| 摘要 |
A voltage source converter (30) comprises: a converter limb (36) extending between first and second DC terminals (32,34) and having first and second limb portions (38,40) separated by an AC terminal (42), the first and second DC terminals (32,34) being connectable to a DC electrical network (44) and the AC terminal (42) being connectable to an AC electrical network (46), each limb portion (38,40) including a primary switching element (48), the primary switching element (48) of each limb portion (38,40) being switchable to switch the corresponding limb portion (38,40) into and out of circuit between the corresponding DC terminal (32,34) and the AC terminal (42) to control the configuration of an AC voltage at the AC terminal (42); an auxiliary limb (50) including an auxiliary converter, the auxiliary converter including at least one auxiliary switching element, the auxiliary limb (50) being connected to the AC terminal (42), the primary switching element (48) of each limb portion (38,40) being switchable to switch the auxiliary limb (50) into and out of circuit with the corresponding limb portion (38,40) and thereby switch the auxiliary limb (50) into and out of circuit with the corresponding DC terminal (32,34); and a control unit to selectively control the switching of the or each auxiliary switching element of the auxiliary converter to control the auxiliary limb (50) as a current source in a primary operating mode to inject a circulation current (68) that flows in one direction in one of the first and second limb portions (38,40) to minimise a limb portion current (66) flowing in the opposite direction in that limb portion (38,40), wherein each primary switching element (48) switches the respective limb portion (38,40) into or out of circuit between the corresponding DC terminal (32,34) and the AC terminal (42), following the minimisation of the limb portion current (66) by the circulation current (68), when a minimal or zero current flows through the corresponding primary switching element (48) during the commutation of current from one of the first and second limb portions (38,40) to the other of the first and second limb portions (38,40). |
