# Hybrid LLC Converter with Wide Range of Zero-Voltage Switching and Wide Input Voltage Operation
## 2 Circuit Configuration  
The conventional LLC converters are provided in Figure 1. Figure 1 provides the converter schematic of the full bridge resonant circuit with center-tapped rectification and the voltage gain can be calculated as \(\mathrm{V_{o}/V_{in}}=\mathrm{G_{ac}(f_{sw})n_{s}/n_{p}}\), where \(\mathrm{G_{ac}(f)}\) is the transfer function of resonant tank by \(\mathrm{L_{m}}\), \(\mathrm{L_{r}}\) and \(\mathrm{C_{r}}\). The half bridge resonant circuit with center-tapped rectification is illustrated in Figure 1. The voltage gain is calculated as \(\mathrm{V_{o}/V_{in}}=\mathrm{G_{ac}(f_{sw})n_{s}/(2n_{p})}\). Therefore, the full bridge LLC converter has two times of gain of the half bridge resonant circuit. However, the rectifier diodes \(\mathrm{D_{1}}\) and \(\mathrm{D_{2}}\) has at least 2 \(\mathrm{V_{o}}\) voltage stress and more winding turns are needed on secondary-side. Figure 1,d are the other two circuit configurations with voltage doubler rectification. The voltage gains of Figure 1,d are obtained as \(\mathrm{V_{o}/V_{in}}=\mathrm{G_{ac}(f_{sw})(2n_{s})/n_{p}}\) and \(\mathrm{V_{o}/V_{in}}=\mathrm{G_{ac}(f_{sw})n_{s}/n_{p}}\), respectively. The voltage rating of \(\mathrm{D_{1}}\) and \(\mathrm{D_{2}}\) is \(\mathrm{V_{o}}\) and only one winding set of transformer is used on the output-side. Compared four circuit topologies in Figure 1, the full bridge LLC circuit with voltage double rectification has the largest voltage gain and the half bridge resonant circuit with center-tapped rectification has the least voltage gain. The proposed converter diagram is shown in Figure 2 to have wide voltage input operation (50 V-400 V) such as solar power or renewable energy conversion. The proposed hybrid LLC converter includes a full bridge resonant circuit (\(\mathrm{S_{1}-S_{4}}\), \(\mathrm{L_{r}}\), \(\mathrm{C_{r}}\) and \(\mathrm{L_{m}}\)) and a half bridge resonant circuit (\(\mathrm{S_{3}}\), \(\mathrm{S_{4}}\), \(\mathrm{S_{ac1}}\), \(\mathrm{L_{r}}\), \(\mathrm{C_{r}}\) and \(\mathrm{L_{m}}\)) on the primary-side and the voltage doubler rectifier with \(\mathrm{N_{s}}\) and \(2\mathrm{N_{s}}\) winding turns on the secondary-side. The converter has three different operating sub-circuits for three voltage input regions (400 V-200 V, 200 V-100 V and 100 V-50 V) as shown in Figure 2  
Figure 1: Diagram of the conventional inductor-inductor-capacitor (LLC) converters (**a**) full bridge resonant circuit with center-tapped rectification (**b**) half bridge resonant circuit with center-tapped rectification (**c**) full bridge resonant circuit with voltage doubler rectification (**d**) half bridge resonant circuit with voltage doubler rectification. circuit in Figure 2b-d is operated to have maximum voltage gain \(\rm G_{max}=2\), then the proposed converter in Figure 2a can achieve wide voltage gain from \(\rm G_{min}=1\) to \(\rm G_{max}=8\). The passive elements \(\rm C_{r}\), \(\rm L_{r}\) and \(\rm L_{m}\) are the basic LLC resonant components. Due to frequency modulation, the LLC resonant tank is controlled to have an inductive input impedance characteristic and the fundamental input voltage of the resonant tank is leading to the fundamental input current. Power devices \(\rm S_{1}\)-\(\rm S_{4}\) have soft switching turn-on characteristics. Power devices \(\rm S_{ac1}\) and \(\rm S_{ac2}\) are implemented by two back-to-back power MOSFETs. If \(\rm S_{ac1}\) is ON (OFF), then half bridge (full bridge) resonant circuit is operated on primary-side. \(\rm S_{ac2}\) is used to determine \(\rm 2N_{s}\) or \(\rm N_{s}\) secondary turns connecting to output-side. In the proposed converter, the circuit needs low (or high) voltage gain under high (or low) voltage input case to control load voltage. If 400 V \(\rm V>V_{in}>200\) V (high voltage region \(\rm V_{in-H}\), Figure 2b, \(\rm S_{1}\), \(\rm S_{2}\) and \(\rm S_{ac2}\) turn off, \(\rm S_{ac1}\) turns on and \(\rm S_{3}\) and \(\rm S_{4}\) are controlled by pulse frequency modulation.