Mechanism Analysis of Additional Damping Control Strategies for the High-frequency Resonance of MMC Connected to AC Grid

High-frequency resonance can occur when a modular multilevel converter(MMC)is inserted into an AC grid.Additional damping control is a relatively low-cost resonance suppression strategy compared to passive damping strategies.This paper analyzes the influences of a feed-forward voltage filter and feedback current filter for the inner controller for the high-frequency impedance characteristics of the MMC based on a model.Moreover,the mechanism,influencing factors,and limitations of the existing strategy including an additional lowpass filter in the voltage feed-forward stage are investigated.Secondly,a resonance suppression strategy for the inclusion of additional cascaded notch filters in the voltage feed-forward stage is proposed,and its parameter design method and applicable scenarios are analyzed.In addition,this paper analyzes the effects of the inclusion of an additional control in other stages for the inner controller of the MMC.Finally,the correctness of the theoretical analysis and the proposed strategy is verified based on the simulation of an actual project on PSCAD/EMTDC.

Over 18.2%efficiency of layer–by–layer all–polymer solar cells enabled by homoleptic iridium(Ⅲ)carbene complex as solid additive

The vertical phase distribution of active layers plays a vital role in balancing exciton dissociation and cha rge transport for achieving efficient polymer solar cells(PSCs).The layer-by-layer(LbL)PSCs are commonly prepared by using sequential spin-coating method from donor and acceptor solutions with distinct solvents and solvent additives.The enhanced exciton dissociation is expected in the LbL PSCs with efficient charge transport in the relatively neat donor or acceptor layers.In this work,a series of LbL all-polymer solar cells(APSCs)were fabricated with PM6 as donor and PY-DT as acceptor,and triplet material m-Ir(CPmPB)_(3)is deliberately incorporated into PY-DT layer to prolong exciton lifetimes of active layers.The power conversion efficiency(PCE)of LbL APSCs is improved to 18.24%from 17.32%by incorporating 0.3 wt%m-Ir(CPMPB)_(3)in PY-DT layer,benefiting from the simultaneously enhanced short-circuit current density(Isc)of 25.17 mA cm^(-2)and fill factor(FF)of 74.70%.The enhancement of PCE is attributed to the efficient energy transfer of m-Ir(CPmPB)_(3)to PM6 and PY-DT,resulting in the prolonged exciton lifetime in the active layer and the increased exciton diffusion distance.The efficient energy transfer from m-Ir(CPmPB)_(3)to PM6 and PY-DT layer can be confirmed by the increased photoluminescence(PL)intensity and the prolonged PL lifetime of PM6 and PY-DT in PM6+m-Ir(CPmPB)_(3)and PY-DT+m-Ir(CPmPB)_(3)films.This study indicates that the triplet material as solid additive has great potential in fabricating efficient LbL APSCs by prolonging exciton lifetimes in active layers.