Abstract: A voltage source converter includes at least one limb connected between DC terminals, the or each limb including: a phase element including switching elements to interconnect a DC electrical network and an AC electrical network; an auxiliary sub-converter configured to be controllable to act as a waveform synthesizer to modify a first DC voltage presented to the DC electrical network; and a tertiary sub-converter connected in parallel with the electrical block and controllable to act as a waveform synthesizer to modify a second DC voltage presented to a DC side of the phase element, the tertiary sub-converter (39) including at least one energy storage device. The voltage source converter includes a controller configured to selectively control the or each tertiary sub-converter to synthesize at least one tertiary voltage component so as to transfer energy to or from that tertiary sub-converter and thereby regulate an energy level of that tertiary sub-converter.

Abstract: A voltage source converter comprises first and second DC terminals for connection to a DC network, and at least one limb connected between the first and second DC terminals. The or each limb includes: a phase element including two parallel-connected sets of series-connected switching elements connected in an H-bridge to define first and second diagonal switching pairs, a respective junction between each set of series-connected switching elements defining an AC terminal for connection to an AC network; and a sub-converter configured to be controllable to act as a voltage waveform synthesizer. The voltage source converter further includes a controller to operate the sub-converter to selectively synthesize a driving commutation voltage to modify a DC side current at a DC side of the H-bridge to minimize any differences in magnitude and direction between the DC side current and an AC side current at an AC side of the H-bridge.

Abstract: A synthetic test circuit, comprising: a device under test including a chain-link converter under test, comprising a plurality of test modules, each test module including module switches connected with an energy storage device; a terminal connected to the device under test; at least one injection circuit operably connected to the terminal, the injection circuit including a source, the source including a source chain-link converter, which includes a plurality of source modules, each source module including a plurality of module switches connected with at least one energy storage device; a controller being configured to operate each source module to selectively bypass the corresponding energy storage device and insert the corresponding energy storage device into the corresponding source chain-link converter so as to generate a voltage across the source chain-link converter and thereby operate the injection circuit to inject a current waveform and/or a voltage waveform into the chain-link converter under test.

Abstract: A synthetic test circuit, for performing an electrical test on a device under test, is provided. The circuit includes a terminal connectable to the device under test; a voltage injection circuit-operably connected to the terminal, the voltage injection circuit including a voltage source, the voltage source including a chain-link converter, the chain-link converter including a plurality of modules, each module including a plurality of module switches connected with at least one energy storage device; and a controller-configured to operate each module of the voltage injection circuit to selectively bypass the or each corresponding energy storage device and insert the or each corresponding energy storage device into the chain-link converter so as to generate a voltage across the chain-link converter and thereby operate the voltage injection circuit to inject a unidirectional voltage waveform into the device under test.

Abstract: A voltage source converter (30) comprises a converter limb (36), having primary and secondary limbs connected in parallel between first and second DC terminals (32,34), the primary limb element including first and second primary limb element portions (38,40) separated by a third terminal (42), being connectable to an AC electrical network (46), each primary limb element portion (38,40) including at least one primary switching element (50), the secondary limb including first and second secondary limb element portions (52,54) separated by a junction (56), and including a DC side chain-link converter (58), and a connection interconnecting the third terminal (42) and the junction (56) wherein the voltage source converter (30) further includes a control unit (62) controlling the switching of the respective switching elements.

Abstract: An alternate arm converter includes at least one converter limb that defines first and second limb portions. Each limb portion includes at least one director switch connected in series with a chain-link converter between one of two DC terminals and an AC terminal of the converter. The chain-link converters are operable to generate a voltage waveform at the AC terminal, and the director switches are operable to switch the respective chain-link converters in and out of circuit between the respective DC terminal and the AC terminal. The converter also includes a controller configured to selectively control the switching of each director switch to form a current circulation path including each limb portion and the DC network. The controller, during formation of the current circulation path, forces an alternating current to flow through the current circulation path to transfer energy between the chain-link converters of the limb portions.

Abstract: A voltage source converter includes a converter limb having limb portions separated by an AC terminal and extending between DC terminals, each limb portion including a primary switching element to switch the limb portion into and out of circuit. The converter further includes an auxiliary limb. The primary switching element of each limb portion is switchable to switch the auxiliary limb into and out of circuit with the corresponding limb portion. The converter further includes a control unit to, in one mode, inject a circulation current that flows in one direction in one of the limb portions and minimize a current flowing in the opposite direction in that limb portion. Each primary switching element switches the respective limb portion into or out of circuit following the minimization of the limb portion current by the circulation current.

