Fault current limitation in DC power transmission systems

摘要

A method, voltage source converter and computer program product for limiting the current in a DC power transmission system are disclosed. The voltage source converter has an AC side and a DC side and a fault current path between these sides. It furthermore includes a control unit and at least one switching unit of a first type provided in the fault current path and that includes a primary switching element together with an anti-parallel secondary controllable rectifying element. Based on a fault being detected in the DC power system when the primary switching elements of the converter are blocked, the control unit changes the control of the controllable rectifying element from acting as a non-controllable rectifying to acting as a controllable rectifying element.

主权项

1. A method for limiting a current in a DC power transmission system using a voltage source converter including a fault current path between an AC side and a DC side of the converter, said fault current path including at least one switching unit of a first type, where each switching unit of the first type includes a primary switching element together with an anti-parallel secondary controllable rectifying element, the method comprising the steps of:
blocking primary switching elements of the converter, detecting a fault in the DC power system, changing the control of the controllable rectifying elements in the fault current path from a first control mode to a second control mode, the first control mode being to control the controllable rectifying elements to act as non-controllable rectifying elements so that they will always conduct current as a positive voltage is applied over them and the second control mode being to control the controllable rectifying elements to act as controllable rectifying elements, and controlling, according to said second control mode, the controllable rectifying elements of the fault current path to limit a current (iDC) at the DC side of the converter, wherein at least one characteristic of at least one power component at the DC side of the voltage source converter is compared with a first threshold level of the at least one characteristic to determine changing the control of the controllable rectifying elements in the fault current path from the first control mode to the second control mode, and is compared with a second threshold level of the at least one characteristic to determine changing the control of the controllable rectifying elements in the fault current path from the second control mode back to the first control mode, and the first threshold level of the at least one characteristic and the second threshold level of the at least one characteristic have different values.