Hybrid Distribution Transformers (HDTs) have been proposed as an alternative to conventional distribution transformers and Solid-State Transformers (SSTs), combining in a single solution a conventional Low-Frequency Transformer (LFT) with one or more power converter stages. Nonetheless, some HDT configurations exhibit a Circulating Active Power Flow (CAPF) while compensating for grid voltage disturbances. The CAPF increases the amount of power processed by the power converters, leading to reduced efficiency. The CAPF can be eliminated if the energy required to compensate for grid voltage disturbances is supplied by a DC source, such as a Battery Energy Storage System (BESS). Another alternative is to connect the DC stage of the HDT to a DC microgrid. In the context of a hybrid microgrid, the HDT can operate as an interlinking converter between both grids. The parallel-connected converter can manage energy flow between the AC and DC microgrids, while the series-connected converter can supply precise voltage regulation to the low-voltage AC grid. This work presents the model and control of an Interlinking Hybrid Distribution Transformer (IHDT) for a hybrid microgrid. A simple adaptive gain is employed to account for the distribution of the CAPF.

This paper studies the fault estimation problem for polynomial fuzzy systems with unmeasurable premise variables. Considering the limitations of existing methods that require the convergence of the original system, a novel augmentedstate observer is proposed for polynomial fuzzy systems. Unlike compensation-vector-based approaches, the proposed method addresses the singularity problem and eliminates the traditional linear growth assumptions on unmeasurable premise variables, while only existence of the corresponding upper bounds rather than knowledge of their specific values is assumed. Moreover, the proposed method enables fully mismatched design, thereby enhancing both design flexibility and computational efficiency. Finally, the effectiveness of the proposed method is demonstrated through a bridge crane system as a case study.

To keep up with the rising demand for electricity, renewable energy sources, including solar and wind power, are being increasingly utilized. However, grid stability is compromised by the intermittent nature of renewable energy resources. Technologies for energy storage provide a solution by enhancing system flexibility. As prosumer-based electrical systems and distributed energy resources expand, energy management systems are becoming more essential for optimizing system functionality and efficiency by coordinating the operation of various devices. This paper deals with a genetic algorithm-based energy management system consisting of PV generation, household load, electric vehicle, and energy storage system. The objective is to reduce electricity costs by defining the objective function and related constraints. The main novelty of this paper is the study of different parameters used in a genetic algorithm, and to find out the best set of parameters in terms of electricity cost reduction, that can be later used as guidelines to design similar types of systems.

The modern power system is facing a high penetration of distributed energy resources such as photovoltaic (PV) powered installations. These systems are subject to intermittent operation due to the changing environmental conditions. The systems can face rapid changes in irradiance that lead to the reinitialization of the converter. In this sense, it is necessary to provide safe procedures that enable the operation of the converter under any condition. In this work, a soft-start method is presented for the boost converter that is part of a two-stage PV system configuration. The open circuit voltage of the PV system is used as an indicator of the estimated available power and to detect rapid irradiance changes. Besides, the implementation consists of simple timers and comparisons that can be carried out in available microcontrollers that are used to implement the control routines. Simulation results confirm the operation of the converter under step changes of irradiance for both flexible and maximum power point operation modes.

The intentional islanded mode of operation is becoming critical for power electronics converters since small energy storages are developed for residential applications. It provides an uninterruptable power supply for the local loads and creates an opportunity to disconnect from the grid if needed. In order to provide the full functionality of the islanding mode, the four-leg power electronics converters are required to work with unpredictable, asymmetrical loads. Maintaining desired voltage levels at the point of common coupling during high power demand is challenging. Moreover, rapid load changes, mainly resistive in residential solutions, can cause a voltage stability problem. The load change study must also focus on the converter’s start of operation without load or total load disconnection, which are crucial for voltage stability. This paper presents control enhancements for the islanded mode of operation. It identifies the issue of rapid asymmetrical load changes and presents a solution based on simulation research.

Hybrid Distribution Transformers (HDTs) are a promising solution to power quality problems on distribution networks, allowing for precise voltage and current regulation. HDTs that connect the series converter on the primary side are subject to a Circulating Active Power Flow (CAPF) between the Low-Frequency Transformer (LFT) and the power converters that appear when compensating for voltage disturbances. This paper analyzes the cause of the CAPF and its behavior, considering varying grid conditions and the impact of the CAPF on the DC-Link ripple.

