Accurate insight into the heat generation rate(HGR) of lithium-ion batteries(LIBs) is one of key issues for battery management systems to formulate thermal safety warning strategies in advance.For this reason,this pap...Accurate insight into the heat generation rate(HGR) of lithium-ion batteries(LIBs) is one of key issues for battery management systems to formulate thermal safety warning strategies in advance.For this reason,this paper proposes a novel physics-informed neural network(PINN) approach for HGR estimation of LIBs under various driving conditions.Specifically,a single particle model with thermodynamics(SPMT) is first constructed for extracting the critical physical knowledge related with battery HGR.Subsequently,the surface concentrations of positive and negative electrodes in battery SPMT model are integrated into the bidirectional long short-term memory(BiLSTM) networks as physical information.And combined with other feature variables,a novel PINN approach to achieve HGR estimation of LIBs with higher accuracy is constituted.Additionally,some critical hyperparameters of BiLSTM used in PINN approach are determined through Bayesian optimization algorithm(BOA) and the results of BOA-based BiLSTM are compared with other traditional BiLSTM/LSTM networks.Eventually,combined with the HGR data generated from the validated virtual battery,it is proved that the proposed approach can well predict the battery HGR under the dynamic stress test(DST) and worldwide light vehicles test procedure(WLTP),the mean absolute error under DST is 0.542 kW/m^(3),and the root mean square error under WLTP is1.428 kW/m^(3)at 25℃.Lastly,the investigation results of this paper also show a new perspective in the application of the PINN approach in battery HGR estimation.展开更多
Teaching is a special profession with complex pedagogical procedures. It prepares qualified workers and citizens who are expected to yield values and bring benefits to the society, the nation, and the whole world (Nes...Teaching is a special profession with complex pedagogical procedures. It prepares qualified workers and citizens who are expected to yield values and bring benefits to the society, the nation, and the whole world (Nessipbayeva, 2012). This makes the profession require well-qualified teachers. In light of this, teachers must have (and be able to exercise) a broad range of competency array every day in an especially complex environment so that students can realize their full academic potential with the help of teachers (Jackson, 1990). The more competent a teacher is, the better students' achievements will be (Johansson, Myrberg,& Rosen, 2015). It is urgent for us to know how to prepare competent teachers.展开更多
It is widely accepted that the variation of ambient temperature has great influence on the battery model parameters and state-of-charge(SOC) estimation, and the accurate SOC estimation is a significant issue for devel...It is widely accepted that the variation of ambient temperature has great influence on the battery model parameters and state-of-charge(SOC) estimation, and the accurate SOC estimation is a significant issue for developing the battery management system in electric vehicles. To address this problem, in this paper we propose an enhanced equivalent circuit model(ECM) considering the influence of different ambient temperatures on the open-circuit voltage for a lithium-ion battery. Based on this model, the exponential-function fitting method is adopted to identify the battery parameters according to the test data collected from the experimental platform. And then, the extended Kalman filter(EKF) algorithm is employed to estimate the battery SOC of this battery ECM. The performance of the proposed ECM is verified by using the test profiles of hybrid pulse power characterization(HPPC) and the standard US06 driving cycles(US06) at various ambient temperatures, and by comparing with the common ECM with a second-order resistance capacitor. The simulation and experimental results show that the enhanced battery ECM can improve the battery SOC estimation accuracy under different operating conditions.展开更多
Double-sided nanostructure has more excellent properties in high efficiency,high yield,and high capability devices,which becomes the attention spots in nanofabrication technology.We proposed a very simple method to fa...Double-sided nanostructure has more excellent properties in high efficiency,high yield,and high capability devices,which becomes the attention spots in nanofabrication technology.We proposed a very simple method to fabricate the double-sided nanostructure on polymer elastic substrate.By using twice soft-nanoimprinting process,the same or different nanostructures array was fabricated onto the elastomeric slab substrate.In this paper,we fabricated double-sided nanopillars array with different diameters of 200nm and 350nm.In order to expand the applications field in optical and electronic devices,metal layer could be deposited onto the substrate before imprinting nanostructure.展开更多
