Power Control Design of Microgrid Applied to Stand-Alone and Grid Connected Systems

Abstract

Due to intermittency in the natural sources and the variations in load, energy balance operation demands storage. The commonly preferred choice of energy storage in micro grid is valve regulated lead acid batteries. When batteries are used as energy storage, due to its low power density, the charge and discharge rate is low. It causes severe stress on the battery under quick load fluctuations and results in increase in the number of charge/discharge cycles. Hence, the lifetime of the battery reduces. The super capacitors have high power density and it can react speedily to quick load fluctuations. However, super capacitors alone cannot be used as energy storage as it cannot supply load for a longer time. Hence, this paper proposes a combined energy storage using batteries and super capacitors with high energy and power density. The photovoltaic (PV) based micro grid with combined energy storage is designed and the control strategy is validated for different atmospheric and load conditions. At present, DC microgrid is an effective solution to integrate renewable energy sources which are DC power supply with DC loads. A DC microgrid structure consisting of photovoltaic generation system, hybrid energy storage systems and AC main grid, is presented in this paper. A new power management strategy for this DC microgrid is proposed. The control strategy divides the DC bus voltage into seven ranges by six critical voltage values which are employed as the represents of power states and according to the range which the bus voltage belongs to the operation mode of the system can be automatically judged and switched freely. A hybrid energy storage system in this microgrid that contains two complementary type storage elements---battery and super-capacitor, can enhance the reliability and flexibility of the system based on their special supply logical. The proposed concept is done with grid connected mode and standalone mode or local loads. Further it is extended to industrial applications using an induction motor at the load and performance of the induction motor is observed and simulated using MATLAB/SIMULINK software.