Energy management strategy for a battery-diesel stand-alone system with distributed PV generation based on grid frequency modulation

A hybrid PV-Battery-Diesel configuration is very attractive for stand-alone systems in terms of cost and reliability. In many applications, the battery and the diesel generator are centralized and generate the AC grid while the PV generators and loads are distributed and are connected to the grid. However, in these cases, long communication cables are required in order to reduce the PV power when the battery is fully charged. This paper proposes an energy management strategy which makes it possible to avoid the use of communication cables, rendering the system simpler, cheaper and more reliable. The strategy dictates that should a power reduction be required, the battery inverter increases the grid frequency. This is detected by the PV inverters, which continuously reduce their power in order to prevent the battery from overcharge or over-current. The strategy also optimizes the efficiency and operating life of the diesel generator. Simulation and experimental validation is carried out for a system with 10 kW PV generation, a 5 kVA battery inverter, a 5 kVA diesel generator and a 5 kVA load.This work was partially funded by the Spanish Ministry of Economy and Competitiveness under Grants DPI2009-14713-C03- 01 and DPI2010-21671-C02-01, by the Government of Navarra and the FEDER funds under project “Microgrids in Navarra: design and implementation” and by the Public University of Navarra