Salvatore De Caro

Bio: Salvatore De Caro is an academic researcher from University of Messina. The author has contributed to research in topics: Inverter & Pulse-width modulation. The author has an hindex of 8, co-authored 24 publications receiving 172 citations.

An Open-End Winding Motor Approach to Mitigate the Phase Voltage Distortion on Multilevel Inverters

Abstract: 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.

An Optimal Current Control Strategy for Asymmetrical Hybrid Multilevel Inverters

Abstract: 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.

Improved space-vector modulation technique for common mode currents reduction

Abstract: Modified space-vector modulations (MSVMs) that reduce the variations of common mode voltage (CMV) for decreasing common mode currents (CMCs) are a low cost interesting approach. Unfortunately the lack of full utilisation of the DC bus voltage is a severe drawback that can limit the exploitation of such modulation techniques, unless special overmodulation methods are adopted. In this study, some solutions are presented that make a trade-off between the DC bus voltage exploitation and CMCs reduction and make MSVMs appealing to most electrical drives on the market. Furthermore, the influence of dead time in CMV generation is considered thus modifying the switching patterns according to the sign of the load currents. Experimental results are presented in order to confirm the feasibility of the proposed approach.

Rotor Flux Position Correction and Parameters Estimation on Sensorless Multiple Induction Motors Drives

Abstract: 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.

Multi-Level Open End Windings Multi-Motor Drives

Abstract: 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.

Stator and Rotor Flux Based Deadbeat Direct Torque Control of Induction Machines. Revision 1

Abstract: A new deadbeat type of direct torque control is proposed, analyzed and experimentally verified in this paper. The control is based on stator and rotor flux as state variables. This choice of state variables allows a graphical representation which is transparent and insightful. The graphical solution shows the effects of realistic considerations such as voltage and current limits. A position and speed sensorless implementation of the control, based on the self-sensing signal injection technique, is also demonstrated experimentally for low speed operation. The paper first develops the new, deadbeat DTC methodology and graphical representation of the new algorithm. It then evaluates feasibility via simulation and experimentally demonstrates performance of the new method with a laboratory prototype including the sensorless methods.

Review on pulse-width modulation strategies for common-mode voltage reduction in three-phase voltage-source inverters

Abstract: With wide application of inverters in modern industry, common-mode voltage (CMV) problems invoked severe negative effects. Hardware and software solutions have been proposed to reduce the CMV. Compared with hardware CMV mitigation solutions, software strategies based on pulse-width modulation (PWM) modifications have aroused widespread attention for their cost-effective and control flexible advantages. Up to date, various reduced CMV PWM (RCMV-PWM) strategies have been reported, such as active zero state PWM, remote state PWM, near state PWM, phase-shifted carrier PWM, carrier peak position modulation and so on. For convenience of understanding and utilising the existed RCMV-PWM strategies, this study conducts a review on this topic. According to the principle of CMV reduction algorithms, the study divides the reported RCMV-PWM strategies into three different categories. It also presents comparisons of CMV reduction techniques and output performances (like CMV value, output ripple and linearity range) between different strategies. Meanwhile, CMV suppression principles, problems in implementation and improvements of each technique are described in detail. Moreover, the inherent characteristics and development tendencies of the RCMV-PWM techniques are discussed so as to offer reference for further research.

A Single-Phase Grid-Connected Inverter with a Power Decoupling Function

Abstract: This paper presents a single-phase grid connected inverter with a power decoupling circuit. In the single-phase grid connected inverter, it is well known that a power pulsation with twice the grid frequency is contained in the input power. In a conventional inverter, electrolytic capacitors with large capacitance have been used in order to smooth the DC voltage. However, lifetime of those capacitors is shortened by the power pulsation with twice grid frequency. The authors have been studied a active power decoupling method that reduce the pulsating power on the input DC bus line, this enables to transfer the ripple energy appeared on the input DC capacitors into the energy in a small film capacitor on the additional circuit. Hence, extension of the lifetime of the inverter can be expected because the small film capacitor substitutes for the large electrolytic capacitors. Finally, simulation and experimental results are discussed.

A single-phase grid-connected inverter with power decoupling function

Abstract: This paper presents a single-phase grid connected inverter with a power decoupling circuit. In the single-phase grid connected inverter, it is well known that a power pulsation with twice the grid frequency is contained in the input power. In a conventional inverter, electrolytic capacitors with large capacitance have been used in order to smooth the DC voltage. However, lifetime of those capacitors is shortened by the power pulsation with twice grid frequency. The authors have been studied a active power decoupling (APD) method that reduce the pulsating power on the input DC bus line, this enables to transfer the ripple energy appeared on the input DC capacitors into the energy in a small film capacitor on the additional circuit. Hence, extension of the lifetime of the inverter can be expected because the small film capacitor substitutes for the large electrolytic capacitors. Effectiveness of the proposed method is confirmed through simulation and experimental results.

The Optimized-String Dynamic Photovoltaic Array

Abstract: This paper presents a novel system for producing the optimum power output from photovoltaic (PV) arrays using dynamic cell reconfiguration. The proposed approach is the first in the literature that creates strings using individual substrings that have been characterized and categorized ensuring maximum power extraction for a given irradiance profile. This optimized and decentralized PV architecture can produce significantly more power than a static equivalent (by an average of 22.6%) and also outperforms the sophisticated alternative known as an irradiance equalized dynamic photovoltaic array (IEq-DPVA) by an average of 13.7% for the relevant tests carried out. This paper identifies the hardware requirements to produce such a system and it describes an algorithm that performs the optimized-string reconfiguration strategy. Finally, a simulator programmed in MATLAB is used to compare the performance of the optimized-string DPVA against an IEq-DPVA in a series of flexibility tests.