The occurrence of high frequency resonances(HFRs)has been frequently observed in several MMC-HVDC projects.To avoid these HFRs,the controller design of an MMC must satisfy two requirements:1)The controller should rema...The occurrence of high frequency resonances(HFRs)has been frequently observed in several MMC-HVDC projects.To avoid these HFRs,the controller design of an MMC must satisfy two requirements:1)The controller should remain stable while in the high frequency range,and 2)MMC impedance should not possess a negative real part in the high frequency range.So far,majority of the related studies on MMC controller design have been unable to address these requirements precisely.This paper first describes the simplified high frequency MMC impedance model developed indigenously by the authors.Subsequently,the driving mechanism of two kinds of HFRs is revealed using the said developed model,including:1)MMC controller instability,and 2)Interaction instability between MMC and AC cables.Furthermore,the mathematical expressions outlining the controller stability constraint and positive damping constraint are proposed.Additionally,NSGA-III based multi-objective optimization algorithm is adopted,to identify the region most suitable for satisfying the proposed stability constraints under the MMC controller parameters.The proposed controller design method is capable of effectively evading the HFRs triggered by the incompatible MMC.The detailed time-domain simulations generated using PSCAD/EMTDC software validate the proposed designed method and endorse the improved results.展开更多
As a new generation of direct current(DC)transmission technology,voltage sourced converter(VSC)based high voltage direct current(HVDC)has been widely developed and applied all over the world.China has also carried out...As a new generation of direct current(DC)transmission technology,voltage sourced converter(VSC)based high voltage direct current(HVDC)has been widely developed and applied all over the world.China has also carried out a deep technical research and engineering application in this area,and at present,it has been stepped into a fast growing period.This paper gives a general review over China’s VSC based HVDC in terms of engineering technology,application and future development.It comprehensively analyzes the technical difficulties and future development orientation on the aspects of the main configurations of VSC based HVDC system,topological structures of converters,control and protection technologies,flexible DC cables,converter valve tests,etc.It introduces the applicable fields and current status of China’s VSC based HVDC projects,and analyzes the application trends of VSC based HVDC projects both in China and all over the world according to the development characteristics and demands of future power grids.展开更多
Due to their high controllability and flexibility,DC power grids have broad application prospects in the fields of networking of renewable energy and the power supply for oceanic archipelagos and future cities.This pa...Due to their high controllability and flexibility,DC power grids have broad application prospects in the fields of networking of renewable energy and the power supply for oceanic archipelagos and future cities.This paper describes the system topology,control strategy,DC breaker configuration,and research,development and testing of converter valves and DC breaker equipment of the Zhoushan multi-terminal DC transmission system.Zhejiang Zhoushan has unique geographical and developmental features to demonstrate the irreplaceable technical advantages of a DC power grid for providing reliable power supply.The experience gained from the Zhoushan DC power grid project can offer valuable insights into the development and utilization of this technology worldwide.展开更多
Reducing carbon emissions in the power sector is critical for transitioning to a sustainable and low-carbon future.Estimating carbon efficiency of demand side response(DSR)in the power system is an important step towa...Reducing carbon emissions in the power sector is critical for transitioning to a sustainable and low-carbon future.Estimating carbon efficiency of demand side response(DSR)in the power system is an important step towards realizing potential environmental benefits.Marginal emission factor(MEF)is an effective tool for estimating incremental changes in carbon emissions as a result of a change in demand.However,estimation methods currently used for evaluating MEF can be improved upon,specifically,by factoring in the ramp-rate constraint of generators in the fuel cost based merit order dispatch.In this paper is described a new method for MEF assessment under ramp-rate constraints;the method is then compared with two conventional estimations in a British power system.Three fuel price scenarios are used to conduct a sensitivity analysis of MEFs to fuel prices.Conclusions are drawn that can pave the way for future improvements in estimating MEF in power systems.展开更多
