Improvements in or relating to chain-link converters

A method of operating a chain-link converter, the chain-link converter including a plurality of series connected chain-link modules, each chain-link module including at least one switching element and an energy storage device which together are selectively operable to provide a voltage source whereby the chain-link converter is able to provide a stepped variable voltage source, the method comprising the steps of:

• (i) identifying one or more unhealthy chain-link modules having a reduced performance characteristic compared to one or more healthy chain-link modules having a normal performance characteristic;
• (ii) utilizing the healthy chain-link modules normally in the operation of the chain-link converter;
• and
• (iii) reducing the utilization of the or each unhealthy chain-link module.

A controller for a chain-link converter, the chain-link converter including a plurality of series connected chain-link modules, each chain-link module including at least one switching element and an energy storage device which together are selectively operable to provide a voltage source whereby the chain-link converter is able to provide a stepped variable voltage source, the controller being configured to:

• (i) identify one or more unhealthy chain-link modules having a reduced performance characteristic compared to one or more healthy chain-link modules having a normal performance characteristic;
• (ii) utilize the healthy chain-link modules normally in the operation of the chain-link converter;
• and
• (iii) reduce the utilization of the or each unhealthy chain-link module.