Means for damping voltage oscillations in solid-state switching circuits

Claim 2

In an electric power circuit comprising a thyristor, a capacitive reactance element connected in parallel with said thyristor, an inductive reactance element connected in series with the parallel combination of said thyristor and said capacitive reactance element, a plurality of input terminals adapted to be connected to a source of voltage, and means including controllable switching means for electrically interconnecting said input terminals and the series combination of said capacitive reactance element and said inductive reactance element, said switching means being periodically operative in a manner that subjects said series combination to a relatively abrupt change of voltage, the improvement comprising: a tuned damping circuit connected in parallel with a predetermined one of said reactance elements, said damping circuit being characterized by resistance, inductance, and capacitance in series with one another, said resistance having an ohmic value selected to damp oscillations in said series combination on the occasion of said abrupt voltage change, and said inductance and said capacitance being tuned to approximately the natural frequency of said series combination.

Claim 3

The circuit of claim 1 in which said predetermined one reactance element is said inductive reactance element.

Claim 4

The circuit of claim 1 in which a resistor is connected across said thyristor in series with said capacitive reactance element.

Claim 5

In an electric power converter comprising a thyristor, a capacitive reactance element connected in parallel with said thyristor, an inductive reactance element connected in series with the parallel combination of said thyristor and said capacitive reactance element, a plurality of input terminals adapted to be connected to a source of voltage, a set of at least first and second output terminals, means including controllable switching means for electrically interconnecting said input and output terminals, said switching means having one recurrent state in which said first output terminal is energized in accordance with the electrical potential of a first one of said input terminals and being periodically operative to another state in which said first output terminal is energized in accordance with the electrical potential of another one of said input terminals, the series combination of said capacitive reactance element and said inductive reactance element being connected between said first output terminal and said first input terminal, whereby upon operation of said switching means the voltage across said series combination is subject to a relatively abrupt change, the improvement comprising: a tuned damping circuit connected in parallel with a predetermined one of said reactance elements, said damping circuit being characterized by resistance, inductance, and capacitance in series with one another, said resistance having an ohmic value selected to damp oscillations in said series combination on the occasion of said abrupt voltage change, and said inductance and said capacitance being tuned to approximately the natural frequency of said series combination.

Claim 6

In an electric power converter comprising a thyristor, a capacitive reactance element connected in parallel with said thyristor, an inductive reactance element connected in series with the parallel combination of said thyristor and said capacitive reactance element, a plurality of input terminals adapted to be connected to a source of voltage, a set of at least first and second output terminals, means including controllable switching means for electrically interconnecting said input and output terminals, said switching means having one recurrent state in which said first output terminal is energized in accordance with the electrical potential of a first one of said input terminals and being periodically operative to another state in which said first output terminal is energized in accordance with the electrical potential of another one of said input terminals, the series combination of said capacitive reactance element and said inductive reactance element being connected between said first output terminal and said first input terminal, whereby upon operation of said switching means the voltage across said series combination is subject to a relatively abrupt change, the improvement comprising: a tuned damping circuit connected in parallel with a predetermined one of said reactance elements, said damping circuit being characterized by resistance, inductance, and capacitance in series with one another, said resistance having an ohmic value selected to damp oscillations in said series combination on the occasion of said abrupt voltage change, and said inductance and said capacitance being tuned to approximately the natural frequency of said series combination.

Claim 7

The converter of claim 4 in which means is provided for connecting said first output terminal directly to one side of an electric power load circuit and for connecting said second output terminal via a current limiting inductor to the other side of the load circuit.

Claim 8

The converter of claim 4 in which said input terminals are adapted to be connected to a source of 3-phase alternating voltage, means is provided for directly connecting said first output terminal to one side of an electric power load circuit and for connecting said second output terminal to the other side of the load circuit, and said controllable switching means comprises a group of six periodically conducting electric valves connected in a first bridge configuration between said input and output terminals, said valves being cyclically fired, when the first bridge is active, in a predetermined sequence so as to supply unidirectional current to the connected load circuit.

Claim 9

The subject matter of claim 6 wherein the converter comprises two groups of valves forming first and second duplicate bridges which share the same input terminals but have separate sets of output terminals, said bridges being alternatively active and their respective sets of output terminals being connected in oppositely poled relationship to said load circuit so that current can flow through said load circuit in a predetermined forward direction when the first bridge is active or in a reverse direction when said second bridge is active, each valve of said second bridge comprising at least one thyristor which is shunted by a capacitive reactance element; and said inductive reactance element is connected between the second output terminal of said second bridge and the first output terminal of said first bridge.

Claim 10

The converter of claim 7 in which said predetermined reactance element is said inductive reactance element.

Claim 11

The converter of claim 8 in which the first output terminal of said second bridge is directly connected to said other side of the load circuit, each valve of said first bridge comprises at least one thyristor which is shunted by a capacitive reactance element, an additional inductive reactance element is connected between the second output terminal of said first bridge and the first output terminal of said second bridge, and said additional inductive reactance element is shunted by another tuned damping circuit which is a duplicate of the tuned damping circuit specified in claim 1.