Abstract: A method for connecting a DC converter to a DC system using a connection circuit, the connection circuit including a first switch connected in series between the DC converter and a second switch, the second switch connected in series between the first switch and the DC system, and a resistive component connected in parallel with the second switch. The method includes operating the first switch from the open configuration to a closed configuration, such that a first current is able to flow through the connection circuit; determining the first current flowing through the connection circuit; adjusting a DC converter voltage of the DC converter, as a function of the first current, to reduce the first current through the connection circuit to or below a threshold value; and then operating the second switch from the open configuration to a closed configuration, thereby connecting the DC converter to the DC system.

Abstract: There is provided a method of energising electrical poles of a rigid bipole power transmission network, the rigid bipole power transmission network comprising a first pair of converters connected to a second pair of converters via first and second electrical poles, and further comprising a ground return path. The method includes determining one or more parameters associated with either of the first or second pair of converters, wherein the one or more parameters indicate a difference in energy between the first and second electrical poles. The method further includes controlling, based on the one or more parameters, at least one converter of the associated first or second pair of converters to regulate the difference in energy between the first and second electrical poles such that a ground current flowing in the ground return path is below a predetermined threshold value.

Abstract: A controller, and a method, for controlling a power dissipating arrangement connected to a converter station, wherein the converter station includes a power converter that is connected to a power transmission medium. The controller is configured to: determine a parameter associated with the power converter, use the parameter to determine a control signal for the power dissipating arrangement; and provide the control signal to the power dissipating arrangement. The power dissipating arrangement is configured to use the control signal to control a switching of the power dissipating arrangement to dissipate energy from the power transmission medium and reduce a transfer of energy between the power transmission medium and the power converter.

Abstract: There is provided a switching valve for a voltage source converter, the switching valve comprising a plurality of modules, each module including at least one switching element and at least one energy storage device, each switching element and each energy storage device in each module arranged to be combinable to selectively provide a voltage source, the switching valve including a regulator programmed to selectively control the switching of the switching elements to select one or more of the modules to contribute a respective voltage to a switching valve voltage, wherein the regulator is programmed to selectively regulate an energy stored in each energy storage device by controlling the switching of the switching elements to regulate a voltage of each energy storage device towards a target voltage, and the regulator is programmed to vary the target voltage of each energy storage device as a function of a number of healthy modules.

Abstract: A method for controlling a converter station in a power transmission network. The method includes: initially controlling, by a controller, the power converter to transfer power between the AC network and the transmission network via the first branch and the second branch; detecting, by the controller, a fault in the second branch; in response to detecting the fault in the second branch: issuing, by the controller, a first command to reduce an AC side voltage of the power converter; issuing, by the controller, a second command to open the first switch, the third switch, and the fourth switch; in response to the fourth switch opening: issuing, by the controller, a third command to close the first switch; and issuing, by the controller, a fourth command to restore an AC side voltage of the power converter to an AC reference value.

Abstract: A method of controlling a bipole power transmission network. The method includes receiving a command for synchronising first and second AC networks; measuring a first AC bus voltage of a first AC bus and a second AC bus voltage of a second AC bus, the measured voltages being defined by voltage magnitudes and phase angles; adjusting a phase angle and a magnitude of a voltage of the first and second power converters based on the measured voltages; issuing a command to electrically connect the first AC bus with the second AC bus, when: a first phase angle difference of the AC bus voltages is within a first pre-defined range; and a first magnitude difference of the AC bus voltages is within a second pre-defined range; and changing the phase angle of the voltage of the power converters to balance the power between the first and second electrical poles.

Abstract: A computer-implemented method of controlling a bipole power transmission network including first, second, third and fourth power converters, a first electrical pole, a second electrical pole, and a neutral arrangement. The method including: configuring the first and second power converters to regulate first and second DC voltages of the first and second electrical poles; configuring the third and/or fourth power converter to control an AC voltage output from the third or fourth AC sides; configuring the third and/or fourth power converter to be synchronised to the AC voltage; and controlling the third and/or fourth power converter to regulate an AC power at the third or fourth AC side and/or to regulate a DC power at the third or fourth DC side, as function of: a measured value of a first electrical current flowing through the neutral arrangement; and a reference value for the first electrical current.

Abstract: A method of controlling a bipole power transmission network, including a first power transmission means electrically connected between DC sides of first and third power converters and defining a first electrical pole, a second power transmission means electrically connected between DC sides of second and fourth power converters and defining a second electrical pole, and a neutral arrangement, wherein the AC sides of the first and second power converters are electrically connected to respective AC networks via respective first and second AC buses, the method including synchronising a first AC bus voltage of the first AC bus with a second AC bus voltage of the second AC bus by synchronising a first voltage-controlled oscillator (VCO) of the first power converter and a second VCO of the second power converter, with a third reference VCO, such that the first VCO and second VCO are synchronised with each other.

Abstract: A method for connecting a DC converter to a DC system using a connection circuit, the connection circuit including a first switch connected in series between the DC converter and a second switch, the second switch connected in series between the first switch and the DC system, and a resistive component connected in parallel with the second switch. The method includes operating the first switch from the open configuration to a closed configuration, such that a first current is able to flow through the connection circuit; determining the first current flowing through the connection circuit; adjusting a DC converter voltage of the DC converter, as a function of the first current, to reduce the first current through the connection circuit to or below a threshold value; and then operating the second switch from the open configuration to a closed configuration, thereby connecting the DC converter to the DC system.

