MECEP Project - Mastering Conducted Emissions on Power Equipment

03/02/2015
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MECEP Project - Mastering Conducted Emissions on Power Equipment

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MECEP Project - Mastering Conducted Emissions on Power Equipment Christian MAROT (1), Jean RIVENC (1), Franck FLOURENS (2), Frédéric THEROND (2), (1) : AIRBUS Group Innovation ; (2) : AIRBUS Group Abstract. : The MECEP project is in the field of the Electro-Magnetic Compatibility (EMC) for avionics application and power electronics integration. It is particularly focused on the management of the parasitic conducted emissions on power supply lines. The historical trend to rely more on high power technologies put into question the relevance of some EMC standards used in aeronautics to constrain emissions below acceptable levels. The benefit brought by increased power and associated switching, power conversion and actuation technologies could be significantly altered if the management of the EMC performances is not revised by offering more flexibility. An interesting way forward would be to adapt the emission levels in relation with an optimized installation of the power circuits on the aircraft for preventing interference on sensitive equipment. The MECEP project must deliver several technical elements and facts to support the development of a new approach for managing the EMC integration. This approach must look at a more balanced definition of the EMC requirements imposed to constrain the emissions from the sources, the coupling from the installation and the sensitivity of the potential victims. At first, two fundamental elements must be identified to understand the possibility to develop such a new approach:  the actual margins on some existing platform, i.e. the difference between the immunity level of a piece of equipment and the conducted emissions levels on harnesses,  the gaps, i.e. the difference between the RF conducted emissions as measured in laboratory conditions and the actual levels observed when the equipment is integrated on the aircraft. 1 Introduction Evolution of aeronautics goes into the direction of more power systems on board: more electrical actuation systems, more high power conversion, more switching devices, increased voltages … On the other hand, despite this significant trend, the EMC integration of the systems relies on the use of historical EMC standards. When developed, these standards were constrained by different factors. One of them was the protection of some RF systems operated in the very low frequency band that are today obsolete. Another one was the high susceptibility of some signals commonly used for sending information between equipment or from a large variety of sensors. The emergence of digital signals, data buses, data concentrators and smart sensors offers some media that are much more robust and less sensitive than old analogue technologies. In addition, other important changes are taking place today in the aeronautic industry. One can note over the last years the use of new materials for the aero-structures (Carbon Fiber Reinforced Plastic), the evolution of the electrical technologies (constant increase of the embarked power) and the evolution of the way electricity is distributed across the aircraft (high voltage, massive use of convertors, dedicated current returns…). Despite all these changes, the historical standards have not evolved. This situation creates a significant risk to constrain some technologies beyond what would be necessary. Constraining emissions requires filters. Filters are extra weight, extra volume and extra complexity. At the extreme, imposing historical standards for limiting emissions could void the interest of using some emerging technologies. EMC integration must be approached in a different way. The first step should be to revise the point of equilibrium between the levels of emission allocated to the power systems, and the protection of the cables (segregation, screening / shielding) to ensure that the levels reaching the possible victims are reduced below a safe threshold. The control of a margin between spurious levels induced on equipment and their immunity could be a good indicator of the EMC robustness. The second step will be to “standardize”. It means to develop relevant and stable conditions for testing equipment that allow anticipating the performance of the equipment when integrated on the A/C and making possible to characterize margins like it has been done for other EM threat like LIE or HIRF. However, today data are missing in order to have an optimized approach of aircraft design with respect to EMC. As a matter of fact: • Margins in A/C is not known between victims susceptibility levels and sources emission levels; • It is likely that excessive weight and money may be spent in filters and / or cables shielding’s, and applied installation rules may be too severe. •In the same way, emission levels required in DO-160 standards may be too severe with respect to actual need. •Above all, quantitative and factual data are missing. The first step of the MECEP project is to quantify all the bricks that contribute to the overall EMC performance:  The sensitivity of the potential victims (RF receivers, signals, power supplies).  The way the spurious conducted energy couples into the victims: radiation, crosstalk, conduction.  