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UCC28950EVM-442: Need help to design Shim Inductance to design 4KW Phase shift full bridge Converter

Soundharya E
Prodigy 110 points
Part Number: UCC28950EVM-442
Other Parts Discussed in Thread: UCC28950

We designing 4KW Phase shift Full bridge converter for below specification,

Input voltage -40Vdc-60Vdc,Typical - 51.7V 

Output Power - 4000W,

Efficiency - 95%,

Output voltage -196.8V,

Output current -20A

Switching Frequency -250kHz

Input Voltage 40 51.70 60
Output Voltage 196 196.00 196
Allowable Output Voltage
Transients (90% Load Step)		     0.6
Output Power (POUT)     4000
Full Load Efficiency 90%    
Inductor (LOUT) Switching Frequency   250.00  
       
Selecting Power Transformer (T1)      
Description Variable   Unit
Set Initial Power Budget  PBUDGET 444.44 W
Estimated FET Voltage Drop VRDSON 1.00 V
Maximum Duty Cycle Nominal DMAX 0.70  
T1 Transformer Turns Ratio=NP/NS a1 0.14  
Select Transformer Turns Ratio a1 0.08  
Typical Duty Cycle DTYP 0.33  
Inductor Ripple Current ΔILOUT 4.08 A
T1 Primary Magnetizing Inductance > or = LMAG 5.66E-03 mH
Please Refer to Figure of T1 Current IPS 22.45 A
Please Refer to Figure of T1 Current IMS 18.37 A
Please Refer to Figure of T1 Current IMS2 20.41 A
Partial RMS Current ISRMS1 12.09 A
Partial RMS Current ISRMS2 8.30 A
Partial RMS Current ISRMS3 0.46 A
Calculate T1 Secondary RMS Current (ISRMS) ISRMS 14.68 A
Primary Magnetizing Current Based on LMAG ΔILMAG 19.81 A
Please Refer to Figure of T1 Current IPP 316.40 A
Please Refer to Figure of T1 Current IMP 267.42 A
Please Refer to Figure of T1 Current IMP2 301.29 A
Partial RMS Current IPRMS1 244.52 A
Partial RMS Current IPRMS2 169.18 A
Calculate T1 Primary RMS Current (IPRMS) IPRMS 297.34 A
Primary Magnetizing Inductance LMAG 0.02 mH
Transformer Primary DC Resistance DCRP 0.12 mΩ
Transformer Secondary DC Resistance DCRS 4.00 mΩ
Measured Transformer Primary Leakage Inductance LLK 0.00 uH
Estimated transform loss, 2X Copper Losses PT1 24.67 W
Recalculate Power Budget PBUDGET 419.78 W
QA, QB, QC, QD FET selection:      
Voltage Applied to FET Gate ≈ VDD Vg 12.00 V
FET drain to source on resistance Rds(on)QA 2.10 mΩ
FET Specified Coss COSS_QA_SPEC 3850.00 pF
QA FET Gate Charge QAg 376.00 nC
Voltage Across Drain to Source Where COSS was Measured, Data Sheet Parameter VdsQA 40.00 V
Calculate average COSS  COSS_QA_AVG 3143.51 pF
Calculate QA losses  PQA 47.54 W
Recalculate Power Budget PBUDGET 229.60 W
Select Shim Inductor (LS)      
Calculated Shim Inductance LS 8.21E-04

uH

I am calculated using the excel tool (https://www.ti.com/tool/download/SLUC222) but still I am getting lower Shim Inductance value .Pls guide me to select shim Inductor for above requirement which I given in the above table.

  • 0
    TI__Guru 70355 points

    Hello,

    Your inquiry has been received and is under review.  I will get back to you shortly.

    Regards,

  • 0 in reply to Mike O'
    TI__Guru 70355 points

    Hello,

    The following link will bring you to an application note that goes through the step by step design process of a PSFB using the UCC28950.  There is a section describing how to select the shim inductor.  This also uses the same equations that are in the excel tool.

    https://www.ti.com/lit/pdf/slua560

    The excel tool selects Ls based on 50% to achieve ZVS and estimate that switch node capacitance is 2X Coss.

    Is this not enough to achieve ZVS down to 50% load?  If not your transformer capacitance and reflected capacitance across the transformer might be substantially greater than the estimated capacitance.

    If you have the ring frequency and know the inductance you can calculate the actual switch node capacitance and then adjust the shim inductance to meet your power needs based on 0.5*C*V^2 = 0.5*L*I^2.

    Regards,