Research On Current-type High Frequency Resonant Converter Based On Magnetic Energy Recovery Switch (MERS)

With the development of power electronic technology and the continuous increase of industrial demand,miniaturization,modularization and integration have led the current developing trend of power electronic devices,wherein the power converter has been increasingly used because it can reduce the device size,increase the power density and improve the reliability due to its high frequency performance.The traditional pulse-width modulation(PWM)converter has hard switching characteristics,and the switching loss increases sharply with the increase of frequency,which is not suitable for high-frequency applications.The resonant converter realizes the zero-voltage switching and zero-current switching of the switching tube by means of the resonance of the LC element,which effectively reduces the switching loss,allows the operating frequency to be further increased,and has obvious advantages in a high-frequency working environment.This paper provides a current-type LCL resonant converter based on the magnetic energy recovery switching(MERS),which solves the problem that the output current of the traditional LCL resonant converter is difficult to be stabilized due to the input disturbance and the element parameter error,and at the same time,the soft switching of each switching tube is realized.This paper firstly introduces the typical topological structure of the MERS,analyzes the three working modes of the MERS in detail,and establishes a mathematical model to derive the equivalent capacitance of the MERS.The results show that the equivalent capacitance value of the MERS can be changed by means of controlling each switching of the MERS,and the feasibility of the MERS being used as a controllable capacitive reactance controller is proposed.Secondly,the working characteristics of the current-type high-frequency resonant converter based on the MERS are studied.There are many methods for controlling the power converter,and the most commonly used one is the variable frequency control.However,the performance of magnetic components in the converter will decrease with the change of frequency,which increases the complexity for designing the system.This paper puts forward a control strategy for the new resonant power converter,that is,the MERS circuit is introduced into the resonant circuit of the converter,and the constant current output characteristics of the converter can be achieved by changing the equivalent capacitance of the MERS.The constant-current working principle of the LCL resonant converter based on the variable capacitance is analyzed,the working process and soft switching characteristics of the MERS-LCL resonant converter are elaborated in detail,and the effectiveness of the proposed topology is verified by simulation.Thirdly,the proposed MERS-LCL resonant converter is applied to the LED constant-current drive,and the control strategy of the LED constant-current drive,based on the MERS-LCL resonant converter,is proposed.In order to satisfy increasing lighting needs,high-power LED loads are usually connected in a blended manner.When a fault occurs in the load assembly,the constant-current effect of the traditional LED driving power source is poor.This paper puts forward a new LED driving circuit by combining the MERS-LCL resonant converter,analyzes the relationship curve between the LED driving current and the MERS equivalent capacitance.And the LED constant-current drive can be realized by regulating the equivalent capacitance.The simulation model of the put forward LED driving circuit is established by using the PSIM software,and simulation verification is performed.Finally,designs of hardware circuits and software systems are performed on the MERS-LCL resonant converter,and a low-power experimental prototype is built.The experimental result further verifies the effectiveness and feasibility of the MERS structure for the output regulation of the LCL resonant converter.