查看更多>>摘要：Grid forming controllers need to operate with a large variation of grid parameters and grid structures,for instance,during black-start operation,connection to HVDC diode rectifiers,etc.This paper proposes a methodology for the synthesis of robust grid forming controllers for HVDC diode rectifier based wind power plants using H∞ control.The different operating modes of an HVDC diode rectifier based wind power plant should be considered for the controller synthesis using the proposed H∞ controller design methodology.The proposed methodology for grid forming controller design improves the performance and robustness of well tuned standard proportional-resonant based controllers.The results have been validated experimentally at the wind turbine level by means of a small power prototype.The validation at the system level has been carried out using a realistic simulation of the HVDC diode rectifier-connected wind power plant.
查看更多>>摘要：Maximum power point tracking(MPPT)systems are being developed to produce switching pulses with proper duty ratios for power switches to exert photovoltaic(PV)panels under maximum instantaneous generated power,usually through a traditional DC-DC boost converter.The fundamental issue,particularly for micro-grid and small-scale green DC or AC energy applications,is that the voltage supplied by the MPPT boost converter is insufficient.In order to increase resulting MPP voltage,this research proposes a new high-voltage gain DC-DC boost converter for a cascade connection with an MPPT boost converter.Input side of the proposed converter employs a switched-inductor cell to reduce input current source ripples which is a critical problem in PV systems for high-reliability applications.Additionally,a switched-capacitor cell is used at the converter's output side to boost voltage gain and reduce voltage stress across converter's power switches,which is a crucial factor for longer life of PV panel and proposed converter components,particularly semiconductor devices.Performance of the converter is assessed while taking into account variations in irradiation and temperature brought on by changing weather conditions.A prototype converter at a laboratory scale is utilized and examined.Outcomes of hardware tests support the findings of theoretical and simulation studies.
查看更多>>摘要：Impedance measurement is an effective solution for evaluating stability of a power system with high penetration of renewable sources.In this paper,the impedance measurement is achieved by a typical high-power impedance measuring converter(HPIM-converter)with chirp signal injection.The modulation saturation phenomenon of the HPIM-converter is revealed,and the frequency sweep boundary is analyzed in detail.To expand the rated frequency range of the HPIM-converter,a spread frequency band control scheme based on an over-modulation technique is proposed in this paper.The proposed control method enlarges the rated frequency band and can inject a disturbance voltage into the system under test with consistent amplitude in the rated frequency band.Also,a smooth transition strategy between linear modulation mode and over-modulation mode is proposed for suppressing signal fluctuation.Finally,the effectiveness of the proposed method is verified by simulation tests.
查看更多>>摘要：DC line protection with high speed and strong robustness against high fault resistance is essential in high-voltage direct current(HVDC)grids.The conventional voltage-derivative-based protections for DC lines exhibit the problem of low reliability on the occurrence of high-impedance faults.In this paper,fault traveling waves at the fault point and at the line side of the DC reactor are first analyzed using phase-modal transformation.Based on the theoretical analysis of the modal fault-component voltages at the line side of the DC reactor,a novel hybrid protection scheme utilizing the single-ended rate of change of voltage(ROCOV)and waveform similarity coefficient is proposed.It utilizes the hybrid ROCOV criterion and waveform similarity coefficient to identify the faulted line and the amplitudes of the 0-and 1-mode fault-component voltages to identify fault type,and the polarities of the 0-and 1-mode fault-component voltages to identify faulted pole.Simulations under various fault conditions verify that the proposed protection scheme can achieve fast and reliable identification of faulted line,fault type,and faulted pole in 1 ms,and effectively improve the reliability against high-impedance faults up to 1200 Q.
查看更多>>摘要：This paper analyzes the optimal switching modes of the dual-active-bridge(DAB)DC-DC converter to minimize losses in DC-DC converters that exhibit a wide voltage range,high efficiency,and high performance.By solving the multi-objective constrained conditional extremums with the Karush-KuhnTucker(KKT)method,a triple-phase-shift(TPS)optimal modulation with full range of operation,global continuity,and simple calculation is obtained.By adopting TPS modulation,the DAB can decrease reactive power when dc voltages are mismatched and obtain global optimization of conduction loss and soft-switching in the full range of operation.Generation of dc-offset current in the ac link is analyzed.Static and dynamic dc-offset currents are suppressed based on TPS modulation.With direct-power feed-forward,high-dynamic control is used to improve system response to external disturbances.The digital control strategy of the whole system is designed,and optimal modulation and high-performance control are verified on the experimental prototype.
