## 2 Three-Phase Single-Stage AC-DC Converter in Inductive-Power-Transfer-Based Wind Power Systems
### Operation Modes of Inductive-Power-Transfer-Based Three-Phase Single-Stage AC-DC Converter
The secondary voltage doubler rectifier operates with the secondary resonant load current (I\({}_{\text{S}}\)) flowing through the path of the secondary winding of the contactless coupler (N\({}_{\text{S}}\)) \(\rightarrow\) secondary resonant capacitor (C\({}_{\text{r2}}\)) \(\rightarrow\) output rectifier diode \(\rightarrow\) output capacitor (C\({}_{\text{o}}\)) \(\rightarrow\) output voltage divider capacitor (C\({}_{\text{o}2}\)) \(\rightarrow\) secondary winding of the contactless coupler (N\({}_{\text{S}}\)). **MODE 5 (t\({}_{4}\)-t\({}_{5}\)):** The period t\({}_{4}\) to t\({}_{5}\) is the dead time for the switching devices Q\({}_{2}\) and Q\({}_{3}\). At t\({}_{4}\), switching device Q\({}_{2}\) turns off, and the boost inductor current I\({}_{\rm B3}\) and the primary resonant current (I\({}_{\rm P}\)) cause the parasitic capacitors (C\({}_{\rm P}\)) of switching devices Q\({}_{2}\) and Q\({}_{3}\) to change and discharge to half the link voltage (V\({}_{\rm Link}\)) and 0 volts, respectively. At this time, the polarity of the voltage (V\({}_{\rm P}\)) at the primary resonant circuit terminals (a-b) reverses, causing the voltage polarity of the secondary winding (N\({}_{\rm S}\)) of the contactless coupler also to reverse. At t\({}_{5}\), the voltage of the parasitic capacitor (C\({}_{\rm P}\)) of switching device Q\({}_{3}\) discharges from V\({}_{\rm Link}\)/2 to 0 volts, and when the negative current flows through the anti-parallel diode of switching device Q\({}_{3}\), Q\({}_{3}\) turns on with zero-voltage switching (ZVS) at t\({}_{5}\). **MODE 6 (t\({}_{5}\)-t\({}_{6}\)):** At t\({}_{5}\), switching device Q\({}_{3}\) turns on with zero-voltage switching (ZVS), and, during the period t\({}_{5}\) to t\({}_{6}\), both switching devices Q\({}_{3}\) and Q\({}_{4}\) remain turned on. During this period, the boost inductor current (I\({}_{\rm B3}\)) flows through the path of boost inductor (L\({}_{\rm B3}\)) \(\rightarrow\) input rectifier diode \(\rightarrow\) link capacitor (C\({}_{\rm I}\)) \(\rightarrow\) circulating diode (D\({}_{\rm I}\)) \(\rightarrow\) flying capacitor (C\({}_{\rm B}\)) \(\rightarrow\) anti-parallel diode of switching device Q\({}_{3}\)\(\rightarrow\) filter capacitor (C\({}_{\rm FC}\)) \(\rightarrow\) boost inductor (L\({}_{\rm B3}\)), and is quickly reset due to the reverse bias provided by the link voltage (V\({}_{\rm Link}\)). A voltage of \(-\)V\({}_{\rm Link}\)/4 is applied to the primary resonant circuit terminals (a-b), allowing the primary and secondary resonant currents (I\({}_{\rm P}\), I\({}_{\rm S}\)) to flow. However, the primary resonant current (I\({}_{\rm P}\)) previously flowing affects the ZVS operation of switching device Q\({}_{3}\) by flowing simultaneously through the paths of anti-parallel diode of switching device Q\({}_{3}\)\(\rightarrow\) resonant capacitor (C\({}_{\rm r1}\)) \(\rightarrow\) primary winding of the contactless transformer (N\({}_{\rm P}\)) \(\rightarrow\) voltage divider capacitor (C\({}_{\rm B2}\)) \(\rightarrow\) anti-parallel diode of switching device Q\({}_{3}\) and anti-parallel diode of switching device Q\({}_{3}\)\(\rightarrow\) resonant capacitor (C\({}_{\rm r1}\)) \(\rightarrow\) primary winding of the contactless transformer (N\({}_{\rm P}\)) \(\rightarrow\) voltage divider capacitor (C\({}_{\rm B1}\)) \(\rightarrow\) flying capacitor (C\({}_{\rm B}\)) \(\rightarrow\) anti-parallel diode of switching device Q\({}_{3}\). **MODE 7 (t\({}_{6}\)-t\({}_{7}\)):** Since both switching devices Q\({}_{3}\) and Q\({}_{4}\) remain turned on, the filter capacitor voltage (V\({}_{\rm CFB}\)) of phase b is applied to the boost inductor L\({}_{\rm B2}\), storing energy. During this time, the boost inductor current (I\({}_{\rm B2}\)) flows through the path of the filter capacitor (C\({}_{\rm FB}\)) \(\rightarrow\) switching device (Q\({}_{3}\)) \(\rightarrow\) switching device (Q\({}_{4}\)) \(\rightarrow\) input rectifier diode.