KR20040033749A - Multiplex modulation driving method and apparatus of the high frequency electronic ballast for the metal halide lamp - Google Patents

Abstract

PURPOSE: A multiple modulation driving method and a multiple modulation driving apparatus are provided to effectively remove acoustic resonance phenomena by continuously maintaining the spectrum of lamp current. CONSTITUTION: A multiple modulation driving method comprises a step of constituting a multiple modulation signal by mixing two or more modulation signals including a double modulation signal so as to continuously maintain the spectrum of lamp current; and a step of multiple modulation driving a lamp in accordance with the multiple modulation signal. A multiple modulation driving apparatus comprises a sawtooth wave generator for generating a sawtooth wave serving as a basic modulation signal; a first chopping wave generator for generating a first chopping wave serving as a modulation signal for modulating the basic modulation signal; a sweep sawtooth wave generator for generating a sweep sawtooth wave serving as a double modulation signal; a second chopping wave generator for generating a second chopping wave serving as an additional modulation signal; and a final modulation signal generator for generating a multiple modulation signal by adding the second chopping wave to the sweep sawtooth wave.

Description

METHOD AND APPARATUS FOR MULTIPLE MODULATION DRIVING HIGH FREQUENCY ELECTRONIC BALLAST FOR METAL HAlide LAMPS {MULTIPLEX MODULATION DRIVING METHOD AND APPARATUS OF THE HIGH FREQUENCY ELECTRONIC BALLAST FOR THE METAL HALIDE LAMP}

The present invention relates to a multiple modulation driving method and apparatus for an electronic ballast using a high frequency modulation as a driving method of a metal halide lamp.

In recent years, high intensity discharge (HID) lamps have been used in many fields. In particular, metal halide lamps, which are one of HID lamps, have excellent color rendering and high light efficiency, and are widely used in various exhibition hall lighting to stage lighting. Is being used. However, since most metal halide lamps employ a bulky and heavy magnetic ballast, there is a problem in that the installation location is limited and the installation work is cumbersome.

Therefore, in recent years, the use of the electronic ballast having the advantages of small size, light weight and high efficiency is increasing. However, at present, most electronic ballasts for metal halides are low frequency electronic ballasts driven by square wave inverters of several hundred Hz. In the case of metal halide lamp, Acoustic Resonance Phenomena occurs more significantly than other HID lamps when high frequency driving is performed.The natural frequency of gas waves in arc tube and its harmonic components are densely distributed in a wide frequency band. This is because the frequency band is not very narrow. When resonance occurs, the arc is unstable, causing the lamp to flicker and, in severe cases, the tube to rupture. Therefore, suppression of resonance is essential.

The first method that can be used to avoid such resonance is to drive the lamp at a very high frequency in the MHz band which does not cause resonance, which has a problem of large switching loss and a large amount of electromagnetic emission. At the present time, which is not technically solved, there are practical problems.

Another method is to suppress resonance by applying a high frequency modulation method. In this case, the shape and frequency of the modulated signal and the frequency modulation range should be considered. If a modulated signal of a certain frequency is used, the frequency selection of the modulated signal is very important, even if the fundamental or harmonics of the modulated signal included in the lamp drive current coincide with the low harmonics of the lamp's natural resonance frequency. This may occur because the spectrum of the lamp drive current still has a discrete distribution when the modulating signal is at a constant frequency. In order to overcome this drawback, an irregular switching method in which white noise is added to a modulated signal may be applied (L. Laskai, PNEnjeti, IJPitel, "White-noise modulation of high-frequency high-intensity discharge lamps). ballasts ", IEEE Transactions on IA, Vol. 34 Issue 3, pp. 597-605, 1998). However, it is difficult to use it as a low cost commercial ballast because it must be equipped with an almost complete white noise generator.

1 shows a spectrum of a modulated signal and a lamp current during constant frequency modulation. Looking at the problem of the frequency modulation method using a modulated signal of a certain frequency in detail, first there is a problem that the resonance phenomenon due to the fundamental or harmonic components of the modulated signal included in the lamp current is large. This possibility is greater with high-power lamps than with low-power lamps, because the larger the power lamp, the larger the discharge tube, and the lower the natural frequency of the input wave. In fact, if the modulated signal is low frequency, resonance is very unlikely. However, in this case, as in the case of driving the lamp at low frequency, the re-ignition phenomenon of the lamp occurs, so the advantage of high frequency driving is reduced. The second problem is that the spectrum of the lamp current is discretely distributed as shown in Fig. 1 because the modulated signal has a constant shape and frequency even when frequency modulation is performed. Therefore, if the frequency modulation width is not widened, the resonance phenomenon due to this discrete frequency component is likely to occur. However, if the frequency modulation width is made very wide to reduce the size of these discontinuous frequency components, there is a disadvantage that the crest factor of the lamp current increases as an opposite benefit.

