Study On Voltage Characteristics Of Active Distribution System With DG

With the development of global economy and the continuous change of energy structure,the permeability of DG in active distribution network is also rising.It also needs higher requirements for voltage stability and power quality of active distribution network.The increasing automation of DG in distribution network has changed the power supply mode of unidirectional power flow in passive distribution network.In chain low voltage distribution network,if the DG output is too high or the system is light load,it is easy to generate the power flow countercurrent,resulting in the voltage limitation of the node.In the process of controlling the DG grid connected inverter,using the energy storage equipment in the system can ensure the stability of network voltage.In this paper,the working principle of DG,which is represented by wind power and photovoltaic power generation,as well as the working principle of supercapacitor and its mathematical model is analyzed.On this basis,the mechanism of the PCC voltage limit is analyzed.Secondly,on the basis of theoretical analysis,a Q(U)Prevention scheme is proposed.In this scheme,the operating state of the inverter is determined by real-time monitoring of the PCC voltage.When the voltage is not limited,the inverter tracks the output according to the maximum output power of DG.When the voltage is higher and the reactive power of the inverter is sufficient,the PCC voltage is adjusted by using the residual reactive capacity of the inverter while the active power output is not changed.When the output of the inverter is too large,the reactive power of the inverter is exhausted and the voltage is still limited,the reference value of active power and reactive power output is calculated dynamically.The maximum power output of the inverter and the optimal reactive power output are realized on the premise of ensuring the prevention and the voltage limit of the node.Then,in order to further solve the problem of network voltage limit and avoid the waste of energy,a solution for the coordinated control strategy of active / reactive power is proposed.Dead zone control is added to active power voltage loop,which ensures reactive power and voltage regulation first,and solves the phenomenon of voltage jitter near dead zone threshold voltage due to the sensitivity of active power voltage regulation.The control link of supercapacitor is configured to effectively improve the voltage quality problem with the network voltage limit.Finally,The voltage of ADS layered coordinated control strategy is proposed.The upper level instruction layer takes the DG output and the inverter running state as the control quantity of the optimal power flow scheduling.With the goal of minimum distribution network loss,minimum voltage deviation and maximum DG output,PSO algorithm is used to calculate the control signal of local layer.The lower level local layer takes the output signal of the upper control layer as the reference value to control the inverter and the energy storage device output,which improve the voltage distribution of ADS and achieve the goal of the upper level optimization.