Browsing by Keyword "Switches"
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Item Circulating current control for modular multilevel converter based on selective harmonic elimination with ultra-low switching frequency(Institute of Electrical and Electronics Engineers Inc., 2016-10-25) Perez-Basante, Angel; Ceballos, Salvador; Konstantinou, Georgios; Liserre, Marco; Pou, Josep; De Alegria, Inigo Martinez; POWER ELECTRONICS AND SYSTEM EQUIPMENTMultilevel converters (MCs) are utilized in medium voltage (MV) high power applications due to its higher efficiency than two level converters. On the other hand, modular multilevel converters (MMCs) provide several advantages with regard to other MCs, such as higher scalability, reliability and no requirement of a common DC capacitor. Particularly, low switching frequency modulations, such as (2N+1) selective harmonic elimination (SHE) - pulse width modulation (PWM), may improve the efficiency of MMCs when they are utilized in MV and high power applications, where the number of sub-modules is not high. This work presents a new circulating current control for MMC when (2N+1) SHE-PWM is utilized. Therefore, it is possible to operate the converter simultaneously with low switching frequency and low capacitor voltage ripple at every sub-module besides a correct energy balance between arms. In addition, a new method to implement (2N+1) SHE-PWM for MMCs, which is also valid to implement standard SHE-PWM for any MC, is provided. Using this method, different equation systems are not required for every switching pattern. In this way, this technique provides simultaneously both the switching patterns and the firing angles which solve the SHE problem, simplifying the searching task. Simulation results which have been obtained from a MMC with 5 sub-modules at every arm, have validated the novel proposed circulating current control. Furthermore, the spectrum of the simulated line to line voltage waveform has proved the correct performance of the proposed (2N+1) SHE-PWM implementation method. Several sets of angles have been provided throughout the ma range, where 17 harmonics have been controlled.Item Elimination of Low-Frequency Ripples and Regulation of Neutral-Point Voltage in Stacked Multicell Converters(2017-01) Ghias, Amer M.Y.M.; Pou, Josep; Acuna, Pablo; Ceballos, Salvador; Heidari, Alireza; Agelidis, Vassilios G.; Merabet, Adel; POWER ELECTRONICS AND SYSTEM EQUIPMENTThis paper introduces a modulation method for the stacked multicell converters (SMCs). The proposed method is implemented using phase-disposition pulse width modulation and is capable of balancing and regulating the voltages of all the capacitors in the topology, i.e., the flying capacitors and the dc-link capacitors. The proposed method is also able to eliminate the low-frequency voltage ripples that may appear in the neutral point (NP) of SMCs. In SMCs with two stacks, the NP voltage level can be generated by direct connection of the output to the dc-link NP, but also using two extra states available. This redundancy is used to regulate the NP voltage. Furthermore, since the proposed method can eliminate the low-frequency voltage ripples in the capacitors, the capacitances of all the capacitors of the SMCs can be reduced, while maintaining high quality of the output voltages and currents. This enables the use of film capacitors. Simulation and experimental results are presented from a three-phase five-level 2× 2 SMC to verify the effectiveness of the proposed method.Item Low-frequency voltage ripples in the flying capacitors of the nested neutral-point-clamped converter(Institute of Electrical and Electronics Engineers Inc., 2016-05-10) Ghias, Amer M.Y.M.; Pou, Josep; Ceballos, Salvador; Agelidis, Vassilios G.; POWER ELECTRONICS AND SYSTEM EQUIPMENTThe flying capacitors (FCs) of the nested neutral-point-clamped (NNPC) converter show an inherent voltage ripple at fundamental frequency. This ripple can be significantly large under some operating conditions of the converter. In this paper, the amplitudes of the low-frequency voltage ripples in the FCs are determined. An averaged model of the NNPC converter is introduced and used in the analysis. The amplitudes of the capacitor voltage ripples are provided using normalized variables so that this information can be used to size the FCs of the converter in different applications. The results of the analysis are validated experimentally in a laboratory prototype.