Low-voltage distribution systems in our country are mostly used in agricultural loads and household loads. The value and using time of these kinds of loads are uncontrollable, which lead to the three-phase imbalance i...Low-voltage distribution systems in our country are mostly used in agricultural loads and household loads. The value and using time of these kinds of loads are uncontrollable, which lead to the three-phase imbalance in low-voltage distribution system, and seriously affect the quality of power supply. A new type of the commutation system and an improved quantum genetic algorithm (IQGA) are proposed in the paper. At last, the rationality and the efficiency of the method are verified by a practical example.展开更多
The transient phenomena of re-oxidation and slag entrapment occurring in the tundish during the ladle change-over process have been proven detrimental to clean steel production.Therefore,an unsteady three-phase turbul...The transient phenomena of re-oxidation and slag entrapment occurring in the tundish during the ladle change-over process have been proven detrimental to clean steel production.Therefore,an unsteady three-phase turbulence model,coupling velocity,temperature,and phase field was established to study the effect of the ladle shroud immersion depth on the slag eye formation,slag entrainment,slag dragging,air dragging,and flow characteristics during the ladle change-over process of a two-strand tundish.The results showed that reducing the immersion depth decreases the high-velocity region area under the slag layer in the quasi-steady process.During the emptying stage,as the molten bath level gradually decreases,the outlet temperature exhibits a trend of initially decreasing and subsequently increasing across all three shroud immersion depths.However,under a 210 mm shroud immersion depth,molten slag and air are dragged into the shroud,forming slag droplets and causing significant fluctuations,with a maximum scalar velocity of 0.0764 m/s at the monitoring point.In the filling stage,air and molten slag are dragged into the molten bath,forming bubbles and slag droplets at an immersion depth of 210 mm.Bubbles are observed within the molten slag layer,which can readily cause an emulsification phenomenon,making it easier to be dragged as slag droplets.Additionally,the slag eye area measured under 210 mm immersion depth at 45 s is 0.303 m^(2),while the maximum scalar velocity of 2.4259 m/s is detected at 12 s.At an immersion depth of 360 mm,the average area of the slag eye is minimized to 0.06268 m2,with corresponding variances of 0.006753,representing the optimal immersion depth.展开更多
This paper proposes a coordinated two-stage real-time market mechanism in an unbalanced distribution system which can utilize flexibility service from home energy management system(HEMS)to alleviate line congestion,vo...This paper proposes a coordinated two-stage real-time market mechanism in an unbalanced distribution system which can utilize flexibility service from home energy management system(HEMS)to alleviate line congestion,voltage violation,and substation-level power imbalance.At the grid level,the distribution system operator(DSO)computes the distribution locational marginal prices(DLMPs)and its energy,loss,congestion,and voltage violation components through comprehensive sensitivity analyses.By using the DLMP components in a firststage optimization problem,the DSO generates two price signals and sends them to HEMS to seek flexibility service.In response to the request of DSO,each home-level HEMS computes a flexibility range by incorporating the prices of DSO in its own optimization problem.Due to future uncertainties,the HEMS optimization problem is modeled as an adaptive dynamic programming(ADP)to minimize the total expected cost and discomfort of the household over a forward-looking horizon.The flexibility range of each HEMS is then used by the DSO in a second-stage optimization problem to determine new optimal dispatch points which ensure the efficient,reliable,and congestionfree operation of the distribution system.Lastly,the second-stage dispatch points are used by each HEMS to constrain its maximum consumption level in a final ADP to assign consumption level of major appliances such as energy storage,heating,ventilation and air-conditioning,and water heater.The proposed method is validated on an IEEE 69-bus system with a large number of regular and HEMS-equipped homes in each phase.展开更多
Unbalanced force produced by the unbalanced mass will affect vibrations of rotor systems,which probably results in the components failures of rotating machinery.To study the effects of unbalanced mass on the vibration...Unbalanced force produced by the unbalanced mass will affect vibrations of rotor systems,which probably results in the components failures of rotating machinery.To study the effects of unbalanced mass on the vibration characteristics of rotor systems,a flexible rotor system model considering the unbalanced mass is proposed.The time-varying bearing force is considered.The developed model is verified by the experimental and theoretical frequency spectrums.The displacements and axis orbits of flexible and rigid rotor systems are compared.The results show that the unbalanced mass will affect the vibration characteristics of rotor system.This model can be more suitable and effective to calculate vibration characteristics of rotor system with the flexible deformation and unbalanced mass.This paper provides a new reference and research method for predicting the vibrations of flexible rotor system considering the unbalanced mass.展开更多
The Vienna rectifier is a widely adopted solution for high-power rectification due to its efficiency and straightforward design.However,its performance can degrade under unbalanced three phase voltage conditions,leadi...The Vienna rectifier is a widely adopted solution for high-power rectification due to its efficiency and straightforward design.However,its performance can degrade under unbalanced three phase voltage conditions,leading to current zero-crossing distortion and compromised dynamic response.This paper investigates the causes of these distortions,identifying a phase shift between the input current and the grid voltage as a primary factor,and proposes an effective distortion phase identification strategy.Furthermore,the dynamic performance is enhanced through improved current reference calculations and a refined power feedforward strategy.This approach optimizes the system's response to load changes and maintains output voltage stability under unbalanced conditions.Simulation results validate the effectiveness of the proposed methods in reducing current distortion and improving overall performance.展开更多
