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Abstract

Converters having a 1st power converter (1) on the mains systems side and a 2nd power converter (9) on the load side may have valve arms with insulated gate bipolar transistors (IGBTs) (T1, T2; T1', T2'). In order to be able to switch high currents, as are required in traction applications, a plurality of IGBTs (T1, T2) and (T1', T2') are operated electrically in parallel with one another. In order to avoid destruction or explosion of a module having IGBTs (T1, T2; T1', T2') of this type in the event of a short circuit, a fuse (Si1, Si2; Si1', Si2') is connected in series with each IGBT (T1, T2; T1', T2') on the cathode side thereof, which fuse blows when a predeterminable limit current intensity is exceeded, and thereby interrupts the short-circuit current. The current then flows only via the parallel-connected IGBT. The fuses (Si1, Si2; Si1', Si2') used are bonding wires whose cross section and number are dimensioned such that they interrupt a short-circuit current when the predeterminable limit current intensity is exceeded. In this case, the anode-side terminals of the IGBTs (T1, T2; T1', T2') must not melt, that is to say they must have a smaller electrical resistance than the cathode-side terminals. In the absence of a short-circuit current limiter (3), in power converters (1, 9) having a DC voltage intermediate circuit (2), very high short-circuit currents occur in the DC voltage intermediate circuit (2) and in the phase modules of the relevant power converter (1, 9) in the event of the short circuit of an intermediate circuit capacitor (C1, C2, C3), as a result of the low-impedance discharge of the latter. In order to limit the short-circuit current intensity to safe values, a reversible short-circuit current limiter (3, 8) is connected in series with at least one intermediate circuit capacitor (C2) or with a capacitor bank (C3) of the DC voltage intermediate circuit (2).

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