Abstract
High-Voltage Direct Current (HVDC) systems are a feasible solution that allows the transmission of energy between several power networks. As a consequence of the use of HVDC systems, renewable energy sources can be integrated more easily into distribution grids and smart grids. Furthermore, HVDC systems can contribute to improving the power quality (PQ) of the grids to which they are connected. This paper presents a multiterminal HVDC system that not only controls the flows of active power between four different networks, but also compensates imbalances and harmonics in the grid currents to maintain balanced and sinusoidal voltages at the point of common coupling of the various grids. The compensation is carried out by the voltage-source converters (VSCs) connected to their respective AC grids. A control scheme based on the use of resonant regulators and proportional–integral (PI) controllers is responsible for of achieving the necessary power flow control with the amelioration of the PQ. A case study of a multiterminal HVDC system that comprises four terminals sharing a DC bus of 80 kV is simulated by means of PSCADTM/EMTDCTM (Power System Computer-Aided Design; Electromagnetic Transients including Direct Current), where the AC grids associated with the terminals suffer from voltage imbalances and voltage harmonics owing to the connection of unbalanced loads and nonlinear loads. The obtained simulation results show the performance of the complete system in terms of active power flow, voltage regulation, and harmonic distortions of the grid current and the grid voltage.
Highlights
This paper proposes a multiterminal multilevel voltage-source converters (VSCs)–High-Voltage Direct Current (HVDC) system that is able to ameliorate the power quality (PQ) of the AC grids connected to the VSC terminals
Balanced and unbalanced voltage sag compensation in a specific AC grid is carried out through the injection of reactive power by the terminal of the HVDC associated with that grid, and by the use of a resonant controller to cancel out the second harmonic component, which is present in the case of imbalances
In order to cancel out these disturbances, each VSC in the multiterminal VSC–HVDC system was employed to inject the unbalanced current and the harmonics components necessary for the correct operation of the various loads connected to the point of common coupling (PCC), while maintaining the grid current with a low distortion, yielding a more sinusoidal waveform for the voltages at the PCCs
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. The HVDC is able to compensate for active power, and to cancel out sags in the grid voltages and harmonics in the currents that flow through the different AC grids. Balanced and unbalanced voltage sag compensation in a specific AC grid is carried out through the injection of reactive power by the terminal of the HVDC associated with that grid, and by the use of a resonant controller to cancel out the second harmonic component, which is present in the case of imbalances. Each terminal of the HVDC offers active-power filter functionality to remove harmonics from the current of each AC grid; Energies 2021, 14, 1306 this compensation is performed by using several resonant controllers implemented in a synchronous reference frame (SRF).
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