The high potentiality of integrating renewable energies,such as photovoltaic,into a modern electrical microgrid system,using DC-to-DC converters,raises some issues associated with controller loop design and system sta...The high potentiality of integrating renewable energies,such as photovoltaic,into a modern electrical microgrid system,using DC-to-DC converters,raises some issues associated with controller loop design and system stability.The generalized state space average model(GSSAM)concept was consequently introduced to design a DC-to-DC converter controller in order to evaluate DC-to-DC converter performance and to conduct stability studies.This paper presents a GSSAM for parallel DC-to-DC converters,namely:buck,boost,and buck-boost converters.The rationale of this study is that modern electrical systems,such as DC networks,hybrid microgrids,and electric ships,are formed by parallel DC-to-DC converters with separate DC input sources.Therefore,this paper proposes a GSSAM for any number of parallel DC-to-DC converters.The proposed GSSAM is validated and investigated in a time-domain simulation environment,namely a MATLAB/SIMULINK.The study compares the steady-state,transient,and oscillatory performance of the state-space average model with a fully detailed switching model.展开更多
A new algorithm is proposed, which immolates the optimality of control policies potentially to obtain the robnsticity of solutions. The robnsticity of solutions maybe becomes a very important property for a learning s...A new algorithm is proposed, which immolates the optimality of control policies potentially to obtain the robnsticity of solutions. The robnsticity of solutions maybe becomes a very important property for a learning system when there exists non-matching between theory models and practical physical system, or the practical system is not static, or the availability of a control action changes along with the variety of time. The main contribution is that a set of approximation algorithms and their convergence results are given. A generalized average operator instead of the general optimal operator max （or rain） is applied to study a class of important learning algorithms, dynamic prOgramming algorithms, and discuss their convergences from theoretic point of view. The purpose for this research is to improve the robnsticity of reinforcement learning algorithms theoretically.展开更多
To improve the forecasting reliability of travel time, the time-varying confidence interval of travel time on arterials is forecasted using an autoregressive integrated moving average and generalized autoregressive co...To improve the forecasting reliability of travel time, the time-varying confidence interval of travel time on arterials is forecasted using an autoregressive integrated moving average and generalized autoregressive conditional heteroskedasticity （ARIMA-GARCH） model. In which, the ARIMA model is used as the mean equation of the GARCH model to model the travel time levels and the GARCH model is used to model the conditional variances of travel time. The proposed method is validated and evaluated using actual traffic flow data collected from the traffic monitoring system of Kunshan city. The evaluation results show that, compared with the conventional ARIMA model, the proposed model cannot significantly improve the forecasting performance of travel time levels but has advantage in travel time volatility forecasting. The proposed model can well capture the travel time heteroskedasticity and forecast the time-varying confidence intervals of travel time which can better reflect the volatility of observed travel times than the fixed confidence interval provided by the ARIMA model.展开更多
The dual active bridge(DAB)converter is gaining more and more attention in various applications such as energy storage systems,electric vehicles and smart grids.To improve the quality of the input current,a LC filter ...The dual active bridge(DAB)converter is gaining more and more attention in various applications such as energy storage systems,electric vehicles and smart grids.To improve the quality of the input current,a LC filter is often cascaded at the input side of the DAB converter.However,there are instable problems of this cascaded system due to the impedance interactions of the DAB converter and the LC filter,although the DAB converter is stable at the individual operation mode.To assess the stability of the cascaded system of the DAB converter and the LC filter,the impedance model of the DAB converter is firstly developed based on generalized state-space averaging method.The developed impedance model can be used to accurately predict the stability of the DAB converter with its LC input filter.Based on the stability analysis,the optimum filter parameter design guideline is determined.The impedance model and stability analysis are validated by the simulation and experimental results.展开更多
The generalized self-consistent finite-element iterative averaging method was adopted to analyze the elasto-plastic tensile properties of SiC whiskers reinforced aluminum matrix composites. The effects of varying fibe...The generalized self-consistent finite-element iterative averaging method was adopted to analyze the elasto-plastic tensile properties of SiC whiskers reinforced aluminum matrix composites. The effects of varying fiber's aspect ratio and volume fraction on the macroscopic elasto-plastic deformation of the composites were studied. By the analysis of microscopic stress fields, the relation between the propagation of the elasto-plastic region in the matrix and the macroscopic elasto-plastic deformation of composites was discussed. It was found that the propagation of the plastic region in the matrix between the fiber's ends would affect prominently the elasto-plastic tensile behaviour of the composites. It was shown that the characterization of the stress-strain response in terms of the 0.2% offset yield strength is incomplete.展开更多