Abstract: A semiconductor switching circuit, for use in a HVDC power converter, includes a main current branch including a main semiconductor switching element through which current flows when the main semiconductor switching element is switched on; and an auxiliary current branch connected in parallel or inverse-parallel with the main current branch. The auxiliary current branch includes an auxiliary circuit having a plurality of active auxiliary semiconductor switching elements connected to form an active switching bridge, and the auxiliary current branch further includes an energy storage device and/or an impedance device. The active switching bridge has a control unit operatively connected therewith, and the control unit is configured to switch the active switching bridge to connect the auxiliary circuit into and out of circuit with the main current branch and thereby selectively create an alternative current path whereby current flowing through the main current branch is diverted to flow through.

Abstract: Embodiments relate to a voltage source converter of the controlled transition bridge type, having three phase limbs, each phase limb having a high side director switch (Sw1, SW3, SW5) and a low side director switch (Sw4, SW6, SW2) connecting a respective DC terminal (DC+, DC?) to an AC node for that phase limb. Chain-link circuits for each phase limb comprise a plurality of series connect cells, each cell having an energy storage element that can be selectively connected in series or bypassed. The chain-link circuits are operated in a voltage mode to provide a defined voltage transition at the AC node during a transition between one director switch being turned off and the other directors switch being turned on. In some embodiments, chain-link circuits are connected to a common node such that, in use, a current can flow from one phase limb to another via the respective chain-link circuits.

Abstract: In the field of HVDC power converters there is a need for an improved semiconductor switching assembly which obviates the difficulties associated with main semiconductor switching elements having inherent limitations in their performance. A semiconductor switching assembly is provided, which includes a main semiconductor switching element that includes first and second connection terminals between which an active auxiliary circuit is electrically connected. The auxiliary circuit includes an auxiliary semiconductor switching element and current capture element that are connected in series with one another. The auxiliary semiconductor switching element has a control unit operatively connected therewith. The control unit is configured to switch on the auxiliary semiconductor switching element to divert into the current capture element a reverse recovery current that flows through the main semiconductor switching element while it turns off.

Abstract: This application relates to methods and apparatus for fault protection in a DC power transmission network or grid that aid in determining the location of a fault in the network. The method involves, in the event of a fault, controlling at least one current limiting element of the network so as to limit a fault current flowing to below a first current level which is within the expected current operating range of the network in normal operation, i.e. a safe level. The fault current is then controlled to maintain a non-zero level of fault current flow and the characteristics of the fault current flow at different parts of the network are determined by fault current detection modules. The location of the fault is then determined based on the determined characteristics.

Abstract: A voltage source converter comprises first and second DC terminals for connection to a DC network, and at least one limb connected between the first and second DC terminals. The or each limb includes: a phase element including two parallel-connected sets of series-connected switching elements connected in an H-bridge to define first and second diagonal switching pairs, a respective junction between each set of series-connected switching elements defining an AC terminal for connection to an AC network; and a sub-converter configured to be controllable to act as a voltage waveform synthesizer. The voltage source converter further includes a controller to operate the sub-converter to selectively synthesize a driving commutation voltage to modify a DC side current at a DC side of the H-bridge to minimize any differences in magnitude and direction between the DC side current and an AC side current at an AC side of the H-bridge.

Abstract: Power converters are disclosed. One power electronic converter for connecting AC and DC electrical networks and transferring power therebetween includes a converter limb extending between two DC terminals and having limb portions separated by an AC terminal. Each limb portion includes a chain-link converter including at least one rationalized module that has first and second sets of series-connected current flow control elements connected in parallel with at least one energy storage device. The current flow control elements and energy storage device(s) in each rationalized module combine to selectively provide a voltage source to control the configuration of an AC voltage at the AC terminal. The converter further includes a controller to selectively control the switching of the current flow control elements to simultaneously switch both limb portions into circuit to form a current circulation path including the converter limb and the DC electrical network.

