The paper proposes a modelling approach and an optimization strategy to exploit a third harmonic current injection for the torque enhancement in multiphase isotropic PMSMs with non-sinusoidal back-EMFs. The modelling approach is based on a proper vector space decomposition and on the associated rotational transformation, aimed to properly select a set of stator current space vectors to be controlled. It is presented for a generic (i.e. asymmetrical, with an arbitrary angular shift) winding configuration. The injection strategy is related to the choice of a constant synchronous current set, aimed at minimizing the average stator winding losses for a given reference torque by using the 1st and the 3rd spatial harmonics of the air-gap flux density. The optimal solution has been found analytically and has been developed in detail for a selected set of asymmetrical winding configurations. Both the numerical and experimental results are in good agreement with the theoretical analysis.

European energy policy guidelines recognise renewable energy sources the main mean to contrast the rapid fossil fuels depletion and the related global warming. Marine energy source represents an attractive and inexhaustible reservoir from which to draw. One of the major difficulties in integrating sea wave generation systems or equivalently wave energy converters (WECs) with existing electrical systems is the management of their generation intermittency. This is essentially due to the inherent nature of the sea wave source. Energy storage represents an effective enabling technology for mitigating such an effect. To this aim, this study proposes an efficient control strategy for embedded floating buoy generation systems with energy storage technologies in order to regularise the injected grid power while minimising the contractual power established by the distribution system operator. The control strategy has been tested numerically on a grid connected DC microgrid formed by a DC bus at which a floating buoy generation system is interfaced with an energy storage system, supercapacitors‐based, having the purpose of smoothing the natural power fluctuations of the WEC.

This work presents a modelling approach and a control strategy for a multiphase surface mounted Permanent Magnet Synchronous Machine (PMSM) drive. The mathematical model is completely general with respect to the machine parameters and to the winding configuration. It also intrinsically considers the effects of eventual constraints for the phase currents, generated from the electrical connections among the phase windings or resulting from faults. The current controller is entirely formalized in the phase variables domain. It is based on a pseudo-inverse decoupling algorithm and on a linear decoupled controller. The current references are computed by means of a Maximum-Torque-Per-Ampere (MTPA) strategy, which can be also easily adapted for torque sharing purposes. The proposed controller requires minimum changes with respect to system reconfigurations or parameters variations and, therefore, it is suited both for healthy and for faulty operations. An extensive set of experimental results has been conducted to validate the proposed approach in several testing scenarios.

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.

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.

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.