Dries Verstraete

Micropower generation with microgasturbines: A challenge

Abstract This paper describes the development of a microgasturbine with a rotor diameter of 20 mm. The target electrical power output lies around 1 kW. The total system fits in a cylinder with a diameter of 95 mm and a length of 120 mm. The system contains the same components as a large gasturbine generator: compressor, recuperator, combustion chamber, turbine, and electrical generator. Major challenges are the high rotational speed (500 000 r/min), high turbine inlet temperature (1200 K), and the efficiency of the components. Because of the small dimensions, the flow through compressor and turbine is characterized by relatively low Reynolds numbers. The higher flow losses and inherently lower efficiency require a higher blade tip speed (524 m/s) than for large turbines (300-400 m/s). To minimize wear and frictional losses, the rotor is mounted on aerodynamic bearings. To withstand the high centrifugal stresses, a high-strength steel is used for compressor and shaft. The turbine is made of a Si3N4-TiN ceramic composite to withstand the combination of elevated stress and temperature.

Hyperion UAV: An international collaboration

The Hyperion aircraft project was an international collaboration to develop an aerial vehicle to investigate new technologies with a focus on performance efficiencies. A delocalized international team of graduate and undergraduate students conceived, designed, implemented, and operated the aircraft. The project taught essential systems engineering skills through long-distance design and manufacturing collaborations with multidisciplinary teams of students located around the world. Project partners were the University of Colorado Boulder, USA, The University of Sydney, Australia, and the University of Stuttgart, Germany. The three teams are distributed eight hours apart; students can relay select work daily so that developments can “Follow-The-Sun”. Select components are manufactured and integrated both in Stuttgart and Colorado, giving the students an opportunity to learn multifaceted design tactics for manufacturing and interface control. Final flight testing was conducted by the global team in Colorado during the month of April 2011.

Preliminary Design of an ACES TSTO Air Launch Vehicle

This paper addresses a detailed preliminary design study of a twin fuselage semi-reusable TSTO launch vehicle. This double fuselage carrier, which would use hydrogen as a fuel, also collects the liquid oxygen (LOX), needed afterwards to propel the all-rocket orbiter. This collection takes place during an extended subsonic cruise phase that precedes the air launch of the orbiter. The concept of this 3 generation semi-reusable launch vehicle will be explained and the results from a detailed preliminary design with the AAA (Advanced Aircraft Analysis) software from Darcorp (USA) will also be given. The results for the aircraft weight distribution will be given as well as performance, aerodynamics and longitudinal stability indications for two reference missions. Besides that, the influence of the collection ratio obtained with the LOX collection plant upon the design of the launch vehicle is also addressed.

Two-transistor step-down DC/DC converters with fault-tolerant capability

This paper presents a family of two-transistor step-down dc/dc converters with fault-tolerant capability which is derived through graph theoretic approach. The fault-tolerant property deals with open-circuit fault of one of the power transistors in a two-transistor dc/dc converter structure. Under normal operation, either one of the two transistors can be used to control the power flow and the other transistor is idle. When the fault occurs, the other transistor will be activated to provide an alternate current path to continue converter operation and maintain output regulation. Derivation procedure and some experimental results are reported.

Structural Design Optimisation and Aerothermoelastic Analysis of LAPCAT A2 Mach 5 Cruise Vehicle

Structural design of hypersonic aircraft is highly affected by their non-conventional shapes and dimensions, and especially by the very high temperature loads encountered during flight. Indeed, compared to classical aircraft, the non-conventional configurations may lead to largely different internal structural stresses, and the temperatures would lead to high thermal stresses and a significant reduction in material strength and stiffness, resulting in innovative concepts. Moreover, the reduction in structural rigidity requires a stronger focus on aerothermoelastic deformations in the design and optimisation of the aircraft structure. This imposes the need for a closer coupling of the aerodynamic and structural tools than current practice. The current paper presents how the different sizing, analysis, design and optimisation tools are coupled in the design of the structure for the LAPCAT A2 vehicle and gives results of the optimisation of the A2 canard and wing. A wing structure with 6 spars and 6 ribs with cross-grid stiffeners, and a movable canard structure with 3 spars and 7 ribs and an ortho-grid stiffened skin lead to the lightest solutions. Buckling has been identified as the main weight driver for both cases, regardless of the number of ribs and spars used. The design and optimisation of the fuselage (ring frames, longerons and skin) is in progress. The aerothermoelastic module has also been implemented and applied successfully to the A2 wing, leading to the static aerothermoelastic solution after only 4 iterations.

