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.

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.

This paper proposes a novel inductor-capacitor-inductor wireless power pickup with directional tuning control (DTC) for a magnetic amplifier. The proposed technique allows the power pickup to achieve full-range tuning/detuning operation to regulate power flow and maintain the output voltage to be constant. The method eliminates the tedious fine-tuning process associated with traditional fixed power pickup tuning methods and eases the component selection. Moreover, it can overcome the online circuit parameter variations and automatically achieve the maximum power transfer capacity when required. In order to meet dynamic load demands, a magnetic amplifier is used as a variable inductor and is controlled by a novel DTC algorithm to change the tuning condition of the power pickup. The effectiveness of the proposed power pickup and its applicability to general wireless power transfer applications have been demonstrated by both simulation and experimental results.

Capacitive power transfer (CPT) has been investigated as an alternative wireless power transfer technology based on electric field coupling. The coupling interface of CPT is formed by a pair of “capacitors” in series with the power source and load. The effective capacitance ranges from tens to a few hundreds of picofarads, yielding high impedance. Therefore, in most CPT systems, a tuning inductor is connected in series with the coupling interface for circuit compensation and power transfer capability enhancement. However, this compensation method suffers from high voltage spikes from the inductor if the secondary side load is removed suddenly causing electrical and health hazards. To address the issue, this paper proposes a CPT system based on a Z-impedance compensation network with inherent open-circuit and short-circuit immunity. It also has the voltage boost capability as a Z-source inverter. Its operating principle is described and a set of design equations are given. Both simulations and experimental results from a 5 W low power design have demonstrated that the proposed compensation method using the Z-impedance matching network exhibited open-circuit and short-circuit immunity, could boost up the output voltage by 50% with power efficiency exceeding 80%.

Recursive algorithms are derived to compute the generalized frequency response function matrix of multi-input multioutput (MIMO) non-linear systems as an analytical map from both non-linear differential equation models and NARX (Non-linear Auto Regressive Models with eXogenous inputs) models of the system. The algorithm is computationally compact and exposes the explicit relationship between the model parameters and the elements of the generalized frequency response function matrix and can thus provide important insights into the behaviour of non-linear systems.