Abstract
Series-series compensated inductive power transfer (SSIPT) systems have been widely studied and characterized for constant resistance loads (CRLs) and constant voltage loads (CVLs), but much less so for constant power loads (CPLs), although CPLs have numerous applications. In this work, we address some of the fundamental knowledge gaps for SSIPT/CPL systems that we believe have not been fully explored in the literature. First, we apply Middlebrook’s stability criterion to derive a closed-form impedance-based stability condition for SSIPT/CPL systems. The derivation of the equilibrium solution is based on small-signal analysis and we show its consistency with intuitive results from perturbation-based arguments. Second, we show that the power transfer efficiency is minimum at the resonant frequency of the primary resonator. Third, the stability criterion is used to develop a straightforward approach for finding the operating frequency and input voltage that achieves near-maximum power transfer efficiency. This solution is useful as a starting point for a more meticulous parameter sweep to find the optimum input voltage and frequency values. Our analytical results are validated by performing frequency sweep measurements with two SSIPT experimental setups – one tuned to 165 kHz and the other to 6.78 MHz. We also provide an intuitive description and comparison of voltage-driven and current-driven CPLs. This topic is rarely treated in an intuitive manner and largely ignored, but we believe a solid conceptual understanding of voltage-driven and current-driven CPLs is beneficial for designers.
Highlights
I NDUCTIVE power transfer (IPT) systems have rapidly gained popularity as an efficient and practical means for wirelessly transferring power by magnetic induction over short distances
2) We show that the efficiency of a series compensated inductive power transfer (SSIPT)/constant power loads (CPLs) system is minimum at the resonant frequency of the primary resonator
In this work, we address some fundamental knowledge gaps for SSIPT/CPL systems that we believe have not been fully explored in the literature
Summary
I NDUCTIVE power transfer (IPT) systems have rapidly gained popularity as an efficient and practical means for wirelessly transferring power by magnetic induction over short distances. The power transfer efficiency η is a key figure of merit for IPT systems It is well-known that for ordinary CRLs, the efficiency η can be maximized at the resonant frequency for a tuned IPT system, provided the optimal choice of load impedance. This result is a defining feature of SSIPT/CPL systems, but it has not been explicitly stated or emphasized before in other works This result is important because it may conflict with expectations gained from the widespread use of tuned SSIPT systems with ordinary CRLs and CVLs in which the maximum possible efficiency is achieved by operating at resonance with an optimum load impedance. 3) We present a novel method for finding the optimal combination of operating frequency and input voltage to maximize the power transfer efficiency for a given set of SSIPT/CPL system parameters Our method speeds up the search by providing a simple and intuitive analytical method for finding the near-optimal combination of operating frequency and input voltage
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