The system identification scheme is shown in Fig.15. Good accuracy of models are achieved by selecting model structures and adjusting the model order of linear terms and nonlinear estimators of nonlinear systems. Finally, output voltage and current waveforms for any type of loads and operating conditions are then constructed from the models. This allows us to study power quality as required.
4.1 Steady state conditions
To emulate working conditions of PVGCS systems under environment changes (irradiance and temperature) affecting voltage and current inputs of inverters, six conditions of DC voltage variations and DC current variations. The six conditions are listed as Table 1. They are 3 conditions of a fixed DC current with DC low, medium and high voltage, i.e., FCLV (Fixed Current Low Voltage), FCMV (Fixed Current Medium Voltage) and FCHV (Fixed Current High Voltage) which shown in Fig. 16. The other three corresponding conditions are a DC fixed voltage with DC low, medium and high current, i.e., FVLC (Fixed Voltage Low Current), FVMC (Fixed Voltage Medium Current), and FVHC (Fixed Voltage High Current) as shown in Fig.17.
Fig. 16. AC voltage and current waveforms corresponding to FCLV, FCMV and FCHV conditions
Fig. 17. AC voltage and current waveforms corresponding to FVLC, FVMC and FVHC conditions