EP1741319A1

EP1741319A1 - Device for generation of voltage pulse sequences in particular for operation of capacitive discharge lamps

Info

Publication number: EP1741319A1
Application number: EP05747449A
Authority: EP
Inventors: Wolfgang Heering; Hans-Peter Daub; Richard Winkelmann
Original assignee: Universitaet Karlsruhe
Current assignee: Karlsruher Institut fuer Technologie KIT
Priority date: 2004-04-30
Filing date: 2005-04-29
Publication date: 2007-01-10
Also published as: DE102004021243B3; WO2005107339A1

Abstract

The invention relates to a device for the generation of electrical voltage pulse sequences, in particular, for the operation of capacitive discharge lamps, with at least two controllable switch elements (S1, S2), for the generation of unipolar or bipolar voltage pulse sequences from the DC voltage applied to an input from a voltage source. The device is characterised in that a storage choke (L1), operated as controlled voltage source by means of the switch elements (S1, S2), is arranged between the switch elements (S1, S2), such that the rise time for voltage pulses in the voltage pulse sequence at a load coupled to the output may be influenced by the charging time of the storage choke (L1) which is adjusted by means of the switching elements (Sl, S2) and that reverse diodes connect the storage choke (L1) to the plus or minus pole of the DC voltage source for recovery of unneeded choke energy. Said device permits the production of a ballast for dielectrically hindered discharge lamps, which self-adjusts to the capacitance of the relevant discharge lamp.

Description

Device for generating electrical voltage pulse trains, in particular for operating capacitive discharge lamps

TECHNICAL FIELD OF APPLICATION The present invention relates to a device for generating electrical voltage pulse trains, in particular for operating capacitive discharge lamps, with at least two controllable switching elements for generating the voltage pulse trains from a DC voltage of a voltage source applied to an input.

Suitable electrical voltage pulse sequences must be generated and applied for the efficient operation of barrier discharges in dielectrically disabled discharge lamps. Dielectric-barrier discharge lamps (DBE), however, have different capacities depending on the design. The ballasts required to operate these lamps must be adapted to the capacity of the discharge lamp. So far, this has led to a restriction of the available lamp types and lamp sizes, since different ballasts are required for different lamp types and lamp sizes, or a special adaptation of the ballasts to the respective lamp has to be carried out.

In the field of illuminated advertising technology in particular, an increased use of dielectrically disabled discharge lamps is becoming possible due to their free formability sought. Since individually designed lamp geometries are desired for this application, each of these lamps has different operating parameters. Providing different ballasts for a large number of different lamps causes high costs, so that usually only a manual adaptation of fewer ballasts to the respective lamp types or lamp sizes can be considered. However, this manual adjustment is also complex and leads to increased costs. The lamp is operated inefficiently without an adaptation of the safety device. In the worst case, the ballast can be destroyed if too much energy is converted into heat in the power semiconductors used as switching elements due to the mismatch.

PRIOR ART Ballasts for dielectrically handicapped discharge lamps are known to date, which use a full-bridge circuit arrangement to generate a high-frequency sine-like AC voltage from a DC voltage. An example of this is the ballast from J. Kunze et al. , "Resonant Power Supply for Barrier Discharge UV Excimer Sources" IEEE Industry Application Society Annual Meeting, Houston, USA, 1992, pages 750-753.

EP 0781078 A2 discloses a circuit arrangement for generating voltage pulse trains for the operation of dielectrically impeded discharges, which generates a unipolar voltage pulse train. This circuit arrangement has one of an input Voltage-fed charging circuit with a charging capacitor, a discharge and pulse circuit with fast controllable switching elements and a pulse transformer with a load that can be connected to it. By suitable control of the switching elements, the electrical energy stored in the charging capacitor is periodically transmitted to the load, the DBE, via the pulse transformer.

However, these ballasts must also be adapted to the capacity of the connected discharge lamp by a specialist.

