An analytical evaluation method for output waveform quality of space vector pulse width modulation(PWM)strategies applied in neutral⁃point⁃clamped three⁃level converter(3L⁃NPC)is proposed in this paper.Low frequency e...An analytical evaluation method for output waveform quality of space vector pulse width modulation(PWM)strategies applied in neutral⁃point⁃clamped three⁃level converter(3L⁃NPC)is proposed in this paper.Low frequency error caused by neutral point voltage ripple and high frequency error introduced by space vector synthesis were both taken into account,and the unified error model of output current ripple was established.By taking continuous and discontinuous modulation strategies as examples,the unified error model was validated through Fourier analysis of the experimental results.The proposed evaluation method will be helpful for the switching sequence optimization and the modulation strategy selection.展开更多
The implementation of modular multilevel converters(MMC)in an electric ship to create a medium voltage direct current(MVDC)energy conversion system that is efficient,small,dependable,and easily scalable has garnered c...The implementation of modular multilevel converters(MMC)in an electric ship to create a medium voltage direct current(MVDC)energy conversion system that is efficient,small,dependable,and easily scalable has garnered considerable interest.In this research,an improved two-step nearest level control(E-NLC)is presented for MMC with a three-level submodule(3L-SM)as the rectifier of the electric ship power generation units in order to ease the economical and reliable operation of MMCs in MVDC systems.To achieve DC fault-clearing capability,the use of MMC with 3L-SM minimizes the number of switching devices when compared to the regular MMC topology.The suggested E-NLC scheme aims to reduce total harmonic distortion(THD)and achieve the nearest zero common mode voltage(CMV).The output voltage vector of the three phases is tuned using eight candidate vectors capable of suppressing CMV rather than the nearest-level vector,and the rounding function is modified to improve harmonic performance by increasing the approximation between stepped and modulated waves.The generator-connected MMC with THD reduction and CMV elimination maximizes the mover's protection in the generating unit of the electric ship's MVDC system.Simulation and experiment results validate the efficacy of the suggested approach with respect to steady-state and dynamic-state performance.展开更多
Realizing a high-performance and energy-efficient circuit system is one of the critical tasks for circuit designers.Conventional researchers always concentrated on the tradeoffs between the energy and the performance ...Realizing a high-performance and energy-efficient circuit system is one of the critical tasks for circuit designers.Conventional researchers always concentrated on the tradeoffs between the energy and the performance in circuit and system design based on accurate computing.However,as video/image processing and machine learning algorithms are widespread,the technique of approximate computing in these applications has become a hot topic.The errors caused by approximate computing could be tolerated by these applications with specific processing or algorithms,and large improvements in performance or power savings could be achieved with some acceptable loss in final output quality.This paper presents a survey of approximate computing from arithmetic units design to high-level applications,in which we try to give researchers a comprehensive and insightful understanding of approximate computing.We believe that approximate computing will play an important role in the circuit and system design in the future,especially with the rapid development of artificial intelligence algorithms and their related applications.展开更多
The demise of Dennard’s scaling has created both power and utilization wall challenges for computer systems.As transistors operating in the near-threshold region are able to obtain flexible trade-offs between power a...The demise of Dennard’s scaling has created both power and utilization wall challenges for computer systems.As transistors operating in the near-threshold region are able to obtain flexible trade-offs between power and performance,it is regarded as an alternative solution to the scaling challenge.A reduction in supply voltage will nevertheless generate significant reliability challenges,while maintaining an error-free system that generates high costs in both performance and energy consumption.The main purpose of research on computer architecture has therefore shifted from performance improvement to complex multi-objective optimization.In this paper,we propose a three-dimensional optimization approach which can effectively identify the best system configuration to establish a balance among performance,energy,and reliability.We use a dynamic programming algorithm to determine the proper voltage and approximate level based on three predictors:system performance,energy consumption,and output quality.We propose an output quality predictor which uses a hardware/software co-design fault injection platform to evaluate the impact of the error on output quality under near-threshold computing(NTC).Evaluation results demonstrate that our approach can lead to a 28% improvement in output quality with a 10% drop in overall energy efficiency;this translates to an approximately 20% average improvement in accuracy,power,and performance.展开更多
基金National Natural Science Foundation of China(Grant Nos.51807140 and 51690183).