With the rapid development of hydropower in the southwest of China, the energy transmitted by ultra high volt- age direct current (UHVDC) is ever increasing. At the same time, the power grid continues to expand westwa...With the rapid development of hydropower in the southwest of China, the energy transmitted by ultra high volt- age direct current (UHVDC) is ever increasing. At the same time, the power grid continues to expand westward, creating a service area. The stability of the Southwest China Power Grid is becoming a major issue. It is necessary to coordinate the development of hydropower and the construction of cross-region interconnections to optimize the grid structure. The Yu-E denotes the connection between the two region Yu (Chongqing) and E (Hubei) in China. The Yu-E project is a back-to-back voltage source converter based high voltage direct current (VSC-HVDC) project designed to realize an asynchronous connection of the Southwest and Central China Power Grids. The project will improve the bi-directional power support capability and optimize the grid structure. In addition, the Yu-E project will improve hydropower cross-region transmission capacity and enable the Southwest China Power Grid to utilize the power from the Three Gorges in the Central China Power Grid. In this paper, the fault isolation, low-frequency oscillation, sub-synchronous oscillation and short-circuit level are investigated and analyzed. Meanwhile, the impact of the Yu-E project on AC systems is studied in detail. In the end, the overall system design of the Yu-E project is introduced. The research results show that the Yu-E project can increase the transmission capability of the Southwest and Central China Power Grids, and enhance the stability of asynchronously interconnected AC systems. At the same time, the Yu-E project also serves as a demonstration project for the future development and application of VSC technology for the world.展开更多
Large time delay is one of the inherent features of a modular multilevel converter(MMC)-based high voltage direct current(HVDC)system and is the main factor leading to the unfavorable’negative resistance and inducta...Large time delay is one of the inherent features of a modular multilevel converter(MMC)-based high voltage direct current(HVDC)system and is the main factor leading to the unfavorable’negative resistance and inductance’characteristic of MMC impedance.Research indicates that this characteristic interacting with the capacitive characteristics of an AC system is the cause of high frequency resonance(HFR)in the Yu-E HVDC project.As the current controller is one of the main factors that affects the MMC impedance,a compensation control to imitate the paralleled impedance at the point of common coupling(PCC)is proposed.Therefore,the structure and parameter design of the compensation controller are core to realizing HFR suppression.There are two potentially risky frequency ranges of HFRs(around 700 Hz and 1.8 kHz)in the studied AC system within 2.0 kHz.The core concept of HFR suppression is to make the phase angle of MMC impedance smaller than 90◦in the two risky frequency ranges according to impedance stability theory.Hence,the design parameters aim to coordinate the phase angle of MMC impedance in the two risky frequency ranges.In this paper,three types of compensation controller are studied to suppress HFRs,namely,first-order low pass filter(LPF),second-order LPF,and third-order band pass filter.The results of parameter design show that the first-order LPF cannot suppress both HFRs simultaneously.The second-order LPF can suppress both HFRs,however,it introduces a DC component into the current control loop.Therefore,a high pass filter is added to form the recommended third-order controller.All parameter ranges of the compensation controller are derived using analytical expressions.Finally,the correctness of the parameter design is proofed using time-domain simulations.展开更多
This paper presents an isolated DC/AC/DC converter using a middle frequency transformer coupling two modular multilevel converters(MMC),suitable for interconnecting DC transmission lines of different voltage levels in...This paper presents an isolated DC/AC/DC converter using a middle frequency transformer coupling two modular multilevel converters(MMC),suitable for interconnecting DC transmission lines of different voltage levels in high voltage direct current(HVDC)system.The basic operational principle of the isolated module multilevel DC/DC converter(IMMDCC)is analyzed.The dynamic model of IMMDCC is studied in detail and the transient relationship between DC side and AC side of IMMDCC is revealed,which is physically straightforward for understanding the power transfer in IMMDCC.The control strategy in D-Q coordinate system is put forward,and the fault characteristic and corresponding protection method is analyzed.Finally,computer simulation using Matlab/Simulink is performed to verify the dynamic model and the proposed control strategy.The simulation results show good performances and the quick response ability of the proposed control strategy.展开更多
Employing the AC/DC impedance analysis method,extensive research has been conducted on issues pertaining to harmonic resonance observed in wind farm-connected MMCHVDC systems over the past 5 years.In general,this meth...Employing the AC/DC impedance analysis method,extensive research has been conducted on issues pertaining to harmonic resonance observed in wind farm-connected MMCHVDC systems over the past 5 years.In general,this method divides the studied system into two subsystems at AC and DC sections.Subsequently,the impedance produced by these subsystems can be used to determine the system stability by implementing Nyquist criterion or generalized Nyquist stability criterion.However,the existing impedance analysis methods usually assume the subsystems to be stable and disregard certain special cases with potentially unstable subsystems,where the unstable poles of these subsystems must be evaluated before applying Nyquist criterion.In view of this consideration,a simplified method for identifying unstable subsystem poles is presented in this paper.Hence,the shortcoming of existing impedance analyses is rectified by considering the unstable subsystem poles.The proposed method and the stability analyses are validated by the electromagnetic transient simulation performed in PSCAD/EMTDC.展开更多
