Comparison of Multiple Circuits Including LCL in Inductive Power Transfer and Capacitive Power Transfer

Typical methods of wireless power transfer are Inductive Power Transfer (IPT) and Capacitive Power Transfer (CPT). Both have different characteristics such as transmission distance, cost, and impact of surrounding foreign matter. In addition, since transmission characteristics differ depending on the circuit. Therefore, in this paper, the design theory for selecting the appropriate circuit and method for various applications is made. The equations for transmission characteristics such as the compensation condition, CC(Constant Current)/CV(Constant Voltage) characteristic, efficiency, optimal load, and output power were calculated. As for compensation condition, it is found that S-P, P-S and P-P for IPT and S-S, S-P and P-S for CPT vary depending on the coupling factor. Substituting specific and impartial values into the calculated equations verified the following. As for the optimal load to achieve maximum efficiency, the value of optimal load in the receiver S is about
$\boldsymbol{k}^{\mathbf{2}}$
times smaller than the others for IPT, and the value of optimal load in the receiver S and LCL are about
$\boldsymbol{k}^{\mathbf{2}}$
times smaller than the others for CPT. Therefore, the circuits should be selected according to the value of the load for high efficiency transmission. As for the maximum efficiency, the efficiency does not depend on the transmission method or circuit, since it is the same for all circuits for both IPT and CPT. In terms of output power with voltage source, transmission S for IPT and transmission S and LCL for CPT can get about
$\mathbf{1}/\boldsymbol{k}^{\mathbf{2}}$
larger power than the other circuits. Regarding the output power with current source, the transmitter P and LCL for IPT and the transmitter P for CPT can get about
$\mathbf{1}/\boldsymbol{k}^{\mathbf{2}}$
larger power than the other circuits. Therefore, in order to get large power, an appropriate circuit should be selected depending on the type of the transmitter circuit, power source and method of transmission. Based on the above, it was found that LCL in IPT was same characteristic as S, but LCL in CPT was same characteristic as P. From the above, the design theory was made for optimal method and circuit selection by fairly evaluating representative circuits of both IPT and CPT methods under unified conditions.