Abstract: A DC to DC converter assembly, for connecting first and second high voltage DC power transmission networks, comprising first and second modular multilevel converters, each converter including a first converter limb having first and second limb portions, each limb portion including a least one module switchable to selectively provide a voltage source and thereby vary the magnitude ratio of a DC voltage (V1, V2) across the first and second terminals of a respective converter and an AC voltage (VAC) at the third terminal of the corresponding converter, the DC to DC converter assembly further including a first link electrically connecting the third terminal of one converter, with the third terminal of the other converter, and at least one converter further including a controller configured to switch the first and second limb portions in the first converter limb of the said converter into simultaneous conduction to divert a portion (IDiV1) of current flowing within the said converter away from the first link.

Abstract: A DC-to-DC converter assembly includes an inverter having first and second terminals connectable to a power transmission network. The inverter has a modular multilevel converter including a first inverter limb extending between the first and second terminals with first and second inverter limb portions separated by a third terminal. Each inverter limb portion includes at least one rationalized module having first and second sets of series-connected current flow control elements connected in parallel with an energy storage device. The current flow control elements include an active switching element directing current through the energy storage device and a passive current check element limiting current flow to one direction. The current flow control elements and energy storage device provide a voltage source to synthesize an AC voltage at the third terminal. A rectifier is electrically connected to the third terminal and connectable to a second power transmission network.

Abstract: A voltage source converter includes DC terminals, a plurality of single-phase limbs, and a controller. Each single-phase limb includes a phase element and switching elements. Each limb is connected between the DC terminals and is controllable to generate an AC voltage at the AC side of the corresponding phase element so as to draw a respective phase current from a multi-phase AC electrical network. The controller is configured to selectively generate a modified AC voltage demand for at least one limb in response to an imbalance in the phase currents and/or a change in electrical rating of at least one limb. The controller is configured to selectively control, in accordance with the or the respective modified AC voltage demand, the or each corresponding limb independently of the or each other limb to modify the voltage at the AC side of its phase element and thereby modify the corresponding phase current.

Abstract: A voltage source converter includes at least one limb connected between DC terminals, the or each limb including: a phase element including switching elements to interconnect a DC electrical network and an AC electrical network; an auxiliary sub-converter configured to be controllable to act as a waveform synthesizer to modify a first DC voltage presented to the DC electrical network; and a tertiary sub-converter connected in parallel with the electrical block and controllable to act as a waveform synthesizer to modify a second DC voltage presented to a DC side of the phase element, the tertiary sub-converter (39) including at least one energy storage device. The voltage source converter includes a controller configured to selectively control the or each tertiary sub-converter to synthesize at least one tertiary voltage component so as to transfer energy to or from that tertiary sub-converter and thereby regulate an energy level of that tertiary sub-converter.

Abstract: A power electronic converter, for connecting AC and DC networks and transferring power therebetween, comprises: first and second DC terminals for connection in use to a DC network; at least one primary converter limb extending between the first and second DC terminals and having first and second primary limb portions separated by a primary AC terminal for connection in use to a respective phase of a multi-phase AC network, at least one of the first and second primary limb portions including at least one primary active switching module to selectively allow current to flow through the corresponding primary converter limb in a first direction from the corresponding primary AC terminal to the DC terminals and in a second direction from the DC terminals to the corresponding primary AC terminal; and at least one secondary converter limb extending between the first and second DC terminals and having first and second secondary limb portions separated by a secondary AC terminal for connection in use to a further respe

Abstract: A voltage source converter includes a converter limb directly connected between first and second DC terminals. The converter limb includes an AC terminal, a first limb portion directly connected between the first DC terminal and the AC terminal, and a second limb portion directly connected between the second DC terminal and the AC terminal. Only one of the first and second limb portions includes a multilevel converter block, the other of the first and second limb portions includes a switching block, the switching block is switchable to selectively permit current flow in at least one direction in the corresponding limb portion and inhibit current flow in at least one direction in the corresponding limb portion, and at least one of the first and second limb portions is controllable to control the configuration of an AC voltage waveform at the AC terminal.

Abstract: An electrical assembly includes a DC tap including first and second tap terminals that are respectively connectable to first and second DC power transmission media, the DC tap including a tap limb extending between the first and second tap terminals and having two limb portions separated by a third tap terminal connectable to an electrical load, each tap limb portion including a DC blocking capacitor. The assembly further includes a current return configured to electrically interconnect the or each AC terminal to the third tap terminal, a converter unit, and a controller configured to selectively control the converter unit to generate at least one first non-fundamental frequency alternating current component at the or each AC terminal and modify the or each first non-fundamental frequency alternating current component to enable the DC tap to draw power from the DC electrical network for supply to the electrical load.