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Repetitive Control (RC) enables inverters to inject, at fundamental frequency, high quality sinusoidal current into the grid or to provide low THD voltages in off-grid applications. However, digital RC, which can obtain a zero steady-state error for each periodic signal with a known period, gets its performance significantly degraded in the case of periodic signals with variable frequency. In other words, RC algorithms require an integer number of samples per period, while in some industrial applications the number of samples per period could be a non-integer time-varying value. Therefore, RC would lead to a significant quality degradation of the provided tracking capabilities when the grid frequency or the off-grid desired frequency changes. According to that, a newly RC structure with adaptive decoupled sampling is proposed to work with a RC implemented with constant delay line, regardless of the desired output frequency in both grid-tied and stand-alone operation. After the FPGA implementation, the experimental campaign highlights the effectiveness of the proposed control architecture.

This article investigates the dc-link voltage control of an active rectifier that is supplied by a variable speed permanent magnet synchronous generator. This configuration is commonly encountered in gearless wind energy conversion systems as well as in variable speed generating units. The proposed control strategy uses an optimal voltage vector based modulated model predictive control (MPC) to achieve direct power control. The studied scheme combines the advantages of finite control set MPC and control techniques that use pulsewidth modulator. The fast dynamics of the former are obtained during large transients, and the constant switching frequency operation, of the latter, is ensured in steady state. At each sampling instant, all the switching states are evaluated and the two adjacent states that give minimum error in the controlled variables are selected. The duty cycle of each of these vectors is computed through linear combination and appropriately limited for overmodulation. Simulations and cosimulation results presented in this article show interesting results. The control strategy has been developed on a field-programmable gate array control platform and experimental results at steady state are shown, with the aim to demonstrate the computational feasibility of the control strategy.

This paper proposes the real-time analysis of the DC-DC boost converter by utilizing the Digital Twin (DT) method. Based on the measurement data from sensors, the DT is a real-time digital model that runs in parallel to the physical DC-DC boost converter providing information for its monitoring and control. The digital model is obtained by a numerical methodology for discrete-time representation of the physical system. The estimation of uncertainty parameters of the physical system is based on the data analysis on the measurement data. The data analysis is done by applying the heuristic algorithm like Particle Swarm Optimization (PSO) method. The proposed analysis is validated through the digital-switching model realized by means of the FPGA and it runs on a suitable control board. Experimental tests on the converter prototype are illustrated.

Proposed paper deals with the complete analysis which is at the basis of the tuning procedure of variable sampling Repetitive Controllers for adjustable output frequency applications such as grid-tied inverters (limited frequency variation) and AC waveform generators (wide frequency variation). The operation of the proposed control strategy is briefly summarized. The effects of the desynchronization between the PWM modulator and the control loop are accurately described, and the inherent delays are expressed in closed form. This investigation helps to introduce a suitable control tuning procedure which can be used in variable sampling applications. Experimental verifications are carried out to prove the effectiveness of the presented analysis and control strategy.

Power-Hardware-in-the-Loop (PHIL) for Permanent Magnet Synchronous Machines (PMSM) emulation is the subject of growing interest in the world of industry and academia. A key challenge in the development of PHIL systems is achieving emulation stability and accuracy, which are necessary elements for appropriate testing of the Device Under Test (DUT). In obtaining such features, when a switching-converter is chosen as power amplifier, a major role is played by the choice of the coupling network. Despite the increased attention gained by PHIL solutions, advantages and drawbacks of the different coupling networks are still object of investigation when PMSM emulation must be performed. This paper addresses PHIL emulation bandwidth, stability, and accuracy, when a LCL coupling network is connected between the power amplifier and the DUT. The proposed analysis is validated at first through the digital-switching model created in Matlab/Simulink.

This paper focuses on the analysis and the design of a power electronic conversion system with reference to wind offshore applications. The proposed conversion system consists of a 6-phase AC-DC converter based on the SiC power semiconductors, to be used to control the achievable power from the wind turbine electrical generator. This system is suitable for applications where reliability and fault tolerance capabilities are the main targets. Voltage and current ratings have been determined to select the power module; furthermore, the analytical analysis to estimate the DC-bus rms current and voltage ripples is carried out. After that, the power loss equations have been derived in order to estimate the efficiency of the conversion. To validate the proposed hardware design, analytical results have been compared to simulation ones using Plexim/PLECS tool in Matlab/Simulink environment.

