Study on dynamical control of bi-directional Inductive Power Transfer system

Bi-directional Inductive Power Transfer (IPT) systems allow contactless power transfer between two sides and across an air-gap, through weak magnetic coupling. These systems essentially constitute high order resonant circuit and their complexity increases with increasing number of pick-ups. A mathematical model which provides an insight into the behaviour of bi-directional IPT systems with multiple pick-ups would therefore be invaluable at design stage. This paper develops a multivariable dynamic model for bi-directional IPT system with multiple pick-ups. A 1.5 kW bi-directional IPT system with 3 pick-ups is simulated in PLECS and the results are presented with comparisons to demonstrate the validity of the proposed model. Results of the simulation indicate that the proposed model accurately predicts the behaviour of bi-directional IPT system with multiple pick-ups and can therefore be used as a valuable tool for both dynamic analysis and controller design.

Bi-directional Inductive Power Transfer (IPT) systems facilitate contactless power transfer between two sides and across an air-gap, through weak magnetic coupling. These systems constitute a 6th order resonant circuit and, as such, are difficult to design and control. A mathematical model which provides an insight into the behaviour of bi-directional IPT systems would therefore be invaluable at design stage. This paper presents a dynamic model through which the behaviour of bi-directional IPT systems can be accurately predicted. A 1.5 kW bi-directional IPT system is simulated in PLECS, and results are presented with comparisons to demonstrate the validity of the dynamic model. Results indicate that the proposed model accurately predicts the dynamics of the bi-directional IPT system and can therefore be used as a valuable tool for both transient analysis and controller design.

Bi-directional inductive power transfer (BD-IPT) systems are suitable for applications such as wireless integration of Electric Vehicle (EV) with the utility grid. This paper presents a comprehensive study of the most widely used BD-IPT systems in EV applications - a series tuned inductor-capacitor (LC) type BD-IPT system. The system parameters used in the paper have been set according to SAE J2954 guidelines for wireless electrical vehicle charging. Mathematical and simulation models of the system have been developed to investigate the behavior and sensitivity of the system to variations in circuit parameters. The validity of the mathematical models is verified and the efficiency of each system is investigated using simulated results based on a 3.7 kW simulated systems. Both frequency and relative phase modulation between converters are being considered for performance optimization of the systems. Nearly a 4% improvement in efficiency can be observed with these optimum modulations values.

Although the demand for high-power inductive power transfer (IPT) systems is on the rise, implementation of such IPT systems using low-cost semiconductor devices has been a challenge. This study presents a new IPT topology that facilitates easy integration of multiple IPT modules, which are made of low cost and freely available semiconductor components, to cater for high-power applications. An intermediate circuit, comprising an inductor-capacitor-inductor resonant network, serves as a contactless interface through which the modules of primary and secondary (pick-up) systems can be either series or parallel integrated. Inductor coils of the intermediate circuit and both primary and pick-up systems are magnetically coupled to allow for contactless power transfer. The proposed topology is parallel compensated to minimise its var requirement, and both the direction and amount of power flow are controlled by phase and/or magnitude modulation of voltages generated by primary and pick-up side converters. Theoretical analysis, together with simulations and experimental evidence of integrating four prototype bi-directional IPT systems to cater for 1.8 kW demand, is presented to show that the proposed new IPT topology is suitable for high-power applications, and flexible for both bi-directional and uni-directional contactless power transfer.

Mobility, continuity and safety are crucial in charging and discharging system of electric vehicles (EV) in smart grid applications. Bidirectional inductive wireless power transfer (BIWPT) system is ideal choice for these services. With accurate and efficient system models in hand, the circuit designers can predict and optimize the system performance. In this paper, an accurate, intuitive, and comprehensive steady-state theoretical model is proposed and implemented in MatLab environment. This model is generalized and can be used for any magnetic design of BIWPT system with the same compensation topology. The model is able to predict the system currents, voltages, power, power factor and equivalent impedance. The proposed model is used to evaluate two different designs for LCL compensation topology based on impedance frequency response analysis. Also, general considerations for the filters design parameters are stated and verified in this paper. A Simulink MatLab model for 1 kW BIWPT system is built to verify the proposed theoretical analysis.

