Asea Brown Boveri Ab

Rolf Palsson

Kjell Svensson

A method and apparatus for eliminating overmodulation in a power plant is provided. The power plant has a direct voltage network connected to at least one alternating voltage network through a station. The station is adapted to transmit power between the direct voltage network and the alternating voltage network and includes at least one converter. The converter is adapted to convert direct voltage into alternating voltage and convert alternating voltage into direct voltage. The method comprises the steps of calculating a reference alternating voltage and measuring a direct voltage between two poles of a direct voltage side of the station. The reference voltage is divided by half of the direct voltage and this quotient is compared with a predetermined value. When the quotient exceeds the predetermined value, a first signal is sent to a means for controlling the converter. In response to receiving the first signal, the converter is controlled to increase consumption of reactive power on the alternating voltage side of the station.

Method and apparatus for eliminating overmodulation in a power plant

A system for transmitting electric power between a direct voltage network and alternating voltage networks through VSC-converters. A first station which transmits electric power is in voltage regulating mode. Switching members at a second station are adapted to be alternatingly switched in and out upon occurrence of a sudden change of power so as to alternatingly connect one of the poles of the direct voltage network through an associated resistance to ground. A ground current generated therethrough is detected by a ground current measuring member of the first station, which is thereby informed about the unbalance. The first station then takes corrective measures to reduce or eliminate the unbalance.

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Saxdalen, Sweden

Rolf Palsson