EP2526742B1 - Circuit arrangement and method for operation of a high-pressure discharge lamp below its nominal power - Google Patents

Description

Technical area

The invention relates to a method for operating a high-pressure discharge lamp below its nominal power with an alternating voltage and an alternating current of a predetermined operating frequency.

background

The invention is based on a method for operating a high pressure discharge lamp below its nominal power with an alternating current of a predetermined operating frequency according to the preamble of the main claim.

If high-pressure discharge lamps, also referred to below as lamps, are operated in dimmed fashion, various problems arise. Virtually all standard high pressure discharge lamps are optimized for nominal power so that the plasma physical processes and the thermal budget of the lamp perform optimally at nominal lamp power and have the highest efficiency. The nominal output of the high-pressure discharge lamp is considered below to be the power specified by the manufacturer for this lamp. Due to the optimized plasma-physical processes and the likewise optimized thermal budget of the high-pressure discharge lamp, the high-pressure discharge lamp has a good operating stability during operation with its nominal lamp power or rated power. When dimming high pressure discharge lamps, the operating stability suffers sometimes considerably, since the thermal budget of the burner with increasing dimming level must always work further away from its optimum. Most of the marketable high pressure discharge lamps are powered by alternating current. In most cases, a rectangular low-frequency operating current is used, which is also called "wobbly DC operation". In this case, a substantially rectangular current with a frequency of usually 50 Hz up to a few kHz is applied to the lamp. With each swing between positive and negative voltage, the lamp commutates, as the current direction reverses and the current thus briefly becomes zero. This operation ensures that the electrodes of the lamp are uniformly loaded despite a quasi-DC operation.

From the EP 1 418 795 A2 An operating method for a high-pressure discharge lamp is known, in which the high-pressure discharge lamp is operated at different frequencies depending on the current lamp voltage and whether the high-pressure discharge lamp is in the power saving mode.

From the US 2007/0024207 a circuit arrangement is known which detects a jumping of the bow approach and then avoids a possible flickering of the lamp.

From the EP 2 043 409 A2 a projector is known which operates a high-pressure discharge lamp with a rectangular current form, wherein the projector can operate the Hochdruckent charge lamp depending on their state (eg aging state) with a pent roof-shaped current form.

The bow approach to the electrodes is fundamentally problematic when operating a gas discharge lamp with alternating current. When operating with alternating current during commutation of the operating voltage, a cathode to the anode and vice versa an anode to the cathode. The transition cathode-anode is inherently unproblematic, since the temperature the electrode has no influence on its anodic operation. In the anode-to-cathode transition, the ability of the electrode to supply a sufficiently high current depends on its temperature. If this is too low, the arc changes during commutation, usually after the zero crossing, from a brief diffuse arc approach mode (so-called, diffuse-mode '), to a punctiform Bogenansatzbetriebsweise (so-called, spot-mode'). This change is sometimes accompanied by an often visible collapse of the light emission, which can be perceived as flickering.

In dimming operation, the electrodes of the high-pressure discharge lamp become ever colder and, when the operating current is commutated, the lamp can start to flicker and become unstable. These instabilities in commutation sometimes cause significant electromagnetic interference.

task

It is an object of the invention to provide a method for operating a high-pressure discharge lamp below its nominal power with an alternating current of a predetermined operating frequency, which causes less electromagnetic interference.

Presentation of the invention

• Absenken der aktuellen Betriebsfrequenz unter eine Obergrenze,
• Ändern der Stromform des Wechselstroms auf eine pultdachförmige Stromform, die abhängig von der Differenz der Lampenspannungen am Ende und am Anfang der Halbperiode ist, bei der sich der Betrag des Stromes |I_start| zu Beginn der Halbperioden zu dem Betrag des Stromes |I_end| am Ende der Halbperioden verhält wie |I_start| : |I_end| = 1:1,2 .. 1:3,0. Durch die pultdachförmige Stromform wird der Gasentladungslampenbrenner bis zur Kommutierung soweit aufgeheizt, dass diese ohne Probleme und ohne die oben beschriebenen elektromagnetischen Störungen aufgrund einer hochfrequenten Stromschwingung kurz nach der Kommutierung durchgeführt werden kann.

