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UCC28180: Improve THD at switching frequency 20kHz

CCphi CCsora
Intellectual 540 points
Part Number: UCC28180
Other Parts Discussed in Thread: TIDA-00779,

Our design are following. We are trying to  achieve THD less than 10% at output power 2KW.  Now, we can achieve less than 10% THD at 600W only. For 2KW, THD still over 10%. 

Input:185-264 Vac

Output:350Vdc

Output  power :2KW

Switching freq. : 20kHz

Base on this TI ref. design TIDA-00779, it can achieved less than 5% THD at Switching Frequency 45kHz. 

But our design is base on Switching Frequency =20kHz,  Is it possible to achieve less than 10% THD at power 2KW ? What are the key portion to be change to achieve this requirement ? 

  • 0
    TI__Mastermind 34465 points

    Can you please provide more details of your application ?

    The schematic diagram and test waveforms would be nice to view.

    THD becomes larger as input voltage increase and load decreases. This is because the inductor current tends to become discontinuous and the UCC28180 is a continuous conduction type of controller. Also as load current decrease it becomes more difficult to detect the current across the sense resistor which cause errors in the sensed current.. However you seem to have good THD at 600W and poor THD at higher power. That is unusual.


    Also for a 264Vac input the bus voltage is normally set at about 390Vdc.

    You have a 264Vac input ( 372Vdc peak) and you have set a 350Vdc output.

    The UCC28180 will shut down in this condition.

    Regards,

    John

  • 0 in reply to John Griffin1
    Intellectual 540 points

    Schematic is attached. Good THD(<10%) at 600W, we got it by changing inductor of PFC( from 2.3mH to 350uH,550uH). But for 2KW, THD still over 10%.