Aiming at the challenge of complex load balancing coordination for a three-phase four-leg(3P4L)based multi-ended low voltage flexible DC distribution system(M-LVDC)considering unbalanced power compensation,this paper ...Aiming at the challenge of complex load balancing coordination for a three-phase four-leg(3P4L)based multi-ended low voltage flexible DC distribution system(M-LVDC)considering unbalanced power compensation,this paper proposes a phase-split power decoupling unbalanced compensation strategy based load balancing strategy for 3P4L based M-LVDC.Firstly,the topology and operation principle of the 3P4L-based M-LVDC system is introduced,and quasi-proportional resonant(QPR)based phase-split power current control for the 3P4L converter is proposed.Secondly,a load-balancing control strategy considering unbalanced compensation for 3P4L-based MLVDC is presented,in which the control diagrams for each 3P4L-based converter are detailed.The core idea of the proposed strategy is to comprehensively consider the imbalance compensation and load rate balancing between the two areas to calculate the split-phase power and current reference values of each 3P4L converter and achieve the static error-free tracking of the reference values through the QPR current inner-loop control.These reference values are then tracked with zero steady-state error using QPR current inner-loop control.Finally,the effectiveness of the proposed control strategy is verified through a 3P4L M-LVDC case study conducted on the PSCAD/EMTDC software.Theresults indicate that the proposed method not only can reduce the three-phase imbalance degrees from>20% to<0.5%,but also achieve excellent balanced load rates,with the load-rate difference smaller than 1.5%.展开更多
The difference in electricity and power usage time leads to an unbalanced current among the three phases in the power grid.The three-phase unbalanced is closely related to power planning and load distribution.When the...The difference in electricity and power usage time leads to an unbalanced current among the three phases in the power grid.The three-phase unbalanced is closely related to power planning and load distribution.When the unbalance occurs,the safe operation of the electrical equipment will be seriously jeopardized.This paper proposes a Hierarchical Temporal Memory(HTM)-based three-phase unbalance prediction model consisted by the encoder for binary coding,the spatial pooler for frequency pattern learning,the temporal pooler for pattern sequence learning,and the sparse distributed representations classifier for unbalance prediction.Following the feasibility of spatial-temporal streaming data analysis,we adopted this brain-liked neural network to a real-time prediction for power load.We applied the model in five cities(Tangshan,Langfang,Qinhuangdao,Chengde,Zhangjiakou)of north China.We experimented with the proposed model and Long Short-term Memory(LSTM)model and analyzed the predict results and real currents.The results show that the predictions conform to the reality;compared to LSTM,the HTM-based prediction model shows enhanced accuracy and stability.The prediction model could serve for the overload warning and the load planning to provide high-quality power grid operation.展开更多
This study addresses the critical challenge of reconfiguration in unbalanced power distribution networks(UPDNs),focusing on the complex 123-Bus test system.Three scenarios are investigated:(1)simultaneous power loss r...This study addresses the critical challenge of reconfiguration in unbalanced power distribution networks(UPDNs),focusing on the complex 123-Bus test system.Three scenarios are investigated:(1)simultaneous power loss reduction and voltage profile improvement,(2)minimization of voltage and current unbalance indices under various operational cases,and(3)multi-objective optimization using Pareto front analysis to concurrently optimize voltage unbalance index,active power loss,and current unbalance index.Unlike previous research that oftensimplified system components,this work maintains all equipment,including capacitor banks,transformers,and voltage regulators,to ensure realistic results.The study evaluates twelve metaheuristic algorithms to solve the reconfiguration problem(RecPrb)in UPDNs.A comprehensive statistical analysis is conducted to identify the most efficient algorithm for solving the RecPrb in the 123-Bus UPDN,employing multiple performance metrics and comparative techniques.The Artificial Hummingbird Algorithm emerges as the top-performing algorithm and is subsequently applied to address a multi-objective optimization challenge in the 123-Bus UPDN.This research contributes valuable insights for network operators and researchers in selecting suitable algorithms for specific reconfiguration scenarios,advancing the field of UPDN optimization and management.展开更多
To achieve high power rating and low current harmonics of motor drive,this paper develops a dual three-phase open-winding permanent magnet synchronous motor(DTP-OW-PMSM)drive with the DC-link voltage ratio of 2:1:1.Ba...To achieve high power rating and low current harmonics of motor drive,this paper develops a dual three-phase open-winding permanent magnet synchronous motor(DTP-OW-PMSM)drive with the DC-link voltage ratio of 2:1:1.Based on this topology,this paper proposes a DTP four-level space vector pulse width modulation(DTP-FL SVPWM)strategy.First,two identical three-phase four-level space vector diagrams are constructed and divided.Then,three adjacent vectors nearest to the reference vector in each diagram are selected for the vector synthesis to guarantee high modulation precision and low switching frequency.Furthermore,to avoid the modulation error caused by the voltage deviation,the proposed DTP-FL SVPWM strategy is further optimized through unified duty ratio compensation(UDRC).The effectiveness of the proposed strategy is verified through experiments.展开更多
The growing demand for efficient high-power switching power supplies has spurred interest in advanced topologies.The three-phase VIENNA converter stands out for its high power factor,simplified structure,and robust pe...The growing demand for efficient high-power switching power supplies has spurred interest in advanced topologies.The three-phase VIENNA converter stands out for its high power factor,simplified structure,and robust performance.Current research focuses on its operational principles,control strategies,and behavior under various load conditions.Key considerations include component selection,thermal management,and EMI/EMC optimization.This topology finds applications across renewable energy systems,industrial equipment,telecommunications,and electric vehicle charging infrastructures.Comparative analyses with alternative topologies and cost-benefit evaluations are also addressed.Future developments are expected to emphasize the integration of wide-bandgap devices and advancements in digital control techniques to further enhance efficiency and system performance.展开更多
