In this paper, a method for power distribution control in communication-free multiple-input and multiple-output (MIMO) wireless power transfer (WPT) through load impedance and mutual inductance estimation is proposed. The proposed method intentionally adjusts the resonant frequency of the secondary side to introduce a reactance, utilizing this information to estimate the load impedance and mutual inductance for power distribution control without the need for communication. The principle of the power transmission algorithm proposed in this paper is designed to be effective regardless of whether the power or frequency is high or low. Therefore, the experimental setup is not designed by specifying the coil size, system frequency, or separation distance between the transmitting (Tx) and receiving (Rx) coils to match specific real applications. To verify the proposed method, four Tx coils and two Rx coils of arbitrary sizes are fabricated, and a MIMO-WPT environment is implemented using LC matching. In the experiment, since the circuit designed for the Tx is not capable of withstanding high currents, power is intentionally transmitted at a low range of less than 1 W to validate the feasibility of the method. Because the transmission power range is set low, the distance between the Tx and Rx coils is set close to approximately 2 cm. Consequently, it is verified that the algorithm for parameter estimation and power transmission to multiple Rx coils is effective as long as the environment allows for the current flowing through the Tx coil to change due to the presence of the Rx coils. All experiments for uniform and non-uniform power distribution to two Rx coils showed good agreement between the desired power and the actual received power.