EP 1110434 B1 describes an electronic ballast and an operating method for a discharge lamp with dielectrically impeded discharge, in which a swinging over of the dielectric discharge is used to initiate re-ignition and thus to improve the efficiency of the lamp. EP 1176853 AI describes a circuit topology of a device for operating a discharge lamp with dielectrically impeded discharge, which has two or four inverse diodes for regenerating energy that is not required.

A circuit arrangement known as ARCPI (Auxiliary Resonant Commutated Pole Inverter), which uses a choke between charging capacitors and the switching elements arranged in parallel, is known from the field of converter technology for electrical drives with powers in the kW range. The throttle is switched via a separate switch only for reloading in the charging circuit in order to To be able to switch switching elements in voltage zero crossings. An implementation of this circuit technology for the operation of lights is not known due to the different requirements.

The object of the present invention is to provide a device for generating electrical voltage pulse trains which is particularly suitable for the operation of dielectrically disabled discharge lamps and which enables an automatic adaptation to the capacity of the load to be operated.

The object is achieved with the device according to

Claim 1 solved. Advantageous embodiments of the device are the subject of the dependent claims or can be found in the following description and the exemplary embodiments.

The present device with at least two controllable switching elements for generating unipolar or bipolar voltage pulse sequences from a DC voltage of a voltage source present at an input is characterized in that a storage choke which can be operated via the switching elements as a controlled current source is arranged between the switching elements, so that a charging time of the storage choke that can be set by the switching elements, the rise times of voltage pulses of the voltage pulse sequences at a load coupled to the output of the device can be influenced, and that inverse diodes for the recovery of unnecessary choke energy Connect the choke to the positive or negative pole of the DC voltage source

The development of the present device is based on the knowledge that a dielectric barrier discharge lamp has the optimum lamp efficiency if the rising edge of the voltage applied to the lamp has a certain steepness. The ballast can then be adapted to the lamp by suitably setting this slope or the associated rise time of the voltage. With the present device, the slope of the voltage rising edge and optionally also the falling edge can be changed solely by controlling the switching elements differently, so that the circuit no longer has to be modified to adapt to different loads. This is realized by a controlled current source in the form of a storage choke in the circuit arrangement, via whose charging time, which can be controlled via the switching elements, the rise time and thus the steepness of the rise edge of the voltage pulses on the load can be influenced. The longer the storage choke is charged, i. H. the more energy is stored in the choke, the larger it is

Current with which the choke then reloads the capacity of the connected load. The rise time of the voltage at the load is thus set with the size of the current which drives the storage inductor. This enables the present device, hereinafter also referred to as ballast, to be adapted to the respective load solely by suitable control of the switching elements for charging and discharging the storage devices. throttle. After the lamp capacity has been charged, the remaining inductor current is fed back into the charging capacity via the inverse diodes in parallel with the switches. In a very advantageous further development of the present device, a measuring device is used for the direct or indirect detection of the rise time of the voltage at the load in connection with a digital regulation, which controls the switching processes of the switching elements for charging and discharging the storage choke in such a way that a specifiable one Rise time or steepness of the voltage rising edges is observed. With this configuration, the automatic adaptation of the ballast to the load to be operated is achieved. The ballast can thus be operated with different DBE or other lights without any additional adjustment. This offers particular advantages in the implementation of DBE or other lights to be operated with electrical voltage pulse sequences, which come in a wide variety of different types

Sizes and thus capacities are to be used for illuminated advertising purposes. Of course, the ballast can also be used for other loads to be operated with electrical voltage pulse trains that require comparable transient charging currents.

