Pulse Density Modulated ZVS Full-Bridge Converters for Wireless Power Transfer Systems

Abstract

Pulse density modulation (PDM) is an advanced technique for maximum efficiency point tracking (MEPT) of wireless power transfer (WPT) systems. By using PDM, both voltage regulation and efficiency maximization can be achieved without dc/dc converters. PDM is also compatible with the dualside soft switching technique that utilizes resonant tanks and synchronous rectification. However, this soft switching technique depends on coupling and load conditions. Hard switching may occur when the coupling of coils gets stronger or the equivalent load is not properly controlled. To eliminate the dependence and ensure the soft switching under various operating conditions, this paper proposes a PDM zero-voltage-switching (ZVS) full-bridge converter for WPT systems. The converter employs a ZVS branch between switching nodes to provide a ZVS current, and uses a specially designed modulator to obtain the valid ZVS current waveforms. Experimental results verified the proposed operating principles and showed that the additional power loss caused by the ZVS current is insignificant. The overall efficiency of the WPT prototype was 93 ~ 73 % when the power transfer distance was 0.1 ~ 0.4 m, among which up to 85% efficiency was observed when the distance equaled the coil diameter. Index Terms-Maximum efficiency point tracking (MEPT), pulse density modulation (PDM), wireless power transfer (WPT), zero voltage switching (ZVS).

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

“…This scheme is defined as TX regulation, which can be achieved by controlling the PA supply voltage [24,32,33], the resonant frequency [34], or the power switch duty cycle [36][37][38][39][40]. The necessity for TX regulation and its implementations are discussed in the following sections.…”

“…TX regulation can also be implemented by a PA power switch duty-cycle control technique based on switching frequency modulation [35,36], pulse density modulation [37,38], and phase shifted modulation [39,40]. These schemes advance the resonant frequency control scheme by keeping a constant f res .…”

“…The aforementioned forms of TX regulation [32][33][34][35][36][37][38][39][40] are achieved only with a single TX, while it can also be implemented by summing the power from multiple TXs. The authors in [41,42] presented a vector power summing control technique to regulate the received power P total as demonstrated in Figure 27.…”

“…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]. Additionally, switching frequency modulation [35,36], pulse density modulation [37,38], and phase-shifted modulation [39,40] can be classified as power switch duty cycle control.…”

“…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]. Additionally, switching frequency modulation [35,36], pulse density modulation [37,38], and phase-shifted modulation [39,40] can be classified as power switch duty cycle control. This paper is organized as follows: Section 2 reviews the operation principles of the previous RX regulation topologies.…”