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A new approach to compensate rotor position errors caused by parameter mismatching in model-based sensorless synchronous reluctance motor drives is presented in this paper. According to the proposed approach, the error in estimating the rotor position is detected by injecting some low-frequency current signals and adjusting the estimated rotor angular position through a gradient descent algorithm until minimizing the ripple generated on the estimated rotational speed. A rotor position correction can be fully on-line accomplished coping with saturation and cross saturation effects, as well as with unmodeled phenomena and unpredictable variations of the stator resistance with the temperature. The correction procedure can be accelerated by starting from an approximated correction table, which can be off-line built using the same technique. The proposed approach does not need additional current or voltage sensors, nor motor design modifications, thus providing an inexpensive mean to improve the control performance and robustness. Although originally conceived to deal with back-EMF based sensorless control techniques, the correction procedure can be extended to other model-based sensorless SynchRel motor drives.

Multiple-motor fed by multiple-converter systems feature a set of electric motor drives sharing the load through a common mechanical coupling. Such a coupling is exploited in this paper to build up a sensorless field oriented control, based on a quite common back-EMF technique to estimate the rotor flux angular position and an original approach to correct estimation errors. The technique is based on the injection of a suitable, very low frequency, sinusoidal signal on the current reference of one of the motor drives. If the estimated rotor flux position is correct, the drive output torque does not show variations. Differently, a torque ripple is generated at the frequency of the injected signal, whose effects on the system speed are easily compensated by the main speed controller. However, due to the mechanical coupling, an additional component of the reference torque current at the frequency of the injected signal is generated on all the other drives. By minimizing such a component, the estimated rotor flux position can be corrected online. The proposed method can also be exploited to estimate actual values of the stator resistance and of the rotor time constant.

Piezoelectric energy harvesters (PEHs) are a reduced, but fundamental, source of power for embedded, remote, and no-grid connected electrical systems. Some key limits, such as low power density, poor conversion efficiency, high internal impedance, and AC output, can be partially overcome by matching their internal electrical impedance to that of the applied resistance load. However, the applied resistance load can vary significantly in time, since it depends on the vibration frequency and the working temperature. Hence, a real-time tracking of the applied impedance load should be done to always harvest the maximum energy from the PEH. This paper faces the above problem by presenting an active control able to track and follow in time the optimal working point of a PEH. It exploits a non-conventional AC–DC converter, which integrates a single-stage DC–DC Zeta converter and a full-bridge active rectifier, controlled by a dedicated algorithm based on pulse-width modulation (PWM) with maximum power point tracking (MPPT). A prototype of the proposed converter, based on discrete components, was created and experimentally tested by applying a sudden variation of the resistance load, aimed to emulate a change in the excitation frequency from 30 to 70 Hz and a change in the operating temperature from 25 to 50 °C. Results showed the effectiveness of the proposed approach, which allowed to match the optimal load after 0.38 s for a ΔR of 47 kΩ and after 0.15 s for a ΔR of 18 kΩ.

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.

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.

A novel three-phase multilevel inverter topology for open-end winding motor drives is proposed, featuring a reduced number of power devices. According to such a topology, only two of the motor phase windings are fed by a single-phase neutral point clamped inverter from one side, and a single-phase full bridge inverter from the other, the third motor phase being connected between the midpoints of the two inverters. The proposed topology can generate six different voltage levels in each motor phase and compared to a conventional three-phase three-level neutral point clamped inverter features a reduced amount of power devices and a higher efficiency. Simulations dealing with steady-state and transient conditions have been performed on a 1kW permanent magnet synchronous motor drive to demonstrate the effectiveness of the proposed configuration in a wide operating range.

A new approach is proposed to enable the self-commissioning on back-EMF based sensorless synchronous reluctance motor drives, providing an inexpensive mean to improve the performance and control robustness. The proposed approach is based on the injection of suitable current signals and on adjusting the estimated value of the rotor angular position in order minimize the ripple generated on a signal produced by a phase locked loop speed estimator. Exploiting such a technique look-up tables can be off-line built which can be used to on-line correct the estimated rotor angular position according to actual d,q stator currents. The proposed approach does not need additional current or voltage sensors, nor motor design modifications and can be also exploited to compensate the effects of the variation of the stator resistance with the temperature.

