MEA Power System Development Facility More Electric Aircraft Power System Development Facility Introduction Over the past decade, the aircraft industry has converged on a shared vision for the future of aircraft power systems. This vision represents a dramatic shift away from various types of power found in traditional aircraft and offers a wide range of benefits for tomorrow’s commercial and military aircraft. The non-propulsive power systems in traditional aircraft are typically driven by a combination of different secondary power types including: hydraulic, pneumatic, electrical and mechanical power [1-6]. All power is extracted from the aircraft engines. Hydraulic power is provided using hydraulic pumps driven by mechanical rotation sourced from the engine gearbox and is distributed to power various aircraft systems including flight control actuators, aircraft braking, landing gear extension/retraction, and door closure. Pneumatic power is extracted from the engine, using software controlled bleed valves, and is used to power the aircraft Environmental Control System (ECS) and wing anti-icing. Mechanical power from the engine gearbox also drives lubrication and fuel pumps. While electrical power contributes to the capability of nearly every aircraft system in modern aircraft that make increasing use of airborne software controlled electronic systems. The market demand for more energy efficient aircraft is driven by many stakeholders including airline operators, legislators, and public opinion. In the meantime, power electronics technology has made tremendous breakthroughs over the past decade in areas including electromechanical actuators (EMA), electro-hydrostatic actuators (EHA), fault-tolerant electric motor/generators, and power converters. This forward-leap of technology creates a viable path, fueled by economic gain, for replacing many and potentially all of the hydraulic, pneumatic, a mechanically powered non-propulsive systems with electrically powered systems [1-25] to design a More Electric Aircraft (MEA). The Challenge Industry has recently achieved general agreement on key elements of the MEA. For example, industry is now focusing on technology based on a high-voltage DC power distribution architectures with 270VDC distribution emerging as the most popular approach. However, optimizing aircraft power systems technology to support a 270VDC distribution system, including generation, distribution topology, power conversion, and the design of specific MEA systems, is a complex effort. There is a high-level of dependency and interaction between the various systems in a given MEA design with complex and fast dynamics. There is a wide range of technology that must be refined and optimized within the context of a single aircraft design in order to achieve the cost reduction goals for the MEA. These challenges give rise to a capability requirement; a requirement for a flexible MEA development platform that can accelerate the pace of development of MEA technology. The Solution The proposed solution relies on Model Based Systems Engineering (MBSE) methodologies and technology that have evolved rapidly over the past two decades and draws on MBSE technology in the area of power systems and power electronics. This whitepaper proposes a Power-Hardware-in-the-Loop Page 1 of 16 Version 1.1 MEA Power System Development Facility development and test facility that enables MEA technology to be combined with simulated flight and simulated power system behavior: The MEA Power System Development Facility. The MEA Power System Development Facility enables technology concepts and prototypes to be tested as pure simulation in closed-loop with real aircraft power systems, operating with representative electrical behavior, and evaluated through normal and failure mode flight conditions. The MEA Power System Development facility is based on Applied Dynamics technology development and contribution to the current state-of-the-art in the aircraft industry’s drive towards the MEA vision. More Electric Aircraft Power Systems Development Facility The More Electric Aircraft Power Systems (MEAPS) Development Facility is a high-performance, realtime, power-hardware-in-the-loop developing and testing capability that: allows high-fidelity aircraft simulation to be combined with real and/or simulated aircraft power system devices; enables the Page 2 of 16 Version 1.1 MEA Power System Development Facility configuration of the MEA power network to be changed and evaluated; allows real and emulated generators to be connected to the MEA power network; provides high-fidelity active load emulation to evaluate the effects and performance of electromechanical and electrohydrostatic actuators; and includes high-speed data acquisition throughout the facility for the characterization of each element of the system. Components of the MEAPS Development Facility include: Active load emulation system Active load Hyperfast real-time simulator Generator emulation system Distributed real-time simulator platform MEA power network Flight and aircraft system simulation models Simulation framework software platform Active Load Emulation System The