DESIGN AND INTEGRATION OF VSC BASED HVDC SYSTEM INTO ETHIOPIAN HVAC GRID FOR POWER SYSTEM STABILITY IMPROVEMENT.

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.