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This paper shows how to exploit the degree of freedom represented by the common-mode voltage, which is inherent in three-phase Cascaded H-Bridge (CHB) converters, to minimize the total Root Mean Square (RMS) current value of the distributed dc sources. An optimal common-mode voltage injection law is derived, constituting a Maximum Power Per Ampere (MPPA) modulation strategy with respect to the currents of the dc sources. The potential benefits introduced by the proposed algorithm are analyzed in the context of battery-fed CHB converters and validated experimentally with a three-time-constant Randles model of a battery cell. The MPPA strategy is compared with traditional common-mode voltage injection methods, and battery loss reduction is demonstrated. The obtained battery energy saving is dependent on the converter modulation index and power factor. Experimental tests on a 36-cell full-bridge CHB converter validates the simulation and numerical derivation. To demonstrate the efficacy of the proposed method in practical applications, a 3 MW Energy Storage System (ESS) and a 110 kW Battery Electric Vehicle (BEV) undergoing standard drive cycles are presented as case studies. Compared to traditional modulation strategies, the MPPA strategy reduces the battery losses by up to 10.9% in the ESS and 27.5% in the BEV application.

The paper presents a control strategy for induction motor which optimizes both efficiency and torque response in both transient and steady state. In the context of vectorial control of induction motor, the optimum problem is defined according to the calculus of variations for a given step change of the reference torque. This allows finding the closed-form analytical solution of the current reference trajectories which minimize the amplitude of the stator current. Simulation and experimental results confirm the validity of the proposed approach that allows getting significant improvements in the drive efficiency. As a consequence, if the induction motor is used in the powertrain of an electric vehicle, the proposed control strategy can determine an increase of the range per charge, as demonstrated by the analysis of a case study.

This paper presents a detailed analysis of the energy saving in battery electric vehicles (BEV) equipped with an induction motor (IM) and modular multilevel converter (MMC) when their control methods are both optimized with respect to the energy losses. Specifically, the IM is driven according to a modified Field Oriented Control (FOC) which guarantees the Maximum Torque Per Ampere (MTPA) both during steady-state and transient operations. This strategy is aimed at the minimization of the stator energy losses and also determines a decrease of the rotor and iron losses. The MMC, based on battery-supplied half-bridge modules, is controlled with a Maximum Power Per Ampere (MPPA) strategy, obtained by the injection of an optimum common-mode voltage. This approach guarantees the minimization of the battery energy losses and, moreover, also reduces the converter switching losses. The whole powertrain is designed and tested during the Worldwide harmonized Light vehicles Test Procedure (WLTP) and the energy saving is quantified in comparison with traditional control methods.

This paper presents a sensorless control for a Doubly Fed Induction Generator (DFIG) in the context of grid-connected turbine-based wind generation systems. The paper proposes a full order adaptive observer able to track with excellent accuracy the DFIG rotor position even in presence of significant parameters deviations. The developed adaptive observer is coupled with a traditional stator flux based Field Oriented Control (FOC). The novel approach has been validated by an extensive numerical analysis.

The study presents a significant development of an advanced control strategy for stand-alone three-phase induction generators. The system under study consists of a squirrel-cage induction generator driven mechanically by an internal combustion engine and electrically by a fault-tolerant converter coupled with a LC filter. As a novelty, in this study three low-cost electrical contactors are introduced in order to re-arrange the converter topology after a fault occurrence and a proper re-starting procedure is developed, allowing the converter to operate with only two legs. The control architecture is mainly described with respect to this last operating condition, evidencing its intrinsic robustness. The study focuses on the composite control of the converter and the prime mover in order to improve the dynamic assessment of the whole system. The converter control is designed around the sliding mode technique, due to its attractive performance, especially as far as parameter uncertainties are concerned. In order to validate the theoretical framework, this study presents the first ever made experimental tests of this system with reference to a generation unit of about 10 kVA. The results confirm the high capability of the proposed system in regulating voltage and frequency with very good dynamic features.

The aim of the paper is to present an optimized procedure for the preliminary sizing of permanent magnet motors used for the hybrid parallel propulsion of passengers aircrafts. The procedure is finalized to obtain high values of the motor power density and is carried out by means of a non-gradient approach with evolutionary algorithm integrated with magnetic and thermal finite element analyses. The target of the procedure is the achievement of a preliminary sizing of the motor suitable for the aircraft propulsion, starting from motors usually employed in other traction applications. Some numerical results are discussed in the paper with reference to significant case studies.

