DE4212189A1 - Pulsed charging of capacitor for laser operation - has inverter driving transformer with output stage including resonator circuit capacitor for low loss operation. - Google Patents

Abstract

The charging system for a capacitor used in a pulsed laser system, has mains voltage applied to a rectifier (1) with d.c. voltage buffered in a capacitor (3). The capacitor is connected with a single phase inventor (2) feeding the primary of a transformer (4). The transformer secondary is connected via a resonator capacitor (5) to a voltage multiplier (6) to charge another capacitor (7). The presence of a resonator circuit capacitor (5) improves the level of the charging power. ADVANTAGE - Reduced power losses in charge process.

Description

The invention relates to a circuit arrangement for pulsed Charging at least one capacitor with a transformer and a rectifier arranged on the primary side thereof.

In the case of pulsed lasers, such as CO ₂ lasers, excimer lasers, Nd-YAG lasers etc., the energy required for a gas discharge or occupation inversion is first temporarily stored in a capacitor and then transferred to the laser medium by means of a pulse-shaped network to become. For example, a gas discharge between the electrodes in the discharge chamber (which is arranged in the resonator) can be carried out with simultaneous discharge of the storage capacitor. Such intermediate storage of the electrical energy in a capacitor and the pulsed discharge of the same is also referred to as "pulsed power" operation. Such "pulsed-power" applications are also common in plasma technology and when shaping with pulse magnetic fields. The buffered energy z. B. a flash lamp or a so-called plasmatron.

At least in such circuit arrangements for pulsed charging a capacitor has the problem of effective charging  capacitor via a converter device (charger) from the electrical supply network to a predetermined one Setpoint. The network delivers a largely constant change voltage and the charger (converter device) has at the stand the technology the tasks of voltage adjustment, rectification device, charging current limitation and completion of charging ganges at a given condition.

The energy transfer when charging capacitors should be so that a uniform and minimal component loading so that the most uniform possible power output is achieved. This is contrary to the fact that at the start of charging, that is to say with a capacitor voltage U _L close to zero, the active power is also close to zero due to the limited short-circuit current. In order to achieve a more uniform energy transfer, the load characteristic of the charger is already designed in the prior art so that a large current flows into the capacitor at small charging voltages, while the current flow in the capacitor is reduced with increasing charging voltage. Ideally, the load characteristic of the charger (with constant power output) is a hyperbole. In principle, any type of load characteristic can be enforced by control circuits. However, such a positive control requires an increased primary apparent power, which means that greater losses and / or a larger overall volume of the circuit must be accepted. An ideal solution would therefore be a circuit with constant power output to the capacitor to be charged with constant primary power consumption. However, this goal is only approximately achieved. Circuits controlled in this way have the disadvantages mentioned above.

Circuit arrangements of the type in question must for extremely high repetition rates (so-called repetition rates) are suitable be net, especially for applications in excimer lasers, where Repetition rates of several 100 Hertz are required.  

For lower repetition rates, the prior art knows circuit arrangements with a stray core transformer. This is shown in Fig. 1. In Fig. 1, the partial figure (a) shows a principle circuit and the partial figure (b) the associated load characteristic. The capacitor to be charged is labeled C _L. A scattering core transformer T _r in the circuit according to FIG. 1a determines both the voltage to be achieved across the capacitor C _L and a current limitation, the latter due to its stray inductance. DC current is generated by means of a downstream rectifier GR. The charging process is terminated when the desired final voltage on the capacitor C _{L is} reached via a 1- or 3-phase alternating current switch which is generally arranged on the primary side. The disadvantage of this circuit arrangement is a relatively low highest repetition rate, a relatively high reactive power with a strongly fluctuating level as well as a relatively large dimensioning of the stray core transformer at a usual mains frequency of 50 or 60 Hz. Fig. 1b shows the load characteristic of the circuit according to Fig. 1 , ie the dependence of the charging current I _L on the charging voltage U _{L of} the capacitor C _{L to be} charged.

Because of the above-mentioned disadvantages of an arrangement with a stray core transformer, the prior art has increasingly used switched-mode power supplies for charging capacitors in the past few years. Fig. 2 shows schematically a circuit arrangement of a flyback converter (see. Eg. For example, DE 32 40 759 A1). FIG. 2a shows the circuit diagram, FIG. 2b the associated signal profile of individual currents i or voltages U of interest, and FIG. 2c the profile of the associated standardized load characteristic.