A Hybrid N-Level T-Type Inverter topology is presented in this paper. It is composed of a multilevel T-type converter and a set of two-level converters, connected according to an open-end winding configuration to the supplied AC machine. Compared to traditional multilevel topologies as Neutral Point Clamped, Flying Capacitor and Cascade H-Bridge, the proposed one features less power devices for a given amount of output voltage levels. Moreover, no additional circuits are required to balance the voltage across the DC bus capacitors, leading to a reduction of cost and power losses. The proposed topology is also superior to more conventional counterparts in terms of efficiency and total harmonic distortion. Simulations confirm the effectiveness and the advantageous features of the proposed topology.

Voltage wave reflection phenomena along power cables are particularly threatening on ac motor drives equipped with silicon carbide power mosfet s due to very short switching times and high switching frequency. Overvoltage suppression resistance inductance capacitance (RLC) networks are usually added but leading to extra cost and a lower efficiency. A completely different overvoltage mitigation approach is presented in this paper exploiting an open-end winding motor configuration. Overvoltage occurring on the terminals of motor phase windings are, in fact, mitigated by simply coordinating the operations of the two inverters; thus, no passive RLC networks are required. The proposed approach is intended as a mean to provide a further valuable feature to open-winding systems at no extra cost, but it can be also valued as an alternative to conventional bridge inverters equipped with overvoltage mitigation devices.

A new approach to realize an integrated battery charger is described in this paper, based on the Asymmetrical Hybrid Multilevel Converter topology. Such a particular open-end winding motor configuration has proved to be more efficient than conventional inverter topologies in EV motor drive applications but it can be also turned in an on-board battery charger only by acting on the control system. Thus, no additional components, nor circuit reconfiguration through extra power switches are required. Moreover, the obtained battery charger can be supplied either by a standard AC single-phase grid, either by a DC power source for fast recharging.

A fault tolerant AC/DC Converter for Electrical Gen-Set applications is presented based on a multilevel, open-end winding, topology managed by a suitable control strategy. More precisely, the considered converter topology provides the mean to independently control the currents of two phases when the third one is open without the need to reconfigure the circuit through auxiliary switches. The electrical generator is thus forced to operate in a two-phase mode, while holding the output DC voltage at the value generated by the system in health conditions. According to the proposed approach, this is achieved only by modifying the reference frame transformation accomplished to control the current vector. The effectiveness of the proposed solution is evaluated by simulations performed on a 2kW PMSG system.

A strong demand for even more compact and reliable power electronic devices has powered the development of advanced design techniques. A key role is played in these techniques by the reliability assessment, a procedure that estimates the expected lifetime according to given mission profiles. The reliability assessment of a low voltage MOSFET working in avalanche mode is considered in this paper through an experimental approach based on the Coffin–Manson law. Differently from previously proposed techniques, based on a thermodynamic analysis, a direct measurement of the thermal strain over the source aluminum layer is instead exploited. The consistence of the proposed technique is evaluated by comparing estimation of the progressive increment of the on -state resistance with results of endurance tests and estimation obtained from previously presented reliability models. The described technique can be applied to assess the reliability of MOSFETs in applications typical of the automotive field, where they are tasked to power inductive loads in unclamped mode. More in general, the method can be exploited to characterize the front metal of MOSFET devices subjected to power cycling, or short-circuit stress tests.

Speed control performance on most sensorless field-oriented control induction motor drives is sensitive to parameters variation. In fact, the speed feedback signal is normally obtained from the rotor flux angular frequency through the machine mathematical model and its precision is strongly affected by errors in estimating the rotor time constant. This paper describes a new method to on-line estimate the rotor time constant, which is accomplished by injecting a low frequency current signal and by tracking to a minimum the produced slip angular frequency ripple. The proposed technique does not require modifications of the controller structure and does not require additional sensors, while featuring a good accuracy and fast convergence to the correct value of the rotor time constant. Although it can be implemented on any kind of sensorless induction motor drive, a straightforward practical implementation can be however accomplished on MRAS based sensorless induction motor drives. Simulation and experimental tests confirm the effectiveness of the proposed approach.

The indirect Field Oriented Control is the standard control technique for high performance induction motor drives. It is simple and effective, but it requires an accurate estimation of the rotor time constant in order to achieve the best possible performance. The paper presents a procedure for on-line estimating the rotor time constant which does not need other transducers than those already present on a standard system, does not affect normal operation and features good precision and robustness. The estimation is performed by processing the effect of a low frequency additional signal and can be used either for on-line tuning working drives, either for commissioning newly installed drives. Simulation and experimental tests demonstrate the effectiveness of the proposed procedure.