This paper investigates a class of constrained distributed zeroth-order optimization(ZOO) problems over timevarying unbalanced graphs while ensuring privacy preservation among individual agents. Not taking into accoun...This paper investigates a class of constrained distributed zeroth-order optimization(ZOO) problems over timevarying unbalanced graphs while ensuring privacy preservation among individual agents. Not taking into account recent progress and addressing these concerns separately, there remains a lack of solutions offering theoretical guarantees for both privacy protection and constrained ZOO over time-varying unbalanced graphs.We hereby propose a novel algorithm, termed the differential privacy(DP) distributed push-sum based zeroth-order constrained optimization algorithm(DP-ZOCOA). Operating over time-varying unbalanced graphs, DP-ZOCOA obviates the need for supplemental suboptimization problem computations, thereby reducing overhead in comparison to distributed primary-dual methods. DP-ZOCOA is specifically tailored to tackle constrained ZOO problems over time-varying unbalanced graphs,offering a guarantee of convergence to the optimal solution while robustly preserving privacy. Moreover, we provide rigorous proofs of convergence and privacy for DP-ZOCOA, underscoring its efficacy in attaining optimal convergence without constraints. To enhance its applicability, we incorporate DP-ZOCOA into the federated learning framework and formulate a decentralized zeroth-order constrained federated learning algorithm(ZOCOA-FL) to address challenges stemming from the timevarying imbalance of communication topology. Finally, the performance and effectiveness of the proposed algorithms are thoroughly evaluated through simulations on distributed least squares(DLS) and decentralized federated learning(DFL) tasks.展开更多
The dual three-phase PMSM(DTP-PMSM)drives have received wide attention at high-power high-efficiency applications due to their merits of high output current ability and copper-loss-free field excitation.Meanwhile,the ...The dual three-phase PMSM(DTP-PMSM)drives have received wide attention at high-power high-efficiency applications due to their merits of high output current ability and copper-loss-free field excitation.Meanwhile,the DTPPMSM drive provides higher fault-tolerant capability for highreliability applications,e.g.,pumps and actuators in aircraft.For high-power drives with limited switching frequencies and highspeed drives with large fundamental frequencies,the ratio of switching frequency to fundamental frequency,i.e.,the carrier ratio,is usually below 15,which would significantly degrade the control performance.The purpose of this paper is to review the recent work on the modulation and control schemes for improving the operation performance of DTP-PMSM drives with low carrier ratios.Specifically,three categories of methods,i.e.,the space vector modulation based control,the model predictive control(MPC),and the optimized pulse pattern(OPP)based control are reviewed with principles and performance.In addition,brief discussions regarding the comparison and future trends are presented for low-carrier-ratio(LCR)modulation and control schemes of DTP-PMSM drives.展开更多
Excessive unbalanced vibrations of rotor-bearing systems significantly affect the stability and safety of high-end rotating machinery,such as aero engines,turbo-generators,and high-end machine tools.To realize the on-...Excessive unbalanced vibrations of rotor-bearing systems significantly affect the stability and safety of high-end rotating machinery,such as aero engines,turbo-generators,and high-end machine tools.To realize the on-line self-recovery of unbalanced vibration faults in a rotor system,a self-recovery regulation method based on the grey wolf optimization-adaptive linear quadratic regulator(GWO-ALQR)is proposed.First,a self-recovery regulation system for unbalanced vibrations was constructed,with the state-space equation of the control system obtained and discretized based on the dynamic equation of the rotor-bearing system.Subsequently,a self-recovery regulation method for unbalanced vi-brations based on GWO-ALQR was designed based on the state-space equation.In this method,the parameters of the control system are optimized using grey wolf optimization(GwO),with the working conditions identified on-line.The optimization parameters were selected independently,while the control commands were generated through a linear quadratic regulator(LQR)to control the action of the actuator to achieve self-recovery of the unbalanced vibration.The experimental results indicate that the unbalanced vibration of the rotor system can be restrained below the expected vibration threshold by the self-recovery regulation system based on GWO-ALQR and the final vibration suppression effect can exceed 70%.展开更多
Unlike previous theories with velocity and/or elastic modulus averaging, we use a three-phase porous rock physics model developed by Santos for analyzing the seismic response of two immiscible fluids in saturated poro...Unlike previous theories with velocity and/or elastic modulus averaging, we use a three-phase porous rock physics model developed by Santos for analyzing the seismic response of two immiscible fluids in saturated porous media. Considering reservoir reference pressure and coupling drag of two fluids in pores, the effects of frequency, porosity, and gas saturation on the phase velocities of the P-and S-waves are discussed in detail under field conditions. The effects of porosity and gas saturation on Vp/Vs are also provided. The data for our numerical experiments are from a sample of deep volcanic rock from Daqing. The numerical results show that the frequency dispersion effect can be ignored for deep volcanic rocks with low porosity and low permeability. It is concluded that for deep volcanic rocks the effect of gas content in pores on Vp/Vs is negligible but the effect of porosity is significant when there is a certain amount of water contained in the pores. The accurate estimate of lithology and porosity in this case is relatively more important.展开更多
For three phase four-wire active power filters （APFs）, several typical power theories and corresponding current reference generation strategies are induced, p-q, d-q, unify power factor （UPF） and instantaneous act...For three phase four-wire active power filters （APFs）, several typical power theories and corresponding current reference generation strategies are induced, p-q, d-q, unify power factor （UPF） and instantaneous active current （IAC） methods are analyzed and compared with each other. The interpretation of active and reactive currents in non-sinusoidal and unbalanced three-phase four-wire systems is given based on the generalized instantaneous reactive power theory. The performance and the characteristic are evaluated, and the application conditions of current reference generation strategies are concluded. Simulation results under different source voltages and loads verify the evaluation result.展开更多