The solution of the object with respect to the method according to the invention is carried out with a method for operating a high pressure discharge lamp below its nominal power, the high pressure discharge lamp is operated at nominal power with an alternating current of a predetermined operating frequency, and the lamp voltage during a half period at least at the beginning of a half period and at the end of a Half-period is measured, with the following steps:

• Lowering the current operating frequency below an upper limit,
• Changing the current form of the alternating current to a lean-to roof shaped current form, which depends on the difference between the lamp voltages at the end and the beginning of the half period in which the amount of the current | I _start | at the beginning of the half periods to the amount of current | I _end | at the end of the half periods behaves like | I _start | : | I _end | = 1: 1.2 .. 1: 3.0. Through the pent roof-shaped current form of the gas discharge lamp burner heated until commutation so far that it can be carried out without problems and without the electromagnetic interference described above due to a high-frequency current oscillation shortly after commutation.

Preferably, the amount of current | I _start | behaves at the beginning of the half periods to the amount of current | I _end | at the end of the half periods like | I _start | : | I _end | = 1: 1, 5 .. 1: 3, 0. These values ensure a clean commutation even with difficult lamps.

In a first embodiment of the method, the upper limit is 120 Hz. This makes it possible to dimming commercially available lamps safely.

In a second embodiment of the method, the upper limit is 80 Hz. Thus, commercially available lamps which are considered to be difficult are reliably dimmable.

In a third embodiment of the method, the upper limit is 1 Hz. With this variant, even very difficult to dimming special lamps can be well dimmed.

The predetermined operating frequency is usually 160Hz.

The amount of current | I _end | the pitched roof-shaped current form according to the invention at the end of the half periods is increased in a preferred embodiment, when a threshold value for the difference of the lamp voltages at the end and at the beginning of the half periods is not reached.

Particularly preferably, the threshold value for the difference of the lamp voltages is divided into a lower threshold value and an upper threshold value, and the magnitude of the current | I _end | at the end of the half-cycles is increased, when the lower threshold is exceeded, and the amount of current | I _end | at the end of the half periods is reduced when the upper threshold is exceeded.

In another embodiment, the threshold value for the difference of the lamp voltages is divided into a lower threshold and an upper threshold, and the magnitude of the current | Istart | increases at the beginning of the half periods, when the lower threshold value is exceeded, and the amount Stromes | Istart | at the beginning of the half periods is reduced when the upper threshold is exceeded.

In a further embodiment, when the lower threshold value is undershot, the magnitude of the current | Istart | at the beginning of the half-periods and the amount of current | Iend | increases at the end of the half periods, and when the upper threshold value is exceeded, the magnitude of the current | Istart | at the beginning of the half-periods and the amount of current | Iend | reduced at the end of the half-periods.

The threshold value for the difference between the lamp voltages is preferably between 0.2 volts and 3 volts. Furthermore, the upper threshold is at most 0.5 volts greater than the lower threshold.

The current form of the alternating current at nominal power is preferably rectangular.

In the case of lamps with an unfavorable ratio of electrode diameter to nominal power, the current form of the alternating current at nominal power is preferably pentachelike, with the magnitude of the current | I _start | at the beginning of the half periods to the amount of current | I _end | at the end of the half periods behaves like | I _start | : | I _end | = 1: 1 .. 1: 1, 2.

The solution of the problem with respect to the circuit arrangement is carried out with a circuit arrangement for operating a High pressure discharge lamp below its nominal power, wherein the high pressure discharge lamp is operated at nominal power with an alternating current of a predetermined operating frequency, and the circuit arrangement carries out the method described above.

The circuit arrangement can be constructed in a conventional manner. The circuit may include a power factor correction circuit which supplies at its output an intermediate voltage circuit to which an inverter in the form of a full or half bridge is connected. The circuit arrangement may include a pulse or a resonance ignition device in order to ignite the high-pressure discharge lamp. The circuitry may include analog or digital control circuitry that controls the power factor correction circuit and the inverter. The circuit arrangement preferably has a digital control circuit with a microcontroller.

Further advantageous developments and refinements of the circuit arrangement according to the invention and of the method according to the invention for operating a high-pressure discharge lamp below its nominal power result from further dependent claims and from the following description.