Solid state transformers based on modular structures have become a suitable alternative to provide high voltage rating, reliability, and fault tolerance at the distribution level. Among them, the SST based on Modular Multilevel Converter with an input-series output-parallel interconnected by Dual Active Bridges configuration appears as a good solution to reach high voltage levels at the input and large currents at the output stage. However, the parallelization of SM generates cross-circulating currents among modules. In this paper, the cross-circulating currents are controlled and mitigated by a decoupled linear control. Simulation results shown the cross-circulating currents and their dependency under mismatches in both inductance and resistances.

Novel reconfigurable rectifier circuit is presented. It features three operating modes: full-bridge rectifier, voltage doubler rectifier, voltage quadrupler rectifier. After the rectifier topology is introduced, a case study dc-dc converter based on quasi-Z-source full-bridge topology is presented. An experimental prototype was assembled to verify concept feasibility. The assembled converter is suitable for the global maximum power point tracking owing to the wide input voltage range achieved. DC voltage gain theoretical expressions are verified experimentally, and measured efficiency is given.

Multilevel higher-sided polygonal (more than six sides) voltage space vector structures are becoming a forefront choice for obtaining high quality low distortion output voltages for variable speed drive applications. Unique class of multilevel inverter topologies generating polygonal voltage space vector structures have advantages - full DC bus utilization, low-order harmonic suppression in output voltage for entire speed range operation with low switching frequency strategies, and extended linear modulation range as near to the base speed, apart from other advantages of multilevel inverters. In this paper, generation of a high density multilevel (13-level) polygonal space vector structure with 24-sides using a single DC source is presented. The realization of space vector structure is discussed, performance of the drive scheme during steady state and transients are extensively studied through simulation and are validated through experiment.

This paper presents a new topology of DC-DC converter with a post-fault operation ability for a Solid-State Transformer. It describes the concept of a Solid-State Transformer as a solution to improve flexibility and functionality of an electrical system. A conventional Solid-State Transformer is presented as well as a proposal for a modified topology based on a hybrid 3-phase Dual Active Bridge with high post-fault operation ability. The study of DC-DC converters takes into account well known topologies and the new proposed topology on which this paper is focused. Post-fault operation schemes are presented for both sides of DAB and for a Medium Voltage Converter, which is integral part interfacing DC-links with medium voltage grid. Simulation results confirm versatility of topology and ability to post-fault operation.

The benefits of using grid connected Voltage Source Converters (VSC) related to processing and improving of electrical power quality in distribution grid heavily depends on current control (CC) method. Research in this field are mainly focused on response dynamics, stability and accuracy of reference current tracking under strongly distorted grid voltage conditions with variable grid impedance in point of common coupling (PCC). This is particularity important in selected operating states of Solid State Transformer (SST) which attends to be main energy management unit in Smart Grid (SG). Low voltage distribution grid is exposed to voltage imbalance, distortions and dips, hence each phase of SST should be controlled separately. This paper presents supreme single phase grid connected VSC control with LCL filter under strongly distorted grid voltage. Proposed solution is based on application of grid voltage distortion compensation loop, which operates in parallel to CC loop. Mathematical analysis and simulation results have proven excellent performance and verified the validity of the proposed solution.

Solar systems have become very competitive solutions for residential, commercial, and industrial applications for both standalone and grid connected operations. This paper presents an overview of the current status and future perspectives of solar energy (mainly photovoltaic) technology and the required conversion systems. The focus in the paper is put on the current technology, installations challenges, and future expectations. Various aspects related to the global solar market, the photovoltaic (PV) modules cost and technology, and the power electronics converter systems are addressed. Research trends and recommendations for each of the PV system sectors are also discussed.

The Multiphase Multilevel Energy Generation Systems (M2EGS) base mainly on utilization of the multiphase machine such e.g. symmetrical, Single Neutral Point (SNP), 6-phase Induction Generator (6IG) that as other multiphase machines displays a feature to operate under phase loss fault condition. This property gives an ability to 'sacrifice' one leg of the generator converter and switch it into the grid converter side in case of its failure within the T-type back-to-back (B2B) topology. Unfortunately, one phase loss in the generator or its converter results in a significant electromagnetic torque ripples that have a negative impact on the machine bearings and elements mounted on its shaft. Then, a proper fault-tolerant algorithm for the generator is necessary. This paper presents the original experimental validation of the full reconfiguration mechanism introduced into the Multiphase Multilevel Energy Generation System (M2EGS). Moreover, a de-rating effect of fault-tolerant operation for the Renewable Energy Source (RES) application is briefly discussed.

