Abstract: A wind turbine that includes a housing, an asynchronous generator disposed in the housing and configured to be electrically connected to a power grid connection; a power converter circuit disposed in the housing and configured to be electrically connected to the asynchronous generator; and a variable impedance device disposed in the housing, connected to the generator and configured to limit current by varying impedance in response to a transient current. The wind turbine delivers reactive power to the power grid when the variable impedance device varies impedance in response to the transient current. The variable impedance device can be arranged in series between the asynchronous generator and the power grid connection, or can be in a shunt arrangement between the asynchronous generator and a neural point.

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 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 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 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: 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 wind turbine that includes a housing, an asynchronous generator disposed in the housing and configured to be electrically connected to a power grid connection; a power converter circuit disposed in the housing and configured to be electrically connected to the asynchronous generator; and a variable impedance device disposed in the housing, connected to the generator and configured to limit current by varying impedance in response to a transient current. The wind turbine delivers reactive power to the power grid when the variable impedance device varies impedance in response to the transient current. The variable impedance device can be arranged in series between the asynchronous generator and the power grid connection, or can be in a shunt arrangement between the asynchronous generator and a neural point.

Abstract: A control method and apparatus are provided to convert a DC voltage into alternating voltage. The apparatus includes a first inverter and a second inverter to generate a first alternating voltage and a second alternating voltage, respectively. Also included is an interphase transformer to combine these alternating voltages in parallel to obtain a first resulting alternating voltage. The apparatus also includes a third inverter and a fourth inverter to generate a third and fourth alternating voltage, respectively. These are combined to form a second resulting alternating voltage. The second resulting alternating voltage is displaced in phase approximately 180° in relation to the first resulting alternating voltage.

Abstract: A control method and apparatus are provided to convert a DC voltage into alternating voltage. The apparatus includes a first inverter and a second inverter to generate a first alternating voltage and a second alternating voltage, respectively. Also included is an interphase transformer to combine these alternating voltages in parallel to obtain a first resulting alternating voltage. The apparatus also includes a third inverter and a fourth inverter to generate a third and fourth alternating voltage, respectively. These are combined to form a second resulting alternating voltage. The second resulting alternating voltage is displaced in phase approximately 180° in relation to the first resulting alternating voltage.