Brief description of the drawings

Fig.1

einen Lampenspannungsverlauf mit sehr schwach ausgeprägtem diffus-spot-Übergang bei Nominalleistung (Kurve 10) und stark ausgeprägtem diffus-spot-Übergang im Dimmbetrieb (53 % der Nominalleistung, Kurve 12),

Fig. 2

einen Lampenstromverlauf bei sehr schwach ausgeprägtem diffus-spot-Übergang bei Nominalleistung (Kurve 20) und stark ausgeprägtem diffus-spot-Übergang im Dimmbetrieb (53 % der Nominalleistung, Kurve 22),

Fig. 3

mehrere Lampenstromverläufe bei 50 Hz, Kurve 30 einen Lampenstromverlauf bei 100 % der Nominalleistung, Kurve 32 einen Lampenstromverlauf bei 55 % der Nominalleistung mit einem Betriebsverfahren nach dem Stand der Technik, Kurve 34 einen Lampenstromverlauf bei 55 % der Nominalleistung mit dem erfindungsgemäßen Verfahren,

Fig. 4

einen Ausschnitt der Kommutierung der Lampenstromverläufe bei 50 Hz aus Fig. 3 in höherer Zeitauflösung, Kurve 40 den Lampenstromverlauf bei 100 % der Nominalleistung, Kurve 42 den Lampenstromverlauf bei 55 % der Nominalleistung mit einem Betriebsverfahren nach dem Stand der Technik, Kurve 44 den Lampenstromverlauf bei 55 % der Nominalleistung mit dem erfindungsgemäßen Verfahren.

Further advantages, features and details of the invention will become apparent from the following description of exemplary embodiments and with reference to the drawings, in which the same or functionally identical elements are provided with identical reference numerals. Showing:

Fig.1

a lamp voltage curve with a very weak diffuse-spot transition at nominal power (curve 10) and a pronounced diffuse-spot transition in dimming mode (53% of the nominal power, curve 12),

Fig. 2

a lamp current profile with a very weak diffuse-spot transition at nominal power (curve 20) and a pronounced diffuse-spot transition in dimming mode (53% of the nominal power, curve 22),

Fig. 3

several lamp current profiles at 50 Hz, curve 30 a lamp current profile at 100% of the nominal power, curve 32 a lamp current profile at 55% of the nominal power with a method of operation according to the prior art, curve 34 a lamp current profile at 55% of the nominal power with the inventive method,

Fig. 4

a section of the commutation of the lamp current waveforms at 50 Hz Fig. 3 in higher time resolution, curve 40 the lamp current profile at 100% of the nominal power, curve 42 the lamp current profile at 55% of the nominal power with a method of operation according to the prior art, curve 44 the lamp current profile at 55% of the nominal power with the inventive method.

Preferred embodiment of the invention

Fig.1 shows a lamp voltage curve with very weak diffuse-spot transition at nominal power (curve 10) and strong diffuse-spot transition 122 in dimming mode (53% of the nominal power, curve 12) at a temporal resolution of 10μs / div.

