Discontinuous modulation of a cascaded H-bridge low-capacitance statcom

• Main Authors: Liu, Qingxiang, Rodriguez, Ezequiel, Farivar, Glen G., Ceballos, Salvador, Townsend, Christopher D., Leyva, Ramon, Pou, Josep
• Other Authors: Interdisciplinary Graduate School (IGS)
• Format: Article
• Language: English
• Published: 2021
• Subjects: Engineering::Electrical and electronic engineering::Power electronics; Static Compensator; Discontinuous Modulation
• Online Access: https://hdl.handle.net/10356/152891
• Institution: Nanyang Technological University

This paper presents a discontinuous modulation (DM) strategy for static compensators (StatComs) based on a cascaded H-bridge (CHB) converter with star configuration. The proposed DM strategy considers the capacitor voltage oscillations at twice the fundamental frequency and the effect of zero-sequence voltage injection on the capacitor voltages. Considering these effects is especially important in CHB-StatComs with large capacitor voltage ripples (low capacitance StatComs), where the assumption of a constant dc-link voltage, which is the basis of conventional DM strategies, does not apply. The paper also describes a coherent set of steady-state waveforms for CHB-StatComs under DM. In addition to the well-known benefit of reducing the switching losses, the proposed DM also reduces the dc-link capacitors size and extends the operating range. The viability of the proposed DM strategy is verified experimentally on a small-scale prototype. In addition, simulation results are obtained using a real-scale system to study feasibility of the DM under unbalanced conditions.