Abstract:
Ethiopia is now increasing power generation and transmission capacity. The Great Ethiopian
renaissance dam (GERD) one of finishing project that generate high power in East Africa. The
expansions of high-power demand, industrialization and large interconnected power system have
their own impact on the stability of the system depending on expansion planning studies and type
of technology used. The Voltage Source Converter based HVDC system is a relatively new
technology which can be designed for high-power transmission. Among different application of
HVDC, improving power system stability is one of advantage of VSC based HVDC system.
Considering power system stability holds major part when planning, designing and operating
electrical power system. Designing VSC based HVDC system is best solution for power system
stability improvements. This thesis presents the design of VSC based HVDC transmission for
dynamic performance improvement of GERD generator output and voltage stability of all 400kv
buses in Ethiopia. This design of HVDC system from GERD to Holeta 500kv, 620km long
transmission line is not only for stability purpose but also for cost minimization. The effective
control system of VSC is modelled and supporting bidirectional power flow and maintaining
stability during fault condition. The thesis also develops bipolar VSC-HVDC transmission model
with PI controller based dq control strategy using MATLAB/Simulink software.
The designed VSC-HVDC transmission model is integrated to Ethiopia high voltage AC grid and
the simulation result are accomplished on MATLAB Simulink software to show performance
with/without HVDC link at peak load and at fault condition. It is obtained that the voltage profile
of all central, Eastern and southern area buses was improved between range 0.9979pu to 1.001pu
after design HVDC system. It also is obtained that during fault at PCC1, the voltages of central,
Southern and Eastern area buses are improved from range of 0.301 pu and 0.802pu to range
between 0.895 and 0.982pu after integration of HVDC link. In general, after integration of HVDC
system the generator output parameters became more stable and voltage stability are improved
during fault and post fault condition. Moreover, the designed VSC-HVDC transmission is more
economical and it is obtained 13.43% is saved out of HVAC total investment cost for VAC-HVDCinvestment cost.
