Nahla Ezz Eldin Zakzouk
Photovoltaic System Design and Control
Modern industrial society, increasing energy demands, and environmental issues have
increased the need for new and clean renewable energy resources, among which
photovoltaic energy has gained considerable interest. For best energy utilization,
photovoltaic maximum power tracking and grid-integration aspects should be addressed.
Generally, variable-step, incremental conductance maximum power point tracking
technique has the merits of good tracking accuracy and fast convergence speed. Yet, the
division processes in its algorithm create a computational burden. Also the conventional
variable step-size encounters steady-state power oscillation and dynamic problems,
especially under sudden irradiance changes. In this thesis, a division-free incremental
conductance algorithm is proposed for photovoltaic maximum power tracking. It features a
modified variable step-size and a direct converter control scheme. The proposed tracking
technique does not only have the merits of superior steady-state and transient performance
but also offers simple implementation and control. Thus, it can be practically implemented
using low-cost microcontrollers, reducing overall system cost.
Grid integration of photovoltaic systems using power electronic converters that vary in
configurations, control loops and mandatory measured signals are investigated. A singlephase
two-stage grid-interfaced photovoltaic system is presented in this thesis. It uses a
boost chopper in the first stage for maximum power tracking and an H-bridge voltage
source inverter in the second stage for grid interfacing. A novel DC-link voltage sensorless
control technique is proposed for this topology. It eliminates the inverter outer DC-link
voltage control loop, thus reducing system size, cost and control complexity. Additionally,
system dynamics are enhanced during sudden changes.
Single-stage based grid-tied photovoltaic power converters receive attention due to
their merits of reduced footprint and losses, but at the cost of a limited degree-of-freedom.
In this thesis, a single-phase single-stage grid-tied photovoltaic system is proposed. It
adopts a single transformerless current source inverter to achieve photovoltaic maximum
power tacking, whilst satisfying grid interfacing requirements. A proportional-resonant
controller, associated with harmonic compensator units, is proposed for the inverter in
order to limit injected grid current harmonics. Thus, a lower-sized inductor can be used in
the inverter DC-link which enhances efficiency without sacrificing system performance.
Simulation and experimental results validate all the proposed systems.|