D. Gonzalez

Interfacing Renewable Energy Sources to the Utility Grid Using a Three-Level Inverter

This paper presents a novel approach for the connection of renewable energy sources to the utility grid. Due to the increasing power capability of the available generation systems, a three-level three-phase neutral-point-clamped voltage-source inverter is selected as the heart of the interfacing system. A multivariable control law is used for the regulator because of the intrinsic multivariable structure of the system. A current source (playing the role of a generic renewable energy source) is connected to the grid using a three-level inverter in order to verify the good performance of the proposed approach. Large- and small-signal d-q state-space averaged models of the system are obtained and used to calculate the multivariable controller based on the linear quadratic regulator technique. This controller simultaneously regulates the dc-link voltage (to operate at the maximum power point of the renewable energy source), the mains power factor (the power is delivered to the grid at unity power factor), and the dc-link neutral-point voltage balance. With the model and regulator presented, a specific switching strategy to control the dc-link neutral-point voltage is not required. The proposed controller can be used for any application, since its nature makes possible the control of any system variable. The good performance of the presented interfacing solution in both steady-state and transient operation is verified through simulation and experimentation using a 1-kW neutral-point-clamped voltage-source-inverter prototype, where a PC-embedded digital signal processor board is used for the controller implementation

EMI reduction in switched power converters using frequency Modulation techniques

Frequency-modulation techniques have been used to reduce electromagnetic interference (EMI) produced by the clock of digital systems working in the range of hundreds of megahertz. The working principle consists of modulating the original constant clock frequency in order to spread the energy of each single harmonic into a certain frequency band, thus reducing the peak amplitude of EMI at harmonic frequencies. Nowadays, the switching frequency of power converters has increased up to values that make interesting the application of such techniques to reduce EMI emissions due to switching of power circuits. This paper presents the theoretical principles of frequency modulation using deterministic profiles for the modulating function. It shows the effectiveness of such methods in terms of EMI reduction for different modulation profiles and other parameters. The method is compared with other methods using random modulation. Tests carried out on a buck converter are presented for experimental validation of the method. A short discussion on optimal modulation profiles and parameters is also included.

Conducted EMI Reduction in Power Converters by Means of Periodic Switching Frequency Modulation

Spread spectrum clock generation techniques were originally developed to reduce electromagnetic interference (EMI) in communications and microprocessor systems working in the range of hundreds of megahertz. Nowadays, the switching frequency of power converters has been increasing up to values that make worthy the application of such switching frequency modulation techniques to reduce EMI emissions in power converters. Although random modulations have been applied before to power converters, periodic patterns can provide some advantages. First, theoretical principles of frequency modulation using three periodic patterns for the modulating function are presented. The influence of some important modulation parameters on the EMI reduction is analyzed and some considerations about the EMI filters design are also presented. The effectiveness of such methods in terms of EMI reduction is demonstrated theoretically and confirmed with experimental results obtained from tests carried out on two converters. The first one is a 2.5 W buck converter that can be switched up to 1 MHz and the second one is a 600 W boost converter switching at 40 kHz. In both cases, attenuations obtained in conducted EMI are evaluated. Finally, special attention has been paid to input current and output voltage ripple in order to evaluate possible undesired side-effects produced by this technique.

New simplified method for the simulation of conducted EMI generated by switched power converters

A new simplified simulation method for the calculation of conducted electromagnetic interference (EMI) caused by switched power converters (SPCs) is presented. EMI simulation in real SPCs presents particular problems due to complex geometry and the wide range of time constants involved. This makes the computation of EMI a complex matter. The method presented here is based on a source propagation path-derived disturbance simulation process and is specially designed to simplify the mentioned computation problems. In the design of the proposed method, quick and robust simulations were preferred rather than very accurate results. The resulting models allow quite accurate predictions and sensitivity analysis when certain changes in components or layout are introduced. The paper presents two validation cases, where simulation and experimental results of conducted EMI generated by a general-purpose VSI, with different switching patterns and different layout, are compared.

Evaluation of switching frequency modulation in EMI emissions reduction applied to power converters

Although most of the power converters are currently designed to operate by using a constant switching frequency and a variable duty-cycle, some attempts were made in order to verify the effect of modulating the switching frequency [F. Lin et al., 1992] and how this modulation affected the power converters EMI emissions. As known, spread spectrum clock generation (SSCG) modulates the originally constant switching frequency by following a certain modulation profile in order to spread the single harmonic energy into an amount of side-band harmonics having the same energy but much smaller amplitudes. This reduction technique has been used and implemented for high frequencies (as those related to clock frequencies in communications and microprocessors systems). This paper is dedicated to SSCG applied to the reduction of EMI emissions in power converters, focusing on the effectiveness of frequency modulation in EMI reduction as a function of the different switching frequency ranges and modulation profiles. Theoretical results were obtained just modulating a sine pure wave following several modulation profiles [A. Santolaria et al., 2002], this one representing each one of the harmonics composing the real square PWM-signal controlling the power converter. A practical arrangement was implemented to generate and measure EMI emissions.

