This article proposes a fast and accurate real-time estimation method for developing a dynamic battery circuit model on the primary side of a series–series (SS) compensated wireless power transfer (WPT) system. By detecting the current of the transmitter resonator only, the charging voltage, charging current, state-of-charge, the equivalent resistance of the Lithium-ion battery, and the mutual inductance in the WPT system can be accurately estimated in real time. The battery equivalent circuit can be transferred to the primary side. The constant-current and constant-voltage charging of the Li-ion battery can, therefore, be realized with primary-side control. The proposal has been successfully implemented and verified in a hardware setup with a Lithium-ion battery load. It provides a new tool to transfer the battery model to the primary side for future optimal primary-side control of SS-compensated WPT systems.

This paper presents a double-layer pulse-width pulse-frequency based optimal control (PWPFC) in achieving maximum energy efficiency tracking (MEET) and quasi-load-independent (QLI) constant current (CC) and constant voltage (CV) outputs for domino wireless power transfer (WPT) systems with full considerations of equivalent series resistances (ESRs). The proposed hierarchical control, which can be implemented using inexpensive digital controllers, is applied to the primary-side inverters based on the measured output current, output voltage, and phase angle of the receiver current via infrared (IR) communication. The upper layer (i.e., Stage-I) of the PWPFC is a reference selection algorithm to provide references of operating frequencies and duty ratios for the tracking algorithm of the lower layer (i.e., Stage-II). To ensure accurate tracking, a hill-climbing method is adopted to regulate the operating frequency of practical domino WPT systems with parasitic components and disturbance. Experimental results have verified the effectiveness of the proposed PWPFC in regulating domino WPT systems with MEET and QLI CC and CV outputs under various loads, compensation networks, and initial frequency conditions.

The coupled mode theory (CMT) and parity-time (PT) symmetry were recently used in studying wireless power transfer (WPT) systems. This paper re-examines these approaches. The limitations of CMT and PT symmetry are identified and highlighted so that WPT researchers can avoid their pitfalls. Electric circuit theory (ECT) is based on laws of physics and offers exact solutions. CMT is actually derived from ECT through two simplification stages, and it only gives approximate solutions. CMT involves assumptions that neglect high-frequency components in the WPT systems. Therefore, CMT cannot offer more information and better accuracy than ECT for WPT studies. The PT symmetry leads to the zero-phaseangle (ZPA) condition that was well known from previous WPT research based on ECT for minimizing reactive power flow and maximizing efficiency. The limitations of these two approaches are explained in detail and compared with ECT with practical examples. Both theoretical and practical results are included in the comparison. These results show that CMT and PT symmetry have shortcomings arising from their respective underlying assumptions. They do not offer new explanations and insights that ECT cannot offer. ECT is still the most appropriate analytical tool to study near-field WPT systems on the conditions that the dimensions of the circuit components are much smaller than the wavelengths of the operating frequencies.

In traditional wireless power transfer (WPT) systems, constant current (CC) and constant voltage (CV)-based battery charging control strategies are applied to DC-DC converters on the receiver sides. In this study, the receiver-side control paradigm is shifted to the transmitter side and lumped as a primary-side current and voltage control that can (i) rapidly determine the mutual inductances between the coupled coils regardless of misalignment (within tens of milliseconds), (ii) eliminate DC-DC converters on the receiver sides, (iii) implement constant frequency operations, and (iv) automatically select current or voltage control mode without battery management chips and radio frequency (RF) communication. The combination of these four features offers a simple solution to reduce the complexities and sizes of receiver circuits for next-generation wireless battery chargers (WBCs). Only additional calibration circuits with limited components are required on the load ends. Both simulation and experimental results have validated the effectiveness of the proposed primary-side control for WBCs operating in both CC and CV modes. Practical results also showcase the automatic smooth transition from the CC mode to the CV mode.

This paper presents and analyzes an AC-DC power converter structure, which is comprised of a Power Factor Correction (PFC) module and a LLC resonant DC-DC converter module. This converter only uses two switches, and requires three less diodes and one less switch compared to popular LLC resonant converter solutions. Compared to its conventional counterpart, the rectifier of interest has high energy efficiency while a smaller size, owing to the soft-switching in the LLC resonant converter. Detailed theoretical analyses are conducted in this study, followed by software simulation and hardware experimentation, which demonstrate that the single stage double-switched (DS)-LLC rectifier is able to realize unity power factor and a wide output range, indicating its effectiveness and applicability.