Research On Dynamic Tuning Method Of Inductive Power Transfer Systems

Inductive power transfer(IPT)technology can deliver power from power sources to loads without contact.It can solve the problems of wear and spark caused by the traditional plug-in systems,and it has the advantages of convenience and safety.In recent years,IPT technology has gradually become a research hotspot at home and abroad,and its theoretical research and application have gradually developed towards high power and high efficiency.However,due to the load variations,misalignment of the magnetic coupling,device aging,heating,and other factors,the impedance of the IPT system are changed,which break the resonant tanks and reduce the system efficiency.Therefore,it is of great significance to study the dynamic tuning method to keep the system resonant in real time with high efficiency.The main contents of the thesis are given as follows:(1)The phase measurement method of the IPT system is studied.Firstly,the working principles of the IPT system are described.Then,an ac phase detection circuit for the phase measurement of the IPT system is analyzed in detail.Subsequently,the method of coaxial phase detection coil is adopted to measure the induced voltage on the secondary side.The principle of obtaining the secondary induced voltage with the coaxial phase detection coil on the primary and secondary side is elaborated.In addition,the measured voltage of the detection coil and the current of the IPT system have harmonic and distortion.Therefore,the corresponding waveform optimization circuit is analyzed and designed,which increase the accuracy of the method.(2)The detuning of the receiver circuit in the IPT system can decrease system efficiency.To tune the receiver circuit of IPT system dynamically,an inductor is parallelly connected with a diode full-bridge rectifier cascaded with a Buck converter serving as a tuning circuit in this chapter.By changing the duty cycle of the Buck converter,the impedance of the tuning circuit can be adjusted to compensate the reactance caused by detuning.The tuning range of the proposed method is analyzed in detail.A corresponding control method is proposed to tune the receiver circuit dynamically while regulating the output voltage.Because the Buck converter is with the dc side of the receiver,no synchronization is required for the switches of the Buck converter,and the switching frequency of the Buck converter can be much lower than the inverter frequency.A 400 W prototype is established to validate the proposed tuning method.The experimental results show that with 15% tolerance of the resonant capacitor in the receiver side,the system efficiency with the proposed tuning method can reach 91% with an improvement by 7.9% compared to the detuned system.(3)The detuning of the primary circuit in the IPT system can decrease the system efficiency results in the increase of the switching losses and temperature of the inverter,as well as the decrease of the system efficiency.To keep the primary circuit of IPT system resonance,this chapter proposed a dynamic tuning method based on the auxiliary inverter.Firstly,the relationship between the efficiency of series-series compensation system and the detuning level in the primary circuit is analyzed.Then,this chapter analyzes the tuning principle and puts forward the tuning scheme.Through real-timely measuring the phase difference of output voltage and output current of the main inverter,the phase angle difference of the inverter driving signal can dynamically be adjusted to tune the primary circuit.Finally,the proposed tuning method is validated by the experiment under various detuning condition.The results show that the proposed tuning method can realize dynamic tuning,and the system efficiency is improved after tuning.Especially,when the detuning reactance in the primary circuit is the 15% tolerance of the resonant capacitor,the system efficiency reaches 92.9% and increases by 6.6% after the tuning.The proposed method effectively reduces the heat of the system.