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In this article, a current control algorithm is conceived for converting solar dc power into ac power of high-quality. This conversion is based only on a dc-ac converter, avoiding the use of two stage converter. The proposed algorithm is founded on tracking the maximum power point which ensures controlling the electrical power exchanged with the grid. To assure a good dynamics and reduce the control errors, a proportional resonant controllers are utilized and a self-tuning founded on particle swarm optimization is utilized. The proposal strategy goodness is verified by means of numerical simulations.

The paper deals with a full sliding mode approach for induction motor drives direct torque and flux control. The proposed solution is composed by an integral sliding-mode control and by a speed-sensorless sliding mode observer. The suggested Integral Sliding-Mode Direct Torque Control (ISMDTC) is formulated in the stator flux reference frame, without employing current regulators. The adopted sliding mode observer provides stator-flux and torque estimation, without rotor-speed adaptation. The numerical results show that the ISMDTC maintains the robustness of the sliding controller, reducing the chattering during the steady state. Moreover, it consents to achieve similar performance like more complex second-order SMC offering more simple implementation. The ISMDTC assures good accuracy and robustness to parameters deviations at low-speed operations as well as in all the operative range of the IM drives. For proving the goodness of the proposal the suggested control is also compared with a conventional DTC control.

The full electric/hybrid electric propulsion is nowadays a promising technology for the aircraft. The problems related to the electric flight are inherent the storage system sizing, the design of lightweight motors and the power electronics converters. In this paper is proposed a preliminary study about the on-board wiring system. In particular, the maximum power transferrable with the common aeronautic wires in a distributed propulsion system has been investigated.

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 paper deals with ball screw actuators used for the electric steering of nose landing gears in civil aircrafts. Design options and performance analyses are carried out with reference to actuators composed by ball screws coupled with two multi-stage axial-flux permanent magnet motors, which are fed by two separate inverters. A redundant configuration of the drives is developed in order to increase the availability of the steering service. Numerical analyses are carried out with reference to some significant operating conditions.

In this paper the control of a grid-tied PV (Photovoltaic) Cascaded H-bridge inverter is discussed. The operation principle of the considered circuit is analyzed and a particular attention is paid to the different modulation techniques well-suited for this configuration. Moreover, some critical implementation issues are addressed, while a fair comparison between the proposed modulation scheme and the Phase Shifted PWM (Pulse Width Modulation) is carried out. The adopted control strategy is based upon a sorting algorithm in order to modulate only one power cell (i.e. H-bridge) per sorting cycle while the others are in fixed state. This technique allows to reduce power switching losses, thus increasing overall system efficiency. The numerical results reported in the paper permit to confirm the feasibility of the proposed modulation strategy and the better performance with respect to PS-PWM in terms of power efficiency.

In this paper a solution is proposed for contra-rotating propellers in electric unmanned aerial vehicles. It is based on a direct drive system where the contra-rotating blades are directly fixed on the rotors of an axial-flux permanent magnet motor. The latter one is constituted by two external rotors and a single internal stator divided in two different sides. The study is focused on a 6 slots-4 poles three-phase motor and on a 10 slots-4 poles five-phase motor, characterized by single-layer armature windings. For each motor configuration some sets of motor sizes are found by using an automatic calculus procedure and by imposing suitable electrical, thermal and mechanical constraints.

This work deals with an optimal control strategy for a three-phase grid-tied photovoltaic (PV) cascade H-bridge inverter. The main challenge for the control of this system topology derives from the inherent power imbalance among the phases as well as from the different power levels of the H-bridge cells in each phase leg. The power imbalance among the phases is compensated by the injection of a proper zero-sequence voltage. The power distribution among the cells of each phase could be affected by uneven irradiance and temperature conditions of PVGs (PV Generators). This latter issue is addressed by means of an adaptive modulation method especially suited to manage unequal dc sources, while assuring stable circuit operation and maximizing the power extraction through a dedicated MPPT (Maximum Power Point Tracking) algorithm. The digital controller is developed and tested in Matlab/Simulink environment integrated with XSG (Xilinx System Generator), thus allowing an easy transfer on FPGA embedded in dSPACE real-time platform. Simulations and experimental results prove the validity of the proposed design and control approach.

