## 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
Simultaneously, a voltage of \(-\)V\({}_{\rm Link}\)/4 is applied to the primary resonant circuit terminals (a-b), causing the primary resonant current (I\({}_{\rm P}\)) to flow through the path of voltage divider capacitor (C\({}_{\rm B2}\)) \(\rightarrow\) primary winding of the contactless coupler (N\({}_{\rm P}\)) \(\rightarrow\) resonant capacitor (C\({}_{\rm r1}\)) \(\rightarrow\) switching device (Q\({}_{3}\)) \(\rightarrow\) voltage divider capacitor (C\({}_{\rm B2}\)). Concurrently, the primary resonant current also flows through the path of the link capacitor (C\({}_{\rm 2}\)) \(\rightarrow\) circulating diode (D\({}_{\rm I}\)) \(\rightarrow\) voltage divider capacitor (C\({}_{\rm B1}\)) \(\rightarrow\) primary winding of the contactless coupler (N\({}_{\rm P}\)) \(\rightarrow\) resonant capacitor (C\({}_{\rm r1}\)) \(\rightarrow\) switching device (Q\({}_{\rm 3}\)) \(\rightarrow\) switching device (Q\({}_{\rm 4}\)), delivering power to the secondary voltage doubler rectifier. The secondary voltage doubler rectifier operates with the secondary resonant current (I\({}_{\rm S}\)) flowing through the path of the secondary winding of the contactless coupler (N\({}_{\rm S}\)) \(\rightarrow\) output voltage divider capacitor (C\({}_{\rm o1}\)) \(\rightarrow\) output capacitor/load \(\rightarrow\) output rectifier diode \(\rightarrow\) secondary resonant capacitor (C\({}_{\rm r2}\)) \(\rightarrow\) secondary winding of the contactless coupler (N\({}_{\rm S}\)), delivering power. **MODE 8 (t\({}_{7}\)-t\({}_{8}\)):** The interval t\({}_{7}\) to t\({}_{8}\) is the dead time for the switching devices Q\({}_{1}\) and Q\({}_{4}\). At t\({}_{7}\), when switching device Q\({}_{4}\) turns off, the boost inductor current I\({}_{\rm B2}\) and the primary resonant current I\({}_{\rm P}\) cause the parasitic capacitors (C\({}_{\rm P}\)) of switching devices Q\({}_{1}\) and Q\({}_{4}\), as well as the parasitic capacitors (C\({}_{\rm ip}\)) of circulating diodes D\({}_{1}\) and D\({}_{2}\), to begin discharging and charging simultaneously. The voltages of the parasitic capacitor (C\({}_{\rm P}\)) of switching device Q\({}_{4}\) and the parasitic capacitor (C\({}_{\rm ip}\)) of circulating diode D\({}_{1}\) are charged to V\({}_{\rm Link}\)/2. In contrast, the voltages of the parasitic capacitor (C\({}_{\rm P}\)) of switching device Q\({}_{1}\) and the parasitic capacitor (C\({}_{\rm ip}\)) of circulating diode D\({}_{2}\) are discharged to 0. Subsequently, the negative current begins to flow through the anti-parallel diode of switching device Q\({}_{1}\), and, at t\({}_{8}\), Q\({}_{1}\) turns on with zero-voltage switching (ZVS). The subsequent operation repeats from MODE 1. Analysis of Power Factor Correction Operation Characteristics in a Three-Phase Single-Stage AC-DC Converter  
The three-phase single-stage AC-DC converter applied to the IPT-based small wind power system controls both the PFC stage power factor compensation and the DC-DC stage, which employs an S-S compensation circuit on the primary and secondary sides of the contactless coupler according to the phase control (D\({}_{1}\)T) of the main switching devices (Q\({}_{1}\), Q\({}_{2}\), Q\({}_{3}\), Q\({}_{4}\)) at a fixed switching frequency. Therefore, because the output voltage (V\({}_{\rm O}\)) of the DC-DC stage and the power factor (PF) must be controlled solely through phase control (D\({}_{1}\)T), the PFC stage boost inductors (L\({}_{\rm B1}\), L\({}_{\rm B2}\), L\({}_{\rm B3}\)) must be designed to operate in Discontinuous Conduction Mode (DCM) rather than in Continuous Conduction Mode (CCM) or Critical Conduction Mode (CRM). Figure 4 shows the AC phase voltages (V\({}_{\rm AN}\), V\({}_{\rm BN}\), V\({}_{\rm CN}\)) of a three-phase PMSG small wind turbine operating in the range of 10 to 47 Hz depending on wind speed and the currents (IB1, IB2, IB3) flowing through the boost inductors (LB1, LB2, LB3) of the three-phase single-stage AC-DC converter.