This paper deals with a gain scheduling synchronous demodulation scheme useful to obtain speed and position measurements from resolver position sensors. The proposed algorithm is devoted to a field-programmable gate array implementation in order to provide the elaborated information for very low latency control loops. The presented design allows getting accurate estimations in a wide range of rotational speeds without requiring costly off-the-shelf integrated circuits and leads to higher accuracy at low speed if compared to commercial solutions. To this purpose, the resolver excitation circuit has been simplified working directly with a square wave signal, and the resolver frequency behavior due to the nonsinusoidal excitation has been considered.

This paper focuses on the analysis and design of two multilevel–multicell converters (MMCs), named 3-phase 5-Level E-Type Multilevel–Multicell Rectifier (3Φ5L E-Type MMR) and 3-phase 5-Level E-Type Multilevel–Multicell Inverter (3Φ5L E-Type MMI) to be used in microgrid applications. The proposed 3-phase E-Type multilevel rectifier and inverter have each phase being accomplished by the combination of two I-Type topologies connected to the T-Type topology. The two cells of each phase of the rectifier and inverter are connected in interleaving using an intercell transformer (ICT) in order to reduce the volume of the output filter. Such an E-Type topology arrangement is expected to allow both the high efficiency and power density required for microgrid applications, as well as being capable of providing good performance in terms of quality of the voltage and current waveforms. The proposed hardware design and control interface are supported by the simulation results performed in Matlab/Simulink. The analysis has been then validated in terms of an experimental campaign performed on the converter prototype, which presented a power density of 8.4 kW/dm3 and a specific power of 3.24 kW/kg. The experimental results showed that the proposed converter can achieve a peak efficiency of 99% using only silicon power semiconductors.

Power-Hardware-in-the-Loop (PHIL) platforms are gaining increasing attention as a valid solution for testing of converters operating in power electronics systems. When the Device-Under-Test (DUT) is represented by a power converter designed to supply a Variable Speed Drive (VSD), electrical machine emulation must be performed by the PHIL. However, emulation of electrical machines imposes several requirements to the design of the PHIL test platform. Indeed, the emulable range of the machine operating points is constrained by the choice of the DC-bus voltage and of the coupling network. Furthermore, coupling network sizing strongly affects the stability of the emulation. In this paper, the analytical relation between the coupling network, the emulator DC-bus voltage and the machine operating range is described. A design procedure is then derived for both the DC-bus voltage and the coupling network. Afterwards, a stability analysis is carried out to determine the stability characteristic of the PHIL emulation as a function of the coupling network choice and of the main parameters of the DUT control loop. The FPGA implementation of the PHIL is then described. Simulation and experimental results show the capability of the proposed implementation, with respect to both transient and steady state machine emulation.

Repetitive Control (RC) enables inverters to inject, at fundamental frequency, high quality sinusoidal current into the grid or to provide low THD voltages in off-grid applications. However, digital RC, which can achieve zero steady state error for each periodical signal with known period, is not able to track or reject variable frequency periodic signals. In fact, digital RC weakness is related to performance degradations when it deals with variable frequency references. In other words, existing RC algorithms require an integer number of samples every period, while in some industrial applications the number of samples per period could be a non-integer time-varying value. Therefore, RC would lead to a significant quality degradation of the provided outputs when the grid frequency or the off-grid desired frequency changes. According to that, a newly RC structure with adaptive decoupled sampling is proposed to work with a constant delay line, regardless of the desired output frequency in both grid-tied and stand-alone operation.

