C. Boccaletti

Fault-Tolerant Strategy for a Photovoltaic DC--DC Converter

The photovoltaic (PV) technology has a small impact on the environment and is suitable for a wide range of applications. The main barrier for a more extensive implementation has been the reliability, mainly related to the power converters. According to this consideration, this paper presents an open-circuit fault diagnosis and fault-tolerant scheme for a three-level boost converter in a PV power system using batteries as storage devices. The fault diagnostic method takes advantage only of the control variables used for maximum power point tracking and output dc-link capacitor voltage balance. The fault-tolerant strategy requires only a few components added to the original three-level boost converter, so that, under an open-circuit power switch fault, it can be partly reconfigured into a two-level boost converter ensuring battery energy supply. Experimental results verify the proposed fault diagnostic method and reconfiguration for fault-tolerant operation.

Open-Circuit Fault Diagnosis in Interleaved DC–DC Converters

Interleaved dc-dc converters have been widely applied, because of their benefits related to efficiency, size, thermal management, modularity, and output current ripple cancellation. These converters present an enhanced fault tolerance capability, but an open-circuit fault can leads to ripple beyond load requirements. This paper presents a fault-diagnostic method for interleaved dc-dc converters using only the dc-link current derivative sign features. The dc-link current derivative is thoroughly studied for both healthy and faulty modes. Its sign variation during different time intervals defined by the number of switches in conduction mode contains important information for open-circuit fault detection. The presented method is robust to transients and current imbalance between phases and no additional sensors are required. A photovoltaic system application is presented to validate this method.

Innovative solutions for stand alone system powering

In the paper, possible hybrid configurations of low power stand alone systems based on renewable energy sources (RES) and alternative sources, suitable for applications in remote areas not connected to the grid such as radio base stations for mobile phone communications, are described and compared. As practical case, different alternative solutions for the powering of a radio base station (RBS) are analysed: the wind-solar technology including also a PEM fuel cell, supplying a conventional refrigeration system or an absorption system for the equipment cooling; a thermally insulated pre-fabricated system that uses the natural air circulation for the equipment cooling.

Rotor bars breakage in railway traction squirrel cage induction motors and diagnosis by MCSA technique Part II : Theoretical arrangements for fault-related current sidebands

In a companion paper (Part I) the bar breakages for a 1.13 MW induction motor used in high speed railway traction drives were studied, by simulating the whole system (converter + motor) and by analyzing frequencies and amplitudes of current sidebands, for various loads (both active and inertial) and with increasing fault severity. It was recognized that faults can be characterized by (1-2s)f sideband, but results vary with load torque and drive inertia. Other sidebands appear less dependent from these disturbs, like (5+2s)f. Unfortunately, no works presented simple and general formulas about sidebands. In this paper, theoretical formulations for computation and prediction of rotor fault-related sideband frequencies and amplitudes are given, aiming to obtain relations useful for diagnostic purposes (fault severity assessment by MCSA), and by using Part I as a case-study. A decomposition by multiphase symmetrical components is performed, taking in account space harmonics. Formulas for (1-2s)f sideband amplitude are carried out, extendable to many other sidebands.

Deterministic and stochastic optimisation algorithms in conventional design of axial flux PM machines

In this paper the authors analyse the algorithms and the relevant numerical optimisation techniques for the design of magnetic power devices, with reference to axial flux PM machines. Some numerical optimisation algorithms are briefly reviewed, such as the simplex method, the Powell method, the genetic algorithms, and their applications to the design technique are described. Objective functions to be minimised are discussed, such as mean torque, power losses, total weight. Numerical results allowed to evaluate the efficiency and the reliability of each method

A Power Loss Measurement Method Applied to Static Power Converters

It is very important to be able to predict the amount of the power losses related to the power switches with good accuracy in the design phase of power converters since a poor estimation can considerably extend the time needed for the development of the devices. This paper illustrates a method to calculate with satisfactory accuracy the power losses in power converters, based on the measured switching currents and voltages of semiconductor devices. It represents a further development and an improvement of previous studies and includes an automatic compensation of voltage and current offsets. Experimental measurements of the conduction voltage drops of insulated-gate bipolar transistors and diodes have been performed and compared with manufacturers data to validate the method. The method was then applied to a power converter chosen as representative, using the experimental data as input. The results are reported and discussed.

Power conditioning and energy management in a renewable energy based hybrid system for telecommunications

Renewable energy based hybrid systems are a practical option to supply telecommunications equipment in remote locations. By combining photovoltaic and wind generators with an energy storage structure, it is shown how such system can simultaneously comply with the load strict requirements, maximize the output of each generator and even promote the optimized operation of batteries by including supercapacitors. Different proper controls that maximize the output of each generator are described and simulations of dynamic transients of the entire renewable energy based hybrid system are presented.

Efficiency analysis of power converters for urban wind turbine applications

The use of wind energy in urban contexts, for a number of small power applications, is of greater and greater interest. The urban environment is characterised by multidirectional winds with a wide speed range, therefore it is necessary that the generation system is capable of delivering power in a wide range of operating conditions. For this reason it is of great interest to determine which power converter is more suitable for a small urban wind application. In this paper the power losses of three of the most used power converter topologies are calculated. Also the output power and the efficiency are compared in a wide range of the wind turbine operation including the extreme overspeed range.

Converter Power Loss Analysis in a Fault-Tolerant Permanent-Magnet Synchronous Motor Drive

Power converters are complex devices subject to failures that can lead to undesired stops. For this reason, many fault-tolerant topologies and strategies have been deeply studied, mainly focusing on improving the electromechanical behavior of the reconfigured drive after the fault. However, it is also very important to evaluate the possible increase of power losses. In this paper, a power loss analysis is performed on a current-controlled three-phase inverter supplying a permanent-magnet synchronous motor (just chosen as an example), for all the operating modes, starting from the fault occurrence until the faulty operation mode is established. This is particularly important because the effectiveness of a fault-tolerant control strategy depends on the possibility to maintain a continuous operation. The latter is ensured only if there is no such increment of the losses that the survival of the component is at risk. The simulations are validated by means of experimental tests, and the results are discussed. The method can be easily applied to other topologies and reconfiguration strategies.

Electrical storage systems in cogeneration plants based on the solar energy source

The intermittent nature of most renewable energy sources makes the choice of appropriate storage systems crucial to ensure the required availability in standalone power systems. Moreover, when the electrical load is characterised by large variations in a short time, the lifetime of conventional batteries can be seriously affected, and the maintenance costs increase accordingly. In the paper, the complete dynamic model of a sawmill supplied by a standalone photovoltaic-thermal (PV-T) power plant is developed, and the case in which the electrical storage system consists only of conventional batteries is compared with the case in which a supercapacitor bank is included. Performance and costs of both cases are discussed.