Search

Virtual Synchronous Generator (VSG) photovoltaic inverter still has the problems of surge current and voltage overcharge when the grid voltage drops. Aiming at the problems mentioned above, the comprehensive control strategy for AC/DC is proposed. The direct current (DC) side adopts the strategy of super-capacitor energy storing and switching Maximum Power Point Tracking (MPPT) derating, the alternating current (AC) side adopts the control strategy of virtual impedance and the vector difference of limited voltage, which are based on the quasi-proportional resonance. Particle swarm optimization (PSO) is used to optimize its parameters because of the difficulties in adjusting parameters of quasi-proportional resonance control by experience. This strategy can track on the voltage with no difference when the voltage is normal, it can also limit the overcharging voltage and the surge current into the demanded range when the voltage drops. Finally, the effectiveness of the strategy proposed in the paper is verified by simulation.

In previous papers, we reported the E-selectivity in the Wittig reaction of phosphorus ylid of the general formula Ph2R′CH2P=CHR (R=alkenyl; R′=H, alkenyl) and aldehydes. This continuing research for the stereochemistry of diphenylphosphorane in the title reaction of Ph2R′CH2P=CHR and R″CHO, where R=Ph, R′=H,Ph and R″=Ph,p-substituted phenyl, has led to thosimilar results. However, the E-selectivity is dependent on the ylid structure, reaction condition and the nature of the substituents on the aromatic ring. Generally the effect is stronger with benzyl diphenylphosphorane(R=H), the proportion of E olefin is produced in a larger quantity in salt-free condition than in the salt-containing medium, and the aromatic aldehyde bearing an electronwithdrawing group on the ring gives a higher E/Z ratio. Moreover, we also found that the logarithms of the E/Z ratio of the substituted stilbene products are linear with the σ constant of the substituents of the aromatic aldehydes: log E/Z=aσ+ b