Electrification of the transportation has become one main effective solution to cope with the deteriorating environment and limited natural resource. As one of the most important part for the electric vehicles, the efficiency and performance of the electrical machine and its drive are always focused by researchers and industry worldwide. In order to improve the efficiency and performance, advanced and robust methods are preferable in the design process. This paper gives a general view for the design of an interior permanent magnet synchronous machine and its control. Simulation results are presented to prove the effectiveness of the design.

This paper presents a digital twin (DT)-based fault recovery method for power electronic converter systems. The method employs a prediction accelerator with a DT model for each subsystem of the converter system and feeds back the predicted system state to the controller. The paper demonstrates that the method can recover from faults such as load and input voltage variations in realtime and can integrate with hardware in the loop for future applications and comparing with other advanced control methods. The paper also highlights the benefits of the method in terms of scalability, replaceability and modularity for power electronic systems.

Aviation is a significant contributor to greenhouse gas (GHG) emissions in the transportation sector. As the adoption of electric cars increases and GHG emissions due to other modes of transport decrease, the impact of air travel on environmental pollution has become even more significant. To reduce pollution and maintenance, and ensure cheaper and more convenient flights, industry and academia have directed their efforts toward aircraft electrification. Considering various types of aircraft, several frameworks have been proposed: more-electric aircraft (MEA), hybrid electric aircraft (HEA), and all-electric aircraft (AEA). In the MEA framework, propulsion is generated by a conventional jet engine; however, all secondary systems (hydraulic, pneumatic, and actuation) are electrified. By further increasing electrification, electric motors can provide propulsion with the electric power supplied by the conventional engine (i.e., HEA) or from electrical energy storage (i.e., AEA). Power electronics and electrical machines play a key role in this scenario in which electric power must be efficiently generated, distributed, and consumed to satisfy extremely high requirements of aviation safety. This article provides an overview of recent advancements in aircraft electrification, and trends and future developments referenced to the global aviation roadmap.

This paper presents a development process of ethically-informed standards for intelligent monitoring systems (IMS). It considers the gap of socio-ethical standards for IMS over global industry, in both general terms and field-specific cases. Ethical issues of IMS are defined to include safety, data security, transparency, privacy, justice, equality, sustainability, and beneficence. We argue that they can be investigated and assessed by answering a set of questions for each ethical issue. This ethical evaluation questionnaire can be considered as an effective assessment tool for standard constructions. Additionally, field-specific industrial cases for the development of IMS ethical standards were demonstrated, including IMS for wind power systems, more electric aircrafts, and agricultural industry. Eventually, the summary of necessary items for building the ethical standards of IMS are presented.

Transportation Electrification and Micro-grid development have raised the requirements for the DC-DC converter that performs the bus interface, the renewable energy and storage integration. The Multiple Active Bridge converter allows for the independent power transfer between its ports while keeping the electrical isolation and offering soft-switching behavior when operated with a phase-shift modulation; however, its performance is affected by the high level of coupling between the ports. In fact, the input voltage, or the phase shift of one port affects the power flow in the whole converter. This paper proposes an Artificial Neural Network (ANN) based decoupling that allows for an improved individual power regulation between the ports, considering the non-linear behavior of the system and the effects of the voltage variations.

This study evaluates the full-linear transfer function model for the dual-active-bridge with the impedance-based small-signal averaged model. Besides, for the better implementation on the FPGA, a discrete-time state-space model has been developed. The model matching comparison of non-linear, full-linear, switching and state-space models has been done. In this paper, each mode of single and cascade connection of dual active bridge have been evaluated and compared.

Employing high frequency (HF) transformer in DC-DC converter is a popular strategy in power electronic industry. Equivalent circuit model of transformer in HF Dual Active Bridge (DAB) converters is investigated along with its impact on power transfer characteristic for Single Phase Shift (SPS) and Extended Phase Shift (EPS) modulation. Equivalent branches of magnetizing inductance allocated in primary and secondary side can inject the inductive current at switching instants to extend Zero Voltage Switching (ZVS) range. ZVS maps are proposed. Based on the power transfer characteristics and ZVS maps, an Advanced Extended Phase Shift (AEPS) modulation method with modified coupling relationship for phase shift is proposed to reduce the current stress and improve the voltage utilization. Finally, AEPS modulation is implemented in PLECS simulations to verify the analyzation presented.

