DE2834561A1 - INVERTER - Google Patents

Description

2S34S0 -3-

SIEMENS AKTIENGESELLSCHAFT Our reference Berlin and Munich VPA 78 P 5086 BRD

Inverter

The invention relates to an inverter with alternately ignitable thyristors that alternate a load with the plus and minus pole of a DC voltage source associate.

An inverter of this type can, for example, be used in an X-ray diagnostic generator to supply the Find high-voltage transformer use. In this Case, the supply frequency of the high-voltage transformer can be placed in the kHz range, so much higher than the mains frequency. Because of this high supply frequency, the high-voltage transformer be constructed much smaller and lighter than an X-ray diagnostic generator, which is operated with the mains frequency.

In the case of an inverter of the type mentioned at the outset, it can happen that two are in series with one another Thyristors that are to be ignited alternately

Tp 5 Ler / 7/24/1978

030007/0432

ORIGINAL INSPECTED

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and to whose connection line the load is connected, can be ignited at the same time due to interference. This means a short circuit, which in the known inverters is caused by the response of the upstream Backup is finished.

The invention is based on the object of designing an inverter of the type mentioned at the outset in such a way that that when a short circuit occurs due to the simultaneous ignition of zv / eier thyristors that the The load should alternately connect to the DC voltage source, a response of the gate-switched Prevents backup and is achieved that the inverter is led back to its normal mode of operation will.

This object is achieved according to the invention in that An LC resonant circuit is connected in parallel to the series connection of zv / eier thyristors to be fired alternately is dimensioned so that when both thyristors of the series circuit are ignited at the same time are, the LC resonant circuit through the. Short circuit current swings around and when swinging back the thyristors due to the voltage drop at each one connected in parallel The free-wheeling diode must be deleted. In the case of the inverter according to the invention, the recharging current builds up of the capacitor of the LC resonant circuit in one Short-circuit at the simultaneously ignited thyristors on a voltage that cancels them. After their The inverter can then continue its normal mode of operation. The one flowing in from the network Current can be limited by an inductance.

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A "particularly useful embodiment of the invention is characterized by a monitoring circuit for the inverter input voltage or the alterna- converter current, which prevents the thyristors from igniting for a certain period of time, if this input voltage or the inverter current assumes a value characteristic of a short circuit. In this development, an additional security against short circuits is given that the Inverter switched off for a short time after a short circuit and thus returned to its normal mode of operation can be.

Further details of the invention emerge from the subclaims.

The invention is explained in more detail below with reference to an exemplary embodiment shown in the drawing.

In the drawing, an inverter 1 is shown, which consists of a bridge of four thyristors 2 to 5, which are bridged by free-wheeling diodes 6 to 9. In one diagonal of this bridge there is a LC resonant circuit 10, 11. The load is in the example the primary winding of a high voltage transformer. The inverter is an inductor 13, two capacitors 12, 14 ·, an inductor 15 and one Fuse 16 upstream. To generate an alternating voltage, two thyristors 2, 5 or 3, 4 alternately recovered by a control circuit 17.

Due to storm impulses or falling below the limit the price increase time when the next one is ignited

030007/0432

- -k - TPA 78 P 5086 FRG

Thyristor pairs can misfire. In this way, for example, the thyristors can be used at the same time 2 and 3 or 4 and 5 can be ignited. In this case, the inverter 1 represents a short circuit Capacitor 12 is discharged via the respective conductive thyristor branch, for example via the Thyristor branch 2, 3. The discharge of the capacitor is limited by the inductance 15 to a value, which is smaller than the oscillating current from the LC resonant circuit 12, 13. After completion of the transfer of the capacitor 12, the simultaneously ignited thyristors 2, 3 or 8, 9 during the The swingback phase via the freewheeling diodes 6, 7 or 8, 9 is deleted. A short circuit therefore only lasts a few / us. The fuse 16 therefore does not respond. After the short circuit has been eliminated, the inverter works 1 back to normal. A diode 18 connected in parallel to the inductance prevents overvoltage on the capacitor 12 after the short circuit has ended.

Another measure to increase the short-circuit security is that a monitoring circuit 19 is provided for the inverter input voltage, which the control circuit 17 for the thyristors Controls 2 to 5 and prevents these thyristors from firing when the voltage is applied to them has characteristic value for the short circuit. The delivery of further ignition pulses is therefore in this Case blocked for a predetermined time, e.g. a few / us. The monitoring circuit 19 can also be used for Monitoring the input current of the inverter 1 used, which increases in the event of a short circuit.

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The transformer 11 can, for example, be a high-voltage transformer be that feeds an X-ray tube via a high-voltage rectifier.

The elimination of short circuits in the inverter according to the invention is not only applicable to an oscillating circuit inverter in bridge circuit according to the embodiment, but applicable to all inverters, in the case of faulty simultaneous ignition of two thyristors that are to be ignited alternately a short circuit occurs, for example also with a square-wave inverter and with inverters in half-bridge circuit.

030007/0432

Claims (4)

Claims 283A561 VPA 78 P 5086 FRG (1.! Inverter with alternately ignitable thyristors, which alternately connect a load to the plus and minus poles of a DC voltage source, characterized in that parallel for the series connection of two thyristors (2, 3; 4, 5) to be fired alternately, an LC resonant circuit (12, 13) is connected, which is dimensioned so that when both thyristors (2, 3; 4, 5) of the series connection are ignited at the same time, the LC resonant circuit (12, 13) swings around by the short-circuit current and when The thyristors (2, 3; 4, 5) swing back as a result of the voltage drop at each one connected in parallel The free-wheeling diode (6 to 9) must be deleted. 2. Inverter according to claim 1, characterized in that the current from the Network limited to one value by an inductance (15) which is smaller than the resonance current of the LC resonant circuit (12, 13) for erasing the thyristors (2, 3; 4, 5). 3. Inverter according to claim 2, characterized in that a at the input Smoothing capacitor; (14) and the inductance between the two capacitors (12, 14) (15) is bridged by a diode (18) which generates an overvoltage after a short circuit on the capacitor has ended (12) of the LC resonant circuit (12, 13) prevented. 4. Inverter according to one of claims 1 to 3, characterized by a monitoring circuit (19) for the inverter input output voltage or the inverter current that the 030007/0432 ORIGINAL INSPECTED - 2 - YPA 78 P 5086 FRG Ignition of the thyristors (2 "to 5) during a predetermined Period of time prevents when this voltage or current is characteristic of a short circuit Assumes value. 030007/0432 ORiOiNAL INSPEC