Search

This paper presents a novel compensation parameter design methodology and maximum efficiency tracking (MET) control strategy for inductive power transfer (IPT) system with an inductance and double capacitance-series (LCC-S) compensation topology. The compensation parameters of a conventional IPT converter are designed for the required output voltage by considering the fluctuation ranges of the battery voltage and coupling coefficient, but without considering the efficiency characteristics of the IPT converter. Additionally, the IPT system efficiency fluctuates with the load, because the battery equivalent resistance continuously changes according to the state-of-charge. To address these problems, this paper presents a compensation parameter design methodology based on a loss analysis of the IPT converter. The losses of the transmitter and receiver in the IPT converter with the optimal compensation parameters are compared and analyzed according to the load. Based on these analyses, a control strategy is proposed for tracking the maximum efficiency according to the load without real-time communication. To validate the proposed compensation parameter design methodology and maximum-efficiency tracking control strategy, a 1.85 kW experimental prototype is configured.

This paper proposes a discontinuous charging technique for switched-capacitor converters that improves the power conversion efficiency (PCE) at low power levels and extends the input power harvesting range at which high PCE is achievable. Discontinuous charging delivers current to energy storage only during clock non-overlap time. This enables tuning of the output current to minimize converter losses based on the available input power. Based on this fundamental result, an input power-aware, two-dimensional efficiency tracking technique for Wireless Sensor Network (WSN) nodes is presented. In addition to conventional switching frequency control, clock non-overlap time control is introduced to adaptively optimize PCE according to the sensed ambient power levels. The proposed technique is designed and simulated in 90nm CMOS with post-layout extraction. Under the same input and output conditions, the proposed system maintains at least 45% PCE at 4μW input power, as opposed to a conventional continuous system which requires at least 18.7μW to maintain the same PCE. Therefore, the input power harvesting range is extended by 1.5x. The technique is applied to a wearable WSN implementation utilizing the IEEE 802.15.4-compatible GreenNet communications protocol. This allows the node to meet specifications and achieve energy autonomy when deployed in environments where the input power is 49% lower than what is required for conventional operation.

Wireless power transfer (WPT) technology has drawn much attention due to its advantages such as safety, convenience, and non-contact. For some movable devices such as intelligent inspection robot, the constant output voltage is very important to ensure its normal operation. In order to improve the system efficiency and steadiness of output voltage, a maximum efficiency tracking and constant voltage charging method is proposed for the dynamic WPT system. In this method, the mutual inductance and optimal input voltage can be estimated accurately no matter the coupling coefficient and equivalent load change or not. The simulation and experimental results have shown that the WPT system realize maximum efficiency tracking and constant voltage charging when the resistance is changed from 10Ω to 5Ω, and the same result was achieved when the mutual inductance is altered from 20μH to 10μH.

This article presents a closed-loop transmitter for wireless power transfer with automatic resonance frequency tracking to maintain high power transfer efficiency in the over-coupled region. The transmitter consists of a source oscillator, power amplifier (PA), PA driver, matching network, and feedback circuitry. By injecting the resonant output of coupled antenna coils into a source oscillator to form a positive feedback loop, the source oscillator is injection-locked and the closed-loop transmitter functions as a power oscillator with the oscillation frequency determined by the resonance of the coupled coils. The proposed resonant frequency tracking minimizes the change in the input impedance presented to the PA, and hence mitigates mismatch that causes a sharp drop in the PA efficiency of conventional transmitters. Implemented in 0.13 μm Bipolar–CMOS–DMOS (BCD) technology, the prototype maintains PA efficiency above 60% even at highly over-coupled spacings (10 mm), which is significantly below the critical coupling spacing (40 mm). Compared to a transmitter without feedback (i.e., running in open loop), the transfer efficiency at a coupling distance of 10 mm is improved by 6.6 times and the charging range with power transfer efficiency over 50% is also doubled. [ABSTRACT FROM AUTHOR]

