M. Lamich

EMI Susceptibility Model of Signal Conditioning Circuits Based on Operational Amplifiers

Circuits based on operational amplifiers (OPAMPs) are susceptible to electromagnetic interference (EMI) in the radio-frequency range due to the AM demodulation produced by non-linearity of internal transistors. Such a phenomenon produces demodulated signals in the low-frequency range. This paper presents a model to predict the susceptibility of analog signal-conditioning circuits, based on a few test parameters, while ignoring the internal structure of OPAMPs involved in the circuit. The method has been experimentally tested in two applications: (1) test of simple instrumentation adapter circuits and (2) predictions of susceptibility of an amplifier for an electret microphone, tested according to EN55020.

On the use of sun trackers to improve maximum power point tracking controllers applied to photovoltaic systems

Nowadays power supply systems based on photovoltaic cells have two main drawbacks, even the primary energy is free and renewable. They are: production cost and efficiency. In order to increase their efficiency, it should be interesting that the energy transfer between cells and load was done at maximum level. In this paper the use of a sun tracker system is presented as an additional improvement applied to a photovoltaic installation that works under a maximum power point tracking (MPPT) control technique. A 50W-prototype has been assembled. Some experimental results are also included in order to validate the whole system.

New Structure for Three Phase Four Wires Hybrid Active Filters

This paper presents a new structure for three phase four wires hybrid active power filters (APF). The main point with regard to other published structures consists of the connection of neutral wire to negative of DC bus in the inverter, thus avoiding the need of split capacitors at the DC bus. A particular control of voltage at the passive section of the filter allows the use of low voltage at the DC bus and provides a symmetry between ton and toff in the current controller. The paper includes a general discussion of the new structure and presents the control method for such a structure. Simulation and experimental results are given to show the behaviour of the system, used for harmonics cancellation

Control of a three phase four wires shunt hybrid filter

This paper describes a new strategy to control a particular structure of three phase four wires LC coupled parallel hybrid power filters (APF) for harmonics cancellation. The main differential point of the studied structure consists of the connection of neutral wire to negative of DC bus in the inverter, thus avoiding the need of split capacitors at the DC bus. The LC coupling and a particular control of the DC+AC voltage at the coupling C allow the use of low voltage at the DC bus and provide the necessary symmetry of available voltage, in the current controller, during ton and toff. The paper includes a general discussion of the structure, comparing it with the classical L coupled shunt APFs and presents a control method to obtain the necessary voltage symmetry to allow lower DC bus voltages and lower values of coupling L. The paper presents a control method based on time domain techniques, which gives a fast response. Simulation and experimental results are given to show the behavior of the system, used for harmonics cancellation.

New method for obtaining SV-PWM patterns following an arbitrary reference

This paper presents a new method for the generation of SV-PWM patterns (space vector pulse width modulation) for three phase inverters, following an arbitrary reference. Instead of using the classical /spl alpha//spl beta/ reference axis, the method is based on a vector split up in two nonorthogonal axes, forming a 60/spl deg/ angle and coinciding with the fundamental state vectors of inverter. The method can be implemented by the use of a specific hardware circuit based on a PLD plus some analog circuitry (analog adders and comparators), or it can be used in fully digital controllers, based on digital processing techniques. The main advantage in both cases is the very fast response and the extremely low processor resources employed due to the simplification of transform matrix to convert the three phase system into a two component state vector. Such features allow the use of the method to obtain SV-PWM to generate arbitrary power waveforms with an extended bandwidth. The method is especially suitable for parallel active filter controllers. Simulated and experimental results obtained with a specific hardware circuit are presented in order to show the features of the method in high frequency applications.

Modeling harmonics of networks supplying nonlinear loads

This work presents the development and validation of a model for electric networks supplying nonlinear loads (NLL). The model is based on Neural Networks (NN) and its purpose is the prediction of harmonic currents sank by the loads, in case of supply impedance changes caused by the insertion or releasing of neighboring loads or by the voluntary insertion of filters to reduce such harmonic currents. The NN is trained using data obtained from several Matlab simulations and the model is validated using the same network with different supply impedances and load conditions.

Modelling of differential mode conducted EMI generated by switched power inverters

This paper presents a method for the calculation of conducted differential mode EMI disturbances produced by switched power inverters. The complex geometry and the wide range of time constants involved, make the simulation of conducted disturbances in such systems a complex matter. The features of the proposed method are shown in the paper by comparing simulation results with experimental results obtained in a conventional H-bridge voltage source inverter.

Nonlinear Loads Model for Harmonics Flow Prediction, Using Multivariate Regression

This paper describes a method for obtaining a model of a single or a set of nonlinear loads (NLL) connected to a certain point of an electrical network. The basic assumption is that the network supplying the NLL has significant series impedances and is disturbed by other parallel, random, and unknown neighbor loads, sharing part of the supply system with the NLL. The main interest for obtaining the model is its further use to predict the amount and flow of harmonic currents generated by the NLL, in the case of adding a filter to reduce the harmonics distortion. The modeling technique used in the paper is based on multivariate multiple outputs regression and leads to a set of equations giving the NLL behavior (one for each of the harmonic currents). The model is obtained from data taken at measuring point and is only valid to predict the NLL behavior when new loads are connected at this point. The modeling method was first tested with V, I data coming from simulations using a MATLAB-Simulink SimPowerSystems toolbox. Finally, the method has been validated using V, I data taken in a real installation with different neighbor loads and under different load conditions.

Power conditioners synchronisation in networks with large frequency deviation

This paper presents a new method for real time calculation of the current reference in active power line conditioners (APLC), splitting up the fundamental and the distortion components. Amplitude and phase of fundamental component are obtained separately, which allows a separate compensation of fundamental lagging current and harmonic currents. The method is based on a sinus-cosinus correlation to obtain the phase of fundamental component. The main advantages of such method are: the fast response to transient changes, the null sensitivity to frequency variations and the low processor resources employed. Simulated and experimental results are presented in order to show the features of the method in several transient situations.

Instruments offset due to RF EMI

One of the main error sources in instruments and sensors are electromagnetic interferences, EMI, acting on linear ICs at the detection and pre-conditioning stages. High frequency interferences with random amplitude cause a DC offset and a ripple due to noise amplitude modulation. This paper is devoted to study the effects of EMI on OPAMP offset. After several tests, a qualitative model for offset prediction is derived. A set of tests allows obtaining the model parameters, which depend on OPAMP type and circuit impedances. Such parameters allow the comparison of susceptibility between different OPAMP types. The model also allows the quantification of improvements when certain set up changes are introduced.