Control of Voltage Source Converters for Power System Applications
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The research work is aimed on the investigation of possible modeling and control schemes for the dc-link of VSC, with the purpose of identifying the impact of such modeling and control on the dynamics of the conversion system. A system consisting of back-to-back converters with equivalent grid interconnection and source representation is designed in the software PSCAD/EMTDC using a detailed switching model of the inverter and rectifier components. The control technique based on the well-established concept of vector control is implemented. The main task of the master thesis is oriented towards the achievement of more reliable dc-link dynamics with smaller required capacitance. The control algorithm is based on balancing the power between inverter and rectifier through the dc-link with the minimum dc voltage variations. Dc-link voltage regulation is achieved by implementing a control based on the energy stored in the dc-link capacitor. Alignment to a dq synchronous reference frame orientation with PI regulators is used in the control philosophy for decoupling purposes.