BRIEF DESCRIPTION OF THE DRAWINGS The present device is explained in more detail below on the basis of exemplary embodiments in conjunction with the drawings. Here show: 1 shows a first example of an embodiment of the present device for generating bipolar voltage pulse sequences; FIG. 2 shows an example of control signals for operating the device according to FIG. 1; 3 shows an example of the course of the lamp voltage with different charging times of the storage inductor of the device according to FIG. 1; 4 shows a second example of an embodiment of the present device for generating unipolar voltage pulse sequences; 5 shows an example of control signals for operating the device according to FIG. 4; 6 shows an example of a measuring circuit for detecting the rise time of the lamp voltage; and FIG. 7 shows a third example of an embodiment of the present device for generating voltage pulse trains.

WAYS OF IMPLEMENTING THE INVENTION FIG. 1 shows a first example of a possible embodiment of the present device which is based on the circuit concept of the ARCPI circuit. This circuit concept was changed in the present device in such a way that an independent adaptation of the ballast to the capacity of the barrier discharge of a DBE is possible. The Circuit arrangement is composed of four switching elements IGBT1, IGBT2, MOS1 and MOS2, which are connected to form a bridge circuit. There is one between the two first switching elements IGBT1 and IGBT2 and the two second switching elements MOS1 and MOS2

Storage choke Ll arranged, which is operated as a controlled current source. The two switching elements IGBT1 and IGBT2, which are designed as IGBTs in the present case, connect the storage inductor L1 to the input voltage E1 applied to the input or to ground. The voltage pulse sequences that can be generated by suitable control of the four switching elements are applied to the transformer TR by means of a separating capacitance C2 for decoupling direct currents. The unipolar square wave voltage at the output of the upper half bridge becomes a bipolar square wave voltage on the primary side of the transformer. The load is present on the secondary side of the transformer, in the present example a dielectric barrier discharge lamp, which is represented by the equivalent circuit diagram with the capacitances Cdl, Cgap, Cd2 and the plasma current II.

The rise and fall times of the voltage at the barrier discharge of the discharge lamp can be set by differently long charging times of the storage inductor L1, which makes up the essential component of this circuit. This influences the coupling of power into the barrier discharge and enables adaptation to different capacities of the barrier discharge.

The output voltage V _{A of} the bridge circuit is together with the current I _Li via the storage inductor Ll and the associated control signals for the switching elements implemented by power semiconductors in FIG. 2. The switching elements can of course also be realized by semiconductor elements other than those shown. Also, for example, MOSFETs can also be used instead of the IGBT's IGBT1 and IGBT2.

The bridge control signals for the operation of the circuit arrangement in FIG. 1 can be seen in FIG. Due to the charging time of the storage inductor, which can be controlled via the combination of the switching processes and which serves as an inductive energy store, the rising edge and the voltage pulses generated during the discharge can be set. This is done by a corresponding control circuit in which the switching cycles can be configured.

Figure 3 shows an example of different rising edges of the lamp voltage U _a , which are obtained by different charging times of the choke L1. The stress curve was calculated on the basis of a simulation model. With the circuit arrangement shown, a ballast for dielectrically disabled discharge lamps is provided, with which the voltage in the parameters frequency, amplitude, rise time and fall time as well as pulse-pause ratio (duty cycle) can be changed in the following areas:

Frequency f: 1 kHz - 200 kHz, especially 20 kHz - 100 kHz tftnstieg / V / ftbf ll / k: 10 nS - 1000 nS, especially 90 ns - 500 ns duty cycle: 0.1% - 99, 9% especially 1% - 70%,

ΔU _lamp : 0 V - 10 kV, especially 0 V - 4 kV.

A measuring device 2 is preferably used to record the rise time or slope of the generated voltage pulses, which feeds the measurement data to a digital control 1. The digital control monitors these rise times and controls the loading times of the storage inductor Ll in order to maintain a predeterminable edge steepness. This is indicated schematically in Figure 4.

FIG. 4 shows a further example of an embodiment of the present device with which, in contrast to the circuit arrangement of FIG. 1, is unipolar

Voltage pulses are generated. In this embodiment of the device, only two switching elements (IGBT1 and MOS2) are required in order to be able to generate the unipolar voltage pulse sequences with an adjustable slope. The storage choke Ll is also arranged within the bridge circuit. This configuration of the device also enables the ballast to be independently adapted to a capacitive load by controlling or regulating the rise time of the voltage edge.