Abstract: A bipole power transmission scheme includes a first converter station positioned in-use remote from a second converter station, and first and second transmission conduits to in-use interconnect the first converter station with the second converter station and thereby permit the first converter station to transmit power to the second converter station. The first converter station includes a first power converter, a second power converter, and a converter station controller which is programmed to selectively transition the bipole power transmission scheme into an asymmetrical monopole configuration, while maintaining the transfer of power from both the first and second power sources.

Abstract: A bipole power transmission network includes a first upstream power converter which has a first DC terminal that is connected with a first transmission conduit which extends, in-use, to a first downstream power converter. The first upstream power converter has a second DC terminal that is connected with a return conduit which extends, in-use, to the first downstream power converter and a second downstream power converter. The first upstream power converter has at least one first AC terminal electrically connected with a first AC power source. The bipole power transmission network includes a second upstream power converter which has a third DC terminal that is connected with the return conduit, and a fourth DC terminal which is connected with a second transmission conduit that extends, in-use, to the second downstream power converter, and at least one second AC terminal electrically connected with a second AC power source.

Abstract: A computer-implemented method of controlling a power converter in a power transmission network, including: measuring a first AC voltage and/or a first AC current at a point of connection, determining whether a fault condition is present in the AC network, setting a current limit for a second AC current output, by: if a fault condition is determined not to be present, setting the current limit to be equal to a first current limit value, and if a fault condition is determined to be present in the AC network, setting the current limit to be equal to a second current limit value, wherein the second current limit value is less than the first current limit value, and regulating, based on the current limit, a second AC voltage that is output from the AC side of the power converter, such that the second AC current does not exceed the current limit.

Abstract: There is provided a switching valve for a voltage source converter, the switching valve including a number of modules, each module including at least one switching element and at least one energy storage device, the or each switching element and the or each energy storage device in each module arranged to be combinable to selectively provide a voltage source, the switching valve including a controller programmed to selectively control the switching of the switching elements to select one or more of the modules to contribute a or a respective voltage to a switching valve voltage.

Abstract: In the field of high voltage direct current (HVDC) power transmission networks, there is a need for improvements to allow a single power converter to control individual AC network voltages carried by multiple AC transmission conduits to multiple AC network elements, such as respective wind parks.

Abstract: A control apparatus is described for controlling a frequency set-point for a first AC network electrically connected to a first HVDC station to regulate active power. The controller has a frequency controller operable in a first mode of operation to determine a frequency set-point for the first AC network based on a measured DC voltage at the first HVDC station. A disturbance detector is configured to monitor the measured value of DC voltage at the first HVDC station for a predetermined characteristic indicative that a variation in measured DC voltage does correspond to a known modulation applied to the DC voltage by a second HVDC station. The frequency controller is configured to determine the frequency set-point for the first AC network based on a measured value of DC voltage if said predetermined characteristic is detected, and to control the frequency set-point to a predetermined default frequency if not detected.

Abstract: A bipole power transmission scheme with two independent converts, two power feed and one return conduit. During operation of the bipole power transmission scheme under abnormal conditions, when a return conduit is faulty and unable to provide a return current path, each converter controller is programmed to monitor the first power feed in the first transmission conduit and the second power feed in the second transmission conduit and, if the first power feed in the first transmission conduit and the second power feed in the second transmission conduit differ from one another, at least one converter controller modifies the power infeed from its corresponding power source to reduce the difference between the first power feed and the second power feed.

Abstract: A bipole power transmission network includes a first upstream power converter which has a first DC terminal that is connected with a first transmission conduit which extends, in-use, to a first downstream power converter. The first upstream power converter has a second DC terminal that is connected with a return conduit which extends, in-use, to the first downstream power converter and a second downstream power converter. The first upstream power converter has at least one first AC terminal electrically connected with a first AC power source. The bipole power transmission network includes a second upstream power converter which has a third DC terminal that is connected with the return conduit, and a fourth DC terminal which is connected with a second transmission conduit that extends, in-use, to the second downstream power converter, and at least one second AC terminal electrically connected with a second AC power source.

Abstract: A voltage source converter having first and second DC terminals for connection to a DC network is provided. The voltage source converter includes at least one converter limb that extends between the first and second DC terminals and first and second limb portions that are separated by a respective AC terminal for connection to a corresponding phase of an AC network. Each limb portion includes a chain-link converter which is defined by a plurality of series-connected switching modules which operate in combination to provide a stepped variable voltage source. The voltage source converter includes a control apparatus configured to coordinate operation of the chain-link converters to cause an exchange of power between the DC and AC networks, evaluate the performance of one of the pluralities of series-connected switching modules, and modify the operation of the respective chain-link converter when the performance becomes degraded to a predetermined amount.

Abstract: A bipole power transmission scheme includes a first converter station positioned in-use remote from a second converter station, and first and second transmission conduits to in-use interconnect the first converter station with the second converter station and thereby permit the first converter station to transmit power to the second converter station. The first converter station includes a first power converter, a second power converter, and a converter station controller which is programmed to selectively transition the bipole power transmission scheme into an asymmetrical monopole configuration, while maintaining the transfer of power from both the first and second power sources.

Abstract: There is provided a switching valve for a voltage source converter, the switching valve comprising a plurality of modules, each module including at least one switching element and at least one energy storage device, each switching element and each energy storage device in each module arranged to be combinable to selectively provide a voltage source, the switching valve including a regulator programmed to selectively control the switching of the switching elements to select one or more of the modules to contribute a respective voltage to a switching valve voltage, wherein the regulator is programmed to selectively regulate an energy stored in each energy storage device by controlling the switching of the switching elements to regulate a voltage of each energy storage device towards a target voltage, and the regulator is programmed to vary the target voltage of each energy storage device as a function of a number of healthy modules.