Browsing by Author "Leyva, Ramon"
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Item Discontinuous Modulation of a Cascaded H-Bridge Low-Capacitance StatCom(2022-03-01) Liu, Qingxiang; Rodriguez, Ezequiel; Farivar, Glen G.; Ceballos, Salvador; Townsend, Christopher D.; Leyva, Ramon; Pou, Josep; POWER ELECTRONICS AND SYSTEM EQUIPMENTThis article presents a discontinuous modulation (DM) strategy for static compensators (StatComs) based on a cascaded H-bridge (CHB) converter with a 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. This article 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.Item Enhancing Inductive Operation of Low-Capacitance Cascaded H-Bridge StatComs Using Optimal Third-Harmonic Circulating Current(2021-09) Rodriguez, Ezequiel; Leyva, Ramon; Liu, Qingxiang; Townsend, Christopher; Farivar, Glen; Ceballos, Salvador; Pou, Josep; POWER ELECTRONICS AND SYSTEM EQUIPMENTThe cascaded H-bridge (CHB) low-capacitance static compensator (LC-StatCom) has a limited operating range in the inductive region compared to a conventional StatCom due to the inherent large oscillations on the capacitor voltages. This limitation constitutes a great drawback of CHB LC-StatComs. This article presents an effective hardware-free solution to overcome this drawback. The proposed solution is based on the injection of an optimal third-harmonic circulating current to suitably shape the capacitor voltages aiming at avoiding overmodulation. Considering all the effects of the third-harmonic circulating current, the article proposes a reference design that guarantees a prescribed safe operating voltage limit, thus increasing the operational range of the LC-StatCom. The proposed approach takes into account the inherent induced oscillation on the capacitor voltages. This approach has been verified by simulation and experimentally with a laboratory prototype, corroborating the excellent performance that agrees with the theoretical analysis.