Duleepa J. Thrimawithana

A Bidirectional Inductive Power Interface for Electric Vehicles in V2G Systems

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.

A Power–Frequency Controller for Bidirectional Inductive Power Transfer Systems

Inductive power transfer (IPT) technology is a well-recognized technique for supplying power to a wide range of applications with no physical contacts. With the emergence of applications such as electric vehicles and vehicle-to-grid systems, IPT systems with bidirectional power flow have become a recent focus. In contrast to simple unidirectional IPT systems, bidirectional systems are complex in nature and essentially require more sophisticated and robust control strategies. This paper proposes a new controller, which is based on power-frequency droop characteristics of IPT systems, to regulate its power flow in both directions without a dedicated communication link. The proposed controller is applicable to unidirectional as well as bidirectional IPT systems with either single or multiple loads and ensures that power intake by the load side is always kept within the capability of the supply side. Analysis, together with both experimental and simulated results, of a 1-kW single-load bidirectional IPT system is presented with discussions to show that the proposed droop controller can successfully be used to regulate the two-way power flow.

An Optimal PID Controller for a Bidirectional Inductive Power Transfer System Using Multiobjective Genetic Algorithm

Bidirectional inductive power transfer (IPT) systems are suitable for applications that require wireless and two-way power transfer. However, these systems are high-order resonant networks in nature and, hence, design and implementation of an optimum proportional-integral-derivative (PID) controller using various conventional methods is an onerous exercise. Further, the design of a PID controller, meeting various and demanding specifications, is a multiobjective problem and direct optimization of the PID gains often lead to a nonconvex problem. To overcome the difficulties associated with the traditional PID tuning methods, this paper, therefore, proposes a derivative-free optimization technique, based on genetic algorithm (GA), to determine the optimal parameters of PID controllers used in bidirectional IPT systems. The GA determines the optimal gains at a reasonable computational cost and often does not get trapped in a local optimum. The performance of the GA-tuned controller is investigated using several objective functions and under various operating conditions in comparison to other traditional tuning methods. It was observed that the performance of the GA-based PID controller is dependent on the nature of the objective function and therefore an objective function, which is a weighted combination of rise time, settling time, and peak overshoot, is used in determining the parameters of the PID controller using multiobjective GA. Simulated and experimental results of a 1-kW prototype bidirectional IPT system are presented to demonstrate the effectiveness of the GA-tuned controller as well as to show that gain selection through multiobjective GA using the weighted objective function yields the best performance of the PID controller.

A Dynamic Multivariable State-Space Model for Bidirectional Inductive Power Transfer Systems

Bidirectional inductive power transfer (IPT) systems facilitate contactless power transfer between two sides, which are separated by an air gap, through weak magnetic coupling. Typical bidirectional IPT systems are essentially high-order resonant circuits and, therefore, difficult to both design and control without an accurate mathematical model, which is yet to be reported. This paper presents a dynamic model, which provides an accurate insight into the behavior of bidirectional IPT systems. The proposed state-space-based model is developed in a multivariable framework and mapped into frequency domain to compute the transfer function matrix of eight-order bidirectional IPT systems. The interaction between various control variables and degree of controllability of the system are analyzed from the relative gain array and singular values of the system. The validity of the proposed dynamic model is demonstrated by comparing the predicted behavior with that measured from a 1 kW prototype bidirectional IPT system under various operating conditions. Experimental results convincingly indicate that the proposed model accurately predicts the dynamical behavior of bidirectional IPT systems and can, therefore, be used as a valuable tool for transient analysis and optimum controller design.

A Generalized Steady-State Model for Bidirectional IPT Systems

Bidirectional inductive power transfer (BD-IPT) systems are high-order resonant circuits, which are complex in nature and sensitive to variations in system parameters and control variables. Consequently, modeling and design of BD-IPT systems are relatively difficult in comparison to unidirectional IPT systems. An accurate model that predicts the behavior of BD-IPT systems under different operating conditions is invaluable but yet to be reported. This paper, therefore, proposes a generalized steady-state model through which the behavior of BD-IPT systems can be accurately characterized. The proposed mathematical model is comprehensive and includes the effects of harmonics and sensitivity to variations in system parameters and control variables. Using the model, this paper investigates the behavior and sensitivity of BD-IPT systems under a range of practical operating conditions. The validity of the proposed generalized model, which is verified using the results of a 1-kW prototype system, provides a clear insight into BD-IPT systems and is expected to be useful at both design and implementation stages.

