Abstract: A converter (30) comprises first and second DC terminals (32,34) connectable in use to a DC network (40), the converter (30) including a converter limb (36) extending between the DC terminals (32,34), the converter limb (36) including first and second limb portions separated by an AC terminal (38), the AC terminal (38) connectable in use to an AC voltage, each limb portion including at least one director switch (44) connected in series with a waveform synthesizer between the AC terminal (44) and a respective one of the first and second DC terminals (32,34), the waveform synthesizers operable to control the modulation of an AC voltage waveform at the AC terminal (38), each director switch (44) operable to switch the respective waveform synthesizer into and out of circuit between the respective DC terminal (32,34) and the AC terminal (38); and a controller (56) programmed to selectively control the switching of the director switches (44) to switch both of the limb portions into circuit concurrently to form a cu

Abstract: A converter (30) comprises first and second DC terminals (32,34) connectable in use to a DC network (40), the converter (30) including a converter limb (36) extending between the DC terminals (32,34), the converter limb (36) including first and second limb portions separated by an AC terminal (38), the AC terminal (38) connectable in use to an AC voltage, each limb portion including at least one director switch (44) connected in series with a waveform synthesizer between the AC terminal (44) and a respective one of the first and second DC terminals (32,34), the waveform synthesizers operable to control the modulation of an AC voltage waveform at the AC terminal (38), each director switch (44) operable to switch the respective waveform synthesizer into and out of circuit between the respective DC terminal (32,34) and the AC terminal (38); and a controller (56) programmed to selectively control the switching of the director switches (44) to switch both of the limb portions into circuit concurrently to form a cu

Abstract: Fault protection of a voltage source converter is provided. An apparatus has a chain-link circuit in series with a director switch. The chain-link circuit includes cells including an energy storage element and cell switching elements connected with anti-parallel diodes. Each cell switching element has a cell switching element controller. The director switch includes director switch units, each having a director switching element and a director switch unit controller. Each cell switching element controller monitors for a fault current and turns-off its associated cell switching element and reports a fault event to a fault controller. Each director switch unit controller monitors for a fault current and reports a fault event to the fault controller but the director switch unit control keeps its associated director switching element turned-on. The fault controller monitors for reports of fault events to order the cell switching elements of at least some of the cells to turn-off.

Abstract: Embodiments for a voltage source converter are disclosed.

Abstract: This application describes methods and apparatus for achieving voltage balancing of clamp capacitors of director switch units of a voltage source converter (VSC). An arm or director switch may be formed from a number of director switch units connected in series, each director switch unit having a semiconductor switching element such as an IGBT. Typically a clamp capacitor may be connected across the IGBT. In some arrangements a floating power supply may draw power from the clamp capacitor to provide power for the director switch unit. In the present application the director switch unit is operable in a voltage balancing mode such that the power drawn from the clamp capacitor varies based on the voltage across the clamp capacitor. In this way the power demand for power drawn from the clamp capacitor may have the characteristic of a resistive load.

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 converter includes first and second DC terminals for connection to a DC network, limb(s) connected between the first and second DC terminals, and a controller. Each limb includes a phase element and DC side sub-converter(s). The phase element has switching elements and AC terminal(s) for connection to an AC network, the switching elements being switchable to selectively interconnect a DC side voltage at a DC side of the phase element and an AC side voltage at an AC side of the phase element, The DC side sub-converter(s) connected to the DC side of the phase element. The controller selectively controls the switching elements and the operation of each DC side sub-converter as a voltage synthesiser. The controller also controls the switching elements to provide a blocking voltage to limit or block the flow of a fault current between the AC and DC networks and through each limb.

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: Fault protection of a voltage source converter is provided. An apparatus has a chain-link circuit in series with a director switch. The chain-link circuit includes cells including an energy storage element and cell switching elements connected with anti-parallel diodes. Each cell switching element has a cell switching element controller. The director switch includes director switch units, each having a director switching element and a director switch unit controller. Each cell switching element controller monitors for a fault current and turns-off its associated cell switching element and reports a fault event to a fault controller. Each director switch unit controller monitors for a fault current and reports a fault event to the fault controller but the director switch unit control keeps its associated director switching element turned-on. The fault controller monitors for reports of fault events to order the cell switching elements of at least some of the cells to turn-off.

Abstract: A voltage source converter includes DC terminals for connection to a DC network, a plurality of converter limbs between the DC terminals, and a controller. Each converter limb includes first and second limb portions separated by a respective AC terminal, the AC terminal of each converter limb connecting to a multi-phase AC network. Each limb portion extends between a corresponding DC terminal and AC terminal. Each limb portion including a valve having switching element(s) and energy storage device(s), the switching element being switchable to selectively insert the energy storage device into the limb portion and bypass the energy storage device to control a voltage across that valve. The controller is programmed to control the switching of valves to form a current circulation path including the limb portions corresponding to the selected valves, the AC phases connected to the limb portions corresponding to the selected valves, and the DC network.