active load emulation system is a power hardware system that provides bidirectional energy transfer for DC sources or loads. The active load system generates a dynamic DC load and feed the resulting power back into the facilities 3-phase AC. The DC voltage is controlled by a setpoint input for each output channel. The figure below shows a schematic of a 3-channel active load emulation system. The active load emulation system is used in the MEAPS Development Facility to draw DC current off the HVDC MEA power network with behavior controlled by simulation of dynamics loads. For example, the Page 3 of 16 Version 1.1 MEA Power System Development Facility active load Hyperfast real-time simulator is used to run high-fidelity electromechanical or electrohydrostatic simulation models, the value of this current draw is sent from the Hyperfast real-time simulator to the active load system which behaves accordingly. The figure below shows the dynamics DC current behavior generated by the active load emulation system when a flight control position step change command is sent to an electromechanical flight control actuator simulation and drive the active load system. Active Load Hyperfast Real-Time Simulator The active load Hyperfast real-time simulator is a real-time simulation computer system dedicated to providing control of the active load emulation system. This real-time system is a multi-core, deterministic simulator capable of running simulation with sub-10us step time. Simulation models (ex: Simulink, C code, etc.) are locked to a processor core with direct access to analog and/or digital interface channels. This real-time simulator uses the ADvantage Framework software for system configuration, operation, and data acquisition. The active load real-time simulator interfaces with the other real-time simulation computers in the MEAPS Development Facility using the ADvNET distributed real-time simulation toolbox. Page 4 of 16 Version 1.1 MEA Power System Development Facility The figure above illustrates an electromechanical actuator simulation that is executed on the active load Hyperfast real-time simulator. The position controller, speed controller, current controller, motor, and gearbox/ballscrew are modelled. The figure below shows this nested closed-loop control simulation implemented in Simulink. The value of DC current, Iload, becomes the setpoint to the active load emulation system. The MEAPS Development Facility allows multiple EMA and EHA actuators to be simulated and allows their electrical behavior and interaction with the MEA power network to be replicated in real-time. This allow all the actuators for a single aircraft to be simulated and electrically emulated. The position and load command sent to the active load Hyperfast real-time simulator is generated by the real-time flight simulation (ex: 6DOF, aerodynamics, flight control system, etc.) executed in the distributed real-time simulation platform. This enables the MEA power network, and all real power systems included in a test to interact with power system dynamics that are highly representative of any desired flight conditions. Generator Emulation System The generator emulation system is a power module that provides bidirectional transfer of energy between AC source and DC loads. In the case of the MEAPS Development Facility, the MEA power network acts as the DC load and the generator emulation system acts as a DC voltage generator with programmable, dynamics voltage setpoint and programmable current limit. The generator emulation system provides behavior that matches a real engine driven generator with AC-DC converter behavior by executing real-time simulation models of the gas turbine engine, the generator, the converter, and the generator/converter control unit. These simulation models are executed on the distributed real-time simulator platform send voltage setpoints to the generator emulation system, and receive voltage and current measurement feedback from the generator link to the aircraft power network. This real-time simulation results in converter output voltage and current characteristics that are sent to the generator emulation system and performed. The figure below shows a schematic of the generator emulation power module. Page 5 of 16 Version 1.1 MEA Power System Development Facility Page 6 of 16 Version 1.1 MEA Power System Development Facility Distributed real-time simulator platform The real-time simulator platform provides the ability to execute high fidelity flight simulation, simulation of aircraft systems, and simulation of power system dynamics with real aircraft systems in-the-loop. This enables the MEAPS Development Facility to incorporate real electrical loads, connected to the MEA power network, stimulated to behave as they do during flight. The MEAPS Development Facility uses a distributed real-time simulation system with multiple simulator nodes, each with multicore processors. The figure above illustrates the distributed real-time simulator platform. The multiple simulator nodes communicate with one another across a high-speed distributed communication interface. The ADvantage Framework software platform allows