Download 112081292 Liu 2009 Advanced Control of Photovoltaic Converters PDF

Title112081292 Liu 2009 Advanced Control of Photovoltaic Converters
Tags Photovoltaics World Energy Consumption Thin Film Solar Cell Photovoltaic System
File Size2.1 MB
Total Pages177
Document Text Contents
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by Ying LIU 
April 2009 

Thesis submitted to the Department of Engineering,  
University of Leicester for the degree of Doctor of Philosophy

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Ying LIU

Thesis submitted to the Department of Engineering, University of Leicester for

the degree of Doctor of Philosophy

April 2009

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or closing the switch.

Fig 5-2 demonstrates the P (I) characteristics of a Thevenin source (a) and a real PV

source (b). It can be seen that they both exhibit a maximum power point (MPP) within

their operating range. Changing RS has a similar effect as the change of irradiance E on

the P (I) characteristics. Therefore, a Thevenin source with switchable series resistance

can be used to study and test certain Maximum Power Point Tracking (MPPT) algorithms

such as hill climbing methods.

However, there are a number of limitations to this approach. Firstly, a Thevenin source is

a good approximation only around the MPP. Also, having only changes in RS does not

reflect the actual characteristics of a PV source. For a real PV source, VS changes

together with RS, under the effect of irradiance and temperature. Therefore, a Thevenin

source can not be used for more complicated or more specific study purposes.

Furthermore, the scope of the present study includes the effect of PV dynamics due to PV

cell capacitance on MPPT algorithms (see Chapter 3). It also includes the detection of

occurrence of partial shading and the development of methods to control the converters to

work at the global maximum power point under partial shading conditions (see Chapter

4). The existing PV source emulator in the form of a simple Thevenin source is unable to

emulate such situations. Therefore, a more practical PV source emulator is needed to

verify the true performance of MPPT algorithms and other aspects of intelligent control.

One possible implementation of a PV source emulator is the use of multiple DC power

supplies with a feedback circuit and fast switches so that the output voltage-current

curves follow a typical PV source characteristic. The fast switches are needed because

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power supplies usually have a large capacitance at the output, which means that the

output voltage can not change quickly. However, with such an emulator it would be

difficult to emulate partial shading conditions which cause multiple local maxima in the

PV characteristic.

(a) Thevenin Source

(b) Real PV source

Fig 5-2. P-I characteristics

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[1] Y. Liu, and J.A.M. Bleijs, “Dynamic Effect of PV Cell Capacitance on MPPT

Algorithms”, Proceedings of the 21st European Union Photovoltaic Solar Energy

Conference, Dresden, 4-8 September 2006, pp. 2604- 2607

[2] Y. Liu, and J.A.M. Bleijs, “Design of a Flexible Solar Emulator to Facilitate the

Study on MPPT Control of PV Panels Using a DSP Based DC/DC Converter”,

Proceedings of the 22nd European PV Solar Energy Conference, 3 - 7 September

2007, Milan, pp. 3059-3063

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