The three-phase bridge inverter is used as the converter topology in the power controller for a 9 kW doubly salient permanent magnet （DSPM） motor. Compared with common three-phase bridge inverters, the proposed inve...The three-phase bridge inverter is used as the converter topology in the power controller for a 9 kW doubly salient permanent magnet （DSPM） motor. Compared with common three-phase bridge inverters, the proposed inverter works under more complicated conditions with different principles for special winding back EMFs, position signals of hall sensors, and the given mode of switches. The ideal steady driving principles of the inverter for the motor are given. The working state with asymmetric winding back EMFs, inaccurate position signals of hall sensors, and the changing input voltage is analyzed. Finally, experimental results vertify that the given anal ysis is correct.展开更多
This paper presents an extensive survey of the most commonly used tools for diagnosing unbalanced flow in the atmosphere, namely the Lagrangian Rossby number, Psi vector, divergence equation, nonlinear balance equatio...This paper presents an extensive survey of the most commonly used tools for diagnosing unbalanced flow in the atmosphere, namely the Lagrangian Rossby number, Psi vector, divergence equation, nonlinear balance equation, generalized omega-equation, and departure from fields obtained by potential vorticity (PV) inversion. The basic thoery, assumptions as well as implementation and limitations for each of the tools are all discussed. These tools are applied to high—resolution mesoscale model data to assess the role of unbalanced dynamics in the generation of a mesoscale gravity wave event over the East Coast of the United States. Comparison of these tools in this case study shows that these various methods agree to a large extent with each other though they differ in details. Key words Unbalanced flow - Geostrophic adjustment - Gravity waves - Nonlinear balance equation - Potential vorticity inversion - Omega equations - Rossby number This research was conducted under support from NSF grant ATM-9700626 of the United States. The numerical computations described herein were performed on the Cray T90 at the North Carolina Supercomputing Center and the Cray supercomputer at the NCAR Scientific Computing Division, which also provided the initialization fields for the MM5. Thanks are extended to Mark Stoelinga at University of Washington for the RIP post-processing package.展开更多
Low pressure sputtering with a controlled ratio of ion flux to deposited atom flux at the condensing surface is one of the main directions of development of magnetron sputtering methods. Unbalanced magnetron sputterin...Low pressure sputtering with a controlled ratio of ion flux to deposited atom flux at the condensing surface is one of the main directions of development of magnetron sputtering methods. Unbalanced magnetron sputtering, by producing dense secondary plasma around the substrate, provides a high ion current density. The closed-field unbalanced magnetron sputtering system （CFUBMS） has been established as a versatile technique for high-rate deposition high-quality metal, alloy, and ceramic thin films. The＇key factor in the CFUBMS system is the ability to transport high ion currents to the substrate, which can enhance the formation of full dense coatings at relatively low value homologous temperature. The investigation shows that the energy of ions incidenced at the substrate and the ratio of the flux of these ions to the flux of condensing atoms are the fundamental parameters in determining the structure and properties of films produced by ion-assisted deposition processes. Increasing ion bombardment during deposition combined with increasing mobility of the condensing atoms favors the formation of a dense microstructure and a smooth surface.展开更多
Generally, most soil slope failures are induced by rainfall infiltration, a process that involves interactions between the liquid phase, gas phase,and solid skeleton in an unsaturated soil slope. In this study, a loos...Generally, most soil slope failures are induced by rainfall infiltration, a process that involves interactions between the liquid phase, gas phase,and solid skeleton in an unsaturated soil slope. In this study, a loosely coupled liquid-gas-solid three-phase model, linking two numerical codes,TOUGH2/EOS3, which is used for water-air two-phase flow analysis, and FLAC^(3D), which is used for mechanical analysis, was established. The model was validated through a documented water drainage experiment over a sandy column and a comparison of the results with measured data and simulated results from other researchers. The proposed model was used to investigate the features of water-air two-phase flow and stress fields in an unsaturated soil slope during rainfall infiltration. The slope stability analysis was then performed based on the simulated water-air two-phase seepage and stress fields on a given slip surface. The results show that the safety factor for the given slip surface decreases first, then increases, and later decreases until the rainfall stops. Subsequently, a sudden rise occurs. After that, the safety factor decreases continually and reaches its lowest value, and then increases slowly to a steady value. The lowest value does not occur when the rainfall stops, indicating a delayed effect of the safety factor. The variations of the safety factor for the given slip surface are therefore caused by a combination of pore-air pressure, matric suction, normal stress, and net normal stress.展开更多
This article presents a novel method to measure unbalanced moments in a two-axis gimbaled seeker commonly believed to seviously influence the tracking accuracy and stabilizing capability.This method enables individual...This article presents a novel method to measure unbalanced moments in a two-axis gimbaled seeker commonly believed to seviously influence the tracking accuracy and stabilizing capability.This method enables individual measurement of unbalanced moments,and judgment of the seeker's status-balanced or not.Furthermore,an instrument is designed based on this method and calibrated.The effectiveness of the proposed method is validated through a simulation.The experimental results show a satisfied level of accuracy the measurements have.This work forms a basis for the further development of a more stabilized gimbaled seeker with less induced vibration and consumed power.展开更多
文摘Low-voltage distribution systems in our country are mostly used in agricultural loads and household loads. The value and using time of these kinds of loads are uncontrollable, which lead to the three-phase imbalance in low-voltage distribution system, and seriously affect the quality of power supply. A new type of the commutation system and an improved quantum genetic algorithm (IQGA) are proposed in the paper. At last, the rationality and the efficiency of the method are verified by a practical example.
