EP1670294A2 - Device and method for operating discharge lamps - Google Patents

Abstract

A setting unit limits current of high pressure gas discharge lamp. A lamp state detector evaluates running voltage of high pressure gas discharge lamp or its proportional value at start and end of time window, to derive a state variable which is suitable for distinguishing between cold and hot discharge lamps. A controller inputs limit current value to setting unit as function of the state variable. An independent claim is also included for a method for controlling start-up of high-pressure discharge lamps.

Description

Technical area

The invention relates to an operating device and a method for operating high-pressure gas discharge lamps. In particular, the invention solves problems that occur during the startup of high-pressure gas discharge lamps. In the following, high-pressure gas discharge lamps are also called lamp for short.

State of the art

High-pressure gas discharge lamps must be ignited by a high voltage, which is provided by an ignition device. After ignition, the lamp heats up during a start-up phase from a starting temperature to an operating temperature. The voltage applied to a lamp after ignition is called burning voltage and is not significantly dependent on the lamp current within wide limits. The burning voltage increases during the start-up phase of a starting voltage to a service operating voltage. The start-up phase is followed by an operating phase when the gas discharge lamps function as intended.

In the field of lamp technology, a distinction is made between high and low pressure gas discharge lamps. In the case of high-pressure gas discharge lamps, it is essential for the mode of operation to increase the pressure in the lamp vessel from an initial pressure to an operating pressure during the start-up phase. This is one reason why the invention described below can be used particularly advantageously in high-pressure gas discharge lamps. However, use in low-pressure gas discharge lamps is also possible.

During the operating phase, it is customary for the operating device to regulate the power of the lamp to a desired power. Since during the start-up phase, the burning voltage is low, with pure power control during the start-up phase, a high lamp current would be needed to set the target power. This current can be many times higher than the lamp current during the operating phase. This would lead to destruction of the electrodes of the lamp. Therefore, in the prior art, the current supplied by the operating device to the lamp during the start-up phase is limited to a constant starting current. Thus, the lamp is supplied with the constant starting current at least during a first portion of the start-up phase. During the start-up phase, the burning voltage increases. If the burning voltage reaches a value which, together with the constant current, results in the desired nominal power, then the power control begins to operate. As the operating voltage increases, the power control reduces the lamp current to such an extent that the setpoint power is reached. The start-up phase is completed when the burning voltage has reached the value of the operating voltage. The operating voltage of the burner is subject to specimen scatters and also changes during the life of a lamp. The operating burning voltage is therefore defined by the burning voltage which remains substantially constant at setpoint power. To mask out fluctuations, the burning voltage is usually measured as a time average. Correlated with the operating firing voltage is an operating lamp current which, together with the operating firing voltage, results in the desired power.

For the value of the starting current, the following must be observed: During the start-up phase, enough power must be coupled into the lamp so that the pressure in the lamp and thus the burning voltage increases steadily until the operating voltage is reached. Otherwise, the case may occur that the lamp remains in a stable state during the start-up phase and the target line is not reached. To safely exclude this case, a starting current is selected in the prior art, which is well above the operating lamp current. This is shown in document US 5,083,065 (Sakata). In this document, an operating device is described that has no power control, but only the lamp current is set via the operating frequency. A control unit records throughout Start-up phase, the increase of the burning voltage and increases the operating frequency, if the increase of the burning voltage is too strong. Indirectly the value of the lamp current is limited.

One aspect in the selection of the starting current is also the desire for the shortest possible start-up phase in order to achieve a target luminous flux in the shortest possible time. This is achieved by a high starting current. However, a high starting current represents a heavy load on the electrodes, which leads to damage to the electrodes and thus reduces the life of a lamp. The electrodes are damaged either by overheating, which leads to melting and burning, or by so-called sputtering, which is caused by ions striking an electrode at high speed.

In the case of state-of-the-art control gear, the starting process is disturbingly long for many applications.

Presentation of the invention

It is an object of the present invention to provide an operating device for operating high-pressure gas discharge lamps and a method for controlling the start-up of high-pressure gas discharge lamps, which accomplish a shortened start-up phase compared to the prior art.