查看更多>>摘要：To improve observability in power distribution net-works(PDN),a two-step framework of multi-topology identi-fication and parameter estimation is proposed in this paper.Specifically,in the first step,a mixed-integer linear program(MILP)model-based split method is proposed to recognize mixed topologies in a multi-record dataset without a prerequisite on the number of topology categories and values of nodal voltage phase angles.In the second step,line parameters and nodal voltage phase angles are estimated using the Newton-Raphson method based on nodal measurements of real and reactive power injections,as well as voltage magnitudes.Furthermore,a modified estimation model is proposed to apply to the multi-topology dataset.Finally,case studies on an IEEE 33-bus system illustrate the effectiveness of the proposed models in identifying the PDN's topologies,as well as estimating line parameters and voltage phase angles.
查看更多>>摘要：Large integration of electric vehicles(EVs)brings uncertainties and challenges for distribution networks.Reliability and allocation of charging systems(charging stations and piles)need strong support from the distribution network,whose expan-sion planning would be also greatly impacted by the incremental load from the charging system.To address this issue,a collabora-tive planning scheme of the EV charging system and distribution networks that combines economic and reliability benefits is proposed,which is formulated as a two-stage distributionally robust optimization model considering source-load uncertainties.First,a candidate EVCS planning scheme is obtained using queuing theory.Then,system reliability is quantified by adopting the average energy not supplied index and correlated integrated into the two-stage mixed-integer linear programming model.Finally,it is solved to perform distributionally robust expansion planning by the column and constraint generation algorithm.Effectiveness and scalability of the proposed planning method are illustrated by numerical case studies.Results indicate the planning scheme that considers economic and reliability benefit can perform better than traditional optimization methods.
查看更多>>摘要：This paper proposes a novel filtering algorithm for simultaneous estimation of unknown inputs and states of a class of nonlinear discrete-time heterogeneous multi-agent systems.Based on the Taylor approximation of the nonlinear multi-agent system,a distributed semi-cooperative switch-mode filter is developed to achieve the minimum-variance unbiased(MVU)estimation of the unknown inputs and states.Compared with the conventional decentralized EKF-based unknown input filter,the proposed distributed filter has a more relaxed existence condition of the filter,which makes it more applicable in reality.This new type of filter is then successfully applied to the simultaneous estimation of state of charge(SOC)and temperature of a battery pack for battery management of electric vehicles and grid-tied energy storage systems.
查看更多>>摘要：Along with the wide-ranging addition of wind power into power systems,multiple uncertainties are produced due to continuous changes of wind power,which in turn will affect the dispatching and operational process of the power grid.In this process,excessive pursuit of the lowest risk of wind energy may bring an apparent influence on the economic effect of the multi-energy complementary power generation system because a continuous imbalance between demand and supply may lead to wind curtailment.To solve these issues,a new model that couples the multi-dimensional uncertainty model with the day-ahead complementary operation model is developed for a wind-hydro-thermal system.A multi-dimensional uncertainty model(MU)is used to deal with wind uncertainty because it can quantitatively describe the complex features of error distribution of hourly day-ahead wind power forecasting.The multi-dimensional interval scenes attained by the MU model can reflect hour-to-hour uncertain interaction in the day-ahead complementary operation for the wind-hydro-thermal system.This new model can make up for the shortcomings of the day-ahead operation model by reducing wind power risk and optimizing the operational costs.A two-layer nested approach with the hierarchical structure is applied to handle the wind-hydro-thermal system's complex equality and inequality constraints.The new model and algo-rithm's effectiveness can be evaluated by applying them to the Shaanxi Electric Power Company in China.Results demonstrated that:compared with the conventional operation strategies,the proposed model can save the operational cost of the units by 7.92％and the hybrid system by 0.995％,respectively.This study can offer references for the impact of renewable energy on the power grid within the context of the day-ahead electricity market.
查看更多>>摘要：This paper presents a two-step procedure to enable residential Demand Response(DR)programs in Multi-Carrier Energy Systems(MCES),including combined heat and power generation,renewable resources,boiler,and energy storage systems.In the first step,an optimization problem is solved to determine the optimal energy cost for each customer.In the second step,the system operator(SO)minimizes the summation of the total loss cost of the electrical distribution system and a designed motivational payment,subject to various operational constraints of the MCES.The motivational payment is the function of deviation of the resulting energy cost of a home in the second step from the desired cost obtained in the first step.The main idea of the proposed procedure is to consider the concerns of customers and the operator,simultaneously.This paper also addresses the uncertainties in renewable resources generation.The proposed procedure is simulated on a test energy system for various cases.The results show that as the level of customer participation in the proposed program is increased,the technical aspects of the integrated energy system are improved.In addition,the customers'costs are decreased by participation in the proposed program.
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