Research On Energy Management Strategy Of Low Voltage AC/DC Hybrid Distribution Network

With the increasing permeability rate of distributed generation and DC loads in low voltage distribution network,the traditional radial form of AC distribution develops to AC/DC hybrid form.The AC/DC hybrid distribution system integrates the advantages of DC and AC distribution,and has obvious advantages in power supply efficiency,reliability and flexibility.However,the randomness and fluctuation of distributed generators in AC/DC hybrid distribution system have a serious impact on the safe and stable operation of distribution network and power quality.A large number of power electronic devices are connected to the distribution network.The structure of the network is complex,the loss of converters is serious,and the control methods are flexible and diverse,which brings great challenges to the energy management of the distribution network.This thesis focuses on the energy management strategy of low voltage AC/DC hybrid distribution network.The specific research contents are as follows:(1)For the problem of serious converter loss and diversity of control modes in the distribution network,the loss model of voltage source converter(VSC)and DC/DC converter is established.By analyzing the control and external characteristics of the converter,the equivalent processing methods of different control methods in energy management are given.On this basis,combined with the structure of low voltage AC/DC hybrid distribution network,a bi-level optimization model of energy management has been established.The upper level is the engergy storage charging and discharging control strategy,and the optimization objective is to minimize the daily operation cost of distribution network.The lower level is the power allocation strategy among regions,and the optimization objective is to minimize the impact of fluctuation of distributed generation on distribution network.Through the simulation of case,it is found that the energy management strategy can improve the economy of distribution network operation and reduce the impact of fluctuation of distributed generation on distribution network,which verifies the correctness and effectiveness of the strategy.(2)Based on the randomness and fluctuation of distributed generation output,three real-time energy management strategies are studied based on model predictive control(MPC)on the basis of previous studies.Strategy 1 is to simplify the real-time energy management strategy of the model.Strategy 2 adds an error correction link based on Strategy 1,which reduces the output error.Strategy 3 considers the real-time energy management strategy of energy storage loss based on Strategy 2.Finally,a case is simulated from two aspects:the economy of distribution network operation and power fluctuation.It is found that the three real-time energy management strategies can improve the economics of distribution network operation and reduce the impact of power fluctuation on the upper-level power grid.The strategy 1 model is the simplest,the strategy 2 target tracking and power fluctuation suppression are the best,and the strategy 3 energy storage loss is the least.(3)The real-time energy management system is designed,and the experiments of target tracking and wave suppression are carried out.Through the performance test of real-time energy management system,it is found that the system is stable and reliable,can collect data in real time,issue instructions,store a large amount of data,and the calculation result of real-time energy management strategy is correct,which achieves the design purpose.Target tracking experiment can reduce target tracking error and improve the economy of distribution network operation.The experiment of suppressing fluctuation can reduce the impact of power fluctuation on the upper-level power grid,which verifies the effectiveness and feasibility of the real-time energy management strategy.