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Defensa Tesi Doctoral de Ngoc Bao Lai

23/03/2022 de 13:00 a 16:00
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Autor: Ngoc Bao Lai
Dimecres, 23 de de març · 1:00-4:00pm
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Director: Pedro Rodríguez Cortés
Títol: Control of Power Converter in Modern Power Systems

Resum: Power system is undergoing an unpreceded paradigm shift: from centralized to distributed generation. As the renewable-based generations and battery storage systems are increasingly displacing conventional generations, it becomes more and. more difficult to maintain the stability and reliability of the grid by using only conventional generations. The main reason for the degradation of grid stability is the rapid penetration of nonconventional sources. these new generations interface with the grids through power electronics converters which are conventionally designed to maximize conversion efficiency and resource utilization. lndeed, these power converters only focus on their interna! operation despite the grid conditions, which often worsens the grid operation. To overcome such a drawback, the grid-forming concept has been proposed for power converters, aiming to redesign the control of the power converters to enforce more grid-friendly behaviours such as inertia response and power oscillation damping to name a few. Despite the rich literature, actual adaptation of grid-forming controller in real-world applications is still rare because incentives for renewable power plants to provide services based on such advanced grid-forming functions were at best scarce. In the last years, however, severa! system operators have imposed new requirements and markets for grid-supporting services. In addition, the existing grid-forming controllers require modification to low-level control firmware of a power converter, which is often unrealistic due to the control hardware limitations as well as-necessary testing and certifications.

To ensure a stable operation of a grid-forming converter under adverse operating conditions, a robust voltage sensorless current controller is developed in this PhD thesis. The proposed controlfer is able to handle most of the possible abnormal conditions of the grid such as impedance variations, unbalanced voltage; harmonics distortion. These abnormalities of the grid are mathematically represented using equivalent linear models such that they can be used for calculating the controller gains. Linear matrix inequality techniques are also used to facilitate parameter tuning. In fact, the · performance and stability of the current control loop can be determined through only two tuning parameters instead of eight parameters for a controller of a similar structure.
The existing grid-forming implementations are designed considering that the control firmware of the power converter can be upgraded at will. However, modifications of the control firmware are not straightforward and cost-effective at mass scale. To overcome such a limitation, an externa! synchronous controller is presented in this PhD thesis. The extemal synchronous controller uses measurements, which are either provided by the power converter or a dedicated measurement unit, to calculate the actual active and reactive power that should be injected by the power converters in a way that the power plant acts as an aggregated _gridform ing converter. As a result, any conventional powér converters, can be utilized for providing grid-supporting services with minimal modification to the existing infrástructure.

Power converters can provide even better performance than a synchronous generator if a proper control scheme is used. In this regard, the final chapter of this PhD thesis presents the multi-rotor virtual machine implementation for grid-forming converter to boost their damping performance to power oscillations. The multi-rotor virtual machine-controller implements severa! virtual rotors instead of only one rotor as in typical grid-forming strategies. Since each of the virtual rotors is tunad to target a specific critica! mode, the damping participation to such a mode can be increased and adjusted individually.

The controllers presented in this PhD thesis are validated through simulations and experiments in the framework of the H2020 FlexiTranstore project.