Research On Voltage Control Of AC(DC) Distribution Network With Distributed Generation

Distributed generations are more and more widely spread in power system,because of its supply efficiency,environmental protection and other characteristics.Modern distribution network is suitable for distributed power access,high quality of power supply,reduce the use of electricity of the city and other characteristics,the development of modern distribution network will be the inevitable requirement of urban power grid.Due to the randomness and fluctuation of the output power of the distributed power,it will inevitably cause the voltage fluctuation of each node in the modern distribution network,the node voltage is an important index to measure the voltage quality of the distribution network,so it is very important to study the voltage control.There are many kinds of DG in modern distribution network,during the power flow analysis process,it is necessary to use appropriate methods to convert different types of nodes to PQ nodes,Therefore,the output power of different types of DG is modeled and its node types are established.This paper studies the optimization model of AC distribution network with various types,using the improved genetic algorithm to solve the model and the stochastic power flow algorithm to solve the power flow,the example shows that the optimization model can reduce the loss of distribution network and improve the economics of the distribution network.The operation mode,control level and control mode of DC distribution network are analyzed.The Voltage source converter(VSC)is an important equipment to connect the DC distribution network and the external network,and it is important to control the stability of the output power for the stable operation of the DC distribution network.Aiming at the control problem of VSC in different operation modes,the voltage coordination control method suitable for DC distribution network is proposed.The voltage coordination control method is reasonable,which combines the voltage control mode with the voltage margin and the power voltage droop control mode.When the power of the DG and the load is fluctuating,the bus voltage can be controlled in the effective range to ensure the stable operation of the system;When the operation mode of the DC distribution network is changed,the control method of the VSC can be switched smoothly,and the bus voltage will not be impacted;The proposed coordinated control model can quickly respond to the change of system power and improve the stability of the system.There are no inductive and capacitive reactance in dc distribution network and the power flow analysis is easier than ac distribution network.The power flow analysis of DC distribution network based on Newton-Raphson method is studied and applied to the study of DC distribution network.Aiming at the voltage fluctuation after a large number of DGs access to the DC distribution network,a two-stage voltage control method for DC distribution network is proposed.In the first stage,the voltage level of the whole network is controlled by the VSC,in the second stage,the voltage of each node of the system is adjusted by optimizing the active output of DG,and the two-stage control result is fed back to each other,realizing the control of the voltage of each node of DC distribution network.The example shows that the two-stage control method can effectively adapt to the access of a large number of DGs,and can effectively control the voltage of each node in the DC distribution network to ensure the safe and stable operation of the system.