Low Voltage Ride Through Control Of Photovoltaic Grid-connected Inverter Based On Model Predictive Control

With the depletion of non-renewable energy sources,human beings are accelerating the development of new energy sources,among them.Solar energy has been focused on development and utilization.The impact of photovoltaic systems on the power grid has become more and more important as its use has expanded.If the photovoltaic power generation system fails and has a large area of off-grid accident,it will have a great impact to the power grid.So the low voltage rides through(LVRT)capability of grid-connected PV system under the voltage drops is demand according the new grid codes or standards.The three-phase grid-connected inverter is being taken as the research object.The LVRT control strategy based on model predictive control is studied.Firstly,the mathematical model of the inverter was established.Based on it,the proportional resonant control method is studied.Aiming at some problems in the proportional resonant control method,the three-phase inverter model predictive control strategy is studied.Based on the basic principle of model predictive control algorithm,a model predictive control model of three-phase grid-connected inverter was established.The simulation model was built to verify the feasibility of the control strategy and compared with the PR control method.Secondly,for the low voltage ride-through problem of photovoltaic grid-connected networks,the low voltage ride-through control strategy based on model predictive control is studied.The types of voltage drop faults in the power grid are introduced.The voltage drops type detection method,positive and negative sequence separation method and system control structure were studied and analyzed.Based on the instantaneous power theory,the reference current commands of three control objectives were deduced.LVRT strategy based on model predictive control eliminates active power fluctuations.By injecting reactive power to raise the positive sequence voltage of the common connection point(PCC),the negative sequence voltage was reduced.Meanwhile the unbalance degree was decreased.The current limiting measures taken prevent the over current problem of the grid-connected inverter from being effectively prevented,and low voltage ride through is realized.Finally,this paper builds an experimental platform for three-phase inverter based on dSPACE real-time simulation system.The proposed control strategy is verified experimentally.The results prove that the feasibility and accurateness of the adopted strategies.