A particular advantage of this embodiment of the device over the bipolar variant of the figure 1 consists in the lower component expenditure and the smaller voltage time area, which is present on the primary side of the transformer TR. This means that a smaller cross-sectional area is required for the transformer core than for the bipolar variant if it is to be ensured that the transformer core does not become saturated. Another advantage is the possibility of triggering the lamp to re-ignite when the switch MOS2 is closed, if the voltage across the gap capacitance (Cgap) has not dropped too much after the first ignition. In the present example, this is achieved by closing the switch approx. 1-3 μs after the first ignition. As a result, the charge stored on the dielectric capacitors can also be used for generating radiation.

FIG. 5 in turn shows the bridge control signals, the voltage V _A and the current I _L ι via the storage inductor Ll. The rising edge of the voltage across the load can be set or regulated in a wide range independently of the size of the capacity of the load over the length of the charging time of the storage inductor L1 which can be controlled with the switching elements IGBTl and MOS2. Here too, of course, in addition to the IGBT1 shown, there are also other semiconductor switching elements, such as

MOSFET, for controlling the charging time of the storage choke Ll possible.

A direct one can be used to measure the rise time of the lamp voltage with the measuring device 2

Measurement may increase the cost of such a ballast too much. Therefore, according to an embodiment of the present device the rise time of the lamp voltage itself, but its maximum derivative (dU / dt) _max measured. For an ideal trapezoidal tension:

Even if the voltage rise of the lamp voltage cannot be regarded as an ideal trapezoid, a useful regulation can nevertheless be implemented by detecting the maximum voltage rise time. In terms of circuitry, the detection of the maximum slope of the lamp voltage can be implemented much more easily than the measurement of the rise time itself. An example of such a measurement circuit is shown in FIG. 6. A small measuring capacity Cmess is connected in parallel to the lamp. A current I _c flows through it, the course of which is given by the derivative of U _a . The following applies:. dU „/ = c- dt

This current is tapped by a current measuring coil with n turns. I _c / n flows through them. This means that electrical isolation from the lamp voltage is achieved. If this current is at a maximum at the time of the switchover, it charges the capacitor Ci to a maximum voltage. Then the resistor Ri takes over the further current flow. In the time until the next positive voltage edge d. slowly over resistors Ri and R ₂ . A positive voltage edge occurs again at the beginning of the new period Ci is reloaded. This process is repeated periodically. A peak value is stored in the capacitor C _x . The voltage at O. is directly dependent on the maximum dU _a / dt. Since it is available throughout the entire period and only drops slowly, sampling is not critical in terms of time. It is measured with an A / D converter about 2 μs after charging and used to calculate the manipulated variable for controlling the rising flank.

For control 1 itself, a digital signal processor (DSP) or a suitable microcontroller is used, possibly in conjunction with a programmable logic. This is programmed in such a way that it can be activated by activating the

Switching elements used power semiconductors can regulate the speed of the rising flank. This regulation is sufficient to set rising edges in the range between 100 ns and 500 ns. In this way, an automatic adaptation of the ballast to different lamp types can be achieved.

For the dimensioning of the storage choke L1 operated as a controlled current source, the following relationships must be observed. To reload the capacity of the load, only the energy in the storage choke is available in the present device. The maximum capacity that can be reloaded with a storage choke is calculated from the energy conservation of inductance and capacity: ^• C- AU ² 2

With exemplary realistic values of ΔU = 2 kV, I = 40A, L = 10 μH, the following results:

\ 2, 40 ₂ C = L - (- ^ - y = ΪOμH • (- ^ - γ = AnF AU 2kV

The energy that can be stored in a storage choke currently in use is therefore sufficient to charge a capacitor with a capacitance of 4nF by a ΔU of 2 kV.

