Influence of third harmonic injection on modular multilevel converter ‐based high‐voltage direct current transmission systems

Abstract

Abstract-Whilst third harmonic injection is extensively used in modular multilevelconverter (MMC) control, its significant advantages over sinusoidal modulation have not been fully explored. This paper evaluates the influence of third harmonic injection on system power losses, submodule capacitance, circulating current, and fault current and mathematical models are derived. Station conduction losses are reduced by 11%, yielding higher efficiency and lowering cooling system capacity. The submodule capacitance is reduced by 24%, which significantly lowers the capital cost, weight, and volume of the station converter. Additionally, the phase energy variation is reduced by around 18%, which benefits circulating current control. Due to the lower AC currents, the semiconductor current stresses are correspondingly reduced. In addition to the performance improvement in normal operation, the third harmonic injection reduces the DC fault currents by 13.4% and thus the fault current stresses on semiconductors and DC circuit breakers are lowered. Simulation of a point-to-point HVDC system demonstrates the effectiveness of the above analysis.Index Terms-DC fault current, HVDC transmission, modular multilevel converter (MMC), power loss, submodule capacitance, third harmonic injection.

Recent contributions and future prospects of the modular multilevel converters: A comprehensive review

“…The fundamental concept of Li et al is to investigate the effect of third harmonic injection in terms of power losses, SM capacitance, circulating current, and fault current on HVDC system based on MMC. Mentioned parameters are clearly improved.…”

Super Capacitor Energy Storage Based MMC for Energy Harvesting in Mine Hoist Application

“…The simulation model parameters of SCES-MMC are listed in Table 2, and the initial SOC value of the SCBs is 100%. The super capacitor parameter design and selection method are similar to [24], and the modulation method adopted in this simulation is carrier phase-shifted sinusoidal pulse-width-modulation, combined with the third harmonic injection method of [25]. In addition, assuming that the synchronous motor reaches the rated speed at 0.6 s and starts decelerating at 0.9 s, the SCES-MMC output performance is shown in Figure 8.…”

“…combined with the third harmonic injection method of [25]. In addition, assuming that the synchronous motor reaches the rated speed at 0.6 s and starts decelerating at 0.9 s, the SCES-MMC output performance is shown in Figure 8.…”

Fault analysis on DC transmission system of PV generation

“…Therefore, the CDSM‐MMC is employed in this paper as the grid‐connected converter in the PV integration system. On the other side, after the DC‐side fault, the AC side of MMCs may also experience over current and over voltage, owing to the influence of the capacitor discharge and harmonics . By controlling the voltage of CDSMs and the active power exchanging with the connected AC grid, limiting the DC fault current, and blocking submodules, the CDSM‐MMC can isolate the fault before DC circuit breakers, if any, operate …”

“…On the other side, after the DC-side fault, the AC side of MMCs may also experience over current and over voltage, owing to the influence of the capacitor discharge and harmonics. 22,23 By controlling the voltage of CDSMs and the active power exchanging with the connected AC grid, limiting the DC fault current, and blocking submodules, the CDSM-MMC can isolate the fault before DC circuit breakers, if any, operate. 24,25 However, to the best knowledge of the authors, a comprehensive study of DC faults in the CDSM-MMC-based DC transmission system of PV generation has not been implemented sufficiently so far.…”