In the context of Battery Electric Vehicles, conventional Voltage Source Inverters (VSI) have been associated with several types of Battery Management System, mainly to balance the state of charge of electrochemical cells and extend their lifetime. Modular Multilevel Converters (MMC) with embedded elementary cells represent a valid alternative, thanks to the possibility of integrating the balancing functionality, ensuring a negligible harmonic content of the output currents and reducing the ringing phenomenon. On the other hand, the MMC topology exposes the cells to a different current waveform, increasing the cells losses in comparison with VSI solutions. This paper analyzes how the cells current waveforms of a MMC topology produce an unbalanced distribution of active power among the cells and evaluates their loss increase with respect to VSI configurations.

This paper focuses on the performance analysis of a sensorless control for a Doubly Fed Induction Generator (DFIG) in grid-connected operation for turbine-based wind generation systems. With reference to a conventional stator flux based Field Oriented Control (FOC), a full-order adaptive observer is implemented and a criterion to calculate the observer gain matrix is provided. The observer provides the estimated stator flux and an estimation of the rotor position is also obtained through the measurements of stator and rotor phase currents. Due to parameter inaccuracy, the rotor position estimation is affected by an error. As a novelty of the discussed approach, the rotor position estimation error is considered as an additional machine parameter, and an error tracking procedure is envisioned in order to track the DFIG rotor position with better accuracy. In particular, an adaptive law based on the Lyapunov theory is implemented for the tracking of the rotor position estimation error, and a current injection strategy is developed in order to ensure the necessary tracking sensitivity around zero rotor voltages. The roughly evaluated rotor position can be corrected by means of the tracked rotor position estimation error, so that the corrected rotor position is sent to the FOC for the necessary rotating coordinate transformation. An extensive experimental analysis is carried out on an 11 kW, 4 poles, 400 V/50 Hz induction machine testifying the quality of the sensorless control.

In the last years the aerospace industry has put a growing effort to develop on-board electrification. The difficulties, which have emerged to implement the transition to the future aircraft, concern above all the constraints to be respected for aircraft applications (reliability, small size, reduced maintenance time, etc.). The present paper proposes to analyze and discuss the power devices and suitable converter topologies that bring the requirements of the airborne applications, especially devoted to match with the reliability and performance issues.

The actual trends in the design of AC drives are directed to the reduction of the total weight, volume and cost. Usually, this implies the necessity to adopt new motor topologies and converter architectures. An important role is played by the mono-inverter dual parallel motor (MIDP), which gives the possibility to reduce the total weight and costs of power converters. This paper proposes a novel model predictive control algorithm in order to improve the transient performances of a MIDP used for an overhead carrier. The effectiveness of the proposal control is verified through some numerical simulations.

The increase of electrical drives power density and reliability allows the possibility to develop an all-electric propulsion systems for the aircraft. A configuration based on a mono-inverter dual-parallel (MIDP) permanent magnet synchronous motors could be suitable in order to reduce the cost and the weight of the propulsion systems. This paper proposes a novel current references limitation strategy to improve the overall dynamic behaviour of the system during transient operations, without the worsening of oscillations damping. The effectiveness of the proposed solution is demonstrated through numerical simulations.

Objective:This paper analyses the Modular Multilevel Converter (MMC) topology, where each individual Sub Module (SM), in half bridge configuration, is directly fed by an elementary electrochemical cell.Methods:The aim is to investigate how the reference voltages influence the cells currents waveforms, determining how the active powers and the losses are distributed among the cells. Considering a 2-level Voltage Source Inverter (VSI) topology working in the same conditions, the ratio between the MMC total cells losses and VSI total cells losses is calculated. After showing the system architecture and mathematical model, the cells current waveform investigation is presented and detailed both for triangular and sinusoidal voltage reference waveform.Results:Finally, the results are critically discussed with particular focus on the comparison between the MMC and the VSI topologies.

