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Dynamic Carrier Pulse-Positioning for Single-Stage Isolated AC-DC Converter
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- Author / Creator
- Perera, Ambegoda Liyanage Vishwa
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The transportation sector is gaining much more attention towards all-electric modes such as electric vehicles (EV), and more electric aircrafts and ships. EVs lead the transportation sector with luxurious, high performance, and intelligent vehicles. The stored battery energy is the most important factor for the operation of the whole vehicle and therefore, EV battery chargers play an important role in the electric transportation sector. High frequency isolated battery charger converters are much preferred in the industry as they provide electrical isolation and reduce magnetic component size. Phase shifted pulse width modulation is commonly used in transformer isolated converters for high frequency power transfer. Generally, the voltage waveforms are phase shifted no more than 45 degrees for grid connected converter applications. In grid connected applications, the high frequency pulse widths (180° to minimum determined by modulation index) may vary when controlling the grid current. If, for certain duration of the low frequency reference signal, the pulse widths are smaller than the externally-commanded phase shift, the pulses would be completely separated. Under these conditions, unwanted reactive content is generated in the converter increasing the high frequency rms current hence increasing conduction losses. An original concept is proposed to lower the reactive content of the high frequency current by positioning the transformer primary and secondary voltage pulses next to each other whenever the phase shift is larger than the pulse width. The voltage pulses are positioned appropriately in each carrier cycle throughout the entire low frequency reference signal. This concept which is referred to as reference-based pulse position (RPP) allows the operation of the converter beyond 45 degree limit and up to 90 degrees allowing for more power output. The concept is tested on an isolated single-stage bidirectional three-phase ac-dc converter which conducts both low frequency grid current and high frequency transformer current. The grid side or the primary of the converter generates the high frequency transformer voltage when controlling the grid current. The switches in the secondary side are then controlled in such a way in each carrier cycle as to coordinate with primary voltage waveform to minimize the reactive content of the high frequency current. The power is transferred utilizing the transformer interlimb leakage inductance. The transformer windings are connected so that the 60Hz grid current does not produce flux in the core leaving only the high frequency flux. Therefore, the size of the magnetics can be reduced which favors a compact design. Furthermore, the dc link utilization is maximized by injecting the third harmonic into the sine reference signals which lowers the dc link requirement by 15%.
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- Graduation date
- Fall 2022
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- Type of Item
- Thesis
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- Degree
- Master of Science
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- License
- This thesis is made available by the University of Alberta Library with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.