Standby and charging of modular multilevel converters
AssigneeABB Schweiz AG
InventorsSimon Herold, Beat Buchmann
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Abstract
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.
Claims14
A method of operating a Modular Multilevel Converter MMC having a converter branch with a plurality of converter cells with a nominal cell voltage, comprising
- applying a branch voltage to the converter branch, the branch voltage being inferior to a nominal branch voltage cumulative of the nominal cell voltages of the cells of the branch;
- selecting a first subset of the plurality of converter cells of the branch, and selecting a second subset of the plurality of converter cells which is distinct from the first subset;
- and
- operating successively the first and second subset in a pulse blocked cell operation mode with cell voltage increase, and operating a respective complementary subset of the plurality of converter cells of the branch in a bypass cell operation mode without cell voltage increase;
- wherein firing pulses or gate pulses to the plurality of converter cells being blocked or suppressed in the pulse blocked cell operation mode.
An MMC controller for operating a Modular Multilevel Converter MMC having a converter branch with a plurality of converter cells with a nominal cell voltage, the MMC controller being adapted to, following application to the converter branch of a branch voltage inferior to a nominal branch voltage that is cumulative of the nominal cell voltages of the cells of the branch;
- select a first subset of the plurality of converter cells of the branch, and select a second subset of the plurality of converter cells which is distinct from the first subset;
- operate successively the first and second subset in pulse blocked cell operation mode with cell voltage increase, and operate a respective complementary subset of the plurality of converter cells of the branch in bypass cell operation mode without cell voltage increase;
- wherein firing pulses or gate pulses to the plurality of converter cells being blocked or suppressed in the pulse blocked cell operation mode.
Dependencies are inferred from the claim text.