Abstract: This application relates to methods and apparatus for voltage balancing of voltage source converters and especially for voltage balancing of clamp capacitors of a director switch of a voltage source converter. Typically a director switch of a voltage source converter includes series connected director switch units, each having a semiconductor switching element. In some voltage source converter designs each director switch unit has an associated clamp capacitor. The method of controls involves switching the semiconductor switching elements of the director switch units to transition the director switch between conducting and non-conducting states where the timing of switching of a semiconductor switching element is based on the voltage level of the associated clamp capacitor and also the degree of any voltage imbalance between the clamp capacitors of the director switch units. A control apparatus may determine suitable switching control signals.

Abstract: This application relates to a voltage source converter, especially for use in High Voltage Direct Current power distribution/transmission, and to methods of control of such a voltage source converter. The voltage source converter has at least one phase limb having a high-side DC terminal, a low-side DC terminal and an AC terminal. In embodiments of the invention each phase limb comprises a voltage wave-shaper operable, in use, to provide a selectively variable voltage level. Each phase limb also has a switch arrangement operable to provide at least first and second switch states. In the first switch state the low-side DC terminal is electrically connected to the AC terminal via a first path that includes the voltage wave-shaper. In the second switch state the high-side DC terminal is electrically connected to the AC terminal via a second path that includes the voltage wave-shaper.

Abstract: Methods and apparatus for hard switching of Alternate-Arm-Converter voltage source converters. Such voltage source converters have a phase limb with a high and low side converter arm connecting an AC terminal to a high and low side DC terminal, respectively, including a chain-link circuit in series with a director switch. Each chain-link circuit includes series connected cells that can be switched to generate a controlled voltage across the chain-link circuit. In embodiments, a controller turns-off the director switch of a converter arm that is conducting current in response to a hard-switching request for a first phase limb. In response to a hard-switching request, the controller controls the chain-link circuits of the first phase limb at any point in a phase cycle to control: a DC voltage across the director switch and/or the current flowing through the director switch to a predetermined level before turning the director switch off.

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.

Abstract: A method of controlling a converter including DC terminals for connection to a DC network, the converter including a limb between the DC terminals, each limb including a phase element having switching elements and a AC terminal for connection to an AC network, the switching elements being configured to switch interconnecting a DC and AC side voltage; a sub-converter connected in series with the DC side of an electrical block and controllably become a first voltage source; and a sub-converter connected in parallel with the block, configured to controllably become a second voltage source. The method includes obtaining a DC side voltage and converter demand which the corresponding limb and converter track; determining a sub-converter voltage that each sub-converter must contribute to track the corresponding required DC side and converter voltage; controlling each sub-converter to achieve the corresponding determined voltage; and determining one or more optimal sub-converter voltages.

Abstract: The control circuit includes first and second primary terminals for connection to a DC network, a secondary terminal connected in series between the first and second primary terminals and at least one auxiliary energy conversion element and an auxiliary terminal. The first and second primary terminals have a plurality of modules and a plurality of primary energy conversion elements connected in series therebetween to define a current transmission path, each module including at least one energy storage device, each energy storage device being selectively removable from the current transmission path.

Abstract: Methods and apparatus for hard switching of Alternate-Arm-Converter voltage source converters. Such voltage source converters have a phase limb with a high and low side converter arm connecting an AC terminal to a high and low side DC terminal, respectively comprising a chain-link circuit in series with a director switch. Each chain-link circuit comprises series connected cells that can be switched to generate a controlled voltage across the chain-link circuit. In embodiments, a controller turns-off the director switch of a converter arm that is conducting current in response to a hard-switching request for a first phase limb. In response to a hard-switching request, the controller controls the chain-link circuits of the first phase limb at any point in a phase cycle to control: a DC voltage across the director switch; and/or the current flowing through the director switch to a predetermined level before turning the director switch off.

Abstract: A voltage source converter of the controlled transition bridge type, having three phase limbs, each phase limb having a high &de 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 director switch being turned on. 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: Described is an electrical machine, including: a rotor having a magnetic flux source mounted thereto; a stator winding arrangement having a first set of electrical connections to provide a first output channel, and a second set of electrical connections to provide a second output channel, the first and second channels being electrically out of phase, wherein the stator winding arrangement is constructed from a plurality of winding portions which are connected in electrical series.

Abstract: One circuit includes first and second primary terminals for connection to first and second power transmission lines and a current transmission path extending between the primary terminals and having current transmission path portions separated by a third primary terminal. A first current transmission path portion includes at least one primary switching element connected in series between the first and third primary terminals, the second current transmission path portion includes an energy conversion block connected between the second and third primary terminals, and the energy conversion block includes at least one primary energy conversion element for removing energy from the power transmission lines. The control circuit further includes a converter limb connected across the second and third primary terminals that includes an auxiliary converter. The control circuit further includes a control unit which controls the auxiliary converter to selectively provide a voltage source.