Patent ID: 8717786

Claim:
A plant for transmitting electric power through High Voltage Direct Current (HVDC) comprising: two converter stations interconnected by a bipolar direct voltage network and respectively connected to two alternating voltage networks for feeding electric power from one of two said alternating voltage networks to the other of said two alternating voltage networks, each converter station having a respective voltage source converter having at least one phase leg connected to a first and second pole of a direct voltage side of the converter and comprising a series connection of switching cells, each said phase leg having a phase output configured to be connected to an alternating voltage side of the converter, the phase output being formed between two switching cells along said series connection of switching cells, each said switching cell having at least one energy storing capacitor, each said switching cell being configured to obtain a first switching state and a second switching state, for obtaining a determined alternating voltage on said phase output, wherein in the first switching state a voltage across said at least one energy storage capacitor is applied across two terminals of the switching cell, and in the second switching state, a zero voltage is applied across the two terminals of the switching cell, wherein said voltage source converters of the two converter stations are configured to utilize a direct voltage having a higher voltage magnitude for the first pole than for the second pole with respect to ground, and said voltage magnitude of said first pole is 5 to 20 times higher than said voltage magnitude of said second pole so as to be asymmetric with respect to ground for creating said alternating voltage on said phase output of the respective converter.