Controlling the number of on-grid multiple photovoltaic inverters to improve their conversion efficiency

摘要

Two experimental PV-grid connected systems of 8.8 kWp and 36 kWp rating have been designed, installed and interfaced with Abu Dhabi utility grid. The PV arrays of both systems are interfaced with the grid via single phase grid-tied inverters. The inverters are installed in three separate groups that each injects 50 Hz, electricity into one phase of the utility grid at the 0.4 kV level. The main objective of this work is to develop a procedure that improves the conversion efficiency of the PV grid-tied inverters during low irradiance times. The procedure calculates the ideal rating of inverters that gives best possible conversion efficiency at different irradiances and ambient temperatures. The ideal rating is then rounded to actual rating corresponding to the practical specifications of the installed inverters. Consequently, the procedure is used to simulate optimal modes of operation that continuously control the number of active (on-grid) inverters in a way that yields best possible conversion efficiency. The evaluation procedure is applied theoretically to the 8.8 kWp and 36 kWp systems to determine their relevant optimal modes of operation. In order to validate the procedure, the simulated mode of operation related to the 8.8 kW system is applied actually. Suitable set of data evaluating the performance of the system is measured before and after applying the operation mode. The measured values, collected through real-time data monitoring system, are compared to its counterpart calculated values. The comparison showed satisfactory convergence between the two that validates the developed procedure.