This paper presents an overview of the most recent state of the art in the field of high-speed electric machines fed through high-frequency converters. This type of systems is rapidly wide spreading in aeronautical and automotive applications, as well as microturbines. Each typology has its own advantages and downsides, which are analytically presented in this paper. Some types of high-speed electric machines require high-frequency voltage supply, highly stressing the dielectric materials of the winding insulation system. For this reason, in high-speed electric drives, premature failure may occur and a reduction of the total system reliability has been observed in the past years. Such issues are comprehensively investigated in this paper.

This paper proposes a simplified optimum control strategy for a monoinverter dual parallel (MIDP) permanent magnet synchronous motor (PMSM). With reference to the parallel PMSM unified model, two different auxiliary conditions are investigated. The first minimizes the supplied inverter current, and the second maximizes the motor's efficiency. Their formal expressions are derived by the introduction of three new normalized variables, linked to the load conditions. Thus, the optimum tracking considerations are general, and the parameters are independent. Simplified closed analytical forms are found for the optimum tracking, independently under steady-state and transient conditions. The selection of the best solution is then found via a parameter independent look-up table, and imposed through a closed-loop control diagram. The proposed control is compared to the present state of the art via experiments on a 1400-W MIDP PMSM test bench, showing an equivalent performance, with a lower computational burden.

This study deals with direct torque control (DTC) of induction motor drives when a multilevel inverter is involved. The proposed control technique is finalised to reduce the amplitude of torque oscillations and to improve the motor dynamic response regardless of operating speed conditions while assuring a satisfactory input current distortion. This is achieved by using a special look-up-table built with a novel approach. The control itself is based on the application in each sampling interval of one or two voltage vectors suitably selected, in order to ensure low electromagnetic torque ripple in steady-state operations and fast dynamic behaviour in transient operations. In the algorithm, the converter voltage vectors selection is carried out by using a novel look-up table whose entry points are computed by means of a specialised relation, starting from the outputs of multilevel hysteresis controllers. The suggested method, suitable for a generic multilevel inverter, is detailed for a neutral point clamped three-level inverter. The proposed algorithm is validated by several numerical results, and compared with a DTC algorithm based on a traditional three-speed range look-up tables. Finally, some experimental results, obtained with a scale laboratory setup, are shown, discussed and compared with the numerical ones.

The power extracted from PV arrays is usually maximized using maximum power point tracking algorithms. One of the most widely used techniques is the perturb &amp, observe algorithm, which periodically perturbs the operating point of the PV array, sometime with an adaptive perturbation step, and compares the PV power before and after the perturbation. This paper analyses the most suitable perturbation step to optimize maximum power point tracking performance and suggests a design criterion to select the parameters of the controller. Using this proposed adaptive step, the MPPT perturb &amp, observe algorithm achieves an excellent dynamic response by adapting the perturbation step to the actual operating conditions of the PV array. The proposed algorithm has been validated and tested in a laboratory using a dual input inductor push-pull converter. This particular converter topology is an efficient interface to boost the low voltage of PV arrays and effectively control the power flow when input or output voltages are variable. The experimental results have proved the superiority of the proposed algorithm in comparison of traditional perturb &amp, observe and incremental conductance techniques.

The paper deals with the control of three-phase voltage source rectifiers (VSRs) with an arbitrary number of voltage levels. By means of an approach borrowed from the “Direct Torque Control” of AC drives, the paper presents an enhanced direct power control (DPC) strategy for VSRs which directly controls both active (P) and reactive (Q) line power by considering the values of their time derivatives. This control strategy can be applied both to the Neutral Point Clamped and to Cascaded H-bridge multilevel converters. In every sampling interval the proposed control technique is able to select the most suitable converter voltage vector to obtain good dynamic response and to maintain P and Q within their respective reference bands. This result is achieved in the different operating conditions by means of a Dynamic Look-Up Table (D-LUT) of the converter voltage vectors, which are ordered on the basis of their influence on P and Q time derivatives. The mentioned D-LUT depends on the instantaneous operating point and is not predetermined. Some significant operating conditions are numerically investigated in order to show the capability of the modified DPC technique to ensure good values of power quality indexes for the grid. Experimental results on a laboratory setup based on a three-level VSR show good accordance with the simulation ones.

