Investigation Of Coordinated Control Of Primary And Secondary Sides In Inductive Power Transfer Systems

The Inductive Power Transfer(IPT)has recently gained much popularity among the automotive industry and academia due to its attractive features that include: no physical wired link;high power transfer capability;high environmental adaptability and good convenience in application,etc.The IPT technique satisfies the automatic charging requirements for the shared and driverless electric vehicles.High efficiency and high power are important indicators for the IPT system.Although significant progress has been made in increasing operational power levels,the efficiency optimization remains an issue to be addressed.The efficiency of the IPT system can be improved through various optimization of control strategy and magnetic design techniques.In addition,the control optimization technique is of great importance for both scientific research and engineering applications.The control methods of the IPT system can be divided into three categories: primary side control,secondary side control,and coordinated control of both primary and secondary sides.All these methods can satisfy the output voltage/current regulation,whereas with the last method maximum efficiency point tracking can be achieved.In applications such as wireless charging for mobile phones and electric vehicles,the mutual inductance changes with coil position in space and the load resistance depends on the state of the charged battery.However,variations in these parameters result in low efficiency.An effective method to solve this problem is utilizing coordinated control method based on equivalent load transformation.Instead of inserting a DC/DC circuit on the secondary side,this study uses an active rectifier to realize AC/DC conversion and equivalent load transformation simultaneously,making the overall system compact and efficient.The active rectifier requires high-frequency AC/DC conversion,therefore,an improper control may cause power oscillations.Besides,the number of control variables increases and the dead time effect is more significant.Therefore,the coordinated control of primary and secondary sides becomes complicated.This study investigates the key technologies of the IPT system with an active rectifier,i.e.,the synchronization technique,the dead-time elimination method,a single-switch active rectifier,dual-side phase control,and maximum efficiency point tracking methods.To eliminate the frequency deviation between controllers and avoid power oscillations in the IPT system with an active rectifier,a high-performance synchronization technique has been proposed.According to the fundamental harmonic analysis method,the influence of the frequency deviation between dual-side controllers on the IPT system has been presented.The frequency locking and phase calibration have been performed by a simple hardware-software combination.To address the dead time effect on the IPT system,the voltage distortion caused by dead time has been analyzed,and a novel dead-time elimination method has been proposed and implemented.To reduce the cost,size,weight,and practical application difficulties of the full active rectifier,a single-switch active rectifier has been proposed.Furthermore,digital and analog phase control methods,digital and analog duty cycle control methods,and simultaneous wireless information and power transfer technique have been demonstrated.To improve the overall efficiency of the IPT system,three maximum efficiency point tracking algorithms based on dual-side phase control have been proposed.These algorithms are based on ergodic method,minimum input current detection,and mutual inductance estimation.In addition,it is found that mutual inductance estimation method is more promising for engineering applications.In order to verify the feasibility of the coordinated control of primary and secondary sides in the IPT system,an experimental platform is built up.The experimental results show that the system can realize equivalent load transformation and output voltage/current regulation.Furthermore,the proposed system contributes to a significant efficiency improvement for large variations in mutual inductance and load resistance,which suits the wireless electric vehicle charging.