The Current Source Inverters (CSIs) are an alternative to Voltage Source Inverters (VSIs) for electric motor applications. Despite the advantageous characteristics of intrinsic voltage boost capability, absence of electrolytic capacitors and reduced machine voltage stress, the increased component count and the need of a pre-stage for the inductor current control have limited the adoption. For some applications which have to operate always above a base speed (e.g. pumps, actuators, fans), single-stage CSI converter with improved efficiencies have been proposed. Owing to the advantage of the direct measurement of the terminal voltage, a simple and robust sensorless control is proposed for a single-stage CSI converter. Simulations on a SiC-based CSI7 converter driving a Permanent Magnet Synchronous Machine (PMSM) confirm the validity of the proposed control, potentially paving the way to a larger adoption of the CSI7 topology for motor drive application.

Voltage Source Inverters (VSIs) are usually adopted for high-speed motor drive applications due to the topology simplicity and the wide availability of control strategies for this topology. An alternative is the Current Source Inverter (CSI) which allows to achieve high speed range with limited DC voltage due to its intrinsic boost capability, and this is of interest in aerospace applications or electrical vehicles (EV), but a pre-stage is necessary to control the DC input current. In this work an hybrid solution is proposed to extend the speed range of a single stage CSI (i.e. CSI without pre-stage) driving a Permanent Magnet Synchronous Machine (PMSM). In fact using a single stage CSI with DC current control, the machine cannot work properly in low speed region, so the control is composed by two different strategies: one is proposed in this work for low speed operations and the other one is already known for high speed.

This work discusses the modelling approach adopted for the estimation of the voltage distribution within hairpin windings of electrical machines. The physical phenomena and the major contributors to the occurrence of the uneven voltage distribution are first described. Then, the equivalent circuit used to predict the voltage distribution is presented in detail. The circuital parameters employed in the equivalent circuit are estimated via finite element electrostatic and electromagnetic analyses. Finally, a numerical tool is used to solve the differential equations describing the equivalent circuit above mentioned. Simulation results are illustrated and discussed. The phenomena under investigation are applied to a pre-defined reference system, consisting of slot motorettes.

One of the advantages of multiphase machine is the capability of fault tolerance. Variety of post-fault control methods based on hysteresis, proportional-integral (PI), proportional resonant (PR) and model predictive controller (MPC) have gradually been developed. Due to simple structure and decoupling of reduced-order matrix, it is used as an alternative to the Clarke matrix in the healthy mode when the fault happens. Although a lot of control methods adopted a reduced-order matrix as the basic derived technology, the performance of controllers is different, and they need to be compared in term of specific applications in fault tolerance. For this propose, the paper deals with the steady-state and dynamic performance of four current control methods, hysteresis control, PI control, PR control and model predictive control in open-circuit fault. The results shows that the PR control method has low torque ripple, copper loss and derating in healthy and post-fault stage, and the MPC control method has low torque ripple in fault stage and fast response capability after applying fault-tolerant methods.

Distributed energy resources and new loads such as fast charging stations for electric vehicles are often dc-based. By using low-voltage dc microgrids to connect such systems to the grid, conversion stages can be omitted and higher efficiencies can be achieved. Challenges exist with respect to the protection of dc microgrids, where dc fuses are a viable solution but selective tripping must be ensured. The grid-forming converter must be able to supply the fault current in the case of a line-to-line short-circuit in a feeder without tripping due to over-current. To avoid expensive over-sizing, this paper proposes to use a virtual resistance in the control of the grid-forming converter to limit its output current. The range of the virtual resistance is discussed for normal grid operation and the effect of the virtual resistance on limiting the bus current during a short-circuit fault is discussed. In addition, the impedance models of the source and load systems are presented. Based on this, the influence of the virtual resistance on the system stability is analyzed. To validate the theoretical part, a switching model is simulated and the results show a good agreement with the theoretical analysis.

