Conventional PV systems integrated with a battery connect the array and the energy storage unit to a dc-link through individual dc-dc converters for maximum power point tracking (MPPT) and battery charge control. This paper proposes a new system configuration, which connects the PV array and battery unit to the dc-link of the system inverter via a single dc-dc converter capable of simultaneously operating as a charge controller and MPPT device. This dc-dc converter is controlled such that it charges/discharges the battery with the amount of power required to maintain the PV array at its MPPT reference voltage. The proposed system ensures that the PV array operates at its MPP for all irradiance conditions, therefore increasing the PV system capacity factor as well as ensuring MPPT stability for all irradiance conditions. Also, this configuration may also be adopted for PV power smoothing, where the curtailed power may be used to smooth the PV inverter output without sacrificing battery state of charge (SOC). The behavior of the proposed system is studied and simulated in PSCAD TM /EMTDC TM . The computations are compared with experimental data retrieved from the LG&E and KU E.W. Brown universal solar facility, which houses a 10MW(ac) PV farm and a 1MW/2MWh battery energy storage system (BESS). The results show that for the examples considered, and allowing curtailment adapted to the current power ratings of the system, an increase in the capacity factor of up to 20% is possible.
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The authors thank Dr. David Link of LG&E and KU and the team of technical experts from Nayak Corp. for their technical advice and contributions. The support of University of Kentucky, the L. Stanley Pigman endowment, Power and Energy Institute of Kentucky (PEIK), and of LG&E and KUis gratefully acknowledged.
Akeyo, Oluwaseun M.; Rallabandi, Vandana; Jewell, Nicholas; and Ionel, Dan M., "Improving the Capacity Factor and Stability of Multi-MW Grid Connected PV Systems with Results from a 1MW/2MWh Battery Demonstrator" (2018). Power and Energy Institute of Kentucky Faculty Publications. 29.