Abb Schweiz Ag

Abb Technology Ag

Abb Power Grids Switzerland Ag

Beat Buchmann

Simon Herold

Beat Ronner

Michail Vasiladiotis

Christoph Haederli

Jerome Fischer

Cosmin Banceanu

Bjoern Wider

A method of discharging a Modular Multilevel Converter (MMC) includes a plurality of phase legs connected in delta configuration. Each leg includes a plurality of series connected submodules, each submodule including an energy storage. The method includes disconnecting the MMC from an electrical grid, discharging the energy storages by means of a circulating current, and reconnecting the MMC to the electrical grid. The discharging includes, for each phase leg, setting a voltage reference, and sequentially selecting submodules in zero state by means of a sorting algorithm for switching each of the selected submodules to plus or minus state until the voltage deviation from the set voltage reference of the energy storage of each submodule in the phase leg is within a predefined range.

Voltage balancing in a Modular Multilevel Converter having delta configuration

A method of controlling a Modular Multilevel Converter (MMC) during a fault in a power grid to which the MMC is connected is disclosed. The MMC includes a plurality of phases, each including at least one phase leg. Each phase leg includes a plurality of series connected converter cells. The method includes determining that a fault has occurred in the power grid, the fault including a reduced voltage in the power grid. The method also includes, for each phase leg of the MMC, reducing the DC voltage of the phase leg by a predetermined amount from a nominal DC voltage to a reduced DC voltage, the DC voltage being the sum of all respective voltages over an energy storage of each cell of the phase leg. The method also includes determining that the fault has been cleared, whereby the voltage in the power grid is returned to nominal. The method also includes for each of the phase legs of the MMC, increasing the DC voltage back to the nominal DC voltage.

Control of MMC during fault

The present invention proposes a hybrid converter branch operating mode for a Modular Multilevel power Converter MMC with MMC cells in distinct subsets operating according to a 'pulse blocked' cell operation mode with DC cell voltage increase or according to a 'bypass' cell operation mode without DC cell voltage increase. Repeated cell subset assignment and corresponding alternation of cell operating mode allows to reduce or at least manage a mean deviation of the cell capacitor DC voltages of the converter cells. The invention also reduces no-load losses of the MMC in standby mode and a charging voltage in an MMC charging mode.

Standby and charging of modular multilevel converters

A modular cell for a phase leg of a Modular Multilevel power Converter (MMC) is disclosed. The cell includes a power storing device, a plurality of semiconductor switches, a cell controller, and a current sensor. The current sensor is connected between a current conducting line in the cell and the cell controller for measuring a current through the cell and signaling information about the measured current to the cell controller. The cell controller includes an optical communication interface and is configured for forwarding the information about the measured current to a higher level controller over the optical communication interface.

Modular multilevel converter cell with integrated current sensor

A method for operating a converter circuit is provided. The converter circuit includes a converter unit and a transformer. The transformer includes at least one winding set with a primary winding and a secondary winding. The converter unit is connected, on the AC voltage side, to the primary winding of the respective winding set. In order to compensate for undesirable saturation of the transformer, the converter unit is used to deliberately apply a DC voltage to the primary winding of the respective winding set of the transformer.

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Nussbaumen, Switzerland

Beat Buchmann