ABSTRACT
There currently exists no formal classification scheme for flexible alternating-current transmission Systems (FACTS) controllers, and the paper aims to remedy this. The proposed classification is based on five characteristics of the controllers: connection, commutation, switching frequency, energy storage and presence of a dc port. There are 180 combinations. Six examples are examined, and all the main existing FACTS controllers are tabulated and classified.
There currently exists no formal classification scheme for flexible alternating-current transmission Systems (FACTS) controllers, and the paper aims to remedy this. The proposed classification is based on five characteristics of the controllers: connection, commutation, switching frequency, energy storage and presence of a dc port. There are 180 combinations. Six examples are examined, and all the main existing FACTS controllers are tabulated and classified.
INTRODUCTION
Flexible alternating-current transmission systems (FACTS) are defined by the IEEE as “ac transmission systems incorporating power electronics-based and other static controllers to enhance controllability and increase power transfer capability” [1]. Similarly, a FACTS controller is defined as “a power electronics-based system or other static equipment that provides control of one or more ac transmission parameters”. In recent years, many different FACTS controllers have been proposed, performing a wide variety of functions. Review papers have surveyed them, the IEEE has listed definitions of them, but to date no classification scheme has been proposed.
There are several reasons why this situation is unsatisfactory, from both academic and practical viewpoints. It would be advantageous to organise the existing FACTS controllers into family groups, rather than regarding them as a collection of disparate items. This would help newcomers to the field to recognise relationships between the various controllers, and to appreciate their similarities and differences. It could aid in the understanding of their operation and characteristics. It would also enable researchers to identify “missing” controllers that have not yet been proposed and develop them.
An ideal classification scheme would have these properties: it would be simple to apply and understand;
it would be objective and quantitative; it would be unambiguous and clear; it would be useful to those interested in the field; and, finally, it would be extendible, to cope with further advances in the field of FACTS. In this paper, we propose a scheme which we believe goes a considerable way towards meeting these goals.
Our proposed classi fication scheme is multi-dimensional, in that it classifies FACTS controllers according to five independent measures, which may be considered as five orthogonal axes. A drawback with any multi-dimensional classification scheme is that certain combinations of characteristics may be impossible or impractical, resulting in gaps. For example, the combination of “high frequency switching” and “natural commutation” is inapplicable, because fast SCRs are not currently available. This is a practical limitation, which might change with the introduction of yet unforeseen devices. A positive aspect of these “missing combinations” is that they can stimulate new ideas which might be developed to improve power system operation. Therefore, we believe our classification scheme for FACTS controllers has value not only in organising existing technology into a coherent body of knowledge, but also in providing a starting point for researchers who wish to develop new techniques.
Flexible alternating-current transmission systems (FACTS) are defined by the IEEE as “ac transmission systems incorporating power electronics-based and other static controllers to enhance controllability and increase power transfer capability” [1]. Similarly, a FACTS controller is defined as “a power electronics-based system or other static equipment that provides control of one or more ac transmission parameters”. In recent years, many different FACTS controllers have been proposed, performing a wide variety of functions. Review papers have surveyed them, the IEEE has listed definitions of them, but to date no classification scheme has been proposed.
There are several reasons why this situation is unsatisfactory, from both academic and practical viewpoints. It would be advantageous to organise the existing FACTS controllers into family groups, rather than regarding them as a collection of disparate items. This would help newcomers to the field to recognise relationships between the various controllers, and to appreciate their similarities and differences. It could aid in the understanding of their operation and characteristics. It would also enable researchers to identify “missing” controllers that have not yet been proposed and develop them.
An ideal classification scheme would have these properties: it would be simple to apply and understand;
it would be objective and quantitative; it would be unambiguous and clear; it would be useful to those interested in the field; and, finally, it would be extendible, to cope with further advances in the field of FACTS. In this paper, we propose a scheme which we believe goes a considerable way towards meeting these goals.
Our proposed classi fication scheme is multi-dimensional, in that it classifies FACTS controllers according to five independent measures, which may be considered as five orthogonal axes. A drawback with any multi-dimensional classification scheme is that certain combinations of characteristics may be impossible or impractical, resulting in gaps. For example, the combination of “high frequency switching” and “natural commutation” is inapplicable, because fast SCRs are not currently available. This is a practical limitation, which might change with the introduction of yet unforeseen devices. A positive aspect of these “missing combinations” is that they can stimulate new ideas which might be developed to improve power system operation. Therefore, we believe our classification scheme for FACTS controllers has value not only in organising existing technology into a coherent body of knowledge, but also in providing a starting point for researchers who wish to develop new techniques.
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