Transmission system and a method for control thereof
First Claim
1. A high voltage direct current transmission system, comprising:
- a converter station arranged at each end of a high voltage direct current transmission line, each converter station being configured to connect said transmission line to an AC system, each said station comprising a series connection of at least two converters having a DC side thereof connected to a pole of said transmission line on high potential and to a neutral bus on zero potential by being grounded, a first of said converter stations being adapted to operate as a rectifier and a second of said converter stations being adapted to operate as an inverter, each converter comprising a by-pass DC breaker connected in parallel in a current path forming a by-pass of said converter when said DC breaker is closed, each converter station comprising an arrangement adapted to control DC current flowing through said pole and comprising for each converter of each station a device for controlling that converter and the current therethrough for either increasing the voltage between said neutral bus and said pole and thereby power transmitted between said stations by starting operation of the converter when being blocked or reducing the voltage between said neutral bus and said pole and thereby the power transmitted between said stations by stopping operation of the converter when being active, wherein each said control device is adapted to unblock a blocked said converter by starting to control the converter at a high delay angle and gradually decreasing the delay angle until substantially all the DC current flows through that converter and to then control said by-pass breaker to open at substantially zero current, and to stop the operation of said converter by controlling the controller at a gradually increasing delay angle until the voltage across the converter is substantially zero and to then control the converter to be blocked by firing a by-pass pair thereof and to then control said by-pass breaker to close for taking over all the DC current.
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Accused Products
Abstract
An HVDC transmission system including a rectifier station and an inverter station each having a series connection of at least two converters. A by-pass DC breaker is connected in parallel with each converter. A control device is adapted to deblock a blocked converter by starting to control the converter at high delay angle and gradually decreasing the delay angle until substantially all DC current flows through the converter and to then control the by-pass breaker to open at substantially zero current, and to stop the operation of a converter by controlling the converter at gradually increasing delay angle until the voltage across the converter is substantially zero and to then control the converter to be blocked by firing a by-pass pair thereof and to then control the by-pass breaker to close for taking over all the DC current when the voltage between a neutral bus and a pole of a transmission line between the stations is to be increased and reduced, respectively.
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Citations
15 Claims
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1. A high voltage direct current transmission system, comprising:
a converter station arranged at each end of a high voltage direct current transmission line, each converter station being configured to connect said transmission line to an AC system, each said station comprising a series connection of at least two converters having a DC side thereof connected to a pole of said transmission line on high potential and to a neutral bus on zero potential by being grounded, a first of said converter stations being adapted to operate as a rectifier and a second of said converter stations being adapted to operate as an inverter, each converter comprising a by-pass DC breaker connected in parallel in a current path forming a by-pass of said converter when said DC breaker is closed, each converter station comprising an arrangement adapted to control DC current flowing through said pole and comprising for each converter of each station a device for controlling that converter and the current therethrough for either increasing the voltage between said neutral bus and said pole and thereby power transmitted between said stations by starting operation of the converter when being blocked or reducing the voltage between said neutral bus and said pole and thereby the power transmitted between said stations by stopping operation of the converter when being active, wherein each said control device is adapted to unblock a blocked said converter by starting to control the converter at a high delay angle and gradually decreasing the delay angle until substantially all the DC current flows through that converter and to then control said by-pass breaker to open at substantially zero current, and to stop the operation of said converter by controlling the controller at a gradually increasing delay angle until the voltage across the converter is substantially zero and to then control the converter to be blocked by firing a by-pass pair thereof and to then control said by-pass breaker to close for taking over all the DC current. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A method for controlling a high voltage direct current transmission system, said system comprising at each end of a high voltage direct current transmission line a converter station for connecting said transmission line to an AC system, each converter station comprising a series connection of at least two converters having a DC side thereof connected on one hand to a pole of said transmission line on high potential and on the other to a neutral bus on zero potential by being grounded, a first of said converter stations being adapted to operate as rectifier and a second of said converter stations being adapted to operate as inverter, each converter comprising a by-pass DC breaker connected in parallel therewith in a current path forming a by-pass of said converter when said breaker is closed, said method comprising:
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controlling a DC current through said pole to be on a substantially constant, full current value under normal conditions of said transmission system, increasing a voltage between said neutral bus and said pole and thereby a power transmitted between said stations by starting operation of the converters being blocked, or reducing the voltage between said neutral bus and said pole and thereby the power transmitted between said converter stations by stopping operation of converters being active, wherein increasing the voltage between the neutral bus and the pole comprises unblocking a blocked converter by starting to control the blocked converter at a high delay angle and gradually decreasing the delay angle until substantially all the DC current flows through that converter and to then control said by-pass breaker in parallel with that converter to open at substantially zero current, and wherein reducing the voltage between the neutral bus and the pole the operation of said converter is stopped by controlling the converter at a gradually increasing delay angle until the voltage across the converter is substantially zero and then controlling the converter to be blocked by firing a by-pass pair thereof and then controlling said by-pass breaker in parallel with that converter to close for taking over all the DC current. - View Dependent Claims (9, 10, 11, 12)
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13. A computer program product, comprising
a non-transitory computer readable medium; - and
computer program instructions recorded on the computer readable medium and executable by a processor for carrying out a method for controlling a high voltage direct current transmission system, said system comprising at each end of a high voltage direct current transmission line a converter station for connecting said transmission line to an AC system, each converter station comprising a series connection of at least two converters having a DC side thereof connected on one hand to a pole of said transmission line on high potential and on the other to a neutral bus on zero potential by being grounded, a first of said converter stations being adapted to operate as rectifier and a second of said converter stations being adapted to operate as inverter, each converter comprising a by-pass DC breaker connected in parallel therewith in a current path forming a by-pass of said converter when said breaker is closed, said method comprising; controlling a DC current through said pole to be on a substantially constant, full current value under normal conditions of said transmission system, increasing a voltage between said neutral bus and said pole and thereby a power transmitted between said stations by starting operation of the converters being blocked, or reducing the voltage between said neutral bus and said pole and thereby the power transmitted between said converter stations by stopping operation of converters being active, wherein increasing the voltage between the neutral bus and the pole comprises unblocking a blocked converter by starting to control the blocked converter at a high delay angle and gradually decreasing the delay angle until substantially all the DC current flows through that converter and to then control said by-pass breaker in parallel with that converter to open at substantially zero current, and wherein reducing the voltage between the neutral bus and the pole the operation of said converter is stopped by controlling the converter at a gradually increasing delay angle until the voltage across the converter is substantially zero and then controlling the converter to be blocked by firing a by-pass pair thereof and then controlling said by-pass breaker in parallel with that converter to close for taking over all the DC current. - View Dependent Claims (14, 15)
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Specification