Study On DC Power Supply Based On LLC Resonant Converter

Since the resonant converter can realize the soft-switching,it is widely concerned that the LLC converter can realize the zero-voltage turn-on of the converter switch tube in the whole load range,greatly reducing the switching loss of the converter,Converter efficiency can be effectively improved,which can improve the switching frequency of the resonant converter.Thus,power density can also be effectively improved.Since the LLC resonant converter can realize ZVS(zero voltage switching),the voltage across the converter switch can be eliminated,which can bring tremendous benefits to EMC.Moreover,the output rectifier diode of the resonant converter can achieve zero-current turn-off and avoid the diode reverse recovery loss,thereby further improving the efficiency of the resonant converter.However,LLC converters also have shortcomings.For example,the design of over current protection circuit is difficult.Larger excitation current will lead to conduction loss and reduce the efficiency of the converter,and the control method is also more complicated.In view of the above problems,the working mechanism of LLC converter was detailed analyzed in this paper.The waveforms of each node of the converter are discussed when the switching frequency of the resonant converter is in different ranges.The equivalent circuit model of resonant converter is established by using fundamental component method.Using the equivalent circuit model,the DC gain function of the converter and the input impedance function are obtained.The variation of input impedance with circuit parameters and converter switching frequency and the range of inductive capacitive region of input impedance are discussed.The influence of converter parameters on DC gain function is analyzed.The equivalent circuit model is used to establish a small signal model of the resonant converter,and the transfer function from converter control to output is obtained.It improves the theoretical basis for the closed-loop design of the converter system.The traditional analog control resonant converter circuit has a large number of circuit elements and the circuit is complex,which limits the reduction of the cost of the resonant converter and the increase of the power density of the converter to some extent.Therefore,a resonant converter with a digital processor DSP as a digital control unit is designed,which consists of a sampling circuit,a switch drive circuit and a resonant frequency detection circuit for converter.The flow chart of each module controlled by the converter system is designed.Finally,the resonant converter is simulated,and the voltage waveforms of each node and the resonant current and the exciting current waveform are analyzed and the results of the theoretical analysis are proved to be reasonable..Finally,a48V/120 W prototype was built and the resonant converter was tested.The test results show that theexperimental prototype performance is relatively stable,and the resonant converter can achieve the soft switching of the switch tube within the controlled operating frequency range.The rectifier diode enables zero current turnoff.According to the calculation and analysis,the full-load efficiency in the paper is 93%,which is 89% higher than that of the reference and the power efficiency is increased by 4.5%.The nominal half-load efficiency is 87%,which is 82% higher than the reference power supply efficiency,which is an increase of 6.1%.