Power loss modelling of MOSFET inverter for low-power permanent magnet synchronous motor drive

This paper investigates an analytical power loss modeling method applied to a three-phase voltage source inverter, aiming to obtain an accurate inverter loss without the need of extensive experimental measurement, under the context of inverter efficiency optimization. Modeling of semiconductor is achieved through analytical equations for conduction and switching losses in the MATLAB/Simulink environment, using drain-to-source current and voltage waveforms. An experimental verification consisting of low power DC-source, three-phase MOSFET inverter and brushless dc motor, is conducted to validate the loss model. It is found that the modeled power loss is generally consistent with experimental verification at incremental dc-link voltage from 12V-18V, with inverter efficiencies in the 94.7-97.4% and 94.5-97.2% regions, respectively. The developed loss model can be used in fast inverter-motor drive power loss optimization where losses depend on circuit parameters and operating point of motor, which are accounted for in the developed model.

Derivation of Dual-Switch Step-Down DC/DC Converters With Fault-Tolerant Capability

This letter presents a graph-theoretic approach to deriving a family of dual-switch step-down dc/dc converters with fault-tolerant capability. The constraint sets in the derivation process ensure that minimum additional component is used to achieve fault-tolerant operation. The operation of converters derived is flexible. Under normal operating conditions, one of the two switches can serve as a main switch to control the power flow (i.e., single-switch converter operation) and the other switch is in stand-by mode. When a fault occurs on the main switch, the other switch will be activated to provide an alternate current path to continue converter operation and maintain output regulation. The fault-tolerant converters are derived by integrating a buck converter with a buck-boost converter. They share all the components except for the power switches. Due to different duty cycles required between the two operating conditions, a feedback controller is necessary to adjust the duty cycle for tight output regulation. The derivation procedure and experimental results on fault occurrence are reported. The converter derivation approach is able to identify reported topologies and can be extended to synthesize other topologies with fault-tolerant capability.

Analysis of a three-port DC-DC converter for PV-battery system using DISO boost and SISO buck converters

Combining a storage device and renewable generation is one of the viable solutions to deal with the intermittency of renewable energy sources. Conventional methods of combining these components involve multistage and single-stage converters. However, there is a trade-off between efficiency and component count. A novel non-isolated three-port DC-DC converter which combines a dual-input single output (DISO) boost and a single-input single output (SISO) buck converters for a photovoltaic (PV) - battery-load system is proposed in this paper. There are five different operation modes to achieve different scenarios for maximum power point tracking, battery charging and load regulation requirements. Experiment results are given to confirm this proposed converter.

Temperature Effects on Flutter of a Mach 5 Transport Aircraft Wing

The high temperatures encountered during flight severely impact the structural design of hypersonic aircraft. They can lead to high thermal stresses and a significant reduction in material strength and stiffness. This reduction in structural rigidity requires innovative structural concepts and a stronger focus on aero-elastic deformations in the design and optimisation of the aircraft structure. This article investigates the effects of high temperatures on the flutter behavior of the wing of the A2 aircraft, a Mach 5 transport aircraft designed as part of the European Commission Framework VI LAPCAT program. The article presents results for various simplified temperature distributions. These temperature distributions were imposed to look at the fundamental trends in the flutter velocity and frequency with both temperature and temperature distribution. The results for the A2 wing are compared with other wing models to identify effects of geometry variations. The analysis shows that the flutter velocity drops by about 20% when a uniform temperature of 500 °C is applied to the wings. When temperature gradients are applied, a drop of 5–10% is found, which is in line with findings in literature.Copyright

Analysis of a Fuel-Cell/Battery/Supercapacitor Hybrid Propulsion System for a UAV using a Hardware-in-the-Loop Flight Simulator

Fuel-cell based hybrid propulsion systems are being considered as a means to increase the endurance and range of small electric powered unmanned aerial vehicles. However fuel cell durability is limited by the rapid load changes requested by the autopilot. In a fuel-cell/battery /supercapacitor triple hybrid the battery provides boost power whilst the supercapacitor increases fuel cell life through load levelling. This paper presents the analysis of a fuel-cell/battery /supercapacitor hybrid propulsion system using a high fidelity hardware-in-the-loop simulator. The hardware-in-the-loop simulator allows accurate application of the expected dynamic electrical loads experienced in flight on the hardware components without the risks associated with flight testing. The triple hybrid system demonstrates load smoothing by the supercapacitor to the fuel cell under simulated operating conditions, with this buffering increasing fourfold under gusty flight conditions.