J. Mon

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.

Reduction of Electromagnetic Interference Susceptibility in Small-Signal Analog Circuits Using Complementary Split-Ring Resonators

Low-frequency analog and digital electronic circuits are susceptible to electromagnetic interference in the radiofrequency (RF) range. This disturbance is produced when the coupled RF signal is rectified by the nonlinear behavior of the semiconductors used in the small-signal analog input stage of the electronic system. Circuits based on operational amplifiers are usually employed for such input stages. These circuits present an amplitude modulation demodulation produced by the nonlinearity of internal transistors. Such a phenomenon generates demodulated signals in the low-frequency range. In this paper, this effect is suppressed by combining the conventional printed circuit board layout with complementary split-ring resonators (CSRRs). CSRRs are constitutive elements for the synthesis of metamaterials with negative effective permittivity, which are mainly excited to the host line by means of electric coupling. Electromagnetic simulations and experimental results show an effective rejection of the undesired RF demodulation effect with no extra cost in terms of the device area or manufacturing process.

Side effects evaluation of switching frequency modulation in power converters

The switching frequency modulation applied to power converters as EMI reduction technique has been explored during the last years. However, there is some lack in the evaluation of side effects in the converter performance produced by this technique. In this paper we present an evaluation of these undesired effects by measuring the output voltage ripple. To carry out this work we have used a buck converter with a digital controller that implements switching frequency modulation according to periodic (deterministic) patterns. The interaction between the modulation process and the controller is evaluated. On the other hand, we also present a first comparison between other kind of modulation techniques, such as pulse width and pulse position modulations, pinpointing their potentialities

EMI reduction by means of switching frequency modulation with variable delay in power supplies

In this article, a new model to predict the amplitude reduction of the interference harmonics in power supplies with parallel topology is presented when the switching frequency modulation with variable delay (VDFM) technique is applied. The VDFM method consists of combining the interleaving and switching frequency modulation (SFM) techniques. The new model presented has been evaluated in a multichannel buck converter, operating with different numbers of converters when a triangular modulation profile is used. Theoretical study and experimental results show the influence of the number of converters and the modulation parameters with regard to electromagnetic interference reduction. From the new model presented, it is possible to predict the value of modulation parameters and the numbers of converters in order to satisfy the required attenuation regarding the electromagnetic compatibility directives, when a triangular modulation profile is used.

Hybrid modulator for power converters in parallel topology

This paper presents a new mixed modulator that combines interleaving and spread-spectrum techniques in order to achieve the lowest level of conducted EMI generation. This modulator is addressed to power converters in parallel arrangement. The practical details of the hybrid modulator and controller implementation on a FPGA are explained. The characteristics of such modulator in terms of EMI reduction and converter performance are theoretically explored and experimentally validated in a four channel parallel buck converter operating in closed loop.

Contribution to conducted EMI reduction in multiconverter topology

This paper contributes to the conducted EMI reduction generated by switched power converters operating in multiconverter arrangement. The EMI reduction is achieved by means of the combination of two techniques: interleaving and switching frequency modulation. The effectiveness of such methods in terms of EMI reduction is experimentally validated in a four channel parallel buck converter. The technique that provides the best attenuation results is identified. Finally, special attention has been paid to possible undesired side-effects produced by these techniques. For this reason the converter efficiency and output voltage ripple are evaluated.

Combined application of interleaving and modulation techniques in multiconverter topology

This paper presents a theoretical study about the combined application of interleaving and switching frequency modulation (SFM) in parallel multiconverter topology. We study the spectrum of the equivalent noise generation pattern that represents the aggregate effect of the switching of the four converters we have considered. Special attention has been paid to the amplitude reduction and harmonic cancellation by means of the application of two techniques: constant delay switching frequency modulation (CDSFM) and switching frequency modulation with variable delay of pulse position (SFMVPP).

Effects of nonidealities in switching frequency modulation techniques: Application to coupled interleaved multicellular parallel converters

This paper explores the application of the Variable Delay Frequency Modulation (VDFM) to an Interleaved Multicellular Parallel converter. VDFM is a modulation technique specially intended to reduce conducted EMI generated by parallel converters. This technique combines interleaving and frequency modulation in such a way that provides the best attenuation. On the other hand, Coupled Interleaved Multicelular Parallel Converters (CIMPC) needs a perfect current sharing among phases. In this paper we consider the effect of VDFM nonidealities on the EMI attenuation in order to consider the application of this technique to CIMPC.

Reduction of EMI by combining interleaving and modulation techniques in multiconverter topology

In this paper an evaluation of different modulations techniques that combine switching frequency modulation and interleaving is presented. The objective of these modulations is to cancel certain harmonics of EMI and to reduce the amplitude of the remaining harmonics. A four channel parallel buck converter has been used in order to evaluate the modulations proposed. According experimental results, significant reduction of EMI is possible by combining both techniques instead of using them separately.

Wavelet-based algorithms for triggering power quality measurement instruments

During the last years, the power quality (PQ) issues have been a subject of major concern. The constraints that must be fulfilled by the voltage wave supplied by utility companies have become more and more exigent. For this reason, the PQ measurement equipment requires new and computational efficient algorithms. This paper presents a Discrete Wavelet Transforms (DWT) based triggering algorithms for PQ measurement instruments. Some typical PQ disturbances (sags, spikes or harmonics) have been considered to define figures of merit that can detect the presence of such disturbances and therefore are suitable to trigger the data recording of the PQ analyzer. All these figures of merit are obtained from the DWT decomposition. The final validations of the triggering algorithms have been done with real measurements.