Study On Coordinated Optimization Control Of Grid-connected Photovoltaic Storage Power Station

As wind,light and other renewable uncontrollable energy power generation are connected to the grid rapidly increasing year by year,the proportion of fossil energy-dominated thermal power unit capacity is gradually decreasing,leading to the severe problem of insufficient active control resources of the power grid,and the operation and control of the power system is faced with challenges.In the process of power grid operation control,the optimization and control of large-scale photovoltaic power stations have become the focus of attention.Firstly,there are problems of asymmetric topology structure and inconsistent operation parameters in large photovoltaic power stations.If the grid-connected operation control strategy is improper,the voltage support problem in the stations will be very prominent.Secondly,with the influence of environmental factors,photovoltaic power generation has strong uncertainty characteristics such as time-variability,volatility and intermittenity,which brings pressure to the regulation of real-time power and electricity balance of the grid.At the same time,based on the rapid development of measurement,communication and Internet technologies,photovoltaic grid-connected inverters and energy storage devices have the potential of flexible and fast active power and reactive power regulation based on the modulation technology of electric power,so as to realize the coordinated optimization and control of their active power and voltage time-varying.Thus,the active power uncertainty and voltage problems caused by photovoltaic power generation can be solved inside the power station,and the robust grid-connection of photovoltaic power station can be controlled and dispatching can be realized.In this context,there are two problems to be solved in the dispatching and control of grid-connected operation of large-scale photovoltaic power stations:first,how to eliminate the grid-connected circulation problem caused by voltage imbalance in the power station;The second is how to ensure that the power station obeys the superior power grid dispatching and outputs safe and stable active power.Therefore,under normal circumstances,this paper focuses on solving these two problems,aims to achieve autonomous operation of photovoltaic power stations,and takes real-time online optimization algorithm as the means to carry out in-depth research on the time-varying coordinated optimization operation and control of grid-connected operation of large optical storage power stations.Based on the control principle and implementation system of photovoltaic grid-connected inverters and energy storage devices,and focusing on the time-varying optimization decision of the inverters and energy storage control points,this paper studies the models and methods of time-varying voltage and active power tracking of large-scale photovoltaic power stations under the condition that the grid-connected transmission power is not restricted and the grid dispatching plan is subject to.The main work and achievements of this paper are as follows:(1)Based on the topological structure and characteristics of large-scale photovoltaic power station,the operation control mode of photovoltaic inverter,energy storage and other equipment in the station is studied.The topological structure characteristics and main equipment of large-scale photovoltaic power stations are described and clarified.The principle and realization of maximum power tracking control and grid-connected inverter control of photovoltaic are described.The operating characteristics and mathematical models of different energy storage devices are deeply analyzed,and the control principles of the bidirectional DC/DC and DC/AC converters are studied.Finally,the effectiveness of the control system combined by a single photovoltaic power generation unit and energy storage and the control system coordinated by multiple inverters are simulated and analyzed respectively,which lays a foundation for the subsequent research on the coordination optimization of active power and reactive power in the grid-connected operation of large optical storage power stations.(2)On the premise of full absorption of photovoltaic power by the power grid,further explore the reactive voltage regulation potential of internal inverters of large photovoltaic power stations.Aiming at the problems of different grid-connected wiring impedance caused by different positions of each generating unit in a large photovoltaic power station and inconsistent operating conditions of each unit’s maximum output photovoltaic power,a time-varying optimization method is proposed to track the maximum output photovoltaic power of a grid-connected photovoltaic power station.Under the premise of complete measurement and communication technology,With the help of electric power electronic technology that inverter can rapidly modulate active power and reactive power output,according to the characteristics of small change of photovoltaic system state quantity in second optimization cycle,linear approximation processing such as Taylor expansion and linear fitting is implemented for nonlinear optimization model,and the power operation base point of inverter is quickly solved through sensitivity calculation.When necessary,the light will be automatically discarded.Thus,the uncertainty of photovoltaic power can be effectively dealt with,and the voltage problems in the connecting network and inside the power station can be alleviated.(3)On the premise that large-scale photovoltaic power stations participate in power grid dispatching,the optimal scheduling method of active and reactive power is explored to coordinate inverters and energy storage.In order to make the grid-connected photovoltaic power stations have the schedulability,a rolling,time-varying day-ahead real-time coordinated optimization scheduling method for grid-connected large-scale optical storage power stations is proposed.In the day-ahead optimization stage,the uncertainty of photovoltaic power generation is considered,and the next day active power plan reported by the power station to the grid dispatching center is determined.In the real-time optimization stage,online measurement and communication technology are used.The hybrid energy storage system and grid-connected inverter with rapid response can adjust the setting basis points of active power and reactive power time varying,track the active power scheduling instructions issued by the dispatching center online,and realize the tracking of grid-connected voltage control within the restricted range.Therefore,the two layer algorithms cooperate with each other to realize the optimization operation of grid-connected dispatching of photovoltaic power station,which can not only ensure that the connecting point of the power station and the voltage in the station do not exceed the limit,but also make the output power execute according to the day-ahead plan.