Local HVDC Network Architectures and Challenges

Auteurs : Benoit Michaud
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Local HVDC Network Architectures and Challenges


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Local HVDC Network Architectures and Challenges MICHAUD Benoît Labinal Power Systems, Power Division, Rond Point René Ravaud – BP 42, 77551 Moissy Cramayel Cedex – France, benoit.michaud@labinal-power.com Abstract Electrical power increase is a long term issue in aircraft installation. Higher voltage is already a challenge that has been faced through latest aircraft development (B787, A350). The following step could be also an important challenge: the High Voltage DC network (named here HVDC). It would enable great weight saving however the challenges to face up are also bigger. A first step already done is to communalize in one equipment different loads drives (B787). A more innovative step would be the use of local HVDC networks to feed some dedicated areas of the aircraft. The definition of the best local architecture can be done only through the knowledge of at least the following constraints: Energy optimization (reversibility); Network stability and protections; Energy conversion and storage. This presentation gives a short overview of the work performed by Labinal Power Systems on the HVDC network theme. Introduction The importance of electricity substantially increases in aeronautical systems. Traditional aircraft power electrical network have a three phase AC network (115 VAC constant or variable frequency). These networks are centralized so the equipments are powered directly by the aircraft network. Most actuators are controlled and powered through static converters that require the use of a DC voltage. Multiplication of rectification stage brings an overweight and do not improve reliability figures. To supply directly the electrical loads with DC network instead of alternating three-phase current network allows the communalization of the AC/DC conversion stage. The resulting High Voltage DC bus is used to supply various power drive units. A local DC network also facilitates load coupling with regenerative load acceptance along with the introduction of an energy storage device allowing energy recovery from Electro Mechanical Actuators and making the local network reversible [1]. The main issues are the compliance with the aircraft network, the energy management, the stability and the capability to clear network and loads faults. This paper presents solutions to address these constraints. A test platform is in progress to validate all these solutions on different loads that will simulate some fly control actuators or some landing gear actuators. The network architecture chosen is presented hereafter. Fig. 1: Local HVDC network architecture with energy storage. Energy storage and DC/DC converter associated To address the different constraints of these applications, the energy storage device chosen was a supercapacitor. Different ways have been studied to improve the performance of these components: • Mixe electrolytes to use the cells at lower temperatures (-55°C with a small ohmic drop) • Increase the energy density using Li electrode (specific energy up to 40 Wh/kg on button cell [2]) Fig. 2: -55°C 650F Cell and high energy density button cell. A new DC/DC converter [3] has been design to charge and discharge the supercapacitor. Fig. 3: RECUPENER Bidirectional chopper for supercapacitors This topology, prevents short-circuit between the network and the supercapacitor banks in case of failure of a semiconductor; allows a low current ripple (multilevel topology and interleaving) and a low Common Mode voltage on the supercapacitor. The efficiency is up to 98% with a high power density. Energy management Energy management algorithms were developed to: • Minimize the power consumption, • Minimize the regenerative energy dissipation, • Optimize the state-of-charge of the supercapacitor for safety operations, • Ensure a Back-up mode (in case of temporary network loss). Several strategies [4] could be used, from conventional ones to an innovative multi-objectives rule-based energy management strategy in order to obtain the most appropriate and optimized energy management according to all the expected objectives. Fig. 4: Flight control system in “turbulent mode” Fig. 5: Same condition with a 5s network loss HVDC Protections The SSPC HVDC protections used for this application must be bidirectional in current to recover the energy produced by the actuators. This study was based on SABER© models. It took into account: • Different network architectures (star or bus), • Fault location, • Saturation of the inductance, • Impedance and control of the DC/DC converter, • Parametric study of the wiring and filtering impedance, • Control and topology of the loads (converters and motors). The impact of the short-circuit [5] in different configurations was used to compare different strategies to switch off the SSPC: • Instantaneous trip, • Switching off after the first peak current, • Current limiter. Fig. 6: Short-circuit with instantaneous trip Table 1: Dolor sit amet Fig. 7: Short-circuit with current limiter The future platform will firstly be fitted with bidirectional SSPC with instantaneous trip in case of short-circuit to verify the model. Stability Passive LC filters are used in power electronics to reduce the ripples. These filters are usually poorly damped to reduce losses. This leads to instability phenomena if the load power exceeds a power limit depending on the filter parameters. Different active stabilisation controls have been developed [6] to drive the loads and the DC/DC converter in order to stabilize the HVDC network and optimize the filters whatever the network configuration. Fig. 8: Stabilization principle Simulations and measurements (taking into account all the delays due to the control and the sensors) show the performances of these stabilization laws, with network resonant at frequency up to 2 kHz. Fig. 9: Actuator current and DC bus voltage with and without stabilization. Conclusions The challenges necessary to control a HVDC network have been overviewed. Several solutions and technologies have been presented to address them. We have shown that is possible to optimize the HVDC network by taking into account improvement of the energy storage and its associated converter, energy management, protections and stability. The way to propose the best solution for each HVDC local network is to: • Master the key technologies (Protection, energy storage, DC/DC converters, …), • Optimize the system energy & power consumption, • Optimize the system design through Stability knowledge, • Optimize the wiring system (weight, protections, …), • Integrate as soon as possible all the elements on a representative test bench. The testing activity is in progress and the platform will enable representative testing on local HVDC network (270V or 540VDC) with energy storage and programmable loads and variable impedances. Fig. 10: Local HVDC network test bench. References 1 Patrick W Wheeler, Jon C Clare, Andrew Trentin and Serhiy Bozhko, An overview of the more electrical aircraft, Journal of Aerospace Engineering 2013 227: 578, originally published 21 December 2012 2 Jérémy Come; Veronica Augustyn, Jong Woung Kim, Patrick Rozier, Pierre-Louis Taberna, Pavel Gogotsi, Jeffrey W. Long, Bruce Dunn and Patrice Simon, Electrochemical Kinetics of Nanostructured Nb2O5 Electrodes, Journal of The Electrochemical Society, 161 (5) A718-A725 (2014) 3 Charif Karimi, Laurent Brosson, Marc Pontrucher et Sebastien Vieillard, Module de conversion de tension entre un réseau électrique haute tension d'un aeronef et un element de stockage d'energie, Patent EP 2659567 (A2), FR 2969861 (B1), 2010 4 Jean-Charles Swierczek, Fabien Mollet, Christophe Saudemont, Régis Meuret and Benoît Robyns, Power management of a regenerative local HVDC aircraft network using supercapacitors, 15th International Power Electronics and Motion Control Conference, EPE-PEMC 2012 ECCE Europe 5 Jean-Charles Swierczek, Fabien Mollet, Benoit Michaud, Régis Meuret, Christophe Saudemont and Benoît Robyns, Protection of local High Voltage DC regenerative network on MEA, EPE'13 ECCE Europe, 2013 6 Pierre Magne, Contribution à l’étude de la stabilité et à la stabilisation des réseaux DC à récupération d’énergie, Thèse présentée à l’Université de Lorraine, 2012.