This paper focuses on the investigation and implementation of a high-performance power conversion system to reduce the overvoltage phenomenon in variable speed electric drive applications. Particularly, the pros and cons of using Silicon Carbide power MOSFETs in the power converter when a long power cable is employed in electric motor drive systems has been addressed. The three-phase two level inverter with the addition of snubber circuits that consist of capacitors and diodes has been investigated, designed and tested in order to mitigate the overvoltage problems without sacrificing the conversion efficiency. Given that the snubber circuit added to the switches can increase losses, an additional circuit is used to recover the energy from the snubber circuit. The proposed analysis has been then validated through an experimental campaign performed on the converter prototype. The experimental results show that the proposed converter can reduce the overvoltage at the electric motor terminals with excellent conversion efficiency compared to the classical solution like the three-phase two level inverter.

A novel fault detection and ride-through method for the three-phase 4-Leg Inverter (3$\Phi$4L Inverter) used in off-grid applications is addressed in this paper. Open circuit and short circuit faults of the power devices located in the $3 \Phi 4 \mathrm{~L}$ Inverter have been theoretically analyzed. Hence, the fault detection and converter protection strategy has been implemented using a combination of a resonant controller in the $\alpha \beta$ frame and a repetitive observer. The proposed strategy has been at first validated by means of simulation results performed in MATLAB/Simulink environment. The fault detection and ride-through algorithm has been then implemented in FPGA using LabVIEW environment and full experimental verification are performed on the prototype of the three-phase 4-leg inverter.

This paper proposes a 3-phase 5-Level Flying E-Type Topology for photovoltaic applications, the converter is able to balance the voltage across the flying capacitors thanks to the modulation technique. The flying capacitor voltages are self-balanced without using any additional balancing circuits or closed-loop controls. Operation modes and characteristics of the proposed converter are presented, as well the voltage balancing approach based on the sinusoidal pulse width modulation scheme is explained. The analysis of the proposed converter has been validated through the digital-switching model realized in Matlab/Simulink environment. Preliminary results show the effectiveness of the proposed converter to balance the DC-bus voltage. Experimental tests on the converter prototype are illustrated.

A new control strategy that combines the resonant controller and therepetitive-controller based on the disturbance-observer (RSCDO) for off gridfour-leg voltage source inverter (VSI) has been presented in this paper.The aim of the new controller is to regulate the inverter output voltage,reducing as much as possible the voltage total harmonic distortion (THDv)in every load condition. The resonant controller allows to adjust the voltageat the fundamental harmonic, while the repetitive observer is able tocompensate the voltage distortions due to inverter nonlinearity. Theproposed strategy has been at first validated by means of simulation resultsperformed in MATLAB/Simulink environment. Then, the new controlstrategy has been implemented in field-programmable gate array (FPGA)using LabView environmental and experimental results are performed on the40 kVA three-phase 4-leg VSI prototype.

This paper deals with the design of an isotropic Permanent Magnet Synchronous Machine (PMSM) power emulator. Power emulators allow the emulation of physical systems to test a Device Under Test (DUT) at its rated power. During PMSM emulation, different electrical and mechanical characteristics must be replicated, such as the back-EMF, the resistive and inductive behavior, the inertia, and the friction coefficient. A power emulator is usually made of a switching converter and a coupling network. A coupling network is the combination of resistors, inductors and capacitors that allows the coupling of the DUT with the emulator switching power converter. In this paper, the analytical relation between the coupling network, the emulator DC bus voltage and the emulator operating range is derived. From the previous analysis a design procedure is obtained. The latter considers the constraint on the converter DC bus voltage, its effects on the coupling network sizing and on the machine operating range that can be emulated. Simulation results show the capability of the proposed method.

This paper describes the design and the optimization of the Interleaved 3-Phase 5-Level E-Type Back-to-Back Converter (I-3F5L BTB E-Type Converter). In the proposed converter, the AC-AC conversion is developed through two parallel 5-level E-Type legs using intercell transformers. A brief introduction to the characteristics of the I-3F5L BTB E-Type Converter is given, the general analysis and the design optimization are presented. Furthermore, the hardware realization of the 20 kW 3F5L BTB E-Type Converter prototype is discussed, striving for the highest possible efficiency. The converter prototype is characterized by the total weight of 6.18 kg and the power density of 8.4kW/dm3. The experimental results validate the presented theoretical analysis.

