Yq. Chen et al., Unified power flow controller (UPFC) based on chopper stabilized diode-clamped multilevel converters, IEEE POW E, 15(2), 2000, pp. 258-267
As the diode-clamped, multilevel converter has been found to have attractiv
e features for STATCOM application, there is interest in extending it to UP
FC application by using multilevel converters as the series and the shunt c
onverters. Unfortunately, as is demonstrated in this paper, the de voltages
at their de links, are inherently unstable. Faced with this impasse, a sol
ution is sought in a system of local feedback controlled Class B choppers t
o equalize the dc.Laboratory experimental model establishes the feasibility
of the proposal. Digital simulations show that current ratings in the chop
pers need be only 10% of the current ratings in the converters. The chopper
cost is estimated as 1% of the cost of the multilevel converters.