these systems to be configured and operated as though they were a single simulation system. A distributed, IRIG-B common clock triggers the time scheduling of each system and maintain synchronized execution of simulation and I/O scheduling. Signal interfaces included in the distributed real-time simulator platform put each aircraft system undertest into closed-loop operation with simulation models and/or other aircraft systems providing realistic and accurate behavior. The real-time simulator platform interface signals can be divided into four main types. The table below lists these interface signal types. Page 7 of 16 Version 1.1 MEA Power System Development Facility Signal Type Example Sensor Emulation Thermocouple, Resistive Temperature Device, Linear Variable Displacement Transducer (LVDT), Digital Encoder, etc. Torque Motor, Solenoid, Igniter, etc. ARINC-664, ARINC-429, CAN, RS232/422/485, MIL-STD-1553, IEEE1394, etc. Analog, Digital Actuator Measurement Serial and Databus Data Acquisition Channels MEA power network The MEA power network is a ‘ring main’ type distribution system offering flexibility for isolating loads, for re-routing power during faults at various locations throughout the network, and providing the ability to share power between generating sources. Protective functionality is provided with switchgear that also provides the ability to insert electrical faults. Fault management, ring configuration and re-routing, and load management are controlled using a real-time controller. Load Emulation Three types of load emulation may be included in the MEAPS Development Facility to represent different aircraft system load characteristics. These include: Resistive loads – This provides a constant load on the DC network in order to replicate “background” loads found in the aircraft such as avionics systems. A variable resistive load allows the load level to be increased in steps up to 50kW. Continuous switching power electronic load – This represents a power electronics interface to drive a number of continuously running loads, such as the aircraft environmental control system, electric fuel pump, and radar communications system. This type of load emulation is provided by the active load emulation system described earlier in this paper. Dynamics switching power electronic load – This represents the “pulse” loads associated with electromechanically actuated flight controls. This type of load emulation is provided by the active load emulation system described earlier in this paper. Flight and Aircraft System Simulation Models Applied Dynamics offers the iAircraft Simulink aircraft model library providing real-time simulation of flight and aircraft systems. iAircraft is a comprehensive set of aircraft simulation capability used in the aircraft industry for a wide range of applications. The iAircraft library is an open architecture set of models enabling users to parameterize, reconfigure, and replace Simulink subsystems as needed. The iAircraft library includes the following: High fidelity 6-degree-of-freedom flight dynamics model with rotating spherical earth & configurable aerodynamics Configurable landing gear with nose wheel steering as a function of rudder pedal and tiller travel, high-fidelity tire model, and dynamics gear suspension Comprehensive autopilot modules including intercept & track, heading hold, bank angle hold, and more Aircraft ‘trim’ module for initializing flight at a selected stable flight condition Page 8 of 16 Version 1.1 MEA Power System Development Facility Scriptable ILS landing capability High fidelity gas turbine engine model for testing application that include an EEC or low fidelity model engine pressure ration based model for simpler development and testing applications High fidelity Environmental Control System (ECS) blockset Out-The-Window (OTW) visuals interface The figure below shows the iAircraft library within the Simulink browser. The iAircraft flight controls library components can be used to simulation hydraulic, electromechanical, or electrohydrostatic flight control actuators and can be put in closed-loop with the dynamics load system. The iAircraft landing gear library components include high-fidelity runway interaction with high-fidelity lateral and longitudinal tire model for steering and antiskid braking. The landing gear model provides the fidelity and detail required to drive the dynamic load system with antiskid braking power behavior. The figure below shows an example iAircraft braking and steering configuration. Page 9 of 16 Version 1.1 MEA Power System Development Facility Power System Simulation Aircraft power system simulation models are required to provide accurate dynamics behavior of all emulated power system components. These power system models include: Generator and generator control unit models – switch level model including exciter, rotating rectifier, and diode bridge/inverter output stage Electrical distribution unit model – feeder electrical dynamics between the generator inverter converter controller (ICC), the actuator loads, and generic loads DC-DC converter models – RMS current models and average current models for boost and