This paper presents a comparison between hairpin and random distributed winding in electrical machines for automotive applications. Indeed, the overall performance of an electrical drive system is seriously affected by its winding design. The considered electrical machine has a peak power of 115kW and a maximum operating speed of 12000 rpm. Both cost and manufacturing aspects are here discussed in detail. Two different machine topologies have been investigated and Finite Element Analysis (FEA) results are presented and discussed. Then, the comparison between hairpin and random winding configuration in terms of AC copper losses are presented for the selected geometry. The accurate AC losses estimation can be done by modelling each single conductor. In order to significantly reduce the simulation time, a domain model reduction has been adopted. Based on two different driving cycles, Urban Dynamometer Driving Schedule (UDDS) and Highway Fuel Economy Test (HWFET), the AC losses have been evaluated. It is shown that horizontal pin segmentation can contribute to considerable AC loss reduction.

One of the challenges brought forward by the gradual electrification undertaken by the aviation sector is the requirement of fault tolerance for machine drive systems to be used for critical on-board tasks such as propulsion or primary flight surface actuation. Their inherent advantages in both volumetric and gravimetric power density makes integrated drives the prime candidates for these applications. Despite the large advances in this field, few key area still need work. Key among which is fault tolerant current control strategies. This paper studies the application of resonant control techniques to achieve a scalable and fault tolerant current control strategy for multiphase machine.

The development of power electronics and control technology provides improved performance of the electrical appliances, making them robust to changes in the supply voltage or frequency. However, power electronic converters behave as constant power loads (CPLs), which have negative impedance characteristics, and this non-linear behavior is challenging the stability of the grid. This paper investigates the input impedance of a three-phase low-voltage grid connected ac-dc converter that operating as a CPL when interfaced to a single DC bus and a changeable load. The possibility of adopting a Smart Transformer (ST), a power electronics converter which feeds a low-voltage grid, for the CPL stabilization is also addressed. To analyze the behavior of CPLs, a strategy of impedance modelling is employed. Gain Margin Phase Margin (GMPM) Criterion is referred to judge the stability of the system and verify the stabilization operation for CPLs. Simulation results are presented to be as a support.

Wireless power transfer systems are characterized by a loosely coupled magnetic circuit and a power electronics interface. For the optimization of the system power factor, a compensation circuit composed of capacitors is adopted to form a resonant tank with the power coil. The behavior of the overall circuit in terms of power transfer and current/voltage waveform depends on several parameters, which can make the analysis and optimization of the system complex. This paper proposes an analytical derivation of an equivalent RLC system that greatly simplify the design in terms of Zero Voltage Switching (ZVS) regions. In addition to this, the RLC equivalent circuit allows an easy analytic calculation of the output power depending on all WPT system parameters. The analytical model will be validated by simulation results.

Electrical motors are required to perform reliably for a certain number of hours/cycles. Assuming the insulation breakdown as the predominant source of failure, then the lifetime of an electrical machine can generally be said to correspond to that of its weakest insulation sub-system. Among all the insulation stressing factors, thermal aging is a primary source of progressive deterioration, and, eventually, failure. In order to guarantee a satisfactory lifetime, motors are designed to have thermal operational points which are always lower than their insulation thermal class. However, this design choice does not allow to maximize the exploitation of the insulation lifetime capability. Technical standards report methods for the thermal qualification of electrical machines based on accelerated thermal aging tests. Such assessment, despite enabling the insulation lifetime estimation, might require several thousand hours of testing. This paper, therefore, proposes and validates a new methodology which considerably shortens the thermal qualification of electric motors.

The concept of multiport dc-dc converter was proposed to reduce the conversion stages of dc microgrid on more electric aircraft (MEA). The structure of multiport dc-dc converter is basically developed from the dual active bridge (DAB) converter because of its galvanic isolation and bidirectional power flow. A power electronics converter as a key element of the electrical power distribution system may cause stability issues. To address these challenges, the impedance characteristic of the multiport converter will be analyzed. In this paper, a transfer function based small signal model is developed and validated with a switching model, to figure out the characteristic of input impedance of triple active bridge (TAB) converter. Preliminary experimental results are presented to be as a support.

In Electric Vehicle (EV) application, the in-wheel motors are driven by the same dc-link voltage. To reduce the space, the Voltage Source Inverters (VSIs) can share one dc-link capacitor. Long-term experiences and experimental data demonstrate that the capacitors are one of the major failures in the motor drive system. The current profile of the dc-link capacitors is the main factor for this degradation, therefore, by reducing the current harmonic components of the dc-link capacitors can increase the lifetime. In this paper, a dc-link capacitor current harmonic reduction method for dual Permanent Magnet Synchronous Motor (PMSM) drive system in EV application is proposed. The Phase Shift Pulse Width Modulation (PSPWM) is employed in the dual inverters to reduce the harmonic components of dc-link capacitor. To verify the proposed method, a experimental platform is established and the experimental results are presented.

