Multi-modal safety analysis of the more electric aircraft starter generator system

Under the more electric aircraft (MEA) theme, many aircraft systems are being electrified. In a previous research work, an electric starter generator system for aircrafts was implemented. This paper presents the reliability of the drive converter – a 3 level neutral point clamped converter (3L-NPC) under an expected mission profile of a short haul aircraft. Wearout failure based reliability of semiconductors and capacitors are considered along with reliability of gate drivers to estimate the overall reliability of the converter.

In this paper a wind electrical power generation system for Distributed on Site (DoS) applications is proposed. This system was developed and conceived in order to guarantee simple installation, use and service, obtaining a product that can be easily industrialized and put into the market with limited costs. The field of application of such an electrical generation system is addressed towards domestic or at the most toward condominium applications concerning moreover the opportunity of working in addition to combined photovoltaic and solar-thermal systems to enhance the renewable energy generation at house level (DoS). The proposed system has its hot spot in the blades shape, in the wind flux canalization system and in the permanent magnet synchronous generator (PMSG) optimized for this specific purpose. In fact with the proposed system intends to search the best aerodynamic profile and electrical generator to ensure the slightest encumbrance and the lowest weight. For this purpose the traditional and classical tangential wind turbine design, equipped with large blades, is overturned in favour of the use of numerous little blades. A further peculiarity of the system is the expected increase of its efficiency thanks to the presence of the wind flux channelling system with the elimination of the part opposing the wind and thanks to the adoption of a specifically designed PMSG.

Opportunities and challenges of brushless evolution for aircraft low-voltage DC generator system

With the development of more electric aircraft (MEA), higher demands for electrical energy are put forward in generation systems. Compared to constant frequency AC (CFAC) generation systems, the constant speed drive (CSD) is eliminated and integrated starter/generator (SG) can be realized in variable frequency AC (VFAC) generation systems. In this paper, an overview of VFAC generators for safety-critical aircraft applications is presented, with a particular focus on the key features and requirements of candidate generators and the starting control strategies. Wound rotor synchronous machines (WRSMs) are typical generators used in VFAC generation systems so far. Meanwhile, hybrid excitation synchronous machines (HESMs) and cage-type induction machines are promising candidates for VFAC generation systems. The generation operation of WRSM is relatively mature, however, the SG technology of WRSM is still full of challenges. As one of the most important issues, the starting excitation methods of WRSM are summarized. An HESM-based VFAC SG system is proposed and developed in this paper. The experimental results show that the starting mode, transition mode and generating mode of the VFAC SG system are realized. The continuous progress of VFAC generation system makes great contributions to the realization of MEA.

This paper introduces an advanced space vector modulation technique for three-level neutral-point-clamped (3L-NPC) converters. The studied 3L-NPC converters within aircraft electric starter generator (ESG) systems normally operate at high modulation index, low pulse ratio and full power factor range for most of the operation time. Conventional modulation techniques exhibit large neutral point voltage ripple and possible voltage imbalance under such conditions. The increase of neutral point voltage ripple implies significant increase in converter capacitor size and decrease in capacitor reliability. The modulation technique introduced in this paper achieves improved neutral point voltage balancing within each switching period through enhanced applications of small vectors and restriction on medium vectors. The advanced implementation of small vectors is achieved using a sharing factor aided by a robust incremental current prediction procedure. With the predicted machine currents, the proposed method enables the optimum application of small vectors to balance the neutral point voltages. Simulation results based on a PLECS/Simulink model and experimental results obtained from a 45kVA, 32krpm aircraft electric starter generator prototype platform validate the reduction of the neutral point voltage ripple.