We propose a maximum efficiency tracking for a multiple-transmitter system that optimizes both the current ratios of transmitter (Tx) coils and the effective Rx load. It is found that unlike the single-Tx case, the optimal load impedance of multiple-Tx system depends on the current ratios among Tx coils. Meanwhile, the Tx current ratios should be controlled to be the same with magnetic coupling ratios between each Tx and Rx. Hence, we propose a two-step tracking method that first optimizes the Tx current ratios and then optimizes the Rx load impedance. To match the Tx current ratio with the magnetic coupling ratio, it is analyzed that the reflected resistances at every Tx become identical to each other when the Tx coil current ratios are equal to the magnetic coupling ratios. It is also revealed that the reflected resistance at specific Tx is reduced (increased) when its Tx current is increased (reduced) relative to other Tx currents. The proposed feedback equalizes all reflected resistances based on this property. The second step of the proposed tracking is to optimize the Rx load while fixing the Tx current ratios by globally scaling up or down the strengths of whole Tx currents. Maximum of 478 W is delivered at 79% efficiency. The algorithm does not have a limit on the number of Txs except the small standby power consumption. The proposed theoretic analysis and control method enable the first-ever maximum efficiency tracking for multiple-Tx system, where the first step optimizes the relative Tx current ratios and the second step optimizes the load impedance. [ABSTRACT FROM AUTHOR]

Charging current and efficiency of a wireless power transfer system depend on the equivalent load resistance of supercapacitor load, which varies during charging. To achieve constant current (CC) charging and maximized efficiency under variable loads, control method that employs primary-side phase shift H-bridge inverter and secondary-side semiactive rectifier are proposed. The proposed secondary-side control method not only achieves CC charging, but also ensures no reactive impedance seen into the semiactive rectifier. Furthermore, the maximum efficiency tracking is based on searching the minimum system dc input current for any given output power. It is realized by phase shift H-bridge inverter that is controlled by the perturbation and observation algorithm. Simulation and experimental results validate the feasibility of the proposed control method. During CC charging of 3 A, the maximum efficiency is 81% and largest efficiency improvement is 15.2% at light load. The proposed control method improves the system performance and is suitable for the applications that require compact receiver and no wireless communication link between the transmitter and the receiver. [ABSTRACT FROM AUTHOR]

Maximum efficiency tracking is an important issue for wireless power transfer (WPT) system. Traditional maximum efficiency tracking method normally focuses on load impedance matching with fixed coupling condition. However, WPT system is a loosely coupling system, the coupling coefficient varies due to relative movement between the primary and secondary sides. Unknown to this variation may result in failure of the tracking. In this paper, a novel maximum efficiency tracking method is proposed with integrated dynamic coupling coefficient estimation. This method can take almost all requirements for maximum efficiency tracking into account including adaption for coupling coefficient and load variation, and output controllability. The tracking method is easy to implement because no additional circuitry or measurement is required. Experimental results have verified the correctness of the proposed coupling coefficient estimation method. And the maximum efficiency tracking results show the system can achieve a good performance against coupling coefficient and load variation with the proposed tracking method. [ABSTRACT FROM AUTHOR]

In this paper, the loading effect of a Class E power amplifier (PA) driven 6.78 megahertz (MHz) wireless power transfer (WPT) system is analyzed at both circuit and system levels. A buck converter is introduced and controlled to track an optimal equivalent load that maximizes the system efficiency under uncertainties in the relative position of coils and the final load. For power control, an additional degree of freedom is provided by adding an ultracapacitor bank. A control strategy is proposed to track the maximum efficiency and charge/discharge the ultracapacitor bank through the on/off control of the Class E PA. Thus, high system efficiency can be maintained under various uncertainties and load power demands. Finally, the theoretical analysis and the control scheme are validated in experiments. The results show that the proposed Class E PA-driven MHz WPT system can stably achieve a high efficiency under different coil distances and various constant/pulsed power profiles. The measured highest system efficiency can reach 72.1% at a load power level of 10 W. [ABSTRACT FROM AUTHOR]

Switch conductance modulation techniques are demonstrated in a fully integrated multi-ratio switched-capacitor voltage regulator with hysteretic control, in 22 nm tri-gate CMOS with high-density MIM capacitor. We present (i) an adaptive switch-size scaling scheme for maximum efficiency tracking across a wide range of voltages and currents, governed by a frequency-based control law that is experimentally validated across multiple dies and temperatures and, (ii) a simple active ripple mitigation technique that modulates the gate drive of select MOSFET switches effectively in all conversion modes. Efficiency improvements up to 15% are measured under low output voltage and load conditions. Load-independent output ripple of < 50 mV is achieved, enabling reduced interleaving. Test chip implementations and measurements demonstrate ease of integration in SoC designs, power efficiency benefits and EMI/RFI improvements. [ABSTRACT FROM PUBLISHER]