Circulating Current Control for Modular Multilevel Converters with (N+1) Selective Harmonic Elimination - PWM
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Author/sPerez-Basante, Angel; Ceballos, Salvador; Konstantinou, Georgios; Pou, J.; Sanchez-Ruiz, Alain; [et al.]
Selective harmonic elimination (SHE)
Modular multilevel converter MMC
Modular multilevel converters (MMCs) require control of the circulating current, i_circ, to improve their operation and efficiency. This is particularly important when low switching frequency modulation techniques, such as selective harmonic elimination (SHE-PWM) are applied. This work provides a novel method to control the circulating current along with (N+1) SHE-PWM. Unlike the case of (2N+1) SHE-PWM, explicit redundant levels are not available and, therefore, different modulation indexes, m_1 and m_2, are employed in the upper and lower arms to obtain the desired modulation index m_a. Unlike previous (N+1) circulating current methods, the distances between m_a, m_1 and m_2 remain constant to not disturb the phase output voltage, with an interchange of m_1 and m_2 between the arms used to follow the desired i_circ. The control adjusts the dc component of the circulating current and the energy stored in the SMs to their references, while maintaining the energy balance between the upper ...