Submodule identification in a modular multilevel converter by means of measuring signal propagation times from the central controller

A method of identifying the location of a chain-link sub-module in an electrical apparatus comprising a chain-link converter having a plurality of chain-link sub-modules each of which is operable to provide a voltage source and a switching control unit to control the chain-link sub-modules, the method comprising the steps of:

• (a) operatively interconnecting an electromagnetic radiation conduit between the switching control unit and each chain-link sub-module, the length of the electromagnetic radiation conduit between the switching control unit and at least one chain-link sub-module differing from the length of the electromagnetic radiation conduit between the switching control unit and at least one other chain-link sub-module;
• (b) propagating an electromagnetic signal through a given different-length electromagnetic radiation conduit;
• (c) determining the time taken for the electromagnetic signal to propagate through the given different-length electromagnetic radiation conduit;
• and
• (d) identifying the or each chain-link sub-module associated with the given different-length electromagnetic radiation conduit according to the time taken for the electromagnetic signal to propagate through the given different-length electromagnetic radiation conduit.