Abstract
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.
| Original language | English |
|---|---|
| Article number | 8725606 |
| Pages (from-to) | 160-170 |
| Number of pages | 11 |
| Journal | IEEE Transactions on Power Delivery |
| Volume | 35 |
| Issue number | 1 |
| DOIs | |
| Publication status | Published - Feb 2020 |
| Externally published | Yes |
Bibliographical note
Publisher Copyright:© 1986-2012 IEEE.
ASJC Scopus Subject Areas
- Energy Engineering and Power Technology
- Electrical and Electronic Engineering
Keywords
- Modular multilevel converter
- pulse width modulation
- SM capacitor voltage
- unbalanced ac-grid conditions
- zero sequence voltage injection