Today, in the railway sector there is considerable interest in studying the best ways for recovering the electrical energy resulting from train braking as it may allow significant energy saving and better management of the railways grid voltage. This paper presents the results of a feasibility study that has been developed in order to sizing both power electronics and energy storage system that could be arranged in the railways AC/DC substations for recovering the train braking energy in 3 kV DC railway systems. Based on the evaluation of the recoverable energy during one day of operation in a given railway station, the paper discusses a suitable configuration for a braking energy recovery system that could be used to feed two associated electrical utilities, such as an electric vehicles charging station and the electrical distribution circuits of the railway station. According to available experimental data concerning the braking transient of a number of train arrangements, a suitable mathematical model in Matlab has been developed by taking into account the overall train traffic in a given mid-size railway station, so as to estimate the recoverable energy during 24 hours traffic operation. Then, the results of this study have been considered as input for developing the technical specification of both the power electronic converter and the battery energy storage that would be used to arrange the envisaged system for recovering energy from train braking transients.

Solar photovoltaic (PV) is one of the most favourable renewable energy types today, the use of which has grown throughout the world, and much more is expected in the future due to the continuous price drop. It is important to further develop renewable systems to generate green energy, which results in the reduction of air pollution and in enabling a future sustainable society for the next generation of people. Accordingly, new topologies of the multilevel converter have been proposed and investigated for PV applications to achieve high efficiency and high-power density. This study presents the analysis and design of the symmetrical three-phase E-type inverter (S-3Φ7L E-type). The proposed topology is directly derived from the T-type converter and exhibits seven voltage levels at the output offering interesting performance in terms of power semiconductors current and voltage stress. The hardware design process of the converter has been carried out to enhance the efficiency conversion. Finally, theoretical results are carefully verified by testing the converter prototype, featuring a peak efficiency of 99%.

Today, for several economic and environmental reasons, Electric Vehicles (EVs) have a notable impact over the automobile world market. Accordingly, the amount of charging stations with reduced charge time is increased. The design aspects and the realization of the isolated Four-Port bidirectional Dual Active Bridge DC-DC Converter (4P-DAB) for fast charging applications are described in this paper. The 4P-DAB can handle different sources and loads thanks to the connection between four full bridges to the four windings of the high-frequency (HF) transformer. The design procedure and the power devices selection are carried out. The conversion efficiency as a function of the output power for different control strategies is presented using the Silicon-Carbide (SiC) power semiconductors. Simulation and preliminary results are verified by realizing the switching model of the 100 kVA 4P-DAB in MATLAB/Simulink.

This paper focuses on the modelling of the current ripple in a Power-Hardware-in-the-Loop (PHIL) emulator of an isotropic Permanent Magnet Synchronous Machine (PMSM). In such applications, one of the main challenges is to replicate the current behavior when the inductance that is installed in the PHIL differs from that of the emulated machine. This is because the power emulator must emulate the current ripple at the switching frequency of the Device Under Test (DUT). A theoretical analysis is carried on deriving the equations that describe the current waveform in the PHIL. An expression for the current error between the PHIL system and the emulated one is derived and the parameters that affect the error are highlighted. Mathematical expressions for the control actions needed to bring the current error to zero are proposed and the technical limitations in their application are discussed. Simulation results confirm the effectiveness of the proposed analysis.

Number of electric vehicles (EVs) continues to expand rapidly. This leads to significantly increase the amount of charging stations with reduced charge time. This paper focuses on design and realization of the isolated Four-Port bidirectional Dual Active Bridge DC-DC Converter (4P-DAB) to be used in fast charging applications. Each port of the 4P-DAB can manage different sources and loads thanks to the full bridge converter. A magnetic node is created connecting all the ports through a high-frequency multi-winding transformer. The efficiency conversion as a function of the output power has been carried out using Silicon-Carbide (SiC) power semiconductors. Different control strategies have been applied to improve the performance of the converter. Simulation and optimization results are verified by realizing the switching model of 100 kVA 4P-DAB in MATLAB/Simulink.

