Design and Control of Charge-Pumped Reboost Converter for PV Applications

Photovoltaic (PV) systems are renewable, DC sources which provide non-linear output power with respect to PV panel operating voltage or current. The majority of PV sources yield poor conversion efficiencies between available solar radiation and electrical output. Additionally, they are expensive compared to other conventional power sources. Power electronic converters are capable of harvesting the most energy from these resources due to their configurability and high-efficiency. These converters form a power conditioning stage which allows for numerous control methods and energy management options. Traditional systems group PV sources into arrays in order to increase operating voltage and power to levels where it is practical to connect them to the utility grid. Grid-tied PV has the potential to increase the acceptance of PV energy by reducing end-user complexity — there are no batteries to manage and additional wiring can be kept to a minimum. However, these arrays of PV panels have significant drawbacks when they are subjected to non-ideal conditions. If a single panel is shaded, or covered in some way, then it will have greatly reduced output current. As a result, any other panel which is connected in series with the affected panel is also subject to the same output current reduction. This series grouping of panels may then indirectly affect other series-sets of panels which are connected in parallel to it by tricking the power electronics unit into operating at a point which is not the true maximum-power-point (MPP). By connecting a single PV panel to a single DC-DC converter, these array-effects can be avoided. Reliability and power output of the whole system should increase at the expense of additional hardware. The outputs of several PV-connected DC-DC converters can be connected either in series or in parallel. If they are connected in parallel, the converters must be able to boost the PV panel voltage up to a level greater than the desired utility-grid voltage. This thesis focuses on the design and control of a high-boost-ratio DC-DC converter suitable for use in a parallel-connected, grid-tied PV system. It demonstrates the feasibility of boost-ratios of up to 10 times while still achieving high efficiency. The design avoids the use of electrolytic capacitors in favor of smaller ceramic capacitors and a few large film-capacitors. A simplified model is proposed which is still suitable for use in the design of high-bandwidth control loops. Testing is done with a PV source showing preliminary results with a maximum-power-point-tracker (MPPT) which achieves very good steady-state performance.

Name thesis:degree_name

Master of Science

Level thesis:degree_level

masters

Discipline thesis:degree_discipline

Electrical and Computer Engineering

Department dc:contributor.department

Electrical and Computer Engineering

Grantor dc:publisher

Virginia Tech

Year dc:date.issued

2010

Author dc:creator

• Hutchens, Christopher L.

Chair dc:contributor.committeechair

• Lai, Jih-Sheng

Committee members dc:contributor.committeemember

• Centeno, Virgilio A.
• Meehan, Kathleen

• DC-DC Converter
• PV

Statement dc:rights

• In Copyright

Licence dc:rights.uri

• http://rightsstatements.org/vocab/InC/1.0/

Dc Identifier Other

etd-05112010-145353

OAI identifier oai:identifier

oai:vtechworks.lib.vt.edu:10919/32600