Andrea Del Pizzo

Improvement of Energy Efficiency in Light Railway Vehicles Based on Power Management Control of Wayside Lithium-Ion Capacitor Storage

The paper suggests an energy management control strategy of wayside Li-ion capacitor (LiC) based energy storage for light railway vehicles (LRV). The installation of wayside supercapacitor (SC) storage devices, as widely recognized, allows the recovery of the braking energy for increasing the system efficiency as well as a better pantograph voltage profile. A new type of SC, LiC, interfaced with dc-interleaved converter has been presented. This technology has an energy density comparable to batteries and power density much higher than the batteries. The authors propose a control strategy based on the maximum kinetic energy recovery throughout braking operations of the running vehicles. The stored energy comes back to the vehicles during the accelerations. The strategy stays on the knowledge of the state of charge of LiC device and the actual vehicle speeds. In particular, the control algorithm evaluates, in real time, the actual value of LiC voltage and current references on the basis of the vehicles inertial forces and acceleration estimations, taking into account the power losses of the system. Experimental tests made on electromechanical simulator, equipped with a 136-V, 30.5-F LiC module, fully confirm the validity of the suggested control. Finally, experimental characterization of LiC module has been achieved.

An Optimized Control Technique of Cascaded H-bridge Multilevel Active Front-ends

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.

Maximum Power Point Tracking Algorithm for Grid­tied Photovoltaic Cascaded H­bridge Inverter

Abstract In this article, a maximum power point tracking algorithm properly adapted for a gridtied photovoltaic multi-level inverter is presented. The inverter structure is based on a singlephase cascaded Hbridge configuration, where each power cell is supplied by an individual photovoltaic panel. The dedicated maximum power point tracking algorithm is based on a suitable hysteresis band, which defines the proper boundaries for maximum power point tracking references to ensure both stable inverter operation and maximum photovoltaic power extraction. The inverter control method is a mixed staircase pulse-width modulation based on a sorting algorithm. Some experimental tests have been performed by using a laboratory prototype of a singlephase fivelevel photovoltaic cascaded Hbridge inverter, which is controlled by means of dSPACE realtime hardware platform (ds1006, dSPACE GmbH, Paderborn, Germany), where the control section is implemented on a field-programmable gate array (Xilinx Virtex5, Xilinx, Inc., San Jose, CA). The experimental results confirm that the proposed control is able to efficiently track the maximum power point while assuring good performance in terms of harmonic distortion and power factor in both standard and mismatch conditions.

A parameter estimation method for on-line failure detection in permanent magnet AC-brushless motors having current-dependent parameters

With reference to anisotropic permanent magnet (PM) brushless motors, the papers deals with a procedure for on-line identification of electrical parameters, based on the “recursive least square method”, designed for the cases of strong parameters variation depending on the operating condition. The identification procedure is superimposed to a conventional control diagram of PM AC-brushless drives (either torque-control or speed-control) and is really very simple. The results of this analysis can be used as identifiers of failure conditions in the drive; otherwise, during motor characterization on a test-bench, the method can be a simple instrument to map motor parameters in different operating conditions. The proposed technique is tested by means of numerical investigation on a motor whose electrical parameters have been off-line evaluated by experimental measurements and mapped in different operating conditions.

A precise torque and high efficiency control for Q-axis flux-based induction motor sensorless vector control system

This paper presents a sensorless vector control system for induction motors by taking into account iron loss, in which a flux-observer-based method is applied. Since the flux observer is constructed in a synchronously rotating reference frame with respect to the rotor flux of a current model and the iron loss resistance of parallel exiting circuit is used, the proposed system is very simple and the compensation of iron loss related to the operating frequency is directly realized while calculating rotor fluxes and slip frequency. The accuracies of estimated torque and speed are improved. Furthermore, a high efficiency control method that minimizes the loss is proposed. The effectiveness of the proposed system has been verified by digital simulation and experimentation

FPGA implementation of an adaptive modulation method for a three-phase grid-tied PV CHB inverter

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.

Development issues of a Neural observer-based and fault-adaptive sensorless strategy for a multiphase BLDC motor

In this paper there will be presented basically two main subjects: the development procedure of a particular fault-adaptive multiphase sensorless strategy, based on Neural techniques, and the design issues involved by the fault-detection and isolation stages included in the proposed sensorless method. The proposed strategy is particularly suitable to be applied for the implementation of a cheap additional redundancy feature in order to augment the still existing fault-tolerant capabilities of some multiphase drives employed in safety-critical applications. In particular this unusual sensorless strategy is based on a back-EMF observer plus a proper set of coordinate transformations and possesses reconfiguration capabilities with respect to the occurrence of some certain classes of phase faults, gained through the use of a specific fault-adaptation mechanism. At first, the developmental steps of the fault-adaptive strategy will be described in detail after a preliminary motor modeling section, while, in a second step, the design issues linked with the fault-detection and remedial stages will be deeper investigated. Detailed simulation results will be shown at the end to validate the fault-adaptive properties of the proposed multiphase sensorless strategy.

A method for “design to range” energy storage systems in catenary free operations of light railway vehicles

The paper deals with line-disconnected operations of light railways vehicles using energy storage systems. In particular the suitability of on-board supercapacitors is investigated with reference to trams running along urban paths in catenary-free mode. Several tests on a real urban vehicle are presented in order to enable the evaluation of the losses in the different sections of the on-board power conversion system. These experimental data are used to estimate with good approximation the energy required for autonomous operations. A methodology called design to range is presented for properly sizing the super-capacitors bank needed to overcome different assigned distances with different road slopes.

A simplified speed-sensorless vector control for induction motor

From the viewpoint of miniaturization and cost reduction, sensor-less vector control systems without using an encoder have been proposed in many papers. We proposed a simplified method which estimates the rotor position using the d-axis voltage without using observer and controls motor speed using the d-axis voltage too. In order to verify the effectiveness of the proposed method, we have performed stability analysis and experiment. The results are discussed in this paper.

Model predictive control for PMSM with flux-current nonlinear maps

Typical operating conditions of permanent magnet synchronous motors correspond to nonlinear relationships between fluxes and currents. The determination of equivalent motor parameters is a non trivial task and can be critical for the design of motor controllers, which is typically based on a mathematical model. In this paper an experimental method to determine the flux-current nonlinear maps and a model based approach to implement a predictive controller capable to deal with such nonlinearities is presented. Numerical results show that the optimization technique is able to provide the maximum torque per ampere tracking.