查看更多>>摘要：The participation of photovoltaic(PV)plants in supporting the transient voltage caused by commutation failure in the line-commutated-converter-based high voltage direct current(LCC-HVDC)system is of great significance,as it can enhance the DC transmission ability.However,it is found that the grid-following(GFL)PV converters face the problem of mismatch between reactive power response and transient voltage charac-teristic when the voltage converts from low voltage to overvoltage,further aggravating the overvoltage amplitude.Thus,this article proposes a transient voltage support strategy based on the grid-forming(GFM)medium voltage PV converter.The proposed strategy takes the advantage of the close equivalent electrical distance between the converter and grid,which can autonomously control the converter terminal voltage through GFM control with adaptive voltage droop coefficient.The simulation results show that the proposed strategy can ensure the output reactive power of the PV converter quickly matches the transient voltage characteristic at different stages,indicating that the proposed strategy can effectively support the transient voltage.
查看更多>>摘要：Bipolar blocking and commutation failure in the renewable energy transmission system through ultra-high voltage direct current will produce significant temporary overvoltage.This paper analyzes the physical process of sending end grid overvoltage caused by two types of DC faults and establishes a DC overvoltage model considering renewable energy sources.According to characteristics of the sending end grid,the influence of the system equivalent impedance,the proportion of renewable energy output,the active and reactive power coefficients of the renewable energy sources during the low voltage ride through process on the overvoltage is analyzed respectively,and the relationship between the proportion of renewable energy output and the short-circuit ratio under the overvoltage constraint is constructed.The validity and practicality of the model and analysis method proposed in this paper are verified by combining the typical transmission system at the sending end of the actual power grid and regional power grid systems.
查看更多>>摘要：Integration of distributed energy storage(DES)is beneficial for mitigating voltage fluctuations in highly distributed generator(DG)-penetrated active distribution networks(ADNs).Based on an accurate physical model of ADN,conventional model-based methods can realize optimal control of DES.How-ever,absence of network parameters and complex operational states of ADN poses challenges to model-based methods.This paper proposes a data-driven predictive voltage control method for DES.First,considering time-series constraints,a data-driven predictive control model is formulated for DES by using measure-ment data.Then,a data-driven coordination method is proposed for DES and DGs in each area.Through boundary information interaction,voltage mitigation effects can be improved by inter-area coordination control.Finally,control performance is tested on a modified IEEE 33-node test case.Case studies demonstrate that by fully utilizing multi-source data,the proposed predictive control method can effectively regulate DES and DGs to mitigate voltage violations.
查看更多>>摘要：Even though smart meters have been widely used in power systems around the world,many consumers are still finding it hard to participate in demand response(DR)due to flat-rate retail pricing policy.To address this issue,this paper proposes a coupon-based demand response(CDR)scheme to achieve equivalent dynamic retail prices to inspire consumers'inherent elasticity.First,a security-constrained unit commitment optimization model is developed in the day-ahead market to obtain coupon rewards,which are then broadcast to consumers to motivate them to reschedule their power consumption be-haviors.To evaluate the adjustment value of consumers'power consumption,a collective utility function is proposed to formulate the relationship between power quantity and coupon rewards.On this basis,the security-constrained economic dispatch model is developed in the intra-day market to reschedule generating units'output power according to real-time load demands and fluctuating renewable energies.After the operation interval,a settlement method is developed to quantify consumers'electricity fees and coupon benefits on a monthly basis.The proposed CDR scheme avoids real-time iterative bidding process and effectively decreases the difficulty of massive,small consumers participating in DR.The proposed CDR is implemented in a realistic DR project in China to verify consumers'energy cost and renewables'curtailment can both be decreased.
查看更多>>摘要：Edge data centers(EDCs)have been widely de-veloped recently to supply delay-sensitive computing services,which impose prohibitively increasing electricity costs for EDC operators.This paper presents a new spatiotemporal reallocation(STR)method for energy management in EDCs.This method uses spare resources,including servers and energy storage systems(ESSs)within EDCs to reduce energy costs based on both spatial and temporal features of spare resources.This solution:1)reallocates flexible workload between EDCs within one cluster;and 2)coordinates the electricity load of data processing,ESSs and distributed energy resources(DERs)within one EDC cluster to gain benefits from flexible electricity tariffs.In addition,this paper for the first time develops a Bit-Watt transformation to simplify the STR method and represent the relationship between data workload and electricity consumption of EDCs.Case studies justifying the developed STR method delivers satisfying cost reductions with robustness.The STR method fully utilized both spatial and temporal features of spare resources in EDCs to gain benefits from 1)varying electricity tariffs,and 2)maximumly consuming DER generation.
