Research On Operation And Control Optimization Of Distribution Grids With Distributed Photovoltaic And Energy Storage Integration

As the continuous growth of energy consumption and environmental pressure,distributed generation(DG)technology has drawn serious attention.The research into photovoltaic and its related technology,driven by naturally replenished renewable resources or national preferential policies,has shown the potential and brilliant future.However,challenges from the integration of distributed photovoltaic(DPV)with high permeability must be carefully met due to its profound impacts on traditional distribution networks.The operational control of DPV is the core point which should be firstly considered.Without proper controls,DPV would definitely cause reverse power flow,deteriorate the voltage quality and even reduce power supply reliability.Notably,due to intermittency and stochastic characteristics of photovoltaic,the active power of DPV usually fluctuate and cause severe indeterminate operations of distribution networks.At the same time,more energy storage system(ESS),contributing to balance the response between sources and loads,have successfully applied in distribution networks.It is attractive to gain benefits if we could take full advantages of DPV,ESS and coordinate them dynamically in distribution networks.This thesis mainly focuses on operational controls of DPV,then study strategies of fast and flexible energy management between DPV and ESS.It firstly carries out theoretical research on the operational optimization and control technology in a distribution network with coordination between DPV and ESS,then verifies the feasibility and practicability of proposed methods through practical engineering application.Detailed works are arranged as follows:1.Regarding the intermittency and stochastic characteristics of PV output,a time series modeling method based on clear sky model is proposed.The author owes to the cluster analysis of historical data and classification of typical weather,then combines independent modeling of deterministic and stochastic components of PV under such circumstance.The feasibility and practicability of the proposed method are verified by comparison with historical data.Compared with traditional ones,the novel method can directly reflect daily or seasonal characteristics of PV outputs,as well as the fluctuation characteristics under different weather.2.Based on the proposed time series model,major influences of PV integration in distribution networks are carefully analyzed,including voltage fluctuations,operational economy,and reliability.In terms of voltage,the maximum probability of voltage-violationindex is defined and calculated with considering different PV integration capacity,load type,load level,line type,line length,and weather type.For the operational economy,various PV penetration levels and PV market-oriented transaction modes are simulated.Concerning reliability,the impact of a hybrid photovoltaic energy storage system(HPVESS)on power supply reliability in distribution networks is analyzed.Then,a dynamic islanding strategy considering the sustainable on-load capacity of HPVESS and the reliability evaluation method of distribution network with HPVESS are presented.The simulation results show that the proposed method can effectively improve the power supply reliability of distribution network.3.A multi-time scale coordinated control method based on reactive voltage optimization in photovoltaic grid-connected nodes is proposed,aiming to solve severe voltage fluctuations and high probability of voltage over-limit caused by high-permeability distributed photovoltaic grid-connected.The reactive power optimization model under a long time scale and the adaptive optimization control strategy under short time scale are proposed according to the differences of the reactive voltage regulation characteristics between reactive power compensation type and voltage control type.With the simulation results of the IEEE33 test system and a real distribution network in Guangdong Power Grid,differences between these two control modes are shown.Then the reactive-voltage coordination control of the distribution network with photovoltaic is discussed.4.With the help of energy storage,a novel control is used to resolve insufficient reactive power regulations of photovoltaic inverters.The author takes voltages of grid-connected nodes as optimization objects,then build a photovoltaic-energy storage hybrid system combined voltage control type of photovoltaic grid,finally propose an active-reactive multi-time scale coordinated control strategy for this system.The central characters include short-time-scale adaptive optimization based on boundary node type transformation and long-time-scale activereactive optimal scheduling.The effectiveness of the proposed control strategy is verified with an IEEE33 test system.5.This thesis studies the optimal configuration of energy storage systems and proposes a method for two-layer stochastic energy storage planning to improve the efficiency of photovoltaic in a distribution network.In general,the operation and maintenance cost of energy storage systems is much higher than the benefit of power loss reduction.An incremental evaluation index based on life-cycle cost in a distribution network lays a ground foundation.A life prediction model for energy storage systems is then established to quantify the difference between the actual and theoretical on life loss.Next,the author proposes the two-layer stochastic energy storage planning model to improve efficiency.Finally,the economic effectiveness and practicability of the proposed method are verified with Guangdong Power Grid.The boundary limits or conditions such as life prediction of energy storage systems,PV penetrations,and load growth rates are all analyzed.6.Based on the demonstration project of active distribution network in Sanshui Industrial Park of Foshan,this thesis analyzes the effectiveness and practicability of several methods,including the time-series forecast of PV based on the clearance model,the multi-time-scale coordinated control based on the reactive power and voltage optimization at photovoltaic grid connection,and the multi-time-scale P-Q coordinated control of PV energy storage systems.This research provides new insights into the possible applications of PV and ESS.The research of this thesis has immeasurable guiding significance and reference values for the operation optimization and control for distribution network with a large number of PV and ESS integration.