of the circuit's input filter can be derived.

Table 1: Set of simplified equations.

II 0

^Z/ ω_f

III — V t z/ ^Z/

IV 0 _j ^KC23* Z/

Where Z_f 1 *LL223 »'VV ^VVCC11P1 'VV ^VVCC1122 >' V ^V C22 ' V ^Y C23

Where, α = ^Vp>

D= ¹^

A simulation of the converter operating with a metal vapor lamp with P_L8 = 70 W was carried out with the objective of demonstrating the operation of the structure with a simple control strategy. By sensing the voltage and current of the lamp (FIGURE 12), current iLa(t) and power PLa(t) are controlled, and by sensing voltages Ve₁Ct) and V_B2(t) one can determine the instant at which i_La(t) inverts itself (hysteresis control) and guarantee that i_La(t) has a zero average value.

Setting the operating parameters to the values in Table 2, the calculation of the circuit elements results in CF_I = C_F2 = 75 nF and Lp₁ = Lp₂ ≡ 483 μH.

Table 2: Design example parameters.

Parameter Value Description

Vp 311 V Peak value of the input voltage fr 60 Hz Operating frequency of the power supply

Pin 8O W Input power

PLa 7O W Lamp power

RLa 100 Ω Equivalent resistance of the lamp (70W)

VB 315 V Bus voltage

ΔVCB 2.5% Ripple relative to bus voltage

ΔV_Cf 20 V Absolute ripple of voltages v_cfl (t) and v_Cf2 (t)

100 kHz Operating frequency of the inverter

The harmonic spectrum of the input current, according to the limits established by standard IEC 61000-3-2 Class C, is presented in FIGURE 13. It can be observed that the ballast meets the requirements. The input current, which tends to be sinusoidal, is illustrated in FIGURE 14. By adding an input filter, designed to attenuate high frequency harmonics near the switching frequency, a filtered input current can be obtained, which is also illustrated in FIGURE 14.

The input and output currents are presented in FIGURE 15. It can be verified that inverting I_L8(Q at the same frequency as the supply ensures that no power perturbations occur at the input nor at the output.

Claims

1) ELECTRONIC BALLAST FOR METAL VAPOR LAMPS USING INTEGRATION TECHNIQUES FOR POWER FACTOR CORRECTION AND ACOUSTIC RESONANCE ELIMINATION is characterized as a single stage electronic ballast, supplied by an ac source, integrating the power factor correction's electronic circuit with a half-bridge voltage-source inverter such that a square output current waveform can be achieved while using only two controlled switches.

2) ELECTRONIC BALLAST FOR METAL VAPOR LAMPS USING INTEGRATION TECHNIQUES FOR POWER FACTOR CORRECTION AND ACOUSTIC RESONANCE ELIMINATION is composed of a single stage electronic ballast, in agreement with claim 1, which does not require additional components for ignition.

3) ELECTRONIC BALLAST FOR METAL VAPOR LAMPS USING INTEGRATION TECHNIQUES FOR POWER FACTOR CORRECTION AND ACOUSTIC RESONANCE ELIMINATION is composed of a single stage electronic converter, in agreement with claim 1, which allows the square current through the lamp to be in phase with and have the same frequency as the voltage supply.

4) ELECTRONIC BALLAST FOR METAL VAPOR LAMPS USING INTEGRATION TECHNIQUES FOR POWER FACTOR CORRECTION AND ACOUSTIC RESONANCE ELIMINATION is composed of a single stage electronic converter, in agreement with claims 1 and 3, which allows the square current through the lamp to have phase and frequency different from those of the supply voltage.

5) ELECTRONIC BALLAST FOR METAL VAPOR LAMPS USING INTEGRATION TECHNIQUES FOR POWER FACTOR CORRECTION AND ACOUSTIC RESONANCE ELIMINATION is composed of a single stage electronic converter, in agreement with claim 1 , which does not require a capacitor to block the average voltage at the output of the half-bridge converter, since the average output current can be controlled by the control circuit. 6) ELECTRONIC BALLAST FOR METAL VAPOR LAMPS USING INTEGRATION TECHNIQUES FOR POWER FACTOR CORRECTION AND ACOUSTIC RESONANCE ELIMINATION, in agreement with claim 1, is characterized by the possibility of using integrated circuits to control the switches, the output power, and to provide overcurrent protection to the output of the ballast.

7) ELECTRONIC BALLAST FOR METAL VAPOR LAMPS USING INTEGRATION TECHNIQUES FOR POWER FACTOR CORRECTION AND ACOUSTIC RESONANCE ELIMINATION, in agreement with claims 1 through 6, is characterized by the possibility of using only one inductor for the power factor correction stage, in place of Lp₁ and L_F2, connected between the mid-point of filter capacitors C_Fi and C_F2 and the common connection point of controlled switches S₁ and S₂.

8) ELECTRONIC BALLAST FOR METAL VAPOR LAMPS USING INTEGRATION TECHNIQUES FOR POWER FACTOR CORRECTION AND ACOUSTIC RESONANCE ELIMINATION, in agreement with claims 1 through 7, is characterized by the possibility of its use with other types of lamps, such as discharge lamps and solid-state lamps, which currently employ LEDs.