The paper deals with the vector control of two surface-mounted permanent-magnet (PM) synchronous-motors in configuration “single-inverter dual-motor”, operating also with unbalanced loads. Since this structure is justified by the objective of obtaining low cost drives, a low computation burden sensorless method is proposed in order to further reduce the system complexity. A very simple algorithm for position/speed estimation coupled with a hybrid adaptive Phase-Locked Loop is indeed sufficient to achieve satisfactory results also in heavy transient operations. Furthermore, a novel control strategy is conceived with reference to an “equivalent” motor, whose rotor position is the average of the separately evaluated positions of the two PM motors. The proposed control technique is validated by an extensive numerical campaign.

Over-temperature occurring in silicon solar panels, subject to partial shadowing, are reduced by means of a series connected voltage divider which sustains part of the reverse voltage developing across the shaded solar cells. The circuit is based on a power MOSFET which is driven by the output voltage of the solar panel. When the solar panel is uniformly illuminated the MOSFET is in the ON state and does not affect the operation of the module, while, when the solar panel is partially shaded, and the output voltage decreases, the MOSFET enters in the pinch-off operation mode, thus subtracting its voltage from the reverse voltage across the shaded cell. Experiments performed on a commercial solar panel showed one third of reduction of the reverse voltage across shaded solar cells, with a reduction of the hot spot temperature of about 25°C.

This paper proposes a new mathematical model of modular multilevel converters for battery electric vehicles with space-vectors enabling a critical analysis of cell balancing for the battery management system. In particular, the requirements for power balancing and the actual number of degrees of freedom of the control are investigated. The paper shows that the traditional approach of cell balancing is a special case of the proposed control methodology. Numerical analyses with Matlab/Simulink™ highlight the reasons of the slow response of the standard balancing technique for specific operating conditions of the battery electric vehicle. The paper suggests potential improvements that could be introduced through the proposed generalised approach.

Marine energy sources represent an attractive and inexhaustible reservoir able to contribute to the fulfillment of the world energy demand in accordance with climate/energy regulatory frameworks. Wave energy converter (WEC) integration into the main grid requires both the maximization of the harvested energy and the proper management of the generation variability. The present paper focuses on both these mentioned issues. More specifically, it presents an embedded point pivoted absorber (PPA) and its related control strategy aimed at maximizing the harvested energy. Experimental and numerical investigations have been carried out in a wave/towing tank facility in order to derive the design characteristics of the full-scale model and demonstrate the validity and effectiveness of the proposed control strategy.

In the context of grid connected photovoitaic (PV) generation systems, there are two paramount aspects regarding the Maximum Power Point Tracking (MPPT) of the photovoltaic units and the continuity of the service. The most diffused MPPT algorithms are based on either perturb and observe, or on an incremental conductance approach and need both PV current and voltage measurements. Several topology reconfigurable converters are also associated with the PV plants, guaranteeing fault-tolerant features. The generation continuity can also be assured by interleaved inverters, which keep the system operating at reduced maximum power in case of failure. In this paper, an evolution of a hysteresis based MPPT algorithm is presented, based on the measurement of only one voltage, together with a novel space vector modulation suitable for a two-channel three-phase grid connected interleaved inverter. The proposed MMPT algorithm and modulation technique are tested by means of several numerical analyses on a PV generation system of about 200 kW maximum power. The results testify the validity of the proposed strategies, showing good performance, even during a fault occurrence and in the presence of deep shading conditions.

With reference to a strong variable parameters AC brushless machine, the paper deals with an online method of fault detection for closed loop controlled PMSM. The proposed technique exploits the monitoring of the motor d,q axes inductances via a Recursive Least Square Algorithm (RLS). The motor parameters, which have been pre-mapped with reference to the d,q axes current components, are compared to the results of the online identification procedure and their discrepancy is evaluated in real time. A fault indicator index is derived and its behavior conditioned in order to properly recognize any anomalous condition. The proposed method is tested via numerical simulations on the basis of a real PM brushless machine whose parameter have been evaluated in different operating conditions by means of several off-line experimental measurements.

