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The traditional approach to calculate the active and reactive power in AC power systems requires the measurement of the phase shift between the voltage and current for the evaluation of the power factor. To do this, power analyzers can implement several methods. In principle, it is always necessary to identify specific points of waveforms (e.g., using a zero-crossing detection technique) and get their time shift. In a similar way, the frequency value must be evaluated in order to calculate the angular frequency. Unfortunately, this kind of common method exhibits some issues, such as the large sensitivity to noise. Moreover, inaccuracies in the evaluation of the power factor have a big impact on the final estimation of the electric power. This paper presents a simple but effective way to calculate the electric power, overcoming the need for a direct measurement of the phase shift and frequency. In particular, it is shown that the active power can be easily calculated as the difference between the peak value of the instantaneous power and apparent power. The reactive power and power factor are evaluated by exploiting the same quantities. The practical implementation of the proposed formulation in power analyzers guarantees several benefits without reducing accuracy. [ABSTRACT FROM AUTHOR]

Electrochemical batteries used in energy storage systems provide a significant contribution to the development of smart grids and green transportation. In recent years, intensive research activities have been oriented to the optimal management of energy storage systems for power electronics applications in fast growing industrial sectors as EVs and HEVs. The accurate modeling of electrochemical batteries is fundamental in the design of control algorithms applied to energy storage systems. Focusing on automotive applications, in this paper a comprehensive analysis of ESS models based on equivalent electric circuits using a multi-criteria approach is presented. An extensive experimental validation has been carried out to evaluate the performance of battery models in automotive applications. [ABSTRACT FROM AUTHOR]

Nowadays, an increasingly present application in the automotive field is the battery charger that usually consists of two high efficiency parts: an AC/DC converter with power factor correction (PFC) capability and a DC/DC converter. In this paper, a three-channel interleaved Power Factor Correction (PFC) based on a new digital controller STNRGPF01 operating in Continuous Conduction Mode (CCM) is presented addressing high efficiency. In the considered applications, the most challenging control issues are the input current control and the fast overcurrent protections. Exploiting mixed signal control approach some benefits have been obtained and confirmed by experimental results on a 3 kW prototype. [ABSTRACT FROM AUTHOR]

To obtain a full exploitation of battery potential in energy storage applications, an accurate modeling of electrochemical batteries is needed. In real terms, an accurate knowledge of state of charge (SOC) and state of health (SOH) of the battery pack is needed to allow a precise design of the control algorithms for energy storage systems (ESSs). Initially, a review of effective methods for SOC and SOH assessment has been performed with the aim to analyze pros and cons of standard methods. Then, as the tradeoff between accuracy and complexity of the model is the major concern, a novel technique for SOC and SOH estimation has been proposed. It is based on the development of a battery circuit model and on a procedure for setting the model parameters. Such a procedure performs a real-time comparison between measured and calculated values of the battery voltage while a PI-based observer is used to provide the SOC and SOH actual values. This ensures a good accuracy in a wide range of operating conditions. Moreover, a simple start-up identification process is required based on battery data-sheet exploitation. Because of the low computational burden of the whole algorithm, it can be easily implemented in low-cost control units. An experimental comparison between SOC and SOH estimation performed by suggested and standard methods is able to confirm the consistency of the proposed approach. [ABSTRACT FROM AUTHOR]

The degradation trend of photovoltaic modules depends on the technology, manufacturing techniques and climatic conditions of the site where they are installed. Longer useful life of the PV modules means that they will be able to produce much more energy than was used to build them; thus, extending the useful life of the modules is beneficial for the environment and increases the cost effectiveness of PVs. The problem of land use has prompted the development of agrivoltaic systems to exploit the same land both for the production of energy and for agriculture, and on water surfaces such as lakes and dams (floating PV). The exploitation of floating PV systems in onshore and offshore areas is currently under study. This constitutes an opportunity for which many factors must be taken into account; a fundamental aspect is the environmental impact, on which some recent studies have focused. Another aspect is the impact of the marine environment on PV system reliability and durability, due to the stress on operating conditions. The aim of this preliminary study is to evaluate the influence of the marine environment on the degradation trend of photovoltaic modules, based on existing models whose inputs are meteorological data from offshore locations. The results obtained from the application of a cumulative exposure model unexpectedly showed a lower degradation value in the offshore environment than on the mainland: −0.95% and −3% values of power decay, respectively. The absolute value of power decay in the onshore case is higher than the typical values because the used model has to be revised, as the empirical coefficients of the model have to be calculated according to the installation environment. The empirical coefficients used in the model were obtained in environmental conditions different from those under study. In the offshore case, the degradation estimated by the model does not take into account some environmental factors typical of the marine environment. Model adaptations calibrated with datasets of plants in environmental conditions similar to those analyzed would allow for greater accuracy in the results. [ABSTRACT FROM AUTHOR]