The way conduction emissions are characterized (influence of external conditions, loads, time or frequency domain). The second step will be to understand the intrinsic performances of some modern power technologies regarding emissions, the possible ways to improve them and the best way to standardize the limits. Then, the reconciliation of all these data should make possible to propose a new balance between the constraints imposed to the contributors to the overall EMC performance. 2 Conducted emissions requirements Conducted emissions requirements are a design driver for equipment with power electronics. Stringent emission requirements oblige equipment suppliers to implement efficient filtering devices with a significant impact on the overall equipment weight. As example, a recent survey performed with some suppliers pointed out that about 10%, around 60kg, of the equipment weight was used for the filtering circuits to comply with D0160 conducted emission limit, section 21 The most difficult bandwidth is not the 2-30MHz (HF band) because filters have limited size, but from 150 kHz to 2MHz where spurious noise generated by switching devices can be severe and more difficult to eliminate. . Figure 1 : D0160 Setup for Conducted RF emissions measurement The RF conducted emissions on power lines are measured from 150 KHz to 152 MHz by using a clamp-on interference measuring device. The primary power lines are not considered to be interconnecting cable bundles and are separated in the test configuration. The current probe shall be at 5 centimeters from the EUT. If the EUT connector plus back shell length exceeds five centimeters the probe shall be placed as close to the connector back shell as possible and the position noted. EUT emissions within the frequency ranges and in excess of the values are given in figure 2. Figure 2 : DO160 CE Levels, P category As the emission standard used for equipment qualification based on the ED14/DO160 has been defined several decades ago, it becomes necessary to come back on its drivers and to re-assess both its severity and the way it is formulated. The lower frequency band for CE levels starting at 150kHz was linked with old terrestrial radio navigation systems such as Omega, ADF, LORAN C. The LOng RAnge Navigation is a terrestrial radio navigation system which operates in the low frequency (LF) portion of the radio spectrum in the 100 kHz range. The OMEGA was the first truly global radio navigation system for aircraft, operated in the VLF portion of the spectrum between 10 to 14kHz and the Automatic Direction Finder (ADF) is a marine or aircraft radio-navigation instrument operating in the LW band between 190 – 535 kHz. All these low frequency systems are no more in use or will disappear soon opening some possible opportunities to revise the standard. At the same time, the protection of the HF band (2-32 MHz) has to be reassessed considering actual integration of HF systems. If the protection of RF navigation systems is no more an issue below 150 kHz, the driver of the emissions will become the power supply network quality (distortion, transients, harmonics…). It is a direct conduction problem. It will be important to understand how far the pollution of the network with spurious can degrade the performance of the supplied network to set a limit, considering as well cumulative effects and consistency with harmonic rejection requirements define by other standards. Finally, in the intermediate bandwidth, the driver of the emissions becomes the cross talk. It is the area where lies the highest interest to draw a formal link between installation effort to decouple circuits and equipment emission limits. 3 MECEP project The MECEP project is focused on:  The margins, i.e. the difference between the immunity level of equipment and the conducted emissions levels on harnesses  The gaps, i.e. the difference between the RF conducted emissions as measured in laboratory conditions and the real level on the aircraft The objectives of MECEP project are:  To help to establish design rules, both at system level (aircraft installation rules) and at equipment level (filters sizing), in order to design an aircraft from EMC point of view with a controlled and optimized margin  To determine whether it is necessary to modify emission requirements levels in DO160 standard in order to set up equipment emission requirement to its optimized level (neither too high nor too low).  To readapt the limit of the historic standard DO160 used for Conducted emissions measurement  To assess the most important factors in the electric specifications and EMC sizing of filters and to acquire an estimation of the relation performance / weight. The MECEP project mobilizes 13 actors in the field of the EMC of the aeronautical level. The consortium is distributed in a homogeneous way between 3 aircraft manufacturers, 5 equipment suppliers of the embedded electronics and 5 research centers. Aircraft manufacturers: AIRBUS, AIRBUS Hélicoptère, DASSAULT aviation Aeronautic suppliers: AIRBUS, LIEBHERR, LPS, THALES, ZODIAC AEROSPACE Industrial and academic Research centers: AIRBUS Innovations, AMPERE, G2ELab, ONERA, SATIE Localization of the partners is presented on figure 3 Figure 3 : Localization of the partners of project MECEP The project MECEP is arranged around 5 Work Packages:  WP1: Assessment of the Margins and of