Abb Schweiz Ag

Abb Technology Ltd

Hitachi Energy Switzerland Ag

Niclas Johannesson

Khirod Kumar-Nayak

A method of controlling a modular multilevel converter, MMC, of a full-bridge or mixed arm type in case of a DC line disturbance is provided. The method includes determining whether a magnitude of a DC voltage (Udp) of the MMC has fallen below an upper voltage threshold (Ud_max_lim), and, if determining that the magnitude of the DC voltage has fallen below the upper voltage threshold, reducing both a magnitude of an AC active current reference (IVD_ORD) and a magnitude of a DC voltage reference (UDC_REF) for the MMC based on the DC pole voltage. An MMC with a controller implementing the method, a converter station including at least one such MMC, and a power transfer system including at least one such converter station, are also provided.

Control of a modular multilevel converter of a full bridge or mixed arm type in case of a DC line disturbance

A method in a power system which includes a protected unit, such as a transmission line, adapted to convey power from a first position in the protected unit to a second position in the protected unit, or vice versa, via a plurality of conductors. A first travelling wave differential current (ITWdiff) is determined based on a comparison between a determined first travelling wave current or a second travelling wave current in first and second positions and an estimation of the first travelling wave current or the second travelling wave current, respectively. The estimation is carried out using a propagation function which takes into account any distortion, attenuation and/or delay of the waveform of a wave due to propagation of the wave in the protected unit. A second or normalized travelling wave differential current (ITWdiff) is determined by means of, based on the propagation function, adjusting at least one of magnitude and phase of the first travelling wave differential current such that all modes attain equal or increasingly equal modal characteristics. The method may facilitate or enable mitigating or even eliminating any false differential current in elements of a travelling wave differential current vector which correspond to healthy conductors, caused by coupling effects between conductors.

Method and apparatus for sensing a fault in a power system

A fault sensing system for a power system including a protected unit is disclosed. The fault sensing system is adapted to sense a fault in the protected unit. The fault sensing system includes at least one current sensing unit adapted to sense at least one first current in a first position in the protected unit and at least one second current in the second position in the protected unit and at least one voltage sensing unit adapted to sense at least one first voltage in the first position and at least one second voltage in the second position, and at least one processing unit. The at least one processing unit is adapted to model any distortion, attenuation and/or delay of the waveform of a wave due to propagation of the wave in the protected unit by means of a propagation function, determine at least one first travelling wave current in the first position based on the at least one first current and the at least one first voltage, determine at least one second travelling wave current in the second position based on the at least one second current and the at least one second voltage, estimate at least one of the at least one first travelling wave current and the at least one second travelling wave current by applying the propagation function to the at least one second travelling wave current or to the at least one first travelling wave current, respectively, on a condition that the at least one first travelling wave current is estimated, compare the estimated at least one first travelling wave current with the determined at least one first travelling wave current, on a condition that the at least one second travelling wave current is estimated, compare the estimated at least one second travelling wave current with the determined at least one second travelling wave current, and, based on the comparison or comparisons, determine whether there is a fault in the protected unit.

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Ludvika, Sweden

Niclas Johannesson