Due to the ever increasing generation and load levels faced by power systems today, electricity transmission networks are experiencing higher levels of load than ever before. Consequently transmission network planners must look for ways to improve their network utilization beyond current limits. Such methods include network expansions and installations of specially designed power electronic devices to ensure successful delivery of electric energy to Queensland customers.
The pledge by the Australian government to produce 20 per cent of Australia’s energy from renewable resources by the year 2020 has also has a significant impact on the electricity transmission network. Growing levels of renewable energy generation in the grid, in an effort to address the growing concerns regarding climate change, are also introducing new stability issues not seen in the past.
To ensure the reliable operation of the network and maintain network stability under increasing demands, utilities have turned their focus to a group of power electronics devices developed over the past decade. Such devices are named Flexible AC Transmission Systems (FACTS) devices, and provide flexibility to the network by enabling the manipulation of network parameters. Of these FACTS devices the Static VAr Compensator (SVC) is widely regarded as most common. In fact, this device has been in use since before the introduction of the term ‘FACTS’. The SVC provides networks with additional reactive power support through a combination of capacitor banks, reactors and thyristor control. This fast switching source of reactive power is used to improve various aspects of system stability. Nine SVCs are currently in operation in Queensland’s HV transmission network, with even more planned in the coming years.
Two key desirable attributes of SVCs and other FACTS devices are their ability to enhance static voltage stability, and their ability to contribute to inter-area oscillation damping through auxiliary controllers. In this thesis the optimal allocation of FACTS devices for voltage stability enhancement is first addressed, through the development of an improved mixed-integer optimization method based on the introduction of quadratic constraints. This method is capable of allocating multiple types of FACTS devices simultaneously. The objective for optimization is to enhance system loading capacity. This is achieved through determination of three critical aspects of FACTS utilization, which are the number of devices, their ratings, and their locations within the network. The developed method is demonstrated on IEEE test networks, a simplified Southeast Australian test network, and an 886 bus network based on Queensland's complex HV transmission network.
Secondly, the estimation of inter-area oscillatory modes is investigated and two state-of-the-art algorithms are applied to demonstrate online estimation of major inter-area oscillatory modes in Queensland's HV network. The first is the Robust Recursive Least Squares (RRLS) algorithm, while the second is an Improved Extended Complex Kalman Filter (IECKF) identifier. The purpose of this investigation is to establish a basis for which adaptive auxiliary controllers, such as the pole-shifting controller, may be developed and implemented. Such controllers aim to improve upon the damping contributions provided by existing POD controller designs currently utilized in Queensland.
These two important aspects of FACTS utilization are addressed in this thesis - that of device allocation, and of inter-area oscillation estimation. By taking the complex real-world system of Queensland's HV transmission network as a basis for case studies, the author demonstrates the practical relevance and applicability of their research to the real and complex power systems currently in operation around the world.