An off-board dc fast battery charger for electric vehicles (EVs) with an original control strategy aimed to provide ripple-free output current in the typical EV batteries voltage range is presented in this article. The proposed configuration is based on modular three-phase interleaved converters and supplied by the low-voltage ac grid. The ac/dc interleaved three-phase active rectifier is composed of three standard two-level three-phase converter modules with a possibility to slightly adjust the dc-link voltage level in order to null the output current ripple. A modular interleaved dc/dc converter, formed by the same three-phase converter modules connected in parallel, is used as an interface between the dc link and the battery. The use of low-cost, standard and industry-recognized three-phase power modules for high-power fast EV charging stations enables the reduction of capital and maintenance costs of the charging facilities. The effect of coupling on the individual input/output inductors and total input/output current ripples has been investigated as well, considering both possible coupling implementations, i.e., inverse and direct coupling. Numerical simulations are reported to confirm the feasibility and the effectiveness of the whole EV fast charging configuration, including the proposed control strategy aimed to null the ripple of the output current. Experimental results are provided by a reduced scale prototype of the output stage to verify the ripple-free output current operation capability.

Three-phase, four-wire, split-capacitor inverters, thanks to their capability to deal with unbalanced systems, are currently employed in photovoltaic installations, electric vehicles battery chargers, active power filters, and many other grid-tied applications. The minimization of ac output current ripple and switching losses positively impacts the inverter's efficiency, volume, weight, and cost optimization. For this reason, a novel variable switching frequency driving strategy independently tunable on each phase is proposed in this article. Taking advantage of phase current ripple prediction, a proper variable switching frequency strategy is applied for obtaining a flat current ripple profile. Having tuned the driving strategy parameters, it is possible to optimize and compare individual metrics such as the maximum peak-to-peak value of the current ripple, current ripple rms, average switching frequency, and switching losses. By applying the proposed modulation method, a significant inverter performance enhancement has been obtained. Converter efficiency is improved without introducing detrimental effects on the current harmonic quality. Analytical derivations are expressed as a modulating index function and the power factor for balanced and unbalanced systems. All the theoretical developments are verified throughout numerical simulations and experimental tests.

A new Modular Multilevel Converter with Interleaved half-bridge Sub-Modules (ISM-MMC) is proposed in this article. The ISM-MMC exhibits higher modularity and scalability in terms of current ratings with respect to a conventional MMC while preserving the typical voltage-level adaptiveness. The ISM-MMC brings the known advantages of classical MMC to low-voltage, high-current applications making it a novel candidate for the sector of ultrafast chargers for all types of electric vehicles (EVs). This advanced topology makes it possible to easily reach the charging power of the EV charging system up to 4.5 MW and beyond with a low-voltage supply. To operate the new converter, a hybrid modulation scheme that helps to exploit the advantages of the interleaving scheme is implemented and explained in this article. It has been verified that the typical MMC control methods are still applicable for ISM-MMC. A comparative study between classical MMC and ISM-MMC configurations in terms of output characteristics and efficiency is also given. Furthermore, it has been demonstrated that the number of ac voltage levels is synthetically multiplied by the number of interleaved half-bridge legs in submodules. Simulations, hardware in the loop, and experimental tests are carried out to demonstrate the feasibility of the proposed topology and the implemented modulation scheme.

An off-board dc fast battery charger for electric vehicles (EVs) with an original control strategy aimed to provide minimum input voltage ripple and zero output current ripple in the typical EV batteries voltage range is presented in this paper. Currently, due to an infant development stage of high-power, high-energy batteries for EV application, there is no clear consensus on allowable output current ripple for fast chargers. However, there are different charging protocols, which are optimized for short charging time and efficiency, while maintaining a long-life cycle of a battery. Common feature of these protocols is an underlying assumption of minimum (or null) instantaneous charging current ripple. The fast charger configuration proposed in this paper is based on a modular three-phase interleaved converter, used as an interface between the dc-link (dc supply) and the battery. The use of low-cost, standard and industry-recognized three-phase power modules for high-power fast EV charging stations enables the reduction of capital and maintenance costs of the charging facilities, enhancing further expansion of the eco-friendly transport. Numerical simulations are carried out in Matlab/Simulink to confirm the feasibility and the effectiveness of the whole EV fast charging configuration, with emphasis to input voltage ripple and output current ripple of the interleaved three-phase dc/dc converter.

A complete analysis of the ac output current ripple in four-leg voltage source inverters considering multiple modulation schemes is provided. In detail, current ripple envelopes and peak-to-peak profiles have been determined in the whole fundamental period and a comprehensive method providing the current ripple rms has been achieved, all of them as a function of the modulation index. These characteristics have been determined for both phase and neutral currents, considering the most popular common-mode injection schemes. Particular attention has been paid to the performance of discontinuous pulse width modulation (DPWM) methods, including DPWMMAX and DPWMMIN, and their four most popular combinations DPWM0, DPWM1, DPWM2, and DPWM3. Furthermore, a comparison with a few continuous techniques (sinusoidal, centered pulse width modulations, and third harmonic injection) has been provided as well. Moreover, the average switching frequency and switching losses are analyzed, determining which PWM technique ensures minimum output current ripple within the linear modulation range at different assumptions. Numerical simulations and laboratory tests have been conducted to extensively verify all the analytical claims for all the considered PWM injections.

A new state observer-based current balancing method for Modular Multilevel Converters with Interleaved half-bridge Sub-Modules (ISM-MMC) is presented in this paper. The developed observer allows estimating currents through interleaved half-bridge legs in each submodule of ISM-MMC basing only on arm current and submodules capacitor voltage measurements. Then, the interleaved current balancing control uses the estimated currents to reduce the interleaved currents imbalance caused by upstream control actions. This technique minimizes the number of required current sensors in ISM-MMC, thereby reducing the converter's cost, weight, and volume. Capabilities of the proposed sensorless interleaved currents balancing control has been tested against standard parameter tolerances of the composing passive elements. In addition to that, a novel capacitor voltage balancing strategy for MMCs is developed. The new algorithm contains main advantages of the classical sorting-based capacitor voltage balancing methods while provides an opportunity to decouple two balancing tasks of ISM-MMC, namely capacitor voltage and interleaved legs current balancing. The feasibility of the proposed methods is verified by extensive simulation and experimental tests on a laboratory prototype by the corresponding system response under the output characteristics variation and interleaved current control perturbation.