Stability Challenges and Solutions in High-PV Penetration Grids: A Case Study of Ethiopia and Kenya HVDC link.
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Date
2025-07
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Addis Ababa University
Abstract
The Ethiopia-Kenya HVDC project represents a significant advance in power transmission,
establishing a ±500 kV bipolar HVDC link with a capacity of 2000 MW to enhance regional
energy integration and promote sustainable development. This ambitious initiative facilitates
the export of Ethiopia’s substantial hydroelectric resources while addressing the growing
demand for electricity in East Africa. As Ethiopia prioritizes renewable energy sources,
including hydro, wind, and solar, its power system faces opportunities and challenges in
integrating large-scale photovoltaic (LSP) systems. Although LSP systems promise carbonfree
electricity and improved grid resilience, their integration introduces complexities such
as reduced system inertia, increased frequency oscillations, and dependence on advanced
inverter technologies.
This thesis explores advanced methodologies for enhancing the stability and resilience
of the Ethiopian power grid amid the increasing integration of renewable energy sources,
particularly photovoltaic (PV) systems. The transition from traditional Synchronous generators
(SGs) to large scale PV plants has reduced system inertia, amplifying the challenges
associated with transient stability and frequency control. To address these concerns, three
distinct yet interconnected studies are presented.
First, the modeling of the Ethiopia-Kenya HVDC link using DIgSILENT software demonstrates
that the implementation ofHVDC technology significantly improves transient stability.
Next, the research evaluates FACTS-based supplementary control strategies, including Power
Oscillation Damping (POD) and a novel Control Lyapunov Function (CLF) approach integrated
with STATCOM to mitigate electromechanical oscillations in grids with high PV
penetration. Simulations of severe three-phase faults near the HVDC rectifier terminal reveal
that the CLF-based controller outperforms POD in damping ratio enhancement and dynamic
response evaluation, particularly in high PV scenarios. Third, the study proposes Battery
Energy Storage Systems (BESS) as a fast frequency control (FFC) solution to counteract the
diminished inertial response of PV systems, effectively reducing the Instantaneous Frequency
Deviation (IFD) during disturbances. The simulations convincingly demonstrate that the
proposed BESS frequency control scheme effectively reduces the maximum frequency deviation
and suppresses significant frequency excursions under various disturbance and PV
penetration conditions.
In general, this thesis emphasizes the integration of advanced control strategies, including
HVDC, FACTS-based supplementary controls, and BESS, to ensure a stable and reliable
power system in the face of the burgeoning adoption of renewable energy. The findings
underscore the necessity of adaptive control frameworks to mitigate risks posed by reduced
inertia and transient instability, safeguarding grid resilience as Ethiopia transitions toward a
renewable-dominated energy future.
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Keywords
large-scale photovoltaic, supplementary control, fast frequency control, instantaneous frequency deviation, and battery energy storage systems.