Michael J. Neath

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 Synchronization Technique for Bidirectional IPT Systems

Bidirectional inductive power transfer (IPT) systems are attractive for applications such as electric vehicles and vehicle-to-grid systems which preferably require “contactless” and two-way power transfer. However, in contrast to unidirectional IPT systems, bidirectional IPT systems require more sophisticated control strategies to control the power flow. An indispensible component of such control strategies is the robust and accurate synchronization between the primary- and pickup-side converters, without which the transfer of real power in any direction cannot be guaranteed. This paper proposes a novel technique that synchronizes converters on both the primary and pickup sides of bidirectional IPT systems. The technique uses an auxiliary winding, located on the pickup side, to produce a synchronizing signal which, in turn, can be utilized to regulate the real power flow. This paper also presents a mathematical model for the proposed technique and investigates its sensitivity for component tolerances. The viability of the technique, which is applicable to both single- and multiple-pickup IPT systems, is demonstrated through both simulations and experimental results of a 1-kW prototype bidirectional IPT system.

A steady-state analysis of bi-directional inductive power transfer systems

The modeling and analysis of bi-directional inductive power transfer (BD-IPT) systems are relatively complicated as they consist of high order resonant circuits, which are complex in nature and sensitive to variations in system parameters and control variables. Consequently, an accurate model that can predict the behavior of BD-IPT systems under different operating conditions has not been reported to-date. This paper therefore proposes a mathematical model through which the steady-state behavior of BD-IPT systems can be accurately characterized. The proposed mathematical model is comprehensive as it accounts for the effects of harmonics and sensitivity to variations in system parameters and control variables. The validity of the proposed model, which is verified using the simulated results of a 7.5 kW system, provides a clear insight into the operation of BDIPT systems and is expected to be useful at both design and optimizations stages.

A Dynamic EV Charging System for Slow Moving Traffic Applications

Inductive power transfer (IPT) is by far the most popular method to transfer energy wirelessly and has attracted considerable attention in recent times. The Wireless Power Consortium has developed a standard (Qi) for low power consumer electronics, whereas the Society of Automotive Engineers (SAE) is working on a standard (J2954) to charge electric vehicles (EVs) wirelessly. SAE’s current efforts are focused only on transferring power to the vehicles at rest (static), whereas no work has been done so far on developing the standards for transferring power to the vehicles on the move (dynamic). This paper presents the magnetic design of an IPT system for a dynamic EV charging application, to continuously deliver a power of 15 kW to an EV, along the direction of travel within the lateral misalignment of ±200 mm. The experimental validation of system operation, however, was conducted at 5 kW. The design aims at distributing the cost and complexity of the system between the primary and secondary sides, while achieving a smooth power transfer profile. In addition, the system is designed to exploit the shielding effect provided by the vehicle, as the field generating components of the system are covered by the vehicle body under all operating conditions.

A new controller for bi-directional inductive power transfer systems

Inductive Power Transfer (IPT) technology is gaining popularity as an efficient technique for supplying contactless power to numerous applications. In contrast to uni-directional IPT systems, bi-directional IPT systems invariably require more sophisticated and effective control strategy to regulate the power flow within the limits of power capability of converters. This paper proposes a new controller that uses power-frequency droop characteristics to regulate the power flow of the system without any additional communications. Simulated results of a 2 kW bi-directional IPT system with a single pick-up are presented with discussions to show that the proposed droop controller can effectively be used regulate the power flow, while limiting the power flow at maximum level when necessary.

Magnetic modeling of a high-power three phase bi-directional IPT system

The demand for high power and bi-directional Inductive Power Transfer (IPT) systems is on the rise due mainly to applications such as electric vehicles (EVs) and vehicle-to-grid (V2G) systems. Three phase bi-directional IPT systems can be considered as a viable option for high power applications as they are more efficient especially at elevated power levels due to lower track currents and lower DC ripple currents in comparison to single-phase bi-directional IPT systems. This paper proposes a new IPT system that adopts a three-phase magnetic circuit for both primary and secondary sides of the system. Analyses related to design of the magnetic circuit for a 10 kW system are presented and validated by 3D simulations using JMAG Studio 10.0™ for four different magnetic circuit configurations. Based on the results, the most effective design is used for further simulations in MATLAB Simulink environment to show that the proposed three-phase IPT system is capable of delivering 10 kW as per design specifications.

Controller Synthesis of a Bidirectional Inductive Power Interface for electric vehicles

Bidirectional Inductive Power Transfer (IPT) systems are preferred for Vehicle-to-Grid (V2G) applications. Typically, bidirectional IPT systems consist of high order resonant networks, and therefore, the control of bidirectional IPT systems has always been a difficulty. To date several different controllers have been reported, but these have been designed using steady-state models, which invariably, are incapable of providing an accurate insight into the dynamic behaviour of the system A dynamic state-space model of a bidirectional IPT system has been reported. However, currently this model has not been used to optimise the design of controllers. Therefore, this paper proposes an optimised controller based on the dynamic model. To verify the operation of the proposed controller simulated results of the optimised controller and simulated results of another controller are compared. Results indicate that the proposed controller is capable of accurately and stably controlling the power flow in a bidirectional IPT system.

Frequency jitter control of a multiple pick-up Bidirectional Inductive Power Transfer system

Bidirectional Inductive Power Transfer (IPT) systems are high order resonant circuits and require relatively sophisticated control strategies to regulate the power flow. The control of multi-pick-up IPT systems is more challenging as the order and complexity of the system increase with number of pick-ups. This paper proposes a new controller to regulate the power flow in both directions in multi-pick-up bidirectional IPT systems. The proposed controller utilises frequency jitter to control the power flow. The controller enables operation at tuned frequency over the entire load range, minimising the VA ratings of converters and eliminating the need for any direct communication. The validity of the jitter control concept is demonstrated through simulated results of a 4 kW bidirectional IPT system with 3 pick-ups (loads).