Abstract
A DC current flow controller (CFC) in a multi-terminal high-voltage direct current (HVDC) (MTDC) grid has the functionality of adjusting and optimizing the power flow on the DC lines. In this paper, the impact of DC CFC parameters on the system stability and dynamic performance is analyzed with three contributions: 1) a mathematical model and a small-signal model of the DC CFC in a meshed MTDC grid are derived; 2) considering the impact of controller parameters on gain margins, phase margins, and cut-off frequencies, the stability analysis is performed in the frequency domain and a parametric optimization scheme is proposed with the deployment of the control variate method and scanning method; 3) a method is proposed to determine the size range and the voltage reference of the common capacitance based on their influence on dynamic behaviors. Two DC CFC equipped multi-terminal meshed HVDC grids are established in PSCAD/EMTDC. The simulation results justify the effectiveness of the theoretical analysis. The proposed parametric selection scheme is demonstrated by dynamic responses shown in the comparative studies.
Highlights
In the past several decades, there has been an increasing number of high-voltage direct current (HVDC) transmission lines in power systems
This paper further investigates the parametric selection and optimization of the DC current flow controller (CFC) in a meshed multiterminal HVDC (MTDC) grid with the main contributions as follows
The mathematical model of a two-line DC CFC equipped three-terminal meshed HVDC grid shown in Fig. 2(a) can be derived according to the Kirchhoff’s current law (KCL) and Kirchhoff’s voltage law (KVL) as follows:
Summary
In the past several decades, there has been an increasing number of high-voltage direct current (HVDC) transmission lines in power systems. The application of this approach is mainly limited by the high losses and cost, since all power transferred has to pass the DC-DC transformer during the control process In comparison with the former approach, method (2), i.e. inserting an equivalent voltage source, is proved to have advantages of lower operational losses and reduced topological complexity [11]–[21]. In [19], a two-line DC current flow controller (CFC), which comprised two full-bridge DC-DC converter sharing a common capacitor, was proposed. The mathematical model of a two-line DC CFC equipped three-terminal meshed HVDC grid shown in Fig. 2(a) can be derived according to the Kirchhoff’s current law (KCL) and Kirchhoff’s voltage law (KVL) as follows: di dt di dt
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