An ICPT-Supercapacitor Hybrid System for Surge-Free Power Transfer

This paper presents a technique for the suppression of voltage transients through the use of dynamically reconfigurable supercapacitor (SC) banks. The technique requires a minimum of two SC banks to transfer power from a mains supply to load in complete isolation. The banks are operated independently as energy-storing elements in one of the three states of charging, discharging, or idling, and transition of banks from one state to another with isolation is realized dynamically by inductively coupled power-transfer technology with no physical contacts. The proposed technique has no direct connection between the mains supply and load at any given moment, and power transfer takes place in complete isolation with built-in protection for both common- and differential-mode transients. Sizing of the banks with respect to various types of SCs and system parameters is analyzed. Comparisons between simulations and experimental results of two prototype systems, subjected to combination transient surges specified by IEC61000-4-5 standard, are presented with a discussion to show the validity of the proposed concept and its suitability for uninterruptible power systems and emergency power supplies.

Design of a bi-directional inverter for a wireless V2G system

Vehicle-to-grid (V2G) or G2V systems essentially require an interface between the electric vehicle (EV) and the grid to facilitate the V2G concept. This paper presents a wireless power interface for the grid integration of EVs. The proposed bi-directional wireless power interface is based on the Inductive Power Transfer (IPT) Technology, and comprises a high frequency IPT system and a low frequency bi-directional grid side inverter. A DQ controller is employed to regulate the power flow to and from the grid. Both simulations and experimental results are presented to demonstrate the viability of the proposed wireless and bi-directional power interface.

A contactless bi-directional power interface for plug-in hybrid vehicles

The alarming rate, at which global energy reserves are depleting, is a major worldwide concern at economic, environmental, industrial and community levels. A partial solution to this crisis is the use of decentralized generations (DG) and vehicle-to-grid (V2G) plug-in electric vehicles. This paper presents a novel multiple pick-up bidirectional inductive power transfer (IPT) system, which enables efficient and contactless integration of hybrid vehicles into typical DG systems. The proposed system uses a reversible rectifier on each side of the contactless IPT system to control both the amount and direction of power flow through phase modulation. Simulation results suggest that the proposed bidirectional V2G IPT link is feasible, and it is expected to gain popularity amongst both commercial and residential users.

A primary side controller for inductive power transfer systems

Inductive power transfer (IPT) technology is gaining popularity as an efficient wireless power transfer mechanism in numerous applications, ranging from microwatt bio-engineering implants to high power battery charging systems. A typical IPT system employs two separate controllers on both powering and receiving sides of the system to facilitate contactless power transfer in an efficient and controllable way. This paper presents a new primary side control technique for IPT, which requires only a single controller located on the powering side to effectively control the amount of ‘contactless’ power delivery to the receiving side. In order to regulate the load voltage, the track current is controlled in the proposed technique by accurately estimating the mutual coupling and output voltage through the variation of reflected primary voltage. Theoretical analysis and simulated results are presented, with experimental measurements of a prototype IPT system to validate the viability of the proposed technique. In contrast to existing IPT systems, the proposed IPT system with only a single controller is low in cost, more efficient, and is expected to be the popular choice in applications such as biomedical implants.

A New Resonant Bidirectional DC–DC Converter Topology

This paper presents a new resonant dual active bridge (DAB) topology, which uses a tuned inductor-capacitor-inductor (LCL) network. In comparison to conventional DAB topologies, the proposed topology significantly reduces the bridge currents, lowering both conduction and switching losses and the VA rating associated with the bridges. The performance of the DAB is investigated using a mathematical model under various operating conditions. Experimental results of a 2.5-kW prototype, which has an efficiency of 96% at rated power, are also presented with discussions to demonstrate the improved performance of the tuned LCL DAB topology. Results clearly indicate that the proposed DAB topology offers higher efficiency over a wide range of both input voltage and load in comparison to conventional DAB topologies.