In the More Electric Aircraft framework, the objective is to increase the efficiency and the reliability of the aircraft by gradually substituting the existing subsystems with electrical ones. Newer aircrafts already incorporate a great share of electric power, making the on-board electrical power distribution system (EPDS) a complex structure composed of generators, actuators and storage. Because of the importance of power electronics in this scenario, the control system is critical to ensure the stability of the EPDS. This paper analyzes the sensitivity to the control parameters of the EPDS stabiltiy. A state-space model is derived and the root loci are used to show in a graphical way the effects of the design parameters.

In the framework of the More Electric Aircraft (MEA), weight reduction and energy efficiency constitute the key figures. In addition to these requirements, the safety and the continuity of operation is of critical importance. These sets of desired feature are in disagreement, because the redundancy needed to guarantee the safety of operation implies necessarily in additional weight. Several concepts of the electrical power distribution systems have been proposed, in this manuscript, an approach based on the widespread use of multi-port power converters both for the DC/DC and for the DC/AC stages is proposed. These two technologies allows for a ring distribution of the electrical power whereas the galvanic isolation is still kept. Simulation and experimental results show the feasibility of the concept in common and fault operation conditions.

This paper highlights the specific design challenges faced while implementing a GaN based phase shifted full bridge (PSFB) converter for battery charger applications. Inherent with the PSFB is the voltage ringing across the secondary side devices. This effect becomes even more severe, when fast switching GaN devices are used. Especially the effects of parasitics in the circuit become a major problem and need to be considered. Effective solutions to mitigate the overvoltages on the secondary side devices are theoretically derived and practically implemented in a 1.4kW GaN based PSFB. The effectiveness of the different solutions is presented.

Nowadays, the design of power converters has been focused on the optimization in terms of reliability, fault-tolerant capability and power density. The use of modular converters leads to natural fault-tolerant capability because the power system can be still operating even when some module has failed. In this paper, the reliability of modular converters, which is high-dependent of several factors like as thermal stress, is studied. In the paper, the power devices aging of dc/dc interleaved power converters is managed. The proposed method is based on sharing conveniently the total managed power between the power modules. This can be done without losing performance in the power system. The proposed power routing technique has been tested in a three-module interleaved boost converter which is used in multiple applications.

A simultaneous wireless information and power transfer system employing separated frequency bands for energy and data, dubbed dual-band SWIPT, is investigated. Elementary circuit elements are optimized numerically. An experimental testbed based on a gallium nitride (GaN) full-bridge converter demonstrates data rates in excess of 450 kbps employing on-off keying in conjunction with a simple diode detector for data recovery.

The more electric aircraft concept is pushing towards a DC distribution system for the on-board electrical appliances. In the scenario where multiple high-voltage and low-voltage buses are present, a power electronics converter interface is mandatory. In order to implement a resilient distribution system, the power exchange between different buses is envisaged, to ensure that a failure in a supply bus does not impair the rest of the distribution system. In this paper, two power converter structures able to achieve this goal are analyzed and compared in view of their contribution to improve the overall system resiliency. A control structure is investigated to manage the load supply with the desired priority. The variable virtual resistor control allows shifting the load priority on demand and, as a consequence, is found suitable for achieving the desired goals. Theoretical analysis and experiments are reported to prove the performance of the chosen solution, which is based on a QAB controlled with virtual resistors.

This paper presents a three-phase converter architecture with a reduced common mode voltage to be used in photovoltaic power systems. The full-bridge architecture is modified by adding two additional switches in the DC path that allow decoupling the load from the source during the freewheeling phases. Optimized modulation strategies are analyzed and compared against the space vector modulation for the full-bridge. Extensive measurements show an improved efficiency when SiC devices are used, and a theoretical analysis links this efficiency to a marked extension of the converter lifetime.

