## 2 Three-Phase Single-Stage AC-DC Converter in Inductive-Power-Transfer-Based Wind Power Systems  
### Three-Phase Single-Stage AC-DC Converter  
This section discusses an IPT-based three-phase single-stage AC-DC converter that uses the generated line voltage (V\({}_{\rm LL}\): 110 V\({}_{\rm rms}\) to 250 V\({}_{\rm rms}\)) from a three-phase small wind turbine as the input power source. The converter aims to improve the power factor (PF) and total harmonic distortion (THD\({}_{\rm i}\)) of the three-phase AC power source and control the isolated output voltage (V\({}_{\rm O}\): 400 V\({}_{\rm DC}\)) for grid connection. The IPT-based three-phase single-stage AC-DC converter, as shown in Figure 2a, consists of input filter inductors (L\({}_{\rm F}\) = L\({}_{\rm FA}\), L\({}_{\rm FB}\), L\({}_{\rm FC}\)) and input filter capacitors (C\({}_{\rm F}\) = C\({}_{\rm FA}\), C\({}_{\rm FB}\), C\({}_{\rm FC}\)), boost inductors (L\({}_{\rm B}\) = L\({}_{\rm B1}\), L\({}_{\rm B2}\), L\({}_{\rm B3}\)), input rectifier diodes, voltage divider link capacitors (C\({}_{\rm C1}\), C\({}_{\rm 2}\)), a flying capacitor (C\({}_{\rm B}\)), voltage divider capacitors (C\({}_{\rm B1}\), C\({}_{\rm B2}\)), circulating diodes (D\({}_{\rm 1}\), D\({}_{\rm 2}\)), and four main switching devices (Q\({}_{\rm I}\), Q\({}_{\rm 2}\), Q\({}_{\rm 3}\), Q\({}_{\rm 4}\)). Additionally, in the IPT-based small wind power system, the air gap between the primary and secondary sides of the contactless coupler is fixed to be less than 1 cm, and, due to minimal coupling variation, the leakage inductances (L\({}_{\rm II}\), L\({}_{\rm 12}\)) and magnetizing inductance (L\({}_{\rm m}\)) parameters of the coupler do not vary significantly. Therefore, an S-S (series-series) compensation circuit with resonant capacitors (C\({}_{\rm r1}\), C\({}_{\rm r2}\)) is applied.  
Therefore, near the resonant frequency of the S-S compensation circuit, where the gain does not vary, the switching devices (Q\({}_{1}\), Q\({}_{2}\), Q\({}_{3}\), Q\({}_{4}\)) operate alternately at a fixed switching frequency with a 50% duty cycle controlled by the phase control (D\({}_{1}\)T). A square wave voltage (V\({}_{\rm P}\)) with a 50% duty cycle at one-fourth of the link voltage (V\({}_{\rm Link}\)) is always applied to the terminal voltage (V\({}_{\rm P}\)) across the primary S-S compensation circuit (a-b). This ensures that the primary switching devices achieve zero-voltage switching (ZVS) under all load and input voltage conditions, and the voltage corresponding to the resonant circuit gain characteristic is transferred to the secondary side of the coupler. Additionally, by applying a doubler rectification method composed of secondary rectifier diodes and doubler capacitors (C\({}_{01}\), C\({}_{02}\)), the voltage applied to the load is approximately doubled compared to the voltage applied to the secondary side of the contactless coupler. According to the phase control (D\({}_{1}\)T) of the switching  
(L\({}_{\rm B1}\), L\({}_{\rm B2}\), L\({}_{\rm B3}\)) is reset, operating in discontinuous mode. The boost inductor currents (I\({}_{\rm B1}\), I\({}_{\rm B2}\), I\({}_{\rm B3}\)), which operate in discontinuous mode, regulate the PFC stage link voltage (V\({}_{\rm Link}\)) to control the output voltage (V\({}_{\rm o}\)) of the rectifier stage at the secondary side of the contactless coupler. The detailed operation of this process is described in Section 2.2.