| China’s “double carbon” target in September 2020(i.e.,“peak carbon” by 2030 and“carbon neutral” by 2060)drives the global energy transition to green and low-carbon.The key to achieving the “double carbon” goal is to build a new power system with a greater capacity to consume new energy.By 2030,the installed capacity of new energy will surpass that of coal power to become the most significant power source.In recent years,as the cost of distributed photovoltaic power generation continues to decline,China’s photovoltaic power generation from the “centralized” development trend to “centralized and distributed” is excessive.In this context,the access of large-scale distributed photovoltaic in low-and medium-voltage distribution networks brings problems such as voltage violations,feeder overloads,and line protection failures to the safe and stable operation of distribution networks.In order to comply with the trend of a high proportion of distributed PV to the grid and promote the local consumption of distributed photovoltaic,how quantifying and enhancing the maximum tolerable photovoltaic installation capacity of the distribution network under the premise of safe operation has become an urgent problem to be solved in the current distribution network-related research,which is also one of the critical scientific issues.In addition,the random and intermittent nature of photovoltaic power output and a large number of new types of loads lead to a significant increase in the uncertainty of distribution network operation,making the network more complex and unpredictable.Therefore,it is crucial to consider the effect of source-load uncertainty in the distribution network during the study of the above problem.This paper follows the development trend of high proportional photovoltaic penetration in medium and low-voltage distribution networks,addresses the technical difficulties of unbalanced medium and low-voltage distribution networks in consuming distributed photovoltaic at this stage and the problems of current research,and conducts in-depth research on distributed static photovoltaic hosting capacity of low-voltage distribution networks under uncertain environment,dynamic hosting capacity assessment and active management strategy with photovoltaic hosting capacity enhancement as the goal.In order to quantify the maximum photovoltaic installation capacity that can be hosted in a three-phase unbalanced distribution network under photovoltaic and load uncertainty,a static photovoltaic hosting capacity assessment method based on possibility theory is studied.Firstly,the exogenous uncertainty of photovoltaic output and endogenous uncertainty of load is taken into consideration,respectively;Secondly,the concept of system static violation is introduced focusing on the maximum system voltage of the distribution network at the most severe operation time;Finally,the method is proposed to evaluate the static photovoltaic hosting capacity of distribution network under photovoltaic and load uncertainty.It is verified by simulation that the proposed method could consider the possibility of voltage violation caused by photovoltaic and load uncertainty in the static photovoltaic hosting capacity assessment.It only requires a few historical statistics,which is still very applicable in the distribution network with limited measured historical data.For the static photovoltaic hosting capacity assessment,relying on the bus voltage of the most severe operation moment of the distribution network may lead to an over-conservative estimation of the network photovoltaic hosting capacity,a dynamic photovoltaic hosting capacity assessment method that captures the voltage violation information of the distribution network throughout the operation time is studied.Firstly,the probability-possibility conversion principle is introduced to improve the fuzzy uncertainty model of load;Secondly,the system voltage violation rate index is defined to reflect the voltage violation degree of the distribution network in the whole simulation time,and the network dynamic photovoltaic hosting capacity assessment method is further proposed;Finally,the impact of distributed photovoltaic grid connection location,inverter operation power factor,feeder impedance ratio,transformer short-circuit capacity and voltage regulation equipment on photovoltaic hosting capacity of the distribution network is simulated and analyzed.The simulation results show that the method overcomes the shortcomings of the original load model,which sets the fuzzy membership function based on the human experience.The dynamic photovoltaic hosting capacity assessment results are based on the voltage violation rate of the whole operation period of the distribution network.This complements the static photovoltaic hosting capacity and provides support for the operator to have a more comprehensive understanding of the photovoltaic hosting capacity of the network distribution network.In addition,the sensitivity of photovoltaic hosting capacity to different factors can provide a reference for the subsequent improvement of photovoltaic hosting capacity through optimal operation,transformation,and expansion of the distribution network.For the urgent need to mobilize the flexible operation of the active management resources of the distribution network to enhance the network photovoltaic hosting capacity and promote the local consumption of distributed photovoltaic in the case of a high proportion of distributed photovoltaic on the grid,the optimal operation strategy of the active management equipment to enhance the photovoltaic hosting capacity of the distribution network is studied.First,a deterministic nonconvex optimization model for the operation of active management devices,including on-load tap changer,capacitor banks,static reactive power compensators,photovoltaic inverters,dynamic network reconfiguration,and multiterminal soft open points with integrated energy storage is developed.Second,the original nonconvex optimization model is organized into a mixed integer second-order cone convex optimization problem.In addition,a polyhedral uncertainty set is used to model the uncertainty of photovoltaic output and load,and the described strategy is reformulated into a two-stage robust optimization model.Finally,a column and constraint generation algorithm is used to transform the original problem into an iterative solution of the master problem and subproblems.The numerical results show that the coordinated operation of multiple active management devices in the distribution network could substantially improve the photovoltaic hosting capacity.In addition to the traditional on-load tap changer control and reactive power compensation,the multi-terminal soft open points with integrated energy storage are the most effective in mitigating overvoltage and improving the photovoltaic hosting capacity of the distribution network.This paper takes the photovoltaic hosting capacity of an unbalanced distribution network under photovoltaic and load uncertainty environment as the research object and analyzes the static photovoltaic hosting capacity,dynamic photovoltaic hosting capacity,and active management operation strategy of the distribution network to enhance photovoltaic hosting capacity respectively.By proposing corresponding methods and strategy,we provide a reference for distribution network operators to understand distribution networks’ inherent characteristics,evaluate and enhance the local consumption capacity of distributed photovoltaic under the trend of a high proportion of distributed photovoltaic grid connection.The validity and feasibility of the method are verified through the simulation of international standard distribution network cases.The research results of this project are in line with the development trend of distributed energy under the goal of “double carbon” in China and improving the flexibility of distribution network operation and planning,which is of reference for the study of flexible and optimal operation of distribution network. |
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