• Eine Vorrichtung, die dazu geeignet ist, für eine angeschlossene Hochdruck-Gasentladungslampe eine Zündung zu auszulösen,
• eine Stelleinrichtung die dazu geeignet ist, einen Lampenstrom von angeschlossenen Hochdruck-Gasentladungslampen auf einen Strom-Grenzwert zu begrenzen,
• eine Lampenzustands-Detektor, der so ausgelegt ist, dass er in einem Zeitfenster das kürzer ist als die Anlaufphase, das sich an die Zündung anschließt, eine Brennspannung von einer angeschlossenen Hochdruck-Gasentladungslampe oder einen dazu proportionalen Wert auswertet und eine Zustandsgröße bereitstellt, die für die Unterscheidung zwischen einer kalten und einer heißen Hochdruck-Gasentladungslampen geeignet ist,
• eine Steuereinrichtung, die der Stelleinrichtung den Strom-Grenzwert in Abhängigkeit von der Zustandsgröße vorgibt.

This object is achieved by an operating device for operating high-pressure gas discharge lamps, which has the following features.

• A device capable of initiating ignition for a connected high pressure gas discharge lamp,
• an adjusting device which is suitable for limiting a lamp current of connected high-pressure gas discharge lamps to a current limit value,
• a lamp state detector designed to be shorter in a time window than the start-up phase following the ignition, evaluates a firing voltage from a connected high-pressure gas discharge lamp or a value proportional thereto and provides a state variable which is suitable for the distinction between a cold and a hot high-pressure gas discharge lamps,
• a control device, which sets the actuator the current limit as a function of the state variable.

• Zünden einer Hochdruck-Gasentladungslampe,
• unmittelbar nach der Zündung wird der Strom durch die Hochdruck-Gasentladungslampe auf einen Strom-Grenzwert begrenzt, der für kalte Hochdruck-Gasentladungslampen geeignet ist,
• in einem Zeitfenster, das sich an die Zündung anschließt und von kürzerer Dauer ist, als die Dauer des Anlaufs , wird die Spannung an der Hochdruck-Gasentladungslampe gemessen und sowohl ein Wert für die Differenz zwischen der Brennspannung und einem Normwert als auch ein Wert für die zeitliche Änderung der Brennspannung ermittelt,
• der Wert für die Differenz und der Wert für die zeitliche Änderung werden gewichtet und anschließend addiert wodurch eine Zustandsgröße gebildet wird,
• liegt der Wert der Zustandsgröße über einem Vergleichswert, so wird der Strom-Grenzwert für den Strom durch die Hochdruck-Gasentladungslampe erhöht.

The object is likewise achieved by a method for controlling the startup of high-pressure gas discharge lamps, comprising the following steps:

• Igniting a high pressure gas discharge lamp,
• immediately after ignition the current through the high pressure gas discharge lamp is limited to a current limit suitable for cold high pressure gas discharge lamps,
• in a time window following the ignition and of shorter duration than the duration of the start, the voltage at the high pressure gas discharge lamp is measured and both a value for the difference between the burning voltage and a normal value and a value for the determines temporal change of the burning voltage,
• the value for the difference and the value for the temporal change are weighted and then added, whereby a state variable is formed,
• if the value of the state variable is above a comparison value, the current limit value for the current through the high-pressure gas discharge lamp is increased.

The solution according to the invention formulated above uses the following facts: The maximum value of the starting current, which does not yet cause any substantial damage to the electrodes, depends on the temperature of the lamp. The lamp current during the start-up phase is therefore in an operating device according to the invention not the same every time a lamp is put into operation. Rather, an operating device according to the invention has a lamp state detector which determines a state variable during a time window at the beginning of the start-up phase which is decisive for the starting current. The state variable allows the operating device to distinguish between a cold and a hot lamp. By means of a control device provides the operating device in a cold lamp low starting current, which has a value that does not significantly damage the cold electrodes. In a hot lamp, the operating device provides by means of the adjusting device a high starting current, which would significantly damage the cold electrodes, but does not cause significant damage to the hot electrodes. In this way, the start-up phase can be significantly shortened with hot lamps.

This is particularly advantageous in applications where the lamp is put back into operation after a short break. For example, this happens in lighting applications that are frequently switched, or in video projections where the projector may have been accidentally switched off and immediately reused.

The state variable determines the lamp state detector according to the invention from the burning voltage. The lamp status detector evaluates the burning voltage in one

Time window after the ignition off. The determination of the state variable from the burning voltage can be done in various ways. For example, the lamp state detector can first evaluate two characteristics of the burning voltage: the absolute value of the burning voltage and the temporal change of the burning voltage.

