Marzio Barresi

This paper proposes a control strategy for a modular multilevel converter (MMC)-based photovoltaic (PV) system operating under non-homogeneous irradiance and unbalanced grid voltage conditions. The considered topology integrates PV units directly into the MMC submodules, enabling distributed maximum power point tracking (DMPPT). The proposed control framework combines a generalized grid controller with dedicated AC and DC circulating current controllers to manage vertical and horizontal power imbalances, respectively. The grid controller accommodates different operating objectives, namely balanced grid current injection, constant instantaneous real power operation, and constant instantaneous imaginary power operation, while regulating the injected total three-phase active and reactive powers to their prescribed references. The AC circulating current controller is formulated by extending a single-phase approach independently to each converter leg, thereby achieving complete decoupling among the legs in the management of vertical power mismatch under general grid unbalance conditions. Furthermore, the proposed DC circulating current controller simultaneously handles power imbalances originating from both partial shading among the converter legs and grid voltage unbalance. The effectiveness of the proposed approach is assessed through detailed simulations under both homogeneous and non-homogeneous irradiance conditions and for different grid control objectives. The results demonstrate effective maximum power extraction, proper regulation of the internal power flows, and stable converter operation under unbalanced grid conditions, yielding an overall system efficiency greater than 97% while fulfilling the desired grid power control objectives.

In recent years, significant resources have been invested by both the research community and industry in the study and development of isolated dc/dc converters for interfacing renewable energy sources and storage systems. In this context, the electrical isolation between different stages of the system is a mandatory requirement for several applications. This study investigated a novel isolated dc/dc current source converter with capacitive isolation. The proposed solution consists of two bridges, each one realized using four reverse-blocking switches, interfaced through two isolation capacitors, and a shunt high frequency capacitor allowing power to be transferred between the two dc sides. The converter structure, operating principles, and component sizing requirements were first analyzed. Then, simulations were performed using MATLAB/Simulink© and LTSpice© to demonstrate the operation of a 10 kW converter, which confirmed the results of a theoretical analysis. Experimental tests were also conducted on a scaled prototype.

Modular multilevel converters (MMCs) are widely used in power-conversion applications, including distributed energy storage integration, because of their scalability, high efficiency, and reduced harmonic distortion. Integrating battery storage systems into MMC submodules using dual active bridge (DAB) converters provides electrical isolation and reduces voltage stress, harmonics, and common-mode issues. However, voltage fluctuations due to the battery state of charge can compromise the zero-voltage switching (ZVS) operation of a DAB and increase the reactive power circulation, leading to higher losses and reduced system performance. To address these challenges, this study investigated an active control strategy for submodule voltage regulation in an MMC with DAB-based battery integration. Assuming single-phase-shift modulation, two control strategies were evaluated. The first strategy regulated the DAB voltage on one side to match the battery voltage on the other, scaled by the high-frequency transformer turns ratio, which facilitated the ZVS operation and reduced the reactive power. The second strategy optimized this voltage to minimize the total power-conversion losses. The proposed control strategies improved the efficiency, particularly at low power levels, achieving several percentage points of improvement compared to maintaining a constant voltage.

The European Call HORIZON-CL5-2024-D5-01-02 suggested goals and future trends for electric powertrains. Focusing on the next-generation electric vehicles, 1.2 kV architectures were recognized to be suitable outcomes for improving the state of the art, enabling a strong reduction in the charging current and enlarging the vehicle driving ranges. Nevertheless, sizing all the vehicle components for such high voltage could be counterproductive. Hence, this work proposes the adoption of a 1.2 kV dc, 350 kW modular multilevel converter with distributed battery packs that can carry out ultra-fast-dc recharges. Its modular nature allows sizing the power electronics and several passive components on much lower voltage levels, with low cost-per-component and limited losses. In addition, this converter topology proved to be flexible, implements cell battery balancing algorithms, and ensures backward compatibility with the existing dc and ac charging modes without the need for any additional on-board charger. Finally, the converter can be installed on a dual motor powertrain. This article shows an electric drive involving two 440 V, 75 kW induction machines. The traction and dc-charging capabilities of the converter were experimentally verified with a small-scale prototype.

This paper proposes a novel balancing control strategy for modular multilevel converters (MMCs) integrating a battery pack (BP) at the submodule level. During the converter operation, balancing the energy of the distributed resources within the converter is necessary to ensure the converter stability, avoid generating undesired current harmonic components, and increase the overall system efficiency. In particular, exploiting the MMC topology, AC and DC circulating currents are controlled to cope with unbalanced conditions. In this context, this paper proposes a circulating current control strategy to equalize the state-of-charge (SOC) values of BPs by properly injecting AC and DC circulating currents. In addition, a dynamic saturation method for the circulating components was designed to reduce the SOC equalization time while continuously preventing the design converter limitations from being overcome. The proposed control algorithm was experimentally tested and compared with a state-of-the-art solution, which demonstrated its effectiveness in terms of the overall efficiency and balancing time.

The increasing penetration of renewable energy sources (RESs) in transmission and distribution systems presents several challenges for grid operators. In particular, the unpredictable behavior of RESs can disrupt the balance between energy production and load demand, potentially affecting the stability of the entire system. Grid-connected energy storage systems (ESSs) offer a possible solution to manage the uncertainty associated with RESs. In fact, ESSs exchange power with the grid through the adoption of suitable energy management strategies, which are typically implemented by power electronics-based grid interfaces. Unlike other current source converter (CSC) solutions described in the literature, which only interface with a single energy storage device, this paper introduces a novel topology for a three-phase delta-type current source converter (D-CSC), which is capable of integrating three independent ESSs using the same number of semiconductors as traditional CSC solutions. Thus, it considerably enhances the flexibility of a power conversion system (PCS) without increasing the number of converter components. In addition, an innovative energy management control strategy is also introduced. This strategy enables the D-CSC to compensate for energy imbalances arising between the three ESSs, which might be caused by several factors, such as different aging characteristics, converter component tolerances, operating conditions, and temperature drifts. Hence, the D-CSC-based interface is capable of proper grid operation even if the three ESSs have different characteristics, thus opening the possibility of employing this converter to integrate both first and second-life devices. First, the topology of the proposed D-CSC is introduced, followed by a detailed mathematical description of its control strategy. The proper grid operation of the D-CSC was tested under different scenarios, considering the grid integration of three independent superconducting magnetic energy storage systems in a marine vessel. The proposed D-CSC is compared to traditional CSC solutions, highlighting the superior performances of the novel converter topology in terms of efficiency, total harmonic distortion of the output currents, and overall cost reduction for the PCS.