Abstract
The application of high voltage (HVDC) transmission for integrating large scale and/or off-shore wind generation systems with the electric grid is attractive in comparison to extra high voltage AC transmission systems due to a variety of reasons. A suitable control system is required for a VSC-HVDC system that provides good performance across a range of operating conditions. Two strategies are studied for their potential to enhance system robustness. The d-axis current control and DC power control are implemented in the outer-loop control at the receiving end of VSC-HVDC system. Small-signal analytical model is used to perform eigenvalues analysis and to design controllers. Both control techniques are investigated and the results are compared. An additional DC voltage droop control is added for both schemes. Its advantages were investigated. The droop gain and the cut off frequency of the DC voltage feedback filter are selected by analyzing the root locus of the analytical model to select the optimum values. It is established that d-axis current control with DC voltage droop control shows better performance practically for very weak AC system at both ends as well as with very long DC cable. The simulation results performed on PSCAD/EMTDC verify the feasibility of the control strategies effectively under different scenarios in order to confirm the obtained conclusions from analytical investigations.
Highlights
Voltage Source Converter (VSC) based HVDC transmission system (VSC−HVDC), newly developed technology on power transmission [1], [2]
The VSC-HVDC control system is split into the receiving (Terminal 1) and sending (Terminal 2) end station controllers which are performing on their connected converters
According to the related research and operation results of VSC-HVDC system, the following control modes are used for the converter of the VSC-HVDC system: DC voltage control mode, AC voltage control mode, DC current control mode, and DC power control mode
Summary
Voltage Source Converter (VSC) based HVDC transmission system (VSC−HVDC), newly developed technology on power transmission [1], [2]. The VSC-HVDC control system is split into the receiving (Terminal 1) and sending (Terminal 2) end station controllers which are performing on their connected converters. Developing this simulation platform provides the possibility of enhancing and analyzing the performance of the modeled system under different operating conditions. Advances in Energy and Power 5(4): 48-57, 2017 voltage at the sending end whereas the DC current model is implemented in outer-loop of the receiving station. The main objective of this study is to present a detailed comparison of the outer-loop control performance at the receiving end station of VSC-HVDC system. Simulation study of detailed model of VSC-HVDC test system using PSCAD /EMTDC will be employed to verify the theoretical model and the selected control method
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