Francisco Javier Meca

FPGA-Based Implementation of a Predictive Current Controller for Power Converters

Predictive control is generating considerable interest when it comes to implementing current control strategies in power converters. Remarkable accuracy and fast dynamic response are its main characteristics. However, this technique is computationally demanding compared to classic control schemes. This is particularly true in multilevel converters, where several variables of the system such as currents, switching frequency and neutral-point voltage balancing, to name a few, are controlled simultaneously. An important issue is to reduce the delay between the variable sampling and the instant at which the switching state is applied to the converter. Although DSP-based implementations have been proven to be an effective solution, the parallel nature of predictive controllers better fits with the architecture of field-programmable gate array (FPGA) devices. This paper presents a new approach to the FPGA-based implementation of a predictive current controller for a multilevel converter. This approach also aims to reduce the average switching frequency and obtain neutral-point voltage balancing. The switching state is applied in the same sampling period in which the controlled variables are measured thereby enhancing the dynamic response of the system.

Optimum conditioning of PbSe photoconductive detectors in measurements without chopping

This paper analyses the most important sources of uncertainty in the circuitry of an infrared radiation measurement system without chopping based on PbSe photoconductive detectors. It studies the influence of the conditioning system on noise and thermal drift, proposing two optimum diagrams depending on the effect to be minimised. Finally, a study of the noise and drift in a complete circuit is carried out, demonstrating the effects generated by the circuitry which may limit the final precision of the system. The overall results obtained demonstrate that with a suitable design the undesired effects of the conditioning circuitry can be kept at acceptable levels for a good number of applications.

Calculation and optimisation of the maximum uncertainty in infrared temperature measurements taken in conditions of high uncertainty in the emissivity and environment radiation values

This paper develops a method that enables the most suitable range of wavelengths to be ascertained in which to take infrared temperature measurements of surfaces in the open air in conditions in which high uncertainty exists in the environmental radiation and emissivity values. The optimisation criterion adopted for the error is that of achieving the narrowest possible band of maximum uncertainty. The results demonstrate that it is possible to cancel out the solar radiation contribution to the maximum uncertainty present in the measurement whilst still working in short wavelengths where this radiation is very intense and, therefore, optimise the band of uncertainty produced by emissivity and environment radiation.

Infrared temperature measurement system using photoconductive PbSe sensors without radiation chopping

This paper proposes an infrared temperature measurement system based on a PbSe photoconductive sensor that enables a high quality measurement to be obtained without chopping the radiation. The main problems that arise from eliminating chopping are analysed and the solutions adopted in order to reduce their effect are described. The quality of the measurement obtained using the system is quantified for a real application and is compared with other contributions that are independent of whether radiation chopping is performed or not.

A Simple Thermal and Electrical Model of an Infrared Pyroelectric Detector Using Spice

This paper shows a complete description of a simple infrared pyroelectric detector model, using SPICE. Both thermal and electrical properties of the detector model have been implemented in order to simulate the detector response versus time and frequency for any radiation stimulus. The detector model has been designed to obtain Ý v and NEP. The effect of the material properties of the detector on its response has been studied. The parameters of the proposed model may be adjusted to the experimental response of the detector, although not all of its properties are known. From this adjustment a good approximation of those unknown properties is deduced. Good agreement has been found between simulated and measured results.

Stability issues of current controllers based on repetitive-based control and second order generalized integrators for active power filters

Starting from previous works [1], this paper analyzes the robustness and stability of two current controller schemes for shunt active power filters, based on repetitive controllers and proportional+resonant controllers using second order generalized integrators connected in parallel. Both controllers are well suited due to their optimum tracking and harmonic rejection capability. The objectives of this paper are: to present a brief description of both controllers, study their behavior under drifts in the value of the plant parameters and in the frequency, and also analyze the suitability of these controllers to work in a current control scheme when a nonlinear load is demanding asymmetric currents. Finally, some comparative results will be shown.

Black-box Identification for an auto-tuned current controller working with Voltage Source Converters connected to the grid through a LCL filter

This work proposes a novel method based on a prediction error minimization (PEM) algorithm to identify the discrete state-space model of a LCL filter which is used as interface between a Voltage Source Converter and the utility grid. This model is used to design directly a discrete state-space current control based on a servo controller. The so-obtained model makes easier the use of advanced control techniques as Linear Quadratic Regulators, state estimators, Robust Control, etc. The main advantage of using an identification process against to design the controller starting from the manufacturer data is that the control is not sensitive to modeled errors. The method can be applied to closed-loop systems, being suitable for adaptive control designs.

New MPPT algorithm for photovoltaic systems connected to NPC converters and optimized for large variations of solar radiation

This paper proposes a new MPPT algorithm (‘Maximum Power Point Tracker’) for photovoltaic panels (‘PV’) with NPC converters (‘Neutral Point Clamped’). One of the characteristic of this proposal is that it is not necessary to modify the voltage references in order to know the state of the MPP (‘Maximum Power Point’). The fundamentals are based on the use of the existing ripple in the NP (‘Neutral Point’) in the NPC converters. Given that the form of the ripple is known, it is possible to determine the power that is supplied by each maximum and minimum of the voltage ripple. The execution period of the algorithm does not depend on the time constant of the DC-bus, rather the frequency of the voltage ripple, which in the NPC converter is three-time the frequency of the grid.

Vigilance system in rails for train hot point temperatures during circulation

Wheels, hubs and brake discs in a train during its circulation are under mechanical strains that make its temperature increase above the environment temperature. Mechanical defects in those elements produce an excessive friction and, as a consequence of it, an important increment of its temperature in relation to normal values. Detecting these anomalies is essential to avoid accidents and it is performed by fixed systems located next to rails which make infrared temperature measurements of hot points and send them to a supervisory station that takes the proper steps. The paper introduces the most important problems which must be dealt with during the designing stage of the measurement system. It also explains the solutions taken by the authors in order to assure the minimum operative aims demanded by the application. These problems includes: the choice of the detector and measurement method, communication with the supervisory station, and the environment conditions. Finally, the research lines followed by the authors in order to improve and extend the systems capabilities are explained.

Main limitations in infrared temperature measurement of train hot points

Nowadays, in order to guarantee the security in passenger and goods railway transport, fixed systems located in rails are used to measure axles, wheels and brake discs temperatures during train circulation so that abnormally high temperatures as a result of a malfunction can be detected. Measurement systems in this kind of application may be affected by different uncertainty sources, characteristic of infrared temperature measurements, which limit the accuracy of the estimated measurement. Uncertainty sources are specially important in these applications due to:Nowadays, in order to guarantee the security in passenger and goods railway transport, fixed systems located in rails are used to measure axles, wheels and brake discs temperatures during train circulation so that abnormally high temperatures as a result of a malfunction can be detected. Measurement systems in this kind of application may be affected by different uncertainty sources, characteristic of infrared temperature measurements, which limit the accuracy of the estimated measurement. Uncertainty sources are specially important in these applications due to: (1) Extremely variable emissivity as a result of stain or different paints used on the surfaces. (2) Difficult evaluation of the environments radiation as measurements are made outdoors. (3) Alarm temperatures are only about 40 degrees Celsius to 80 degrees Celsius above the environment temperature. The paper analyses the effects of these uncertainties. The results show that, in order to get the minimum uncertainty peaks in the estimated temperature, the proper duty waveband is 3 - 5 micrometer. They also show that, with a proper choice of the wavelength, the uncertainty due to solar radiation remains masked by the uncertainty due to the lens emissivity.