In continuous speech,the pitch contour of the same syllable may vary much due to its contextual information.The Parallel Encoding and Target Approximation (PENTA) model is applied here to Mandarin speech synthesis wit...In continuous speech,the pitch contour of the same syllable may vary much due to its contextual information.The Parallel Encoding and Target Approximation (PENTA) model is applied here to Mandarin speech synthesis with a method to predict pitch contours for Chinese syllables with different contexts by combining the Classification And Regression Tree (CART) with the PENTA model to improve its prediction accuracy.CART was first used to cluster the syllables' normalized pitch contours according to the syllables contextual information and the distances between pitch contours.The average pitch contour was used to train the PENTA model with the average contour for each cluster.The initial pitch is required with the PENTA model to predict a continuous pitch contour.A Pitch Discontinuity Model (PDM) was used to predict the initial pitches at positions with voiceless consonants and prosodic boundaries.Initial tests on a Chinese four-syllable word corpus containing 2048 words were extended to tests with a continuous speech corpus containing 5445 sentences.The results are satisfactory in terms of the Root Mean Square Error (RMSE) comparing the predicted pitch contour with the original contour.This method can model pitch contours for Mandarin sentences with any text for speech synthesis.展开更多
This paper proposes a robust bang-bang controller(RBC)based on the high-gain nonlinear observer for a nonlinear system with intermittent disturbances.The intermittent distur-bances are able to model the system faults ...This paper proposes a robust bang-bang controller(RBC)based on the high-gain nonlinear observer for a nonlinear system with intermittent disturbances.The intermittent distur-bances are able to model the system faults and sudden changes of operating conditions of practical nonlinear systems.A bang-bang constant funnel controller(BCFC)is employed,and the largest control capabilities of the control system is explored to stabi-lize the nonlinear system against the disturbances.The BCFC functions with the estimates of tracking error of control target and its derivatives estimated with a high-gain state observer,which eliminates the requirement on the derivative calculations of the system output tracking error.The error convergence of the observer is verified.The closed-loop stability of the RBC is proved in a bounded-input bounded-state sense.Simulation studies are undertaken with a single-machine infinite-bus(SMIB)power system to test the performance of the RBC.展开更多
This paper presents a method to design a monolithic complete-light modulator(MCLM) that fully controls the amplitude, phase, and polarization of incident light. The MCLM is made of birefringent materials that provide ...This paper presents a method to design a monolithic complete-light modulator(MCLM) that fully controls the amplitude, phase, and polarization of incident light. The MCLM is made of birefringent materials that provide different refractive indices to orthogonal eigen-polarizations, the ordinary o and extraordinary e states. We propose an optimization method to calculate the two relief depth distributions for the two eigen-polarizations. Also, a merging algorithm is proposed to combine the two relief depth distributions into one. The corresponding simulations were carried out in this work and the desired light distribution, including information on amplitude,phase, and four polarization states, was obtained when a laser beam passed through a 16-depth-level microstructure whose feature size is 8 μm. The structure was fabricated by common photolithography. An experimental optical system was also set up to test the optical effects and performances of the MCLM. The experimental performance of the MCLM agrees with the simulation results, which verifies the validity of the algorithms we propose in this paper.展开更多
