Pietro Tricoli

Speed-Based State-of-Charge Tracking Control for Metro Trains With Onboard Supercapacitors

This paper suggests a novel energy management control algorithm for metro trains based on speed measurement and acceleration estimation. The aim of the control is to recover in a supercapacitor (SC) storage device the maximum energy regenerated during train electrical braking and to limit the contact line peak current. The energy management control is integrated with the motor drive control, since discharge and charge of SC are connected to motoring and braking operations of the train. The algorithm is based on two nested loops on voltage and current of SC. The voltage and current references are calculated on the basis of the estimation of the train inertial force and acceleration, taking into account the power losses of the system. A simplified mathematical model of the whole electrical drive has been developed and the main features of the control strategy have been presented. Numerical simulations show the efficacy of suggested control and the energy saving obtained for metro trains. Experimental tests made on an electromechanical simulator fully confirm theoretical results.

Current Source Topology for Wind Turbines With Decreased Mains Current Harmonics, Further Reducible via Functional Minimization

The paper presents a current-source inverter topology tailored for large multi-megawatt wind turbines. The proposed topology can inherently benefit from the distance between the generator and the mains because the consequent length and possible layout of the power cables may enable the realization of a significant portion of the dc-link inductance. In order to improve the efficiency and to allow the possible utilization of rugged inexpensive thyristors, pulsewidth modulation (PWM) modulation is not used. Unity fundamental power factor at the mains is guaranteed at any load condition while the fifth and seventh harmonics of the mains line currents can be reduced by proper system design at a desired turbine speed, considered most suitable for its operation. Further harmonic reduction is achievable through an active filter controlled via a newly proposed PWM methodology that does not belong either to a carrier-based or to a classical space vector modulation approach. Such a controller relies on a real-time minimization of a proper functional and is capable of implementing true-feedback current regulation. Experimental results from a 10 kW prototype are presented and validate the developed analytical computations.

Metro trains equipped onboard with supercapacitors: A control technique for energy saving

The paper suggests a control technique for improving energy saving in metropolitan trains equipped by onboard supercapacitors. On the basis of the typical duty-cycle of a metro-train, the supercapacitor system has been sized with reference to an energetic criterion that tries to limit overhead line current and, consequently, voltage drop at the train pantograph. The control algorithm is then based on a changeover scheme that properly manage the charge and discharge of supercapacitors in order to keep constant the line current during acceleration, coasting and braking of the train. Experimental results on a scale model, reproducing forces and inertias of a real railroad vehicle, validate completely both the sizing procedure and the control technique proposed.

Design and Control of Modular Multilevel Converters for Battery Electric Vehicles

New advanced power conversion systems play an essential role in the extension of range and life of batteries. This paper proposes a new modular multilevel converter with embedded electrochemical cells that achieves very low cell unbalancing without traditional balancing circuits and a negligible harmonic content of the output currents. In this new topology, the cells are connected in series by means of half-bridge converters, allowing high flexibility for the discharge and recharge of the battery. The converter features a cell balancing control that operates on each individual arm of the converter to equalize the state of charge of the cells. The paper shows that the proposed control does not affect the symmetry of the three-phase voltage output, even for significantly unbalanced cells. The viability of the proposed converter for battery electric vehicles and the effectiveness of the cell balancing control are confirmed by numerical simulations and experiments on a kilowatt-size prototype.

An efficient architecture of a PV plant for ancillary service supplying

The use of Distributed Generation (DG) units for grid ancillary services, in particular for smart grid applications, has been deeply considered in the last few years. It has been demonstrated that DG units can produce not only active power, which is obviously the principal role, but also they can provide ancillary services such as: voltage control, spinning reserve, backup supply, harmonic compensation, peak shaving and others. Recently, the use of Photovoltaic (PV) DG units has been proposed for reactive power ancillary service production; the concept has been fully demonstrated, highlighting the potentiality of PV DG units as ancillary service provider. In this paper, some improvements are proposed for a PV DG unit as provider of ancillary services in terms of single components modeling and global optimization of the system. The capability of a PV plant of generating both active and reactive power is demonstrated.