Integration of charging stations for electric vehicles (EVs) will result in severe stress on electric grid. The EVs connected to the grid can also act as a source of energy and this demands greater control as well as coordination for better utilization. Conventional power transformers (CPTs) utilized in the EV charging stations are not well equipped for meeting these challenges. Recently, smart transformer (ST) has been proposed as an alternative to CPT. The ST connects medium voltage (MV) grid to low voltage (LV) grid with two intermediate MV and LV dc links. This paper utilizes the availability of the dc links of the ST to integrate the EVs charging station to electric grid rather than connecting these through the CPTs to the grid. A comprehensive analysis of sizing of the power converters utilized in the considered system has been presented. A comparison of efficiency for the different configurations is carried out and the possible more efficient scenario is suggested. Infact, the ST based EV charging system is found to be more efficient in comparison to CPT based EV charging station. The performance of ST based EV charging station is verified through simulation studies.

Current source inverter (CSI) is a family of power converters which has been recently investigated for photovoltaic power conversion in grid-tied operation, due to the inherent boost capability and ease of control. This paper assess Photovoltaic three-phase Current Source Inverters by two different CSI topologies and space vector modulation commutation strategies. Different CSI solutions are therefore analyzed by means of numerical simulations and the results are compared in terms of ground leakage current and THD of the injected grid currents. Extensive simulation results show that the CSI7 topology can improve the common mode performance while at the same time increasing the efficiency of the conventional CSI, at the price of a negligible added complexity.

Interactions between power electronic converters are typically investigated by means of impedance-based model analysis. The effects of the PLL are usually neglected, but recent studies have shown the importance of including those effects for stability analysis purposes. This paper focuses on the investigation of interactions between synchronization units of converters operating in parallel. The impedance-based approach is used for the investigation in the frequency-domain. The converters are supposed to share the same point of common coupling (PCC) and the characteristic of the grid at the connection point is crucial for determining the effects of the interactions between the operating units. In order to isolate the effects of the synchronization, the converters is modeled as a current sources, whose reference currents are calculated using the angle detected by their PLLs. Time-domain simulations are performed as well as experimental laboratory tests in order to validate the presented analysis.

Parallel Neutral-Point Clamped (NPC) inverters are commonly employed in medium voltage high power applications, such as wind energy system, smart transformer, and power conditioners. In literature, it is shown that the Phase Disposition modulation (PD) strategy provides better performance in terms of harmonic profile and current ripple for single NPC application. Therefore, the PD has been commonly employed as an optimal solution and used for optimized Space Vector Modulation (SVM). However, in case of interleaved operation and common dc-link, one of the main challenges is: the circulating current between inverters. With this consideration, comparisons between the PD and another carrier-based modulation - Alternative Phase Opposite Disposition (APOD) are carried out based on the space vector representation. The analysis shows that the APOD modulation offers much lower circulating current compared to the PD modulation, maintaining similar current ripple as well as spectrum quality of the total current. As a result, an APOD-based SVM technique is proposed in this paper, in order to reduce the circulating current and meanwhile maintain other superior characteristics. Full switching sequences as well as design criteria are presented for all sectors. Simulation and experimental results are provided to validate the effectiveness of the proposed modulation technique.

The Smart Transformer (ST) is a solid-state transformer performing not only a voltage step-down function but also energy and information management. With the help of control and communication technology, the ST can increase hosting capacity of renewable energies and provide ancillary services to utility and customers. To better exploit the potential of a ST-fed grid, a proper design of architecture, control scenarios and its corresponding communication network has to be done. This paper aims at giving a better understanding of the functionality of the ST-fed grid and of the associated communication challenges.

Power Semiconductors undergo thermal stress during operation, which is caused by thermal cycling. This refers to heating up and cooling down of the junction temperature and leads to aging and finally failures. Active thermal control can reduce the thermal stress of power semiconductors by regulating the power losses. Most algorithms proposed so far are only applicable to hard switching power converters and implement a regulation of the switching frequency, which is not applicable for the isolated DC/DC converters. This work proposes to regulate the duty cycle of the DC/DC converter to control the semiconductor losses, aiming at influencing the consequent thermal stress. The proposed algorithm is analyzed analytically and a thermal controller is designed, which is capable of reducing thermal cycles during operation without prior knowledge about the mission profile. The capability and the limitations of the proposed algorithm are demonstrated with simulations and the effectiveness is validated on a laboratory prototype with junction temperature measurement.

