Research On Wireless Power Transmission Based On Adjustable Gain Constant Current Or Voltage Compensation Netwoeks

The inductive power transmission(IPT)technology can transfer the energy in a predefined distance via the alternating electromagnetic field without the direct electrical contact.IPT has many unique advantages with electrical and mechanical isolation to improve the safety and reliability,friendly operation in harsh environments,flexibility and convenience,etc.Thus,IPT has been widely used in many applications,such as electric vehicle charging,consumer electronics,LED lighting,etc.Due to the large leakage inductance of the loosely coupled transformer,compensation technology is crucial to improve the transfer efficiency in the magnetic coupled wireless power transfer system.The IPT converter should provide not only the required load-independent driving current or voltage directly,but also zero reactive power and soft switching,resulting in lower component ratings and higher transfer efficiency.In the basic four IPT converters,the output gain relies on the transformer parameter significantly.However,the transformer parameters need an iterative design according to the input and output values of the system,which makes the transformer hard to optimize,especially in some applications with the constrained space.To solve it,this paper proposes a family of compensation circuits with high freedom of current or voltage gain by adjusting the compensation parameters,using two-port network theory,whilst zero reactive power and soft switching can be achieved simultaneously.Analysis,design and implementation of these compensation circuits are detailed involving the characteristics,reactive power circulation,and output gains.Finally,the experiment setups are built using the same topology and unique transformer to realize the IPT LED drive circuit of 0.5A,1A,1.5A outputs.The experimental results verify the theoretical analysis well.This method is also applicable to other high order compensation networks.In addition,this paper will also analyze the harmonic problems in the IPT converter.IPT converters can easily enter discontinuous current mode(DCM)operation due to the non-linearity of the output diode rectification circuit at some loading conditions.The first harmonic approximation(FHA)analyzing method and the load-independent constant output property are no longer applicable when the converter enters DCM operation.To solve it,this paper uses the harmonic approximation analysis to establish mathematical mode of the IPT converter.This paper will give the quantitative expression of the rectifier bridge input current and voltage to reveal the main reason why the converter enters the DCM operation.Subsequently,this paper will present a method for obtaining the load boundary between CCM and DCM operations.Finally,two high order compensation circuits are used to verify the theoretical analysis.Moreover,a solution by increasing the higher order input impedance is also suggested to extend the load range against DCM operation.