The study deals with a novel torque derivative control of induction motor drives. The proposed technique is mainly finalised to improve the motor dynamic response regardless of speed operating conditions, ensuring satisfactory values of both motor currents distortion and torque ripple. The core of the discussed approach is a special look-up table, in which the converter voltage space vectors are sorted with respect to their influence on the torque derivative, taking also into account their influence on the flux magnitude. The table is indeed accessed by a desired torque derivative value, obtained by properly processing the output of hysteresis controllers. Moreover, a variable duty-cycle technique is implemented in order to ensure a satisfactory torque ripple in steady-state conditions. The proposed algorithm, suitable for a general multilevel inverter, is numerically tested on a three-level neutral point clamped inverter and its performance are compared with the ones obtained by a traditional direct torque control method based on three speed ranges look-up tables. The control is then validated experimentally by means of a reduced scale laboratory prototype fixing the same condition used for numerical analysis.

The diffusion of distributed electric generation sources is a growing phenomenon, encouraged by the changes in the electric energy market and the concerns about gas emission. Microgrids are composed by different types of generators, several loads and power converters necessary to interface all the microgrid components and the microgrid itself with the main AC grid. This paper presents a new flexible power converter capable of changing its topology by means of static switches so that it can provide different conversion functions using the same hardware. This proposal aims to reduce the number of components, enhancing compactness and simplicity, and resulting in lower equipment costs. The proposed converter is conceived for domestic microgrids, is connected to the AC grid and a renewable energy source (RES) and is configurable as a single-input dual-output (SIDO) converter, providing two different DC voltage levels. After showing all the possible configurations of this converter, the analysis focuses on SIDO, deriving its mathematical model and discussing a procedure to design its elements. The controllability of the SIDO is tested via numerical simulations showing good performance even during fast transient conditions.

In recent years lithium iron phosphate batteries are spreading because of their high energy and power density, long lifetime and high inherent safety. In technical literature different models have been proposed to characterize these batteries. These models have different complexity but give results of different accuracy. In this paper a comparison of three equivalent models is performed. The comparison is made taking into account the impedance of the cells as function of the working frequency. For this reason electrochemical impedance spectroscopy method is used. The real and imaginary parts of the impedance calculated at each frequency are compared with that resulting from experimental tests in order to understand which are the frequency limit of each model. From the analysis clearly results that the traditional simple models obtained with 2 or more RC branches cannot represent the behavior of these batteries in all the frequency range. On the contrary, the models presenting a Warburg impedance, even if more complex, can represent the frequency behavior of these batteries in a wider frequency range.

Typical operating conditions of permanent magnet synchronous motors correspond to nonlinear relationships between fluxes and currents. The determination of equivalent motor parameters is a non trivial task and can be critical for the design of motor controllers, which is typically based on a mathematical model. In this paper an experimental method to determine the flux-current nonlinear maps and a model based approach to implement a predictive controller capable to deal with such nonlinearities is presented. Numerical results show that the optimization technique is able to provide the maximum torque per ampere tracking.

In the paper is discusses the project, the design and overall performance of a micro-cogenerator prototype of 2.0 kW of electric power and about 5.0 kW of thermal power, suitable for single off-grid applications and fuelled by gas produced from biomass anaerobic digestion. This unit is based on a previous prototype designed and developed at Istituto Motori CNR of Italy and it has been conceived specifically as a local individual off-grid energy platform, born to be mated with small biomass reactor, which need part of the heat produced by the internal combustion engine to have a stable and efficient behaviour. The adopted internal combustion engine maintains many technical solutions and constructive elements already experimented in previous prototypes, the unit has been modified in order to be fuelled by natural gas with partial methane content, or with LPG when necessary. The generation system is a permanent magnet generator fed by a low cost inverter which can offer very high efficiency and a reasonable bulk and weight and gives to possibility to include an electric energy storage to compensate service discontinuity. The proposed cogeneration unit has in cost reduction, durability, low noise/vibration and a good electric efficiency the most important achieved objectives. It is very flexible in terms of gas supply and in respect of the electric needs of a generic utility, representing a very smart way for energy conversion in many situations when electricity couldn't be easily produced because of fuel availability and a cheap way to reach the full utilization of fuel energy together with a significant CO2 reduction.