This letter proposes a novel primary-side parameter estimation method for bidirectional inductive power transfer (BD-IPT) systems. This method can estimate mutual inductance at startup and monitor secondary-side phasor information continuously during operation. The proposed method can be used to simplify existing optimal control methods in BD-IPT systems by providing necessary feedback information without a wireless communication link. Besides, it helps to implement new control methods to further improve system performance. A current decoupling concept is utilized to estimate both the mutual inductance and secondary phasor information. A circuit model based on the superposition principle is presented to describe the current decoupling concept. The validity and accuracy of the proposed estimation method are demonstrated using the measured results of a 1-kW prototype BD-IPT system.

Matrix converter (MC) based grid connected bi-directional inductive power transfer (BD-IPT) systems are preferable for numerous applications such as electric vehicle (EV) charging and vehicle-to-grid (V2G) systems due to their single-stage grid integration as opposed to two-stage grid integration of conventional BD-IPT systems. However MC based BD-IPT systems essentially produce harmonics which can have adverse effects on power quality of the utility grid. This paper presents a new control technique, through which the grid side harmonic distortion of MC based BD-IPT systems can be improved. A theoretical analysis is presented with simulations to show that the proposed approach is viable, and results suggest that the presented technique improves the power quality of the system significantly by minimizing the grid side harmonic distortion.

Depletion of fossil fuels and growing concerns about climate change have resulted in an increasing trend towards the use of sustainable technologies such as electric vehicles (EVs). As a result, effective means of charging EVs and managing EVs has become one of the most researched topics in the past few years. Among the many solutions proposed, inductive power transfer (IPT) systems, especially bi-directional IPT systems, are gaining popularity as an effective method to wirelessly interface EVs with the utility grid for charging as well as dynamic demand management. To enable wide spread use of bi-directional IPT technology for interfacing EVs with the gird essentially requires low cost and efficient magnetic couplers. As such, this paper investigates three new low cost magnetic designs, as alternatives to commonly used circular couplers. The proposed designs along with a standard circular coupler with similar ratings are modeled and simulated on JMAG studio to compare the performance. Based on the simulation data and experimental results gathered from a prototype implementation, the most effective design that yields a good coupling for the lowest cost has been identified as a possible solution for magnetic couplers used in bi-directional IPT systems.

An inductive power transfer (IPT) system usually consists of four parts: an AC-DC power factor correction (PFC) converter, a high frequency DC-AC inverter, a compensation network comprising a loosely coupled transformer (LCT) and the resonant capacitors, and a rectification output circuit. Due to the relative large air gap, the magnetic coupling coefficient of the IPT system is poor, different from the closely-coupled IPT systems. As a result, the efficiency of the IPT system is always a main concern for different applications. To ensure high power transfer efficiency, these IPT systems should have high tolerance for different gap variation and horizontal misalignment conditions. In this paper, some design considerations to reduce gap and misalignment effects for the IPT system is proposed. By using finite element analysis (FEA) simulation method, the performance of different transmitter and receiver coil dimensions are compared. In order to validate the performance of the proposed design considerations, a hardware prototype is built and the corresponding experiments are carried out. The experimental results shows that the LCT prototype could maintain coupling coefficient between 0.237∼0.212 within 40 mm horizontal misalignment.

In recent years, a number of bidirectional inductive power transfer systems (BD-IPT) suitable for wireless grid integration of electric vehicles have been developed. These developments have been fueled by the enhanced efficiency and spatial tolerance offered by BD-IPT systems. A typical BD-IPT system utilizes two synchronized full-bridge converters operating at fixed duty cycles to drive the primary and secondary magnetic couplers. However, in order to cater for a wide range of loading conditions, additional circuitry is employed at the expense of cost and power density. As an alternative solution, this paper proposes a novel power converter, named a boost active bridge (BAB), to replace the full-bridge converters. The BAB topology caters to a wide range of loading conditions without the need for any extra switching devices. A comprehensive mathematical model that predicts steady-state currents, voltages, and power transfer is presented to highlight the operating principles of the BAB technology. Experimental results obtained from a 3.5-kW prototype show a nearly constant efficiency under all loading conditions, validating the viability of the proposed BAB topology.

