TY - JOUR
T1 - A nearest level PWM method for the MMC in DC distribution grids
AU - Wang, Yi
AU - Hu, Can
AU - Ding, Ruoyu
AU - Xu, Lie
AU - Fu, Chao
AU - Yang, Erlin
N1 - (c) 2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.
PY - 2018/1/11
Y1 - 2018/1/11
N2 - For modular multilevel converters (MMCs) applied to medium-voltage DC distribution grids, using the traditional Nearest Level Modulation (NLM) as in HVDC systems can lead to severe current distortion due to significantly reduced module number. This paper proposes a hybrid modulation method combining NLM and Pulse Width Modulation (PWM) where only one module per arm operates under PWM mode. The proposed Nearest Level PWM (NL-PWM) method not only significantly reduces the current distortion, but also avoids the complicated voltage balancing control in each module. The harmonic characteristics of NL-PWM are derived using double Fourier transform, which provides theoretical basis for selecting module number and switching frequency for medium-voltage application in accordance with grid harmonic requirements. Finally, the harmonic characteristics and feasibility of the proposed modulation method are validated by simulation and experimental studies on a MMC with 6 modules per arm. The simulated and experimental results reveal that NL-PWM has better voltage and current harmonic characteristics over NLM and CPS-PWM, thereby suiting the application of MMC with few models.
AB - For modular multilevel converters (MMCs) applied to medium-voltage DC distribution grids, using the traditional Nearest Level Modulation (NLM) as in HVDC systems can lead to severe current distortion due to significantly reduced module number. This paper proposes a hybrid modulation method combining NLM and Pulse Width Modulation (PWM) where only one module per arm operates under PWM mode. The proposed Nearest Level PWM (NL-PWM) method not only significantly reduces the current distortion, but also avoids the complicated voltage balancing control in each module. The harmonic characteristics of NL-PWM are derived using double Fourier transform, which provides theoretical basis for selecting module number and switching frequency for medium-voltage application in accordance with grid harmonic requirements. Finally, the harmonic characteristics and feasibility of the proposed modulation method are validated by simulation and experimental studies on a MMC with 6 modules per arm. The simulated and experimental results reveal that NL-PWM has better voltage and current harmonic characteristics over NLM and CPS-PWM, thereby suiting the application of MMC with few models.
KW - harmonic analysis
KW - pulse width modulation
KW - voltage control
KW - power system harmonics
UR - http://ieeexplore.ieee.org/document/8253885/
U2 - 10.1109/TPEL.2018.2792148
DO - 10.1109/TPEL.2018.2792148
M3 - Article
SN - 0885-8993
JO - IEEE Transactions on Power Electronics
JF - IEEE Transactions on Power Electronics
ER -