## 4 Simulation and Experiment
### Large-Signal Stability Experiments of a Single-Node CSO Undersea DC Power System  
An equivalent experimental prototype of a single-node CSO undersea DC power system was designed to verify the results of the above theoretical analysis and computer simulation. The equivalent experimental prototype is a medium-voltage simplified system model of a single-node CSO undersea DC power system, as shown in Figure 6. Its experimental configuration block diagram is shown in Figure 9. The shore station PFE is represented by an AC 220 V to DC 400 V converter. Every cable segment of 10 km is represented by a \(\pi\)-type lumped parameter equivalent circuit, and 36 circuits are cascaded to represent the 360 km submarine cable. The undersea station is represented by a DC 240 V to DC 48 V converter, feeding power to an electronic load which represents the undersea science payloads.  
Five parameter sets for prototype experiments are applied to verify the effects of the shore station PFE output voltage, the undersea station power consumption and the submarine cable parameters on the large-signal stability of a single-node CSO undersea DC power system. The parameter sets are shown in Table 5. \(U_{S}\) represents the output voltage of the AC/DC converter. \(R_{0}\), \(L_{0}\) and \(C_{0}\) represent the resistance, inductance and capacitance of a cable segment respectively. \(P_{L}\) represents the power consumption of the DC/DC converter with the electronic load.  
Figure 8: (**a**) The voltage transient processes in the parameter set #1; (**b**) the current transient processes in the parameter set #1; (**c**) the voltage transient processes in the parameter set #2; (**d**) the current transient processes in the parameter set #2; (**e**) the voltage transient processes in the parameter set #3; (**f**) the magnified view of voltage transient processes in the parameter set #3; (**g**) the voltage transient processes in the parameter set #4; (**h**) the voltage transient processes in the parameter set #5.  
Figure 9: The block diagram of the prototype experiment configuration.  
In the experiments, we assumed the startup of the AC/DC converter had encountered a large disturbance. The oscilloscope #1 and #2 were used to record the voltage and current transient processes in the prototype. The experiment results for the five sets are shown in Figure 10. In Figure 10, the red line indicates the output voltage of the AC/DC converter. The blue line indicates the voltage in the middle section of the submarine cable. The black line indicates the input voltage of the DC/DC converter. The green line indicates the output voltage of the DC/DC converter. The yellow line indicates the output current of the AC/DC converter.  
Comparing the results of the five parameter sets for prototype experiments, it can be seen that during the startup of the AC/DC converter, the parameter sets #1 and #2 were stable. The parameter set #3 would return to the steady-state equilibrium point after a period of voltage oscillation. According to the curve of the input voltage of the DC/DC converter, its oscillation amplitude is 8% of the steady-state voltage. But the parameter sets #4 and #5 would experience large fluctuations and were unable to return to a steady-state equilibrium point. According to the curve of the input voltage of the DC/DC converter, their oscillation amplitude is 15% of the steady-state voltage.  
This leads to the conclusion that increasing the output voltage of the shore station PFE or the capacitance of the submarine cable, or decreasing the power consumption of the undersea station or the inductance of the submarine cable are beneficial to enhance the large-signal stability of a single-node CSO undersea DC power system.