The Key Technology Research On Energy Coordinated Control Of PV-ESS DC Microgrid

As the global energy depletion and the deterioration of the ecological environment become increasingly prominent,it is imperative to develop renewable energy and promote distributed application technologies.Due to PV-ESS dc microgrid has good compatibility with micro-sources,energy storage and loads,it becomes an important way for distributed photovoltaic power generation to access the future intelligent power distribution system.PV-ESS dc microgrid is a multisource and multi-load system.Its control and operation modes are relatively flexible.Thus,the focus and difficulty that PV-ESS dc microgrid needs to solve is how to coordinate,manage and distribute the energy output of each unit under different operating conditions,so as to achieve the optimal utiliz ation of energy under the premise of ensuring the reliable and stable operation of system.For this,this paper carried out the following work:1)The structure of PV-ESS dc microgrid and its internal components are briefly introduced.The equivalent models of distributed photovoltaic unit,hybrid energy storage moudle and DC/AC grid-connected converter are established.The working characteristics and corresponding control methods of each unit are analyzed in detail,respectively.The above work lays the foundation for the research on the power optimization allocation of hybrid energy storage system and the energy coordinated control between DC microgrid and large grid.2)Based on the analysis of hybrid energy storage topology and power allocation principle between different energy storage units,a power autonomous frequencydivision control method for hybrid energy storage system is proposed.In this method,the equivalent output impedances of converters are reshaped by introducing the virtual impedance or virtual capacitor into the control loop of ultracapacitors and batteries,respctively.This control method not only achieves the energy optimal distribution of energy storage system,but also improves the dynamic characteristics of system and prolongs the service life of hybrid energy storage.The simulation results verify effectiveness of the proposed method.3)In order to realize the stable operation and energy high-efficient utilization for PV-ESS dc microgrids system,an energy coordinated control metho d based on DC bus voltage deviation is designed to manage the system energy in a hierarchical area.Under the premise of considering the power converter transmission capacity,state of charge of energy storage system and operating state of the large grid,the energy flow direction of system and working state of each converter in different layers are analyzed.The transition conditions of each unit between different control strategies are also obtained.By this way,it not only achieve smooth switching of system between different layers,but also ensures the real-time balance of energy between power generation terminal and power consumption terminal.The effectiveness of the proposed method is verified by the simulation.