Multi-terminal VSC-HVDC Transmission Research Articles

Review on Voltage Control of Multi Terminal Vsc-Hvdc Transmission System for Offshore Wind Power Plant

Review on Voltage Control of Multi Terminal Vsc-Hvdc Transmission System for Offshore Wind Power Plant

A VSC-based Model for Power Flow Assessment of Multi-terminal VSC-HVDC Transmission Systems

This paper puts forward a new practical voltage source converter (VSC) based AC-DC converter model suitable for conducting power flow assessment of multi-terminal VSC-based high-voltage direct current (VSC-MTDC) systems. The model uses an advanced method to handle the operational limits and control modes of VSCs into the power flow formulation. The new model is incorporated into a unified framework encompassing AC and DC power grids and is solved by using the Newton-Raphson method to enable quadratically convergent iterative solutions. The use of complementarity constraints, together with the Fischer-Burmeister function, is proposed to enable the seamless incorporation of operational control modes of VSC and automatic enforcement of any converter's operational limits that become violated during the iterative solution process. Thus, a dedicated process for checking limits is no longer required. Furthermore, all existing relationships between the VSC control laws and their operational limitsare considered directly during the solution of the power flow problem. The applicability of the new model is demonstrated with numerical examples using various multi-terminal AC-DC transmission networks, one of which is a utility-sized power system.

A droop line tracking control for multi-terminal VSC-HVDC transmission system

In theory, the control mode of a voltage-sourced converter (VSC) within a multi-terminal HVDC (MTDC) transmission system can be represented by using a droop line characteristic in the active power and DC voltage relationship (Pac–Udc) curve. However, operating the droop control as an extension of the Udc control mode with a steep slope was found to be difficult since it introduces instabilities. This also happens in the extended Pac control with a shallow slope. This paper proposes a droop line tracking (DLT) method for mitigating these issues, i.e. by calculating the new operating point of the converter based on the displacement distance from the droop line. The simulation results show that the proposed method enables the converter to operate in different control modes by simply changing the droop line characteristic. Furthermore, the same concept can be extended to implement the advanced droop control, i.e. represented by a multi-slope droop line characteristic such that the converter can be operated in different control modes depending on the DC system disturbance level. Simulation using a three-terminal HVDC system with an offshore wind farm (OWF) station has been performed to demonstrate the functionality of the proposed method in realizing the advanced droop control mode.

Design and Transient Studies on Multi-Terminal VSC-HVDC Systems Interconnecting Offshore Wind Farms

In recent years, offshore wind energy has increased significantly. The continuous increase in the offshore wind power generation level brings the requirement of the offshore wind farms (OWFs) integration with an AC grid. The multi-terminal (MT) voltage source converters (VSC)-based high voltage direct current (HVDC) transmission system is an emerging technology and also the best option to interconnect the large-scale OWFs to the AC grid. This paper presents the design, modeling, and control of MT VSC-HVDC transmission system linked offshore wind farms. Different cases of MT VSC-HVDC transmission systems are developed, and its simulation studies are carried out using PSCAD/EMTDC. The test results show the transient performance of the MT VSC-HVDC transmission systems under various AC and DC fault conditions. The studies also include the influence of wind variabilities as in the form of gust and ramp pattern during steady state and fault conditions.

Transient analysis of super conducting fault current limiter integrated with multi-terminal direct current system

Since the extension of voltage source converter (VSC) based high voltage direct current (HVDC) transmission system to multi-terminal direct current (MTDC) system is easy, the application of MTDC system is more attractive than before. But the VSC based HVDC system is more vulnerable to DC line faults due to the high discharge current from the DC link capacitance. In this aspect, a super conducting fault current limiter (SCFCL) is a better choice to reduce the consequences of DC line faults. The main objective of this paper is to improve the dynamic performance of an offshore wind farm connected multi-terminal VSC-HVDC transmission system by incorporating SCFCL at different locations. Here, the SCFCL integrated MTDC system is modelled in MATLAB/Simulink and the results are presented for various AC/DC fault conditions.

Modelling and Control for Bounded Synchronization in Multi-Terminal VSC-HVDC Transmission Networks

The extension and size of the power grid is expected to increase in the near future. Managing such a system presents challenging control problems that, so far, have been approached with classical control techniques. However, large scale systems of interconnected nodes fall within the framework of the emerging field of complex networks. This paper models multi-terminal VSC-HVDC systems as a complex dynamical network, and derives conditions ensuring bounded synchronization of its trajectories for a family of controllers. The obtained results are validated via numerical simulations.

Design and Implementation of Multi-Terminal VSC-HVDC Transmission Systems for Offshore Wind Power Plants

This paper discusses a multi-terminal VSC HVDC system proposed for integration of deep sea wind farms and offshore thermal and nuclear platforms in to the grid onshore. An equivalent circuit of the VSC in synchronous d-q reference frame has been established and decoupled control of active and reactive power was developed. A three terminal VSC-HVDC was modeled and simulated in MATLAB/SIMULINK software. Voltage margin method has been used for reliable operation of the HVDC system without the need of communication. Simulation results show that the proposed multi-terminal VSC-HVDC was able to maintain constant DC voltage operation during load switching, step changes in power demand and was able to secure power to passive loads during loss of a DC voltage regulating VSC-HVDC terminal without the use of communication between terminals.

Design and Implementation of Multi-Terminal VSC-HVDC Transmission Systems for Offshore Wind Power Plants

Design and Implementation of Multi-Terminal VSC-HVDC Transmission Systems for Offshore Wind Power Plants

Voltage Control of Multiterminal VSC-HVDC Transmission Systems for Offshore Wind Power Plants: Design and Implementation in a Scaled Platform

This paper deals with multiterminal voltage source converter (VSC) HVDC transmission systems for the connection of offshore wind power plants to the main land ac grid. A droop-based control scheme is considered. The droop controllers have been designed base on a mixed sensitivity criterion by solving a convex optimization problem with linear matrix inequalities. The system is analyzed by means of simulations and experimentally in a scaled platform. Simulations show the control performance during a wind speed change and a voltage sag in the main ac grid. Experimental results include wind power changes (increase and decrease) and an eventual VSC loss (both considering grid-side and wind farm VSC loss). In all the cases, the simulation and the experimental results have shown a good system performance.