A Method to Measure the Load Power Received in an Inductive Charging System Without Accessing the Receiver Side

A new load power estimation technique that operates based on the ground side measurements alone in a wireless charging system is presented. In most of the reported works, receiver side ohmic losses are ignored while estimating the load power from the transmitter side. In a flexible charging scenario, the mutual inductance is unknown, making it difficult to estimate the receiver side ohmic losses from transmitter side. In this work, a method to accurately estimate the load power from the transmitter side, without the need for accessing the receiver is proposed. A small planar circular sensing coil is introduced just on top of the transmitter, which can indirectly sense the loss occurring in the receiver coil. In this technique, after the load is automatically isolated, a set of no load parameters are calculated based on the sensing coil voltage. Subsequently, during the wireless power transfer stage, these parameters are used as per the proposed method to estimate the load power. The estimation is not affected by the receiver side losses. The proposed measurement scheme is detailed theoretically, verified through simulation and validated through experimentation on a developed test setup. A measurement error of less than ±3.5% has been obtained for a wide load variation, tested for three sets of coupling factors. The proposed method’s practicality has been assessed through various tests and sources of error have been studied.