基金supported by the National Natural Science Foundation of China(Nos.52422408 and 52171031)the Liaoning Xingliao Talents-Top-notch Young Talents Project(No.XLYC2203064)+1 种基金the Excellent Youth Fund of Liaoning Natural Science Foundation(No.2023JH3/10200001)the Fundamental Research Funds for the Central Universities(No.N2425004).
文摘The transient phenomena of re-oxidation and slag entrapment occurring in the tundish during the ladle change-over process have been proven detrimental to clean steel production.Therefore,an unsteady three-phase turbulence model,coupling velocity,temperature,and phase field was established to study the effect of the ladle shroud immersion depth on the slag eye formation,slag entrainment,slag dragging,air dragging,and flow characteristics during the ladle change-over process of a two-strand tundish.The results showed that reducing the immersion depth decreases the high-velocity region area under the slag layer in the quasi-steady process.During the emptying stage,as the molten bath level gradually decreases,the outlet temperature exhibits a trend of initially decreasing and subsequently increasing across all three shroud immersion depths.However,under a 210 mm shroud immersion depth,molten slag and air are dragged into the shroud,forming slag droplets and causing significant fluctuations,with a maximum scalar velocity of 0.0764 m/s at the monitoring point.In the filling stage,air and molten slag are dragged into the molten bath,forming bubbles and slag droplets at an immersion depth of 210 mm.Bubbles are observed within the molten slag layer,which can readily cause an emulsification phenomenon,making it easier to be dragged as slag droplets.Additionally,the slag eye area measured under 210 mm immersion depth at 45 s is 0.303 m^(2),while the maximum scalar velocity of 2.4259 m/s is detected at 12 s.At an immersion depth of 360 mm,the average area of the slag eye is minimized to 0.06268 m2,with corresponding variances of 0.006753,representing the optimal immersion depth.
文摘This paper proposes a coordinated two-stage real-time market mechanism in an unbalanced distribution system which can utilize flexibility service from home energy management system(HEMS)to alleviate line congestion,voltage violation,and substation-level power imbalance.At the grid level,the distribution system operator(DSO)computes the distribution locational marginal prices(DLMPs)and its energy,loss,congestion,and voltage violation components through comprehensive sensitivity analyses.By using the DLMP components in a firststage optimization problem,the DSO generates two price signals and sends them to HEMS to seek flexibility service.In response to the request of DSO,each home-level HEMS computes a flexibility range by incorporating the prices of DSO in its own optimization problem.Due to future uncertainties,the HEMS optimization problem is modeled as an adaptive dynamic programming(ADP)to minimize the total expected cost and discomfort of the household over a forward-looking horizon.The flexibility range of each HEMS is then used by the DSO in a second-stage optimization problem to determine new optimal dispatch points which ensure the efficient,reliable,and congestionfree operation of the distribution system.Lastly,the second-stage dispatch points are used by each HEMS to constrain its maximum consumption level in a final ADP to assign consumption level of major appliances such as energy storage,heating,ventilation and air-conditioning,and water heater.The proposed method is validated on an IEEE 69-bus system with a large number of regular and HEMS-equipped homes in each phase.
基金Support by Shanxi Provincial Key Research and Development Plan of China(Grant No.2024GH-ZDXM-29)National Natural Science Foundation of China(Grant No.52175120)Shaanxi Provincial Innovation Capability Support Program of China(Grant No.2024RS-CXTD-15)。
文摘Unbalanced force produced by the unbalanced mass will affect vibrations of rotor systems,which probably results in the components failures of rotating machinery.To study the effects of unbalanced mass on the vibration characteristics of rotor systems,a flexible rotor system model considering the unbalanced mass is proposed.The time-varying bearing force is considered.The developed model is verified by the experimental and theoretical frequency spectrums.The displacements and axis orbits of flexible and rigid rotor systems are compared.The results show that the unbalanced mass will affect the vibration characteristics of rotor system.This model can be more suitable and effective to calculate vibration characteristics of rotor system with the flexible deformation and unbalanced mass.This paper provides a new reference and research method for predicting the vibrations of flexible rotor system considering the unbalanced mass.
