| dc.description.abstract | Studying the dynamic behaviour of non-linear complex power systems in a laboratory
is very challenging. Early experimental platforms used micro-alternators to emulate the
behaviour of fixed steam and hydro turbine models. The micro-alternator is a three-phase
synchronous generator with similar electrical constants (in per unit on machine rating) as
those typically found in alternators in large power stations. It is an electrical scaled-down
model of machines up to 1000 MW rating and is rated between 1 to 10 kVA. Researchers
used these micro-machines up to the 90s to study large electric generators’ transient and
steady-state performance. The department of electrical engineering at the Indian Institute
of Science (IISc) was also very active in experimental research in power engineering.
The department still retained two-three kVA and one ten kVA micro-machine sets, but
the control panels of these machines became obsolete as the manufacturer of these machines
Mawdsley, London, doesnt exist anymore. Advancements in simulation software
packages and real-time simulators have primarily replaced the experimental models of
electric power systems worldwide. The push for green energy technologies worldwide due
to climate concerns has increased the presence of power electronic converters in the power
grids. Reduction of overall inertia, frequent occurrence of electromechanical oscillations,
electromagnetic transients, and control interaction modes has become a concern for the
power grid operators. The need for understanding the physical insights of the oscillatory
modes introduced by fast-acting power electronic converters, the need for developing practically
feasible control algorithms for mitigating the interaction modes, and the need for
developing dispatchability and grid support features like conventional generation sources
have triggered the development of laboratory-scale experimental power grids across the
world in the past decade.
In this thesis, initially, an attempt is made to revive the old 3 kVA micro
alternator controls. An IGBT-based buck converter static excitation system has been
developed for the micro-alternator. This exciter also incorporates several limiters which
were non-existent in the old analog control panels. An under-excitation limiter, overexcitation
limiter, and V/Hz limiter as per IEEE standard 421.5 have been designed to
protect the micro-alternator during abnormal conditions such as overloading, overheating,
and over-fluxing of the machine. A digital time constant regulator (TCR) is incorporated
to modify the micro-alternator field’s time constant to mimic large synchronous machines’
dynamics as micro-machine time constants are very small. The detailed tuning procedure
of limiters and TCR is discussed to comply with IEEE STD 421.2 and IEEE STD 421.5.
Overheating of old micro-machines was observed due to the creation of multiple shortcircuit
faults. Hence, a custom 5 kVA micro-alternator is manufactured through a local
vendor having parameters like the old machines.
A single micro-alternator can represent only one large alternator dynamics,
thereby limiting the scalability of the platform. Emulating machines of different ratings
using a single micro-machine would undoubtedly boost the capabilities of experimental
platforms for investigating conventional and non-conventional source interactions in laboratories.
To the best of our knowledge, only one such attempt was made in the literature,
where a model reference control algorithm is proposed to mimic any rating alternator
dynamics using a doubly excited laboratory micro-alternator. However, doubly excited
micro-alternators are non-existent today. A reconfigurable experimental single machine
infinite bus testbed using the 5 kVA singly excited micro-alternator is developed reconfigurable
options to emulate different types of IEEE Standard excitation systems, standard
turbine governor models and different machine parameters.
A non-linear output matching control based on the dynamic inversion technique
is proposed for emulating the synchronous generators of different ratings with the IEEE
standard excitation system and governor turbine models using a single micro-alternator.
IEEE Model 1.1 is used for representing the behaviour of large alternators. The singlemachine
infinite bus (SMIB) experimental testbed has been used to validate the proposed
emulation approach. The dynamics of the synchronous generator model in per unit corresponding
to 128 MVA and 192 MVA machines have been physically emulated on the 5 kVA
laboratory micro-alternator. Good tracking performance is obtained with the proposed
approach under small and large disturbances in MATLAB simulations and experimental
evaluations. Using a systematic scaling procedure the proposed emulation approach has
been extended to evaluate the possibility of emulating the WSCC 3 machine 9 bus system
in the laboratory using MATLAB simulations. The simulation results are found to be very
promising in replicating the dynamics of WSCC system using the 5 kVA micro-machines.
Emulation of large machine dynamics with different types of turbines, governors, and excitation
controls using a singly excited micro-alternator enabling a generalized synchronous
machine emulation platform is a first-of-its-kind effort in the literature to the best of our
knowledge. | en_US |