An electrically assisted internal combustion engine is obtained by combining a conventional engine and one or more electrical motors of considerably smaller size. A key feature of such an innovative vehicle hybridization approach is that the torque generated by electric machines is not transmitted to the wheels. The electric motors are, in fact, intended only to assist the internal combustion engine in low efficiency, low performance, or high polluting working conditions. They however, draw extra power and energy from the battery. This paper presents a tool to evaluate different possible solutions in terms of energy balance, efficiency, battery stress and battery ageing. The method, which is based on suitable mathematical models and specific analysis criteria is also exploited to compare eight different configurations of a C-segment vehicle, pointing out limits and capabilities of traditional 12−14 V systems.

Energy harvesters are today gaining ever more interest, enabling the recovery of otherwise wasted energy in a large variety of systems. Among them, piezoelectric devices are particularly suitable to generate electrical energy from vibrations and surplus mechanical energy. A two-stage power conditioning circuit, consisting of a AC-DC converter followed by a DC-DC stage, is usually placed at the output of piezoelectric devices in order to optimize the power yield. The efficiency of the piezoelectric device is, in fact, a very critical parameter, due to the poor power density of energy harvesters based on piezoelectric devices. This paper describes a new single-stage, low-power, converter able to automatically follow the variations of the resistive component of the output impedance of a cantilevered PZT (Lead Zirconate Titanate) based piezoelectric energy harvester in order to maximize the energy yield.

This paper presents a three-phase six-level Asymmetrical Hybrid Multi-Level Photovoltaic Inverter (AHMLPI) for medium voltage grid connected applications. A Low to Medium Voltage Transformer is operated in an open-end winding configuration. Thus the low voltage winding is supplied on one end by a three-phase three-level Neutral Point Clamped Inverter (NPC) and, on the other side, by an auxiliary Two-Level Inverter (TLI). A key feature of the proposed approach is that the NPC controls the main active power flow extracted by PV strings, while also accomplishing the MPPT (Maximum Power Point Tracking), thus avoiding the need of additional DC/DC power converters. The NPC operates at a low switching frequency, according to a step modulation, and can be equipped with very low on-state voltage drop IGBT devices. The auxiliary TLI instead operates at low voltage, according to a conventional high frequency two-level PWM technique, in order to accomplish a twofold task. First it controls the inverter output current. Second it acts as an active power filter in order to compensate low order harmonic components caused by the NPC step modulation. As the DC bus voltage of the TLI is remarkably lower that of the main NPC, the auxiliary inverter can be equipped with low switching losses IGBTs, or even Power MOS devices. Simulations results confirm that, compared to conventional systems, the proposed approach, features a remarkably reduced phase current harmonic content is and an increased efficiency.

On Multiple-Motor systems fed by Multiple-Converter systems a set of electric motor drives share the load through a common mechanical coupling. Such a coupling is exploited in this paper to realize a sensorless field oriented control, based on a quite common back-emf technique to estimate the rotor flux angular position and an original approach to correct the estimation errors. The technique is based on the injection of very low frequency, sinusoidal signals on the current references of one of the motor drives. If the estimated rotor flux position is correct, the drive output torque does not show variations. Differently, if the estimation is incorrect, a torque ripple is generated at the frequency of the injected signal, whose effects on the system speed are easily compensated by the main speed controller. However, due to the mechanical coupling, an additional component of the reference torque current at the frequency of the injected signals is generated on all the other drives. By minimizing this component, the rotor flux position estimation can be effectively corrected, as well as errors in estimating the stator and rotor resistances.

An original overvoltage mitigation technique is presented in this paper for Sic based motor drives, exploiting an open-end winding motor configuration. According to the proposed solution over-voltage occurring at the terminals of the motor phases is mitigated by driving the two inverters through a modified switching pattern including a suitable dwell time. No passive RLC networks are required, thus avoiding additional costs and extra power losses. A comparison between IGBT and SiC MOSFET equipped motor drives is first provided, highlighting the difference in terms of power cable critical length and other factors affecting peak terminal over-voltages. The proposed approach is then theoretically introduced and its consistency is finally assessed by simulations and experimental results.

