Capacitive Power Transfer (CPT) technology has been proposed and investigated recently as an alternative contactless power transfer solution which has the advantages of being able to transfer power across metal barriers and having low standing power losses. Alignment between the primary and secondary plates is one of the most important factors affecting the performance of a CPT system because any misalignment may cause a significant drop in the output power. This paper analyses the effect of the coupling variation caused by misalignments of the coupling plates and suggests improvement methods for achieving better tolerance. A simple circuit model is established and the system voltage transfer function is derived to investigate the 2-D alignments. It has been found that placing the tuning inductor on the primary side of the circuit can greatly improve the misalignment tolerance between the primary and secondary plates and even increase the system output voltage. The theoretical analysis has been verified by simulation and experimental results.
This paper investigates the effect of integration of solar PV generation with wireless power transfer (WPT) on DC loads with varying PV input parameters. The power converter of the system is designed to operate at around 85 kHz, and two operating conditions of solar irradiance are considered. The first case is an ideal solar PV array with standard solar irradiance and cell temperature; and the second scenario considers the change in the irradiance for the PV array. This study is conducted based on PLECS software simulation. The results show that solar PV can be integrated as a renewable source via a WPT interface for stand-alone and grid-connected applications although the system needs to be optimised according to practical requirements.
This paper presents a second-order sliding-mode (SOSM) control approach for inductively coupled power transfer (ICPT) systems based on zero-current-switching. A second-order dc equivalent model of a series-series (SS) compensated ICPT system is established by replacing its primary side with a dc source and simplifying the rectifier on the secondary side. A SOSM controller implemented by a digital state machine is designed to regulate the output voltage of ICPT systems by controlling the switches on the primary side. Parameters of the controller are derived with a simplified dc equivalent circuit model of the ICPT system. The proposed controller achieves fast dynamic response, robustness against load disturbances and parameter uncertainties without requiring current sensing or any integral terms in the controller. As a result, the output voltage of the system can reach steady state without any overshoots in several switching actions under load disturbances or mutual inductance variations. Simulation results on a 12V/2A system verify the effeteness of the proposed approach.
ZVS (zero voltage switching) is critical for the reliable operation of normal current fed DC-AC resonant converters. In the steady state, ZVS can be achieved by many available techniques such as PLL, VCO and other integral controllers. However, during the transient process like start up, to achieve ZVS is not an easy task for these controllers and consequently switch failure may occur. Based on numerical and analytical analyses, this paper proposes a novel method using an initially forced DC current to achieve ZVS during start up. Start up conditions are discussed and complete dynamic ZVS is achieved. Considering the ramp up delay of the DC power supply, the start up can be controlled completely overshoot free at no extra cost. The validity of this method has been proven with PSpice simulations and experimental results.
An improved power flow control method for contactless moving sensor applications is proposed. The method allows the design of a system where sensors with different power ratings or a wide range of load variations can be implemented. A phase-controlled variable inductor is used to tune the resonant circuit of the power pickups of an inductively coupled power transfer (ICPT) system according to the actual power requirements of the sensors, thereby, helping to reduce the power losses without affecting the maximum power transfer capacity. Soft switching is achieved in the variable inductor control, and the effect of the equivalent tuning parameters on the power flow is analyzed theoretically. Simulation results show that a significant improvement of the existing controllers is achieved at no load or very lightly loaded conditions.
Capacitively coupled contactless power transfer (CCPT) technology has been proposed as a new contactless/wireless power transfer method recently. By employing electric field as the energy transfer medium, CCPT has advantages of being able to transfer power across metal barriers and reduced electromagnetic interference. However, there is very limited understanding and experience in the CCPT system modelling and analysis. This study models a typical CCPT system and analyses its performance under steady-state operations. An accurate non-linear circuit model is established and the stroboscopic theory is extended to determine the zero-voltage switching (ZVS)-operating frequency of the system. The tuning inductance for achieving exact ZVS operation is derived, and the effects of the coupling and load variations on the system performance are analysed. A prototype CCPT circuit is built, and practical measurements show that the steady-state time domain waveforms and efforts of coupling and load variations calculated from the theoretical model are in good agreements with experimental results. The power efficiency predicted is slightly higher than the practical results, particularly at heavy loads, because ideal power semiconductor switches and wires are used in the theoretical model.