A control strategy of frequency self-adaptation without phase-locked loop(PLL)underαβstationary reference frame(αβ-SRF)for a VSC-HVDC system is presented to improve the operational performance of the system under ...A control strategy of frequency self-adaptation without phase-locked loop(PLL)underαβstationary reference frame(αβ-SRF)for a VSC-HVDC system is presented to improve the operational performance of the system under severe harmonic distortion conditions.The control strategy helps to eliminate the cross-coupling under dq synchronous reference frame(dq-SRF),and is achieved through two key technologies:1)positive phase sequence(PPS)and negative phase sequence(NPS)fundamental components are extracted from the AC grid voltage with an improved multiple complex coefficient filter(IMCF),and 2)grid instantaneous frequency is rapidly and precisely tracked using a frequency self-adaptation tracking algorithm(FATA)without PLL.The proposed strategy is applied to a point-to-point VSCHVDC system and validated by means of simulations.The results are compared to those with the traditional vector control strategy under dq-SRF.Simulation results illustrate that the proposed strategy results in better system performance than that with the traditional strategy in terms of harmonic suppression under normal and severe operating conditions of the AC system.展开更多
基金funded by the Artificial Intelligence Technology Project of Xi’an Science and Technology Bureau in China(No.21RGZN0014)。
文摘Accurate insight into the heat generation rate(HGR) of lithium-ion batteries(LIBs) is one of key issues for battery management systems to formulate thermal safety warning strategies in advance.For this reason,this paper proposes a novel physics-informed neural network(PINN) approach for HGR estimation of LIBs under various driving conditions.Specifically,a single particle model with thermodynamics(SPMT) is first constructed for extracting the critical physical knowledge related with battery HGR.Subsequently,the surface concentrations of positive and negative electrodes in battery SPMT model are integrated into the bidirectional long short-term memory(BiLSTM) networks as physical information.And combined with other feature variables,a novel PINN approach to achieve HGR estimation of LIBs with higher accuracy is constituted.Additionally,some critical hyperparameters of BiLSTM used in PINN approach are determined through Bayesian optimization algorithm(BOA) and the results of BOA-based BiLSTM are compared with other traditional BiLSTM/LSTM networks.Eventually,combined with the HGR data generated from the validated virtual battery,it is proved that the proposed approach can well predict the battery HGR under the dynamic stress test(DST) and worldwide light vehicles test procedure(WLTP),the mean absolute error under DST is 0.542 kW/m^(3),and the root mean square error under WLTP is1.428 kW/m^(3)at 25℃.Lastly,the investigation results of this paper also show a new perspective in the application of the PINN approach in battery HGR estimation.
文摘Teaching is a special profession with complex pedagogical procedures. It prepares qualified workers and citizens who are expected to yield values and bring benefits to the society, the nation, and the whole world (Nessipbayeva, 2012). This makes the profession require well-qualified teachers. In light of this, teachers must have (and be able to exercise) a broad range of competency array every day in an especially complex environment so that students can realize their full academic potential with the help of teachers (Jackson, 1990). The more competent a teacher is, the better students' achievements will be (Johansson, Myrberg,& Rosen, 2015). It is urgent for us to know how to prepare competent teachers.
基金Project supported by the National Natural Science Foundation of China(Grant No.51675423)
文摘It is widely accepted that the variation of ambient temperature has great influence on the battery model parameters and state-of-charge(SOC) estimation, and the accurate SOC estimation is a significant issue for developing the battery management system in electric vehicles. To address this problem, in this paper we propose an enhanced equivalent circuit model(ECM) considering the influence of different ambient temperatures on the open-circuit voltage for a lithium-ion battery. Based on this model, the exponential-function fitting method is adopted to identify the battery parameters according to the test data collected from the experimental platform. And then, the extended Kalman filter(EKF) algorithm is employed to estimate the battery SOC of this battery ECM. The performance of the proposed ECM is verified by using the test profiles of hybrid pulse power characterization(HPPC) and the standard US06 driving cycles(US06) at various ambient temperatures, and by comparing with the common ECM with a second-order resistance capacitor. The simulation and experimental results show that the enhanced battery ECM can improve the battery SOC estimation accuracy under different operating conditions.
基金the National Nature Science Foundation(No.61605211)of ChinaScience and Technology Support Program of Sichuan province(No.2016RZ0067).
文摘Double-sided nanostructure has more excellent properties in high efficiency,high yield,and high capability devices,which becomes the attention spots in nanofabrication technology.We proposed a very simple method to fabricate the double-sided nanostructure on polymer elastic substrate.By using twice soft-nanoimprinting process,the same or different nanostructures array was fabricated onto the elastomeric slab substrate.In this paper,we fabricated double-sided nanopillars array with different diameters of 200nm and 350nm.In order to expand the applications field in optical and electronic devices,metal layer could be deposited onto the substrate before imprinting nanostructure.