Power Flow Control Strategy for Electric Vehicles with Renewable Energy Sources

The paper analyses the benefits given by a compound storage system with batteries and supercapacitors on board of road electrical vehicles supplied by fuel cells. A control strategy for the management of the energy is developed for the maximization of the vehicle autonomy and for the increase of the electrochemical battery life. The controller is based on two finite state machines and it is implemented on the DC/DC converters that interface fuel cells and supercapacitors to the batteries. Experimental tests made on a sample electrical drive fully validate the effectiveness of the suggested control technique.

Control of High-Energy High-Power Densities Storage Devices by Li-ion Battery and Supercapacitor for Fuel Cell/Photovoltaic Hybrid Power Plant for Autonomous System Applications

This study presents an energy management approach for a hybrid energy system comprised of a photovoltaic (PV) array and a polymer electrolyte membrane fuel cell (PEMFC). Two storage devices [a Li-ion battery module and a supercapacitor (SC) bank] are used in the proposed structure as a high-energy high-power density storage device. Multisegment converters for the PV, fuel cell (FC), battery, and SC are proposed for grid-independent applications. Nonlinear differential flatness-based fuzzy logic control for dc-bus voltage stabilization for power plant is investigated. To validate the control approach, a hardware system is realized with analog circuits for the PV, FC, battery, and SC current control loops (inner controller loops), and with numerical calculation (dSPACE) for the external energy control loop. Experimental results with small-scale devices [a PV array (800 W, 31 A), a PEMFC (1200 W, 46 A), a Li-ion battery module (11.6 Ah, 24 V), and an SC bank (100 F, 32 V)] demonstrate the excellent energy-management scheme during load cycles.

A sample application of supercapacitor storage systems for suburban transit

The advance in energy storage technologies allows to improve significantly the performances of electrified light transportation systems. This is aligned with the massive requirement of competitiveness compared to other transportation technologies in terms of sustainable energy and high reduction of environmental impact. The installation of stationary storage devices, as widely recognized, allows the recovery of the braking energy for increasing the energy efficiency as well as lower line voltage drops. In the paper, the storage system under investigation is based upon a bidirectional dc-dc converter with supercapacitors, characterized by high power density. The main parameters of the storage system are determined by employing an optimization technique, which in a quite general way is capable of taking into account contemporaneously several aspects in an integrated manner. Some simulations of lines of a suburban railways in Southern Italy managed by Sepsa Company are presented, pointing out how supercapacitors can be practically designed with the proposed technique.

High Efficiency Wind Generators with Variable Speed Dual-Excited Synchronous Machines

Wind power seem to be one of the most interesting technology for electrical energy generation by renewable sources. It is necessary to set up carefully the wind turbine taking into account that the wind speed is variable with the time and there is a fluctuation of power output of wind energy conversion systems. There are many technical solutions adopted to increase the system efficiency by utilizing proper generators. In the paper the case of variable speed dual-excited synchronous machine is investigated. For its control possibilities, this machine is particularly suitable for variable-speed constant frequency applications like wind power generation systems. In the paper, after presenting the mathematical model of the wind turbine and the generator, a control technique for output power maximization is proposed. Results obtained by numerical simulations are discussed in the paper to demonstrate that using the proposed control algorithm it is possible to achieve a significant increment on the power generated in comparison with that obtained using an unregulated induction machine.

Monitoring, Diagnosis, and Power Forecasting for Photovoltaic Fields: A Review

A wide literature review of recent advance on monitoring, diagnosis, and power forecasting for photovoltaic systems is presented in this paper. Research contributions are classified into the following five macroareas: (i) electrical methods, covering monitoring/diagnosis techniques based on the direct measurement of electrical parameters, carried out, respectively, at array level, single string level, and single panel level with special consideration to data transmission methods; (ii) data analysis based on artificial intelligence; (iii) power forecasting, intended as the ability to evaluate the producible power of solar systems, with emphasis on temporal horizons of specific applications; (iv) thermal analysis, mostly with reference to thermal images captured by means of unmanned aerial vehicles; (v) power converter reliability especially focused on residual lifetime estimation. The literature survey has been limited, with some exceptions, to papers published during the last five years to focus mainly on recent developments.