查看更多>>摘要：Consensus has been widely used in distributed control,where distributed individuals need to share their states with their neighbors through communication links to achieve a common goal.However,the objectives of existing consensus-based control strategies for energy systems seldom address battery degradation cost,which is an important performance indicator to assess the performance and sustainability of battery energy storage(BES)systems.In this paper,we propose a consensus-based optimal control strategy for multi-microgrid systems,aim-ing at multiple control objectives including minimizing battery degradation cost.Distributed consensus is used to synchronize the ratio of BES output power to BES state-of-charge(SoC)among all microgrids while each microgrid is trying to reach its individual optimality.In order to reduce the pressure of commu-nication links and prevent excessive exposure of local information,this ratio is the only state variable shared between microgrids.Since our complex nonlinear problem might be difficult to solve by traditional methods,we design a compressive sensing-based gradient descent(CSGD)method to solve the control problem.Numerical simulation results show that our control strategy results in a 74.24％reduction in battery degradation cost on average compared to the control method without considering battery degradation.In addition,the compressive sensing method causes an 89.12％reduction in computation time cost compared to the traditional Monte Carlo(MC)method in solving the control problem.
查看更多>>摘要：This paper presents an Expanding Annular Domain(EAD)algorithm combined with Sum of Squares(SOS)program-ming to estimate and maximize the domain of attraction(DA)of power systems.The proposed algorithm can systematically construct polynomial Lyapunov functions for power systems with transfer conductance and reliably determine a less conservative approximated DA,which are quite difficult to achieve with traditional methods.With linear SOS programming,we begin from an initial estimated DA,then enlarge it by iteratively determining a series of so-called annular domains of attraction,each of which is characterized by level sets of two successively obtained Lyapunov functions.Moreover,the EAD algorithm is theoretically analyzed in detail and its validity and convergence are shown under certain conditions.In the end,our method is tested on two classical power system cases and is demonstrated to be superior to existing methods in terms of computational speed and conservativeness of results.
查看更多>>摘要：Increasing distributed generators(DGs)and flexible loads(FLs)enable distribution systems to provide both active and reactive power reserves(P-Q reserves)in supporting the frequency and voltage regulations of transmission systems.How-ever,such requirements at the interface between the transmission system operator(TSO)and distribution system operator(DSO)affect the distribution system operation security,considering the uncertainties of DGs and FLs.To exploit the reserve potential of distribution systems,this paper investigates the voltage-dependent P-Q reserve capacity(V-PQRC)of such types of distribution systems.V-PQRC reflects the feasible space of P-Q reserves that the DSO can provide to the TSO taking the voltage deviation limit at TSO-DSO interface into consideration,while ensuring the distribution system operation security under uncertainties of DGs and FLs.An evaluation method for V-PQRC at the TSO-DSO interface is proposed.To improve the robust performance of the evaluation method,the DG uncertainty is captured by a generalized ambiguity set and the FL uncertainty is addressed by designing a constrained sliding mode controller(CSMC).Three objectives are considered in the evaluation,i.e.,P reserve capacity,Q reserve capacity,and the voltage deviation limit at the TSO-DSO interface.Then,a multi-objective optimization model integrating the generalized robust chance-constrained optimization and CSMC(GRCC-CSMC)is established for V-PQRC evaluation to obtain the Pareto optimal reserve schemes.Finally,a non-approximated selecting(NAS)method is proposed to build up a simplified V-PQRC linear model,which can be convenient to apply in the transmission-distribution system coordination.Simulation results reveal that the V-PQRC evaluation method can achieve a good performance of accuracy and robustness against uncertainties.
查看更多>>摘要：Establishing a suitable closed-loop transfer function model for the grid-connected PMSG system is the key basis in performing inter-harmonic characteristics analysis.Multiple closed-loop transfer functions can be constructed when different components of the converter controller are taken into account.However,the effect of different components of the converter controller on inter-harmonic stability analysis is not clear.In this paper,the complete transfer function,considering different loops,is first given.Based on the complete closed-loop transfer function,the DC-link,PLL and voltage forward-feed are removed step by step to derive different closed-loop transfer functions.The inter-harmonic related poles of different closed-loop transfer functions are further calculated to analyze the effect of closed-loop transfer functions on inter-harmonic characteristics analysis.Finally,by performing time domain simulation,the correctness of the theoretical analysis results is verified.The results show that under the conditions of a weak AC system,each loop of the converter control system will reduce the stability of the inter-harmonic in the sub-synchronous frequency range and influence the inter-harmonic oscillation frequency.The transfer function needs to consider the influence of each loop to accurately calculate the inter-harmonic stability of the system.
查看更多>>摘要：A rational partition is the key prerequisite for the application of distributed algorithms in distribution networks.This paper proposes community-detection-based approaches to a distribution network partition,including a non-overlapping partition and a border-node partitioning method.First,a novel electrical distance is defined to quantify the coupling relationships between buses and it is further used as the edge weight in a transformed equivalent graph.Then,a vertex/link partition community detection approach is applied to over-partition the network into high intra-cohesive and low inter-coupled subre-gions.Following this,a greedy algorithm and a tabu search method are combined to merge these subregions into target numbers according to the scale similarity principle.The proposed approaches take the influence of three-phase imbalance into con-sideration and they are decoupled from the power flow.Finally,the approaches are tested on an IEEE 123-bus distribution system and the results verify the effectiveness and the credibility of our proposed methods.
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