Therefore, there is a limit to a high frequency modulation method using a modulated signal of a certain frequency, and there is an urgent need for another method for driving a high frequency of a metal halide lamp.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to propose a multiple modulation method as a method of high frequency driving of a metal halide lamp and to provide a high frequency electronic ballast employing the same. More specifically, lamp driving power is achieved by employing a multiple modulation method in which a modulated signal is composed of two signals having different frequencies and waveforms, one of which is composed of a double modulated signal that modulates the modulated signal itself. The purpose is to remove the resonance phenomenon generated during the high frequency driving of the metal halide lamp by continuously distributing the spectrum.

1 is a graph showing a modulated signal spectrum and a lamp current spectrum during constant frequency modulation according to the prior art;

2 is a flowchart of generating a multiple modulated signal according to the present invention;

3 is a graph showing a lamp driving characteristic according to the modification of the modulated signal;

4 is a graph showing the crest factor of the lamp current according to the symmetry ratio of the triangular wave,

FIG. 5 illustrates a process of generating a modulated signal used in a multiple modulation method according to an embodiment of the present invention. FIG. 5A illustrates a basic modulated signal (first modulated signal), and FIG. 5B illustrates a modulated signal of a basic modulated signal. 2 modulated signal), FIG. 5C is a dual modulated signal (third modulated signal), FIG. 5D is a fourth modulated signal to be added to the dual modulated signal, FIG. 4E is a graph showing a final multimodulated signal (5 modulated signal),

6 is a graph illustrating a modulated signal spectrum and a lamp current spectrum according to an embodiment of the present invention;

7 is a circuit diagram of a lamp driving inverter,

8 is a block diagram of a modulated signal generator according to an embodiment of the present invention;

9 is a view showing a transition of a modulated signal according to an embodiment of the present invention;

10 is a circuit diagram of an AC / DC converter,

11 is a graph showing a voltage and a current of an AC / DC converter input terminal;

12 is an overall control block diagram of an inverter for an electronic ballast according to an embodiment of the present invention;

13 is a graph showing a modulated signal and a lamp current during lamp power control;

14A and 14B are graphs illustrating power spectra of modulated signals, lamp currents, and lamp currents during constant frequency modulation and multiple modulation according to an embodiment of the present invention, respectively, according to the prior art;

In order to achieve the above object, the present invention constructs a multiple modulated signal by mixing two or more modulated signals including a dual modulated signal modulating the modulated signal itself in order to maintain the power spectrum of the lamp continuously, A multimodulation driving method of a high frequency electronic ballast for a metal halide lamp, characterized in that the lamp is multimodulated by a modulated signal.

More specifically, generating a first modulated signal corresponding to a basic modulated signal, generating a second modulated signal which is a modulated signal to modulate the basic modulated signal, and converting the first modulated signal into a second modulated signal. Modulating to generate a third modulated signal that is a dual modulated signal, generating a fourth modulated signal that is an additional modulated signal to be added to the dual modulated signal, and adding the dual modulated signal and the additional modulated signal to a final modulated signal; High frequency electronics for metal halide lamps, comprising: driving a metal halide lamp using a high frequency multiple modulation drive signal generated by generating a 5-modulated signal and modulating the lamp drive signal by the final multiple modulation signal A method of driving multiple modulations of a ballast is provided.

In another aspect, the present invention provides a sawtooth wave generator for generating a sawtooth wave which is a basic modulated signal; A first triangular wave generator for generating a first triangular wave as a modulated signal to modulate the basic modulated signal; A swept sawtooth generator for generating a swept sawtooth wave which is a dual modulated signal; A second triangle wave generator for generating a second triangle wave as an additional modulation signal; It provides a multi-modulation drive device of the high frequency electronic ballast for a metal halide lamp comprising a; final modulation signal generator for generating a multi-modulation signal to be used for driving the lamp by adding the second triangular wave to the sweep sawtooth wave. .

According to another aspect of the present invention, when controlling lamp power, a lamp is driven by using a modulated signal in which a control input which is a DC component for power control is added to the multiple modulated signal.

Another feature of the present invention is to use a sawtooth wave that is increased during frequency modulation and a sawtooth wave that is decreased during periodic modulation as a basic modulation signal to minimize the crest factor of the lamp current and to maintain the lamp voltage stable.