• A simple method for Performance Loss Ratio estimation is applied step by step to PERC bifacial photovoltaic modules. • The results of the applied method are compared with the solar simulator lab test. • The PLR has been estimated by the "5-STEP method" using classical PR, temperature corrected PR and bifacial PR as metric, calculated within a narrow Irradiance range filter. The need to replace fossil energy sources with renewable energy sources to combat global warming has prompted the growth and development of various technologies, including photovoltaics. At the same time the PV technology is evolving to enhance efficiency and durability of PV modules. Bifacial PV modules is gaining larger share of market due to the higher energy and power density at almost the same price of conventional PV modules. In recent years, as PV systems have been operating for a long time, understanding the aging phenomenon of PV modules has become increasingly important. Various types of defects are known that occur during the life of the modules, however, understanding the trend of degradation through a simple quantification of the decrease in performance over time can be a useful tool. The Performance Loss Ratio can give indications about the state of health of the system and can be used for a rough comparison on the performance reduction guaranteed by the module manufacturer and check if the warranty terms are actually respected. In the present study a simple method is used to evaluate Performance Loss Ratio (PLR) on a real PV plant equipped with bifacial PERC modules. Criticalities were highlighted within each phase of the application of the method. The numerical results of the PLR estimate of the photovoltaic modules of the system are reported, calculated on a two-year dataset starting from the date of installation. Finally, the PLR values, that have been estimated using three different metrics and linear fitting, have been compared with the measured average Power decay values associated exclusively with PV modules. The simplicity of the method allows it to be replicated to other case studies. [ABSTRACT FROM AUTHOR]

Power generation systems (PGSs) based on hybrid renewable energy are one of the promising solutions for future distributed generation systems. Among different configurations, hybrid photovoltaic-wind turbine (PV-WT) grid connected PGSs are the most adopted for their good performance. However, due to the complexity of the system, the optimal balance between these two energy sources requires particular attention to achieve a good engineering solution. This paper deals with the optimal sizing of PV-WT by adopting different multicriteria decision analysis (MCDA) optimization approaches. Sensitivity of MCDA algorithms has been analyzed, by considering different weighting criteria techniques with different fluctuation scenarios of wind speed and solar radiation profiles, thus highlighting advantages and drawbacks of the proposed optimal sizing approaches. The following study could be assumed as a powerful roadmap for decision makers, analysts, and policy makers. [ABSTRACT FROM PUBLISHER]

In this paper, the design, realization, and performance evaluation of a single-phase 3-kW dc/ac power converter, using an active-bridge dc/dc converter and a full-bridge dc/ac, are introduced, presenting a novel solution on the industrial scenario for the considered application. Control algorithms, including the maximum power point tracking, paralleling to the grid, and converter switching signals, are digitally implemented on a standard microcontroller. [ABSTRACT FROM AUTHOR]

In this paper, a new approach is presented aimed at improving the power factor of pulsewidth-modulation inverters that equip low-power electric motor drives for household appliances. The key feature of the proposed approach consists of exploiting the dc-bus current as a suitable dither generator by means of a high-frequency transformer. Such a strategy is used to force the diode rectifier to draw current from the mains in those periods when, in conventional systems, the diodes are reverse biased, i.e., when the dc-bus capacitor voltage exceeds the ac input voltage. The proposed method allows for elimination of the power-factor controller (PFC) front end, traditionally used to comply with power quality requirements. In comparison with standard PFCs based on a dc/dc converter, the proposed approach represents a cheaper and more feasible solution, not using additional power devices and control circuits. Simulation and experimental results confirm the consistency of the proposed approach. [ABSTRACT FROM AUTHOR]

In this paper, an innovative converter topology is presented that allows to improve the performance of electronically commutated motor drives, aimed to equip home appliances. The proposed topology is based on a modified C-dump converter configuration, where the energy recovery stage acts as an active power factor controller (PFC) for offline operation. This is made possible by introducing a new technique to manage the free-wheeling energy that is recovered back to the dc bus by a suitable high frequency (HF) transformer. The proposed approach allows to omit the PFC stage that is included in motor drives devoted to home appliance applications in order to comply with power quality requirements. Moreover, the proposed converter topology features only low side or high side configuration switches, allowing to simplify the design of the drive and easily integrate the power semi-conductors in a single chip exploiting smart power technologies. Simulations and experimental results confirm the validity of the proposed approach. [ABSTRACT FROM AUTHOR]

Provides information on a study that examined a common-mode current paths and generation mechanisms in pulsewidth modulation (PWM) inverter. Information on common-mode currents; Details on the two proposed switching strategies; Evaluation of the characteristics of a standard PWM induction motor drive; Discussion of the problem of reducing common-mode current in electric motor drives; Experimental results.

