This thesis investigates the use of flexible AC transmission systems (FACTS) and voltage source converter (VSC) high-voltage direct current (HVDC) transmission systems for improving the power transfer capability of the Libyan internal tie-line between east and west, for a secure, reliable and efficient operation of this power corridor. Mathematical-based analysis supported by numerical-based analysis, which employs NEPLAN power system analysis tool, are carried out to investigate the steady state and dynamic behaviour of the power system.Different FACTS technologies, including variable impedance based and converter-based shunt and series FACTS devices, are studied during steady-state and transient operating conditions to evaluate the capabilities, control systems and weaknesses in these technologies. The investigations focus on the common types of shunt and series FACTS including: the static VAr compensator, static synchronous compensator, and thyristor controlled series compensator. A challenge in this thesis is to find an efficient method to allocate and size FACTS devices, to ensure maximum utilization of the tie-line considering technical constraints including:; voltage rise at a point of voltage collapse, equipment terminal voltage and subsynchronous resonance risk.For the VSC-HVDC system, a mathematical model that calculates power flow throughout the HVDC link and at both AC sides is confirmed as an efficient steady-state model facilitating estimation of reactive power requirements at the converter terminal and at the point of common coupling. This model can be used to estimate the optimal converter rating based on the system strengthens at both sides. Further modelling and analysis investigates the operation of a hybrid AC/DC system. Multi-tasking control systems for voltage source converter HVDC systems are used to facilitate operation of the hybrid AC/DC system during normal and emergency operating conditions.The controllers include: frequency control in the case of an unsynchronized connection and power management control necessary to balance the power flow during an emergency, in additional to the primary control of the AC and DC voltages, and active and reactive powers.Well-known and referenced two areas Kundur test system with a weak tie-line, which suffers from a limited power transfer capability between the operating areas, is used throughout the analysis. the tie-line between two regions in the Kundur test system is investigated when incorporating different FACTS technologies and a VSC-HVDC system. Based on the introduced approaches and models the benefits and challenges of these technologies in the Libyan internal tie-line are explored. The research shows that the power transfer capability of the tie-line can be improved by shunt and to a lesser extent, by series compensation. Comparison between FACTS devices and VSC-HVDC indicates, apart from the cost, VSC-HVDC transmission may be the better option for Libyan internal tie-line improvement, especially in the near future, when secure and reliable interconnected power system is required.
|Date of Award||15 May 2016|
- University Of Strathclyde
|Supervisor||Stephen Finney (Supervisor) & Keith Bell (Supervisor)|