Multiterminal HVDC System with Power Quality Enhancement

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.

A VSG-Based Coordinated DC Voltage Control for VSC-HVDC to Participate in Frequency Regulation

“…Several novel ancillary control strategies are proposed to enable the frequency regulation capability of the VSC-HVDC systems [7][8][9][10]. To provide an inertial response for the grid, the energy stored in the capacitor of HVDC transmission is exploited.…”

Critical Technical Issues with a Voltage-Source-Converter-Based High Voltage Direct Current Transmission System for the Onshore Integration of Offshore Wind Farms

“…Because they may be utilized to connect several AC grids [45] using DC networks, VSC-HVDC systems enable us to take advantage of a multidirectional power flow [46,47]. Since HVDC systems have several advantages over HVAC schemes, including the asynchronous connection of multiple independent AC networks, the absence of reactive power in the DC link, and lower power losses [48,49], they can help to build a more dependable power network and smarter grids [50,51].…”