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For dc–ac modular multilevel converters (MMCs) in double-star configuration, this paper proposes a fast closed-loop control method based on optimized pulse patterns (OPPs). Thanks to the direct manipulation of the OPP switching instants, OPPs with discontinuous switching angles can be used, and the intrinsic cell capacitor voltage ripple is compensated for to preserve the OPPs’ superior harmonic performance. This model predictive pulse pattern controller is combined with a fast acting dead-beat circulating current controller and linked to an upper layer voltage balancing control scheme. The proposed control and modulation method is particularly suitable for medium voltage MMCs with a low number of cells. Despite operation at very low switching frequencies close to and including the fundamental frequency, a superior harmonic performance can be achieved. [ABSTRACT FROM AUTHOR]

The grid-connected modular multilevel converter (MMC) is very likely to operate under asymmetric grid conditions. Such a converter features several unique characteristics, which make its analysis different from other types of power converters in similar cases. In this paper, the three well-established control techniques, i.e., balanced current and negative sequence current injection for active/reactive power oscillation elimination, are tailored for the MMC case taking into account grid current limitation under fault conditions. Since the focus is laid on the MMC design impact during grid asymmetries, the three methods are compared in terms of branch energy variation increase as well as maximum achievable active power transfer. Moreover, the effect of circulating current second-order harmonic injection for capacitive storage reduction as well as dc-link oscillation elimination is also studied. Finally, experimental results from a downscaled laboratory prototype verify the theoretical studies. [ABSTRACT FROM PUBLISHER]

This paper proposes a power converter architecture for the implementation of an ultrafast charging station for electric vehicles (EVs). The versatile converter topology is based on the concept of the power electronic transformer. For the direct transformerless coupling to the medium-voltage grid, a cascaded H-bridge (CHB) converter is utilized. On the level of each submodule, integrated split battery energy storage elements play the role of power buffers, reducing thus the influence of the charging station on the distribution grid. The power interface between the stationary split storage stage and the EV batteries is performed through the use of parallel-connected dual-half-bridge dc/dc converters, shifting the isolation requirements to the medium-frequency range. By choosing several different submodule configurations for the parallel connection, a multiport output concept is achieved, implying the ability to charge several EVs simultaneously without the use of additional high-power chargers. All possible charging station operating modes among with the designed necessary control functions are analyzed. The state-of-charge self-balancing mode of the delta-connected CHB converter is also introduced. Finally, the development of a downscaled laboratory prototype is described, and preliminary experimental results are provided. [ABSTRACT FROM PUBLISHER]

Single-phase active rectifiers exhibit an inherent strong second-order current harmonic on their dc-link. The latter is often undesirable from a load point of view and is therefore chosen to be eliminated. A common method is the use of a resonant passive LC filter tuned at the frequency, which increases the order of the system, posing certain difficulties for the voltage control design. This paper presents a comprehensive analysis of the dc-link dynamics. The equations are linearized by means of small variations, and a respective closed-loop regulator is formed utilizing the partial state feedback control theory for pseudocontinuous systems. The control output is fed to an inner current regulator, following the well-known cascaded loop method. The stability of the proposed controller is validated throughout the whole operating point regime and its robustness against system parameter variations is evaluated. A comparison with a conventional controller proves the advantages of the utilized method. The theoretical analysis is verified by means of simulations as well as real-time implementation on an experimental laboratory setup. [ABSTRACT FROM AUTHOR]

In this paper, the analytical solution for the submodule voltage ripple equations of a modular multilevel converter (MMC) is derived, based on the knowledge of the external voltage/current magnitudes, and enhancing a concept previously presented in the literature. In order to achieve high accuracy, all passive elements of the converter, common-mode voltage injection as well as intentionally imposed circulating current harmonics are taken into consideration. The natural charge level mechanism of the capacitor voltages is also explained. As application examples, the three- as well as the two-phase grid-connected MMC cases are chosen. The control of line and circulating currents is also discussed and two respective independent feedback loops are formed. The concept of fictive-axis emulation is tailored for the two-phase MMC case, in order to achieve vector control of the line current and therefore straightforward desired injection of active and reactive power. Finally, the development of a reduced-scale laboratory prototype is presented and a full set of experimental results are provided, verifying the aforementioned concepts. [ABSTRACT FROM AUTHOR]