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Novel Full Range Soft Switched Single Phase Inverter Design, Optimization and Implementation
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- Author / Creator
- Hazrati Karkaragh,Mohammadreza
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Single-phase inverters are widely used as an interface between the load (or utility grid) and DC energy resources such as photovoltaic systems or battery storage systems in low-power residential applications. There has been a trend in the industry to increase the power density of the converters, which saves costs by requiring less heatsink, enclosure and fewer components in developing commercial inverters. To improve the power density, normally the switching frequency of the converters is increased, which results in the reduction of passive filter and energy storage requirements of a converter. However, increasing the switching frequency leads to higher switching losses and lower efficiency, which can be avoided if soft-switching topologies are used. In commercial inverters, unlike DC-DC converters, achieving soft-switching is not normally straightforward due to the change in the operating point in a line cycle. This thesis focuses on the design and implementation of high-frequency, high power density, soft-switched single-phase inverters.
A soft-switching topology for a single-phase inverter is introduced, where an auxiliary circuit is added to a single-phase full-bridge DC-AC converter. The auxiliary circuit incorporates two active switches that are magnetically connected to the filter inductor of the inverter output filter. The auxiliary circuit does not add any components in the main power path, and does not need any floating gate driver. The proposed auxiliary circuit does not need any extra passive component, and the required coupling with the main circuit is achieved through a secondary winding on the inverter's output inductor. The coupled inductor's turns ratio provides an extra optimization variable to reduce the voltage stress on the switches and enables the utilization of faster switches. Moreover, a variable-timing method controls the auxiliary circuit and reduces the conduction losses in the auxiliary switches. Experimental results exhibit a satisfactory performance of an implemented prototype and high switching frequency while maintaining the efficiency over a wide power range.
To provide soft-switching for the full-range of operation in the proposed inverter, a combination of unipolar and bipolar modulation is proposed. In addition, the proposed modulation guarantees soft switching for low duty cycles and non-unity power factors. A thorough loss analysis is performed to compare the losses in hard-switching and soft-switching cases and to justify the utilization of the auxiliary circuit. A design strategy based on this loss analysis is provided to implement an efficient design of the system.
Additionally, core losses in the filter inductor of inverters is studied, and a generalized equation is proposed to calculate the total core losses of inverter inductors for one 60Hz cycle. Utilization of this generalized equation in the design process of the output filter inductor of the inverter increases the speed and accuracy of the design and avoids over-designing of the filters. This core loss calculation method is also used in the loss analysis of the soft-switching inverter to predict an accurate core loss for the soft-switching inverter. Same generalization method is also employed to predict an accurate conduction loss in the inverter in a line cycle.
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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.