文摘The Vienna rectifier is a widely adopted solution for high-power rectification due to its efficiency and straightforward design.However,its performance can degrade under unbalanced three phase voltage conditions,leading to current zero-crossing distortion and compromised dynamic response.This paper investigates the causes of these distortions,identifying a phase shift between the input current and the grid voltage as a primary factor,and proposes an effective distortion phase identification strategy.Furthermore,the dynamic performance is enhanced through improved current reference calculations and a refined power feedforward strategy.This approach optimizes the system's response to load changes and maintains output voltage stability under unbalanced conditions.Simulation results validate the effectiveness of the proposed methods in reducing current distortion and improving overall performance.
基金supported by the key technology project of China Southern Power Grid Corporation(GZKJXM20220041)partly by theNational Key Research and Development Plan(2022YFE0205300).
文摘Aiming at the challenge of complex load balancing coordination for a three-phase four-leg(3P4L)based multi-ended low voltage flexible DC distribution system(M-LVDC)considering unbalanced power compensation,this paper proposes a phase-split power decoupling unbalanced compensation strategy based load balancing strategy for 3P4L based M-LVDC.Firstly,the topology and operation principle of the 3P4L-based M-LVDC system is introduced,and quasi-proportional resonant(QPR)based phase-split power current control for the 3P4L converter is proposed.Secondly,a load-balancing control strategy considering unbalanced compensation for 3P4L-based MLVDC is presented,in which the control diagrams for each 3P4L-based converter are detailed.The core idea of the proposed strategy is to comprehensively consider the imbalance compensation and load rate balancing between the two areas to calculate the split-phase power and current reference values of each 3P4L converter and achieve the static error-free tracking of the reference values through the QPR current inner-loop control.These reference values are then tracked with zero steady-state error using QPR current inner-loop control.Finally,the effectiveness of the proposed control strategy is verified through a 3P4L M-LVDC case study conducted on the PSCAD/EMTDC software.Theresults indicate that the proposed method not only can reduce the three-phase imbalance degrees from>20% to<0.5%,but also achieve excellent balanced load rates,with the load-rate difference smaller than 1.5%.
基金This study is supported by the National Natural Science Foundation of China(No.61801019).
文摘The difference in electricity and power usage time leads to an unbalanced current among the three phases in the power grid.The three-phase unbalanced is closely related to power planning and load distribution.When the unbalance occurs,the safe operation of the electrical equipment will be seriously jeopardized.This paper proposes a Hierarchical Temporal Memory(HTM)-based three-phase unbalance prediction model consisted by the encoder for binary coding,the spatial pooler for frequency pattern learning,the temporal pooler for pattern sequence learning,and the sparse distributed representations classifier for unbalance prediction.Following the feasibility of spatial-temporal streaming data analysis,we adopted this brain-liked neural network to a real-time prediction for power load.We applied the model in five cities(Tangshan,Langfang,Qinhuangdao,Chengde,Zhangjiakou)of north China.We experimented with the proposed model and Long Short-term Memory(LSTM)model and analyzed the predict results and real currents.The results show that the predictions conform to the reality;compared to LSTM,the HTM-based prediction model shows enhanced accuracy and stability.The prediction model could serve for the overload warning and the load planning to provide high-quality power grid operation.
基金supported by the Scientific and Technological Research Council of Turkey(TUBITAK)under Grant No.124E002(1001-Project).
文摘This study addresses the critical challenge of reconfiguration in unbalanced power distribution networks(UPDNs),focusing on the complex 123-Bus test system.Three scenarios are investigated:(1)simultaneous power loss reduction and voltage profile improvement,(2)minimization of voltage and current unbalance indices under various operational cases,and(3)multi-objective optimization using Pareto front analysis to concurrently optimize voltage unbalance index,active power loss,and current unbalance index.Unlike previous research that oftensimplified system components,this work maintains all equipment,including capacitor banks,transformers,and voltage regulators,to ensure realistic results.The study evaluates twelve metaheuristic algorithms to solve the reconfiguration problem(RecPrb)in UPDNs.A comprehensive statistical analysis is conducted to identify the most efficient algorithm for solving the RecPrb in the 123-Bus UPDN,employing multiple performance metrics and comparative techniques.The Artificial Hummingbird Algorithm emerges as the top-performing algorithm and is subsequently applied to address a multi-objective optimization challenge in the 123-Bus UPDN.This research contributes valuable insights for network operators and researchers in selecting suitable algorithms for specific reconfiguration scenarios,advancing the field of UPDN optimization and management.
基金supported in part by the National Natural Science Foundation of China under Grant 62303333in part by the Project of Hetao Shenzhen-Hong Kong Science and Technology Innovation Cooperation Zone under Grant HZQB-KCZYB-2020083.
文摘To achieve high power rating and low current harmonics of motor drive,this paper develops a dual three-phase open-winding permanent magnet synchronous motor(DTP-OW-PMSM)drive with the DC-link voltage ratio of 2:1:1.Based on this topology,this paper proposes a DTP four-level space vector pulse width modulation(DTP-FL SVPWM)strategy.First,two identical three-phase four-level space vector diagrams are constructed and divided.Then,three adjacent vectors nearest to the reference vector in each diagram are selected for the vector synthesis to guarantee high modulation precision and low switching frequency.Furthermore,to avoid the modulation error caused by the voltage deviation,the proposed DTP-FL SVPWM strategy is further optimized through unified duty ratio compensation(UDRC).The effectiveness of the proposed strategy is verified through experiments.