Power electronic converters have a heavily influence in our lifestyle, as they are used today in several applications, such as in-home and office appliances, electromedical apparatus, industry machine tools, as well as in electrical energy transmission and distribution systems. Power electronic converters are based on using fast-switching power semiconductors, which allow the desired shaping of the output electrical quantities waveforms, however, these power devices are also the most fragile component of the power conversion apparatus. Thus, to ensure safety and reliability of the power conversion system, a fault detection method must be suitably embedded in the control system. When a failure occurs, the fault detection and protection system become the most important function of the converter control unit. This article is devoted to the theoretical analysis of all the possible faults occurring in the three-phase five-level E-type converter (3Φ5L E-type converter) and based on such an analysis, a suitable fault management strategy is proposed. Fault effects are initially analyzed on the long-term time scale, from 10 μ s up to 100 ms. The fault effects, the detectability, and the safety shutdown actions are identified and summarized. The analysis is covered by simulation results performed in MATLAB/Simulink. Following the theoretical analysis, a control algorithm has been implemented in field-programmable gate array using LabVIEW. Finally, experimental tests have been performed on a prototype of the proposed multilevel converter in order to validate the proposed approach to management of the envisaged fault conditions.

Nowadays, a multilevel converter represents a good idea for commercial and industrial applications, where small size and cost, low maintenance, reliability in a wide range of environments, and good efficiency are required. Furthermore, the multilevel converter can provide control for both maximum power tracking and output power factor reducing the filter weight and volume. The proposed power converter topology, called five-level E-type inverter (5L E-Type Inverter), for grid-connected applications is presented and analyzed in this paper. The performance of the three-phase 5L E-Type Inverter has been theoretically investigated. The thermal models of the power semiconductor have been created taking into account the parameters provided by the manufactures and employing multidimensional lookup tables in the Plexim/PLECS environment. The design and selection of passive components have been described in order to obtain amazing performances in terms of weight, volume, and efficiency and power quality. New control strategy, named concurrent control, for 5L E-Type Inverter has been implemented and validated in the LabVIEW development environment. The peak efficiency of the converter above 98.3% and the total harmonic total harmonic distortion current ( THDi ) less than 3% have been achieved.

The power electronic converters have a heavily influence in our life-style, since they are today used everywhere in-home applications, office, medicine, industry, and energy transmission machines and processes. The power electronic systems are based on fast-switching power semiconductors, such as diodes, mosfets, igbts, etc. These power devices represent the fragile part in a power electronic converter. Thus, to ensure safety and reliability of the power conversion system, a fault detection method must be provided. When a failure occurs, the fault detection and protection system become the most important function of the converter control unit. If the fault management is not adequate, the entire converter can be totally destroyed, causing catastrophic effects on the entire power conversion system. Accordingly, fault detection, classification, and diagnoses for all power electronic converters, including three phase rectifiers, three phase inverters, DC-DC converters and AC-AC converters, have to be investigated. In this paper, the fault analysis of the 3-phase 5-level E-Type Converter (3Φ5L E-Type Converter) is addressed. The 3Φ5L E-Type Converter is proposed for grid connected applications. All possible converter semiconductor switches and diodes faults are theoretically analyzed. The fault effects, the detectability and the safety shutdown actions are identified and summarized. The analysis is covered by simulation results performed in MATLAB/Simulink. The control algorithm has been implemented in FPGA using LabVIEW environmental. The experimental tests have been performed on the 20kVA prototype multilevel converter in order to validate the proposed analysis.

A deep analysis on the current overshoot and the overvoltage issues when high-dynamic power devices are used in motor drive applications is discussed in this paper. The influence of the power cable and of the electrical motor at the commutation events of the power semiconductors is verified through a double pulse test setup. To overcome the problem of the overvoltage at the motor side, the design and implementation of the Passive Soft-Switching Snubber Inverter for motor drive applications are presented. The proposed topology is analyzed and tested through the simulations and the experimental campaign. The results show that this topology allows to reduce the overvoltage at the motor terminals when fast commutations and long power cables are used.

