Research On Improvement Of Power Quality In Micro-Grid Containing Distributed PV Source

In order to relief the crisis of energy,new energy power industry has gained strong support from the world.With the development of micro-grid,photovoltaic(PV)source and the associated technologies,PV,as a kind of distributed generation,is increasingly applied in the micro-grid system and doing its job.Due to the particularity of PV and micro-grid system itself,compared to the traditional distribution network,micro-grid is prone to arise power quality problems.Power quality problems are restricting the development of micro-grid.Hence,it is necessary to make research on the control strategy to improve the power quality.Firstly,the structure of PV system is introduced,the equivalent circuit of PV is analyzed,and the mathematical model of PV cell is established.DC-DC converter,as the interface of PV,is designed,and the control strategy of maximum power point tracking(mppt)is verified to make mppt rapid and accurate under fast-changing environmental conditions.Secondly,the control strategies of power quality in micro-grid based on inverter are studied.In this paper,LCL is chosen as the filter of the system and the scheme of active damping is applied in the inverter to restrain the resonance peak of LCL.Repetitive controller combined with PI controller is analyzed and applied in current loop for PQ control and voltage loop for vf control to make the steady-state error of closed loop less and guarantee the dynamic performance of closed loop.Considering the harmonic problem caused by non-liner load,active filtering algorithm is explained and added into the control scheme of inverter.Considering the influence of three-phase unbalanced system,to damp voltage fluctuation in DC bus,the control strategy for inverter based on space phase analysis of the vector of voltage and current is analyzed.Besides,to suppress negative sequence component in AC bus,three unbalanced control strategy based on DSOGI-PLL including harmonic eliminating modules is studied.Finally,the control strategies of power quality in micro-grid based on hybrid energy storage are studied.The mathematical model of hybrid energy storage is established.To suppress the micro-grid power fluctuation and improve the quality of the PCC voltage,the energy management method for hybrid energy storage is designed,which can not only exert respective advantage of the energy storage components but also control the operation of energy storage components in the safe range.In order to maintain the phase angle of AC bus smooth during kinds of mode transfer condition,pre-synchronization phase control strategy is researched.Based on the pre-synchronization phase control strategy,in order to improve the quality of AC bus and DC bus,a novel control strategy for smooth tranfer between grid-connected and islanded operation modes of micro-grid is proposed,which can improve the overshoot of the system through resetting the output of outer loop so that the system can regain stability during the mode transfer.The simulation models of these control strategies are built in Matlab/Simulink environment.The simulation research has been carried on from four aspects,which are grid-connected&off-grid control strategy including repetitive controller of PV micro-grid,three phase unbalanced control strategy,energy management method for hybrid energy storage,control strategy for smooth switching between grid-connected and islanded operation modes respectively.The simution results of simulation verify that these strategies can improve power quality problems.