Common-mode Emissions Research Articles

Comparison of control techniques for three-phase distributed generation based on VOC and DPC

This paper presents a comparison among control strategies of active rectifiers used for grid connected distributed generation systems from renewable sources. The considered techniques are: Voltage Oriented Control (VOC), Direct Power Control (DPC), two DPC based techniques to minimize the Common Mode (CM) emissions called DPC-EMC1 and DPC-EMC2 set up by the authors and their versions based on virtual flux. All the described techniques have been implemented using Matlab-Simulink® environment and PLECS®. In the results the current injected into the grid, the THD of the injected current vs. generated power and vs. DC link voltage and the CM voltage are shown.

Comprehensive Conducted Emission Analysis of the Three-Phase and Single-Phase LLC Resonant Converters for EV Application

Resonant <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> converter is a preferred candidate for emerging electric vehicle (EV) applications, thanks to its high efficiency and high power density characteristics, which are achieved due to high switching frequency and soft-switching operation. On the other hand, planar transformers (PTs) for EVs offer power density in a small package and withstand vibrations. However, large parasitic capacitance is a characteristic of PT, which along with the large <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dv/dt</i> of the converter leads to severe conducted emission problems. Therefore, multifold complicated and bulky electromagnetic interference (EMI) filters are required to suppress conducted noise and meet the requirements of the relevant standards. In this article, a comprehensive analysis has been conducted to model and study both single-phase and three-phase <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> resonant converters from a conducted noise perspective. With this study, a better understanding of the EMI behavior of these converters can be obtained. Owing to the symmetrical design of the three-phase converter, several harmonics cancel out each other, resulting in lower common-mode (CM) emissions. It is also shown that differential-mode (DM) current generated from the three-phase converter contains lower peak amplitude at high frequency. For comparison purposes, two prototype converters based on the conventional single-phase and the three-phase configuration are fabricated and their conducted emissions are measured and compared experimentally. Simulation and experimental results verify that the three-phase converter effectively suppresses CM and DM noise by a considerable amount.

Common-Mode EMI Unterminated Behavioral Model of Wide-Bandgap-Based Power Converters Operating at High Switching Frequency

With wide-bandgap semiconductors increasing their commercial availability, high switching frequency operation has become an accepted practice to increase power density in power converters. High switching frequency operation, nonetheless, increases the electromagnetic interference (EMI) emissions of converters, for which accurate models are needed in order to predict their EMI noise and aid in the design of necessary filters. To this end, this paper assays first the impact that high switching frequency has on converter EMI emissions, and second, uses an unterminated behavioral model (UBM) to predict the common-mode (CM) emissions in the conducted EMI range (150 kHz–30 MHz). To achieve this, a new extraction procedure is developed for a UBM to effectively capture the rich high-frequency content of the CM emissions, providing a solution to the inherent limitations of previous behavioral models developed for insulated-gate bipolar transistor-based converters. The experimental results obtained with two setups: a 3-kW, 300-V dc, silicon-carbide-based three-phase inverter switching at 70 kHz and a 1-kW, 400-V dc, gallium nitride -based three-phase inverter switching at 500 kHz are presented to validate the approach and the model capabilities.

Fault Detection Methods for Three-Level NPC Inverter Based on DC-Bus Electromagnetic Signatures

This paper proposes two new open-circuit fault detection methods suitable for the diagnosis of power electronics converters. The faulty semiconductor devices are identified using conducted and radiated electromagnetic signatures of the dc bus through nonintrusive measurements. The first method uses a low-cost electromagnetic interference filter to collect the common-mode emissions signature. The second one utilizes an external antenna to collect the emitted near-field signature. Both methods are tested on a three-level neutral point clamped inverter (NPC) inverter with the aim to identify the clamping diodes open-circuit faults. Indeed, each open-circuit fault affects the common-mode emission signature in the time-domain, while the fast Fourier transform of the emitted near-field showed substantial reduction of spectrum amplitude at a specific radio frequency range and the appearance of a new spectral rail. The effectiveness of these two methods has been tested through numerical simulations and validated by experimental results which confirmed its high performance in detecting single as well as multiple open-circuit faults for three-level NPC inverter.

Comparative Analysis of Control Techniques for PWM Rectifiers in Grid Connected Distributed Generation Systems Based on VOC and DPC

This paper presents Virtual flux based and Voltage based control schemes for PWM rectifiers in grid connected distributed generation systems from renewable sources are presented. In particular, the so-called Voltage Oriented Control (VOC), Direct Power Control (DPC), two DPC based techniques to minimize the Common Mode (CM) emissions called DPC-EMC1 and DPC-EMC2 set up by the authors and their versions based on virtual flux. All the described techniques have been implemented using MATLAB/Simulink® (Classic version 8.2 Release name (R2013b)) and compared with each other. Theoretical background with results of simulations is provided. The advantages and disadvantages of the individual control strategies are documented.

A Comparative Study Between the Nearest Three Vectors and Two-Level Hexagons Based Space Vector Modulation Algorithms for Three-Level NPC Inverters

Multi-level power converters are nowadays the most appropriate solution for medium-voltage grid-connected Renewable Energy Sources (RES) such as variable speed wind-turbines and photovoltaic (PV) generators. Basically, there exist two space vector modulation (SVPWM) schemes which are commonly used to modulate the output voltages provided by three-level inverters . For the first method, namely the nearest three vectors (NTV), the position of the space vector is identified in one of the triangles forming the space vector diagram. As for the second method that is referred to as the hexagon technique, the opportune position of the space vector is determined within a two-level hexagon. This paper is therefore focused on a comprehensive comparative study between the performances of the two aforementioned techniques. The evaluation is performed in terms of Common Mode Voltages (CMV), Total Harmonic Distortion (THD), conducted emissions, and efficiency. The proposed comparison is based on numerical simulations and experimental tests. The obtained results confirm that the NTV technique provides the better performances in terms of THD and CMV for low modulation index values. It also provides less common mode emissions when the modulation index is near its maximum value. As for the efficiency, both methods provide the same performance for a modulation index superior or equal to 0.8.

