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: A power transmission network including a single-phase or multi-phase AC electrical system, a converter including an AC terminal, a point of common coupling, a phase reactance connecting the common coupling to each AC terminal, and a transmission medium to interconnect the common coupling and the electrical system. The network includes a controller to: process the voltage and current at the common coupling to compute a state vector; derive a converter demand by combining the state vector with control parameters, including the capacitance of the power transmission medium presented at the common coupling and the impedance of the phase reactance; and operate the converter according to demand controlling the voltage at each terminal and/or the common coupling to inhibit any perturbation in the converter voltage from a target converter voltage or range resulting from the interaction between the capacitance of the power transmission medium and the impedance of the phase reactance.

Abstract: A power transmission network including a single-phase or multi-phase AC electrical system, a converter including an AC terminal, a point of common coupling, a phase reactance connecting the common coupling to each AC terminal, and a transmission medium to interconnect the common coupling and the electrical system. The network includes a controller to: process the voltage and current at the common coupling to compute a state vector; derive a converter demand by combining the state vector with control parameters, including the capacitance of the power transmission medium presented at the common coupling and the impedance of the phase reactance; and operate the converter according to demand controlling the voltage at each terminal and/or the common coupling to inhibit any perturbation in the converter voltage from a target converter voltage or range resulting from the interaction between the capacitance of the power transmission medium and the impedance of the phase reactance.

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: 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: A voltage source converter including a DC terminal for connection to a DC electrical network, and a converter limb operatively connected to the DC terminal. The converter limb including at least one limb portion operatively connected to an AC terminal. The limb portion including a valve, the valve including at least one module, the module including at least one switching element and at least one energy storage device, the switching element and each energy storage device in the module combining to selectively provide a voltage source. A controller including a valve voltage demand sub-controller. The controller being configured to provide AC and DC output voltage demands to the valve voltage demand sub-controller. And, a switching control unit configured to control switching of the switching element in the module so as to generate a voltage across the valve.

Abstract: A control apparatus configured to control a chain link voltage source converter, the control apparatus comprising; two converter controllers, each converter controller configured to receive a measure of the output voltage and/or current from the converter and determine a control signal therefrom for controlling the voltage source converter, each converter controller including at least one integrator element configured to perform an integration operation and output an integrator term in said determination of the control signal, a selector configured to select which one of the converter controllers provides its control signal to the converter; wherein each integrator element is configured to have two modes, a first mode in which the integrator element determines the integrator term and a second mode in which the integrator term is provided by a corresponding integrator element in the other converter controller.

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: 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: A controller (40), for controlling a multiphase voltage source converter, comprises a vector control module (42) that is configured to generate multiphase voltage demand waveforms (va, vb, vc) that the voltage source converter subsequently is required to provide. The vector control module (42) generates the multiphase voltage demand waveforms (va, vb, vc) from respective converter voltage output phase waveforms (Va, Vb, and Vc) that are measured at corresponding AC outputs of the voltage source converter. The vector control module (42) includes a transformation element (44) which is configured to transform the respective converter voltage output phase waveforms (Va, Vb, and Vc) into symmetrical sequence rotating reference frame terms. The vector control module (42) also includes a distortion element (46) that is configured to introduce harmonic distortion into the generated multiphase demand waveforms (va, vb, vc).

Abstract: A control apparatus configured to control a chain link voltage source converter, the control apparatus comprising; two converter controllers, each converter controller configured to receive a measure of the output voltage and/or current from the converter and determine a control signal therefrom for controlling the voltage source converter, each converter controller including at least one integrator element configured to perform an integration operation and output an integrator term in said determination of the control signal, a selector configured to select which one of the converter controllers provides its control signal to the converter; wherein each integrator element is configured to have two modes, a first mode in which the integrator element determines the integrator term and a second mode in which the integrator term is provided by a corresponding integrator element in the other converter controller.

Abstract: A voltage source converter including a DC terminal for connection to a DC electrical network, and a converter limb operatively connected to the DC terminal. The converter limb including at least one limb portion operatively connected to an AC terminal. The limb portion including a valve, the valve including at least one module, the module including at least one switching element and at least one energy storage device, the switching element and each energy storage device in the module combining to selectively provide a voltage source. A controller including a valve voltage demand sub-controller. The controller being configured to provide AC and DC output voltage demands to the valve voltage demand sub-controller. And, a switching control unit configured to control switching of the switching element in the module so as to generate a voltage across the valve.

