A Multicycle Q-Modulation for Dynamic Optimization of Inductive Links

Abstract

This paper presents a new method, called multi-cycle Q-modulation, which can be used in wireless power transmission (WPT) to modulate the quality factor (Q) of the receiver (Rx) coil and dynamically optimize the load impedance to maximize the power transfer efficiency (PTE) in two-coil links. A key advantage of the proposed method is that it can be easily implemented using off-the-shelf components without requiring fast switching at or above the carrier frequency, which is more suitable for integrated circuit design. Moreover, the proposed technique does not need any sophisticated synchronization between the power carrier and Q-modulation switching pulses. The multi-cycle Q-modulation is analyzed theoretically by a lumped circuit model, and verified in simulation and measurement using an off-the-shelf prototype. Automatic resonance tuning (ART) in the Rx, combined with multi-cycle Q-modulation helped maximizing PTE of the inductive link dynamically in the presence of environmental and loading variations, which can otherwise significantly degrade the PTE in multi-coil settings. In the prototype conventional 2-coil link, the proposed method increased the power amplifier (PA) plus inductive link efficiency from 4.8% to 16.5% at (RL = 1 kΩ, d23 = 3 cm), and from 23% to 28.2% at (RL = 100 Ω, d23 = 3 cm) after 11% change in the resonance capacitance, while delivering 168.1 mW to the load (PDL).

An Overview of Regulation Topologies in Resonant Wireless Power Transfer Systems for Consumer Electronics or Bio-Implants

“…To achieve a high VCE, a switching-based current-mode (SCM) regulating technique was proposed in [28][29][30][31]. This technique differs from voltage-mode ones by firstly storing the received energy in the RX LC resonant tank (as the resonant phase) and then delivering it to the load (charging phase).…”

“…The measured results showed that the V R can be boosted to 5.5 V. Figure 16. The switching waveforms of (a) Q-modulation [28] and (b) multi-cycle Q-modulation (MCQ) [30]. Ctrl is on-off control signal of the switch S 1 .…”

“…To allow for a higher resonant frequency, a multi-cycle Q-modulation (MCQ) technique was introduced in [30] that works at a 13.56 MHz resonant frequency. The principle of MCQ is similar to that of [28], but both the resonant and charging phase are extended to multiple carrier cycles as in Figure 16b.…”

“…MCQ can work without synchronizing the SW turn-on instant to the I RX zero-crossing points, which reduces the design difficulty. To overcome resonant frequency shifting due to the parasitic capacitance in the wireless link, an automatic resonance tuning scheme is also introduced in [30]. The measured result showed a 28.02% PTE at R L = 100 Ω.…”

“…Therefore, the regulation schemes investigated in the previous works can also be categorized into two types: RX and TX regulation. As illustrated in Figure 3, RX regulation includes post-stage regulation (achieved by a cascading low dropout regulator (LDO [12][13][14][15] or a DC-DC converter [16][17][18][19][20]) and one-stage regulation, including active diode conduction time control [21][22][23], reconfigurable regulating rectification [24][25][26][27], and switching-based current-mode regulation [28][29][30][31]. On the other hand, TX regulation can be achieved by PA supply voltage control [32,33], resonant frequency control [34], PA power switch duty cycle control [35][36][37][38][39][40], and vector power summing control [41,42].…”