Based on the characteristic of Fig. 2c it can be determined that the use of flyback converters for capacitor charging is well suited because of the given short-circuit strength. The requirements outlined above are approximately met. With each switch-on, a constant energy is temporarily stored in the transformer (with constant switch-on duration), which is then transferred to the storage capacitor C _{L in the} blocking phase. Since the integrals of the voltage over time must be the same on the primary side and secondary side of the transformer, the frequency is load-dependent, so that the average output current is limited in the event of a short circuit. It has been shown, however, that with such flyback converters, only permanent power of approximately 500 watts is achievable under practical conditions, which corresponds to charging capacities between 250 and 400 J / s.

If higher charging capacities are required, so-called single-ended and push-pull flow converters can be used. Fig. 3 schematically shows a circuit arrangement for the pulsed charging of a capacitor by means of a forward converter. In this Figure 3a principle, Figure 3b shows. The circuit diagram of Fig. Zeitab the dependent gradients of interest voltages and currents, and Fig. 3c normalized load characteristics.

With this circuit, the leakage inductance of the transformer has a current-limiting effect. The current limitation can also be effected by a primary (or more rarely secondary) additional inductance. Because of the time profile of the Sekundärstro mes and the characteristic of the switching power supply of FIG. 3, the transformer is loaded with an active power in comparison to beträcht union apparent power. At high charging powers, this circuit arrangement is therefore problematic due to the losses and / or the required size of the primary-side switch and the transformer. This problem can only be partially solved by push-pull circuits. For charging capacities greater than 1 KW, very strong cooling is required, e.g. B. by fans and / or oil. The production of transformers with a low effective capacity in the high-voltage range is also very complex. The performance limits of the circuit principle of FIG. 3 are currently around 3 KJ / s and depend on the overall development of semiconductors.

So-called load-erased vibrations are also known (DD 25 125) circular inverters with thyristors as switches. These are advantage in terms of robustness and performance arrested. In particular, such circuit arrangements for ge pulsed charging of capacitors extremely robust electromagnetic interference because the circuit behavior in is essentially determined by passive components. For one Power ranges of up to a few 10 KW are such rows compensated resonant circuit inverter can be used. Indeed are such circuits because of unwanted network feedback limited in terms of their performance down to values of approx. 50 KW. Above these values, parallel compensation is made Oscillating circuit inverters can be used, but they do require high control effort.

Reduced versions of Series resonant circuit inverters can be used in power ranges from 1 to 10 KW, although an even smaller one Power factor for the switching power supply is to be accepted (see e.g. DD 291 426).

Fig. 4 shows a circuit arrangement with such a series resonant circuit inverter, Fig. 4a shows the basic circuit diagram as a half-bridge, Fig. 4b the signal curves of interest and Fig. 4c show normalized load characteristics.

From the characteristics of such a switching power supply is clear Lich that there is a similar behavior to the flyback converter can be achieved. However, there are limits to the transition too high inverter frequencies with high charging voltages. These become necessary with high repetition rates of the condens  sator discharge (e.g. high repetition rates of the excimer lasers) as well as with small tolerances with regard to the drawer final tension. The reason for this is the winding capacity of the High voltage transformer. Reloading this capacity ver causes a considerable one with increasing frequency Reactive power with which the transformer and the switch be be charged, while on the other hand the deletion conditions for the thyristor is difficult to follow exactly.

In view of this prior art, the present Invention the aim of a circuit arrangement for to periodically charge at least one capacitor, with a small size, a low load on the construction elements guaranteed and losses despite high accuracy of the Charging voltage reduced.

The circuit arrangement according to the invention to achieve this The aim is characterized in claim 1.

Preferred configurations of the circuitry according to the invention order are described in the dependent claims.

An exemplary embodiment of the invention is described below the drawing explained in more detail. It shows:

FIG. 5a schematically shows a circuit arrangement for pulsed charging at least one capacitor;

Fig. 5b temporal profiles of interest currents and voltages in a circuit arrangement according to Fig. 5a;

Fig. 5c load characteristics in a circuit according to Fig 5a once with a resonant circuit capacitor and one without such.

Fig. 5d an embodiment of a voltage multiplier circuit according to Fig. 5a; and

Fig. 5e an embodiment of a self-commutated inverter according to Fig. 5a;

Fig. 6a shows the course of the primary current consumption of the transformer tor in a circuit arrangement according to Fig. 5a depending on the charging voltage and

Fig. 6b further load characteristics in a circuit arrangement according to Fig. 5a.

As stated above, the goal is to use simple means by means of a suitable circuit arrangement with a low charge span voltage to increase the charging current relatively and with higher charging reduce voltages accordingly, taking the primary current of the transformer should remain almost unchanged. With a such circuit arrangement becomes the transmitted active power at low charging voltages of the capacitor to be charged, he considerably increased and the power factor of the device sert.