The Smart Transformer (ST) represents an enabling technology for providing new services to Low Voltage (LV) and Medium Voltage (MV) grid, overcoming the problems that are limiting the widespread diffusion of distributed renewable sources in conventional distribution systems. The ST 3-stage configuration includes a DC/AC 4-wires converter at the LV side, that must be able to cope with the equipment already installed in the LV grid in which ST wants to substitute conventional distribution transformer. Grid converters with capacitance towards ground, when connected to ST-fed LV grid can cause common mode current problems not yet discussed in the literature. This paper aims to fill this gap through an in-depth analysis of the problem and indicating possible solutions.

The Smart Transformer (ST) offers ancillary services in the low voltage grids. These new services in a real distribution grid can be demonstrated by means of simulation software, but it is difficult to prove them in lab due to the complexity and heterogeneity of the distribution grids. The Power-Hardware-In-Loop (PHIL) evaluation is an interesting solution for emulating the interaction between the real grid, simulated in a Real Time Digital Simulator (RTDS), and the ST. However the PHIL evaluation requires careful analysis. Depending on the interface topology the stability and the accuracy of the loop can be affected. This is mostly true when the interface converter is not a linear power amplifier, but just a simple DC/AC switching converter. Actually, no considerations have been made in the literature about the accuracy and stability of the PHIL in case of non-linear interface converter. This paper focuses on evaluating the harmonic behavior of the PHIL in case of current harmonic content in the grid. Depending on the bandwidth of the interface converter, the accuracy of the PHIL in simulating harmonic currents can be affected. The analytical considerations on the accuracy of the loop have been verified experimentally in a complex LV grid.

Smart grids have attracted the attention of the scientific community for years, since the ability to better manage distributed resources in a dynamic grid scenario is of paramount importance. Among the solutions that have been investigated, there is the smart transformer (ST) distribution concept, where an AC/AC power converter substitutes the traditional distribution transformer while enabling additional services. Considering that the ST can generate arbitrary voltage waveforms, power distribution is not restricted anymore to the fundamental frequency, but additional harmonics can be used. This paper analyzes different control possibilities for multi-frequency converters, comparing the results in terms of dynamic performance, control complexity, and communication requirements.

This paper discusses the effect of Constant Power Loads (CPLs) on the stability of a Smart Transformer (ST). The main characteristic of a CPL is that its current decreases when its voltage increases and vice versa. Therefore, in small signal analysis a CPL behaves as a negative impedance, and as a consequence it can impact the system stability. The aim of this work is to establish how it is possible to stabilize the system by acting on the filter parameters and the control strategy. A distributed power generating systems supplied by a ST has been considered as case study. The analysis and the simulation results show that it is not possible to stabilize the system by using standard controllers without an appropriate selection of the output filter components.

In safety critical applications, such as for the aerospace industry, where fault tolerant systems are mandatory, the ability of an electric actuator to detect a malfunctioning and eventually operate in faulty conditions is of paramount importance. This paper is concerned with the fault tolerance operation of a linear actuation drive, consisting of a tubular, linear motor controlled and driven by a high performance matrix converter for an aerospace application. The aim of this work is thus to propose and validate techniques addressing specific faulty operation conditions. The main points of interest addressed in this paper are the operation of the position sensor and operation during a fault on one of the phases of the motor. An Extended Kalman Filter is adopted for the double goal of improving the measured data of the position sensor and to continuously monitor its condition. On the other hand, the TLPM motor is operated under the assumption of a total fault of a single phase. In this work the modification to the Field Oriented Control (FOC) with only two phases is described, and the results are compared to those of the healthy machine. Theoretical analysis, simulations and experiments confirms the feasibility of the described strategies.

Due to the possibility to drastically reduce the Solid State Transformer (SST) volume and weight, its use is becoming a reality in traction and wind power plant applications, while, in the electric distribution system, it is still considered futuristic. A SST, with managerial role in the electric distribution grid, is generally called Smart Transformer (ST). Unfortunately the low efficiency, the low reliability and the high cost still act as barriers for its widespread use in the real world. This paper focuses on the impact of a modular design, by benchmarking different ST topologies. Moreover, the paper provides guidelines on how to choose the semiconductor modules and assessments on how the choice affects the efficiency of the ST.

