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Small-Signal Modeling and Stability Specification of a Hybrid Propulsion System for AircraftsLin, Qing 17 May 2021 (has links)
This work utilizes the small-signal impedance-based stability analysis method to develop stability assessment criteria for a single-aisle turboelectric aircraft with aft boundary-layer propulsion (STARC-ABL) system. The impedance-based stability analysis method outperforms other stability analysis methods because it does not require detailed information of individual components for system integration, therefore, a system integrator can just require the vendors to make the individual components meet the impedance specifications to ensure whole system stability. This thesis presents models of a generator, motor, housekeeping loads, and battery all with power electronics interface which form an onboard electrical system and analyzes the relationship between the impedance shape of each component and their physical design and control loop design. Based on the developed small-signal model of the turbine-generator-rectifier subsystem and load subsystem, this thesis analyzes the impact of electromechanical dynamics of the turbofan passed through the generator on the dc distribution system, concluding that the rectifier can mitigate the impact. Finally, to ensure the studied system stable operation during the whole flying profile, the thesis provides impedance specifications of the dc distribution system and verifies the specifications with several cases in time-domain simulations. / M.S. / Electric aircraft propulsion (EAP) technologies have been a trend in the aviation industry for their potential to reduce environmental emissions, increase fuel efficiency and reduce noise for commercial airplanes. Achieving these benefits would be a vital step towards environmental sustainability. However, the development of all-electric aircraft is still limited by the current battery technologies and maintenance systems. The single-aisle turboelectric aircraft with aft boundary-layer (STARC-ABL) propulsion concept is therefore developed by NASA aiming to bridge the gap between the current jet fuel-powered aircraft and future all-electric vehicles. The plane uses electric motors powered by onboard gas turbines and transfers the generated power to other locations of the airplane like the tail fan motor to provide distributed propulsion.
Power electronics-based converter converts electricity in one form of electricity to another form, for example, from ac voltage to dc voltage. This conversion of power is very important in the whole society, from small onboard chips to Mega Watts level electrical power system. In the aircraft electrical power system context, power electronics converter plays an important role in the power transfer process especially with the recent trend of using high voltage dc (HVDC) distribution instead of conventional ac distribution for the advantage of increased efficiency and better voltage regulation. The power generated by the electric motors is in ac form. Power electronics converter is used to convert the ac power into dc power and transfer it to the dc bus. Because the power to drive the electric motor to provide distributed propulsion is also in ac form, the dc power needs to be converted back into ac power still through a power electronics converter. With a high penetration of power electronics into the onboard electrical power system and the increase of electrical power level, potential stability issues resulted from the interactions of each subsystem need to be paid attention to. There are mainly two stability-related studies conducted in this work. One is the potential cross-domain dynamic interaction between the mechanical system and the electrical system. The other is a design-oriented study to provide sufficient stability margin in the design process to ensure the electrical system’s stable operation during the whole flying profile.
The methodology used in this thesis is the impedance-based stability analysis. The main analyzing process is to find an interface of interest first, then grouped each subsystem into a source subsystem and load subsystem, then extract the source impedance and load impedance respectively, and eventually using the Nyquist Criterion (or in bode plot form) to assess the stability with the impedance modeling results.
The two stability-related issues mentioned above are then studied by performing impedance analysis of the system. For the electromechanical dynamics interaction study, this thesis mainly studies the rotor dynamics’ impact on the output impedance of the turbine-generator-rectifier system to assess the mechanical dynamics’ impact on the stability condition of the electrical system. It is found that the rotor dynamics of the turbine is masked by the rectifier; therefore, it does not cause stability problem to the pre-tuned system. For the design-oriented study, this thesis mainly explores and provides the impedance shaping guidelines of each subsystem to ensure the whole system's stable operation. It is found that the stability boundary case is at rated power level, the generator voltage loop bandwidth is expected to be higher than 300Hz, 60˚ to achieve a 6dB, 45˚ stability margin, and load impedance mainly depends on the motor-converter impedance.
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Smart Resistor: Control and Stabilization of DC Distribution Networks Utilizing Energy Storage with High Bandwidth Power ConvertersPotty, Karun Arjun January 2020 (has links)
No description available.
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Elektrické sítě využívající stejnosměrné napětí do 1000 V / Electric networks with DC voltage up to 1000 VFiala, Martin January 2016 (has links)
This master´s thesis deals with the proposal of DC low voltage network at a voltage level of 1000 V DC in Praskolesy u Mrakotina village. Direct distribution will be realized only at the terminal, which will power the village. Next part of this thesis is theoretical and its main focus is description of both DC and AC distribution systems. The proposed DC grid will use existing distribution grid. The thesis further describes the problems of long terminals in low voltage distribution systems and electrical installation in buildings. The result of this work is a comparison of the losses between AC and the proposed DC system. The last part deals with economical evaluation and technical solution for the proposed network variant, including their advantages and disadvantages.
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