In this paper, we present two parallel algorithms to compute common fixed points of a finite family of quasi-nonexpansive mappings in real Hilbert spaces, which improve and generalize some known results in this direct...In this paper, we present two parallel algorithms to compute common fixed points of a finite family of quasi-nonexpansive mappings in real Hilbert spaces, which improve and generalize some known results in this direction.展开更多
Due to the advanced features of multidirectional power transfer and fast smoothing of the power fluctuation in renewable energy systems,the multiple-active-bridge based power-electronic-transformer(MAB-PET)with integr...Due to the advanced features of multidirectional power transfer and fast smoothing of the power fluctuation in renewable energy systems,the multiple-active-bridge based power-electronic-transformer(MAB-PET)with integrated energy storage units is becoming popular.However,the accurate electromagnetic transient simulation of the MAB-PETs is extremely time-consuming due to the large number of circuit nodes and small time-step.This paper proposes a simplified EMT modeling approach for the MAB-PETs by employing the generalized state-space averaging method.First,the switching function method and Dommel algorithm are used to build the equivalent model of each power module.Further,the PET equivalent model is presented in a multi-port PM polymerization mode.The system is simplified by applying Fourier Decomposition to its state functions by ignoring high-order harmonics.Finally,a four-port equivalent voltage source circuit is obtained.The proposed simplified equivalent model is compared with the detailed model in PSCAD/EMTDC.Simulation results show the proposed approach has excellent accuracy and is 2–3 orders of magnitude faster than the DM.展开更多
The dual active bridge(DAB)is a widely used DC-DC topology owing to its ease of control and ability to achieve various control objectives.When designing a DAB-based system under broadband perturbations,one must model ...The dual active bridge(DAB)is a widely used DC-DC topology owing to its ease of control and ability to achieve various control objectives.When designing a DAB-based system under broadband perturbations,one must model the DAB,calculate its input impedance,and analyze the system stability.In this study,two continuous-time impedance models of the DAB,i.e.,a reduced-order model named the power-based impedance model(PBIM)and a full-order model named the generalized state-space average impedance model(GSSAM),are proposed and used to calculate the input impedance in a single-phase modulation mode.The modeling errors are analyzed,the participation factors and residuals are calculated,and a Bode diagram is constructed to illustrate the change in the input impedance with increasing leakage inductance.Simulations are conducted using various circuit parameters to verify the results.The results show that the PBIM exhibits simplicity and accuracy in the low-frequency domain,whereas the GSSAM performs better in the high-frequency domain.展开更多
The modeling approaches of power converters occupy an important position in power electronic systems and have made considerable progress over the past years.Continuous modeling approaches and linearization techniques ...The modeling approaches of power converters occupy an important position in power electronic systems and have made considerable progress over the past years.Continuous modeling approaches and linearization techniques are reviewed,including the state-space average model,generalized average model,averaged small-signal model,and describing function method.A Buck converter with PWM modulation and voltage-mode control is taken as an example to compare the advantages and disadvantages of different methods through simulation analysis.Moreover,the corresponding equivalent circuit with an intuitive physical meaning of state-space average model,generalized average model,and averaged small-signal model is given.The results point out that the generalized average model can improve the modeling accuracy based on the state-space average model.In the linearization techniques,the averaged small-signal model reflects accuracy at low frequencies,but introduces phase lag in the high-frequency region.The describing function method is derived from harmonic linearization,which takes into account the sideband effect and improves the modeling accuracy at high frequencies.展开更多
This paper proposes a system identification framework based on eigensystem realization to accurately model power electronic converters.The proposed framework affords an energy-based optimal reduction method to precise...This paper proposes a system identification framework based on eigensystem realization to accurately model power electronic converters.The proposed framework affords an energy-based optimal reduction method to precisely identify the dynamics of power electronic converters from simulated or actual raw data measured at the converter’s ports.This method does not require any prior knowledge of the topology or internal parameters of the converter to derive the system modal information.The accuracy and feasibility of the proposed method are exhaustively evaluated via simulations and practical tests on a software-simulated and hardware-implemented dual active bridge(DAB)converter under steady-state and transient conditions.After various comparisons with the Fourier series-based generalized average model,switching model,and experimental measurements,the proposed method attains a root mean square error(RMSE)of less than 1%with respect to the actual raw data.Moreover,the computational effort is reduced to 1/8.6 of the Fourier series-based model.展开更多
In this paper,we obtain the sharp Hardy space estimate of the maximal wave operator.Some applications on spherical averages and their combinations are also given.