Power Network impedance effects on noise emission of DC-DC converters

The characterization of electromagnetic noise emissions of DC-DC converters is a critical issue that has been analyzed during the desing phase of CMS tracker upgrade. Previous simulation studies showed important variations in the level of conducted emissions when DC-DC converters are loaded/driven by different impedances and power network topologies. Several tests have been performed on real DC-DC converters to validate the Pspice model and simulation results. This paper presents these test results. Conducted noise emissions at the input and at the output terminals of DC-DC converters has been measured for different types of power and FEE impedances. Special attention has been paid to influence on the common-mode emissions by the carbon fiber material used to build the mechanical structure of the central detector. These study results show important recommendations and criteria to be applied in order to decrease the system noise level when integrating the DC-DC.

Direct power control of three-phase VSIs for the minimization of common-mode emissions in distributed generation systems

This paper presents two new direct power control (DPC) strategies of three-phase grid connected VSIs for distributed generation, devised for the minimization of common-mode emissions. These strategies have been called DPC-EMC 1 (electro magnetically compatible) and DPC-EMC 2. Both of them reduce the common-mode emissions of the VSI by using either even or odd voltage vectors in each of the six sectors in which the grid voltage lies, without using any null vector. DPC-EMC 2 outperforms DPC-EMC 1 in terms ripple of the active and reactive power waveforms. These approaches permit the common-mode emissions to be reduced in comparison with the classic DPC algorithm, at the expense of an increase of the harmonic content of the injected current waveform which can be further corrected by a proper power line filter. An experimental comparison among the classic DPC, DPC-EMC 1 and DPC-EMC 2 is presented in terms of dynamic performance, harmonic content of the injected current and harmonic content of the common-mode voltage.

Modal Characterization of Power-Line Filter Capacitors

A typical power-line filter is composed, essentially, by common-mode chokes, X-class and Y-class capacitors. A good characterization of these components is needed to develop a technique to design the optimal power-line filter for an electric or electronic device by finding their best values. In this paper, a new methodology to characterize the behavior of power-line filter capacitors is presented. This methodology is based on a model where common-mode and differential-mode interference are separated into different ports in order to facilitate the study of the propagation phenomena. The methodology is used to explain modal conversion inside impedance networks with X-class and Y-class capacitors, to predict the common-mode and differential-mode emissions when these capacitors are connected to electric or electronic devices, and to improve the classical methodology of power-line filter implementation finding the optimal capacitances of the impedance networks. This new methodology has been successfully tested by using real measurements from capacitors and electric devices.

Electromagnetic Considerations for Designing Double-Sided Power Modules

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Double-sided power modules are particularly attractive due to their high thermal performance. Thanks to the stacking of two direct bond coppers, very low stray inductances may be expected, particularly because of the proximity of the two rear metalizations. On the other hand, capacitive effects may be increased. In this paper, the complete electromagnetic behavior of double-sided power modules is studied, regarding both internal coupling and unwanted electromagnetic compatibility emissions. Some layout and active solutions are proposed to reduce common-mode emissions. </para>

Automatic EMI Measurement and Filter Design System for Telecom Power Supplies

Tests for compliance with conducted emission limits are usually carried out during the electrical product design process. Electromagnetic interference (EMI) filters are widely used for filtering excessive conducted emissions on a power cord. In this paper, a personal computer (PC)-based automatic EMI measurement and filter design system for telecom power supplies is proposed. The common-mode (CM) and differential-mode (DM) emissions in the live or the neutral line can be measured and recorded separately. The trial-and-error guesswork in selecting the filter components can be minimized by the proposed automatic filter design system. In other words, the EMI suppression effort is greatly reduced by the fast PC computing speed and the man-machine interface. The developed system can be an effective noise diagnosis and filter design tool for EMI engineers.

A new direct torque control strategy for the minimization of common-mode emissions

This paper presents a new direct torque control (DTC) algorithm for induction machine drives capable of reducing the common-mode conducted emissions of the drive. It is based on the application of only odd or only even voltage vectors in each sector in which the stator flux lies. In the work, after an overview of the generation of common-mode emissions of inverter fed drives and the most employed techniques for their minimization, a simplified equivalent circuit of the common-mode path has been identified to be used in numerical simulation on the basis of experimental measurements. Then, the new DTC technique has been described and applied to an induction machine drive, both in numerical simulation and experimentally on a suitably developed test setup. Finally, results are presented and compared to those obtained with the classic DTC technique. It has been shown that this methodology is able to reduce the common-mode voltage repetition rate, and therefore the resulting common-mode currents in comparison with the classic DTC in a frequency range of about tens of kilohertz. Finally the analysis of the impact of both control techniques in terms of the current absorbed by the grid has been performed.

Derivation of a Closed-Form Approximate Expression for the Self-Capacitance of a Printed Circuit Board Trace

The electric fields that couple traces on printed circuit boards to attached cables can generate common-mode currents that result in significant radiated emissions. Previous work has shown that these radiated emissions can be estimated based on the self-capacitances of the microstrip structures on a board . In general, the determination of these self-capacitances must be done numerically using three-dimensional static modeling software. In this paper, an approximate closed-form expression for the self-capacitance of microstrip traces is derived. This expression can be used to estimate the voltage-driven common-mode emissions from boards with various microstrip trace geometries. The expression also provides insight relative to the microstrip parameters that have the greatest effect on radiated emissions.