# Robust Optimal Tracking Control of a Full-Bridge DC-AC Converter
## 4 Simulation and Experimental Results
Earlier works have shown the behavioral response of the full-bridge DC-AC converter to inductive loads and have also revealed that power factor and efficiency can be improved by using a capacitor [86]. Figures 9 and 10 show the experimental output-waveshapes of the full-bridge DC-AC converter controlled by the proposed strategy and the typical TA under resistive full \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Value** \\ \hline Filter inductor, \(L\) & 0.1 mH \\ Filter capacitor, \(C\) & 20 μF \\ Resistive load, \(R\) & 12 ohm \\ DC-link voltage, \(V_{dc}\) & 200 V \\ AC Output voltage, \(v_{o}\) & 110 V\({}_{\text{rms}}\) \\ AC Output-voltage frequency & 60 Hz \\ Switching frequency & 30 kHz \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Parameters of the converter with inductor capacitor filter. Figure 4: Photo of the experimental setup. load conditions, respectively. The output voltage is both distortion-free and presents a beautiful sine wave; this means that under the condition of pure resistance linear load, the full-bridge DC-AC converter is difficult to be affected by its interference. Figure 11 illustrates the experimental output-waveshape of the full-bridge DC-AC converter under the proposed strategy with a step change in load (trigger angle of 90, changing from no load to 12 ohm at full load). In line with the simulation result, a small immediate voltage drop appears and then quickly returns to the reference voltage level. Figure 12 exhibits the experimental output-waveshape of a typical TA-controlled full-bridge DC-AC converter with a step change in load (90 trigger angle from no load to full load of 12 ohm). This tells us that the descent of the controller's compensation capability is due to bad transient tracking response, large voltage dip, and slow retrieval time. Figures 13 and 14 reveal the experimental output-waveshapes of the full-bridge DC-AC converters with the proposed strategy as well as a typical TA in the presence of LC parameter variations, where the output-voltage of the proposed full-bridge DC-AC converter (output voltage of 0.08% THD) is closer to a sinusoidal waveshape and less prone to deformation than a typical TA full-bridge DC-AC converter (output voltage of 12.91% THD). From the comparison amidst the proposed strategy and a typical TA, the proposed full-bridge DC-AC converter has better transience and steady-state tracking behavior than the typical TA-controlled full-bridge DC-AC converter under various load tests. Table 3 provides the experimental output-voltage dip and %THD under step-load changes and LC variations. Figure 5: Simulated output voltage and current with the proposed strategy under TRIAC (triode for alternating current)-controlled load (vertical: 50 V/division and 15 A/division). Figure 6: Simulated output voltage and current with the typical TA (terminal attractor) under TRIAC-controlled load (vertical: 50 V/division and 15 A/division). Figure 8: Simulated output voltage and current with the typical TA under rectified load (vertical: 50 V/division and 25 A/division). \begin{table}
\begin{tabular}{c c c} \hline \hline  & \multicolumn{2}{c}{**Proposed Strategy**} \\ \cline{2-3}  & TRIAC-controlled load & Rectified load \\  & (Voltage dip) & (\%THD) \\  & 8.36 Vmax & 0.14\% \\ \cline{2-3} Simulations & Typical TA & \\ \cline{2-3}  & TRIAC-controlled load & Rectified load \\  & (Voltage dip) & (\%THD) \\  & 41.31 Vmax & 13.57\% \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Simulations of output-voltage dip and %THD (total harmonic distortion) under TRIAC-controlled load and rectified load. Figure 7: Simulated output voltage and current with the proposed strategy under rectified load (vertical: 50 V/division and 25 A/division). Figure 11: Experimental output voltage and current with the proposed strategy under step change in load (vertical: 100 V/division and 20 A/division; horizontal: 5 ms/division).