Investigation On Modeling Method Of Photovoltaic Generation Systems

Due to the intermittent and uncertainty of photovoltaic(PV)generation system,largescale PV power plants will exert non-negligible influence on the safe and stable operation of the power system.Furthermore,large PV power station usually consists of hundreds of PV units.In order to access the influence of large-scale PV groups upon the power system,researches on the effective and equivalent model of PV generation systems are urgently needed.Establishing the model that can exactly characterize the dynamic behaviors of actual PV system under balanced voltage dip is the basis of PV system modeling.This paper includes the PV system balance-voltage-dip model by modeling the PV array,the maximum power point tracking(MPPT)and the active and reactive decoupling control,respectively.The active and reactive current reference during the whole low voltage ride through(LVRT)periods is formulated according to the grid-connected standard of PV system.These obtained reference values are sent to the current controller for the model control.The accuracy of this modeling method is confirmed by field test results.To improve the universally applicability of PV model,the condition under unbalanced voltage dip is researched.Due to the variety of real response in actual PV system,as well as the otherness of current distortion and active/reactive power fluctuation,the power quality factor is induced based on the relationship of the current and power fluctuation under unbalanced voltage dips.Multi-objective coordinated control is proposed.As last,the dynamic responses of the PV system model is proved coincident with the actual PV system during the whole LVRT process.To improve the rapidity and accuracy of the PV station model,this paper has studied the equivalent modeling method of PV station.A PV station consists of three PV units is given to formulate the function expression of dynamic behaviors under the whole LVRT period.It is found that the error of the traditional equivalent method is caused by the power error during the fault-duration and the error during fault-recovery period.This conclusion can be applied to more complicate PV station and the improved equivalent modeling method of PV station is proposed based on the dynamic analysis under LVRT period.At last,simulations based on several groups of field test results are carried out and the result indicates that the proposed equivalent modeling method shows good performances under different working conditions and voltage dips.