# Stability Analysis of Buck Converter Based on Passivity-Based Stability Criterion
## 5 Simulation Validation
### Experimental Validation of Buck-CPL  
To validate the correctness of the simulation analysis, the experimental platform of Buck-CPL subsystem was built as shown in Figure 14.  
Figure 15 gives the comparative waveforms of the bus voltage and output current of the Buck-CPL system under traditional control and improved control. It can be seen that when the system adopts the improved control strategy, the system meets the passive condition and is in a stable state, while after transforming to the traditional control, due to the fact that its total system conductance is not passive at this time and is in a critical stable state, the system appears to have divergent oscillations after the switching phenomenon. Therefore, the improved control strategy can improve the stability margin of the system.  
Figure 13: Simulation waveforms of the Buck converter with a DC bus voltage decrease. (**a**) Traditional control; (**b**) improved control.  
Different control strategies of the Buck converter are given. The experimental waveforms of input voltage \(v_{s}\), the bus voltage \(v_{dc}\) and the inductor current \(i_{L2}\) are shown in Figure 16 when the desired value of DC bus voltage increases. The corresponding experimental waveforms of the Buck converter at the time when the desired value of bus voltage decreases are shown in Figure 17.  
Figure 16: Experimental waveforms of a Buck converter with a DC bus voltage increase. (**a**) Traditional control; (**b**) improved control.  
Figure 14: Experimental platform of the Buck-CPL system.  
Figure 15: Experiment waveforms in steady state of traditional control and improved control.  
In Figure 16a, when the Buck converter adopts the traditional control strategy, the bus voltage desired value increases from 60 V to 80 V. Compared with the steady-state value, the maximum offset of the system bus voltage is 10 V, the overshoot is 12.5% and it is stabilized at 80 V after 0.36 s of oscillation. The maximum offset of the system inductance current is 6A; it is stabilized at 3A after 0.36 s of oscillation. When the Buck converter adopts the improved control strategy, the system waveform is shown in Figure 16b; the bus voltage is stabilized at 80 V after 0.16 s when the bus voltage expectation value increases from 60 V to 80 V. The bus voltage does not overshoot; the system inductance current has a maximum offset of 3.5A compared with the steady-state value, which is stabilized at 3A after 0.16 s. The simulation and experiment change rule are consistent; when the system adopts the improved control strategy, the system anti-interference ability is improved and the dynamic performance is better.  
According to Figure 17a, when the Buck converter adopts the traditional control strategy, the bus voltage expectation value decreases from 80 V to 60 V compared with the steady state value, and the maximum offset of the system bus voltage is 15 V and stabilizes at 60 V after 0.36 s of oscillation. The system inductor current falls to 0A before the oscillation converges and stabilizes at 4A after 0.36 s of oscillation. When the Buck converter adopts the improved control strategy, the system waveform is shown in Figure 17b; the desired value of the bus voltage decreases from 80 V to 60 V, the bus voltage is stabilized at 60 V after 0.16 s and there is no overshooting of bus voltage. The system inductor current falls to 1A and then converges and stabilizes at 4A after 0.16 s. The system oscillation converges after 0A and stabilizes at 4A after 0.36 s of oscillation, and the system inductance current is stabilized at 4A. Therefore, when the system adopts the improved control strategy, the system anti-interference capability is improved and the dynamic performance is better. Therefore, the passive margin of the system is increased when the Buck converter adopts the improved control strategy and has better interference immunity.