Voltage Control Strategy For Grid-connected Inverter In Distribution Network To Reduce The Amount Of Light Curtailment

The research content of this article comes from the key project of Shanxi province's key research and development program "key technology of 10 MW lithium battery energy storage system and engineering demonstration sub-topic:theoretical research of energy storage system on improving the application of large-scale intermittent energy access to grid(201603D112001)".Due to impedance in low-voltage distribution network,the voltage is decreased gradually along the direction of power flow.And voltage at grid-connected point increases when PV output increases,and it may occurs over-voltage when PV output increases to a certain degree.In order to regulate the voltage and to limit the voltage deviation,a control strategy applied to grid-connected photovoltaic system(GCPVS)in distribution network is proposed.The effectiveness is verified based on Matlab/Simulink and dSPACE platforms respectively.The main contents are as follows:On account of the large ratio of line resistance and reactance in low-voltage distribution network,the voltage is decreased gradually along the direction of power flow.Based on this principle,the relationship among grid-side voltage,the voltage at PCC and power flow is deduced firstly to study over-voltage mechanism of GCPVS.Then,an active/reactive power and voltage(PQ(U))control strategy based on the magnitude of voltage at PCC and line impedance is proposed,in which the reference value of power is generated adaptivly accordingto three different over-voltage conditions(up over-voltage,no over-voltage and down over-voltage).During the up over-voltage at PCC,an active/reactive power matching method is designed to minimize the amount of light curtailment and maintain the voltage quality at grid-connected point.Secondly,due to aging problems of transmission line in the distribution network,the actual line impedance is not equal to the rated line value.As a result,the detection of line impedance,which is the reference value of PQ(U)control,based on the local signals is designed.Thirdly,PQ(U)control strategy for parallel operation of two photovoltaic grid-connected inverters is proposed based on PQ(U)control strategy for single inverter.Aimed at the problem of line impedance matches/mismatches from the others,and the voltage quality at grid-connected point can be maintained through this control strategy.Fourthly,PQ(U)power&voltage control strategy is verified through software Matlab/Simulink.The simulation models of single PV grid-connected inverter,based on traditional PQ control,direct-curtailment light control and PQ(U)control,are built respectively.The model of parallel photovoltaic grid-connected inverters based on PQ(U)control strategy are built for matched/mismatched impedance,which could maintain the voltage quality at grid-connected point similarly.Lastly,the experimental platform based on dSPACE real-time simulation system is built.Based on this platform,three experimental schemes are designed.The effectiveness of PQ(U)control strategy is verified through the analysis of experimental results.