Experimental verification of operation and method of decision of maximum DC link voltage in wireless power transfer system

This paper deals with a developed system that allows to drive an induction motor and charge a battery using wireless power transfer (WPT) for automated guided vehicle (AGV). The developed system enables to control output voltage of WPT by constantly moving the receiving coil and adjusting the gap length. It is desired that the system should withstand high voltage, and reduce copper loss and conduction loss in coil and power conversion circuits, respectively, to achieve high efficiency for the system. However, methods for determining the output voltage in the WPT system for AGVs has not been investigated yet. From the viewpoints, we investigate the allowable maximum output voltage provided by the developed WPT system. The maximum voltage is calculated using control equations including parameters of voltage booster, power supply voltage and battery current when the battery current control is adopted. Furthermore, experimental results reveal that the battery current control cannot be used beyond a maximum DC link voltage. In addition, a properly selected gap length of the coil is found to allow an induction motor to be driven and the battery to be charged using the WPT system. As a result, it is clarified by the experiments that the developed control system provides additively effective function to WPT for AGVs.