Research On Operation And Control Of DC Power Distribution System With High Proportion Of Distributed Photovoltaics

DC power distribution system has been widely used in city industrial park and urban power distribution system because of its obvious advantages in capacity,loss,cost,power supply quality and flexible access.With a higher proportion of distributed and intermittent sources coming in,higher requirements have been put forward for the operation and control of DC power distribution system.Existing operational control startegys can be summarized as centralized,distributed and decentralized control according to the degree of communication it demands.Centralized control has the highest level and best control effect,but it relies too much on communication and detection means and has low reliability.Decentralized control only needs local information and local control,namely plug and play,but the control effect is the worst while the control objective is single,and the flexibility is low.Distributed control devolves part of control function to local controller,which can achieve tradeoff between communication and control effect,but the control is relatively complex.Aiming at the problems in existing operation control methods,this paper is carried out from three aspects of distributed and decentralized control: how to achieve better power balance,reduce the bus voltage fluctuation;how to reduce the dependence on communication means and improve the reliability of control strategy;how to achieve richer control objectives,adapt to the current development trend of high proportion of photovoltaic access,and improve the flexibility of control strategy.DC power distribution system with a high proportion of distributed photovoltaics in Zhangbei,China is taken as the research object.Two types of control strategies are proposed from the perspective of distributed and distributed,as follows:First of all,according to different light conditions between multiple converters,a distributed coordinated control strategy based on discrete consistency is proposed.Through the exchange of information between adjacent photovoltaic nodes,the local photovoltaic controller can automatically calculate and update the operating mode instruction and power reference value instruction,and each distributed PV group can adaptively switch between MPPT and constant power mode,which can fully mining the complementism between multiple pv groups,and it can better suppress the power fluctuation caused by uneven illumination and load fluctuation among multiple pv groups,and effectively reduce the dependence on communication means and energy storage.The simulation results verify the effectiveness and reliability of the control strategy.Further,to achieve better implement the photovoltaic power allocation and real scheduling response,a distributed operation control strategy aiming at scheduling response and power balance control objectives based on the same consistency theory is proposed,which balances cheduling response and power allocation well.Without forecasting the output power of photovoltaics,the precise allocation can be achieved.The effectiveness and reliability of the control strategy are also verified by simulation.Then considering the accees of more and more distributed power supply,the operation control method often requires both reliability and flexibility.Distributed control,although can reduce reliance on communication,but the quality of communication and the demand of the distributed control algorithm is still high.Therefore,from the perspective of distributed control,a new decentralized control strategy based on DC bus voltage active adjustment method is proposed,where the bus voltage is directly taken as the “communication medium”.The proposed decentralized control principally combines a master-slave control and thus changes the passive bus voltage regulation in the traditional decentralized control to the active adjustment of bus voltage.Then,the balancing node adjusts the bus voltage actively according to its own power deviation and the photovoltaic nodes adjust their outputs adaptively according to local bus voltage deviation and utilization rate information.In this way,two kinds of nodes support each other and no extra communication is needed.The photovoltaics can be fully excavated to smooth the power fluctuation,and the dispatching command of station and optimal power control of battery can be simultaneously realized.Meanwhile,the static error of bus voltage can be eliminated and the photovoltaics still have a certain voltage stabilizing capacity if the balancing node exits due to malfunction.Finally,the simulation model and experiment platform under different scenarios are built,and the simulation and experiment results prove the effectiveness and reliability of the proposed control idea.