Modular MMC phase arm and control thereof
There is provided a method of controlling a plurality of converter cells in a phase arm of a modular multilevel converter (MMC) in accordance with a main reference. The method includes dividing the main reference into a plurality of reference parts, and, by using a grouping of the plurality of converter cells into a plurality of groups, operating a plurality of modulators in parallel, each modulator controlling a respective one of the groups of converter cells in accordance with one of the reference parts. A phase arm controlled in accordance with such a method is also provided, as well as an MMC including at least one such phase arm, and a converter station including at least one such MMC.
1. A method of controlling a plurality of converter cells in a phase arm of a modular multilevel converter (MMC) in accordance with a main reference, including:
dividing the main reference into a plurality of reference parts, and
by using a grouping of the plurality of converter cells into a plurality of groups, operating a plurality of modulators in parallel, each modulator controlling a respective one of the groups of converter cells in accordance with one of the reference parts, each modulator controlling its respective group of converter cells according to a sorting criterion, and each modulator balancing a voltage of its respective group of converter cells based on said sorting,
wherein:
one of the groups of converter cells controlled by one of the modulators includes converter cells of a first type, and another one of the groups of converter cells controlled by another one of the modulators includes converter cells of a second type different from the first type,
the main reference is a voltage value,
the reference parts are constructed according to a weighting factor based at least in part on a number of converter cells in a group, such that a sum of the reference parts corresponds to said voltage value, and
said sorting criterion includes an increasing or decreasing converter cell voltage.
2. A phase arm for a modular multilevel converter (MMC), wherein the phase arm includes a plurality of modulators and a plurality of converter cells groupable into a plurality of groups of converter cells, and wherein:
one of the groups of converter cells controlled by one of the modulators includes converter cells of a first type, and wherein another one of the groups of converter cells controlled by another one of the modulators includes converter cells of a second type different from the first type,
each modulator is configured to receive a reference part of a main reference and to, independent of and in parallel with any other modulator in the phase arm, control a respective one of the groups of converter cells in accordance with the received reference part, each modulator controlling its respective group of converter cells according to a sorting criterion, and each modulator balancing a voltage of its respective group of converter cells based on said sorting, wherein said sorting criterion includes an increasing or decreasing converter cell voltage, and
the phase arm is configured to:
receive the main reference as a voltage value,
divide the received main reference into a plurality of reference parts according to a weighting factor based at least in part on a number of converter cells in a group, such that a sum of the reference parts corresponds to said voltage value, and
provide one of the reference parts to each modulator.
3. The phase arm of claim 2 , wherein the first type is a half-bridge (HB) converter cell type and the second type is a full-bridge (FB) converter cell type.
4. A modular multilevel converter (MMC) including at least one phase arm according to claim 3 .
5. A converter station, including at least one MMC according to claim 4 .
6. A modular multilevel converter (MMC) including at least one phase arm according to claim 2 .
7. A converter station, including at least one MMC according to claim 6 .