The application of controllable inverter-based series compensation to power oscillation damping.
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Date
2000
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Abstract
Poorly damped oscillations that occur between the generators in large interconnected
power systems often limit the amount of power that can be transmitted through a
transmission corridor and are a threat to secure system operation. Coordinated
insertion and removal of capacitors in series with a transmission line is one of the
approaches that has been known for many years to be capable of enhancing the
damping of power system oscillations. Unfortunately however, this approach
historically relied on the operation of mechanical circuit breakers which were too
slow and unreliable for the high-speed and repetitive operation that such an
application demands. Recently-emerged, high-speed power-electronic-based
switching devices are finding increasing use in modem power systems in the so-called
Flexible AC Transmission Systems (F ACTS) concept. One particular FACTS
impedance controller, namely the inverter-based series compensator, can rapidly alter
the magnitude of capacitive compensating reactance in series with the line to make it
practically feasible to enhance the damping of power system oscillations via
dynamically-controlled series compensation.
This thesis identifies, in the literature, an insightful approach to the design of an
idealised controllable series compensator (CSC) damping scheme; such an approach
has been considered in the analyses of the thesis. Three mathematical models of a
single-machine infinite bus (SMIB) system are developed and are subsequently used
in the initial design and analysis of a CSC damping controller carried out in the thesis.
The simple SMIB system case study is used to identify and investigate the factors that
have a significant impact on the performance of a CSC damping controller before
studying the more complex issue of inter-area mode damping using a CSC.
This thesis successfully confirms the results of a previous analytical study in which an
idealised representation of the CSC was used, and extends the scope of that previous
study by also considering a detailed representation of one particular type of CSC: the
inverter-based series compensator. The two key findings of this extended
investigation are that the inverter-based form of controllable series compensator can
successfully be used to damp power oscillations and that, where the damping of oscillations is the particular focus of study, an idealised representation of the inverterbased
CSC is suitable for the analyses.
In the case of the inter-area mode damping problem, the selection of an appropriate
input signal to the CSC damping controller is a key issue, since the oscillations that
are to be damped involve a number of participating generators. This thesis examines
the suitability of a few candidate input signals that have been proposed in the
literature using the conceptually simpler SMIB system analytical models that have
been developed. Finally, the thesis applies the understanding of CSC damping
controller design gained from the SMIB study to the problem of inter-area mode
damping on a four-generator study system. Time-domain simulation results are
presented to demonstrate the impact of the controlled inverter-based series
compensator on the damping of the inter-area mode of this system.
Description
Thesis (M.Sc.Eng.)-University of Natal, Durban, 2000.
Keywords
Electric inverters., Oscillations., Electric power systems--Control., Electric power transmission., Theses--Electrical engineering.