Another feature of the invention is further provided with an operation mode selector; The operation mode selector controls the ballast to operate in a soft starting mode, a fixed frequency or fixed period operation mode, and a multiple modulation mode sequentially from the time of lamp lighting; In the soft starting mode, in the case of frequency modulation, the lamp is driven at a frequency at which the driving frequency decreases from the starting frequency to a fixed frequency. In the case of periodic modulation, the driving period is driven in a period in which the driving period is increased from the starting cycle to the fixed cycle. Mode, wherein the fixed frequency or fixed period operation mode is a mode for driving the lamp at the fixed frequency or fixed period while the lamp is stabilized through an initial transient state, and the multiple modulation mode drives the lamp using the multiple modulation signal. It is a mode to do.

Hereinafter, a configuration and operation of a high frequency electronic ballast for a multi-modulation metal halide lamp according to a preferred embodiment of the present invention will be described with reference to the accompanying drawings.

According to an embodiment of the multiple modulation driving method according to the present invention, the sawtooth waveform is used as a basic modulation signal as shown in Figure 5a, the reason is as follows.

When the lamp is driven by frequency modulation, the results as shown in FIG. 3 can be obtained by observing the trend of the voltage and current waveforms of the lamp according to the modification of the modulated signal. Here, the frequency of each modulation signal is 1.2 kHz, and the symmetry ratio of the triangular waveform is changed from 0 to 1 in 0.1 units. This is a result of the experiment for observing the crest factor of the current according to the modification of the modulated signal, and shows the relationship between the symmetry ratio of the triangular wave modulated signal and the crest factor of the lamp current in FIG. 4 using this result. As the symmetry ratio of the modulated signal increases, the crest factor of the lamp current decreases.

3 and 4, when the increasing sawtooth wave is applied as the frequency modulated signal 21, the crest factor of the lamp current is minimal and the voltage of the lamp is the most stable. This is interpreted to be due to the difference in the transient characteristics of the lamp current with the change of the driving frequency. Therefore, when using a triangular waveform modulated signal, it is desirable to select an increasing sawtooth waveform which is most effective for suppressing the crest factor of the lamp current as the basic waveform of the lamp drive signal. However, in the embodiment of the present invention, since the digital controller is used as the ballast controller, the period of the lamp driving signal is modulated to indirectly modulate the lamp driving frequency. Selected. That is, the modulation scheme according to the embodiment of the present invention is not a frequency modulation scheme but a periodic modulation scheme, and as a result, characteristics such as frequency modulation can be obtained through periodic modulation.

Next, waveforms constituting a multiple modulation signal according to an embodiment of the present invention will be described. Fig. 5A shows a sawtooth waveform that is reduced as described above as the basic modulated signal (first modulated signal). This basic modulated signal is first modulated with a triangular wave (second modulated signal) of FIG. 5B to produce a double modulated signal (third modulated signal) of FIG. 5C. That is, in the dual modulated signal, the modulated signal itself is first modulated. As a result, the frequency spectrum is considerably dispersed as compared with the case where the basic modulated signal is used as a modulated signal. When the dual modulation signal of FIG. 5C is used as a modulation signal, the lamp is driven by double modulation. However, in the exemplary embodiment of the present invention, the low frequency triangular waveform (fourth modulated signal) of FIG. 5D is added to the dual modulated signal again to derive the final multimodulated signal (fifth modulated signal) of FIG. 5E. This aims to spread the spectrum of the lamp current more effectively by shaking the entire spectrum of the dual modulated signal once again.

Using the final multiplexed modulation signal of FIG. 5E, the result of FIG. 6 can be obtained, which yields a spectrum of nearly continuous lamp currents as shown. Here, the modulation frequency of the basic modulated signal, i.e., the frequency of the second modulated signal (FIG. 5B) is set to a low frequency, but it does not cause re-lighting because it does not appear in the spectrum of the lamp current. However, since the lamp power includes components of an additional modulated signal (fourth modulated signal), it is necessary to select a frequency such that a change in lamp power cannot be recognized, and the smallest possible size limits the crest factor of the lamp current. Also effective. On the other hand, in the case of controlling the power of the lamp for dimming control, etc., a DC component (control input) for power control is added to the final multi-modulation signal (the fifth modulated signal) that is primarily modulated and mixed with low frequency, so that the final modulation signal Will be configured.

The following describes the electrical characteristics of the waveforms. The basic modulated signal of FIG. 5A may be represented as in Equation (1) below.

