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Debuging problems about Solar Micro Inverter Development Kit

JK Lin
Prodigy 80 points

We are debugging TMDSSOLARUINVKIT: Solar Micro Inverter Development Kit recently with the application of AC Grid 220Vrms/50Hz. The steps are based on the user's guide: UG_SOLAR_Micro_Inverter. Unfortunately, two development kits both are partly damage.

The first development kit runs well before the stage: 6.3.1 Full PV Inverter System Check without MPPT. Grid is connected to the kit. When we step into 14 in page 56, the development kit seems to trigger the state machine and them the kit is damaged, the electricity is cut off with leakage-current protection. Moreover, DC regulator TPS73033 of U5 and C50 in the F28035_ISOcontrolCARD is damaged. Also, MOSFET Q9 and its related driver are damaged too.

The second kit is firstly damaged when we debug the DC-DC flyback function. At first, we have finished the open-loop and closed-loop test. But when we finished the closed-loop DC-DC test (6.2.1 Flyback Closed Current Loop without MPPT), and turn on the power source again without running the kit, the input current is 0.03A instead of 0.0A. Q9 and U16 are broken when running the program. Then, we replace Q9 and U16 with new components, and add a snubber capacitance with 1nF to the DSpin pf Q9. It seems working in normal regard to 6.2 experiments. But when we carry out the 6.3.1 Full PV Inverter System Check without MPPT, we have observed some abnormal behavior of the circuit with turn on the AC grid. In that time, AC grid is connected to the development kit without turn on. From the CCS, we can observe the AC voltage is 230Vrms, but the DC link voltage Vbus raise up to 125V or so. We think the Vbus voltage is abnormal and stop the experiment debugging.

Please tell us how to debug the development kits, and the possible reasons. Or shall we return the kits to TI for some repairing?

Thanks for your help.

  • 0
    TI__Mastermind 43730 points
    1. For the first kit, the reason is improper isolation of the board and power supplies. PV is a floating source. Hence the Dc Source must be completely isolated, also the bias power supplies have to be isolated. We have documentation for this in the UG. This is the likely cause of the failure.

    2. For the second kit, what do you mean we had the power source turned on without running the kit? did you just have the DC voltage without the board being powered? Did you have DC power on while the code was being flashed into the device?
  • 0 in reply to Manish Bhardwaj
    Prodigy 80 points

    Dear Manish, thanks for your reply. 

    1. For the first kit, the reason is improper isolation of the board and power supplies. PV is a floating source. Hence the Dc Source must be completely isolated, also the bias power supplies have to be isolated. We have documentation for this in the UG. This is the likely cause of the failure.

    Yes, the isolated requirement is documented in the UG. We use the bias power supplies provided by the development kit, and the DC source is also isolated power supply. If it is caused by improper isolation, why it can pass the close-loop test in buildlevel 2.

    2. For the second kit, what do you mean we had the power source turned on without running the kit?

    It means that we have stepped into step 13 connect the power grid, and the kit can detect the grid voltage, GUI_InvStart remains 0

    did you just have the DC voltage without the board being powered? Did you have DC power on while the code was being flashed into the device?

    the board is powered, and the code is flashed into the device.

    Also, I have a photo to show the status of the experiment of Build 3, please check it.

  • 0 in reply to JK Lin
    TI__Mastermind 43730 points
    Lin,

    1. The DC source is isolated : Some time the Chasis is tied to the earth of the AC supply and hence the DC source needs to be floated , did you check this? If this was not checked this can cause high currents through the ground loop which can damage the board, and it will be beyond repair.

    2. Looks like the board is damaged as it is boosting even in idle state. I would suggest removing the extra components you added and then checking BUILD 1 and 2,
  • 0 in reply to Manish Bhardwaj
    Prodigy 80 points

    Dear Manish,

    1. What is the meaning of DC source floated? We have checked the DC source via multimeter, the output DC terminals have no connection with the earth of  AC supply.

    2. Yes, it looks like the board is damaged. When I connect the AC plug with only line and neutral wires, the Vbus is about 25V. In fact, We have checked BUILD 1 and 2 previously without any extra components, it seems working. Is there any possible cause of this damage? Maybe We can change some components to fix it.

    BTW, for the Solar Micro Inverter Kit, should all the AC power supply are connected with only two wires, i.e. line and neutral, and earth is left unconnected for safety, including AC-DC adapter, AC plug for grid-connected terminal and AC supply of DC source?

  • 0 in reply to JK Lin
    Prodigy 80 points

    Hi Manish, 

    I have removed the added capacitor, and checked BUILD 1 and 2 without MPPT, it looks OK. What should I do next? For Kit 1, should I send it back for repair?

  • 0 in reply to JK Lin
    TI__Mastermind 43730 points
    Lin,

    1. Yes you need to completely disconnect the earth ground, please observe appropriate precautions while doing these tests.

    2. For Kit 2, i would recommend doing the grid connected test with a floating AC source instead of the grid first, so you are in a more controlled environment.

    Regards
    Manish Bhardwaj