Design and implementation of regulator-less wireless power transfer system for electric bikes

Abstract

Because of the limited fossil fuel and environmental pollution problems around the world, the interest on eco-friendly transportation has increased among people. In addition, researches and commercialization of the wireless power transfer system (WPTS) that is operated by electricity for more convenient and safe transportation are being studied and commercialized actively. The demand of the public bike sharing system, which is one of the public transportation for citizens, has increased rapidly and continuously these days. It suggests that the new mechanism for the ecofriendly electric bikes should be applied to the public bike sharing system. The system is disclosed to the public in many different environment. Generally, the charger has to be plugged-in, but it has the risk of getting an electric shock when rain and snow comes because of their humid atmosphere. Therefore, to share the electric bikes the wireless power transfer system is certainly needed. However, cost, volume and weight of a pick-up part, which is installed to apply the wireless power transfer system to the electric bike, are limited unlike those of an electric vehicle. Therefore, the regulator-less wireless power transfer system, which takes the greatest space in pick-up part, is proposed. There is no additional equipment needed to remove the regulator, but the only thing needed is the charging algorithm to an inverter, using a battery profile. Regulator is an equipment that allows charging with the constant voltage and the constant current. It controls the output power that is entered to a battery. However, in the regulator-less wireless power transfer system for electric bike, there are external environmental variables. Those variables can cause the misalignment from the minimum value of mm to the maximum value of cm, by different conditions for occurrence of misalignment. The output voltage can rapidly change because of those misalignments. Therefore, a novel coil structure is suggested and analyzed to decrease the loss caused by the misalignments, with the increase in misalignment tolerance. To verify the high electrical performance of the proposed coil structure, the proposed model is compared with the bar type and the E type. Then, the proposed model shows the extremely improved results than the bar type and the E type. As a result, the regulator-less wireless power transfer system for electric bike is implemented and measured by the actual wireless charging electric bike experiment, using a proposed coil structure. By reduc-ing the loss caused by the switching of a regulator, the efficiency of pick-up part could be improved. Also the cost, volume and weight could be reduced. The battery charging experiment without a regulator is succeeded, with the maximum 200 W-class.