Abstract:
This paper analyzes the characteristics of the submodule (SM) voltage fundamental frequency and second-order harmonic ripples with the consideration of negative voltage s...Show MoreMetadata
Abstract:
This paper analyzes the characteristics of the submodule (SM) voltage fundamental frequency and second-order harmonic ripples with the consideration of negative voltage state of the full-bridge SM. The optimal operation point, which minimizes the fundamental frequency ripples, is derived. Both the design principle and analytical expressions for SM capacitance dimensioning are presented, and the comparison between energy storage requirements with and without negative voltage states in the arm reference voltages are also carried out under the same constraints on the transmission power, modulation index, and SM voltage fluctuations. However, the SM voltage fundamental frequency ripples increase significantly with reactive power increasing. Therefore, a circulating current injection (CCI) method is proposed in order to suppress the ripples caused by reactive power. Comparative simulations on a ±200 kV hybrid modular multilevel converter (MMC) and experimental results on a laboratory prototype verified the correctness of the presented design principle and the effectiveness of the proposed CCI method. It is shown that the energy storage requirements of the hybrid MMC with negative voltage in arm reference voltages can be reduced about 15%, and it achieves a significant reduction about 45% with the proposed CCI method.
Published in: IEEE Transactions on Industrial Electronics ( Volume: 66, Issue: 9, September 2019)