(One)

Where f _b is the frequency of the basic modulated signal. As described above, the basic modulated signal is modulated by the triangular wave of FIG. 5B, which can be represented by the following equation (2).

(2)

Where f _f is the modulation frequency of the basic modulated signal. Therefore, the dual modulated signal of FIG. 5C can be represented by the following equation (3).

(3)

(4)

Since the dual modulation signal is mixed with the additional modulation signal shown in Equation (4) (FIG. 5D), the final modulation signal including the control input u (t) for power control can be represented by the following equation (5).

(5)

Therefore, the maximum and minimum periods of the ramp drive signal modulated by Equation (5) can be represented by the following Equations (6) and (7), respectively.

(6)

(7)

On the other hand, Figure 7 shows a circuit of a lamp driving inverter according to the present invention, the output voltage is given by the following equation (8).

(8)

Where V _dc represents the magnitude of the DC link voltage and T represents the switching period of the inverter. Since the harmonic components of the output voltage are filtered by the resonant circuit and hardly appear in the lamp current, the effective value of the lamp current fundamental wave components is given by the following equation (9) when only the fundamental wave components are considered.

(9)

Where R _eq is the equivalent resistance of the lit lamp. According to the multiple modulation method according to an embodiment of the present invention, since the lamp driving switching period is modulated at a uniform density from T _min to T _max , the average value of the effective current of the lamp during modulation can be obtained as shown in Equation (10) below. .

10

(11)

Here, K is given by equation (12), and since the solution of equation (10) is very complicated, the approximate equation (11) will be applied.

(12)

From the above, the average power of the lamp can be obtained as in the following equation (13).

(13)

In addition, the maximum value of the lamp current in the multiple modulation method according to an embodiment of the present invention is as shown in the following equation (14).

(14)

Therefore, the crest factor of the lamp current by the multiple modulation method according to the embodiment of the present invention is as shown in the following equation (15).

(15)

An embodiment of the modulated signal generator applying the multiple modulation method as shown in FIG. 8 includes a swept sawtooth generator 71 and a triangular wave generator 72 having a variable size and a fixed frequency. Also included is an operation mode selector 73 consisting of a timer and a sequential logic circuit to select one of soft start mode, fixed period operation mode or multiple modulation mode, triangular wave generator 72 provides soft start and fixed period It does not work in the operation mode.

9 shows the transition of the modulation signal from the time of lamp lighting to the steady state.

According to this, the ramp starts driving at the start time T _start at time t ₀ , and is set to the soft starting mode by the operation mode selector 73, so that the driving period is increased to the fixed period T _fix until time t ₁ . have. Here, the modulated signal for soft starting is produced by the following procedure. First, an initial start cycle preset at time t ₀ is applied to the up / down counter 74. At this time, the swept clock generator 75 is controlled to generate a clock of a predetermined frequency during the soft start period t ₀ to t ₁ , and the counter operates as an up counter.

When the lamp is normally started, the ballast is set to the fixed cycle mode of operation to drive the lamp with a fixed period T _fix while it is stable through the initial transient state of the lamp. During this mode, the swept clock generator 75 does not generate any clock.

After time t ₂ , the lamp operates in a multiple modulation mode that includes a power control algorithm for dimming control. At this time, the counters 74 and 78 are controlled by the controllers 76 and 77 configured as comparators, and generate a double modulated signal using the swept clock 75. The swept clock generator 75 is itself a type of modulator with a modulated signal generator.

An electronic ballast is essentially provided with a lamp driving inverter, and since most electronic ballasts need to be supplied with power from a commercial AC power source, an AC / DC converter is required to supply power to the inverter. Hereinafter, the experimental results of the electronic ballast for the 150W metal halide lamp manufactured by applying the above-described multiple modulation driving scheme will be described.

FIG. 10 shows an AC / DC converter using a boost type active power factor correction circuit 92 at a power input for high input power factor and a constant DC link voltage, and a dedicated IC as an active power factor improvement circuit. The MC34262 can be used to independently control the ballast inverter. In addition, a passive filter 91 was added to remove converter input current and power supply noise. As a result, as shown in FIG. 11, the ballast was able to maintain the AC input power factor to almost 1 and control the DC link voltage constantly.

12 is a control block diagram of a ballast inverter. The controller is configured to perform power control, real-time resonance detection and avoidance algorithm as well as multiple modulation driving proposed in the present invention. All controllers except the filter and the amplifier are implemented as EPLD. It was.