基金supported by the National Natural Science Foundation of China (52207099).
文摘The occurrence of high frequency resonances(HFRs)has been frequently observed in several MMC-HVDC projects.To avoid these HFRs,the controller design of an MMC must satisfy two requirements:1)The controller should remain stable while in the high frequency range,and 2)MMC impedance should not possess a negative real part in the high frequency range.So far,majority of the related studies on MMC controller design have been unable to address these requirements precisely.This paper first describes the simplified high frequency MMC impedance model developed indigenously by the authors.Subsequently,the driving mechanism of two kinds of HFRs is revealed using the said developed model,including:1)MMC controller instability,and 2)Interaction instability between MMC and AC cables.Furthermore,the mathematical expressions outlining the controller stability constraint and positive damping constraint are proposed.Additionally,NSGA-III based multi-objective optimization algorithm is adopted,to identify the region most suitable for satisfying the proposed stability constraints under the MMC controller parameters.The proposed controller design method is capable of effectively evading the HFRs triggered by the incompatible MMC.The detailed time-domain simulations generated using PSCAD/EMTDC software validate the proposed designed method and endorse the improved results.
基金This work was supported by National Natural Science Foundation of China(No.51261130471).
文摘As a new generation of direct current(DC)transmission technology,voltage sourced converter(VSC)based high voltage direct current(HVDC)has been widely developed and applied all over the world.China has also carried out a deep technical research and engineering application in this area,and at present,it has been stepped into a fast growing period.This paper gives a general review over China’s VSC based HVDC in terms of engineering technology,application and future development.It comprehensively analyzes the technical difficulties and future development orientation on the aspects of the main configurations of VSC based HVDC system,topological structures of converters,control and protection technologies,flexible DC cables,converter valve tests,etc.It introduces the applicable fields and current status of China’s VSC based HVDC projects,and analyzes the application trends of VSC based HVDC projects both in China and all over the world according to the development characteristics and demands of future power grids.
基金supported in part by the National Natural Science Foundation of China(No.51261130471)by the Science and Technology Research Project of the State Grid Corporation of China(No.SGRIPGKJ(2013)166).
文摘Due to their high controllability and flexibility,DC power grids have broad application prospects in the fields of networking of renewable energy and the power supply for oceanic archipelagos and future cities.This paper describes the system topology,control strategy,DC breaker configuration,and research,development and testing of converter valves and DC breaker equipment of the Zhoushan multi-terminal DC transmission system.Zhejiang Zhoushan has unique geographical and developmental features to demonstrate the irreplaceable technical advantages of a DC power grid for providing reliable power supply.The experience gained from the Zhoushan DC power grid project can offer valuable insights into the development and utilization of this technology worldwide.
基金This work was supported in part by the EPSRC UK and the NSFC,through the ERIFT project(51261130471).
文摘Reducing carbon emissions in the power sector is critical for transitioning to a sustainable and low-carbon future.Estimating carbon efficiency of demand side response(DSR)in the power system is an important step towards realizing potential environmental benefits.Marginal emission factor(MEF)is an effective tool for estimating incremental changes in carbon emissions as a result of a change in demand.However,estimation methods currently used for evaluating MEF can be improved upon,specifically,by factoring in the ramp-rate constraint of generators in the fuel cost based merit order dispatch.In this paper is described a new method for MEF assessment under ramp-rate constraints;the method is then compared with two conventional estimations in a British power system.Three fuel price scenarios are used to conduct a sensitivity analysis of MEFs to fuel prices.Conclusions are drawn that can pave the way for future improvements in estimating MEF in power systems.
基金This work was supported in part by the National Natural Science Foundation of China(No.U1866210).