the Gaps in the RF conducted emissions levels  WP2: Filtering of the conducted emissions, P > 10kW  WP3: Filtering of the conducted emissions, 1kW < P< 10kW  WP4: Filtering of the conducted emissions, P < 10kW  WP5:Impact on conducted emissions with emergent technologies in Power electronic Figure 4 present links between WP and the WP arrangement. Figure 4 : links between WP in MECEP 3.1 WP1 : Assessment of the Margins and of the Gaps in the RF conducted emissions levels Within the framework of this working group, the need is to quantify the margin which we need between the level of immunity of equipment victims and the level of emissions of the emissions equipment into the aircraft and to quantify the gaps between the level of conducted emissions of an equipment during a normative test of qualification on table, and the level of the same equipment integrated into the aircraft within a given installation. The knowledge of these margins and the gaps are going to allow determining better how to distribute the constraint EMC between a normative requirement for the equipment, and the rules at the electric installation, with in particular rules on the topology of the electric connections, on distances to be respected, etc. … Figure 5 give an overview of the WP1 objectives. Figure 5 : overview of the WP1 objectives The following approach will be put in place in order to achieve the work package target: - Conducted emissions measurements will be performed on an aircraft, on specific equipment; - Results will be compared to conducted emissions measured, on same equipment, during their qualification (DO160); - Gaps will be identified (amplitude and frequency range), hypothesis will be made to explain these gaps. Further experiments and / or simulations will be performed to assess hypothesis and to raise conclusions regarding main parameters (coupling to ground plane, differences in functional modes, in electrical load, LSIN influence…) driving the gaps; - Generic immunity profiles of victim equipment will be built in order to evaluate the margin from conducted emissions measured in aircraft. Conditions on electrical installation, which ensure compatibility between emission and immunity profiles, will be proposed. 3.2 WP2,3,4 : Filtrage des Emissions Conduites 3 Working Groups are going to analyze 3 ranges of power, P>10kW, 1kW>P>10kW and P<1kW. The power electronics is an electronics stages of switching. That is an important source of electromagnetic pollution. More than their amplitude, it is especially variations of the voltage and current which are at the origin of the conducted electromagnetic disturbances on the harness. To reduce the level of the these disturbances it is easier to filter than to design converters with optimized switching stage and components. In the case of 10KW power converters, the size and the weight of these filtering stage can be up to 10 % of the weight of the on- board Equipment. The works realized in these 3 working groups are going to assess the efficiency of the differential mode and the common mode filtering stages of the RF conducted emissions) versus the weight of the components of the filters and the levels specified in the DO160 section 21 and to define tools to help in the optimization of the design of these filters and equipment of power. Objectives of this working group are: To define models of configurable tests for the evaluation of the levels of conducted emissions on "table". To draw the graph of the efficiency of filtering according to the weight of components and levels of the RF conducted emission measured in a normative setup. To propose modellings and simulations for the help during the design step. 3.3 WP5 : Impact on conducted emissions with emergent technologies in Power electronic The works of this workgroup are the analysis of the impacts of the voltage levels increasing in the power networks in order to reducing the weight of the harness and on the other hand the use of new technologies of components of powers authorizing the higher frequency switching of the converter with the aim of reducing the losses and the EMC filtering. The expectations for this workgroup are to identify solutions of filtering connected to the emergent technologies of converter of power, to identify the impacts of these emergent technologies on the normative constraints according to the potential earnings (kg / dB) and to obtain the laws of evolution giving the impact in terms of kg / dB onto the filtering according to the range of power, technologies of filter. 4 Conclusion Expected key output of MECEP project are : Estimation of margins between victims immunity levels and sources emission levels in aircraft from one part, and gaps between emission levels in aircraft and emission levels during standard qualification test from another part; Installation rules: mainly cables shielding and distances between routes, which ensures compatibility between immunity and emission profiles; Optimized conducted emissions requirements to be given to an equipment, and sensitivity of filters weight on emissions levels (dBµA), Impact of new technologies: benefits of new filtering components, and new constraints linked to wide gap switches. In that way, it will be possible to perform an optimized design of an aircraft, from an EMC point of view. That project is presented in CORAC road map and should start beginning of 2015