Integrated Modular Power Electronics: Achievements and Challenges

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Integrated Modular Power Electronics: Achievements and  Challenges


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Integrated Modular Power Electronics: Achievements and Challenges T. Bensalah (1), P. Thalin(1) 1 : Thales Avionics Electrical Systems, 41, Rue de la République 78400 CHATOU Abstract: Driven by weight reduction and reliability, the more electric aircraft approach has become the design standard for future aircraft programs. Power Electronic Modules (PEMs) are used to address both active power conversion & motion control functions for multiple systems: engine start, air-conditioning, wing ant-ice, hydraulics, etc. Unfortunately overall aircraft systems weight cannot be optimized if each system uses its dedicated power electronics. The challenge therefore is to work on electrical architectures and equipment driving weight to lowest possible levels. This paper deals with advanced studies whose main objective is demonstrating the feasibility of such new architectures for a single aisle aircraft and the way forward in the weight reduction of power converters thanks to emerging technologies of power components. Introduction To achieve MEA targets, various approaches have to be explored in order to evaluate potential weight and volume savings. One of them is the Integrated Modular Power Electronics (IMPE) architecture involving high density power electronic modules meeting the very demanding MEA requirements in terms of reliability, maintainability and weight. Sharing resources such as the power electronic modules, that can be paralleled, for supplying power to different loads with high power ratings, reduces the KVA power installed on board. In addition, the modular power electronics enable optimized power management strategies. Thales is currently working on both the modular and high power density aspects of the PEMs. Both architecture/technology feasibility studies and demonstration have been carried out within the French advanced research project PRISCA. Activities on improved PEM power density, industrialization, installation and removal times, etc have been the major focus of the European Clean Sky project. This paper describes the benefits of solutions addressing specific loads : engine start via a Variable Frequency Starter Generator (VFSG), 115VAC-400Hz constant frequency network power supply, Environmental Control System (ECS)… Modular versus dedicated Power Electronics The reference architecture (Figure 1) is similar to the one studied in the European MOET (More Open Electrical Technologies) project. It is based on power electronics dedicated to each load except for engine start & ECS wherein the same power electronics ensure the control of both functions. Figure 1 Dedicated Power Electronics The Integrated Modular Power Electronic architecture is based on a disruptive principle developed and tested in the frame of PRISCA. It consists in implementing power management strategies including multiple ”available”, reconfigurable, modular and shared PEMs. IMPE requires a contactor or switch matrix ensuring reconfiguration and allowing paralleling of PEMs. The number of paralleled PEMs depends on load power requirements. For example, upto a maximum of three PEMs are switched in parallel for electrically starting the aircraft engines. Nevertheless, resource sharing comes with some limits. It was proven difficult to share PEM output filters which therefore need to be customized to suit load requirements. The IMPE architecture is shown in Figure 2. . Figure 2 Modular Power Electronics PRISCA IMPE achievements The IMPE electrical architecture deals with the following stringent PEM requirements among others : -High-speed datalink due to power device switching frequencies and PEM paralleling -PEM hosting capability of several application softwares depending on loads being addressed -Configuration/re-configuration of PEMs depending on loads being addressed. The IMPE demonstrator (Figure 3) allowed functional testing and weight/ reliability estimations. Some key advancements compared to the reference architecture are listed below :  Modular power electronics time-shared by power systems. Power management and PEM reconfiguration feature  Overall system weight reduction by around 10% compared to reference architecture  Two fold probability reduction for the “loss of engine start capability” functional hazard transformer 115 V board CID board C28V board CPRO computer dSpace board PSHVDC board CDIS plate HVDC distribution 115 V/WIPS distribution VFSG distribution coupler VFSG/Fan distribution ECS/VCS cold plates = 2 inverters / plate Figure 3: PRISCA IMPE Demonstrator VFSG in engine starting mode Paralleled PEMs working as motor control units in interleaved mode were used, along with inter-phase inductors and appropriate controls, to supply power to the VFSG in engine starting mode. Figure 4 shows VFSG stator current, voltage, torque and speed parameters during the successful engine start test sequence. Figure 4 Engine start with VFSG and 3 PEMs in parallel 115VAC- 400Hz power supply Reverse operation of a PEM in conjunction with a filter and transformer (Figure 5) allows yet another functional capability of the PEM by generating a 115VAC- 400Hz power supply from a High Voltage DC bus. Figure 5: PEM Filter and 400Hz transformer The following stability and harmonic distortion performances were demonstrated for that power supply: - Regulated output voltage = 115V +/- 2V - Voltage Harmonic distortion factor < 2.5% - Frequency accuracy < 1% - Voltage overshoot during step load variation (100% to 0%) < 20V Clean Sky IMPE : a step further Industrialization of PEMs and filters is part of Thales’ focus within the ongoing Clean Sky project. In fact, in order to ease maintainability, mounting and dismounting time was optimized by implementing electrical and hydraulic pluggable connectors for rackable PEMs. Figures 5 and 6 highlight PEM and filter/transformer advancements as regards manufacturability and compactness. From Concept to « Industrial » product and Power density increasing, Figure 6 : PRISCA and Clean Sky PEMs With PRISCA, the PEM reached a power density of 3 kW/kg whilst Clean Sky allowed doubling that performance to 6 kW/kg with similar liquid cooling. For the Clean Sky PEM, IGBT power losses have been dramatically cut thanks to advanced PWM control patterns for switching. Moreover, advanced mechanical design and packaging helped minimize loop and stray inductances. Testing carried out shows (Figure 7) low overvoltage build-up across IGBT switching for the following conditions : - Vcc = 540VDC - Load current = 120A Figure 5 : Voltage/Current across IGBT Conclusion The IMPE research activities carried out this far and presented in this paper show the huge benefits arising from architecture, technology and control strategy advancements with primary focus in the following areas : - System modularity - Power density The PEM power density of 6kW/kg reached is a step change paving the way for future miniaturization. Nevertheless, further efforts are needed to increase power density by introducing wide bandgap semiconductor switching devices such as Silicon Carbide along with high temperature components in order to challenge current cooling techniques and the incurred weight penalties. References [1] T. Bensalah, M. Py and P. Thalin, PRISCA Modular Electrical Power Management, More Electric Aircraft, 20-21 Nov. 2012, Bordeaux, France [2] Ming Hua, Haibing Hu, Yan Xing, Zhongyi He, “Decoupled Control of Inverters in Parallel Operationfor AC Motor Drives” IECON 2009 Proceedings,pp.1065- 1069. [3] Richard Zhang, “High performance power converter systems for nonlinear and unbalanced load/source” Phd dissertation Nov 1997 Virginia. [4] P-L. Wong, P. Xu, B. Yang and F. C. Lee, “Performance Improvements of Interleaving VRMs with Coupling Inductors”, IEEE Transactions on Power Electronics, vol. 16, no. 4, 2001, pp 499-507. [5] A. Tardy, “Device for supplying a plurality of loads from an electrical power feed network”, Thales Patent WO 2007/113312.