Five level cross connected cell for cascaded converters

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

“…The synchronization of the main power stage and cascaded FB cells is achieved by slowing down the rate of change of their respective output voltages and by restricting the switching transition to one voltage level per modulation period. When considering the number of devices in the conduction path and the current stresses per device, the proposed converter is expected to be competitive with the hybrid converters in [2,14,15,18].…”

“…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].…”

“…Based on active controlled power electronic components, the dc transformer is presented in [10,12]. Although it has been claimed this approach can isolate dc faults rapidly and contribute to dc voltage and power flow control, these added functionalities are achieved at the expense of much higher capital cost and power losses, and a larger footprint compared to that suggested in [11,[13][14][15][16].…”

Full bridge MMC converter optimal design to HVDC operational requirements

“…Several topologies of DC fault tolerant MMC have been reported in the literature [9] - [18], such as the MMC using the clamp double submodules [9], the hybrid cascaded multilevel converter (HCMC) [10], the alternate arm converter [11], a series connected double sub-module [12], the cross-connected half-bridge submodules [13], the hybrid MMC with HB submodules at the DC side and FB submodules at the AC side [14]- [15], the MMC based on unipolar voltage full-bridge SM and three-level cross-connected SM [16], the MMC based on FB (full bridge) submodules [9], [17]- [18] and the MMC with mixed HB submodules and FB submodules [19]- [21]. Among all these DC fault tolerant MMCs, the MMC based on FB submodules (including the mixed submodules MMC) is the only commercially available fault tolerant technology for HVDC application.…”