The state variable can emerge from the evaluation of one or the other parameter. To get a more reliable information about the temperature of the lamp, both parameters can also be combined. An easily realizable combination consists in the weighted addition of both parameters. The result of this addition is again a state variable which gives information about the temperature of the lamp by comparison with a predetermined comparison value.

Brief description of the drawings

Figur 1

Blockschaltbild eines Ausführungsbeispiels für ein erfindungsgemäßes Betriebsgerät,

Figur 2

Diagramm, das den zeitlichen Verlauf des Lampenstroms und der Brennspannung darstellt.

In the following the invention will be explained in more detail by means of embodiments with reference to drawings. Show it:

FIG. 1

Block diagram of an embodiment of an inventive operating device,

FIG. 2

Diagram showing the timing of the lamp current and the burning voltage.

Bcvorzugte embodiment of the invention

1 shows a block diagram of an embodiment of an inventive operating device is shown, which is suitable for the operation of high-pressure gas discharge lamps. The basic structure and the basic operation of such a control gear is described in the document WO 95/35645 (Derra). The individual blocks will be briefly described below.

Block 1 contains a DC power supply which generally draws its power from a mains voltage supply. The value of the DC voltage supplied is above the burning voltage of a connected lamp 6.

The DC voltage supply feeds a buck converter 2, which subtracts the voltage value supplied by the DC voltage supply to a value which corresponds to the burning voltage of a connected lamp 6. The buck converter 2 contains an adjusting device with which the lamp current can be adjusted. This is done by choosing the voltage that will be set at the output of the buck.

An adjustment option usually consists of a so-called pulse width modulation (PWM). This determines the ratio of turn-on and turn-off durations of electronic switches included in buck converter 2.

The embodiment of the buck converter 2 can be found in the general literature on power electronics. In WO 95/35645 (Derra) a topology with a switch is selected. However, it is also a version with multiple switches possible, as z. B. represents a half bridge. The buck converter 2 contains a throttle, which serves as a current limit. This gives the buck 2 a characteristic that corresponds to an adjustable current source for the lamp current.

Depending on the selected topology, the step-down converter 2 supplies a direct current or an alternating current. In the event that the buck converter 2 supplies an alternating current, the output of the buck converter 2 is fed to a rectifier 3, which supplies a direct current at its output. The rectifier 3 can be omitted if the buck converter 2 supplies a direct current.

The direct current from the rectifier 3 or the buck converter 2 is fed into a full bridge 4, which converts the direct current into a rectangular alternating current. The frequency of the rectangular alternating current is low compared to conventional frequencies at which the buck converter 2 operates, and is at values between 50 Hz and 1 kHz. The conversion to rectangular alternating current is necessary in applications that operate AC lamps and require a uniform luminous flux. Examples of such applications are so-called projectors and rear projection televisions. However, the lamp start-up control according to the present invention may be applied to DC lamps or AC lamps operated with non-square-wave AC. Depending on the application can therefore block 3 or 4 or both omitted.

As a device which is suitable for triggering an ignition for a connected high-pressure gas discharge lamp, an ignition unit 5 is connected between the full bridge 4 and the lamp 6. It supplies the voltage required to ignite the lamp. After the ignition of the lamp, the ignition unit 5 usually takes over No more function. The ignition can be accomplished without a separately constructed ignition unit 5 by a known resonance ignition.

A control unit 7 is connected to the buck converter 2, the rectifier 3, the full bridge 4 and the ignition unit 5. The control unit 7 includes the controller, a controller, the lamp condition detector and measuring means for detecting operating parameters (e.g., burning voltage, lamp current) and means for storing lamp type data such as standard values and comparison values for distinguishing cold and hot lamps. The individual devices are combined in the control unit 7, since the control unit 7 usually contains a microcontroller which combines the function of several or all devices in itself. In many cases, the realization of a device either by hardware or by software is possible. Increasingly, control and regulation tasks are taken over by software, since this solution is cost-effective and flexible.

All connections leading to control unit 7 can be both inputs and outputs. Switched as inputs, the compounds can supply information about the burning voltage and the lamp current arbitrarily from one of the blocks 2-5 of the control unit 7.

Switched as outputs control the connections coordinated by the control unit 7 ignition, start-up, operation and shutdown of the operating device.

The control device, which is contained in the control unit 7, calculated from the lamp current and the burning voltage, the lamp power and compares them with a stored target power for the lamp to be operated. If the lamp power is lower than the target power, the control device increases the lamp current via the adjusting device as long as the lamp power and the target power coincide.

