Research On New Rural Distribution Network Control With Photovoltaic/battery Units

With the state’s advocacy and policy support for coal to electricity in rural,and the improvement of people?s living standards,great changes have taken place in the overall structure of the electric load of modern power system.Residents? electricity consumption and electricity equipment have increased significantly,the demand for power quality is getting higher and higher.There are many indicators that affect the users power quality,it is mainly three phase voltage imbalance for rural areas.Three phase voltage imbalance will have a negative impact on the user’s electrical equipment and bring losses to the power grid enterprises.However,due to the influence of natural conditions or human factors,the failure of grid is inevitable.When the grid fails,the distribution network enters the mode of off-grid.The user electrical equipment will be outage,because of the lost support from grid.With the increasing of photovoltaic installation in rural areas,the adverse effects of grid failures on users can be reduced by using PV/Battery units.When a plurality of energy storage units are put into use together,improper design of the control scheme may lead to unreasonable output between units,resulting in some units being overuse,state of charge(SoC)can not be balanced,reducing the life of the energy storage unit.First,the system structure of the low voltage distribution network with PV/Battery power generation device in rural is studied.The three phase voltage imbalance problem in the grid-connected mode is explored in depth,and the reason of three phase voltage imbalance is deduced.A scheme to reduce the voltage imbalance of dynamic changing the load power supply phase is proposed based on the reason of voltage imbalance.The scheme does not require additional compensation devices and has strong executability.It will not adversely affect the user’s electrical equipment in the process of changing the phase of power supply.Then,the structure of a small capacity microgrid system which consisting of a number of energy storage units with different capacities in off-grid mode is researched.The SoC unbalance and unreasonable output problems for energy storage unit in microgrid when adopts conventional droop control are analyzed.Based on this analysis,a SoC balance scheme for energy storage units with different capacities is proposed.This scheme does not requires communication between units,the SoC balance of energy storage units with different capacities can be achieved based on their local information.When the SoC is balanced,the output power of each energy storage unit is according to their own capacity.Finally,a microgrid experiment platform containing two energy storage units is built,and the software and hardware design of the experimental platform is also introduced.Then,the SoC balance scheme for energy storage units with different capacities proposed in the fourth chapter is verified by using experimental platform.The experimental results show that the scheme can achieve SoC balance of energy storage unit and ensure the output of energy storage units is reasonable.