TY - JOUR
T1 - Capacitor voltage reduction in modular multilevel converters under grid voltages unbalances
AU - Li, Jinke
AU - Konstantinou, Georgios
AU - Wickramasinghe, Harith R.
AU - Townsend, Christopher D.
AU - Pou, Josep
PY - 2020/2
Y1 - 2020/2
N2 - Negative-and zero-sequence internal currents of a modular multilevel converter (MMC) under unbalanced ac-grid conditions can increase the peak voltage of the submodule (SM) capacitors, which should be kept below a maximum voltage limit. This paper investigates the impact of offset pulsewidth modulation (OPWM) and zero-sequence voltage injection on reducing peak SM capacitor voltages of the MMC during unbalanced ac-grid conditions. It is demonstrated that OPWM extends the operating range of the MMC for a given set of restrictions, as it leads to a reduction of capacitor voltage in every phase by utilizing all the SMs in the arms. Zero-sequence voltage injection further reduces the maximum SM capacitor voltage among three phases under certain conditions. Simulation results from an 800-MVA MMC-based high-voltage direct current transmission system demonstrate the effect of OPWM in the operation of the converters and the efficacy of the method compared to standard modulation methods.
AB - Negative-and zero-sequence internal currents of a modular multilevel converter (MMC) under unbalanced ac-grid conditions can increase the peak voltage of the submodule (SM) capacitors, which should be kept below a maximum voltage limit. This paper investigates the impact of offset pulsewidth modulation (OPWM) and zero-sequence voltage injection on reducing peak SM capacitor voltages of the MMC during unbalanced ac-grid conditions. It is demonstrated that OPWM extends the operating range of the MMC for a given set of restrictions, as it leads to a reduction of capacitor voltage in every phase by utilizing all the SMs in the arms. Zero-sequence voltage injection further reduces the maximum SM capacitor voltage among three phases under certain conditions. Simulation results from an 800-MVA MMC-based high-voltage direct current transmission system demonstrate the effect of OPWM in the operation of the converters and the efficacy of the method compared to standard modulation methods.
KW - Modular multilevel converter
KW - pulse width modulation
KW - SM capacitor voltage
KW - unbalanced ac-grid conditions
KW - zero sequence voltage injection
UR - http://www.scopus.com/inward/record.url?scp=85078715044&partnerID=8YFLogxK
U2 - 10.1109/TPWRD.2019.2919788
DO - 10.1109/TPWRD.2019.2919788
M3 - Article
AN - SCOPUS:85078715044
SN - 0885-8977
VL - 35
SP - 160
EP - 170
JO - IEEE Transactions on Power Delivery
JF - IEEE Transactions on Power Delivery
IS - 1
M1 - 8725606
ER -