Browsing by Keyword "capacitor voltage ripple"
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Item Circulating current injection methods based on instantaneous information for the modular multilevel converter(2015-02-01) Pou, Josep; Ceballos, Salvador; Konstantinou, Georgios; Agelidis, Vassilios G.; Picas, Ricard; Zaragoza, Jordi; POWER ELECTRONICS AND SYSTEM EQUIPMENTThis paper studies different circulating current references for the modular multilevel converter. The circulating current references are obtained from the instantaneous values of the output current and modulation signal of the phase leg. Therefore, the determination of the amplitude and phase of the output current is not needed, which is a significant improvement compared to other methods such as those based on injecting specific harmonics in the circulating currents. Among the different methods studied in this paper, a new method is introduced, which is able to reduce the capacitor voltage ripples compared to the other methods. A closed-loop control is also proposed which is able to track the circulating current references. With the discussed methods, the average values of the capacitor voltages are maintained at their reference while the voltage ripples are kept low. Experimental results are presented to demonstrate the effectiveness of the proposed and discussed methods.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.