Browsing by Subject "Decentralized Control"

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    Design and Control of Hydrostatic Continuous Variable Transmission for a Community Wind Turbine
    (2019-10) Mohanty, Biswaranjan
    This research aims to develop an efficient and reliable hydrostatic drive train (HST) for community wind turbines by implementing an advanced controller to maximize energy capture and stabilize the power grid. An HST is a continuously variable transmission (CVT) consisting of a hydraulic pump driving a variable displacement motor. HSTs are simple, light, cost-effective, and offer high power density. An HST drive train was designed for application in community wind turbines. To validate the performance of the HST, a novel power regenerative test platform was successfully designed, constructed and commissioned. It has two hydrostatic closed loops, coupled to each other. The research platform is capable of generating 100 kW output with only 55 kW of electrical input by taking advantage of power regeneration. The performance of each hydraulic component was measured on the test platform. The test platform is a multi-domain system, consisting of electrical, mechanical and hydraulic components. Using a bond graph-based method, a dynamic model of the system was developed. All possible pairings between inputs and outputs were studied in this multi input and multi output system to select the pair with the strongest coupling. A decentralized controller was later designed to control the rotor speed and pressure of the system. The start-up and shut down algorithms developed, enabled smooth operation of the testbed without a cavitation and pressure spikes. The performance of the HST was validated under various wind profile inputs. A pressure control strategy was developed to maximize power capture. To implement the above controller, one only needs measurement of the rotor speed for the reference command and pressure for tracking. The control law automatically drives the turbine to the optimum point, since the optimal parameters of the turbine are included in the control gain. A hardware-in-the-loop simulation was implemented to mimic the wind turbine environment. The turbine rotor dynamics are emulated on the test platform by implementing a decoupling controller. We examined the results of the HST drive train in transient and steady conditions. The efficiency of the HST wind turbine estimated from these experiments was comparable with that of a conventional turbine. Finally, the feasibility of connecting an HST wind turbine to the grid via a synchronous generator is studied. Furthermore, we investigated the electromechanical dynamics of the synchronous generator and performance of the system under large disturbances in incident wind, through detailed time-domain simulations. We found that the generator terminal voltage and frequency comply with the grid regulation band under all operating conditions. This strategy circumvents the need of expensive power electronics. This research have offered a novel insides of the HST for wind turbine applications. The outcomes of the project will stimulate industry to develop more efficient hydraulic components, system and control for wind applications and contribute to our green economy.
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    On Decentralized Control of Power Electronics Using Nonlinear Oscillators
    (2018-11) Sinha, Mohit
    This dissertation develops theoretical tools and hardware prototypes for the decentralized control of power electronic circuits connected through an electrical network. The research thrust is timely and relevant given that renewable generation, storage devices, and electric vehicles continue to be rapidly integrated via these power electronic interfaces into various power systems with ad-hoc control architectures. In particular, controllers are developed for two key applications of inverter control for dc-ac conversion for standalone and grid-connected microgrids, and switch interleaving for multiphase dc-dc conversion, where decentralized control lends a way to ensure robust, efficient and modular operation. The control philosophy derives from the rich subfield of coupled oscillator theory and focuses on a particular class of second order systems called Lienard-type oscillators. Depending upon the nature of coupling, such oscillators demonstrate emergent patterns of sustained oscillations that can be leveraged to engineer steady-state behavior with stability certificates. Based upon this premise, the core idea is to program the second order nonlinear differential equation onto a micro-controller and use its states to construct switching signals for the power-electronic converters. To close the loop, the output current is used to design a local feedback strategy that guarantees desirable steady-state behavior : synchronized solutions are of interest in inverter systems and phase-balanced solutions are of interest in interleaving switching waveforms for multiphase systems. Theoretical stability proofs based on Lyapunov and passivity arguments along with extensive hardware results are presented to demonstrate the suitability of the proposed paradigm. In the case of inverters, the work establishes a link between oscillator-based control and the classical droop laws that affords a comprehensive design procedure for synthesis of oscillators which incorporates steady state regulation, control of harmonic content and rate of convergence. Furthermore, a completely communication-free switch interleaving for dc-dc converters has a distinct advantage over the state-of-the-art methods that are at best distributed in nature and have a single point of failure.