A new approach, based on a current controlled Asymmetrical Hybrid Multilevel Inverter (AHMLI), is proposed to reduce power losses and output current distortion on Multi-Level Inverters (MLI) used in AC motor drives, STAT COM devices, Photovoltaic and Wind generators. A key feature of the proposed approach is that the AC machine (motor or transformer) is operated in an open-end winding configuration, being supplied on one end by a main Multi-Level Inverter and, on the other side, by an auxiliary Two-Level Inverter (TLI). The MLI controls the main active power stream; it operates at a low switching frequency and can be equipped with very low on-state voltage drop IGBT devices. The auxiliary TLI is instead operated according to a conventional high frequency two-level PWM technique and acts as an active power filter providing only a null-average power to the AC machine. As the DC bus voltage of the TLI is remarkably lower that that of the main MLI, the auxiliary inverter can be equipped with low switching losses IGBTs, or even Power MOS devices. Simulations and experimental results confirm that using the proposed approach, the phase current harmonic content is remarkably reduced, the efficiency is increased and in motor drive applications, the torque ripple is mitigated.

A two-stage converter working in dual mode time sharing is proposed for single-phase photovoltaic applications. The converter encompasses a dual boost front end and a single-phase three-level Neutral Point Clamped grid inverter. According to the time sharing strategy, the boost stage is by-passed and only the Neutral Point Clamped inverter is operated when the input voltage is greater than the actual absolute value of the grid voltage. Otherwise, the boost stage operates as a current shaper and the inverter works in unfolder mode. As only one of the two stages of the converter is active at a time, power losses are reduced. Moreover, a suitable input DC voltage amplification is provided, extending the input voltage range. This also enables the exploitation of a neutral point clamped inverter, which, thanks to the characteristic quite rail switching, generates very low leakage ground currents.

Among single stage, single phase, inverter configurations the Neutral Point Clamped topology is advantaged by its quiet rail switching mechanism, producing negligible common mode currents. However, it requires a double input voltage if compared with a classic full bridge inverter. A modified Neutral Point Clamped, three level, single phase, inverter topology is presented in this paper intended for Thermoelectric Generation Systems applications. The proposed topology owns an inner voltage boosting capability, thus, it can be supplied with an input DC voltage equivalent to that of a conventional H bridge inverter, or even lower. Moreover, it is able to compensate voltage drops caused by variations of the thermoelectric generator operating temperature. Finally, no extra high frequency switching devices are introduced to implement the voltage boosting function.

An over-voltage mitigation technique for open-end winding electrical drives with long power cables is proposed in this paper. In particular, a suitable dwell time is included in the switching patterns of the two inverters to minimize the over-voltage occurring at the stator terminals of this kind of systems. No passive RLC networks are required, thus avoiding additional costs and extra power losses. The proposed approach is first theoretically introduced, then validated by numerical simulations and experimental tests. Finally its effectiveness is compared with that of conventional passive RC filters.

In open-end winding AC motor drives, terminals of stator phases are normally connected between two inverters, normally, of the same type and size. In the present paper, an alternative configuration is studied where the machine is supplied exploiting two different converters: a main multi-level inverter and an auxiliary two-level inverter. The last operates as active power filter in order to eliminate undesired low-frequency voltage harmonics produced by the multi-level modulation process. Furthermore, the two level inverter is operated at a rather low voltage, thus it can be equipped with power MOSFETs. Consequently, a voltage PWM at a remarkably higher frequency is allowed, if compared with standard multilevel inverters. According to the proposed approach, the phase current harmonic content is remarkably reduced, the torque ripple is mitigated while the drive efficiency is increased. Numerical simulations and experimental results confirm the consistency of such new methodology. A particular emphasis is given to stator current harmonic content and power losses analysis as well as to specific implementation issues.

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.

Electrically Assisted Internal Combustion Engines are gaining a large popularity, as they allow to obtain a noticeable average vehicle efficiency improvement at a low cost. Two different approaches are considered in designing last generation vehicles: StartStop, or Micro-Hybrid, and Electrically Assisted Turbocharger. The energy balance of a vehicle equipped with electrically assisted internal combustion engines is a quite critical point, as it has effects on the consistency of the hybridization, the design of the electric power generation system and of the battery. The energy balance of a C-segment vehicle adopting the two solutions is analyzed in this paper by suitable mathematical models. Moreover, the possibility to exploit the two approaches at the same time is discussed.