Hybrid tuning topologies had been proposed with polarized magnetic couplers to improve the alignment tolerance of inductive power transfer (IPT) systems. However, the technologies are mainly applicable to IPT systems with directional coupling and relatively low inductance variations. This article proposes an IPT system with a dual-concentric-coil transmitting (Tx) and single-coil receiving (Rx) coupling configuration with hybrid tuning networks for improving the output voltage characteristics over a wide range of coupling and load variations. The concentric coils allow free rotation while integrated hybrid tuning networks help reduce the output voltage fluctuation under varying horizontal and spatial misalignments. A design procedure is proposed using finite-element method (FEM) and circuit simulations to select tuning parameters accounting for varying self and mutual inductances. Simulation and experimental results show that the self-inductance of the proposed coil can change by 48%, and the coupling coefficient varies between 0.43 and 0.74 under misalignments, leading to over 100% change of the unregulated output voltage if the system is series–series tuned. In contrast, a laboratory prototype of the proposed system demonstrates a stable output voltage within ±9% of fluctuation around 13.25 VDC.
Compared to traditional simultaneous wireless power and information transfer (SWPIT) technologies, communication technology utilizing the output harmonic component of an inverter as a signal carrier can achieve high-performance signal transmission without affecting power transmission. The SWPIT technology based on phase-shift modulation in inductively coupled power transfer (ICPT) system is proposed in this article. By changing the phase angle of the inverter, a trapezoidal wave current is generated on the primary coil, and a frequency selection circuit is added on the secondary side to separate the fundamental and harmonic currents. The fundamental component current is used for wireless power transfer while the harmonic current is used to transmit the signal. Firstly, the structure and working principle of SWPIT system based on phase-shift modulation in ICPT system are analyzed. Then, a system equivalent model is established and the reactive power is analyzed in depth. Next, the phase angle variation range is determined by crosstalk analysis. Finally, the correctness and effectiveness of the proposed technology are verified with an experimental platform at 50 W. The experimental results demonstrate that the power and information can be transmitted stably with output voltage fluctuation less than 3%, and the signal transmission rate up to 6 kbps.
This paper presents a three-phase contactless sliprings system based on axially moving magnetic field. The contactless slipring is a new alternative to conventional slipring systems for transferring power to and from a rotating shaft. To increase the power transfer capability of single phase pulsating field-based contactless slipring systems, this three-phase travelling field-based system is proposed for rotating applications such as wind turbine pitch control systems.Complete analytical expressions are derived for system performance analysis. A 3-D FEM (Finite Element Model) is developed, and simulation study conducted for system assessment and verification. A method of canceling the mutual inductance between the primary phases is proposed and practically verified by testing a prototype model. It has been shown that the proposed system can transfer up to 2096 Watts of power to a load at the secondary circuit with a quality factor QS of 9.8. The maximum power efficiency of the system is about 95.8% over a large air gap of 22.5 mm. A 3-D FEM thermal model is developed and simulated as a coupled analysis with the magnetic model, and it has been found that the temperature rise is only 4.5°C in an hour under maximum power transfer conditions. The FEM simulation results show that the travelling field-based system can transfer about 15.64 times more power than the counterpart pulsating field-based system at a much higher efficiency.
Capacitive Power Transfer (CPT) technology has been proposed and investigated recently as an alternative contactless power transfer method which has the advantages of being able to transfer power across metal barriers and causing low power losses in metal surrounding circumstances. However, more fundamental researches are needed to guide CPT coupling analysis and design. Based on the Duality Principle, this paper proposes a generalized coupling model to describe the electric field coupling between the primary and secondary side of CPT systems. The concept of mutual capacitance is extended in a CPT system to decouple the primary and secondary circuits. A new term capacitive coupling factor is introduced to provide a direct comparison for different coupling design. The coupling model for multiple pickups is also developed. A CPT prototype has been built and the experimental results have shown that the new model can be used to improve the circuit tuning for significant output power increase.
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