# Experimental Investigation of Controlled and Uncontrolled Rectifiers for Low-Power Wind Turbines
## 5 Full-Wave Uncontrolled Rectifiers  
Full-wave rectifiers are more efficient than half-wave rectifiers in producing pure DC from an AC power supply. The main advantage of full-wave rectification is that they provide a higher average output voltage with fewer ripples. In full-wave topology, positive and negative AC cycles are made to pass through the load in a positive direction. As a result, the frequency of the obtained pulsating DC is double compared to half-wave rectifiers [20]. There are two standard configurations of full-wave rectifiers, center-tapped and full-bridge. The center-tapped rectifiers have the advantage of using only two diodes, reducing losses. However, a bulky transformer is also needed, increasing the losses and cost [18]. On the other hand, a full-bridge rectification only requires four switches without a transformer, as shown in Figure 8. The average and RMS values of the full-wave bridge rectifier's output voltage are expressed in Equations (10) and (11). \[V_{\alpha_{\text{erg}}}=\frac{V_{in}*\sqrt{2}}{\beta} \tag{10}\]  
\[V_{\alpha_{\text{RMS}}}=\frac{V_{in}}{\sqrt{2}} \tag{11}\]  
First, the simulations were performed to verify the operation principles of the full-wave bridge rectifiers. During the first positive AC cycle, the diode \(D_{3}\) becomes forward-biased, making the current through the load and completing the circuit by making \(D_{2}\) forward-biased. However, during the negative AC cycle, \(D_{1}\) and \(D_{4}\) are forward-biased, thus continuously supplying a pulsating DC to the output load. The voltages across all four diodes are shown in Figure 9a. In contrast, the current flowing across the diodes is shown in Figure 9b. Finally, Figure 9c shows the input and output voltages and currents. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameters** & **Without Capacitor** & **With Capacitor** \\ \hline RMS Output DC Voltage & 23.45 V & 22.35 V \\ RMS Output Voltage Ripple & 2000 mV & 440 mV \\ RMS Secondary AC voltage & 16.04 V & 24.4 V \\ RMS Secondary Current & - & 2.028 A \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Effect of output capacitor on various parameters. The simulation also shows that the ripple frequency was doubled on the output voltage and current compared to half-wave rectifiers. The simulations were validated further by developing a hardware prototype. Table 2 shows the input and output parameters recorded from the experiments. In Figure 10a, channel 1 shows the input AC waveform connected to the bridge rectifier supplying the DC power to the load. The capacitor filter on 10 mF is also connected in parallel to the load, resulting in input sinusoidal wave clamping because the capacitor voltage becomes higher to input AC, and the capacitor holds this charge for both positive and negative AC cycles. Figure 10b shows the AC current measurement at the source before the bridge rectifier. The differential probe measurement shows 7.82 mV, which corresponds to 1.56 A. The output DC voltage at the load is slightly higher than the half-wave rectifier. The oscilloscope trace shows the DC output voltage as 26 V. The output DC voltage is further zoomed in Figure 10b to observe the DC voltage ripples at channel 3. The voltage ripple span is 174 mV, almost two times less than the half-wave rectifier. Effect of Load Change  
The full-wave bridge rectifier is better in terms of voltage regulation and voltage ripple performance [27]. However, testing the rectifier in varying load conditions is important, especially with an intermittent power source, such as a small wind turbine. The output DC voltage, ripples, and power parameters were observed while increasing and decreasing the load. The load resistance gradually increased from 25 \(\Omega\) to 250 \(\Omega\) in four steps. As the load reduced, the output voltage ripple also decreased. However, the relationship between the output voltage ripple and load is non-linear, as shown in Figure 11c. Similarly, the output