There was a time when wireless charging could scarcely be imagined. A cable or a wire was always a necessity. But today, we have wireless charging for our phones, and cars, and even for pacemakers! We’ve come quite a long way.
Wireless charging has the advantages of enhanced safety and greater convenience compared to wired charging. These advantages are driving its rapid adoption across both low- and high-power applications. This has opened up the need for measurement systems for receiver detection, positioning, foreign object detection, and load estimation.
Load power monitoring is a vital part of wireless power transfer methods to charge a device. Load power refers to the electrical power consumed by a device. Load power monitoring is required to ensure efficient charging control, safety of the load, and transparent billing of the energy consumed.
One widely used method of wireless power transfer for charging devices is the inductive charging system. There are two main components in an inductive charging system – a transmitter, and a receiver.
The transmitter, or the charging pad or base, is connected to a power source and contains a primary coil. It converts alternating current (AC) electrical power into an alternating magnetic field.
The receiver refers to the device that is being charged. It has a secondary coil, and the AC current is converted into direct current (DC) to charge the battery.
Existing solutions for measuring receiver-side load power primarily rely on methods that require direct access to, or communication from, the receiver. While numerous such techniques have been reported in the literature, estimating the load power using only transmitter-side measurements remains an active area of research and is advantageous, as it avoids the need for receiver-side access or communication.
There are problems in determining the load power. Firstly, the mutual inductance (M) [mutual inductance is a measure of how effectively current in one coil induces a voltage in another nearby coil] and load are unknown. Also, any measurement made from the transmitter side will be a function of both M and load. Hence estimating the load power, without having to find M first, is challenging.
Another problem arises when the load power is monitored from the transmitter side: the receiver coil’s ohmic losses (this happens when due to electrical resistance, the electrical energy is converted to heat), which is usually neglected, leading to their inclusion in the estimated load power.
Therefore, in this study, the authors Dr. Thomas P. Rajan and Prof. Boby George from the Department of Electrical Engineering, Indian Institute of Technology (IIT) Madras, Chennai, India, have overcome these challenges by using a new sensing coil that is placed on top of the transmitter coil.
The proposed measurement scheme was detailed theoretically, verified through simulation, and validated through experimentation on a developed test setup. The proposed method’s practicality has been assessed through various tests, and sources of error have been studied.
The proposed load power estimation technique had the following benefits:
- The receiver side was not physically accessed for measurement.
- The value of mutual inductance M, was not required.
- Ohmic losses in the receiver coil and compensation circuit could be separated from load power.
- The technique is independent of the values or parametric variations of the coils and compensation elements.
Dr. Subhas Mukhopadhyay, from Mechanical/Electronics Engineering, with the School of Engineering, Macquarie University, New South Wales, Australia, acknowledged this breakthrough research by the authors with the following comments: “The published work has introduced a novel method for estimating load power in wireless charging systems using only transmitter-side measurements. With a sensing-coil–based approach, it has tackled a critical challenge by enabling accurate power estimation without requiring physical access to the receiver, even under varying coupling conditions. Separating the receiver-side losses from true load power and achieving an experimental error within ±3.5%, the reported technique has delivered a breakthrough with strong applicability to flexible, real-world wireless charging solutions. The researched and reported methodology has showcased technical rigor, blending solid theoretical development with well-validated experimental results and opened up a huge opportunity for real-life applications.”
Article by Akshay Anantharaman
Click here for the original link to the paper
