Research On Wireless Power Transmission System Based On Ultrasonic

Wireless power transmission(WPT)has received more and more attention in recent years and has been greatly developed due to its high mobility and environmental adaptability.However,in the case where a metal medium exists,a wireless energy transmission method using electromagnetic waves or the like as a transmission medium is affected by electromagnetic induction,and the energy cannot be efficiently transmitted.As a kind of mechanical wave,ultrasonic wave has the characteristics of directionality,and can be propagated in any medium,so it cannot be affected by electromagnetic induction.The ultrasonic wave provides a new type of safe and reliable power supply for some special electrical equipment,especially metal sealed equipment.Therefore,this paper studies the wireless power transmission system based on ultrasound.In order to realize wireless transmission of energy in the form of ultrasonic waves,this paper has conducted in-depth research on the ultrasonic power transmission(UPT)system.The piezoelectric transducer is a device that realizes the electrical energy-mechanical energy-electric energy conversion of the UPT system.The equivalent circuit of the piezoelectric transducer is derived by the electromechanical analogy method,and the operating characteristic is analyzed.The correctness of the theoretical derivation is verified by measuring the impedance characteristics.For the ultrasonic power source and receiving circuit,according to the characteristics of the UPT system,the full-bridge inverter circuit is selected as the main circuit topology of the ultrasonic power source,and the bridge rectifier and the Buck circuit are used as the main circuit topology of the receiving circuit.The transmission characteristics of the UPT system are calculated by the equivalent circuit diagram.The factors causing the system loss are studied and calculated and the calculation method of the overall efficiency of the UPT system is given.It is pointed out that the optimization of the conversion efficiency of the piezoelectric transducer is a key factor to improve the overall efficiency of the system.In order to optimize the efficiency of UPT system,an adaptive control strategy based on frequency tracking technology is proposed.The efficiency of the UPT system is optimized by keeping the piezoelectric transducer operating at the highest efficiency point.According to the operating characteristics of the piezoelectric transducer,three control schemes of current,power and phase control are proposed.After detailed comparison,the phase control scheme is selected.The phase control can be realized by the form of phase-locked loop.The digital and analog phase-locked loops are studied separately.Combined with the characteristics of the transducer,the specific implementation method of the analog phase-locked loop is given.The piezoelectric transducer is always controlled to work at the resonant frequency,and the efficiency of the system is optimized.In this paper,a complete UPT system is developed.The transmission medium is metal aluminum with a thickness of 38 mm and a resonant frequency of about 40 kHz.When the AC load is controlled,the input power is controlled to be equal to 10 W,and the efficiency of the UPT system with the different frequency of excitation voltages is compared.At the same time,the phase-locked control loop keeps the transducer always operating at the resonant frequency point,achieving the optimization of the system efficiency.When the DC load is applied,the output voltage is controlled to 24 VDC,which can supply power to the internal battery of the metal sealed container.The feasibility of wireless transmission of energy in the form of ultrasonic waves and the correctness of the efficiency optimization method proposed in this paper are verified by experiments.