It is more convenient and safer to employ inductive power transfer (IPT) systems to charge the battery pack of electric bicycles (EBs) than conventional plug-in systems. An IPT charging method suitable for charging massive EBs is proposed to achieve constant current (CC) and constant voltage (CV) output without feedback control strategies or communication link between transmitter side and receiver side. Two ac switches (ACSs) and an auxiliary capacitor utilized at receiver side are employed to be operated once to change the charging modes from CC mode to CV mode. The characteristics of the load-independent current output in the CC mode and load-independent voltage output in the CV mode are achieved by properly selecting the passive parameters of inductances and capacitors, so that no sophisticated control strategies are required to regulate the output as per the charging profile. The feasibility of proposed method has been verified with an experimental prototype in form of efficiency, stability of output current and voltage in CC/CV mode. The simple and economical approach is suitable for the massive EBs charging system with only one inverter, especially in China.

Inductive Power Transfer for Massive Electric Bicycles Charging Based on Hybrid Topology Switching With a Single Inverter

The technique of wireless power transfer (WPT) via magnetic coupling resonance provides a way to transfer power wirelessly to cardiac pacemakers from external source. For wireless charging system to be used in clinical environment, this paper gives priority consideration to three technical difficulties, i.e., implantation, efficiency, and safety. The LCC-C compensation topology for pacemaker wireless charger is presented, where only one secondary side resonance capacitor needs to be implanted, and resonance compensation parameters are derived. The compensation network can make the WPT system operate at stable resonance and high efficiency. The prototype of the wireless charging system for implantable cardiac pacemaker is developed, where a thin flexible receiving unit was designed to effectively shield eddy currents in the pacemaker shell. The experiments of wireless charging through pork tissues reveal that 3.072-W power can be received from a 3.919-W power source at 300 kHz, reaching a rather high WPT efficiency of 78.4%, such that the charging is fast, i.e., the 1050 mA·h, 4.2-V Li-ion battery voltage increases from 3.98 (80% residual capacity) to 4.2 V within only 27 min, and only 3.3 °C maximum temperature rise of the pork is in safe limits. The feasibility and safety of the charging system were further evaluated by simulations of specific absorption rate and temperature rise in human tissues and electromagnetic fields in the pacemaker case.

An LCC-C Compensated Wireless Charging System for Implantable Cardiac Pacemakers: Theory, Experiment, and Safety Evaluation

Maximum energy efficiency in wireless power transfer (WPT) systems can be achieved through the use of magnetic resonance technique at a certain load resistance value However, practical load resistance is not constant Previously, a switched mode dc–dc converter was used in the receiver circuit to emulate an equivalent load resistance for maximum energy efficiency In this paper, a new approach based on the On–Off Keying is proposed to achieve the high energy efficiency operation over a wide range of load power without using an impedance-matching dc–dc power converter This simple and effective method has reduced average switching frequency and switching losses It can be applied to any series-series resonant WPT system designed to operate at a constant output voltage Practical measurements have confirmed the validity of the proposal

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Maximum Energy Efficiency Operation of Series-Series Resonant Wireless Power Transfer Systems Using On-Off Keying Modulation

Inductive power transfer (IPT) for battery charging applications has significant advantages over the traditional plug-in system. Since misalignment between the primary and secondary windings is inevitable, it is of significance to improve the misalignment tolerance of IPT systems with constant-current (CC) and constant-voltage (CV) outputs for battery charging. In this paper, the load-independent output characteristic of the hybrid topology and the function switching between CC and CV of the reconfigurable topology are analyzed. Besides, a hybrid and reconfigurable IPT system with 3-D misalignment tolerance for CC and CV outputs is proposed, simplifying or even canceling control schemes. Moreover, a novel parametric design method is given for the IPT system, which can suppress the fluctuation of the output voltage/current within a certain range of misalignment. In order to validate the performance of the proposed topology, a 1-kW prototype is built, and the corresponding experiments are carried out. In the CC/CV mode, the system can operate with the longitudinal misalignment to 50% when the load varies from 36 to 480 Ω, and the fluctuation of the output current/voltage is within 5%. Similarly, the misalignment in Y - and Z -axis is 12.5% and 33.3%, respectively.

Hybrid and Reconfigurable IPT Systems With High-Misalignment Tolerance for Constant-Current and Constant-Voltage Battery Charging

Wireless power transfer (WPT) has attracted a large amount of attention owing to its inherent advantages such as convenience, safety, low maintenance, being weather proof, etc. A parameter tuning method is crucial for a WPT system due to its function of reducing reactive power and improving system efficiency. Three deficiencies of the conventional double-sided inductor–capacitor–inductor (DS- LCL ) compensated system, i.e., low design freedom, weak high-order harmonic suppression capability, and discontinuous input current of a full-wave diode rectifier (FDR), are first analyzed by means of theoretical derivation, numerical calculation, and Pspice simulation. In order to overcome these disadvantages, a novel parameter tuning method is proposed. The characteristic of constant current output of the proposed DS- LCL system is analyzed, followed by a detailed derivation about secondary compensation inductance. Theoretical analysis indicates that the proposed system has four attractive characteristics: higher design freedom, reduced coil current, enhanced high-order harmonic suppression capability, and continuous input current of the FDR. The overall efficiencies of two comparative WPT prototypes, tuned by conventional and proposed methods, are 87.3% and 90.2%, respectively. Experimental results show great coincidence with theoretical analysis, demonstrating the superiority of the newly proposed parameter tuning method.