文摘With the rapid development of hydropower in the southwest of China, the energy transmitted by ultra high volt- age direct current (UHVDC) is ever increasing. At the same time, the power grid continues to expand westward, creating a service area. The stability of the Southwest China Power Grid is becoming a major issue. It is necessary to coordinate the development of hydropower and the construction of cross-region interconnections to optimize the grid structure. The Yu-E denotes the connection between the two region Yu (Chongqing) and E (Hubei) in China. The Yu-E project is a back-to-back voltage source converter based high voltage direct current (VSC-HVDC) project designed to realize an asynchronous connection of the Southwest and Central China Power Grids. The project will improve the bi-directional power support capability and optimize the grid structure. In addition, the Yu-E project will improve hydropower cross-region transmission capacity and enable the Southwest China Power Grid to utilize the power from the Three Gorges in the Central China Power Grid. In this paper, the fault isolation, low-frequency oscillation, sub-synchronous oscillation and short-circuit level are investigated and analyzed. Meanwhile, the impact of the Yu-E project on AC systems is studied in detail. In the end, the overall system design of the Yu-E project is introduced. The research results show that the Yu-E project can increase the transmission capability of the Southwest and Central China Power Grids, and enhance the stability of asynchronously interconnected AC systems. At the same time, the Yu-E project also serves as a demonstration project for the future development and application of VSC technology for the world.
基金supported by the National Natural Science Foundation of China(No.U1866210).
文摘Large time delay is one of the inherent features of a modular multilevel converter(MMC)-based high voltage direct current(HVDC)system and is the main factor leading to the unfavorable’negative resistance and inductance’characteristic of MMC impedance.Research indicates that this characteristic interacting with the capacitive characteristics of an AC system is the cause of high frequency resonance(HFR)in the Yu-E HVDC project.As the current controller is one of the main factors that affects the MMC impedance,a compensation control to imitate the paralleled impedance at the point of common coupling(PCC)is proposed.Therefore,the structure and parameter design of the compensation controller are core to realizing HFR suppression.There are two potentially risky frequency ranges of HFRs(around 700 Hz and 1.8 kHz)in the studied AC system within 2.0 kHz.The core concept of HFR suppression is to make the phase angle of MMC impedance smaller than 90◦in the two risky frequency ranges according to impedance stability theory.Hence,the design parameters aim to coordinate the phase angle of MMC impedance in the two risky frequency ranges.In this paper,three types of compensation controller are studied to suppress HFRs,namely,first-order low pass filter(LPF),second-order LPF,and third-order band pass filter.The results of parameter design show that the first-order LPF cannot suppress both HFRs simultaneously.The second-order LPF can suppress both HFRs,however,it introduces a DC component into the current control loop.Therefore,a high pass filter is added to form the recommended third-order controller.All parameter ranges of the compensation controller are derived using analytical expressions.Finally,the correctness of the parameter design is proofed using time-domain simulations.
文摘This paper presents an isolated DC/AC/DC converter using a middle frequency transformer coupling two modular multilevel converters(MMC),suitable for interconnecting DC transmission lines of different voltage levels in high voltage direct current(HVDC)system.The basic operational principle of the isolated module multilevel DC/DC converter(IMMDCC)is analyzed.The dynamic model of IMMDCC is studied in detail and the transient relationship between DC side and AC side of IMMDCC is revealed,which is physically straightforward for understanding the power transfer in IMMDCC.The control strategy in D-Q coordinate system is put forward,and the fault characteristic and corresponding protection method is analyzed.Finally,computer simulation using Matlab/Simulink is performed to verify the dynamic model and the proposed control strategy.The simulation results show good performances and the quick response ability of the proposed control strategy.
文摘Employing the AC/DC impedance analysis method,extensive research has been conducted on issues pertaining to harmonic resonance observed in wind farm-connected MMCHVDC systems over the past 5 years.In general,this method divides the studied system into two subsystems at AC and DC sections.Subsequently,the impedance produced by these subsystems can be used to determine the system stability by implementing Nyquist criterion or generalized Nyquist stability criterion.However,the existing impedance analysis methods usually assume the subsystems to be stable and disregard certain special cases with potentially unstable subsystems,where the unstable poles of these subsystems must be evaluated before applying Nyquist criterion.In view of this consideration,a simplified method for identifying unstable subsystem poles is presented in this paper.Hence,the shortcoming of existing impedance analyses is rectified by considering the unstable subsystem poles.The proposed method and the stability analyses are validated by the electromagnetic transient simulation performed in PSCAD/EMTDC.
