This paper introduces a study on the charging infrastructures, integrated with distributed energy sources, showing their ability to support the electric and hybrid mobility in a smart grid scenario. This analysis starts from a description of the main AC and DC architecture and then goes through the advantages derived by the integration of renewable energy sources within the existing electric power network. A section of this paper is then dedicated to the main technologies of energy storage systems, which allow and support the integration of unpredictable energy sources into the grid. Finally, the power on-board and off-board vehicle charging devices are analyzed with specific focus on PWM control schemes, for the regulation of AC/DC and DC/DC power converters, and on grid operations (V2G) related to different aggregation schemes.

Medium voltage grids are a suitable selection for the connection of high power applications. However, for certain applications, such as PV energy conversion systems or fast charging stations for PEVs, the DC voltages are limited to be below 1000 V, making difficult their connection to such grids without the use of a step-up transformer. Multilevel converters allow the grid connection of such DC loads, by connecting them in one of their multiple dc sources, however, due the nature of these applications unbalanced operation is inherent, and cannot be completely solved by the modulation stage, thus additional circuitry is required. On the other hand, the use of a multilevel converter provides higher efficiency in the power conversion stage, higher power quality and reduced stress on the switching devices, which is also beneficial due the power ratings being reached by the mentioned applications. This paper explores a four-level double star multilevel converter as interface for central or mul-tistring inverter for grid-connected photovoltaic energy systems. The topology is capable of handling three PV arrays with different MPPT (with or without additional DC-DC converters), with the use of an additional balancing stage. The four-level output voltage improves the power quality of the PV energy conversion system, while reducing the grid filter size. This paper presents the operating principle of the converter, the control scheme and the simulation results, that show this topology can be an interesting alternative for large-scale PV plants.

This chapter provides an overview of the different charging architectures available for electric vehicles and plug-in hybrid electric vehicles. The charging architectures are addressed following two main categories: onboard chargers, used mainly for slow and semi-fast charging (generally AC connection), and off-board chargers, used for fast charging (DC connection). The chapter focuses on the mainstream solutions available in the industry, and also presents some recent advances and trends found in the literature. In addition, the chapter provides an introduction to well-established charging standards being used by manufacturers. Finally, the control schemes used in charging configurations, including the control schemes for DC-DC and AC-DC converter stages, are discussed, the latter considering both single- and three-phase control schemes.

With the increasing popularity of electric vehicles, there is an urgent demand to shorten the charging time, so the development of high-power charging stations with fast chargers is necessary to alleviate range anxiety for drivers. The charging station based on the neutral-point-clamped (NPC) converter can bring many merits, but it has unbalanced power problems in the bipolar dc bus. To solve this issue, comprehensive dc power balance management (PBM) in conjunction with high-power three-level dc-dc converter based fast charger is proposed in this paper. The active dc power balance management (APBM) is proposed to assist the central NPC converter in balancing power so that the additional balancing circuit is eliminated; while the passive dc power balance management (PPBM) is proposed to eliminate the fluctuating neutral-point currents and to ensure the balanced operation of fast chargers. The principles of APBM and PPBM are researched, the efficient integration between them is studied, and the overall control scheme for the fast charger is proposed. The power balance limits of APBM are explored, while the circulating currents of PPBM are analyzed. Simulation and experimental results are presented to verify the effectiveness of the proposed fast charger with PBM functions.

The use of conventional half-bridge submodules in the Modular Multilevel Converters brings important benefits such as the reduction in the power losses and semiconductor devices. However, the system with half-bridge submodule lacks the capability of blocking DC-faults currents. In this paper, a 5-level submodule with DC-fault blocking capability is presented. The proposed submodule allows to operate with different internal capacitances in order to reduce the cost of the system. Furthermore, a control and balance strategy for the novel 5-level submodule is proposed.

The technical challenges associated with distributed generation along with the increased adoption of electric vehicles has motivated the development of new configurations for dc microgrids. In this paper, a novel unidirectional multi-port power converter acts as the building block for interfacing different configurations of PV energy conversion systems, allowing it to reach high efficiency for a wide range of input power. Additionally, depending on the connection of the sources, the converter can act as a buck-boost converter or a buck converter, where the former offers wider input voltage range and the latter offers higher efficiency. Additionally, a sum/difference control scheme suitable for both configurations is presented. Simulation results are provided for a 32 kW PV system, establishing a comparison between the two configurations and validating the proposed topology and control scheme.

