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TIDM-1000: TIDM1000 PFC Vienna eval board : current distorsion

Julien Djn
Intellectual 840 points
Part Number: TIDM-1000
Other Parts Discussed in Thread: SFRA

Tool/software:

Hello,
I started using TIDM1000 PFC Eval Board with Power Suite tooling.
I went through INCR_BUILDS 1 to 4 but I have an issue with current quality.

My set-up is :
Use of power suite with TI software
TIDM board is supplied with up to 230Vrms (phase-neutral) / 50Hz voltage through an autotransformer (we set the voltage between 0Vrms and 230Vrms)
Earth of TIDM board (connector J3, pin 2) is connected to autotransformer earth
Output neutral of autotransformer is connected to DC mid point for builds 1 to 3 as requested by user manual
500 ohms / 1 kW resistor is used as a load

Im using F28377 µC board, configured as shown here :

Oscilloscope channels :
C1, C2 and C3 : input phase-neutral voltages
C4, C5 and C6 : input phase currents

Test results :
INCR_BUILD_1, input voltage = 120Vrms (phase-neutral), VIENNA_dutyPU_DC = 0.5 :


=> input voltages are noisy because our autotransformer is sized for 230Vrms ; I used 120Vrms to be representative of what is done in user manual
=> nevertheless currents are as expected (fig. 25 and 26 of user manual)
=> I consider this build with my set-up to be OK

INCR_BUILD_2, input voltage = 120Vrms (ph-N), VIENNA_iLRef_pu = 0.2 :


=> currents on phases 1 and 3 (C4 and C6) look correct, while phase 2 current is distorded (C5)
=> I checked PWM signals, they all look correct and are similar together, including for phase 2 (I didn't go into details, I just checked general shape)

INCR_BUILD_2, input voltage = 230Vrms (ph-N), VIENNA_iLRef_pu = 0.11 :


=> input voltages are cleaner now
=> but phase 2 current is still distorded
=> at this step I tested different Kp value for current regulation, without any improvment ; finally I kept default value Kp = 2

INCR_BUILD_3, input voltage = 208Vrms (ph-N), VIENNA_vBusRef_pu = 1.32 [600V] :


=> not in accordance with figure 56 from user manual

INCR_BUILD_4, neutral disconnected, input voltage = 208Vrms (ph-N), VIENNA_vBusRef_pu = 1.32 [600V] :
=> not in accordance with figure 56 from user manual

Do you have any idea why current are distorded ? What can I check ?

I am working with 50Hz input voltages, is it a problem ?

Thanks,
Best regards,
Julien

  • 0
    TI__Mastermind 42165 points

    Julien,

    No i do not have a good reason why the current waveforms would be distorted as they are.

    Did you attempt to reprogram the controller coefficients using SFRA and compensation designer? If yes i would recommend moving the compensator values back to default and trying again.

    Regards,
    Cody 

  • 0 in reply to Cody Watkins
    Intellectual 840 points

    Hello Cody,

    Thanks for your feedback.

    Im using all default values because Im running PFC on 500ohms resistor, which is the advised value in user manual.

    Could you confirm if I have to connect DC voltage mid-point to input supply neutral for build 2, 3 and 4 ? According to user manual yes, but Im not sure I have to do this.

    Yesterday I checked a lot of internal SW variables using DACs (voltage and current reference, duty cycles, and so on...) and found nothing abnormal.

    Should I connect earth of the board (currently it is connected) ?

    I also measured my THDi for the same test than on figure 56 (build 4) and found 4.9%, which is superior to 2.5% shown in user manual (only difference is that I work at 50Hz, not 60Hz).

    Now I will focus on build 4. Im not so far away from your results. I'm wondering if my current probes could be an issue : their measurement range is 150A, maybe too large and we're measuring noise ? This afternoon I will try to change the probes.

    Best regards,

    Julien

  • 0 in reply to Cody Watkins
    Intellectual 840 points

    Hello Cody,

    I just made new measures with different probes for the working point of figure 56 (208Vrms in / 600VDC out / 600W). Here are the results, with THDi calculation :

    Manufacturer LEM Fluke Hioki (initial probes)
    Current probe range 0-30A 0-30A 0-150A
    Current probe bandwidth DC to 100kHz DC to 20kHz DC to 10MHz
    Input current THDi 5.35% 9.83% 6.83%

    Fluke bandwidth is too low, measured current is not correct.

    LEM probe may be better to measure small current, THDI is lower than Hioki one.

    Do you know which probes were used at TI ?

    I also checked that earth connection has no impact on results.

    For current measurement on the board itself, Im using classical ADC, not the one with AMC1305M25DWR component. Do you think it could have an impact?

    Do you have any other ideas I could check ?

    Next step for me will be to use a power analyser for THDI calculation. It will eliminate any doubt about the current probes.

    Best regards,

    Julien

  • 0 in reply to Cody Watkins
    Intellectual 840 points

    Hello Cody,

    I finally found that my results for build 4 are in line with TI user manual for 230V/50Hz power supply input.

    Regarding builds 2 and 3, I guess that neutral should not be connected to DC voltage mid-point, but it is in contradiction with what is indicated on figure 16 of user manual ("Neutral from the power supply is connected to the DC Mid Point for the build level 1-3").

    Thanks,

    Best regards,

    Julien