Fig. 2 shows the lamp current waveform of the signals Fig. 1 with very weak diffuse-spot transition at nominal power (curve 20) and pronounced diffuse-spot transition 221 in dimming mode (53% of nominal power, curve 22) with a temporal resolution of 10μs / div. These two figures make clear the problems underlying the invention. In dimming, the electrodes are too cold, and at each commutation problems arise in the transition from the diffuse Bogenansatzbetriebsweise punctiform Bogenansatzbetriebsweise, just the above-mentioned diffuse-spot transition 121, or 221. This is clearly in the curves 12 and 22 to see where, at this transition, there is a strong up-swing at the diffused-spot junction 121, 221, which manifests itself as a high-frequency perturbation in the spectrum. In order to be able to comply with the limit values for the electromagnetic compatibility with such a mode of operation, large and expensive filter components are necessary. In addition, these commutation instabilities become noticeable as flickering during operation. Therefore, a dome-shaped lamp current according to the invention is proposed for the dimmed operation, the magnitude of which is _initiated at the beginning of the half periods to the amount | I _end | behaves at the end of the half periods as | I _start | : | I _end | = 1: 1.2 to 1: 3.0. Particularly preferably, the lamp current at the end of the half-period is twice as large as at the beginning of the half-period. According to the invention, the lamp current is variable during the half periods and depends on the change of the lamp voltage during a half period. The height of the lamp current increase during one Half-period, ie the ratio of starting current to final current | I _start | : | I _end | depends on the lamp voltage and especially after the change of the lamp voltage, which is applied during the half-period. The change in the lamp current in a half period is set so that the lamp voltage has increased by a previously calculated or a predetermined value ΔU ₁ , ΔU ₂ . The threshold value for the voltage increase of the lamp voltage in the half-period is between 0.2V and 4V depending on the gas discharge lamp. The threshold is preferably divided into a lower threshold and an upper threshold. The voltage increase is calculated from the difference of the lamp voltage at the end of the half-period to the lamp voltage at the beginning of the half-period. If the threshold value for the lamp voltage rise is not reached within the half period, the ratio of starting current to final current for the next half cycle | I _start | : | I _end | increased in order to heat the cathode more and avoid a pronounced diffuse-spot transition during commutation as possible. In order to achieve a robust control characteristic, the ratio of starting current to final current for the next half-cycle | I _start | : | I _end | increases when a lower threshold value for the voltage increase of the lamp voltage is exceeded in the half-period, and lowered when an upper threshold value for the voltage increase of the lamp voltage in the half-period is exceeded. If the increase of the lamp voltage lies in the range between the lower and the upper threshold, then the ratio of starting current to final current for the next half cycle | I _start | : | I _end | maintained.

Fig. 3 shows the lamp current characteristics at 50 Hz, curve 30 shows the lamp current profile at 100% of the nominal power, curve 32 shows the lamp current profile at 55% of the nominal power with a method of operation according to the prior art, curve 34 shows the lamp current profile at 55% of the nominal power with the operating method according to the invention at a time resolution of 10 ms / div. The pent roof-shaped current profile can be clearly seen in the curve 34, here the lamp current at the end of the half-period is twice as large as at the beginning of the half-period. However, this would not be enough to ensure stable operation of the high-pressure discharge lamp at low dimming levels. Surprisingly, it has been shown that a safe operation of the high-pressure discharge lamp can be achieved by combining the pent roof-shaped current form with a very low-frequency operation. This can be explained by the fact that the short-time quasi-DC operation always heats the electrode, which becomes the cathode at the next commutation, since the high operating temperature of the electrode is only necessary for its cathodic operation. Of course, the other electrode cools more in this phase, but this is not a problem for the next commutation, since the electrode then undergoes a change from the cathode to the anode, and the temperature for the anodic operation of the electrode is not relevant. After this commutation, however, it is heated up again in the anodic mode for just as long, in order then to have a sufficiently high temperature for the transition anode-cathode. According to the invention, therefore, the dimming operation, the operating frequency is lowered below an upper limit to achieve this stable operation. The upper limit is a maximum of 120Hz, preferably the operating frequency is lowered to a frequency around 50Hz to 60Hz. Lower frequencies can be problematic because at an operating frequency below 50Hz, the human eye exhibits increased flicker sensitivity on the dimming operation has a negative effect. Only below a hertz decreases the flicker sensitivity of the human eye, so that even very low operating frequencies are possible. At very low dimming levels, astonishingly stable operation of the high pressure discharge lamp can be achieved at very low operating frequencies below one hertz. The particularly preferred operating frequency of the invention is thus at 50Hz to 60Hz, at very low dimming levels below 1Hz. Again, according to the invention, the rise of the lamp voltage in a half period is measured again and the ratio of starting current to final current | I _start | : | I _end | adjusted for the next half period according to the voltage increase in the current half period.

Fig. 4 shows a section of the commutation of the lamp current waveforms at 50 Hz Fig. 3 in higher time resolution, curve 40 the lamp current profile at 100% of the nominal power, curve 42 the lamp current profile at 55% of the nominal power with a method of operation according to the prior art, curve 44 the lamp current profile at 55% of the nominal power with the inventive method. The time resolution is no longer 10ms / div, but only 10μs / div. Shown in particular is the commutation of the lamp current. It can clearly be seen that significantly fewer disturbances occur in the operating method according to the invention (curve 44) than in a method of operation according to the prior art (curve 42). With the operating method according to the invention occur virtually no disturbances in the commutation of the lamp current more, and a circuit arrangement that performs the operating method according to the invention is significantly easier to suppress interference, and thus also significantly cheaper to produce.