文摘The high potentiality of integrating renewable energies,such as photovoltaic,into a modern electrical microgrid system,using DC-to-DC converters,raises some issues associated with controller loop design and system stability.The generalized state space average model(GSSAM)concept was consequently introduced to design a DC-to-DC converter controller in order to evaluate DC-to-DC converter performance and to conduct stability studies.This paper presents a GSSAM for parallel DC-to-DC converters,namely:buck,boost,and buck-boost converters.The rationale of this study is that modern electrical systems,such as DC networks,hybrid microgrids,and electric ships,are formed by parallel DC-to-DC converters with separate DC input sources.Therefore,this paper proposes a GSSAM for any number of parallel DC-to-DC converters.The proposed GSSAM is validated and investigated in a time-domain simulation environment,namely a MATLAB/SIMULINK.The study compares the steady-state,transient,and oscillatory performance of the state-space average model with a fully detailed switching model.
基金Project supported by the National Natural Science Foundation of China (Nos. 10471088 and 60572126)
文摘A new algorithm is proposed, which immolates the optimality of control policies potentially to obtain the robnsticity of solutions. The robnsticity of solutions maybe becomes a very important property for a learning system when there exists non-matching between theory models and practical physical system, or the practical system is not static, or the availability of a control action changes along with the variety of time. The main contribution is that a set of approximation algorithms and their convergence results are given. A generalized average operator instead of the general optimal operator max （or rain） is applied to study a class of important learning algorithms, dynamic prOgramming algorithms, and discuss their convergences from theoretic point of view. The purpose for this research is to improve the robnsticity of reinforcement learning algorithms theoretically.
基金The National Natural Science Foundation of China(No.51108079)
文摘To improve the forecasting reliability of travel time, the time-varying confidence interval of travel time on arterials is forecasted using an autoregressive integrated moving average and generalized autoregressive conditional heteroskedasticity （ARIMA-GARCH） model. In which, the ARIMA model is used as the mean equation of the GARCH model to model the travel time levels and the GARCH model is used to model the conditional variances of travel time. The proposed method is validated and evaluated using actual traffic flow data collected from the traffic monitoring system of Kunshan city. The evaluation results show that, compared with the conventional ARIMA model, the proposed model cannot significantly improve the forecasting performance of travel time levels but has advantage in travel time volatility forecasting. The proposed model can well capture the travel time heteroskedasticity and forecast the time-varying confidence intervals of travel time which can better reflect the volatility of observed travel times than the fixed confidence interval provided by the ARIMA model.
文摘The dual active bridge(DAB)converter is gaining more and more attention in various applications such as energy storage systems,electric vehicles and smart grids.To improve the quality of the input current,a LC filter is often cascaded at the input side of the DAB converter.However,there are instable problems of this cascaded system due to the impedance interactions of the DAB converter and the LC filter,although the DAB converter is stable at the individual operation mode.To assess the stability of the cascaded system of the DAB converter and the LC filter,the impedance model of the DAB converter is firstly developed based on generalized state-space averaging method.The developed impedance model can be used to accurately predict the stability of the DAB converter with its LC input filter.Based on the stability analysis,the optimum filter parameter design guideline is determined.The impedance model and stability analysis are validated by the simulation and experimental results.
基金Supported by the Key Project of the Natural Science Foundation of China
文摘The generalized self-consistent finite-element iterative averaging method was adopted to analyze the elasto-plastic tensile properties of SiC whiskers reinforced aluminum matrix composites. The effects of varying fiber's aspect ratio and volume fraction on the macroscopic elasto-plastic deformation of the composites were studied. By the analysis of microscopic stress fields, the relation between the propagation of the elasto-plastic region in the matrix and the macroscopic elasto-plastic deformation of composites was discussed. It was found that the propagation of the plastic region in the matrix between the fiber's ends would affect prominently the elasto-plastic tensile behaviour of the composites. It was shown that the characterization of the stress-strain response in terms of the 0.2% offset yield strength is incomplete.