We propose a new hybrid electric vehicle which uses natural energy, consumes little fuel, and operates over a long distance. We are designing a series hybrid system, in which a diesel engine operating on plant oil rotates an electric generator, and runs the vehicle using the generated electricity. The generated electricity may also be stored in batteries, which are also able to power the electric vehicle. The general intention of the proposed system is to reduce the use of non-renewable fossil fuels, and to reduce overall costs. Plant oil is ecological, and allows for the creation of a carbon neutral system in its production. Some forms of plant oils, such as non-esterified straight vegetable oil (NE-SVO) and waste vegetable oil (NE-WVO), are promising alternatives used in order to reduce fuel costs. In this paper, we will explain the concept of the proposed series hybrid electric vehicle system using plant oil, and will provide some experimental results of mechanical optimization in the electric generation system and the vehicle drive system. Considering fuel efficiency and the drive torque, optimum reduction ratios were obtained in the experimental results.

In more electric aircraft (MEA) system, both AC and DC electric power with multiple voltage levels are required for various aircraft loads. This paper presents an induction generator based AC/DC hybrid electric power generation system for MEA. In the proposed system, a high speed induction starter/generator and a low speed induction generator are installed on the high pressure (HP) and low pressure (LP) spools of the engine, respectively. In generating mode of operation, all of the constant voltage variable frequency AC power is generated by the HP generator while the DC power demand is shared by both HP and LP generators. A control scheme is developed to regulate the AC load voltage and coordinate DC power generation between the two generators. The proposed induction generator based AC/DC hybrid generation system presents reduced hardware installment compared to existing AC and DC primary generation systems.

Curium-244 sesquioxide has many properties that makes it attractive as a heat source in electric power generator systems. Current radioisotopic thermoelectric generator designs generally specify fuel-containing interface temperatures from 800 to 1400$sup 0$C. Results of compatibility tests of $sup 244$Cm$sub 2$O$sub 3$ with a variety of materials are reported. Test conditions included 5000 h at 900 and 1400$sup 0$C, 2500 h at 1100$sup 0$C, and static helium and dynamic vacuum environments. Materials included graphite, ThO$sub 2$, superalloys, noble metals, and refractory metals. (auth)

The More Electric Aircraft (MEA) has been identified to be a major trend for future aircrafts. One of the key improvements introduced in MEA is its electrical power generation system. The generator system studied in this paper comprises of a permanent magnet machine and an active front-end rectifier. Rather than just using PI controllers to control the generation system, Model Predictive Control (MPC) is considered due to its ability to achieve fast dynamic performance and multivariable control. A variant of MPC called Modulated Model Predictive Control (MPC with intrinsic modulator) was recently introduced that showed significantly better performance than the standard MPC method. This paper presents a control scheme that utilizes Modulated Model Predictive Control for the current inner loop and PI controllers for the outer loop. The proposed control is compared with a full cascaded PI control scheme. Simulation tests are carried out to compare the two control methods and the results are presented and analysed.

A process scheme of using the absorption refrigeration machine in electricity generation systems in case of application of air cooling system of the steam turbine electric generators has been developed. The proposed scheme increases thermal power plant efficiency by 0.1-0.2% according to preliminary estimates, primarily by reducing power consumption on pumps and fans drive, as well as by reducing temperature of cooling heat carrier in the period with high ambient temperatures. A feature of the proposed technology is the combination of the most efficient air-cooling scheme and the absorption plant cycle in a single power technology complex. In this refrigeration machine, the working fluid is a binary mixture, one of the components of which is called a refrigerant, and the other one is an absorbent, where the liquid absorbent can absorb the refrigerant vapor. For the first time it is proposed to use an absorption refrigerating machine as the cooling system element of steam turbine electric generators. Currently, there are advanced air-cooling systems using multi-jet cooling for turbo-generators with a capacity of 3 to 180 MW. Finally, it can be used to increase the unit capacity of power units on the thermal power plants that use air-cooled power generators.

