Integration of photovoltaic sources and battery based storage systems – A DC analysis and distributed maximum power point tracking solution

Student thesis: Doctoral Thesis

Abstract

In this thesis the integration of photovoltaic (PV) generation and energy storage into
the electrical grid is discussed. Although the studied system is for grid tied applications, here the integration of the PV generation and the energy storage system
(ESS) on the direct current (DC)-side of the system is addressed. The work contained
in this thesis focuses on the integration of the DC-working parts before interfacing
them with the grid through the use of an inverter and seeks an increasing in the
energy that the system can deliver.
First, a study of classical systems that present well-differentiated parts is presented:
PV generation, a lithium-ion battery based ESS, the utility grid and a residential
electricity consumer. PV installations of 3 and 10kWp are considered together
with storage capacities ranging from 1 to 9kWh. This yields interesting insights on
how the system works based on the timing of the generation and consumption of
energy. The results are used to highlight the weaknesses of the selected converter
arrangement for the interfacing of the PV source and the ESS. Results show that the
system is rather stiff and lacks from conversion efficiency when it needs to work in a
wide range of powers, mainly due to low consumer power demand during battery
discharge. In this first part of the thesis, three solutions to workaround the efficiency
problem are proposed: reducing the difference between the ESS and the DC-bus
voltages, using isolated converters to interface the ESS, or adopting a new arrangement of the parts of the system. One of the first two proposed solutions should be
adopted if the same system topology is to be kept. These two solutions address the
efficiency problem when the ESS is involved in the energy conversion. The third
solution is proposed as alternative to the classical systems
Date of Award22 Jan 2019
Original languageEnglish

Keywords

  • PV system
  • Battery system
  • Power Electronics
  • Control system

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