Multi-level voltage sourced converter

A voltage sourced converter comprising:

• a plurality of AC terminals and a DC terminal between which electrical power is transferred;
• a plurality of power electronic modules each including at least one capacitive element arranged to maintain a predetermined voltage and electronic switches operatively connecting the at least one capacitive element to terminals of the respective module such that current can be guided through or to bypass the at least one capacitive element;
• the modules being connected in a chain between two connections defining the DC terminal such that DC current passing through the DC terminal passes through the chain of the modules;
• the AC terminals being connected to the chain at prescribed locations between the modules in the chain so that on at least one side of each connection is formed an arm of the modules;
• a plurality of DC-blocking capacitive elements each connected between a respective one of the AC terminals and the corresponding respective connection at the chain such that the DC current passing through the chain is prevented from propagating out of the AC terminals beyond the converter;
• a controller for controlling the modules so as to (i) form an AC voltage waveform at each AC terminal, (ii) maintain the predetermined voltage of each of the at least one capacitive element of the respective module, and (iii) maintain a total voltage of all the modules which are operated to have current passed through the at least one capacitive element thereof substantially equal to a voltage at the DC terminal;
• each arm including a prescribed number of the modules which is related to the sum of the magnitude of a peak AC voltage which can appear across the respective arm and a DC voltage drop across the respective arm.