FIG. 13 shows experimental results when the lamp power is controlled and shows the multiple modulation signal and the lamp current. The DC level of the modulated signal is different depending on the power of the lamp, since the control input of the power controller is added to or subtracted from the final multiple modulated signal, and it can be seen that it is driven stably over a wide power range.

As described above, the electronic ballast implemented by applying the multiple modulation driving method according to the present invention is very effective in eliminating resonance phenomena. 14A and 14B illustrate power spectra of a modulated signal, a lamp current, and a lamp current according to a conventional high frequency modulation method having a modulated signal of a predetermined frequency and a multiple modulation driving method according to the present invention, and comparing the two figures. It can be seen that the effect of the present invention is excellent.

As shown in FIG. 14A, in the conventional high frequency modulation method, a discrete frequency spectrum having a separation of the modulation signal frequency magnitudes can be viewed. This is an unavoidable phenomenon when the modulated signal is at a certain frequency. In particular, when the modulation signal and the modulated driving signal are tuned, this phenomenon becomes larger, and when the modulation signal and the modulated driving signal are synchronized, the spectrum of the lamp current becomes a completely discrete distribution of immutation, so it is very important to avoid the resonance phenomenon. it's difficult. On the other hand, as shown in Figure 14b, in the case of the electronic ballast using the multiple modulation drive method according to the present invention, it can be seen that the power spectrum of the lamp current is almost continuous.

Therefore, applying the new multiple modulation driving method proposed in the present invention to a metal halide lamp has an effect of effectively eliminating resonance while maintaining a low lamp current crest factor by continuously maintaining a spectrum of lamp currents. In addition, in order to reduce the production cost using the ASIC in the future, in the implementation of the embodiment of the present invention, implemented using only EPLD without using a microprocessor, soft starting, no load protection, power control for dimming control, overload protection, etc. Since all algorithms are easily implemented, there is no problem in employing a commercial ballast.

Claims (6)

In a multiple modulation driving method of a high frequency electronic ballast for a metal halide lamp for eliminating the instability of the arc due to the resonance phenomenon by modulating the frequency or period of the drive signal of the metal halide lamp using a modulated signal, In order to continuously maintain the power spectrum of the lamp, a multimodulated signal is formed by mixing two or more modulated signals including a double modulated signal modulated by the modulated signal itself, and the multimodulated drive is driven by the multimodulated signal. A multiple modulation driving method of a high frequency electronic ballast for a metal halide lamp, characterized in that. In the multiple modulation drive device of the high frequency electronic ballast for a metal halide lamp for eliminating the instability of the arc due to the resonance phenomenon by modulating the frequency or period of the drive signal of the metal halide lamp using the modulation signal generated by the modulation signal generator, A sawtooth wave generator for generating a sawtooth wave which is a modulated signal; A first triangular wave generator for generating a first triangular wave as a modulated signal to modulate the basic modulated signal; A swept sawtooth generator for generating a swept sawtooth wave which is a dual modulated signal; A second triangle wave generator for generating a second triangle wave as an additional modulation signal; And a final modulation signal generator for generating a multiple modulation signal to be used for driving a lamp by adding the second triangle wave to the swept sawtooth wave. The method of claim 2, When controlling the lamp power, the multi-modulation driving device of the high frequency electronic ballast for a metal halide lamp, characterized in that for driving the lamp by using a modulated signal to which the control input which is a direct current component for power control to the multi-modulated signal. The method of claim 2, The basic modulated signal is a sawtooth wave which increases during frequency modulation and decreases when a period modulation modulates the crest factor of the lamp current and keeps the lamp voltage stable. Multiple modulation drive of ballasts. The method of claim 2, An operation mode selector for controlling the ballast to operate in a soft starting mode, a fixed frequency operating mode and a multiple modulation frequency mode sequentially from the time of lamp lighting; The soft starting mode is a mode for driving the lamp at a frequency at which a driving frequency decreases from the starting frequency to a fixed frequency, and the fixed frequency operation mode drives the lamp at the fixed frequency while the lamp is stabilized through an initial transient state. And the multi-modulation frequency mode is a mode for driving the lamp using the multi-modulation signal. The method of claim 2, An operation mode selector for controlling the ballast to operate in a soft starting mode, a fixed period operation mode, and a multiple modulation period mode sequentially from the time of the lamp on; The soft starting mode is a mode in which the lamp is driven in a period in which a driving period is increased from a startup period to a fixed period, and the fixed period operation mode is a mode in which the lamp is driven in the fixed period while the lamp is stabilized through an initial transient state. And wherein the multiple modulation cycle mode is a mode for driving the lamp by using the multiple modulation signal.