An Automatic Coil Design Method with Modified AC Resistance Evaluation for Achieving Maximum Coil-Coil Efficiency in WPT Systems

In wireless power transfer systems, coil design has a great impact on coil-coil efficiency. This article analyzes the relationship between coil-coil efficiency and design parameters (three geometric parameters of coupling coils and working frequency) under typical constraints, and the function between optimal working frequency and geometric parameters is derived. Hence, the solution space of design parameters is reduced from four dimensions (geometric parameters of the coil and frequency) to three dimensions (geometric parameters), and particle swarm optimization (PSO) algorithm is applied to solve it. Moreover, a modified ac resistance evaluation method is proposed, in which conductive resistance is calculated with a frequency-dependent formula and proximity-effect resistance is calculated with a modified analytical method. Experimental results show that the modified method is precise for coils wound closely or sparsely. It is highlighted that extra finite element analysis software is not needed due to the modified calculation method of ac resistance, which makes the design process automatic and faster. Finally, a practical example is given, and two systems are designed with the PSO-based method and a conventional method, respectively. The coil-coil efficiency of the PSO-based method and the conventional method is 95.6% and 94.0%, respectively.