Energy Balance Based Grid Tied Battery Connected Multistage Bidirectional PV Inverter System

Renewable energy resources especially solar is emerging as the modern power sources to electrify remote areas and to power the modern industry.The main reason behind there emergence is due to their environment friendly behavior,unlimited availability and short period for replenishment over nonrenewable energy resources.Due to these reasons renewable energy penetration in smart grids is more feasible than nonrenewable resources,economically as well as technically.The smart grid power systems are becoming more and more complex due to integration of multiple renewable energy sources,electric vehicles and storage systems.This complex structure consists of multistage power inverters,converters and their control units.Power inverters and converters are responsible for inversion and rectification operations respectively whereas their control units are accountable for switching of inverters and converters to properly manage the power flow between power sources like PV,Grid and Battery.To control the power flow more flexibly between aforementioned sources,different control techniques have been proposed in literature.With similar objective,a similar system which consist of MPPT power extraction from PV and power flow between PV,Grid and Battery;and a proposed control algorithm is presented in this research work.The intermittent nature of PV requires a strategy to extract maximum power from the available PV power.Therefore,Perturb and observe(P&O)MPPT algorithm is implemented on buck converter which extracts maximum power from PV with the desired voltage for the battery charging.During power flow from DC side to AC side,an energy balance algorithm is proposed which stabilizes energy stored in the DC-link capacitor thereby stabilizing DC-link voltage and DC-bus voltage to meet the battery requirement of 48 V and grid requirement of over 311 V across the DC-bus capacitor.The proposed energy balance algorithm generates the reference grid current for current control algorithm which controls the inverter to inject balanced sine wave current into the grid which meets the Grid requirement of balanced sine wave current injection.Hence fulfilling the battery requirements and grid current requirements,the proposed algorithms accordingly balance the voltage across the DC-link capacitor and controls the inverter to inject sine wave current into the grid.Similarly,during power flow from grid to the battery,a simple control algorithm controls the inverter and converter bridges in reverse direction to rectify the 220 V rms grid voltage into 48 V DC for charging the battery.The system shows an excellent performance based on the proposed algorithms which includes tracking accuracy,tracking speed,settling time and overshoot,which can be analyzed in the simulation results.