LLC Power Converter design: LLC resonant frequency Fr measured values is different than the calculated values of Fr when we measure the results by through comparing Freq vs Vout

Hi 

I am using a document SLUP263 which is produced by Texas Instruments for designing a LLC based Power Converter. 

With this documents, I have designed my FULL BRIDGE Resonant Power Converter. There is an example written in this document. Following the same path, I have calculated the Resonant capacitor Cr, Resonant Inductor Lr and Magnetizing Inductance Lm values as given below.

By using this formula,

The Converter is designed for Load RL= 5.6 ohm, Vin = 60V, Vout = 30, Transformer turns ratio = 2, full  bridge inverter, full bridge rectifier using diodes, Switching Freq F= 120Khz . I started my calculation based on above formulas prescribed in the documents.

Turns ratio: n = Vin (full bridge inverter) / Vout = 60 / 30 = 2;

Mg_min = [2 * { 30 * (1-1%) + 0.3}]  /  [{75}-Full bridge]       =  0.8

Mg_max = [2 * { 30 * (1+1%) + 0.3 + 0.5}]  /  [{45}-Full bridge]      =   1.4

Qe= 0.45 and Ln = 3.5 are extracted by through Matlab Qe, Ln vs switching freq F graphs.

Re = { 8n² /  pi² } * RL(5.6ohm)   =  18.1ohm 

therefore,

Cr = 1  /  {2 * pi * Qe * F * Re}     =    162nF

Lr = 1  /  {2 * pi * F }² *  Cr}     =    10.8uH

Lm = Ln * Lr = 3.5  * 10.8v    =  38uH

Fr = 1  /  {2 * pi * √ Lr * √Cr } *  Cr}   =  120 Khz .. Resonant Freq Fr

The above values are calculated values. 

The Problem is when I bought the nearest values for the hardware like Cr =150n, Lr= 10uH & Lm = 39uH, the test or the below measurment results between Frequency F vs Vout shows that the resonant freq F is somewhere in between 25-55KHz which is not matched with resonant frequency Fr calculated in the above calculations.   Please suggest how can i move the resonant frequency to 120Khz, Also which values of Lr, Cr & Lm are required if the above-calculated values are incorrect. I have tested my LLC hardware with different  loads like RL = 10, 5.6 ohm, 50 ohms, 125 ohms. but in all cases the resonant freq F  in calculation is not matched when comparing with measurment results to find the resonant Frequency F.

Frequency F              Vin                RL = (5.6)->6ohm                Vout                     ILoad                     Pin                     Pout                       Efficiency * 100 

Note * Burned = Lr is burned due to high current because of higher Mg.

 Frequency              Vin                RL = 50ohm                Vout                     ILoad                     Pin                     Pout                       Efficiency * 100 

Please suggest this issue.

Kind Regards

Arsalan