Modular voltage source converter

A modular voltage source converter comprising one or more phases, each of said phases comprising one or more converter cell modules connected in series to each other, each of said converter cell modules comprising a first and a second phase leg with self- commutated valves, an output voltage of said voltage source converter is controlled by control signals applied to said converter cell modules, each converter cell module having an output voltage AC terminal (UAC),

• wherein in case of a failure in the phase leg of a converter cell module, said failed converter cell module is controlled only by the control signals controlling the valves of the second, non-faulty phase leg of said failed converter cell module, such that a zero output voltage is provided at the output voltage AC terminal (UAC), and
• wherein for each converter cell module four external diodes are arranged in parallel to each of the valves of the module, said external diodes are arranged separately from, and are protected from the cell module, and said external diodes are used upon failure of said cell module(s).