基金Supported by the National Natural Science Foundation of China(Grant No.11071053)
文摘In this paper, we present two parallel algorithms to compute common fixed points of a finite family of quasi-nonexpansive mappings in real Hilbert spaces, which improve and generalize some known results in this direction.
基金supported by Beijing Natural Science Foundation under grant 3222059.
文摘Due to the advanced features of multidirectional power transfer and fast smoothing of the power fluctuation in renewable energy systems,the multiple-active-bridge based power-electronic-transformer(MAB-PET)with integrated energy storage units is becoming popular.However,the accurate electromagnetic transient simulation of the MAB-PETs is extremely time-consuming due to the large number of circuit nodes and small time-step.This paper proposes a simplified EMT modeling approach for the MAB-PETs by employing the generalized state-space averaging method.First,the switching function method and Dommel algorithm are used to build the equivalent model of each power module.Further,the PET equivalent model is presented in a multi-port PM polymerization mode.The system is simplified by applying Fourier Decomposition to its state functions by ignoring high-order harmonics.Finally,a four-port equivalent voltage source circuit is obtained.The proposed simplified equivalent model is compared with the detailed model in PSCAD/EMTDC.Simulation results show the proposed approach has excellent accuracy and is 2–3 orders of magnitude faster than the DM.
基金Supported by the National Natural Science Foundation of China(52005436).
文摘The dual active bridge(DAB)is a widely used DC-DC topology owing to its ease of control and ability to achieve various control objectives.When designing a DAB-based system under broadband perturbations,one must model the DAB,calculate its input impedance,and analyze the system stability.In this study,two continuous-time impedance models of the DAB,i.e.,a reduced-order model named the power-based impedance model(PBIM)and a full-order model named the generalized state-space average impedance model(GSSAM),are proposed and used to calculate the input impedance in a single-phase modulation mode.The modeling errors are analyzed,the participation factors and residuals are calculated,and a Bode diagram is constructed to illustrate the change in the input impedance with increasing leakage inductance.Simulations are conducted using various circuit parameters to verify the results.The results show that the PBIM exhibits simplicity and accuracy in the low-frequency domain,whereas the GSSAM performs better in the high-frequency domain.
基金Supported by the National Natural Science Foundation of China(51777049,51707051).
文摘The modeling approaches of power converters occupy an important position in power electronic systems and have made considerable progress over the past years.Continuous modeling approaches and linearization techniques are reviewed,including the state-space average model,generalized average model,averaged small-signal model,and describing function method.A Buck converter with PWM modulation and voltage-mode control is taken as an example to compare the advantages and disadvantages of different methods through simulation analysis.Moreover,the corresponding equivalent circuit with an intuitive physical meaning of state-space average model,generalized average model,and averaged small-signal model is given.The results point out that the generalized average model can improve the modeling accuracy based on the state-space average model.In the linearization techniques,the averaged small-signal model reflects accuracy at low frequencies,but introduces phase lag in the high-frequency region.The describing function method is derived from harmonic linearization,which takes into account the sideband effect and improves the modeling accuracy at high frequencies.
基金supported by the Project Support Program for Research and Technological Innovation of UNAM(DGAPA,PAPIIT-2021)(No.TA101421)the strategic project PE-A-04 of CEMIE-Redes。
文摘This paper proposes a system identification framework based on eigensystem realization to accurately model power electronic converters.The proposed framework affords an energy-based optimal reduction method to precisely identify the dynamics of power electronic converters from simulated or actual raw data measured at the converter’s ports.This method does not require any prior knowledge of the topology or internal parameters of the converter to derive the system modal information.The accuracy and feasibility of the proposed method are exhaustively evaluated via simulations and practical tests on a software-simulated and hardware-implemented dual active bridge(DAB)converter under steady-state and transient conditions.After various comparisons with the Fourier series-based generalized average model,switching model,and experimental measurements,the proposed method attains a root mean square error(RMSE)of less than 1%with respect to the actual raw data.Moreover,the computational effort is reduced to 1/8.6 of the Fourier series-based model.
基金Supported by the National Key Research and Development Program of China(Grant No.2022YFA1005700)the National Natural Science Foundation of China(Grant Nos.12571109 and 12101562)。
文摘In this paper,we obtain the sharp Hardy space estimate of the maximal wave operator.Some applications on spherical averages and their combinations are also given.