This paper presents a control technique for smoothing voltage oscillations in the sub-modules of Modular Multilevel Converter during start-up operations of high-power medium-voltage induction motor drive. At steady-state, the power fluctuations in each sub-module at fundamental and 2 nd harmonic frequencies generate capacitor voltage oscillations which are much higher as the current frequency decreases and tend to infinite at zero frequency. This is a problem in variable speed drives, where very low frequency values are needed during start-up. The control injects a homopolar component of the converter output voltage and an alternative high frequency circulating current, whose magnitude is much higher than the induction motor one during start-up operations. A space vector modulation technique is used in the control implementation. A numerical investigation is carried out with reference to some relevant cases-study in order to show the validity of the proposed control which allows an effective reduction of voltage oscillations on the dc-link capacitors of the different converter sub-modules.

In this paper a power converter based on a modular multilevel topology is discussed. The Modular Multilevel Converter (MMC) is one of the emerging technology for high- or medium-voltage transformerless power conversion. The paper presents a space vector modulation technique developed for a MMC with arbitrary number of voltage levels; the presented technique integrates the modulation of the homopolar component of the converter output voltage. A numerical investigation is carried out with reference to some relevant cases-study in order to show the validity of the proposed modulation technique which allows an effective control of the converter recirculating currents.

In this paper an analysis of a power converter based on a modular multilevel topology is discussed. A mathematical model of the MMC is developed in order to evaluate its dynamic behavior and to better understand the incidence of the circulating current phenomenon which could compromise converter performance in variable speed drive applications. In fact, if such problem is not properly addressed reliability problems arise.

In the paper some of the battery models proposed in literature are analysed in order to predict the battery performance and, then, make sure that the Battery Management System (BMS) that is a key component to check and control the status of the batteries within their specified safe operating conditions, works in best conditions.

In the last years the interest towards Power Electronic Transformers (PET) is increasing. These new conversion apparatuses perform either voltage transformation or power quality functions, using power electronics both on primary and secondary sides of a transformer operating at medium frequency. In the technical literature are proposed several circuital configurations, with different control strategies. However these are not exhaustive yet, especially if is considered that PET can be utilized in a lot of different fields of application. Simplicity, effectiveness and high-resolution of the control are important aspects which can strongly improve performance of PETs. The paper presents an overview of the main topologies of converters for PET with a Medium Frequency (MF) transformer, and the control strategies are analyzed.

An high performance control technique of dc-brushless drives is presented in the paper, with the aim to considerably reduce current and torque ripples. The proposed control algorithms are very simple and are separately pointed out for “two phase on” and “three phase on” operations, i.e. either far or during the commutation of two consequent armature phases. They can be successfully used in those dc-brushless drives which uses permanent magnet motors with any arbitrary shape of the air-gap flux-density distribution generated by rotor magnets. A magnetically isotropic motor configuration can be considered with respect to the air-gap field generated by the armature m.m.f. The smoothing torque control procedure is a “current control technique” operating in two cascaded phases. As first step it evaluates the value of the instantaneous reference current able to reduce to zero the torque oscillations magnitude. Afterwards, a simple model-based predictive algorithm computes the voltage reference values for the PWM motor supplying inverter. As in many other applications, the voltage predictive control provides better performance than PI or hysteresis controller because more homogeneous results can be yield for low and high speed (or load) operating conditions. Some cases-study are numerically investigated in order to validate the proposed control technique.

With reference to medium-voltage grid-connection of large photovoltaic (PV) plants, the paper proposes and analyses a high performance solution based on a power electronic transformer (PET). It Includes dc-links and multilevel converters either in low-voltage or in high-voltage side, and a medium-frequency (MF) transformer. Together with the very reduced sizes of the whole conversion apparatus, an important feature of the proposed topology is the permitted presence of unbalanced voltages on the different dc-links corresponding to the partitions of the PV plant. This is enabled by the multilevel cascaded H-bridge configuration of the low-voltage side converter, in order to take into account the nonuniform distribution either of temperature or (mainly) of solar radiation on the different cells arrays, together with eventual different kind or age of used cells. another advantageous feature is the good level of power quality indexes on grid quantities, ensured by a multilevel NPC front-end: mainly low values of either harmonic distortion, or voltage and current dissymmetry. this occurs even if the commutation frequency of the switching devices of this converter is not high (1÷2 kHz). However, the paper is mainly focused on the control technique of the multilevel converters connected to the primary and secondary windings of the MF transformer, imposing multistep- or square-wave voltages. Some simple control algorithms are presented in order to maximize the power generated by every partition of the plant (also in unbalanced operations) together with the minimization of the joule losses of the central conversion unit in quasi-stationary operating conditions.