基金Supported by the National Natural Science Foundation of China (Nos.60805008,60928005,and 61003094)the Ph.D.Programs Foundation of the Ministry of Education of China (No.200800031015)
文摘In continuous speech,the pitch contour of the same syllable may vary much due to its contextual information.The Parallel Encoding and Target Approximation (PENTA) model is applied here to Mandarin speech synthesis with a method to predict pitch contours for Chinese syllables with different contexts by combining the Classification And Regression Tree (CART) with the PENTA model to improve its prediction accuracy.CART was first used to cluster the syllables' normalized pitch contours according to the syllables contextual information and the distances between pitch contours.The average pitch contour was used to train the PENTA model with the average contour for each cluster.The initial pitch is required with the PENTA model to predict a continuous pitch contour.A Pitch Discontinuity Model (PDM) was used to predict the initial pitches at positions with voiceless consonants and prosodic boundaries.Initial tests on a Chinese four-syllable word corpus containing 2048 words were extended to tests with a continuous speech corpus containing 5445 sentences.The results are satisfactory in terms of the Root Mean Square Error (RMSE) comparing the predicted pitch contour with the original contour.This method can model pitch contours for Mandarin sentences with any text for speech synthesis.
基金This work was supported in part by the National Natural Science Foundation of China under Grant No.U1866210 and No.51807067the Young Elite Sci-entists Sponsorship Program by the Chinese Society for Electrical Engineering under Grant No.CSEE-YESS-2018and the Fundamental Research Funds for the Central Universities of China.
文摘This paper proposes a robust bang-bang controller(RBC)based on the high-gain nonlinear observer for a nonlinear system with intermittent disturbances.The intermittent distur-bances are able to model the system faults and sudden changes of operating conditions of practical nonlinear systems.A bang-bang constant funnel controller(BCFC)is employed,and the largest control capabilities of the control system is explored to stabi-lize the nonlinear system against the disturbances.The BCFC functions with the estimates of tracking error of control target and its derivatives estimated with a high-gain state observer,which eliminates the requirement on the derivative calculations of the system output tracking error.The error convergence of the observer is verified.The closed-loop stability of the RBC is proved in a bounded-input bounded-state sense.Simulation studies are undertaken with a single-machine infinite-bus(SMIB)power system to test the performance of the RBC.
基金National Natural Science Foundation of China(NSFC)(61605211,51703227)Instrument Development of Chinese Academy of Sciences(YJKYYQ20180008)+3 种基金National R&D Program of China(2017YFC0804900)Sichuan Science and Technology Program(2019YJ0014)Youth Innovation Promotion Association,CASCAS “Light of West China” Program
文摘This paper presents a method to design a monolithic complete-light modulator(MCLM) that fully controls the amplitude, phase, and polarization of incident light. The MCLM is made of birefringent materials that provide different refractive indices to orthogonal eigen-polarizations, the ordinary o and extraordinary e states. We propose an optimization method to calculate the two relief depth distributions for the two eigen-polarizations. Also, a merging algorithm is proposed to combine the two relief depth distributions into one. The corresponding simulations were carried out in this work and the desired light distribution, including information on amplitude,phase, and four polarization states, was obtained when a laser beam passed through a 16-depth-level microstructure whose feature size is 8 μm. The structure was fabricated by common photolithography. An experimental optical system was also set up to test the optical effects and performances of the MCLM. The experimental performance of the MCLM agrees with the simulation results, which verifies the validity of the algorithms we propose in this paper.
基金supported by the Science and Technology Project of the State Grid Corporation of China(SGRIZLKJ[2015]457)。
文摘A control strategy of frequency self-adaptation without phase-locked loop(PLL)underαβstationary reference frame(αβ-SRF)for a VSC-HVDC system is presented to improve the operational performance of the system under severe harmonic distortion conditions.The control strategy helps to eliminate the cross-coupling under dq synchronous reference frame(dq-SRF),and is achieved through two key technologies:1)positive phase sequence(PPS)and negative phase sequence(NPS)fundamental components are extracted from the AC grid voltage with an improved multiple complex coefficient filter(IMCF),and 2)grid instantaneous frequency is rapidly and precisely tracked using a frequency self-adaptation tracking algorithm(FATA)without PLL.The proposed strategy is applied to a point-to-point VSCHVDC system and validated by means of simulations.The results are compared to those with the traditional vector control strategy under dq-SRF.Simulation results illustrate that the proposed strategy results in better system performance than that with the traditional strategy in terms of harmonic suppression under normal and severe operating conditions of the AC system.