| dc.description.abstract | In this dissertation, several new approaches to interface the renewable energy resources to a utility grid are explored. It is shown a DC collection grid is preferred due to its simplicity, low cost in terms of structure and low losses.
In the first study, a medium voltage DC collection grid photovoltaic PV power plant using 12-pulse SCR converter and line frequency phase-shift transformer is presented. The proposed concept includes a new hybrid step-up DC-DC converter to boost the PV plant voltage to the medium voltage scale. The features of this topology are simple, bidirectional power flow, and reliable due to the absence of the DC link capacitor. The key point to improve the power density of power electronics converters is to minimize the magnetic elements inductor/transformer, and eliminate DC link capacitor if it is possible.
Responding to this key point, the second study proposes a medium voltage DC collection grid for large-scale PV power plant using 12-pulse SCR converter and employing an integrated medium frequency (720 Hz) solid-state transformer. The advantages of this topology are simple, easy to control, higher power density, eliminating the need of DC link capacitor, and bidirectional power flow capability.
To improve the reliability, efficiency and power density for the second study further, an open delta phase-shift medium frequency solid-state transformer is proposed. The analysis and simulation results show that the open delta concept has the same quality performance as the second approach.
In the final study, a tractive bidirectional power flow current source converter using selective harmonics elimination SHE pulse width modulation PWM technique is proposed. This approach is employing a high frequency (20 kHz) integrated solid-state transformer for galvanic isolation. The analysis shows a very good input current quality by removing the low order harmonics e.g. (5th, 7th, 11th, 13th). Bidirectional power flow is allowable to use this approach for either renewable energy harvesting or electrical vehicle EV charging system.
In general, the results of this dissertation show that the presented topologies have beneficial features in terms of bidirectional power flow, simplicity, high reliability, good input current quality, and high power density compared to the conventional approaches. | en |
