Guideline to Series-Series Compensation Design and Bifurcation Mitigation in Multi-Modular IPT Systems

The compensation and high-efficiency operation of the multi-modular inductive power transfer (IPT) systems has been a challenge because of the inter- and cross-coupling between modular charging pads. This paper analyzes the series-series (S-S) compensation and the associated bifurcation problem in multi-modular IPT systems based on closed-form analytical modelling of the coupled circuits. From the analytical results, an improved compensation tuning method for multi-modular systems is demonstrated. This improved compensation addresses the inter-coupling between coils on the same side, in addition to the self-inductance of the charging pad. As a result, the system's efficiency improves while also saving an extra capacitor compared to other circuit-based decoupling methods. Additionally, a design guideline based on the sum of the coupling coefficients including cross-coupling is derived to avoid bifurcation. The phase angle of the input impedance is studied under various scenarios, demonstrating the validity of the proposed design guideline. Experimental results on a downscaled prototype show that the improved compensation method enhances efficiency by more than 2 % compared to scenarios where inter-coupling is not compensated, and verification of the proposed bifurcation mitigation guideline.