Soft-switched three-phase PV microinverter
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Authors
Bagawade, Snehal
Date
Type
thesis
Language
eng
Keyword
DC-DC converter, DC-AC inverter, DC-bus voltage controller
Alternative Title
Abstract
This thesis presents novel soft-switching converter topologies for designing two-stage PV microinverters. The emphasis is placed on grid-tied, three-phase AC systems. Two-stage microinverter architecture comprises a DC-DC converter and a DC-AC inverter. This type of a microinverter provides maximum power point tracking (MPPT) and eliminates the use of short-life electrolytic capacitors. The two-stage power conversion, however, requires extremely high conversion efficiency from each stage.
A novel soft-switching DC-DC converter topology is first proposed. The proposed converter utilizes a standard phase-shift DC-DC converter, but with an additional resonant circuit that is used to regulate the input DC bus. The fundamental concept is to connect a variable-voltage source in series with the PV panel voltage to obtain a regulated DC voltage at the input of the DC-DC converter. In the proposed converter, frequency is used to regulate the input voltage and phase-shift angle to perform MPPT. A detailed analysis of the proposed converter has been carried out and necessary design equations developed. It has been shown in the thesis that the proposed converter topology results in low conduction and switching losses for all the active devices over the entire range of operation.
A novel soft-switching full-bridge DC-AC inverter is also proposed that provides ultra-low ripple output current. In the proposed inverter, the output filter network comprises a transformer, an inductor, and a capacitor. This inverter circuit utilizes the inherent current ripple cancellation property of the proposed circuit to inject ultra-low ripple grid current. It has been shown in the thesis that the proposed converter topology results in low switching loss for all the switches over the entire line-cycle and current level.
A composite non-linear feedback (CNF) based DC-bus voltage controller is proposed that exhibits a fast transient response for DC-AC inverters. Increased speed of the DC-bus voltage controller limits the fluctuations of the capacitor voltage from its set-point during transient conditions. This results in a lower value of DC-bus capacitance as compared to the conventional controller.
The concepts proposed in this thesis and their theoretical analyses are verified through circuit simulations and laboratory experiments.
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Queen's University's Thesis/Dissertation Non-Exclusive License for Deposit to QSpace and Library and Archives Canada
ProQuest PhD and Master's Theses International Dissemination Agreement
Intellectual Property Guidelines at Queen's University
Copying and Preserving Your Thesis
This publication is made available by the authority of the copyright owner solely for the purpose of private study and research and may not be copied or reproduced except as permitted by the copyright laws without written authority from the copyright owner.
Attribution-NonCommercial 3.0 United States
ProQuest PhD and Master's Theses International Dissemination Agreement
Intellectual Property Guidelines at Queen's University
Copying and Preserving Your Thesis
This publication is made available by the authority of the copyright owner solely for the purpose of private study and research and may not be copied or reproduced except as permitted by the copyright laws without written authority from the copyright owner.
Attribution-NonCommercial 3.0 United States