“Using Differential Power Processing Converters in Photovoltaic Systems to Improve Lifetime Energy Production”
January 27, 2014
Ms. Katherine Kim, PhD Candidate
University of Illinois at Urbana-Champaign
When: Friday, February 14, 2014 at 3:05 p.m.
Where: Warnock 1230
Photovoltaic (PV) energy systems are gaining popularity in both residential and commercial markets. Traditionally, PV panels are connected in series to a central inverter that maximizes power production and delivers energy to the power grid. When PV cells are connected in series, they often experience mismatch that reduces the total output power. PV mismatch can be caused by various factors, such as non-uniform lighting, partial shading, inconsistent manufacturing, local temperature gradients, and degradation from aging and environmental stress. Dc optimizers are panel-level dc-dc converters that can be used to mitigate this mismatch by independently optimizing each panel’s power. However, dc optimizers must be rated at the full panel power and process all of the power from the PV panel. Differential power processing (DPP) is an alternative solution that achieves high system efficiency by processing a fraction of the total power, while still optimizing power output from each PV panel. DPP converters can also be rated at a lower power level than dc optimizers, which offers potential cost reduction, reliability enhancement, and higher efficiency.
This presentation details the operation of two DPP architectures: PV-to-bus and PV-to-PV. Simulations for both DPP architectures are used to evaluate system performance over 25 years of operation. The level of mismatch among PV panels at 25 years is estimated based on data from long-term field studies. Converter ratings of 15-17% for PV-to-bus and 23-33% for PV-to-PV architectures are identified as appropriate ratings for a 15-submodule PV system. Using Monte Carlo simulation, lifetime performance of the PV-to-bus and PV-to-PV architectures is compared to conventional architectures. DPP converters are shown to deliver 6% more energy compared to the conventional series string architecture at 25 years of operation. This presentation will also speak to future applications of DPP converters in mobile PV applications, such as vehicles and wearable electronics.
Katherine Kim graduated with a B.S. in Electrical and Computer Engineering from Franklin W. Olin College of Engineering in 2007. She received her M.S. in Electrical and Computer Engineering at the University of Illinois at Urbana-Champaign in 2011, and plans to complete her Ph.D. degree in 2014 under Prof. Philip Krein. Katherine’s dissertation research is in power electronics, modeling, control, and protection for photovoltaic systems. She received the National Science Foundation’s East Asia and Pacific Summer Institutes Fellowship in 2010 and Graduate Research Fellowship in 2011. She is currently the Student Membership Chair for the IEEE Power Electronics Society and is active in the student chapter at the University of Illinois.