Research On Grid-connected/off-grid Control Of Single-phase Cascade Photovoltaic Battery Hybrid System In Microgrid

The microgrid integrates distributed energy,energy storage systems,loads and related power electronics to address not only the randomness,intermittent and volatility of distributed energy to provide stable electrical energy,but also undertake the power supply mission after the grid fault,as a result,more and more studies have been conducted.In order to make the microgrid operate in a more efficient and economical state,a parallel/off-grid control method based on single-phase cascade Photovoltaic(PV)battery hybrid system in microgrid is proposed in this paper.The topology of single-phase cascade PV battery hybrid system is analyzed in this dissertation.The main circuit parameters are designed and the number of cascade links between PV cells and energy storage is selected.And the step wave modulation method and carrier phase shift SPWM method for cascaded PV battery hybrid system are analyzed.In the grid-connected research of cascaded PV battery hybrid system,combined with the economic benefits brought by time-of-use electricity price,three operating modes of optical storage hybrid energy storage system are proposed: power smooth mode,self-charging mode and night mode.Based on three modes,a layered control method is proposed for power smooth mode and self-charging mode,a nighttime control method is proposed for night mode,the effectiveness of the proposed method are verified by simulation.By performing vector analysis on off-grid operation,a closed-loop off-grid control method based on the inductor current inner loop of the PI and the voltage outer loop of the quasi-resonance is proposed.The closed-loop control method can obtain a stable off-grid voltage,but the system has high switching loss.Therefore,a hybrid modulation method combining the advantages of step wave method and carrier phase shift SPWM method is proposed,which can obtain lower switching loss,then the hybrid modulation method based on conduction angle and phase is analyzed,and the proposed off-grid control method is verified by simulation.On this basis,a hardware in-loop experimental platform for a single-phase cascade optical storage hybrid energy storage system has been established,the software and hardware design of the experimental platform was completed,and the proposed grid-connected/off-grid control method was verified.The experimental results verify the effectiveness of the proposed control method.