Development of A Reconfigurable Synchronous Machine Emulation Platform

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.