The lamp state detector, as described above, provides the state quantity that allows discrimination between a cold and a hot lamp.

The state variable is determined by the lamp state detector from the burning voltage. There are several possibilities for that. A simple possibility is that the lamp state detector measures the burning voltage at a time in the time window and subtracts a standard value from this measured value. This results in a difference that forms the state variable.

In order to suppress disturbances, the burning voltage can also be averaged over the period of the time window and the state variable can be formed from the mean value.

It has been found that also the temporal change of the burning voltage is well suited to derive a state variable from it. With cold lamps, the burning voltage remains constant or even drops in the first few seconds after ignition, while with hot lamps, the burning voltage immediately increases after ignition. In order to easily determine the temporal change of the burning voltage, the lamp state detector measures an instantaneous value of the burning voltage at the beginning and at the end of the time window. The difference between these two values is a measure of the temporal change of the burning voltage and can serve as a state variable.

If a very reliable state variable is required, then both an instantaneous or average value of the burning voltage and the temporal change of the burning voltage can be used to determine the state variable. A simple combination of these two parameters consists in a weighted addition. Suitable weighting factors depend essentially on the lamp to be operated and can be determined by test series.

After the lamp state detector has determined the state quantity, the control device evaluates the state variable. The result of this evaluation is decisive for the specification of a current limit value for the actuating device. The simplest possibility of the evaluation consists in comparing the state variable with a comparison value. If the value of the state variable is above the comparison value, a hot lamp is assumed, for example, and the control device gives the actuating device a current limit that is suitable for a hot lamp is. If the value of the state variable is below the comparison value, a cold lamp is assumed, for example, and the control device gives the adjusting device a current limit which is suitable for a cold lamp. Suitable values for the current limit value depend on the lamp to be operated and must be determined by tests.

A more complex possibility of evaluating the state variable is that the control device of the adjusting device specifies a current limit, which depends linearly on the state variable. A nonlinear dependence in the form of a characteristic is also possible. The elaborate evaluation allows the shortest possible start-up phase. Required proportionality factors or characteristic curves can be determined by tests.

FIG. 2 shows, by way of example, the time profile of the lamp current and the burning voltage. The abscissa forms the time axis on which time t is plotted in seconds. The left ordinate applies to the burning voltage and gives values in volts (V). The right ordinate applies to the lamp current and gives values in amps (A). The curve 3 shows the time course of the lamp current and curve 2, the burning voltage. The example shown in Figure 2 shows the start of a hot lamp. For comparison, the curve 1 shows the time course of the burning voltage of a cold lamp until the end of the time window.

The example shows curves of a high-pressure or high-pressure gas discharge lamp for projection applications with an electrical output of approx. 150W.

At time t1, the ignition has taken place and the time window begins. During the time window, the adjusting device adjusts a lamp current which is suitable for cold lamps, in the example 2 A. The lamp in the example was re-ignited after 35 seconds and has a burning voltage of 24 V at the time t1. For comparison, it can be seen from curve 1 that a cold lamp would have a burning voltage of 18V. If it is assumed that the standard value for the burning voltage is 20 V, the result is a difference of 4 volts. A simple determination the state variable could already take place at the time t1 by using the difference as a state variable. The lamp in the example would be rated as hot and the starting current could be increased immediately. However, it can happen that lamp specimens after aging have a burning voltage of more than 20 V even when cold. Therefore, the example shows a more complex determination of the state variable.

The time window extends until time t2. A cold lamp would still have a burning voltage of 18 V at this time, as curve 1 shows. Curve 2 shows, however, that at the time t2, the burning voltage of the hot lamp has already risen to 34 V. This results in a time increase of the burning voltage of 1.1 V / s. The time increase of hot lamps is typically above 0.7 V / s. To determine the state variable, the difference calculated above and the increase in time can now be added together in a weighted manner. For lamps as used in the example, the following weighting has proved favorable: $$\mathrm{state\; variable}=\mathrm{Change\; of\; the\; burning\; voltage}*70+\mathrm{difference}*\mathrm{8th.}$$

This results in a value for the state variable of 109. For comparison: For the cold lamp according to curve 1, a value for the state variable of -16 would result.

The control device evaluates the state variable at time t2. In the example, lamps with a value of the state size over 50 were classified as hot. The value 109 is well above 50. Thus, in the example, the control device detects a hot lamp and gives the actuator a higher starting current of 2.4 A. This is achieved at the time t3, as can be seen from the curve 3. Curve 2 shows the effect of the increased starting current on the burning voltage. From the time t3, the burning voltage increases faster than before.