文摘An analytical evaluation method for output waveform quality of space vector pulse width modulation(PWM)strategies applied in neutral⁃point⁃clamped three⁃level converter(3L⁃NPC)is proposed in this paper.Low frequency error caused by neutral point voltage ripple and high frequency error introduced by space vector synthesis were both taken into account,and the unified error model of output current ripple was established.By taking continuous and discontinuous modulation strategies as examples,the unified error model was validated through Fourier analysis of the experimental results.The proposed evaluation method will be helpful for the switching sequence optimization and the modulation strategy selection.
文摘The implementation of modular multilevel converters(MMC)in an electric ship to create a medium voltage direct current(MVDC)energy conversion system that is efficient,small,dependable,and easily scalable has garnered considerable interest.In this research,an improved two-step nearest level control(E-NLC)is presented for MMC with a three-level submodule(3L-SM)as the rectifier of the electric ship power generation units in order to ease the economical and reliable operation of MMCs in MVDC systems.To achieve DC fault-clearing capability,the use of MMC with 3L-SM minimizes the number of switching devices when compared to the regular MMC topology.The suggested E-NLC scheme aims to reduce total harmonic distortion(THD)and achieve the nearest zero common mode voltage(CMV).The output voltage vector of the three phases is tuned using eight candidate vectors capable of suppressing CMV rather than the nearest-level vector,and the rounding function is modified to improve harmonic performance by increasing the approximation between stepped and modulated waves.The generator-connected MMC with THD reduction and CMV elimination maximizes the mover's protection in the generating unit of the electric ship's MVDC system.Simulation and experiment results validate the efficacy of the suggested approach with respect to steady-state and dynamic-state performance.
基金supported by the Fundamental Research Funds for the Central Universities of China under Grant No.BLX202015Beijing Municipal Natural Science Foundation under Grant No.6222038the National Natural Science Foundation of China under Grant No.92164203.
文摘Realizing a high-performance and energy-efficient circuit system is one of the critical tasks for circuit designers.Conventional researchers always concentrated on the tradeoffs between the energy and the performance in circuit and system design based on accurate computing.However,as video/image processing and machine learning algorithms are widespread,the technique of approximate computing in these applications has become a hot topic.The errors caused by approximate computing could be tolerated by these applications with specific processing or algorithms,and large improvements in performance or power savings could be achieved with some acceptable loss in final output quality.This paper presents a survey of approximate computing from arithmetic units design to high-level applications,in which we try to give researchers a comprehensive and insightful understanding of approximate computing.We believe that approximate computing will play an important role in the circuit and system design in the future,especially with the rapid development of artificial intelligence algorithms and their related applications.
基金Project supported by the National Natural Science Foundation of China(Nos.62076168 and 61772350)Beijing Nova Program(No.Z181100006218093)the Research Fund from Beijing Innovation Center for Future Chips(No.KYJJ2018008)。
文摘The demise of Dennard’s scaling has created both power and utilization wall challenges for computer systems.As transistors operating in the near-threshold region are able to obtain flexible trade-offs between power and performance,it is regarded as an alternative solution to the scaling challenge.A reduction in supply voltage will nevertheless generate significant reliability challenges,while maintaining an error-free system that generates high costs in both performance and energy consumption.The main purpose of research on computer architecture has therefore shifted from performance improvement to complex multi-objective optimization.In this paper,we propose a three-dimensional optimization approach which can effectively identify the best system configuration to establish a balance among performance,energy,and reliability.We use a dynamic programming algorithm to determine the proper voltage and approximate level based on three predictors:system performance,energy consumption,and output quality.We propose an output quality predictor which uses a hardware/software co-design fault injection platform to evaluate the impact of the error on output quality under near-threshold computing(NTC).Evaluation results demonstrate that our approach can lead to a 28% improvement in output quality with a 10% drop in overall energy efficiency;this translates to an approximately 20% average improvement in accuracy,power,and performance.