In this paper, a procedure to simulate an electronic power converter for control design and optimization purposes is proposed. For the addressed application, the converter uses SiC-MOSFET technology in bidirectional battery chargers composed of two power stages. The first stage consists of a single-phase AC/DC power factor correction synchronous rectifier. The following stage is a DC/DC dual active bridge. The converter has been modulated using a phase-shift technique which is able to manage bidirectional power flows. The development of a model-based simulation approach is essential to simplify the different design phases. Moreover, it is also important for the final validation of the control algorithm. A suitable tool consisting of a system-level simulation environment has been adopted. The tool is based on a block diagram design method accomplished using the Simulink toolbox in MATLAB™. [ABSTRACT FROM AUTHOR]

The main aim of this work is to present a step-by-step procedure to model and analyze the power loss distribution of three-level Gallium Nitride (GaN) inverters. It has been applied to three distinct three-phase three-level voltage source inverters utilized in electric traction drives: Active Neutral Point Clamped, Neutral Point Clamped and T-Type Neutral Point Clamped. The proposed analytical power loss modelling, combined with an equivalent representation of the electrical machine proved to be a viable solution to achieve a time-saving and low computational burden simulation platform, leading to satisfying accurate results. This has been confirmed by comparing the results carried out from the simulations of a 110 kW permanent magnet synchronous motor drive and those determined by considering a simplified circuital representation based on the proposed analytical power loss modelling. [ABSTRACT FROM AUTHOR]

This paper deals with the study and implementation of a losses minimization control strategy for an integrated multidrive (IMD) topology used in the drivetrain of parallel hybrid electric vehicles. In this IMD, the stator sections of a multiwinding induction machine are interfaced to the storage units through standard three-phase inverters. The goal of this study is to optimize the management of multidirectional power flows in an IMD configuration, reducing both the power losses of the induction machine and the energy storage units while keeping the computational complexity suitably low. To this aim, the proposed approach consists in a control strategy that continuously searches for the best compromise between the torque response and the power capability of each storage unit while minimizing the overall power losses. Using such an approach, a significant improvement in the overall efficiency is obtained. Simulations and experimental tests confirm the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Recent developments in fields such as portable devices, electric and hybrid vehicles and renewable energy harvesting are the main reasons why the energy storages/batteries are an object of intense research. Lead-acid batteries still play a key role, and it is old known technology. Other battery chemistries having higher power are still too much expensive for small and medium energy storages for smart grid. To achieve an effective exploitation of battery packs, it is important to have a robust and reliable battery management. Accurate state of charge estimation in battery management is a critical part. To achieve the economical and suitable energy performance including life-time extension battery nonlinearities must be considered. Analysis and comparison of widely used SOC estimation methods including Coulomb counting and Kalman filter with various battery models is the goal of the paper. Internal parameters dependencies on SOC were added to battery models used by Kalman filter to achieve high accuracy. SOC methods are verified by using two different discharge/charge tests. [ABSTRACT FROM AUTHOR]

The paper deals with the analysis and implementation of a vector control strategy devoted to integrated multidrive systems used in starter alternator applications with several dc buses at different voltage levels. The electromechanical system of the considered multidrive topology is obtained by splitting the conventional stator winding of an induction machine into different n three-phase subunits, maintaining the same magnetomotive force distribution and sharing the same rotor. Each stator unit together with rotor can be considered a submotor, thus the entire electromagnetic system behavior can be considered as the combination of all submotors contributions. The submotors are suitably supplied through standard three-phase inverters whose technical specifications are also established according to the storage unit voltage levels. First, a detailed mathematical representation of the electromagnetic system has been developed, then the conditions to carry out the field orientation in each generic subdrive are determined. Addressing a starter-alternator system, the integrated multidrive configuration has been experimentally tested, highlighting the capability of the proposed approach to efficiently handle multidirectional power flows among the storage units and mechanical system while ensuring high dynamic performance. [ABSTRACT FROM AUTHOR]

