Design Of An Efficiency Optimized 5W Wireless Power Transfer System Based On Adaptive Frequency Control

As an emerging technology of power transmission,wireless power transfer(WPT)is more advantageous than traditional method of wired power transfer,which has been widely used in various fields such as smart phones,wearable portable electronic products,electric vehicles,and biomedical devices.Although the WPT system is widely used,the main bottleneck of the current WPT technology development is the robustness of system control and relatively low transmission efficiency.Aiming at the problem of output voltage unconstant and efficiency degradation caused by load and coupling coefficient variation,this paper has proposed a WPT system with adaptive frequency control and efficiency optimization.The proposed control method can simultaneously satisfy the output constant voltage and maximize efficiency.By establishing the equivalent mutual inductance coupling circuit model of the SS compensated WPT system,the effects of load,coupling coefficient and frequency on the output characteristics and efficiency of the system are studied by mathematical derivation and theoretical analysis.The output voltage can be controlled by frequency when it is closed or away to the resonant frequency,and there is an optimal equivalent load within the full load range to maximize efficiency.On this basis,this paper uses a DC-DC converter in the receiver for load conversion.When the load changes,the equivalent load is always at the optimal value by controlling the rectified output voltage to track the maximum efficiency point while changing the duty cycle of the DC-DC converter to keep the output voltage constant.The sampled rectified voltage is compared with the estimated value to caculate error value,which is sent to the transmitter by ASK modulation wireless communication,and the transmitter demodulates the communication information and then adaptively adjusts the frequency through PID algorithm.Based on this,the key circuit design of the transmitter and the receiver and the software implementation of the system control is completed.Based on the Matlab/Simulink platform,the open-loop and closed-loop simulation of the system is performed,and the system experiment platform is built to test the system function and performance.The test results show that the designed WPT system can work correctly.Under the condition that the input DC voltage is 5V and the operating frequency is 110~205kHz,the maximum power of 5W can be realized in the transfer distance of 3~10mm.The output voltage is constant at 5V,the constant voltage accuracy is within ±1%,the load regulation rate is within ±1.4%.When the load and coupling coefficient change,the frequency can be adaptively adjusted to control the rectified voltage for efficiency optimization.The maximum efficiency of the WPT system is 79%,under the condition of typical transfer distance of 3mm,the full load efficiency is 75%,the average efficiency is 73%.Compared with the unoptimized efficiency,the light load efficiency is increased by 14.1% and the heavy load efficiency is increased by 8.9%.The test results show that the WPT system satisfies the design index,the designed WPT system in this paper is compliant to the Qi standard with a high integration,and has a good application prospect.