Hybrid converter with ac side cascaded H‐bridge cells against H‐bridge alternative arm modular multilevel converter: steady‐state and dynamic performance

Hybrid Cascaded Modular Multilevel Converter With DC Fault Ride-Through Capability for the HVDC Transmission System

“…As a result the proposed HC-MMC is expected to have reduced on-state losses compared to hybrid converters presented in [11]. The use of the MMC in the main power stage, instead of a two-level converter or neutral-point clamped (NPC) converter as in [22][23][24], makes tracking of the voltage possible by sequential switching of the FB cells in and out the power path. For more detailed comparison with the recent state of art multilevel converters, please refer to references [16,22,[25][26][27].…”

“…The use of the MMC in the main power stage, instead of a two-level converter or neutral-point clamped (NPC) converter as in [22][23][24], makes tracking of the voltage possible by sequential switching of the FB cells in and out the power path. For more detailed comparison with the recent state of art multilevel converters, please refer to references [16,22,[25][26][27]. MMC can be controlled using hybrid modulation, where low and main power stages are controlled using two different modulation strategies [13]; or multilevel modulation, where the proposed converter is controlled as one unit using level shifted disposition carriers [19].…”

“…But the drawback of HC-MMC is that it requires more cell capacitors than FB-MMC, see Table II. For more detailed comparison with the recent state of art multilevel converters, please refer to references [16,22,[25][26][27].…”

Neutral-point-clamped hybrid multilevel converter with DC fault blocking capability for medium-voltage DC transmission

“…By employing IGBTs in series as director switches (DSs) in place of some SMs, the AAC and HCMC employ fewer SMs, and therefore can reduce the number and cost of power electronic devices. By using FBSMs as SMs, the two converters are capable of blocking the DC fault current during a pole-to-pole DC fault [16]. Under normal conditions, the DSs in the AAC operate at the fundamental frequency (i.e., 50/60 Hz), thereby reducing the switching loss of the DSs.…”

“…However, as analyzed in [14], the AAC needs to operate at the ''sweet spot'' to maintain the energy balance of stacks; thus, the modulation range is limited [17]. Compared with the AAC, the HCMC reduces the number of power electronic devices [16]. By employing a symmetrical modulation scheme [18,19], the modulation range of the HCMC can be [0, 4/p], which is wider than that of the AAC.…”