Abstract: There is provided a switching valve for a voltage source converter, the switching valve including a number of modules, each module including at least one switching element and at least one energy storage device, each switching element and each energy storage device arranged to be combinable to selectively provide a voltage source, the switching valve including a controller programmed to selectively control the switching of the switching elements to select zero, one or more of the modules to contribute a or a respective voltage to a switching valve voltage. The controller is programmed to selectively control the switching of the switching elements to carry out a switching operation and to apply a time delay if a charging current is flowing through the modules and/or apply a time delay to a start time of the switching operation if a discharging current is flowing through the modules.

Abstract: A controller, for a chain-link converter having a number of series-connected chain-link modules that are operable in combination to provide a stepped variable voltage source, is programmed to obtain for each chain-link module an indication of whether the current flow through the corresponding chain-link module is in a first flow direction or a second flow direction. The controller is additionally programmed to evaluate the number of indications in the first flow direction and the number of indications in the second flow direction, and thereafter to establish an overall current flow direction through the chain-link converter equal to the flow direction having the largest number of indications.