Claims (15)

1. Method for operating a high-pressure discharge lamp below its nominal power, wherein the high-pressure discharge lamp is operated at nominal power with an alternating current having a predetermined operating frequency, and the lamp voltage is measured during a half-cycle at least at the start of a half-cycle and at the end of a half-cycle, comprising the following steps:

   - reducing the present operating frequency, starting from the predetermined operating frequency, to below an upper limit, and

   - changing the current shape of the alternating current to a monopitch roof-shaped current shape, which is dependent on the difference in the lamp voltages at the end and at the start of the half-cycle, in which the absolute value of the current |I_start| at the beginning of the half-cycles with respect to the absolute value of the current |I_end| at the end of the half-cycles is, for example, |I_start| : |I_end| = 1 : 1 . 2 .. 1:3.0.
2. Method according to Claim 1, characterized in that the absolute value of the current |I_start| at the beginning of the half-cycles with respect to the absolute value of the current |I_end| I at the end of the half-cycles is, for example, |I_start| : |I_end| = 1:1.5 .. 1:3.0.
3. Method according to Claim 1 or 2, characterized in that the upper limit of the present operating frequency is 120 Hz.
4. Method according to Claim 1 or 2, characterized in that the upper limit of the present operating frequency is 80 Hz.
5. Method according to Claim 1 or 2, characterized in that the upper limit of the present operating frequency is 1 Hz.
6. Method according to one of Claims 1 to 5, characterized in that the predetermined operating frequency is 160 Hz.
7. Method according to one of the preceding claims, characterized in that the absolute value of the current |I_end| at the end of the half-cycles is increased when a threshold value for the difference between the lamp voltages at the end and at the start of the half-cycles is not reached.
8. Method according to one of the preceding Claims 1 to 7, characterized in that the threshold value for the difference between the lamp voltages is split into a lower threshold value and an upper threshold value, and the absolute value of the current |I_end| at the end of the half-cycles is increased when the lower threshold value is undershot, and the absolute value of the current |I_end| at the end of the half-cycles is reduced when the upper threshold value is overshot.
9. Method according to one of the preceding Claims 1 to 7, characterized in that the threshold value for the difference between the lamp voltages is split into a lower threshold value and an upper threshold value, and the absolute value of the current |I_start| at the start of the half-cycles is increased when the lower threshold value is undershot, and the absolute value of the current |I_start| at the start of the half-cycles is reduced when the upper threshold value is overshot.
10. Method according to both of the preceding Claims 8 and 9, characterized in that, in the event that the lower threshold value is undershot, the absolute value of the current |I_start| at the start of the half-cycles and the absolute value of the current |I_end| at the end of the half-cycles is increased and, in the event of the upper threshold value being overshot, the absolute value of the current |I_start| at the start of the half-cycles and the absolute value of the current |I_end| at the end of the half-cycles is reduced.
11. Method according to one of Claims 1 to 10, characterized in that the threshold value for the difference between the lamp voltages is between 0.2 volt and 3 volts.
12. Method according to Claim 11, characterized in that the upper threshold value is at most 0.5 volt greater than the lower threshold value.
13. Method according to one of Claims 1 to 12, characterized in that the current shape of the alternating current at nominal power is rectangular.
14. Method according to one of Claims 1 to 12, characterized in that the current shape of the alternating current at nominal power is monopitch roof-shaped, wherein the absolute value of the current |I_start| at the beginning of the half-cycles with respect to the absolute value of the current |I_end| at the end of the half-cycles is, for example, |I_start| : |I_end| = 1:1 .. 1:1.2.
15. A circuit arrangement for operating a high-pressure discharge lamp below its nominal power, wherein the high-pressure discharge lamp is operated at nominal power with an alternating current having a predetermined operating frequency, characterized in that it is designed to implement a method according to one of Claims 1 to 14.

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