This paper presents an AC/AC active power filter based on a single-phase matrix converter (SPMC). The use of a matrix topology allows to eliminate the reactive components normally used for temporary energy storage, reducing the size of the power converter and improving its reliability. The filter operates in series with the load through a step-down transformer, also allowing for a limited regulation of the fundamental voltage (boost/reduction). Several control methods are evaluated; in particular, a novel zero voltage compensation technique is introduced in order to reduce distortion around the input voltage zero crossing. Simulations and experiments are used to validate the considered control methods, and confirm the feasibility of the proposed solution.

Early detection of incipient faults in AC drives is one of the most difficult challenges for condition monitoring, especially for faults related to insulation degradation of the windings. This is because insulation degradation is very difficult to be detected on-line, so these faults may pass unnoticed before turning into a major faults. This paper looks at the feasibility of using coaxially insulated windings not only to increase reliability against winding insulation problems, but as an alternative to advance condition monitoring that may be suitable for the detection of insulation degradation, and other faults not easily detected by conventional schemes such as demagnetization issues, and the presence of inter-turn short circuits. The concept of insulation degradation for the case of coaxially insulated windings is analytically considered in this work and a novel condition monitoring alternative proposed. The proposed scheme and winding topology are extensively evaluated numerical to determine their feasibility to drive condition monitoring.

Many transformerless topologies for photovoltaic systems were proposed in order to minimize power losses and avoid high levels of ground leakage current (that can arise in such systems). The most efficient PWM strategies achieve this goal by decoupling the grid from the DC Link during the freewheeling phases of the output current. These strategies usually operate only with a unity power factor. However, as solar inverters have penetrated into power distribution networks, new issues have arisen and modifications of regulations governing grid connection of distributed systems were introduced in some countries. One of the new requirements for the inverters connected to the low-voltage grids is the possibility to provide reactive power. This paper proposes a transformerless inverter topology with a wide-range power factor operation. Simulation results and extensive experimental results, focused mainly on ground leakage current analysis, showed the effectiveness of the proposed solution.

This paper is aimed at the modeling and simulation of wind power system, with particular emphasis on small wind turbines employing surface permanent magnet synchronous generators (SPMSGs). Generator and inverter front-end interaction is analytically and numerically modeled, in order to evaluate the generator's efficiency depending on its electric parameters, both during normal and power limited operation. Passive and active rectifier front-end are taken into account to assess the influence of power electronics front-end over system performances. The final target of this work is to determine design guidelines for small wind turbine system optimization. The analysis is carried out through simulations which take into account the interactions of the SPMSG's electrical parameters and through the evaluation of the generator's efficiency at different operating conditions and inverter front-end architectures. The data obtained was further validated with experimental characterization of two different system architectures.

In the recent years the research on photovoltaic converters has been focused on topologies that do not feature a line frequency transformer, in order to reduce costs and successfully increase the overall efficiency. The main problem in removing the galvanic isolation is that the parasitic capacitance present between the cell and the metal frame enclosing the panel (usually earth-connected) enables a common-mode current to be injected into the grid by the converter. This paper proposes an active common-mode filter able to compensate the high-frequency common-mode voltage variations at the output of the power converters, that represent the principal cause of ground leakage current. The advantage of this solution concerns the capability to operate with an arbitrary power factor. In this work it is applied in cascade to a converter with standard full-bridge topology driven by a three-level PWM strategy. Simulation and experimental results shows the feasibility of the proposed approach.

The design of a photovoltaic (PV) grid-connected converter usually comprehends a galvanic isolation between the grid and the photovoltaic panels. Recently, in low power systems, the galvanic isolation has been removed with the aim to increase efficiency and reduce the cost of the converter. Due to the presence of a parasitic capacitance between the photovoltaic cells and the metal frame of the PV panel, usually connected to earth, a high value of common mode current (i.e., ground leakage current) can arise. In order to limit the ground leakage current (which deteriorates the power quality and generates EMI), new converter topologies have been proposed. Their effectiveness is based on the symmetrical (ideal) commutations of the power switches and some of them adopt a further voltage level derived from a capacitive divider of the DC bus voltage. Unfortunately, in actual implementations, asymmetrical power switches transients and variations of this added voltage lead to higher ground leakage current with respect to the ideal case. After a review of the state of the art this paper investigates these two issues and presents a particular solution (based on digital control and PWM strategy) that, in conjunction with a compensation strategy of power switches actual commutations, guarantees low ground leakage current regardless the parameters tolerance of the power circuit. Simulation and experimental results confirm the effectiveness of the proposed solution.