Considering the importance of lithium-ion (Li-ion) batteries and the attention that the study of their degradation deserves, this work provides a review of the most important battery state of health (SOH) estimation methods. The different approaches proposed in the literature were analyzed, highlighting theoretical aspects, strengths, weaknesses and performance indices. In particular, three main categories were identified: experimental methods that include electrochemical impedance spectroscopy (EIS) and incremental capacity analysis (ICA), model-based methods that exploit equivalent electric circuit models (ECMs) and aging models (AMs) and, finally, data-driven approaches ranging from neural networks (NNs) to support vector regression (SVR). This work aims to depict a complete picture of the available techniques for SOH estimation, comparing the results obtained for different engineering applications. [ABSTRACT FROM AUTHOR]

• Data from a string of bifacial PV modules were monitored for a full year. • A filtering method is described and has been applied. • Models for voltage and current at the maximum power point, originally developed for monofacial modules, have been applied. • Modified empirical models for bifacial photovoltaics have been proposed and applied. • The method can be replicated using experimental datasets from other sites. The bifacial photovoltaic (PV) modules are able to convert the irradiance that hits both the front and the back side of the modules into electrical energy, this allows to increase the output power compared to monofacial modules. However, the mathematical models used for traditional PV modules do not consider the contribution of rear irradiance, even recent works deal with the modeling of the rear irradiance influence on bPV power output. In the present work some empirical models capable of estimating the current and voltage at maximum power point conditions are unveiled; the models consider only the front irradiance, as monofacial PV modules, or the back irradiance through the concept of equivalent irradiance and module temperature. In addition, some modifications to the current and voltage models have been proposed. In all cases, the optimal parameters of the models are obtained starting from a dataset of experimental data acquired from a string of bifacial photovoltaic modules installed in Catania (Italy). The PV plant under study was monitored for an entire year, thus allowing the use of data acquired in different weather conditions. The method description includes the filtering of the input signals and the searching method of the empirical coefficients in order to estimate the current and voltage at the maximum power point (MPP) for bifacial photovoltaic modules. [ABSTRACT FROM AUTHOR]

A technique to improve the performance of grid-connected induction motors by exploiting an auxiliary winding set is proposed in this paper. This auxiliary winding features the same distribution of the main winding, although with a reduced number of turns and it is fed by an inverter a fraction of the power in comparison with the rated size of the induction motor. As shown in the paper, through the auxiliary winding, it is possible to set the machine power factor, increasing the efficiency of the power conversion system and mitigating speed oscillations due to torque disturbances. A mitigation of the grid current peaks due to motor start-up is obtainable. First, the proposed technique is theoretically introduced, then a feasibility assessment is accomplished by simulations. [ABSTRACT FROM AUTHOR]

Distributed power converters represent a technical solution to improve the performance of large or utility-scale photovoltaic (PV) plants. Unfortunately, evaluation of the yield obtained in large PV fields by using distributed converters is a difficult task because of recurring partial unavailability, inaccuracy of power analyzers, operating constraints imposed by the Power Plant Controller and so on. To overcome such issues in real operating scenarios, a new modeling strategy has been introduced and validated in terms of computational complexity and accuracy. This approach is based on the state-space averaging technique which is applied to large PV plants with multiple conversion stages by performing some elaborations in order to get a final integrated model. The new modeling strategy has been tested in MatLab Simulink environment using data coming from a 300 MW PV plant located in Brazil representing the case study of this work. In this plant, one subfield is equipped with central inverters while another is with string inverters. The proposed model, whose accuracy is in the range from 2.2 to 2.7% with respect to the measured energy, effectively supports data analysis leading to a consistent performance assessment for the distributed conversion system. Final results highlight that string inverters ensure a gain of about 2% in terms of produced energy. [ABSTRACT FROM AUTHOR]

A novel approach of exploiting the stator-temperature-monitoring system to perform sensorless rotor-position estimation is described in this paper. The rotor position is, in fact, estimated by processing the voltages induced in thermistor cablings, which are modified in order to work as search coils (SCs). Using SCs, some typical drawbacks of sensorless position-estimation techniques based on the manipulation of fundamental components of stator voltages and currents, such as those related to inverter non-linearities, stator-resistance voltage drops, magnetic saturation and cross-coupling, can be overcome or mitigated. According to the proposed approach, a rotor-position-tracking technique for synchronous reluctance motor drives is developed independently from motor parameters. Such a sensorless rotor-position-estimation technique can be directly used to build up a sensorless controller or to improve the performance of conventional model based sensorless control systems. Simulations and experimental tests confirm the effectiveness of the proposed approach. [ABSTRACT FROM AUTHOR]

