| 摘要 |
A pair of thyristor converters are connected by a DC power transmission line, and their AC terminals are connected through tapped transformers to AC systems respectively. The output signal of a constant-current circuit in a converter control unit associated with the forward converter is selected to control the gate of the forward converter, while the output signal of a constant-voltage circuit in a converter control unit associated with the reverse converter is selected to control the gate of the reverse converter. When the reactive power is to be controlled, a reactive power signal is applied for the gate control. A voltage limit indication circuit in each control unit receives the AC terminal voltage e2 of the transformer and the DC current Id so as to increase the control angle limit with a decrease in the values of e2 and Id. When the control advance angle or control delay angle determined by the output signals of the control circuits is larger than the control angle limit, this angle is limited to the control angle limit. When the reactive power is to be controlled, the tap position of either transformer is lowered to decrease e2 and to increase the control angle limit thereby widening the controllable range of the reactive power. During the start-stop stage or during the protective operation, the output of the voltage limit indication circuit in each control unit is inhibited to permit free variations of the control angle. |
