| 摘要 |
A voltage source converter 30 comprises first and second DC terminals 32, 34, a plurality of single phase limbs, each limb including a phase element 36. Each phase element includes two parallel-connected pairs of series connected switching elements 40. The AC terminals 42 of each phase element are connectable to a respective phase of a multi-phase AC electrical network 50. Each single-phase limb is controllable to generate an AC voltage at the AC side of the corresponding phase element so as to draw a respective phase current (ia) from the multi-phase AC electrical network. A controller is configured to selectively generate a modified AC voltage demand (Vconv) for at least one single-phase limb in response to an imbalance in the plurality of phase currents and/or a change in electrical rating of at least one single-phase limb. The controller is configured to selectively control, in accordance with the respective modified AC voltage demand Vconv, each corresponding single phase limb independently of the other single-phase limbs to modify the AC voltage at the AC side of its phase element and thereby modify the corresponding phase current. An auxiliary converter 38 may be provided to selectively act as a waveform synthesizer to modify the DC voltage at the DC side of the corresponding phase element. |