At the time t4, the burning voltage reaches a value which, together with the starting current, gives the predetermined rated power of the lamp. From time t4, the power control takes over the regulation of the lamp current. A not shown further increase in the burning voltage leads to a falling lamp current, until an equilibrium state has set and the start-up phase has ended.

In the example, when a hot lamp was detected, the starting current was increased by a value of 0.4 A determined by tests to a value of 2.4 A. It is also possible to make this increase dependent on the value of the state variable, for example via the following formula: $$\mathrm{starting\; current}=\mathrm{Starting\; current\; for\; cold\; lamp}+\mathrm{additional\; power}*\left(\mathrm{state\; variable}-a\right)/b$$

The values for a, b and the additional current must be determined by tests. In the example, the following values have proved favorable: a = 30, b = 50 and additional current = 0.25 A.

In the example of Figure 2, the start-up phase is shortened by the inventive control of the starting current by about 15 s. In the example, the time window is 9 s long. However, it has been shown that a time window of 3 s is sufficient. Thus, start-up phase can be shortened even further.

Claims (11)

Operating device for operating high-pressure gas discharge lamps, having the following features: A device capable of initiating ignition for a connected high-pressure gas discharge lamp, A control device which is suitable for limiting a lamp current of connected high-pressure gas discharge lamps to a current limit value, characterized in that the operating device comprises the following features: A lamp state detector which is designed to be in a time window which adjoins the ignition and is shorter than a start-up phase,
evaluates an operating voltage from a connected high-pressure gas discharge lamp or a value proportional thereto and derives therefrom a state variable which is suitable for distinguishing between a cold and a hot high-pressure gas discharge lamps, • A control device, which sets the actuator the current limit as a function of the state variable. Operating device according to claim 1, characterized in that
in that the lamp state detector contains a subtractor with two inputs and one output, wherein the value of the operating voltage is present at one time in the time window, at the other input a predetermined standard value is present and at the output of the subtractor provides a difference from that of the lamp state Detector forms the state variable. Operating device according to claim 2, characterized in that
the lamp state detector includes an averager providing an average of the burn voltage within the time window at an input of the subtracter. Operating device according to claim 1, characterized in that
that the lamp state detector measures the burning voltage at the beginning and at the end of the time window and determines from the difference of these two measured values a temporal change of the burning voltage and from this forms the state variable. Operating device according to claim 2 and 4, characterized in that
the lamp state detector for taking the state quantity uses both the difference and the temporal change of the burning voltage. Operating device according to claim 3 and 4, characterized in that
the lamp state detector for forming the state quantity uses both the mean value and the temporal change of the burning voltage. Operating device according to Claim 5, characterized in that the lamp state detector forms the state variable according to the following formula: $$\mathit{state\; variable}\mathit{=}\ddot{\mathit{A}}\mathit{change\; of\; the\; burning\; voltage}\mathit{*}\mathit{70}\mathit{+}\mathit{difference}\mathit{*}\mathit{8th}\mathit{.}$$

wherein the change of the burning voltage in volts per second and the difference in volts are measured. Operating device according to one of the preceding claims, characterized in that the control device includes a comparator which compares the state variable with a stored comparison value
and the actuator sets a current limit for hot lamps, if the state quantity is greater than the comparison value
and the actuator sets a current limit for cold lamps, if the state quantity is smaller than the comparison value. Operating device according to one of claims 1 to 7, characterized in that the control device specifies a current limit, which depends linearly on the state variable. Method for controlling the startup of high-pressure gas discharge lamps, characterized by the following steps: Igniting a high-pressure gas discharge lamp, • immediately after ignition, the current is limited by the high-pressure gas discharge lamp to a current limit value that is suitable for cold high-pressure gas discharge lamps, In a time window following the ignition and shorter than a start-up phase, the voltage at the high-pressure gas discharge lamp is measured and both a value for the difference between the burning voltage and a standard value and a value for the temporal change of the burning voltage determined, The value for the difference and the value for the time change are weighted and then added together, whereby a state variable is formed, • If the value of the state variable is above a comparison value, the current limit for the current through the high-pressure gas discharge lamp is increased. Operating device according to one of the preceding claims, characterized in that the time window is shorter than 3 seconds.

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