The development of high-power charging stations with fast chargers is a promising solution to shorten the charging time for electric vehicles (EVs). The neutral-point-clamped (NPC) converter-based bipolar-dc-bus-fed charging station brings many merits, but it has inherent voltage balance limits. To solve this issue, a voltage balance control (VBC) method based on a new modulation together with three-level (TL) dc-dc converter-based fast charger is proposed. Additionally, an effective VBC coordination between the TL dc-dc converter and the NPC converter is formulated. Through the proposed VBC coordination, the controllable balancing region is extended so that additional balancing circuits are eliminated. Meanwhile, the quality of the grid-side currents is improved as the NPC converter has more freedom to control currents. The low-frequency voltage fluctuations in dc buses are removed because the TL dc-dc converter performs most of the balancing tasks. Faster VBC perturbation performance is achieved due to higher available balancing current at TL dc-dc converter side. In addition, the voltage balance limits of both the TL dc-dc converter and the NPC converter are explored. The voltage balancing performances are compared when VBC is located at different sides. Simulation and experimental results are provided to verify the proposed VBC and the VBC coordination.

This paper proposes a bipolar-dc-bus Electric Vehicle (EV) charging station without a line-frequency transformer at the medium-voltage grid side. It is mainly composed of the Neutral Point Clamped (NPC) converter based central ac-dc station and the parallel isolated three-level DC-DC converter based fast chargers. Due to the elimination of the line-frequency transformer, the volume and cost of the system are reduced. Meanwhile, the isolation and step-down between high dc-bus voltages and low load voltages are performed through the high-frequency transformers, leading to increased voltage utilization of switching devices. In order to guarantee the bipolar dc buses balance and minimize the dc-bus voltage ripples, the 180°-interleaved operation for the two parallel isolated three-level DC-DC converters is proposed to make the total neutral-point current zero so that all fast chargers do not bring any unbalance problems. The proposed 180°-interleaved operating principle has been analyzed in detail, then simulation results are presented to verify its performance.

This paper proposes an effective voltage balance control (VBC) together with a new modulation technique for a high-power bidirectional three-level dc-dc converter based fast charger. The proposed VBC method can assist charging stations in balancing the dc-bus voltages so that additional balancing circuits are eliminated, leading to improved system efficiency. Meanwhile the proposed modulation method is not only intuitive to be implemented, but also have merits of reduced switching frequency, resulting in lower switching losses. The modulation principle is formulated, and its effective combination with the voltage balance control are analysed in detail. Based on which, the overall control scheme for the charging system is proposed. Simulation results are presented to validate the effectiveness of the proposed methods.

This paper proposes a novel architecture for plug-in electric vehicles (PEVs) dc charging station at the megawatt level, through the use of a grid-tied neutral point clamped (NPC) converter. The proposed bipolar dc structure reduces the step-down effort on the dc-dc fast chargers. In addition, this paper proposes a balancing mechanism that allows handling any difference on the dc loads while keeping the midpoint voltage accurately regulated. By formally defining the unbalance operation limit, the proposed control scheme is able to provide complementary balancing capabilities by the use of an additional NPC leg acting as a bidirectional dc-dc stage, simulating the minimal load condition and allowing the modulator to keep the control on the dc voltages under any load scenario. The proposed solution enables fast charging for PEVs concentrating several charging units into a central grid-tied converter. In this paper, simulation and experimental results are presented to validate the proposed charging station architecture.

This paper presents a grid-connected seven-level cascaded H-bridge converter operating as photovoltaic inverter. The main issue with this topology are the natural power imbalances between the power cells and the phases of the converter. The control problem is addressed with a Multiobjective Finite Control Set Model Predictive Control, where a dc-link voltage balance among the cells and good tracking of the active and reactive power references injected to the grid are achieved. Furthermore, an average switching frequency control per cell has been included. The proposed control scheme is validated trough simulation results and tested under dynamic conditions.

