Study On Reactive Voltage Control Of Photovoltaic Microgrid

Solar energy has received worldwide attention with its advantages of cleanliness,renewable and flexibility.Photovoltaic(PV)microgrid is one of the effective ways to develop and utilize solar energy.However,the intermittency,randomness and volatility of solar energy affects the voltage quality of PV microgrid.How to use effective reactive voltage control method to control the output power of DG and make the system load realize reasonable distribution among DGs is the key to study the reactive voltage of PV microgrid.Therefore,this thesis studies the problem of reactive voltage control in PV microgrid,which has certain application value and theoretical significance.Firstly,the factors affecting the voltage fluctuation of PV microgrid are analyzed.The mechanism of voltage fluctuation caused by distributed PV source is further analyzed.The reactive voltage characteristics of microgrid with distributed PV source are given.PV microgrid reactive voltage mathematical model is established.Secondly,aiming at the voltage problem caused by PV source difficulty in reasonably distributing load according to droop gain,thesis compares three grid connected control strategies(PQ,V/f and droop control).Thesis presents an improved droop control strategy based on virtual impedance.A virtual impedance feedback loop is introduced in the voltage current controller,which makes the DG output impedance present perceptual.That can solve the power coupling problem when droop control is applied to low-voltage microgrid.After that,the output voltage of each micro source is subtracted from the point of common coupling as compensation.An improved droop control equation is constructed.By adjusting the compensation coefficient Ku,reactive power can be reasonably distributed among DGs,which reduces the influence of line impedance mismatch on traditional droop control,maximizing the capacity of PV grid-connected inverter,and improves the voltage quality of micro grid.Finally,Matlab/Simulink environment has set up a simulation model of the PV microgrid system.Simulation analysis of traditional droop control and improved droop control shows the improved droop control strategy can realize the reasonable distribution of power between inverters,improving the voltage quality of the system.The control strategy is simple,and the dynamic characteristics are good.