Wavelet-Based Performance Evaluation of Power Converters Operating With Modulated Switching Frequency

It has been demonstrated that modulating the switching frequency of a power converter is a valuable way for reducing the electromagnetic interference (EMI) due to the switching process. Since we are considering a signal whose frequency content varies with time, wavelets are well suited to analyze the performance of such techniques. In this paper, we evaluate the performance of spread spectrum frequency modulation (SSFM) applied to the EMI reduction of a real power converter that uses periodic pattern switching frequency modulation. The performance of the converter under investigation includes the analysis of the switching voltage spectrum (as the main source of EMI) and the output voltage ripple. This evaluation is performed with two coefficients, i.e., maximum energy ratio (MER) and energy dispersion ratio (EDR), which are figures of merit defined in this paper using time-dependent energy density distribution in frequency, obtained from the scalograms of the analyzed signals. Such figures of merit allow comparison in the time-frequency domain of different modulation techniques and the choice of the best solution for each case in terms of reduction of the peak of noise spectrum.

EMI reduction in switched power converters by means of spread spectrum modulation techniques

Spread spectrum clock generation techniques (SSCG) were originally developed to reduce EMI in communications and microprocessor systems working in the range of hundreds of MHz. The working principle consists of modulating the original constant clock frequency, in order to spread each single harmonic energy into a certain frequency band, thus reducing amplitudes at each individual frequency. Nowadays, the switching frequency of power converters has been increasing up to values that make feasible the application of such techniques to reduce EMI emissions in power circuits. This paper deals with SSCG applied to reduction of EMI emissions in switched power converters, following certain modulation profiles. It is focussed on studying the effectiveness of EMI reduction as a function of frequency ranges, modulation profiles and other modulation parameters. A buck converter, whose switching frequency can be swept from 100 kHz to 1 MHz, has been used for experimental validation. Conducted disturbances produced by the converter, using different modulation parameters, were measured and compared with those produced by the same converter when driven with the classical constant frequency, variable duty, switching pattern. Significant reductions in conducted EMI may be observed. Optimal modulation profiles and parameters are identified.

Exponential Effective SIR metric for LTE downlink

3GPP LTE is the evolution of UMTS which will make possible to deliver next generation high quality multimedia services according to the users expectations. The flexibility of the downlink OFDM radio interface with Adaptive Modulation and Coding (AMC), MIMO and H-ARQ plays a crucial role in achieving the low latency and high spectral efficiency promised by the new radio access standard. This paper presents a LTE DL link level simulator whose main purpose is to generate suitable look-up tables to interface with a system level simulator. In this context, the Exponential Effective SIR (EESIR) metric is a link abstraction model that is used to properly characterize multistate channels. The reference BLER curves in AWGN channel and the parameters of the EESIR model are given for the complete list of CQIs specified for LTE DL. The obtained results also include curves of mean link level throughput for different AMC formats and MIMO configurations.

Analysis and simulation of conducted EMI generated by switched power converters: application to a voltage source inverter

This paper presents a frequency-domain analysis method for the calculation of conducted EMI disturbances produced by power electronic converters. Switched power converters have a singular behaviour from the EMC point of view. The complex geometry and the wide range of time constants involved, make the calculation of conducted disturbances a complex matter. The new modelling method presented here is based on a source-propagation path-derived disturbance simulation process and is specially designed to overcome the above mentioned problems. In the design of the proposed method quick and robust simulations were preferred rather than very accurate results. The features of the proposed method are shown in the paper by comparing simulation results with experimental results obtained in a general purpose three-phase voltage source inverter.

Wavelet-Based Approach to Evaluation of Signal Integrity

In this paper, we present a new approach to evaluation of signal integrity that is based on signal energy density as a function of time and frequency, represented by its wavelet scalogram. Using signal integrity ratio and cumulative energy ratio, we illustrate signal integrity analysis with simulated examples, followed by the demonstration of their usefulness through analysis of experimental data of a real audio amplifier. These figures of merit represent the extent to which the integrity of a signal is diminished by the electromagnetic interference effects and/or nonlinear processes.