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Abstract: The control strategy and modulation scheme of DC system have great effect on transient stability and dynamical stability in AC/DC hybrid power grid. In order to decrease the effect of UHVDC blocks and AC lines faults, a coordinated control strategy of emergency power modulation and small signal modulation is put forward by making use of the fast controllability and the overload capability of HVDC system. Simulation results show that the coordinated control strategy may decrease power loss and improve the dynamical stability of the AC/DC hybrid system. [Copyright &y& Elsevier]

Abstract: This paper analyzed the control strategy of dynamical reactive power in AC/DC hybrid power grid, and presented the limitation of the control strategy based on location bus voltage, which can improve the transient stability under AC line faults but not DC block faults. Thus, control strategy of STATCOM based on real-time wide-area signal was presented by introducing the tie-line power flow of power grid. To consider the transient stability, the dynamical stability and the voltage stability at the same time, a nonlinear control mode in sections is also proposed. Simulation results showed that the control strategy would increase the transient stability and improve the dynamical stability of the AC/DC hybrid system under AC line faults either DC block faults [Copyright &y& Elsevier]

• An intermediate band is presented in the main band gap of SnS 2 after Sb doping. • Sb can be doped at Sn site in SnS 2. • Sb-doped SnS 2 as a low cost and non-toxic absorber for IBSC has been proposed. Tin disulfide has attracted much attention on solar cell study due to its excellent optoelectronic properties in addition to just containing low-cost and non-toxic elements. Based on the HSE06-hybrid function calculations combined with Grimme's dispersion-correction method, a half-filled and delocalized intermediate band(IB) is presented in the main band gap of SnS 2 after partially Sb substituting on Sn site, which is made of the antibonding states of Sb-s and S-p states. Three-photon absorption can be realized in the doped sample and its corresponding absorption coefficient is enhanced at the visible light region thanks to the isolated and half-filled IB above the original valence band. Furthermore, Sb Sn always has the lowest formation energy than other Sb-related defects (i.e. Sb S and Sb i) based on the defect formation energy calculations. Therefore, Sb-doped SnS 2 is suggested as a promising candidate for the absorber of intermediate band solar cell. [ABSTRACT FROM AUTHOR]

• This paper establishes a small signal model of variable speed pumped storage unit with full size converter. • The oscillation modes and key influencing factors are clarified. • A coordinated control strategy for suppressing the ultra-low frequency oscillation is proposed. The research on control strategies of the variable speed pumped storage unit with full size converter (FSC-VSPSU), mainly focuses on the rapidity of power regulation. But the speed oscillation and slow speed regulation performance caused by fast power regulation are ignored, which is not conducive to the safe and efficient operation of the unit. This article investigates the dynamic stability characteristics of the FSC-VSPSU in detail. In turn, the stability risks are clarified and serve for the design of its control strategy and the improvement of operational efficiency. The small-signal model of FSC-VSPSU considering the variation of water head and load in fast power mode is established. The dominant instability control link and key parameters are revealed based on the eigenvalue analysis. Oscillation mode analysis shows that the unit has a wide-band oscillation characteristic. The dominant oscillation mode is the ultra-low frequency oscillation (ULFO) caused by the governor control system. To suppress the ULFO and improve the optimal speed tracking performance of the unit to the greatest extent, a coordinated control strategy of governor variable parameter control and governor power system stabilizer (GPSS) is proposed. The electromagnetic transient simulation based on PSCAD verifies the effectiveness of the proposed measures. [ABSTRACT FROM AUTHOR]

Chalcopyrite compounds like Cu(In,Ga)(S,Se) 2 have been widely studied as the absorber for single-junction solar cell. Other wide band gap Chalcopyrite compounds like CuGaS 2 have been utilized as the host of the absorber for intermediate band solar cell (IBSC). Here, a Chalcopyrite compound LiGaTe 2 with a suitable band gap as the host of the absorber for IBSC has been investigated by HSE06 first-principles calculations. Our results revealed that a partially-filled and isolated intermediate band (IB) is generated in the forbidden band gap of LiGaTe 2 after group ⅣA elements (i.e., Si, Ge and Sn) substituting at Ga site and three-photon absorption can be achieved in the doped systems. Combining the suitable IB position induced by Sn-doping and its low formation energy, Sn-doped LiGaTe 2 as a promising candidate has been proposed to be the absorber for IBSC. [ABSTRACT FROM AUTHOR]