With reference to light railways transportation systems, in the paper a comparison is carried out between vehicles equipped with either Induction Motor Drive or Permanent Magnet Brushless Motor Drive. The attention is particularly focused on energetic performance, in term of losses and efficiency. The main characteristics of the traction units of the two compared vehicles have been chosen in accordance with the real constraints, usually imposed or suggested by the motor type, which influences mechanical and electrical configurations, control architectures and techniques. Thus, the analysis has not the aim to compare specific devices, which are different for the two considered cases, but the whole traction units, each one with its own proper characteristics. Based on both assigned characteristic of the railways sections and vehicle mission, an extensive numerical analysis has been carried out in various operating conditions, with the aim to comparatively evaluate either fast dynamic performance, in response to the PWM modulation, or slow dynamic performance, concerning the time constant of mechanical quantities, or losses and energy efficiency.

The paper presents a mathematical model of Permanent Magnet AC brushless machines (PMSM) having a number of stator poles-obtained via the distribution of the three-phase winding- different from the rotor one, realized by the displacement of the permanent magnets. For these so- called ‘Fractional-Slot’ motors (where few total slots generate high equivalent number of poles) the available mathematical models appear partial and/or incomplete, despite of numerous designing considerations made in literature. In this paper an analytical approach is developed to point out an instantaneous- values mathematical model with concentrated parameters, that can be suitable for control architecture systems when some simplification hypotheses are added. The model takes into account a general distribution of the armature magnetomotive force field, and the total harmonic content of the rotor flux density. The whole MMF harmonic content is then properly reduced and the result is compared to a traditional PMSM model

The paper focuses on an innovative energy management control strategy of a wayside supercapacitor (SC) applied in DC electrified light transit networks. In order to achieve minimum energy demand from the electric feeding substations, the target of the control is the optimal tracking of the storage device voltage subject to the minimization of the mean square of the supply currents and, consequently, the reduction of power losses along the line. Hence, optimization theory has been used for the analytical determination and implementation of real time control strategy. Therefore the proposed strategy has been verified and validated via numerical simulations with reference to realistic LRV operation and different headway among the operating vehicles. A comparison with a classical energy storage system (ESS) state of charge control has been also carried out, as well as the energy saving improvement has been highlighted and the energy storage system integration and challenges are addressed. The results validate the theoretical approach and prove that the suggested control strategy is quite effective, putting in evidence its potentiality and the possibility of an actual implementation.

As Vehicle-to-Grid (V2G) concept convenes strong interests among automakers, electric utility owners, and policy makers, it is critical to investigate the potential impacts of V2G on the electric distribution system. Such study, together with other benefits of V2G, may encourage utility support for V2G commercialization. This paper focuses on a pressing technical issue associated with the penetration of V2G into the electric distribution network-the energy loss in the feeders. Mathematical models are formulated to investigate how V2G reactive power injection and different load patterns can impact energy loss on a distribution system. It is shown that loss reduction can be greatly influenced by reactive loading factor, the pattern of loading, the amount of V2G reactive power injection, and the position of V2G parking lot on the feeder segment. Useful results are obtained, with a promise that more than 95% energy loss reduction (relative to energy loss in the system without V2G installed) is possible by optimally locating a V2G parking lot along the feeder. The results in this study may serve as a nomogram to determine energy loss at the planning stage of installing a V2G parking lot on a distribution feeder segment.

The paper discusses the concept and the overall performance of a 20 kW micro-cogeneration unit, suitable for distributed energy conversion and based on a 4-cylinder, supercharged methane fuelled, spark ignited, internal combustion engine (ICE). The latter is coupled to a three-phase PM-brushless electric generator, whose armature is controlled by an active front-end [12,14]. The ICE is derived from a widespread Diesel unit, which has been properly modified; it is chosen among many other engines as a reliable, very high efficiency, cost effective unit [6], suitable for energy conversion systems (such as residential or commercial applications). The paper starts by defining the criterion which led to the adoption of a high brake mean pressure, in order to produce the above mentioned electric power. After the description of the solutions adopted to optimize the ICE operation performance, a very simple and efficacious control strategy of the generator+converter set is presented. This technique is able to conveniently reduce the magnitude of shaft-torque ripple produced by a high brake mean pressure (and consequently cycle peak pressure), in order to reduce vibrations, noise and rotating speed oscillations. The control is based on assigned curves of ICE torque vs. shaft angular position. Some considerations are also made to define the right generator sizing, in order to allow an efficacious damping action, maintaining good efficiency levels of the generator+converter set. The effectiveness of the control is validated by a series of numerical results in significant operating conditions.