Zero-Current Switching Control of the Alternate Arm HVdc Converter Station With an Extended Overlap Period

The Alternate Arm Converter “Extended-Overlap” Mode: AC Faults

“…3 for the sake of clarity, smaller current components relating to SM capacitor energy regulation denoted by I circx (see Section II-B). Furthermore, both arms conduct current components relating to "active filtering" so that an ideally ripple free DC current can be obtained [24], [26]. When a DS is required to open at the end of an "overlap" period, "zero-current" turn-off is achieved by actually opening the DS when its anti-parallel diodes are conducting [44] (not shown in the valve currents of Fig.…”

“…This paper concerns the more recently disclosed "extendedoverlap" mode [24], [25], where the nominal "overlap" angular duration is 60 • [12]. This operating mode causes the AC currents sum to zero at a point within the converter and makes a conduction path for the DC current through a phase-leg always available and therefore a ripple free DC current can be obtained [12]; this attribute is termed "active filtering" [24], [26]. As the DC current no longer has a characteristic ripple, a bulky passive filter is not required and therefore the related drawbacks of the AAC described in [27] are resolved.…”

Review of technologies for DC grids – power conversion, flow control and protection

“…Whilst the latter increases the power capability with no filtering requirements at ac and dc sides, thanks to additional current path provided by the thyristor based director switches which conduct alternately, i.e., upper director switch conducts for half fundamental cycle with the upper arm of the FB-MMC and vice versa. The latter hybrid converter resolves the current commutation problem of the conventional AAC and its variants [39,40,42,53,54,57,90]. These hybrid converters are wellsuited for generic and large dc grids, , where the LCCs are expected to operate alongside VSCs.…”

“…1: High-level comparison MMCs the employ unipolar cells, and asymmetric and symmetric bipolar cells[42,50,54,[97][98][99][100][101][102][103][104][105][106][107][108][109], where P and Q stand for active and reactive powers, Vdc is the dc voltage, and Vdc0 stands for rated dc voltage.…”

“…2: High-level comparison selected hybrid converters (A≡ AAC, B≡ CMC-MMC, C≡ AFC-B converter, and D≡ hybrid converter with alternate common arm and director switches)[42,54,55,57,[110][111][112][113][114][115][116] …”