Scheduling Framework Using Dynamic Optimal Power Flow for Battery Energy Storage Systems

Battery energy storage systems(BESS)are instrumental in the transition to a low carbon electrical network with enhanced flexibility,however,the set objective can be accomplished only through suitable scheduling of their operation.This paper develops a dynamic optimal power flow(DOPF)-based scheduling framework to optimize the day(s)-ahead operation of a grid-scale BESS aiming to mitigate the predicted limits on the renewable energy generation as well as smooth out the network demand to be supplied by conventional generators.In DOPF,all the generating units,including the ones that model the exports and imports of the BESS,across the entire network and the complete time horizon are integrated on to a single network.Subsequently,an AC-OPF is applied to dispatch their power outputs to minimize the total generation cost,while satisfying the power balance equations,and handling the unit and network constraints at each time step coupled with intertemporal constraints associated with the state of charge(SOC).Furthermore,the DOPF developed here entails the frequently applied constant current-constant voltage charging profile,which is represented in the SOC domain.Considering the practical application of a 1 MW BESS on a particular 33 kV network,the scheduling framework is designed to meet the pragmatic requirements of the optimum utilization of the available energy capacity of BESS in each cycle,while completing up to one cycle per day.

Hydrological and sediment connectivity under freeze-thaw meltwater compound erosion conditions on a loessal slope

Freeze-thaw processes can influence hydrology,soil erosion,and morphological development by altering the connectivity between active pathways of water and sediment transport.Concentrated flow experi-ments were conducted involving frozen,shallow thawed,and unfrozen soil slopes under 1,2,and 4 L/min runoff rates at a temperature of approximately 5℃.In this study,hydrological connectivity was analysed via the simplified hydrological curve and relative surface connection function.Sediment con-nectivity was analysed via the sediment structure connectivity and sediment functional connectivity.Results indicated that hydrological connectivity was greatest on frozen slopes(FS),followed by shallow thawed slopes(STS),and unfrozen slopes(UFS)given a constant flow rate.Hydrological connectivity increased with increasing runoff rate for each freeze-thaw condition.Freezing condition and runoff rate exhibited a positive response to the hydrological connectivity.Sediment structure connectivity increased with increasing runoff rate for each slope condition.The ordering of sediment structure connectivity across freeze-thaw condition was that FS was greater than STS while STS was greater than UFS inde-pendent of flow rate.Sediment functional connectivity included longitudinal,lateral,and vertical con-nectivity components.Sediment longitudinal and vertical connectivity indicated a trend of first increasing and then decreasing under the different runoff rates and freeze-thaw conditions.For a given runoff rate,the ordering of sediment longitudinal and vertical connectivity across freeze-thaw condition was that FS was greater than STS while STS was greater than UFS.Sediment lateral connectivity exhibited a trend of first decreasing and then stabilizing.The ordering of sediment lateral connectivity across freeze-thaw condition was that UFS was greater than STS while STS was greater than FS.FS could more easily reach longitudinal and vertical penetration.Sediment longitudinal and vertical connectivity rates demonstrated increasing trends with increasing runoff rate after runoff generation stabilization and gradually approached unity.This research further improves our understanding of the hydrological and erosional mechanisms of meltwater and the generation of flooding in frozen soil conditions.