Grid connected photovoltaic plants for residential applications are normally designed through deterministic methods on the basis of system requirements as: PV array peak power, available budget, or available space. Unfortunately, these approaches give only suboptimal results. More effective design techniques are those oriented to fulfill given performance targets as minimum pay-back time, minimum life cycle cost, or minimum annual electrical energy cost. However, they require very complex optimization techniques, especially if the plant encompasses energy storage systems. An analytic approach is presented in this paper to optimally sizing the photovoltaic module array and the energy storage system in a grid-connected generator serving a set of residential loads, on the basis of annual average solar radiation data and load demand. The configuration with the shorter pay-back time is identified through a mathematical model, describing the variation of the annual energy cost as a function of the plant configuration. The proposed method can be easily modified to take into account different optimization targets, as maximum life-cycle profit.

The paper describes a simulation framework able to accomplish a simulation of a PV plants including a Wireless Sensor Network (WSN). The developed framework is entirely implemented in a Matlab/Simulink environment, and can be used to accomplish in-depth performance evaluation of two very different systems interacting between them, the power generator and the wireless data transfer network. As an example, the developed framework is exploited to investigate the effects of possible data losses, or delays, on the efficiency of a PV generator based on the Module Integrated Converter concept and equipped with a centralized MPPT system exploiting a WSN to monitor PV modules electric variables and the distribution of solar irradiation and temperature over the plant area.

Thanks to their characteristic quiet rail switching mechanism, derivatives of the basic half bridge converter, such as the Neutral Point Clamped topology, are advantaged among single stage, single phase, inverter configurations for PV applications by very low ground currents. On the other hand, as the majority of single stage inverters, they are unable to boost the input voltage, therefore featuring a narrow operating range. Moreover, if compared with full bridge derived topologies, half bridge derivatives require a double input voltage. A new inverter configuration, based on a three level Neutral Point Clamped configuration, owning an inner voltage boosting capability is presented in this paper. No extra high frequency switching devices are introduced, thus featuring reduced power losses. Moreover, no reactive currents flow back to the DC bus, due to the inner AC side bypass and no common mode current filters are required, thanks to the quite rail switching operation.

The paper presents an effective method for the measurement, using a standard infrared camera working at 25 Hz frame rate with 320256 pixels full frame, of very fast temperature transients (i.e., having a bandwidth of 10 kHz or more) which, in principle, would require a much faster acquisition rate. The proposed method is based on triggering multiple time-delayed acquisitions (MTDA) of the observed thermal phenomenon, which has to be reproducible, by means of a very precise and stable programmable digital micro-controller and by reconstructing the time domain IR sequence using the frames acquired at each trigger event. The method could find application in assessing the reliability of power electronic devices and, in particular, to measure dynamically temperature distribution over the source metal of Power MOSFETs or IGBTs, which feature very fast thermal transients, even in the hundreds of microsecond scale and might develop local hot spots as a consequence of aging or failures.

Some of DC actuators used in home automation, office automation, medical equipment and automotive systems require a position sensor. In low power applications, the introduction of such a transducer remarkably increases the whole system cost, which justifies the development of sensorless position estimation techniques. The well-known AC motor drive sensorless techniques exploiting the fundamental component of the back electromotive force cannot be used on DC motor drives. In addition, the sophisticated approaches based on current or voltage signal injection cannot be used. Therefore, an effective and inexpensive sensorless position estimation technique suitable for DC motors is presented in this paper. This technique exploits the periodic pulses of the armature current caused by commutation. It is based on a simple pulse counting algorithm, suitable for coping with the rather large variability of the pulse frequency and it leads to the realization of a sensorless position control system for low cost, medium performance systems, like those in the field of automotive applications.

A procedure to compare the performance of Wind/Photovoltaic hybrid plants owning the same PV cell array and wind turbine, but different internal configurations is presented in this paper. The selection of the optimal internal configuration for a hybrid generation plant from renewable energies is a complex task and no widely accepted design tools are today available to compare the features of different possible architectures for a given combination of solar irradiation, wind speed and load profiles. To do this a procedure is proposed based on the evaluation of four performance indexes, namely: the global efficiency, the efficiency in transferring energy from RES to BSS, the efficiency in transferring energy from BSS to load and the fraction of useful renewable energy. The paper is mainly focused on low power hybrid Wind/Photovoltaic plants for distributed generation, however, the proposed procedure may also be adapted to high power systems.

