Application of Battery State of Charge Swing Control for Overall Performance Improvement in Diesel-Solar Hybrid Off-Grid Power Systems

For the improved performance of hybrid electric vehicles, new control strategies have been proposed in the recent literature to limit the operation of Internal Combustion Engine (ICE) in a high efficiency region on the torque-speed plane with the help of battery energy storage. While maintaining the operation of ICE in a constant high efficiency region has been proved as optimum for some drive cycles, operation of ICE in a variable high efficiency region in tandem with a battery state of charge swing control strategy has been shown as the best strategy for some other drive cycles. This paper proposes to apply such novel control strategies to reduce the fuel utilization, increase battery life and minimize diesel engine start-ups in meeting the variable, predictable energy demand of an off-grid power system utilizing a variable-speed diesel generator, a solar photovoltaic array and a battery bank. The paper demonstrates through computer simulations for varying size battery banks, a variable charging current strategy with a variable high efficiency region of ICE yields best overall performance of the system.