For bidirectional inductive wireless power transfer systems, zero voltage switching (ZVS) of switching devices and system efficiency are always the keys to research. In this paper, the efficiency of the bidirectional dual-LCC compensation topology is firstly modelled, and the optimal bilateral modulation strategy is quantitatively derived. Then, a half-bridge modulation method under light load conditions is proposed. Compared with the full-bridge modulation strategy, the operating efficiency of the system is further improved. Finally, a 3.3 kW two-way wireless power transfer system simulation model is built in MATLAB. Compared with the full-bridge triple-phase-shift modulation strategy, it is proved that the half-bridge modulation scheme proposed in this paper has higher energy transfer efficiency under light load conditions.

In this article, two power factor corrector (PFC) control strategies for a bidirectional inductive power transfer (IPT) system are proposed. These control strategies are presented for a novel power circuit without input and output interfaces for a wireless electric vehicle battery charger application. This compact topology comprises: unfolding rectifier, primary resonant bridge, and secondary-side active rectification. Two PFC controls are described in detail: a primary-side PFC control, performed in the primary resonant bridge; and a secondary-side PFC control, implemented in the secondary-side active rectification stage. Both strategies are based on a duty-cycle control operating close to the resonance frequency, integrating different functionalities, i.e., PFC, current shaping (CS), and power control on a single control strategy. We analyze each control strategy, evaluating them for different operating points of the charging process. The performance of the wireless charger applying both control strategies is evaluated in terms of power losses, power factor, harmonic distortion, and bifurcation. Additionally, the theoretical results are validated using a GaN-based experimental prototype. The presented analysis and experimental results clearly identify the advantages and limitations of each control strategy leaving no doubt about their usefulness for the future IPT systems.

Conventional time-domain model of bidirectional inductive power transfer (BIPT) systems highly rely on specific compensation network and lacks universality. To address this issue, we propose a universal time-domain model for voltage-fed BIPT systems. The proposed state-space model applies to all compensation networks and resonant parameters, The input of the state space consists of the output voltage of the H-bridge. While the voltage combinations of the H-bridge are adaptive to different phase shift conditions. Based on the circuit analysis and by solving the state equations, analytical expressions for the state variables can be obtained. The time-domain analytical model is piecewise and accurately predicts the coil currents and capacitor voltages under all fundamental modulation schemes and compensation topologies. The simulation and experimental results of different compensation topologies and modulation strategies are presented, verifying the effectiveness of the proposed model. Compared with commercial software, the computation burden is obviously alleviated. The simulation is accelerated by 64 times than Simulink and 10 times than Psim.

This article studies magnetic forces between transmitter (Tx) and receiver (Rx) coils in an inductive power transfer (IPT) system aiming to use those forces to align the coils and, consequently, improve power transfer. Due to its popularity, the analysis is conducted on a series–series compensated IPT system with planar spiral coils. The proposed method utilizes the bifurcation operation mode of the system and unloaded resonating receiver to maximize attractive force between magnetic couplers. Three-dimensional finite-element method simulations indicate that high-power IPT systems can develop enough attractive force to align coils even under nominal current. Regardless of the coil shape, e.g., spiral or Double-D (DD), the attractive forces tend to align the coils. Hence, a smart charging station can be devised based on self-aligning capability. Furthermore, this article proposes a mechanical structure to facilitate the attractive lateral force for the alignment of high power applications, i.e., wireless fast-charging stations. The forces are analyzed, modeled, and simulated for a 100-kW IPT system with an operating frequency of 20 kHz, while the self-aligning capability is experimentally verified on a downscale 11-kW prototype.

Demand for supplying contactless or wireless power for various applications, ranging from low-power biomedical implants to high-power battery charging systems, is on the rise. Inductive power transfer (IPT) is a well recognized technique through which power can be transferred from one system to another with no physical contacts. This paper presents a novel bidirectional IPT system, which is particularly suitable for applications such as plug-in electric vehicles (EVs) and vehicle-to-grid (V2G) systems, where two-way power transfer is advantageous. The proposed IPT system facilitates simultaneous and controlled charging or discharging of multiple EVs through loose magnetic coupling and without any physical connections. A mathematical model is presented to show that both the amount and direction of power flow between EVs or multiple systems can be controlled through either phase or/and magnitude modulation of voltages generated by converters of each system. The validity of the concept is verified by theoretical analysis, simulations, and experimental results of a 1.5-kW prototype bidirectional IPT system with a 4-cm air gap. Results indicate that the proposed system is an ideal power interface for efficient and contactless integration of multiple hybrid or EVs into typical power networks.