| With the development of DC load such as data center as well as DC distributed generation such as photovoltaic,the DC characteristics of power source and load become significant in distribution network.DC distribution network can effectively reduce the use of converters,improve the acceptance capacity of distributed generation and energy utilization efficiency,which shows the broad development prospects.This dissertation studies the key technologies of optimal operation and control of DC distribution network considering the uncertainties of renewable energy and load.The main contributions are as follows:1)The power flow calculation method and power flow sensitivity model of DC distribution network that can be effectively applied to different topologies and control modes are proposed.Firstly,the power flow calculation Newton method for DC distribution network is presented based on the equivalent branch model.The proposed equivalent branch model represents the influence of droop control on power flow and provides the relaxation node for power flow calculation of droop-controlled DC distribution network.Secondly,the power flow sensitivity model of DC distribution network is established,which includes the sensitivity model of node injection power to node voltage,line power and converter power,as well as the sensitivity model of droop control parameters and master-slave control parameters to node voltage,line power and converter power.2)The optimal operation method of master-slave controlled DC distribution network is proposed,which considers the converter control modes and the uncertainties of renewable energy and load.Firstly,the coordinated optimization method of converter and energy storage system in DC distribution network is proposed.The voltage and power control parameters of converter is optimized with the goal of minimizing deviation of node voltage from rated value through interval optimization method.The charge and discharge power of energy storage system is optimized with the goal of minimizing power purchase cost.The coordination between energy storage system and converter is realized through iterative optimization.In addition,an uncertain optimization method of DC distribution network based on information gap decision theory is proposed.For the period with high risk of exceeding the limit of operation constraints,the voltage and power control parameters of converter is optimized with the range constraint of node voltage deviation from the reference value as well as the goal of maximizing the capacity to withstand the random variation of load and renewable energy output.3)A coordinated optimization method of droop coefficient and operation reference power is proposed considering the randomness of load and renewable energy output in DC distribution network.Firstly,the operation reference power optimization method with the goal of improving voltage level and balancing converter load is proposed for power flow optimization.Secondly,the droop coefficient is optimized to balance converter load of DC distribution network,which considers the node voltage constraint and converter power constraint when the load and renewable energy output changes randomly.The droop coefficient optimization method can effectively realize the power distribution of droop control while ensuring the voltage level.4)A secondary voltage regulation method of DC distribution network based on the coordination of adaptive control and centralized control is proposed.Firstly,the centralized optimal control is performed based on the measured node voltages to improve the system voltage level and balance converter load.Secondly,between two centralized controls,the operation reference power is adaptively adjusted according to the converter outlet voltage.The corresponding converter outlet voltage that the operation reference power needs to be adjusted is determined according to the power flow distribution considering the random distribution characteristics of load and renewable energy output.The operation reference power is adjusted according to the converter capacity,which can improve the voltage level and balance the converter load. |