In this paper Model Predictive Control (MPC) with finite control states set (FS) is proposed as the new control approach for 3-level 4-leg Flying Capacitor Converter (FCC) operating as a Shunt Active Power Filter (SAPF). The main concerns and solutions regarding the algorithm development and experimental studies are described. The first is addressed to the modeling of the 4-wire SAPF and 3-level 4-leg FCC. The second relates to the control of Flying Capacitors voltages, which is performed outside the prediction loop. The issue regarding undesirable transitions of switching states is described and the solution to eliminate it is shown. Also, an analysis of possible delays on laboratory model is performed and the compensation method is presented. Finally, the control performance was tested experimentally on the 10 kVA FCC laboratory model and the results are shown in the last section.

Operation under partial shading condition (PSC) significantly decreases energy extracted from photovoltaic (PV) power plants. Non-uniform insolation caused by the passing clouds and natural obstacles results in some PV modules to be effectively excluded from operation. Commercially used maximum power point tracking (MPPT) algorithms do not have any information about the global behavior of the PV string or array which they control. This can induce significant error in determining the optimum operating point and in turn affect efficiency of the system. This paper focuses on Global Maximum Power Point Searching (GMPPS) methods based on fast, hardware power-voltage (p-v) sweeping techniques. Two methods based on variable channel resistance of the MOSFET and switched inductor are analyzed and tested for a 3.5 kW PV array in the field conditions. Study shows that both solutions are suitable for accurate p-v sweep independently of the PV array configuration or shading pattern.

This paper presents a new control algorithm of High Instantaneous Power Impulse Converter (HIPIC). HIPIC is characterized by high power in megawatt range delivered to the output in very short time. A new algorithm allows fast rising of output current to the set value and a proper peak current control during the impulse by using two types of controllers: hysteresis and PID. Moreover capacitor voltage change compensation (CCVC) has been introduced because high power impulse causes significant discharge of capacitors in this system. Additionally, interleave of switching for parallel transistor yields an improvement of the output peak current control. Thanks to all of those features the output current control response is accurate, fast in range of few microseconds and it allows operation in very dynamic conditions. The output current is almost rectangular in shape.

This paper describes control and modulation algorithm of a simplified multilevel AC-DC-AC converter for small power generation system which is based on well known Neutral Point Clamped (NPC) topology. Main advantage of this approach allows single 3-phase, 3-level converter to be utilized as a full interface between Permanent Magnet Synchronous Generator (PMSG) and the single-phase grid. Study of control and modulation for simplified converter are supported by simulation and experimental results. The three-phase AC-DC converter is controlled with regard of Field Oriented Control (FOC) principle. The current control of the single-phase DC-AC converter is based on the P+Multi-Resonant controller and Second Order Generalized Integrator Phase Locked Loop (SOGI-PLL). The multi resonant structure in single-phase converter allows a proper operation under non-ideal grid voltage.

This paper proposes a new power converter topology for the Wave Dragon multi-megawatt wave energy conversion platform. The current wave dragon power converter system is composed of several low-voltage two-level voltage source converters in back-to-back configuration; one per turbine-generator. Although this is a well known and proven technology, the use of distributed power electronic converters among all turbines does not bring any additional benefit in terms of efficiency and power quality. The proposed topology remains operating at low voltage and distributed at the generator side, but is combined at the grid side into a three-phase cascaded H-bridge (CHB) multilevel converter operating at medium voltage. This is achieved interfacing each PMSG through a low-voltage full bridge diode rectifier, followed by a boost dc-dc converter connected to the dc-link of the power cells of a 7-level CHB. The proposed configuration allows to concentrate the whole Wave Dragon platform into a single grid-tied converter with higher power quality and efficiency. Control schemes for both grid- and generator-side converters, and simulation results are presented in this paper.

This paper presents operation of the four-leg three-level Flying Capacitor Converter (FCC) interfacing renewable energy source (RES) with the grid. Such converter with proposed control method enables work in association of electrical grid disturbances by switching all legs separately to stand-alone or grid connected mode of operation, what allows for energy transfer between them. Four-leg FCC with described control method may be treat as DC microgrid supplied from three independent AC sources and RES. Therefore, very popular in last few years, hierarchical control can be adapted to make power management of such system. Paper describe proposed control method as well as experimental results are shown and discussed.

This paper presents a new small-scale single-phase photovoltaic (PV) energy conversion system. The topology is based on the series connection of two three-level T-type converters, which form a 5-level converter with two independent maximum power point tracking (MPPT) string connections. The topology merges benefits of string and multi-string PV configurations. The operating principle, the switching states, modulation scheme and control method are addressed in the paper. Simulation results are presented under dynamic conditions and different operating points for the two PV strings, to provide a preliminary validation of the topology and its performance.