# Calculation of Main Circuit Steady-State Parameters for Capacitor Commutated Converter System
## 5 Case Study  
In this section, the modified Guizhou-Guangdong II \(\pm\)500 kV/3000 MW LCC-CCC HVDC transmission system is presented to verify the validity of the main circuit parameter calculation method. The simulation in PSCAD/EMTDC is carried out to reflect the operation of the LCC-CCC HVDC system and show a comparison between the calculation result and the experimental result. Figure 6: Flow chart of the detailed procedure for the main circuit parameter design. The conventional LCC at the rectifier side adopts the constant DC current control and the CCC at the inverter side adopts the constant DC voltage control. The angle control mode is adopted for the converter transformers at both sides. The operating condition is under bipolar mode, forward direction, full voltage operation, high resistance and normal AC voltages. The system parameters and the converter parameters are shown in Tables 3 and 4, respectively. The rated apparent extinction angle is chosen as 1.57\({}^{\circ}\) and the commutation capacitor is chosen as 129.75 uF from the steady-state mathematical model of the CCC in Section 3.1.2. Considering various measurement errors, the equipment manufacture tolerance and the adjustment range of control parameters (e.g., firing/extinction angle), the calculation results of the converter transformer parameters at both side are shown in Table 5. Due to the commutation capacitors, the ideal no-load DC voltage of the CCC is smaller than that of the LCC. Following the calculation procedure in Section 4, the calculation results of the main circuit parameters at the rectifier side and the inverter side are shown in Tables 6 and 7, respectively. \begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**System Parameters**} & \multicolumn{2}{c}{**Value**} \\ \cline{2-3}  & **LCC at Rectifier** & **CCC at Inverter** \\ \hline Rated angle/\({}^{\circ}\)\({}^{1}\) & 15 & 1.57 \\ Minimum angle of the transformer & 12.5 & 1.57 \\ angle control mode/\({}^{\circ}\) & 17.5 & / \\ Rated AC voltage/kV & 525 & 525 \\ Minimum reactive power & 140 & 0 \\ consumption of the converter/Mvar & / & 129.75 \\ Commutation capacitor/uF & / & 129.75 \\ \hline \hline \end{tabular} \({}^{1}\)Rated firing angle for the rectifier and rated apparent extinction angle for the inverter.  
\end{table} 
Table 4: Converter parameters of the LCC-CCC HVDC transmission system. \begin{table}
\begin{tabular}{c c} \hline \hline \multirow{2}{*}{**Main Parameters**} & \multicolumn{2}{c}{**Value**} \\ \cline{2-3}  & **LCC at Rectifier** & **CCC at Inverter** \\ \hline Rated ideal no-load DC voltage \(U_{\text{dionN}}/\text{kV}\) & 283.49 & 237.02 \\ Maximum ideal no-load DC voltage & 286.77 & 243.27 \\ Minimum ideal no-load DC voltage & 259.33 & 203.82 \\ \(U_{\text{dionin}}/\text{kV}\) & 525/209.92 & 525/175.51 \\ Tap changer range & \(-\)5 to 24 & \(-\)6 to 32 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Main parameters of the converter transformer. \begin{table}
\begin{tabular}{c c} \hline \hline \multirow{2}{*}{**System Parameters**} & \multicolumn{2}{c}{**Value**} \\ \hline Bipolar rated DC power/MW & 3000 \\ Rated DC current/kA & 3 \\ Rated DC voltage/kV & 500 \\ DC line resistance/\(\Omega\) & 10.4 \\ System frequency/Hz & 50 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: System parameters of the LCC-CCC HVDC transmission system. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \(P_{\text{dR}}\)/MW & \(U_{\text{dR}}\)/kV & \(I_{\text{d}}\)/kA & \(\alpha^{\prime}\)\({}^{o}\) & \(\mu_{\text{R}}\)\({}^{o}\) & \(Q_{\text{R}}\)/Mvar & Tap \\ \hline  
38 & 926.3 & \(-1\) \\
1800 & 500 & 3.6 & 14.01 & 24.67 & 962.9 & \(-1\) \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Main circuit parameters at the rectifier side (data per pole).