Browsing by Keyword "modular multilevel converter (MMC)"
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Item Circulating Current Control for Modular Multilevel Converters with (N+1) Selective Harmonic Elimination - PWM(2020-08) Perez-Basante, Angel; Ceballos, Salvador; Konstantinou, Georgios; Pou, J.; Sanchez-Ruiz, Alain; Lopez, Iraide; Martinez de Alegria, Inigo; POWER ELECTRONICS AND SYSTEM EQUIPMENTModular multilevel converters (MMCs) require control of the circulating current, i_circ, to improve their operation and efficiency. This is particularly important when low switching frequency modulation techniques, such as selective harmonic elimination (SHE-PWM) are applied. This work provides a novel method to control the circulating current along with (N+1) SHE-PWM. Unlike the case of (2N+1) SHE-PWM, explicit redundant levels are not available and, therefore, different modulation indexes, m_1 and m_2, are employed in the upper and lower arms to obtain the desired modulation index m_a. Unlike previous (N+1) circulating current methods, the distances between m_a, m_1 and m_2 remain constant to not disturb the phase output voltage, with an interchange of m_1 and m_2 between the arms used to follow the desired i_circ. The control adjusts the dc component of the circulating current and the energy stored in the SMs to their references, while maintaining the energy balance between the upper and lower arms. Simulation tests and experimental results, obtained from a single-phase laboratory prototype MMC, validate the proposed control technique.Item New Measuring Technique for Reducing the Number of Voltage Sensors in Modular Multilevel Converters(2016-01-01) Picas, Ricard; Zaragoza, Jordi; Pou, Josep; Ceballos, Salvador; Balcells, Josep; POWER ELECTRONICS AND SYSTEM EQUIPMENTThis paper presents a new technique for measuring the capacitor voltages in a modular multilevel converter using a reduced number of voltage sensors.With this technique, the minimum number of voltage sensors per arm is two. Each sensor measures the output voltage of a set of submodules (SMs) connected in series and acquires a new measurement when there is only one SM activated within the set. The acquired value corresponds to the capacitor voltage of the activated SM minus the voltage drops produced in the switches. A simple mathematical model is used to estimate all the SM capacitor voltages, and it is then updated whenever there is a newmeasurement available. An algorithm that enforces the periodic update of the voltage measurements is also presented. The proposed measuring technique highly reduces the number of voltage sensors; hence reducing the complexity and costs of the signal conditioning and data acquisition stages. Simulation and experimental results are presented to demonstrate the efficiency of the proposed technique.