Abstract: A voltage source converter for high voltage DC power transmission is disclosed. According to one aspect, the voltage source converter is connectable between a DC network and another electrical network to interconnect the DC network and the other electrical network. The voltage source converter includes a converter unit configured to convert power flowing between the DC network and the other electrical network and at least one fault unit. One or more of the fault units includes at least one fault module having a voltage source that is operable, in the event of a short circuit in a DC network connected to the voltage source converter, to produce a voltage that acts to reduce current flowing through the voltage source converter and the short circuit.

Abstract: A circuit for a hybrid voltage source converter suitable for high voltage DC power transmission and reactive power compensation. The circuit comprises an assembly of electrically interconnected elements (Elements 1 to 20) including a plurality of first elements (Elements 1 to 6) and a plurality of second elements (Elements 7 to 20). Each of the first and second elements is configurable to be bypassed, to be disconnected or to include a circuit arrangement of one or more electronic components to construct, in use, a hybrid voltage source converter including at least one first element and at least one second element and in which the circuit arrangement included in the or each first element is different to the circuit arrangement included in the or each second element.

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 circuit breaker for high voltage direct current (HVDC) power transmission includes a module with a pair of terminals for connection to an electrical network, and four of conduction paths. Each first conduction path includes a mechanical switch connected in series with at least one first semiconductor switch to selectively allow current to flow between the first and second terminals through the first conduction path in a first mode of operation or commutate current from the first conduction path to the second conduction path in a second mode of operation. The second conduction path also has a semiconductor switch to selectively allow current to flow between the terminals through the second conduction path or commutate current from the second conduction path to the third conduction path in the second mode of operation.

Abstract: A circuit breaker apparatus for use in high voltage direct current (HVDC) power transmission is provided. The circuit breaker apparatus has one module or a plurality of series-connected modules, the or each module including: first, second, third and fourth conduction paths and first and second terminals for connection to an electrical network, each conduction path extending between the first and second terminals, the first conduction path including a mechanical switching element, the second conduction path including at least one semiconductor switching element, the third conduction path including a snubber circuit having an energy storage device and the fourth conduction path including a resistive element.

Abstract: A circuit breaker apparatus (32) comprises one module (30) or a plurality of series-connected modules (30), the or each module (30) including: first and second conduction paths (34, 36); and first and second terminals (38, 40) for connection to an electrical network (42), each conduction path (34, 36) extending between the first and second terminals (38, 40); the first conduction path (34) including a first vacuum switching element (52) to selectively close to allow current to flow between the first and second terminals (38, 40) through the first conduction path (34) in a first mode of operation, or open to block current from flowing between the first and second terminals (38, 40) through the first conduction path (34) in a second mode of operation; the second conduction path (36) including a second vacuum switching element (56) to selectively open to block current from flowing between the first and second terminals (38, 40) through the second conduction path (36) in the first mode of operation, or close to a

Abstract: A voltage source converter for high voltage DC power transmission is disclosed. According to one aspect, the voltage source converter is connectable between a DC network and another electrical network to interconnect the DC network and the other electrical network. The voltage source converter includes a converter unit configured to convert power flowing between the DC network and the other electrical network and at least one fault unit. One or more of the fault units includes at least one fault module having a voltage source that is operable, in the event of a short circuit in a DC network connected to the voltage source converter, to produce a voltage that acts to reduce current flowing through the voltage source converter and the short circuit.

Abstract: A circuit for a hybrid voltage source converter suitable for high voltage DC power transmission and reactive power compensation. The circuit comprises an assembly of electrically interconnected elements (Elements 1 to 20) including a plurality of first elements (Elements 1 to 6) and a plurality of second elements (Elements 7 to 20). Each of the first and second elements is configurable to be bypassed, to be disconnected or to include a circuit arrangement of one or more electronic components to construct, in use, a hybrid voltage source converter including at least one first element and at least one second element and in which the circuit arrangement included in the or each first element is different to the circuit arrangement included in the or each second element.