POLARIZATION PHENOMENA IN COLLAGENS FROM VARIOUS TISSUES

International audiencexx

CMV reduction in a three-to-seven phase direct matrix converter using SVPWM

The pulse-width modulation (PWM)-controlled modern electric drives causes some serious problems such as the generation of common-mode voltage (CMV) and high dv/dt. The CMV might cause high-frequency leakage currents that flow through the possible path that is bearing of the motor. Thus, the flow of current through the motor bearing leads to its premature failure. One of the main challenges in developing PWM methods for control of motor drives is the problem of CMV and its reduction/elimination. In this study, a modulation technique based on space-vector approach is developed to reduce the CMV in a three-to-seven-phase direct matrix converter. CMV reduction becomes possible by selecting suitable zero-voltage vectors for a specific duration and the use of a selected set of active vectors for the output voltage synthesis. The proposed space-vector PWM (SVPWM) for the reduction of CMV is performed with a seven-phase R-L load to show the viability of the proposed technique. The proposed SVPWM technique is implemented experimentally in dSPACE working in conjunction with field-programmable gate array processor board using a system generator. Hardware results that validate the proposed control algorithm are discussed. - The Institution of Engineering and Technology 2019This publication was made possible by the Qatar University internal Grant QUCP-CENG-17\18-2. The statements made herein are solely the responsibility of the authors.Scopu

A resolver converter based upon a novel open-Loop Technique

The paper presents a novel technique for the determination of the angle from slowly-varying quadrature co-sinusoidal signals produced, for example, by position sensors. In the presented scheme applied to a resolver, the separately generated constant-frequency sine wave used for exciting the resolver together with an additional cosine wave are used as reference against which the amplitudes of the angle-dependent demodulated resolver sine and cosine signals are compared. At the instant equality between respective amplitudes of the signals are detected, two sample and hold circuits sample a voltage proportional to the angle of the shaft of the resolver from a triangular waveform generated from the reference signals. In theory, the sample and hold devices produce identical output voltages proportional to the unknown angle of the transducer. In order to improve the precision of the proposed converter, the two sample and hold circuits outputs are fed into a multiplexer to produce a single output that takes full advantage of the accurate comparison outside the peak regions of the signals. With this method, the validated output is obtained from the accurate comparisons involving the alternating pseudo-linear segments of the trigonometric signals. Another important feature of this converter is its robustness to amplitude fluctuations in the trigonometric reference signals which are used for the excitation of the resolver. A converter based on this technique has been successfully implemented using basic electronic components. Theory of operation, computer simulation and experimental results are given

A New Low Cost Linear Resolver Converter

A new low cost converter topology is proposed for sinusoidal position encoders. The converter enables determination of the angle from the sine and cosine signals of the encoder. When used with resolvers, the implementation of the present scheme takes advantage of the available excitation signal used to operate the device. This trigonometric reference signal is optimally used to generate an analogue signal equivalent to a digital look-up table (LUT). This enables determination of the mechanical angle without using LUT, A/D, and D/A converters. The scheme is optimized in order to achieve highest possible precision. Beside simplicity of its implementation, the proposed converter offers the advantage of robustness to amplitude fluctuation of the transducer excitation signal. The converter was implemented using ordinary low-cost analog components. The theory of operation, computer simulation, and experimental results are given