buck mode converter operation EMA and EHA actuator models – segment level actuator models including input EMI filters, active switching, and rotating machine All aircraft power system simulation models are developed in Simulink using the SimPowerSystems toolbox. The accuracy and detail of component blocks within SimPowerSystems are ideally suited for modeling complex electrical behavior. However, the real-time performance of these models can be problematic in terms of the computational efficiency of the generated code and the ability to execute these models at a frequency sufficient to represent fast dynamics. Applied Dynamics has been successful in solving this problem by systematically replacing some of the inefficient generated code with highly optimized code[40]. The figure below shows a Simulink SimPowerSystems model of the MAE electrical distribution unit. Page 10 of 16 Version 1.1 MEA Power System Development Facility Simulation framework software platform Software to rapidly configure and operate the MEAPS Development Facility is provided using the ADvantage Framework MBSE software platform. ADvantage provides real-time simulation and analysis capability for advanced aircraft development projects throughout the world and at leading aerospace and defense companies including: Boeing, Gulfstream, Rolls-Royce, Crane Aerospace, Parker Aerospace, COMAC, BAE Systems, Mitsubishi Heavy Industries, and General Dynamics. ADvantage includes desktop tools and run-time services software. Tools include: ADvantageDE – Development environment used to configure the MEAPS facility, add Simulink models, connect real and simulated equipment, compile and package projects ADvantageVI – Operator environment used to control the facility through interactive or automated tests SIMplotter – Data acquisition, plotting and analysis of distributed real-time streaming data ADvantageDB – Configuration of analysis of serial and databus networks ADvantageFC – Electrical fault insertion macro definition and control Page 11 of 16 Version 1.1 MEA Power System Development Facility The ADvantage run-time services software provides the high-performance software capabilities within each real-time simulator in the MEAPS facility including: logical device engine, serial communications handler, assembly containers probe engine, data acquisition engine, real-time scripting engine, supervisory schedule, and Ethernet connected control adapter. Generator-in-the-Loop In addition to generator emulation, the MEAPS Development Facility also allows real generators to be put in-the-loop for the development of generator control units, to evaluate performance, fault tolerance, etc. The figure below shows a real generator incorporated into the MEAPS Development Facility. In order to add a real generator to the facility, a dynamometer is used to provide mechanical drive that is controlled in closed-loop with the gas turbine engine simulation. A control loop is incorporated within the real-time simulator to set speed commands to the dynamometer AC drive, measure shaft load, and turn the real generator with behavior matching the generator operating during simulated flight. Page 12 of 16 Version 1.1 MEA Power System Development Facility Testing Aircraft Electrical Network Protection HVDC aircraft power networks represent significant challenges for electrical network protection. The high levels of stored energy and low impedance interconnections between systems can lead to the creation of high peak fault current magnitudes and rapidly propagating fault effects. Therefore, very fast acting protection schemes must be developed to achieve the desired levels of protection to minimize disruption to the remainder of the electrical network. Furthermore, the electronic converters required by this type of HVDC network worsen the protection challenge. The MEAPS facility is the ideal development and test platform for developing protection strategies and testing prototype fault protection equipment. Significant work is on-going across the industry to develop fast acting solidstate circuit breakers such as the Emitter Turn Off (ETO) based DC circuit breaker shown below. Test and Evaluation of Advanced Power Electronics A critical component of the MEA HVDC architecture is high-efficiency DC-DC converter used to convert from 270VDC distributed power to low voltage power used by aircraft systems. Significant innovation is happening across the industry for a range of MAE power electronics technologies. The figure below shows an advanced Dual Active Bridge (DAB) DC-DC converter designed for MEA applications and tested at the IEPNEF facility in the UK. Page 13 of 16 Version 1.1 MEA Power System Development Facility References [1] I. Moir and A. Seabridge, “Aircraft systems : mechanical, electrical, and avionics subsystems integration”. London, 2001. [2] M. J. J. Cronin, "The all-electric aircraft," IEE Review, Vol. 36,1990, pp. 309-311. [3] R. I. Jones, "The More Electric Aircraft: the past and the future?," in IEE Colloquium on Electrical Machines and Systems for the More Electric Aircraft, , 1999, pp. 1/1-1/4. [4] R. E. J. 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