An optimized control of PWM voltage source rectifiers (VSR) is presented. First, in a multi-input look-up table the different converter voltage-vectors are ordered with respect to their aptitude to increase (or decrease) the active power, depending on the angular position of the input voltage vector. A simple procedure allows the quick selection of the most suitable converter-voltage which ensures the correct slope sign of both active and reactive power, in order to satisfy the respective reference values. A predictive procedure evaluates the application time of the selected voltage vector within the actual sampling interval, in order to keep the instantaneous active power inside prefixed hysteresis bands. The proposed algorithm quickly evaluates also the voltage vector to be applied in the remaining part of the sampling interval. Numerical investigations in some heavy operating conditions are carried out at a fixed average value of the switching frequency, especially with reference to current distortion and asymmetry.

The paper deals with active voltage source rectifiers (PWM-VSR) having multilevel cascaded H-bridge configuration. With reference to operations with unsymmetrical supply voltages and/or unbalanced three-phase loads, some optimized control strategies are presented and compared. Particular attention is devoted to the most effective control algorithm in terms of distortion of the input-currents and limitation of the line-current unbalancing. The algorithms are represented by a set of algebraic equations able to generate in a very simple way the actual reference values for the dynamic control of VSRs. Some heavy transient operations are analyzed in order to show the validity of the proposed techniques and the capability to limit negative influence on the line power-quality indexes by means of optimized control of cascaded H-bridge active front-ends.

The paper deals with some problems concerning fault analysis in multilevel V.S.I. converters. With reference to cascaded H-bridge topology, first the possible conditions of "single fault" are classified by analyzing the modification of output voltages when a generic power device is damaged ("short-circuited" or "definitely open"). Then a procedure for on-line quick identification of the corrupted device is explained. It is based only on output voltages and currents measurements and does not require additional sensors. The minimum number of measurements allowing fault identification is linked to the number of converter levels. Finally, failure adapted techniques of converter modulation are presented and simulation results are discussed with reference to some significant cases. These techniques have the aim to minimize the influence of the different faults on the service of the whole drive.

In the paper a mathematical model of multilevel PWM-rectifiers is pointed out. The model formulation is generalized to "m" voltage levels and is unified for neutral-point-clamped, cascaded-H-bridge, and flying-capacitors topologies. A modulation technique is described for active front-ends. Specific solutions are proposed for the different regions of the complex plane correspondent to the m-level structure of the converter. Instead of complex look-up tables, very simple relations are given in order to identify the region and to select the most effective modulation pattern. Some opportunities to conveniently use the intrinsic redundancy of the converter topology are described.

With reference to multilevel converters in cascaded H-bridge configuration, the paper presents a technique suitable to quickly identify fault conditions during normal operations. First a modulation technique generalized to m-level converters is synthetically illustrated in order to evidence the presence of different modulation patterns and the corresponding criteria of selection in normal operating conditions. Then, all the "single- fault" conditions are classified, evidencing symmetrical situations, and some consequences on the converter voltage- vector star are analysed. On this basis, a procedure is presented for on-line identification of the corrupted switching device and of the converter module where it is located. No additional sensors are requested, because the procedure is based only on the values of phase-voltages and currents already detected for the closed loop converter control. The fault identification is carried out in a few modulation intervals, also thanks to modifications automatically introduced in the modulation algorithm exploiting redundancies of different converter voltage vectors. Numerical results are presented with reference to some significant fault conditions in cascaded H-bridge inverter having an assigned number of voltage levels.

The paper is devoted to the investigation of a three-phase multilevel H-bridge PWM-Rectifier operating as a first stage of a back-to-back converter in high-power ac drives. First, a predictive control technique is described with reference to a 5-level converter. Starting from properly defined reference values, the algorithm pointed out allows the direct evaluation of the duty-cycles of all the voltage vectors involved in the VSR modulation. By means of the evaluated switching functions, at the end of every sampling interval the line-currents assume values practically equal to the imposed ones. Some unrestrictive hypotheses are introduced in order to efficaciously simplify the analytical expressions. As a second step, in the paper a specially designed modulation technique is shown. In addition to low values of dc-link voltage oscillations and of line-current distortion in steady-state operations together with high values of the power-factor, this modulation technique allows to keep balanced the different capacitor voltages, by properly using the intrinsic redundancy of the converter topology. Numerical results are presented with reference to some significant operative conditions in order to validate the theoretical considerations.