Date of Award

Spring 1-1-2015

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Electrical, Computer & Energy Engineering

First Advisor

Dragan Maksimovic

Second Advisor

Khurram K. Afridi

Third Advisor

Robert W. Erickson

Fourth Advisor

David C. Jones

Fifth Advisor

Christopher A. Deline

Abstract

System efficiency of conventional photovoltaic (PV) systems is adversely affected by mismatches among series connected cells, submodules, and modules. Module-level power converters, often referred to as dc optimizers, mitigate mismatch related losses by performing maximum power point tracking (MPPT) locally, at the PV module level. However, dc optimizers must process all PV power and in the process they introduce insertion losses even when there are no mismatches. Differential power processing (DPP) architectures mitigate mismatch-related losses while processing only a fraction of the PV system rated power, and without insertion losses. This thesis is focused on the design, implementation and evaluation of submodule integrated converters (subMICs) in the isolated-port DPP architecture. Using a simple voltage balancing approach where voltage reference is set by the shared isolated port, the subMICs can be controlled autonomously in a distributed manner, without the need for a central controller or communication among units. A custom CMOS controller integrated circuit is developed, which demonstrates voltage-balancing control, power limiting, and protection features on prototype subMICs based on bidirectional flyback converters. A system prototype, including three subMICs, is placed in the junction box of a standard 72- cell PV module, replacing conventional bypass diodes. Performance of the subMIC-enhanced PV module is evaluated through laboratory and outdoor field experiments. Experimental results show greater than 99% module-level efficiency under 25% mismatch, using subMICs rated at one third of the PV power. A performance/cost analysis is performed to select the optimum subMIC design for a given PV system, resulting in best energy-yield improvements at minimum incremental cost.

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