The single stage architecture is often preferred to realize grid connected Photo-Voltaic generators for residential applications. In fact,by halving the power processing steps, the power losses can be considerably reduced if compared with those of a two stage configuration. However, single stage power conditioners are generally unable to boost the voltage of the PV modules, therefore, they feature a narrower input voltage range. A new approach to design a power conditioner for grid connected PV plants for residential applications is presented in this paper. It is based on the series connection between a buck-boost converter,and the PV array. According to such an approach, the buck-boost converter processes only a fraction of the inverter input power, while always operating in conditions of high efficiency. Experimental tests show that the proposed solution features an efficiency level very close to that of a single stage power conditioner, but owns a voltage boosting capability, similar to that of a two stage configuration.

This paper presents a general design methodology to optimally select the ratings of step-up transformers for grid connected Wind Turbine Generators on the basis of the statistical distribution of the wind energy and the mathematical model of the plant. The methodology exploits a probabilistic approach based on the evaluation of the so called LPPP (Loss of Produced Power Probability) index. The Internal Rate of Return (IRR) and the Discount Payback Period (PBP) can be computed from the results of the LPPP analysis and exploited to detect the most advantageous solution.

Step-up transformers are exploited to connect large PV plants to the utility network, their sizing being often accomplished only taking into account the PV plant peak power. In the present paper a general design methodology is proposed to optimally select the size of these transformers on the basis of the statistical distribution of the solar irradiation in the selected site and the mathematical model of the plant. It is based on a probabilistic approach based on the evaluation of the so called LPPP (Loss of Produced Power Probability) index. Taking into account full life costs the proposed approach is exploited to find the optimal transformer size for a grid connected 2 MW PV plant located in different geographical sites. Moreover, the effect of the introduction of energy storage systems in the PV plant is also evaluated.

A major shortcoming in the exploitation of renewable energy sources relies in the effective power availability, that depends from the variability of the primary energy resource over the time. Because of the variability and unpredictability of primary power both photovoltaic arrays and wind turbines cannot ensure the minimum level of power continuity required to supply in island mode a generic set of residential loads. Therefore, they must be complemented with suitable energy storage devices to form a hybrid power generation system. The design of a hybrid generation system including energy storage devices is a quite complex task. A probabilistic design approach is then proposed in this paper based on the LPSP index. Such an approach is also used to detect the most advantageous combination of wind turbines, PV plant and energy storage system, for a stand-alone generator aimed to supply a small set of domestic loads.

Step-up transformers are used to connect large PV plants to the utility network, their sizing being often accomplished only taking into account the PV plant peak power. However, a largely unpredictable power injection on the main grid is obtained if a too large rated power is selected, leading to grid instabilities. This may result in frequent plant shutdowns, while requiring a remarkable reserve power to be provided by conventional generation systems. On the other hand, a too small transformer lead to the creation of a bottleneck, preventing an optimal exploitation of the solar energy. This situation becomes more complex if the introduction of an energy storage system is considered. In the present paper a design technique is proposed to optimally select the step-up transformer, either on conventional PV plants, either on PV plants with energy storage. It is based on the evaluation of initial and operating costs. Moreover, the effects of induced network instabilities are also considered. Taking into account full life costs optimal solutions have been detected according to the network power control capabilities for a 2 MW PV plant.

Small photo-Voltaic generators for residential applications are rapidly spreading all over the world in an effort to reduce polluting emissions. In this kind of applications the AC solar module concept has recently proven to be more advantageous than the conventional string architecture. According to the AC solar module concept, single PV modules are directly connected to the AC grid through a DC/DC converter and an inverter. However, in this case a periodical power unbalance is generated because the power drawn by a single-phase residential grid features a large ripple at twice the fundamental frequency, while PV modules generate a DC power. Such a power unbalance affects the Maximum Power Point Tracking and forces the system to operate under suboptimal conditions and is faced with the introduction of bulky electrolytic capacitors. In this paper a alternative approach is presented enabling a standard DC/DC converter to also act as a power ripple damper, without the introduction of extra power devices. A hybrid PWM/unfolder approach has been also developed to reduce the switching power losses of the inverter connecting the DC/DC converter to the grid.