Research On LLC Resonant Converter

With the development of power semiconductor components, the high frequency hasbecome a trend, the volume and weight of power converter can be significantly reduced bythe high-frequency transformation, and then effectively improve the power density of theconverter,but the traditional PWM converter has been difficult to adapt to the development ofhigh-frequency.Compared to the PWM converter, resonant converter has the advantage ofhigher operation frequency, lower switching loss, higher efficiency, wider range of inputvoltage, smaller volume, lighter weight, lower switching stress and smaller EMI. LLCresonant converter can achieve zero voltage switching (ZVS) with any load condition andzero current switching (ZCS), witch effectively reduce the switching losses, and the powerefficiency is greatly improved.In addition, LLC resonant converter can achieve integrationwith resonant inductor and transformer. Based on the above advantages, LLC resonantconverter has been widely used in modern switching power supply.Firstly, the basic classification and their advantages and disadvantages of resonantconverters are summarized and induction, and compared to the PWM converter, the mainadvantages of LLC resonant converter were summed up; the principle and waveform of LLCresonant converter in each frequency region are analyzed in detailed; the DC gaincharacteristic of LLC resonant converter were studied in detail based on the FHA(FirstHarmonic Approximation)，and put forward an easy method to design parameters ofconverter，each parameter calculation results are given combined with design examples；Based on the extended describing function method, the small signal model of LLC resonantconverter is designed in detail.On this base,the small signal characteristics of the converter isanalyzed when the switching frequency is changed, and according to the requirements of thedynamic characteristics,the design problems of the compensator are analyzed, the basicstructure of the compensator is designed;Through the technology of magnetic integration, theresonant inductance will be integrated into the transformer by leakage inductance andexcitation inductance of the transformer, the number and size of the magnetic pieces will bereduced; The correctness of theoretical analysis were validate through the SABER simulationresults.