In the circuit arrangement according to FIG. 5a, the mains voltage is first rectified with a rectifier 1 . The DC voltage thus generated feeds a 1-phase inverter 2 , which is equipped with switches that can be switched off. The DC voltage is buffered by a capacitor 3 . In this way, the transformer 4 receives an AC voltage, the frequency of which is determined by the inverter 2 . On the output side, the secondary winding of the transformer 4 is connected to a resonant circuit capacitor 5 . A so-called voltage multiplier circuit 6 is connected in parallel with the oscillating circuit capacitor 5 . The secondary winding of the transformer 4 thus supplies a voltage to the voltage multiplier circuit 6 .

The capacitor 7 is to be charged. The charging current is I _L and the voltage prevailing at the capacitor 7 is denoted by U _L.

In the so-called short-circuit-near area of a charging process, that is to say with relatively low charging voltages at the capacitor 7 , the charging current I _L is essentially determined by the ratio of the transformer 4 to Ver. On the primary side of the transformer 4 , the current is limited by the leakage reactance of the transformer or alternatively (or additionally) by an additionally arranged choke 8 . The primary-side transformer current is designated i _T , while the primary-side transformer voltage is designated U _T (cf. also FIG. 5b).

Without the resonant circuit capacitor 5 , the charging current I _L would decrease rapidly at a higher charging voltage and the charging power would be greatly reduced. Since the primary apparent power would remain largely constant in a circuit arrangement without the resonant circuit capacitor 5 shown in FIG. 5a, a high reactive power component would put a heavy load on the transformer and the associated switches. The reactive power would oscillate between the buffer capacitor 3 , the transformer 4 and the voltage multiplier circuit 6 . By the inventive insertion of the resonant circuit capacitor 5 but the reactive power is greatly reduced. This result becomes clear in the load characteristic shown in FIG. 5c. The inserted capacitor 5 increases the current output in the middle and upper range of the charging voltage U _L. On the one hand, this increases the active power output (charging power) of the circuit with the same primary current, and on the other hand, by increasing the resonance, higher charging voltages than can be achieved without the capacitor 5 . By coordinating the inverter frequency, the transformer leakage inductance, the resonant circuit capacitance and the capacitances in the voltage multiplier circuit 6 , the courses of the charging current and charging power can be adapted within wide limits to the requirements of the device currently being used (e.g., to the gas discharge of the Excimer lasers to be operated with the circuit arrangement).

Fig. 5d shows an embodiment for a voltage multiplier circuit 6 according to Fig. 5a. The entered AC voltage AC _in is entered into the circuit and the charging voltage for the capacitor is tapped at the output HV _out . The circuit reveals itself due to the known symbols used and the specified connection of the individual elements, so that a literal description is superfluous.

FIG. 5e shows an exemplary embodiment for a self-commutated inverter 2 according to FIG. 5a. Again, the AC voltage U _ac and the DC voltage U _{dc are} shown and the circuit results from the symbols used and the connection of the elements.

Fig. 6 shows the relative embodiments. FIG. 6a shows on the ordinate the primary current of the transformer 4, while the charge voltage U _L is plotted on the abscissa. There is a slight variation in the primary current over a wide range of charging voltages over a wide range.

Fig. 6b shows variations of the characteristic field that can be achieved with the above-mentioned vote. The case of a missing resonant circuit capacitor 5 is shown schematically with a solid line (C (5) = 0). The other characteristic lines show exemplary embodiments with a resonant circuit capacitor 5 and differently tuned inverter frequencies, transformer leakage inductances, resonant circuit capacitances and capacitances in the voltage multiplier circuit 6 .

Claims (4)

1. Circuit arrangement for pulsed charging of at least one capacitor ( 7 ) with a transformer ( 4 ) and a primary rectifier arranged on the same side ( 1 ), characterized in that the transformer ( 4 ) on the secondary side with a resonant circuit capacitor ( 5 ) is connected and charges the at least one capacitor ( 7 ) to be charged via a voltage multiplier circuit ( 6 ). 2. Circuit arrangement according to claim 1, characterized in that on the primary side of the transformer ( 4 ) behind the rectifier ( 1 ), a buffer capacitor ( 3 ) is connected. 3. Circuit arrangement according to one of claims 1 or 2, characterized in that a primary choke ( 8 ) is connected on the primary side of the transformer ( 4 ). 4. Circuit arrangement according to one of the preceding claims, characterized in that an inverter ( 2 ) is connected on the primary side of the transformer ( 4 ).