• Energy Research

The paper deals with a fuzzy logic based strategy managing the power flows in an hybrid generation plant. Such a plant works in island mode and is composed of: a wind turbine, a photovoltaic generator and a fuel cell/electrolyzer energy storage system. The performances of the proposed strategy are evaluated by simulation in different operating conditions. To this purpose some performance indexes are considered, such as: the frequency deviation, the stability of the DC bus voltage and the AC voltage total harmonic distortion. Simulation results confirm the effectiveness of the proposed power management strategy, providing the ground for the practical realization of a fuzzy logic based control system. Moreover the efficiency of the developed fuzzy logic controller is compared to that of a more conventional controller taking into the fuel cell H 2 consumption, the amount of H 2 generated from the Electrolyzer and the final battery state of charge (SOC).

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.

A multi-level open-end winding converter topology for multiple-motor drives is presented featuring a main multi-level inverter processing the power delivered to the motors and an active filter based on an auxiliary two-level inverter. The main inverter operates at the fundamental frequency in order to achieve low switching power losses, while the active filter is Pulse Width Modulation (PWM) operated to suitably shape the motor currents. The proposed configuration features less phase current distortion than conventional multi-level inverters operating at the fundamental frequency, while achieving a higher efficiency compared to PWM multi-level inverters. Experimental results confirm the effectiveness of such a configuration on both multiple motors-single converter and multiple motor-multiple converter drives.

The paper presents a self-sensing control technique for a special type of multilevel motor drive featuring an Open-end Winding Permanent-Magnet Synchronous Motor fed on one side by a main multilevel inverter (MLI) and on the other side by an auxiliary two-level inverter (TLI). In order to minimize the power losses, the MLI manages the machine active power operating at a low-switching frequency. The TLI instead acts as an active power filter and operates at a higher switching frequency and a lower DC-Bus voltage than the MLI. The current control task is shared between the two inverters, as a predictive action is exerted by the MLI, while a feedback action is accomplished by the TLI. Common sensorless rotor position estimation techniques cannot be straightforwardly applied on such a system, due to the particular drive structure. Therefore, a specific technique has been carried out, able to ensure satisfactory efficiency and control performance in all the operating speed ranges by optimally exploiting the different features of the two inverters. Simulation and experimental results confirm the effectiveness of the proposed approach.

The development and the validation of an averaged-value mathematical model of an asymmetrical hybrid multi-level rectifier is presented in this work. Such a rectifier is composed of a three-level T-type unidirectional rectifier and of a two-level inverter connected to an open-end winding electrical machine. The T-type rectifier, which supplies the load, operates at quite a low switching frequency in order to minimize inverter power losses. The two-level inverter is instead driven by a standard sinusoidal pulse width modulation (SPWM) technique to suitably shape the input current. The two-level inverter also plays a key role in actively balancing the voltage across the DC bus capacitors of the T-type rectifier, making unnecessary additional circuits. Such an asymmetrical structure achieves a higher efficiency compared to conventional PWM multilevel rectifiers, even considering extra power losses due to the auxiliary inverter. In spite of its advantageous features, the asymmetrical hybrid multi-level rectifier topology is a quite complex system, which requires suitable mathematical tools for control and optimization purposes. This paper intends to be a step in this direction by deriving an averaged-value mathematical model of the whole system, which is validated through comparison with other modeling approaches and experimental results. The paper is mainly focused on applications in the field of electrical power generation; however, the converter structure can be also exploited in a variety of grid-connected applications by replacing the generator with a transformer featuring an open-end secondary winding arrangement.

Abstract 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.

The problem of analysing harmonic and interharmonic distortion in multiconverter industrial power systems is considered. An useful updating of the iterative harmonic analysis algorithm to include interharmonics, based on automated EMTP simulations of nonlinear loads, is presented and its capabilities are discussed, also in the perspective of utilisation in a distributed computing environment.

ABSTRACT The paper presents a simple technique for correctly and fastly tuning the slip gain in Indirect Field Oriented Control drives. To this aim no other transducers than the tachogenerator, usually included in such drives, are needed, as the tuning operation is performed by processing the effects of a suitable test signal injected in the system. The proposed approach can be used either for on-line retuning of working drives, either for the initial tuning of new installed drives. Simulation and experimental tests show that the procedure is effective and does not Interfere with normal operations of the drive.