Bipolar double voltage cell and multilevel converter with such a cell

摘要

A multilevel converter cell includes a first section with a first group of series connected switching units in parallel with a first energy storage element, where a junction between a first and second switching units of the first group of series connected switching units forms one cell connection terminal, a second section with a second group of series connected switching units in parallel with a second energy storage element, where a junction between a third and fourth switching units of the second group of series connected switching units forms another cell connection terminal, and an interconnecting section with a third group of series-connected switching units comprising a fifth, sixth and seventh switching unit, with the fifth and sixth switching units connected in parallel with the first energy storage element and the sixth and seventh switching units connected in parallel with the second energy storage element.

主权项

1. A cell for use in a phase arm of a multilevel converter converting between alternating current and direct current, said cell comprising:
a first section with a first group of series connected switching units, which first group is connected in parallel with a first energy storage element, where a junction between a first and a second switching unit of the first group forms a first cell connection terminal; a second section with a second group of series connected switching units, which second group is connected in parallel with a second energy storage element, where a junction between a third and a fourth switching unit of the second group forms a second cell connection terminal; and an interconnecting section interconnecting the first and the second sections and comprising a third group of series-connected switching units, which third group comprises a fifth, sixth and seventh switching unit, where the fifth and sixth switching units are connected in parallel with the first energy storage element and the sixth and seventh switching units are connected in parallel with the second energy storage element, wherein the switching units are controllable to provide a first voltage contribution state that provides a voltage contribution that is a sum of the voltages of the first and second energy storage element, and a second voltage contribution state that provides a voltage contribution caused by the first energy storage element being connected in parallel with the second energy storage element, and wherein the first and second voltage contribution states are positive voltage contribution states, and the second state is obtained when the first, fourth, fifth and seventh switching units are on.