Improved post‐fault operation strategy for a cascaded H‐bridge based STATCOM

A hybrid redundancy scheme for medium‐voltage three‐phase cascaded H‐bridge electronic power transformer

“…Meanwhile, the power in three phases will be rebalanced by increasing the DC voltage/power of the normal operational PM in the faulted phase. The detailed control strategies of the increasing DC voltage/power operations are discussed in [16][17][18][19][20][21]. When the charging process is complete, the DC voltages/power of the remaining normal operational PMs will decrease and the charged LR PMs will be in the operational mode.…”

“…Redundancy is a common approach to improve the reliability of the power-electronics-based apparatus. At present, relevant researches on redundancy mainly focus on MMCs [15][16][17], CHB-based static synchronous compensators [18], multilevel inverters [19][20][21] etc. By comparison, related researches about redundancy on the EPT are relatively less [22][23][24].…”

“…The redundancy schemes can be classified as the hot redundancy scheme [16][17][18][19][20][21][23][24][25][26][27] and the cold redundancy scheme [28,29], depending on the charging status of the DC capacitors of the redundant PMs.…”

“…More specifically, in the hot redundancy scheme, the redundant PMs work along with other PMs under normal operational conditions. When one PM fails, the faulted PM will be bypassed and the DC voltages or the modulation ratios of remaining healthy PMs in the faulted arm/phase will be increased to rebalance the power in different arms/phases [16][17][18][19][20][21]. This scheme is suitable for the HV MMC-HVDC, but not for EPTs employed in the MV fields, since the number of PMs in the EPT is small and the transition impact of healthy PMs cannot be ignored when the faulted PMs are bypassed.…”