On the analysis of the dc dynamics of multi-terminal VSC-HVDC systems using small signal modeling

Abstract

In this paper, an analysis of the dc dynamics of multiterminal VSC-HVDC systems using the small signal modeling method is presented. Usually, the VSC controllers are designed under the consideration that they operate independently of each other. However, the possible interactions among them and the dc grid should be studied, especially in multi-terminal topologies. In this paper, three VSC-HVDC systems are modeled and, after linearization, the eigenvalues of the system are calculated for different loading conditions. The results from this analysis are compared to those obtained from more detailed models using PSCAD. It is shown that the operating point, the gains of the direct-voltage controller and the cable dynamics have an impact on the system performance.

Analysis of the dc dynamics of VSC-HVDC systems using a frequency domain approach

“…The basis of the procedure was to implement state space models of the individual elements to be later interconnected as shown in Figure 1, where two converters are connected to the HVDC grid (a cable). In [10] the eigenvalues of the system were calculated for a two-terminal and a threeterminal HVDC systems and it was found that undamped oscillations appeared when the power injected by VSC 1 (which controls the direct voltage) exceeds a certain value below the rated power, which, in the studied case was 0.8 pu.…”

“…In [10], a procedure to derive the state space model for VSC-based multi-terminal HVDC systems (VSC-MTDC) was presented. The basis of the procedure was to implement state space models of the individual elements to be later interconnected as shown in Figure 1, where two converters are connected to the HVDC grid (a cable).…”

“…The advantage of the poles calculation is that they can be done numerically from the state space matrices. In [7]- [10], small signal analysis has been performed for VSC system. Procedures are presented to derive the state space models of the VSC multi-terminal HVDC systems (VSC-MTDC) and the location of the eigenvalues in the complex plane are plotted for different control strategies and parameter.…”

Frequency‐dependent cable modelling for small‐signal stability analysis of VSC‐HVDC systems

“…However, VSC HVDC systems are characterised by faster control loops and system dynamics. This has triggered research efforts in small-signal modelling and analysis of VSC HVDC systems during the last decade [10][11][12][13][14][15]. The focus has largely been on model development for interaction studies with the surrounding ac grid, whilst incorporating the dynamics of the ac-and dc-sides of the HVDC converter station.…”

“…Therefore, it has been common practice to undertake small-signal stability studies with the dc cables represented as either a single pi-equivalent circuit [10][11][12]15] or by multiple pi-equivalent circuits [13,14].…”