This paper proposes a novel architecture for Plugin Electric Vehicles (PEVs) dc charging stations, through the use of a single dc-link 3-level h-bridge (HB) converter as the grid interface. This feature is achieved by the use of an open-ended secondary windings transformer at the grid side. The proposed solution enables fast charging for PEVs concentrating several charging units into a single grid-Tied converter. The selected topology provides a three-level waveform without any balancing requirements, enabling a stable dc-bus. Finally, because of the simple nature of the converter, it can be implemented with off-The-shelf components, enabling a low cost alternative for the grid connection of Level III fast chargers.

This paper presents a generalized multilevel direct power control (ML-DPC) scheme for grid-connected multilevel power converters. The proposed method extends the original DPC operating principle by considering only the closest subset of two-level voltage vectors to the present switching state. The implementation of this principle requires the power derivatives for feedback, which can present numerical problems when applied experimentally, mainly due to high measurement noise sensitivity. Therefore, a derivative estimator is proposed based on the converter-grid model in the synchronous reference frame. In addition, a virtual flux observer is developed to achieve synchronization and improve robustness in the presence of grid voltage harmonics. The proposed method is applicable to any multilevel converter topology of any number of levels. In this paper, simulations and experimental results are presented for a seven-level cascaded H-bridge converter.

This investigation presents a grid-connected five-level H-bridge neutral-point-clamped converter operating with a single dc-link as photovoltaic power source. The operation with a single dc-bus is enabled by adding a transformer with open-end winding secondary, where each power cell of the converter is connected. The proposed control scheme is validated trough simulation results and tested under dynamic conditions. It can be implemented with a good tracking of the active and reactive power references injected to the grid. The results serve as a preliminary validation to potential utilization of the converter in large scale photovoltaic energy conversion systems.

This paper presents a new grid connected photovoltaic energy conversion system configuration for large scale power plants. The grid-tied converter is based on a modular multilevel converter using voltage source H-bridge cells. The proposed converter is capable of concentrating a multimegawatt PV plant with distributed string MPPT tracking capability, high power quality and increased efficiency compared to the classic two-level voltage source converters. The main challenge is to handle the inherent power unbalances which may occur, not only between the different cells of one phase of the converter, but also between the three phases. The control strategy to deal with these unbalances is analyzed in this paper. Simulation results for a downsized 7 level MMC composed of 18 H-bridge cells and PV strings are presented to validate the proposed topology and control method.

The automotive industry is making important changes towards the electrified transportation. Several Electric Vehicles (EVs) and Plug-in Hybrid EVs are currently on the market offering a clean and environment friendly alternative to conventional vehicles. However, limited mileage capacity and long refueling times have lead to a lukewarm reception from the consumers. In order to reduce the charging time fast charging architectures are being developed, usually as off-board solutions located in public installations. This paper presents a centralized charging station architecture, using a bipolar dc grid to power off-board chargers and integrate of DGs and storage systems. The central converter topology is an NPC and a novel balancing technique is implemented to extend the operating range of the power converter.

The increase in the power levels of photovoltaic (PV) energy conversion systems has resulted in new large-scale grid connected configurations that have reached the megawatt level. This substantial increment in the power levels imposes new challenges to the grid interfacing converter, and therefore results in new opportunities to be explored. This work introduces a new medium voltage multilevel scheme based on a three-phase cascaded H-bridge (CHB) converter and multiple PV strings. The proposed configuration enables a large increase of the total power capacity of the PV system, while the introduction of a multilevel converter helps to improve both power quality and efficiency and medium voltage operation at the grid side. The main challenge of the proposed configuration is to handle the inherent power imbalances that occur not only between the different cells of one phase of the converter but also between the three phases. Simulation results of a 7-level CHB PV system are presented to validate the proposed topology and control method.

Large scale grid connected photovoltaic (PV) energy conversion systems have reached the megawatt level. This imposes new challenges on existing grid interface converter topologies and opens new opportunities to be explored. In this paper a new medium voltage multilevel-multistring configuration is introduced based on a three-phase cascaded H-bridge (CHB) converter and multiple string dc-dc converters. The proposed configuration enables a large increase of the total capacity of the PV system, while improving power quality and efficiency. The converter structure is very flexible and modular since it decouples the grid converter from the PV string converter, which allows to accomplish independent control goals. The main challenge of the proposed configuration is to handle the inherent power imbalances that occur not only between the different cells of one phase of the converter but also between the three phases. The control strategy to deal with these imbalances is also introduced in this paper. Simulation results of a 7-level CHB for a multistring PV system are presented to validate the proposed topology and control method.