Pemex Exploracion y Produccion offshore marine platforms are located in the Gulf of Mexico. Inhabited platforms need electric energy to operate their processes and motors. This energy is supplied by motor generators and turbo generators. Typically, a marine platform has 2, 3 or more generators to always have electric energy available. The motor generators and turbo generators have a control system where operating personnel can start, stop and parallel them. Parallel generators mean to connect 2 or 3 generators to the same bus. The energy supplied to the bus is divided among the paralleled generators and each generator supplies energy proportional to its maximum capacity. The greater the capacity, the greater the energy it supplies. Most electric generator systems are stoped, started, and paralleled manually, but some systems have changed to automatic control systems based on Programable Logic Controllers (PLC). P. 109

Thermoelectric (TE) modules are a thermo-element device that can harness the heat and convert it into electrical energy. As an electrical generator system, TE has several advantages i.e not noisy, easy maintenance, relatively small, lightweight and environmentally friendly because it does not produce pollution. In this paper, the research about the performance of TE modules that used for electric generator has been done. TE modules utilize low temperature waste-heat from a solar cell that simulated with a combination of a bulb and a collector plate. TE modules which tested are single and double modules, in which for double modules, connectivity Thermal-Series was used. Parameters of performance such as output power generated are determined by measuring the temperatures difference and the voltages difference at the test module as well as using several equations. The results show that the distance of heat source and load applied will greatly affect the performance of thermoelectric generator (TEG) modules. The results showed that the number of modules and loading will greatly affect the performance of TEG modules. The use of heat pipes generate a far greater power 4-6 times on the single TE Module (0.84 mW) than without heat pipe (0.14 mW), and a double TE modules that uses heat pipe will became 4 times larger (1.48mW) than without heat pipe (0.37mW).

This paper studies the excitation of torsional vibrations by electromechanical interaction after the connection of electrical loads. Electrical generation and power system in aircraft are becoming of key importance, especially considering the current roadmap for aerospace systems' electrification. However, since the drivetrain which links electrical generators to the main engine is relatively flexible in most aircraft structures, torsional vibrations can be excited by the sudden connection or disconnection of electrical loads, thus increasing the drivetrain's fatigue and reducing its reliability and lifetime. Because of the increased amounts of intermittent electrical loads on aircraft systems, which excite torsional vibrations through electromechanical interactions, the electrical load connections are investigated in this paper. Specifically, a method for reducing torsional vibrations in aircraft drivetrains is proposed to extend their lifespan. This method is applied directly to the load being connected and it proposes the connection of the electrical loads following a pulsating pattern, for which the pulse connection time is determined as a function of the drivetrain vibration modes. Simulations results show that the proposed method provides a significant reduction in the drivetrain shaft torsional vibrations. Experimental results validate the simulation data showing the benefits this method can provide in drivetrain reliability, weight reduction and cost.

In more electric aircrafts, more motor loads are applied onboard. When the motor is braking, the regenerated energy need to be absorb to avoid dc-link voltage variations. Two regenerated energy absorption methods are proposed for the generator based on diode rectifiers and the starter/generator (SG) based on active rectifiers respectively. When the regenerated power is lower than other loaded power, both SG and generator systems can absorb it by reducing the output power. When the regenerated power is higher than other loaded power, if the SG is directly connected to the engine shaft, the regenerated energy can be absorbed by changing the SG operation from generating to motoring. The regenerated energy can be returned directly to the dc-link without extra devices and the dc-link voltage is under control during the regenerated energy absorption. The efficiency is improved and the heat is reduced by the proposed regenerated energy absorption methods. The generator and SG systems are implemented and the regenerated energy absorption methods are verified by experiments. The efficiency of the onboard electrical power system is improved.

Belt slip is an important type of mechanical fault in the automotive electric power generation and storage (EPGS) system. This paper proposes a robust and sensorless solution for detecting serpentine belt slip. The speed of the claw-pole alternator is directly extracted from the rectifier ripple frequency from the alternator output voltage. The estimated alternator speed is then continuously compared with the engine speed to detect possible belt slip. The proposed method is implemented in a real-time fashion on an EPGS test bench. The experimental results show that the method is able to estimate the alternator speed accurately even during fast mechanical transients. The belt-slip fault can thus be reliably detected within a wide speed range. Although originally developed for automotive alternators, the sensorless speed estimation method can be also applied to other AC generators with a DC-link rectifier.