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
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.
