Pedro Rodríguez Cortés

Towards fully controllable multi-terminal DC grids using flexible DC transmission systems

This paper develops a flexible DC transmission system (FDCTS) to power control and load flow control within the multi-terminal (MTDC) grids. The FDCTS include static power electronics-based elements for electric energy transmission inside a DC grid. Considering the current advancements in the field of power electronics, this paper proposes a cascaded power flow controller (CPFC) as the first element of the FDTCS for providing power control in MTDC grids. It is shown through dynamic simulations that the CPFC is able to control power flowing through a particular DC transmission line, and thus enhancing controllability in the MTDC grids.

Power density investigation on the press-pack IGBT 3L-HB-VSCs applied to large wind turbines

With three different DC-side and AC-side connections, the three-level H-bridge voltage source converters (3L-HB-VSCs) are alternatives to 3L neutral-point-clamped VSCs (3L-NPC-VSCs) for interfacing large wind turbines with electricity grids. In order to assess their feasibility for large wind turbines, they should be investigated in terms of power density, which is one of the most important design criteria for wind turbine converters due to turbine nacelle space limitation. In this study, by means of the converter electro-thermal models based on the converter characteristics, the power capabilities, DC capacitor sizes, converter cabinet volumes of the three 3L-HB-VSCs utilizing press-pack IGBTs are investigated in order to quantify and compare the power densities of the 3L-HB-VSCs employed as grid-side converters. Also, the suitable transformer types for the 3L-HB-VSCs are determined and comparatively studied in terms of volume and weight in order to estimate the size effects of the 3L-HB-VSC topology on the whole wind turbine connection system. Finally, based on the power density and transformer-size investigations, the feasibility of each 3L-HB-VSC is discussed.

Power station for large scale photovoltaic power plants

Most of the large scale photovoltaic power plants (LS-PVPP) count on power converters with a central configuration. Advantages such as robustness, low maintenance and installation cost makes this configuration the preferred specially suitable in large scale systems. However, important drawbacks like the low efficiency level make necessary to develop new solutions for future power plants. In this paper a power station for large scale PV systems is proposed, which consists of power inverters synchronized with an interleaving modulation and connected to a multi-winding transformer. The main principles that support this proposal, as well as, simulation results are presented to validate the effectiveness of the proposed configuration.Most of the large scale photovoltaic power plants (LS-PVPP) count on power converters with a central configuration. Advantages such as robustness, low maintenance and installation cost makes this configuration the preferred specially suitable in large scale systems. However, important drawbacks like the low efficiency level make necessary to develop new solutions for future power plants. In this paper a power station for large scale PV systems is proposed, which consists of power inverters synchronized with an interleaving modulation and connected to a multi-winding transformer. The main principles that support this proposal, as well as, simulation results are presented to validate the effectiveness of the proposed configuration.

Grid resonance attenuation in long lines by using renewable energy sources

In this paper the grid harmonic resonance on long lines is studied, in particular the resonance phenomena between the grid series inductance and the line parallel capacitor. Later, the resonance is attenuated by using a renewable energy generator. Experimental results are depicted and the conclusions are stated.In this paper the grid harmonic resonance on long lines is studied, in particular the resonance phenomena between the grid series inductance and the line parallel capacitor. Later, the resonance is attenuated by using a renewable energy generator. Experimental results are depicted and the conclusions are stated.

Re-synchronization strategy for the synchronous power controller in HVDC systems

Frequency and voltage regulation are required to support the grid under different scenarios. In order to handle these scenarios, classical control strategies demand complex systems to fulfill these requirements. However, synchronous controllers are trending strategies to contribute with frequency and voltage regulation functionalities without the requirement of external elements. Among these strategies, the Synchronous Power Controller (SPC) is exceptional, due to its ability to operate a power converter in grid-forming or grid-feeding mode while providing grid supportive functionalities. Nevertheless, to avoid high power oscillations at the point of common coupling during grid connection, a grid synchronization strategy is mandatory. This paper proposes a synchronization strategy to adjust the angle, voltage amplitude and frequency of the converters controlled with the SPC. The proposed strategy has been simulated in an HVDC system with the SPC controlling the grid connected converter. Simulation results demonstrate the validity and effectiveness of the proposed strategy.Frequency and voltage regulation are required to support the grid under different scenarios. In order to handle these scenarios, classical control strategies demand complex systems to fulfill these requirements. However, synchronous controllers are trending strategies to contribute with frequency and voltage regulation functionalities without the requirement of external elements. Among these strategies, the Synchronous Power Controller (SPC) is exceptional, due to its ability to operate a power converter in grid-forming or grid-feeding mode while providing grid supportive functionalities. Nevertheless, to avoid high power oscillations at the point of common coupling during grid connection, a grid synchronization strategy is mandatory. This paper proposes a synchronization strategy to adjust the angle, voltage amplitude and frequency of the converters controlled with the SPC. The proposed strategy has been simulated in an HVDC system with the SPC controlling the grid connected converter. Simulation results demonstrate the validity and effectiveness of the proposed strategy.

Heuristic Optimization of Supplementary Controller for VSC-HVDC/AC Interconnected Grids Considering PLL

Abstract This paper presents a new approach to enhance the dynamic responses of AGC in power systems by means of heuristic optimization of VSC-HVDC supplementary controllers. The upcoming power electronics-based VSC-HVDC transmission systems offer new features that would be advantageous for improving the frequency control and thus for enhancing the stability of the transmission grids. In this paper, the parameters of the proposed control modulation are tuned using Genetic Algorithm and Simulated Annealing methods. The performance of the proposed intelligent based tuning approach is assessed through MATLAB simulations for an AC/DC interconnected system. For the sake of detailed analysis, the effects of PLL and frequency measurements are also included in the VSC-HVDC system modeling. Furthermore, to show merits of the proposed strategy, a comparison between AC and DC transmissions is presented.

Dynamics estimation and generalized tuning of stationary frame current controller for grid-tied power converters

Abstract The integration of ac-dc power converters to manage the connection of generation to the grid has increased exponentially over the last years. PV or wind generation plants are one of the main applications showing this trend. High power converters are increasingly installed for integrating the renewables in a larger scale. The control design for these converters becomes more challenging due to the reduced control bandwidth and increased complexity in the grid connection filter. A generalized and optimized control tuning approach for converters becomes more favored. This paper proposes an algorithm for estimating the dynamic performance of the stationary frame current controllers, and based on it a generalized and optimized tuning approach is developed. The experience-based specifications of the tuning inputs are not necessary through the tuning approach. Simulation and experimental results in different scenarios are shown to evaluate the proposal.