Research On Dispatching And Control Strategies For High Proportion Photovoltaic In DC Grid

In pursuit of ”carbon peaking and carbon neutrality,” the worldwide installed capacity of photovoltaic(PV)systems is witnessing a substantial increase.However,given their environmental characteristics,notably their high permeability,PV systems produce uncertain and intermittent outputs.This variability poses significant challenges to the economic and safe operation of power grids.Therefore,the enhancement of active support and regulation capabilities of PV systems is crucial for optimizing output performance.Additionally,the development of efficient dispatching strategies is necessary to ensure economical and safe grid operation.This thesis focuses on the study of high-proportion photovoltaic systems in DC grids,addressing economic dispatch,coordinated control,and output control issues.The research findings,when applied to high-proportion photovoltaic DC grids,demonstrate considerable advantages.1.Multi-time scale economic dispatching strategy for high-proportion photovoltaic DC gridA multi-time scale dispatching algorithm is proposed for the economic dispatching problem of PV systems in high-proportion photovoltaic DC grid,which solves the conflict between the dispatching burden and real-time dispatching of traditional centralized dispatching algorithms under the power output fluctuation of PV systems.The proposed multi-time scale dispatching strategy is divided into two layers: The first layer is a centralized dispatching algorithm that operates on a long-time scale,achieving global optimization based on global information;The second layer is a distributed dispatching algorithm that acts on a short-time scale,adjusting the reserve power of PV systems based on exchanged information with adjacent nodes.Rules for information exchange and power adjustment between PV systems are developed,and a global convex optimization model based on second-order cone relaxation for the DC grid is created.Simulation tests on IEEE-14 bus test system show that the proposed algorithm enhances the utilization and efficiency of PV systems reserve and keeps the voltage of nodes more stable.2.Dispatchable droop control strategy for PV systems in DC gridA dispatchable droop control method for PV systems in the DC grid is proposed to complement the economic dispatching of PV systems.The method adopts a hierarchical control structure,with the first layer exhibiting droop characteristics to achieve power sharing and the second layer conforming to dispatching orders.Unlike the traditional control method based on (1- droop control,the proposed method is based on (1-dp/dv droop control,using dp/dv as the control variable to avoid overload issues and estimate the PV power margin.The small signal stability of the proposed algorithm is analyzed,and the second layer control parameter design method and overload prevention structure are given.The basic dispatchable function of the proposed algorithm was tested on a hardware-in-the-loop platform and compared with the traditional (1- droop control based method.The results show that the proposed algorithm has advantages in overload prevention and abnormal command response compared to the traditional dispatchable method based on (1-droop control.3.Spatial-domain dp/dv calculation method based PV output control methodA spatial-domain dp/dv calculation method is proposed to improve the underlying output control performance of the dispatchable droop control method.The method uses current data and adjacent data in the space domain to calculate the dp/dv value,avoiding the zero denominator problem in the steady state.The PV output control based on the proposed method can track different dp/dv references to achieve maximum power point tracking(MPPT)or power reserve control without steady-state oscillations.This thesis explains the operation mechanism of the PV control method,the operation principles of spatial-domain dp/dv calculation,and the advantages of this calculation method compared to time-domain dp/dv calculation.The implementation flow chart and parameters design of spatial-domain dp/dv calculation is provided.Through simulation and experimental tests,the effectiveness of the control method based on spatial domain dp/dv calculation is verified.The results show that the proposed calculation method outperforms traditional methods such as the P&O method,the latest steady output and fast-tracking(SOFT)method,and the time-domain dp/dv calculation method in PV control.4.Example of dispatching and control application of high proportion photovoltaic in direct current gridTo deepen the understanding of the deployment method and application advantages of the research results in high-proportion photovoltaic DC grids,a detailed design of a high-proportion photovoltaic DC grid is meticulously crafted based on the widely used 21-node DC grid topology.In addition,a comprehensive DC grid electromagnetic transient simulation model,which encompasses a detailed underlying switch circuit modeling,is established.Subsequently,the advantages of the three presented research findings are sequentially compared and verified.This includes the operational benefits of the high-proportion photovoltaic DC grid under the combined effect of the three proposed strategies.Then,the advantages of the three presented research results are sequentially compared and verified,including the operation advantages of the high-proportion photovoltaic DC grid under the combined effect of the three proposed strategies based on the real historical illumination data collected by the Zero-Carbon New Energy Laboratory of Zhejiang University.