This paper presents the development of inverter simulation model in Grid-Connected Photovoltaic System (GCPV) in Matlab/Simulink software. This work is a part of the development of a complete GCPV system simulation model. The inverter simulation model accepts solar irradiance and temperature parameters as inputs (at PV array) and outputs AC power.  A phase-shift control method is used to ensure that the inverter output is synchronized with unity power factor to the utility grid.  The developed model is validated against data obtained from an actual installed GCPV system at Malaysia Green Technology Corporation (MGTC) in Bangi, Malaysia with system capacity of 45.35 kWp. The validation of model is through Root Mean Square Error (RMSE) and Mean Absolute Percentage Error (MAPE). Results showed that inverter output power from simulation is acceptable with small deviation from the actual data. This is due to inaccuracies of predicting de-rating factors listed in this work.