文摘The growing demand for efficient high-power switching power supplies has spurred interest in advanced topologies.The three-phase VIENNA converter stands out for its high power factor,simplified structure,and robust performance.Current research focuses on its operational principles,control strategies,and behavior under various load conditions.Key considerations include component selection,thermal management,and EMI/EMC optimization.This topology finds applications across renewable energy systems,industrial equipment,telecommunications,and electric vehicle charging infrastructures.Comparative analyses with alternative topologies and cost-benefit evaluations are also addressed.Future developments are expected to emphasize the integration of wide-bandgap devices and advancements in digital control techniques to further enhance efficiency and system performance.
基金supported in part by the National Key Research and Development Program of China(2022ZD0120001)the National Natural Science Foundation of China(62233004,62273090,62073076)the Jiangsu Provincial Scientific Research Center of Applied Mathematics(BK20233002)
文摘This paper investigates a class of constrained distributed zeroth-order optimization(ZOO) problems over timevarying unbalanced graphs while ensuring privacy preservation among individual agents. Not taking into account recent progress and addressing these concerns separately, there remains a lack of solutions offering theoretical guarantees for both privacy protection and constrained ZOO over time-varying unbalanced graphs.We hereby propose a novel algorithm, termed the differential privacy(DP) distributed push-sum based zeroth-order constrained optimization algorithm(DP-ZOCOA). Operating over time-varying unbalanced graphs, DP-ZOCOA obviates the need for supplemental suboptimization problem computations, thereby reducing overhead in comparison to distributed primary-dual methods. DP-ZOCOA is specifically tailored to tackle constrained ZOO problems over time-varying unbalanced graphs,offering a guarantee of convergence to the optimal solution while robustly preserving privacy. Moreover, we provide rigorous proofs of convergence and privacy for DP-ZOCOA, underscoring its efficacy in attaining optimal convergence without constraints. To enhance its applicability, we incorporate DP-ZOCOA into the federated learning framework and formulate a decentralized zeroth-order constrained federated learning algorithm(ZOCOA-FL) to address challenges stemming from the timevarying imbalance of communication topology. Finally, the performance and effectiveness of the proposed algorithms are thoroughly evaluated through simulations on distributed least squares(DLS) and decentralized federated learning(DFL) tasks.
基金supported by the National Key Research and Development Program of China under the grant of 2022YFB3403100。
文摘The dual three-phase PMSM(DTP-PMSM)drives have received wide attention at high-power high-efficiency applications due to their merits of high output current ability and copper-loss-free field excitation.Meanwhile,the DTPPMSM drive provides higher fault-tolerant capability for highreliability applications,e.g.,pumps and actuators in aircraft.For high-power drives with limited switching frequencies and highspeed drives with large fundamental frequencies,the ratio of switching frequency to fundamental frequency,i.e.,the carrier ratio,is usually below 15,which would significantly degrade the control performance.The purpose of this paper is to review the recent work on the modulation and control schemes for improving the operation performance of DTP-PMSM drives with low carrier ratios.Specifically,three categories of methods,i.e.,the space vector modulation based control,the model predictive control(MPC),and the optimized pulse pattern(OPP)based control are reviewed with principles and performance.In addition,brief discussions regarding the comparison and future trends are presented for low-carrier-ratio(LCR)modulation and control schemes of DTP-PMSM drives.
基金Supported by National Natural Science Foundation of China(Grant No.51875031)Beijing Municipal Natural Science Foundation of China(Grant No.3212010).
文摘Excessive unbalanced vibrations of rotor-bearing systems significantly affect the stability and safety of high-end rotating machinery,such as aero engines,turbo-generators,and high-end machine tools.To realize the on-line self-recovery of unbalanced vibration faults in a rotor system,a self-recovery regulation method based on the grey wolf optimization-adaptive linear quadratic regulator(GWO-ALQR)is proposed.First,a self-recovery regulation system for unbalanced vibrations was constructed,with the state-space equation of the control system obtained and discretized based on the dynamic equation of the rotor-bearing system.Subsequently,a self-recovery regulation method for unbalanced vi-brations based on GWO-ALQR was designed based on the state-space equation.In this method,the parameters of the control system are optimized using grey wolf optimization(GwO),with the working conditions identified on-line.The optimization parameters were selected independently,while the control commands were generated through a linear quadratic regulator(LQR)to control the action of the actuator to achieve self-recovery of the unbalanced vibration.The experimental results indicate that the unbalanced vibration of the rotor system can be restrained below the expected vibration threshold by the self-recovery regulation system based on GWO-ALQR and the final vibration suppression effect can exceed 70%.
文摘Unlike previous theories with velocity and/or elastic modulus averaging, we use a three-phase porous rock physics model developed by Santos for analyzing the seismic response of two immiscible fluids in saturated porous media. Considering reservoir reference pressure and coupling drag of two fluids in pores, the effects of frequency, porosity, and gas saturation on the phase velocities of the P-and S-waves are discussed in detail under field conditions. The effects of porosity and gas saturation on Vp/Vs are also provided. The data for our numerical experiments are from a sample of deep volcanic rock from Daqing. The numerical results show that the frequency dispersion effect can be ignored for deep volcanic rocks with low porosity and low permeability. It is concluded that for deep volcanic rocks the effect of gas content in pores on Vp/Vs is negligible but the effect of porosity is significant when there is a certain amount of water contained in the pores. The accurate estimate of lithology and porosity in this case is relatively more important.