FIG. 7 finally shows a further example of an embodiment of the present device, with which unipolar voltage pulses are also generated. In the figure, S1 and S2 are used for switching elements, with D1 to D4 diodes. In this embodiment of the device, the storage inductor Ll is loaded between the switching elements S1 and S2. If the storage choke Ll has stored enough energy, the switching element S2 is rendered non-conductive, so that the current no longer flows through the elements D4 and S2, but rather charges the lamp (DBE) via the capacitor C2 and the transformer TR. The voltage at the lamp and at point V _A increases. Will the

If the ignition voltage of the lamp is reached, it ignites and the energy is absorbed by it. If the lamp does not ignite or does not absorb all of the energy provided, there is a voltage surge at the lamp and at point V _A. If the voltage surge at V _{A is} large enough compared to the voltage supply at the input, then the current in the storage choke Ll turns around and flows back into the voltage supply via the inverse diode D2. As soon as the reverse current flows through the inverse diode D2, the switching element S1 is switched off almost without voltage and thus with little loss

(made non-conductive). Approximately 0.5 μs to 5 μs after the first lamp ignition, the switching element S2 is switched on hard (lossy) (made conductive). The lamp ignites a second time, caused by the remaining charge on the lamp (DBE). If not all energy is absorbed by the lamp during the second ignition, a negative voltage builds up between the points V _A and the negative supply connection after the second lamp ignition. This voltage is then reduced in a circulating current via the components D4, S2, D3 and Ll until the entire energy is converted into heat. There is no further energy in the circuit, ie no parasitic oscillation processes take place until the next charging process of the storage inductor.

Even if the present description deals with the operation of dielectrically disabled discharge lamps with the proposed device, this device can of course also be used for other lamp types that require appropriate control. Laser diodes are an example of this. The same applies to other loads which have to be operated with unipolar or bipolar voltage pulse sequences and in which an adaptive adaptation of the ballast to the respective load impedance of the device is desirable.

Claims

claims

1.Device for generating electrical voltage pulse trains, in particular for operating capacitive discharge lamps, with at least two controllable switching elements (S1, S2) for generating the voltage pulse trains from a DC voltage of a voltage source applied to an input, characterized in that at least one via the switching elements ( Sl, S2) as a controlled current source operable storage choke (Ll) is arranged between the switching elements (Sl, S2), so that the rise times of voltage pulses of the voltage pulse trains at a Load coupled to the output of the device can be influenced, and that inverse diodes for regenerating unnecessary choke energy connect the storage choke (Ll) with a positive or negative pole of the voltage source.

2. Device according to claim 1, characterized in that the switching elements (Sl, S2) are connected to a controller (1) which the switching elements (Sl, S2) in dependence on the rise time recorded with a measuring device (2) to maintain a predeterminable rise time.

3. Device according to claim 2, characterized in that the control (1) comprises a digital signal processor or a microcontroller in connection with a programmable logic.

4. Device according to one of claims 1 to 3, characterized in that the switching elements (S1, S2) are arranged to generate unipolar voltage pulse trains.

5. The device according to claim 4 in connection with claim 2 or 3, characterized in that the controller (1) is designed such that it a switching element connecting the storage inductor (L1) to ground following a first ignition of a discharge lamp connected as a load closes so early that a second ignition of the discharge lamp is triggered without further charging of the device.

6. Device according to one of claims 1 to 3, characterized in that four switching elements are provided, which are arranged for generating bipolar voltage pulse trains.

7. Device according to one of claims 1 to 6, characterized in that the storage inductor (Ll) via one of the Switching elements is connected directly to the voltage source.

8. Device according to one of claims 1 to 7, characterized in that the switching elements (Sl, S2) are transistors.

9. Use of the device according to one of claims 1 to 8 as an adaptive ballast for dielectrically disabled discharge lamps.