Page 12 - PEN eBook October 2022

DESIGN Design

is essential for designing the shape and structure of the coils and for predicting which parts
of the system will produce more heat during the charge. The software model will represent all
power losses as power dissipated by resistors belonging to the modeled circuit. The results of the

proposed approach have been validated by comparing the predicted loss with the measurements
conducted on a 10-W WPT system, considering both alignment and misalignment condition of the
coils. Read the original article here.

The block diagram of a classical WPT system for phone-battery charging is shown in Figure 1.
The transmitter includes the DC/AC inverter and the TX coil, whereas the receiver includes the RX
coil, the AC/DC rectifier, and other conversion systems for the battery charger. Capacitors C and
rTX
C maximize the power transfer in the range of the switching frequency by introducing a negative
rRX
reactance. The intermediate voltage V is usually regulated through a low-bandwidth control loop,
mid
which wirelessly transmits the feedback signal to the transmitter. This, in turn, can adjust the
target voltage by changing the switching frequency or the phase shift of the TX full-bridge. In this
circuit, losses are mainly due to the copper and core losses of the TX and RX coils.

A Software-Based

Approach to Wireless

Power Transfer

Modeling

By Stefano Lovati, technical writer for EEWeb Figure 1: Block diagram of a wireless phone charger

Wireless power transfer (WPT) is a process that has been known for quite some time, dating back
to the invention of the Tesla coil. Due to some valuable benefits (lack of cables and connectors, as CIRCUIT MODEL
well as high isolation between power transmitter and receiver), this technology plays a relevant role The following relations describe the voltage and current characteristics of the transmitting and
today in applications such as EV charging, phone charging, medical devices, and more. Based on receiving coils:
1,2
the standard or on the inductive coupling process, WPT needs to achieve a high level of efficiency,
minimizing the power losses.

This article suggests an innovative software-based approach to the modeling of WPT circuits.
By extracting the equivalent circuit for a given positioning of the coils, an accurate estimation of the Where:
power losses can be provided. In particular, the model can estimate the type of loss (conduction,
eddy current, or core) and where it has originated (TX/RX winding or TX/RX core). Loss analysis

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