An optimal current control strategy for asymmetrical hybrid multilevel inverters (MLIs) is proposed in this paper enabling their use on motor drives, static synchronous compensators, and photovoltaic and wind generators, where a fast and precise current regulation is required. A key feature of these highly efficient converters is that an ac machine (motor or transformer) operates according to an open-end winding configuration, connected on one side to a main MLI and, on the other side, to an auxiliary two-level inverter (TLI). The first efficiently controls the main power stream operating at a low switching frequency, while the TLI acts as an active power filter, exploiting a conventional high-frequency two-level pulsewidth modulation (PWM) technique. The proposed control scheme optimally exploits the key features of the two inverters by suitably sharing the control task. In fact, a predictive current control is assigned to the MLI, which can be accomplished by low switching frequency operations, while the high switching frequency of the PWM-operated TLI is exploited to accomplish a fast and precise closed-loop current control, processing only a part of the power stream flowing through the system, thus producing low power losses. Simulations and experimental results confirm the consistency of the proposed approach. [ABSTRACT FROM AUTHOR]

An open-end winding machine configuration and a suitable control strategy for medium-voltage ac motor drives applications are proposed in this paper in order to reduce the distortion of phase voltages in multilevel inverters (MLIs). Differently than standard open-end winding configurations, where two inverters provide active power to both sides of the stator winding, a main MLI supplies in this case the machine on one side, while an auxiliary two-level inverter acts as active power filter on the other side. A high efficiency step modulation manages the MLI, while the auxiliary unit is pulse width modulation (PWM) operated. As the phase current harmonic content is improved, the torque ripple is reduced and the drive efficiency is increased. By exploiting the proposed approach, the apparent switching frequency of the system is that typical of a PWM inverter, although the main unit is operated according to a voltage step modulation strategy. Simulation and experimental results confirm the consistency of the proposed methodology. [ABSTRACT FROM PUBLISHER]

A novel control algorithm devoted to remove undesired low-order current harmonics in AC motor drives is presented in this article. The proposed control algorithm combines a suitable multiple reference frame synchronous harmonic estimator and multiple reference frame vector control implementation to suppress the undesired harmonics contained in the motor stator currents. This control technique can handle positive-, negative-, and zero-sequence sets, keeping a satisfying dynamic behavior. The control technique has been evaluated by numerical simulations and experimentally tested on a permanent magnet synchronous motor drive. [ABSTRACT FROM PUBLISHER]

Due to their inner structural redundancy, ac multidrive systems (MDSs) can achieve a fault-tolerance capability with minor circuit modifications. However, some additional components are generally required in order to create emergency current paths. According to a recently presented approach, the amount of additional components can be reduced by exploiting healthy drives to support faulty drives. This can be obtained by connecting together the neutral points of motor stator windings and suitably sharing the neutral current of faulty units among some, or all, healthy units. Following such an approach, three current-sharing methodologies for fault-tolerant MDSs are presented in this paper, which are able to cope with single or multiple failures. They are first theoretically introduced and then validated by mean of simulations and experimental test results. [ABSTRACT FROM PUBLISHER]

This paper deals with the analysis and implementation of a new scalar control technique for industrial interior permanent-magnet synchronous motor drives that exploits energy-saving capability. In particular, the proposed control strategy forces the conditions of maximum torque per ampere (MTPA), flux weakening (FW), and maximum torque per voltage (MTPV) simply by assigning polynomial relationships between the operating angles of the machine. Although the dynamic performance of the drive is worsened compared to that of vector control schemes, the modified scalar control allows us to work in energetic conditions, very close to those obtained with vector-controlled drives exploiting MTPA, FW, and MTPV strategies. The control techniques are implemented without using any speed and voltage measurement and with only a single current feedback. This paper provides a detailed study of the control strategy, showing the effectiveness and limitations of the method through simulations and experimental results. [ABSTRACT FROM PUBLISHER]

A three-phase multi-level multi-input power converter topology is presented for grid-connected applications. It encompasses a three-phase transformer that is operated on the primary side in an open-end winding configuration. Thus, the primary winding is supplied on one side by a three-phase N-level neutral point clamped inverter and, on the other side, by an auxiliary two-level inverter. A key feature of the proposed approach is that the N-level inverter is able to perform independent management of N − 1 input power sources, thus avoiding the need for additional dc/dc power converters in hybrid multi-source systems. Moreover, it can manage an energy storage system connected to the dc-bus of the two-level inverter. The N-level inverter operates at a low switching frequency and can be equipped with very low on-state voltage drop Insulated-Gate Bipolar Transistor (IGBT) devices, while the auxiliary inverter is instead operated at low voltage according to a conventional high-frequency two-level Pulse Width Modulation (PWM) technique and can be equipped with very low on-state resistance Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) devices. Simulations and experimental results confirm the effectiveness of the proposed approach and its good performance in terms of grid current harmonic content and overall efficiency. [ABSTRACT FROM AUTHOR]