文摘For three phase four-wire active power filters （APFs）, several typical power theories and corresponding current reference generation strategies are induced, p-q, d-q, unify power factor （UPF） and instantaneous active current （IAC） methods are analyzed and compared with each other. The interpretation of active and reactive currents in non-sinusoidal and unbalanced three-phase four-wire systems is given based on the generalized instantaneous reactive power theory. The performance and the characteristic are evaluated, and the application conditions of current reference generation strategies are concluded. Simulation results under different source voltages and loads verify the evaluation result.
文摘The three-phase bridge inverter is used as the converter topology in the power controller for a 9 kW doubly salient permanent magnet （DSPM） motor. Compared with common three-phase bridge inverters, the proposed inverter works under more complicated conditions with different principles for special winding back EMFs, position signals of hall sensors, and the given mode of switches. The ideal steady driving principles of the inverter for the motor are given. The working state with asymmetric winding back EMFs, inaccurate position signals of hall sensors, and the changing input voltage is analyzed. Finally, experimental results vertify that the given anal ysis is correct.
文摘This paper presents an extensive survey of the most commonly used tools for diagnosing unbalanced flow in the atmosphere, namely the Lagrangian Rossby number, Psi vector, divergence equation, nonlinear balance equation, generalized omega-equation, and departure from fields obtained by potential vorticity (PV) inversion. The basic thoery, assumptions as well as implementation and limitations for each of the tools are all discussed. These tools are applied to high—resolution mesoscale model data to assess the role of unbalanced dynamics in the generation of a mesoscale gravity wave event over the East Coast of the United States. Comparison of these tools in this case study shows that these various methods agree to a large extent with each other though they differ in details. Key words Unbalanced flow - Geostrophic adjustment - Gravity waves - Nonlinear balance equation - Potential vorticity inversion - Omega equations - Rossby number This research was conducted under support from NSF grant ATM-9700626 of the United States. The numerical computations described herein were performed on the Cray T90 at the North Carolina Supercomputing Center and the Cray supercomputer at the NCAR Scientific Computing Division, which also provided the initialization fields for the MM5. Thanks are extended to Mark Stoelinga at University of Washington for the RIP post-processing package.
文摘Low pressure sputtering with a controlled ratio of ion flux to deposited atom flux at the condensing surface is one of the main directions of development of magnetron sputtering methods. Unbalanced magnetron sputtering, by producing dense secondary plasma around the substrate, provides a high ion current density. The closed-field unbalanced magnetron sputtering system （CFUBMS） has been established as a versatile technique for high-rate deposition high-quality metal, alloy, and ceramic thin films. The＇key factor in the CFUBMS system is the ability to transport high ion currents to the substrate, which can enhance the formation of full dense coatings at relatively low value homologous temperature. The investigation shows that the energy of ions incidenced at the substrate and the ratio of the flux of these ions to the flux of condensing atoms are the fundamental parameters in determining the structure and properties of films produced by ion-assisted deposition processes. Increasing ion bombardment during deposition combined with increasing mobility of the condensing atoms favors the formation of a dense microstructure and a smooth surface.
基金supported by the National Natural Science Foundation of China(Grants No.51579170 and 51179118)the Science Fund for Creative Research Groups of the National Natural Science Foundation of China(Grant No.51321065)
文摘Generally, most soil slope failures are induced by rainfall infiltration, a process that involves interactions between the liquid phase, gas phase,and solid skeleton in an unsaturated soil slope. In this study, a loosely coupled liquid-gas-solid three-phase model, linking two numerical codes,TOUGH2/EOS3, which is used for water-air two-phase flow analysis, and FLAC^(3D), which is used for mechanical analysis, was established. The model was validated through a documented water drainage experiment over a sandy column and a comparison of the results with measured data and simulated results from other researchers. The proposed model was used to investigate the features of water-air two-phase flow and stress fields in an unsaturated soil slope during rainfall infiltration. The slope stability analysis was then performed based on the simulated water-air two-phase seepage and stress fields on a given slip surface. The results show that the safety factor for the given slip surface decreases first, then increases, and later decreases until the rainfall stops. Subsequently, a sudden rise occurs. After that, the safety factor decreases continually and reaches its lowest value, and then increases slowly to a steady value. The lowest value does not occur when the rainfall stops, indicating a delayed effect of the safety factor. The variations of the safety factor for the given slip surface are therefore caused by a combination of pore-air pressure, matric suction, normal stress, and net normal stress.
文摘This article presents a novel method to measure unbalanced moments in a two-axis gimbaled seeker commonly believed to seviously influence the tracking accuracy and stabilizing capability.This method enables individual measurement of unbalanced moments,and judgment of the seeker's status-balanced or not.Furthermore,an instrument is designed based on this method and calibrated.The effectiveness of the proposed method is validated through a simulation.The experimental results show a satisfied level of accuracy the measurements have.This work forms a basis for the further development of a more stabilized gimbaled seeker with less induced vibration and consumed power.
