| 摘要 |
In the field of HVDC power converters there is a need for an improved semiconductor switching string which obviates the difficulties associated with respective semiconductor switching elements exhibiting different performance characteristics and having inherent limitations in their performance. A semiconductor switching string (100), for use in a HVDC power converter, comprises a plurality of series-connected semiconductor switching assemblies (10; 70; 110). Each semiconductor switching assembly (10; 70; 110) has a main semiconductor switching element (12) that includes first and second connection terminals (14, 16) between which current flows from the first terminal (14) to the second terminal (16) when the main semiconductor switching element (12) is switched on. The main semiconductor switching element (12) also has an auxiliary semiconductor switching element (28; 72; 1 12) electrically connected between the first and second connection terminals (14, 16) thereof. Each semiconductor switching assembly (10; 70; 110) also includes a control unit (30) which is operatively connected with each auxiliary semiconductor switching element (28; 72; 112). The or each control unit (30) is configured to switch on a respective auxiliary semiconductor switching element (28; 72; 112) to selectively create an alternative current path (32; 114, 116) between the first and second connection terminals (14, 16) associated therewith whereby current is diverted to flow through the alternative current path (32; 114, 116) to reduce the voltage across the corresponding main semiconductor switching element (12). The or each control unit (30) is further configured to switch on the said respective auxiliary semiconductor switching element (28; 72; 112) when the voltage across the corresponding main semiconductor switching element (12) differs from a voltage reference derived from the voltage across all of the main semiconductor switching elements (12) in the semiconductor switching string (100). |
