Decoupled discontinuous modulation for cascaded H-bridge StatCom with star configuration

• Main Authors: Liu, Qingxiang, Rodriguez, Ezequiel, Farivar, Glen G., Pou, Josep, Townsend, Christopher D., Leyva, Ramon
• Other Authors: Interdisciplinary Graduate School (IGS)
• Format: Conference or Workshop Item
• Language: English
• Published: 2022
• Subjects: Engineering::Electrical and electronic engineering; Engineering::Electrical and electronic engineering::Power electronics; Cascaded H-Bridge; Discontinuous Pulse Width Modulation; Static Compensator
• Online Access: https://hdl.handle.net/10356/162978
• Institution: Nanyang Technological University

This paper presents a novel zero-sequence voltage injection method for discontinuous modulation (DM) in star-connected cascaded H-bridge (CHB) static compensators (StatComs). Conventional DM methods in CHB StatComs suffer from control interactions during unbalanced grid conditions. This paper proposes a DM that eliminates this control interaction by inserting a clamping transition within a third of the fundamental period. The transition instant is decided by comparing a duty cycle, which is calculated to mitigate the fundamental-frequency in the zero-sequence voltage for discontinuous operation, with a triangular carrier signal with a frequency of three times the fundamental. The clamping intervals under the proposed DM are affected by the phase-shift of this carrier. Specifically, the paper analyses the effects on the harmonic content of the proposed zero-sequence voltage, switching loss, twice-fundamental-frequency capacitor voltage ripple, and current total harmonic distortion, for different phase-shift angles of the DM carrier signal. Besides, the feasibility of the proposed DM in dealing with a grid voltage sag is also discussed.