Analysis of an Oscillatory System With Three Coupled Coils for Wireless Power Transfer

In near-field power transfer, the distance between the transmitter and receiver resonators can be extended with the aid of an intermediate resonator, which may also be used to circumvent an obstacle such as a wall or desktop. Most previous works analyze the coupled system when driven by an independent source, which will typically require a power amplifier. Instead, an oscillator will be considered here, which will eliminate the need for the signal generator and driver. However, the two resonator couplings will have an impact on the oscillator behavior and its stability properties. We will initially address a cubic-nonlinearity oscillator and demonstrate that the coupled multiresonance network may lead to undesired oscillation modes. In the second stage, we will consider a transistor-based oscillator, which will be analyzed through a semianalytical formulation capable of providing all the coexisting periodic solutions. The undesired modes will be suppressed with the aid of a trap resonator. To maximize the power transfer, we will first obtain the optimum oscillator load admittance by means of a new procedure. Then, the admittance will be implemented using a relationship between the coupling factors. The methods will be applied to a Class-E oscillator, which has been experimentally characterized.