A Novel Parameter Tuning Method for a Double-Sided LCL Compensated WPT System With Better Comprehensive Performance

Compensation is crucial for improving performance of inductive-power-transfer (IPT) converters. With proper compensation at some specific frequencies, an IPT converter can achieve load-independent constant output voltage or current, near zero reactive power, and soft switching of power switches simultaneously, resulting in simplified control circuitry, reduced component ratings, and improved power conversion efficiency. However, constant output voltage or current depends significantly on parameters of the transformer, which is often space constrained, making the converter design hard to optimize. To free the design from the constraints imposed by the transformer parameters, this paper proposes a family of higher order compensation circuits for IPT converters that achieves any desired constant-voltage or constant-current (CC) output with near zero reactive power and soft switching. Detailed derivation of the compensation method is given for the desired transfer function not constrained by transformer parameters. Prototypes of CC IPT configurations based on a single transformer are constructed to verify the analysis with three different output specifications.

Higher Order Compensation for Inductive-Power-Transfer Converters With Constant-Voltage or Constant-Current Output Combating Transformer Parameter Constraints

The magnetic coupled wireless power transfer driver based on adjustable gain constant-current compensation network

The control design of inductive power transfer (IPT) converters can be greatly simplified by exploring the property of load-independent output. However, IPT converters can easily enter a discontinuous current mode (DCM) operation due to the non-linearity of the output diode rectification circuit at some loading conditions. The switching between operations of continuous current mode (CCM) and DCM within a switching cycle is highly non-linear, making the converter behaviour difficult to predict and analyse. The well-known first harmonic approximation (FHA) analysis method and the load-independent output property are no longer applicable when the converter enters DCM operation. This paper presents a simple and yet effective harmonic analysis method to reveal the main reason for the converter to enter DCM operation. Subsequently, the load boundary between CCM and DCM operations is derived in detail as a design criterion. A solution by increasing the input impedances at some higher order harmonic frequencies is also suggested to extend the load range against DCM operation. Finally, IPT prototypes using two higher order compensation circuits, having load-independent voltage output and capacitor filter, are demonstrated to verify the theoretical analysis.

https://ietresearch.onlinelibrary.wiley.com/doi/epdf/10.1049/iet-pel.2018.6275

Design for continuous-current-mode operation of inductive-power-transfer converters with load-independent output

The invention relates to a method for determining the constant voltage compensation network topology of a wireless power transmission system. According to the compensation network, the output voltage of the wireless power transmission system is not affected by load, and not limited by a non-contact transformer parameter, and thereby the design of the non-contact transformer can be simplified. According to the method, the compensation circuit parameter is determined with the aim that the voltage gain of the system is not affected by the system, the input impedance of the system is pure resistive, and the system efficiency is maximal, then the constant voltage compensation network topology is determined, and the constant voltage compensation network topology of which four groups of primary and secondary resonant networks can all be equivalent to T-type or n-type networks. The output voltage of the IPT system is not limited by the parameter of the non-contact transformer, and the design of the non-contact transformer is simplified; and the constant voltage output and unit power factor which are not affected by the load can be achieved at the same time, the reactive power is reduced, the requirement on device stress is lowered, and the transmission efficiency is improved.

Method for determining constant voltage compensation network topology of wireless power transmission system

The invention discloses a method for determining the constant current compensation network topologies of a wireless power transfer system and belongs to the technical field of wireless power transfer. The method comprises the step of determining the network parameters of the system on the premise that the current gain of the system is irrelevant to load, the input impedance of the system is purely resistive, and the efficiency of the system is maximized, so that the four sets of constant current compensation network topologies are determined, wherein primary-side and secondary-side resonance networks are both equivalent to the T-type or pi-type network. The output current of the IPT system is not limited by the parameters of a non-contact transformer, and the design of the non-contact transformer is simplified; load-independent constant-current output and unity power factors can be realized at the same time, reactive power is reduced, the requirement for device stress is reduced, and transfer efficiency is improved.

Yanyan Jing

Papers

Higher Order Compensation for Inductive-Power-Transfer Converters With Constant-Voltage or Constant-Current Output Combating Transformer Parameter Constraints

The magnetic coupled wireless power transfer driver based on adjustable gain constant-current compensation network

Design for continuous-current-mode operation of inductive-power-transfer converters with load-independent output

Method for determining constant voltage compensation network topology of wireless power transmission system

Method for determining constant current compensation network topologies of wireless power transfer system