This paper proposes a Two-Level Hierarchical Model Predictive Energy Management method (MPEM) for off-shore oil platforms with renewables. An economic cost function is at the basis of the High-Level controller, while a tracking cost function is designed for the Low-Level control layer. The power sources, the load and possible variation of the wind profile have been properly modeled. The control structure has been validated through simulations carried out in the MATLAB environment. Results are presented for different scenarios, which prove the robustness and effectiveness of the proposed control strategy.

This paper studies the control structure for a flywheel energy storage system (FESS) used in the grid-connected applications. The power conversion structure uses a double conversion AC/AC through a three-phase thee level Neutral Point Clamp (NPC) inverter. The control structure allows a seamless connection of the FESS to the load and a simultaneous reduction of the current harmonic content to the load. A Fractional PI (FOPI) has been used to regulate the DC-link. Simulation results show excellent dynamic performance of the proposed control system, reducing both the DC-link voltage fluctuations and total harmonic distortion (THD) of the output currents.

A newly conceived symmetrical three-phase E- Type (3 $\Phi$7L E-Type) Inverter is proposed and analyzed in this paper. Converter topology is based on the single leg T- Type Inverter. The proposed topology shows seven voltage levels at the output providing better performance in terms of current and voltage stress of the power semiconductors and efficiency. The theoretical investigation has been carried out with reference to photovoltaic (PV) applications. A suitable thermal model of the power semiconductors has been developed in Plexim/PLECS environment. Simulation results of the 3 $\Phi$7L E-Type Inverter are performed in Matlab/Simulink environment. Furthermore, the prototype of the proposed converter has been carefully tested in order to validate the theoretical analysis.

The last few decades have seen a significant increase in the number of electric vehicles (EVs) for private and public transportation around the world. This has resulted in high power demands on the electrical grid, especially when fast and ultra-fast or flash (at the bus-stop) charging are required. Consequently, a ground storage should be used in order to mitigate the peak power request period. This paper deals with an innovative and simple fast charging infrastructure based on supercapacitors, used to charge the energy storage system on board electric buses. According to the charging level of the electric bus, the proposed fast charging system is able to provide the maximum power of 180 kW without exceeding 30 s and without using DC&ndash, DC converters. In order to limit the maximum charging current, the electric bus is charged in three steps through three different connectors placed between the supercapacitors on board the bus and the fast charging system. The fast charging system has been carefully designed, taking into account several system parameters, such as charging time, maximum current, and voltage. Experimental tests have been performed on a fast charging station prototype to validate the theoretical analysis and functionality of the proposed architecture.

This article is an investigation on the analysis and performance of the passive soft-switching snubber inverter (PSSSI). The efficiency of the power cable and electric motor used in industrial electric drive applications is also taken into consideration. As reported in the literature, the PSSSI is used to reduce the overvoltage on the motor side when both voltage source inverters are equipped with high-speed semiconductor devices and a long power cable is used. The PSSSI configuration derives from the conventional two-level inverter by adding a diode–capacitor snubber for each switching power device. Furthermore, an additional circuit is used to recover energy from the snubber capacitors. The three-phase PSSSI is carefully designed taking into account several system parameters, such as the dV/dt , the length of the power cable between the motor and the inverter, the gate resistance of the switches, the dead-time, the snubber capacitors’ value, and the switching frequency. Experimental results show a good efficiency performance of the entire electric drive as well as a reduced dV/dt at the electric motor terminals when the PSSSI is used compared to when the two-level three-phase inverter is adopted.

This paper deals with a multilevel ac–ac double conversion system that uses the intercell transformer (ICT) for applications which include generating systems and the interfacing of renewable energy sources with the utility grids. Each phase of the proposed configuration is formed through the ICT interleaving operation of two multilevel 5-level E-type legs to achieve the 3-phase 5-level back-to-back E-type converter (3Φ5L BTB E-type converter). The analytical procedure to select the inductance and capacitance values of both the input and output filters is described in the paper. Furthermore, the design and implementation of the input/output ICTs and inductors is discussed. The simulation and the experimental results on the 20-kVA interleaved 3Φ5L BTB E-type converter prototype are presented to validate the proposed analysis.