Electronics > Repair
Inverter drive module overvolt fault
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Eamon:

--- Quote from: florentbr on October 11, 2022, 04:43:23 pm ---The AC input voltage in question could be measured at R94 even though it's rectified.

--- End quote ---

Firstly, thanks for that link, it does look strikingly similar to my board's circuit apart from specific component values (though DB2 does not seem to have a reciprocal part in the diagram). And reading the article was a bit enlightening too, I think I have identified the phase current measurement blocks as a result (3 x MV7221 OP-Amps connected to the low side shunt resistors from the IBGT driver)

Just double checked with the multimeter in DC mode and I don't see more than about 3V variation at the start of the resistor chain at R94 when the compressor starts and the inverter reports the big jump in AC voltage, unfortunately every time I try to measure the voltage at the end of the resistor chain after R99 as the compressor starts, the inverter reports "PFC Failure" code.  Hopefully the oscilloscope will be more of a passive observer when I get the chance to set it up and try.


--- Quote from: florentbr on October 11, 2022, 04:43:23 pm ---What's strange is that the inverterDCvoltage is supposed to rise well over 320v when the PFC is turned on, but your measure doesn't show that.

--- End quote ---
How high is "well over"? I double checked the +vDC plane serveral times with the multimeter in DC mode and the highest I have seen is about 325V.  Is there something I can do with a multimeter to check if the PFC circuit is turning on?  My assumption from reading the article you provided is that it will be running at a frequency too high for a multimeter to be of much use?


--- Quote from: florentbr on October 11, 2022, 04:43:23 pm ---If the reported AC voltage jumps from ~220v to ~320v, it could indicate that the output DC is finding it's way back to the output of the bridge rectifier. I might be wrong, but I don't think it's supposed to.

--- End quote ---
My thoughts are similar; the reported AC voltage when it jumps is almost exactly the same as the reported DC voltage, i'm just not sure where to measure to test that theory.  Hopefully when I can get a scope onto it I'll learn more.


--- Quote from: florentbr on October 11, 2022, 04:43:23 pm ---I would remove and test C53A, Q1, Q2, D1, D2 and DB2.
DB2 is not used as a bridge rectifier but as a single diode.

--- End quote ---
De-soldering is not a strength of mine :) trying to avoid if possible. though if the problem is the +DC leaking back to the output of the bridge rectifier, it would seem that C53A could cause that?

WattsThat:
The inverter supply of 320vdc should not rise above that value, unless the compressor pressure/piston is pushing back against the motor, causing it to be become a generator rather than a motor. This can lead to overvoltage trips and this may be a sign of a bypass valve not opening for startup to reduce the pressure to allow the use of smaller motors. Don’t know what the refrigeration system schematic looks like but it should be easy to locate anything in the refrigerant lines with wires on it. It might be a pressure switch but you should be able figure out if this is going to an input or output on the control board.

Your approach of trying to run the inverter with a different load is good idea but even better, the inverter may run without a motor. If not, a suitable load can many times be made with three 220v incandescent light bulbs wired in delta.
Eamon:

--- Quote from: WattsThat on October 12, 2022, 12:42:08 am ---The inverter supply of 320vdc should not rise above that value, unless the compressor pressure/piston is pushing back against the motor, causing it to be become a generator rather than a motor. This can lead to overvoltage trips and this may be a sign of a bypass valve not opening for startup to reduce the pressure to allow the use of smaller motors. Don’t know what the refrigeration system schematic looks like but it should be easy to locate anything in the refrigerant lines with wires on it. It might be a pressure switch but you should be able figure out if this is going to an input or output on the control board.

Your approach of trying to run the inverter with a different load is good idea but even better, the inverter may run without a motor. If not, a suitable load can many times be made with three 220v incandescent light bulbs wired in delta.

--- End quote ---

I've disconnected the heat pump controller board and I'm turning the inverter on an off directly with a small application I wrote using a USB to rs485 converter. I've reverse engineered enough of the communication protocol between the heat pump controller and the inverter module and that I can disconnect the heat pump controller and drive the inverter and compressor directly from a laptop so none of the various other sensors related to the refrigeration system should matter. The application essentially just polls the inverter for its state and sends the compressor on instruction in response to me pressing a toggle button on the laptop.  I'm pretty confident that the compressor is not faulty.

If I try to run the Inverter without anything connected to the U, V and W outputs of the inverter module it faults with a "Comp. Driver Failure", I've tried the only 3 phase motor I have at hand and it caused the inverter to report "PFC Fault" instead.  I'll see if I can try 3 resistive loads in delta, but I suspect it will not work as I believe the inverter would be using the phase differences on the three inputs to measure frequency or rotor position or something like that?
WattsThat:
Is there any feedback from the motor back to the inverter? Some motors use three Hall effect sensors to tell the inverter where the rotor is, needed for proper switching. If there are no sensors/feedback, it should run with a resistive load so long as the current is close to that of the compressor load.
Eamon:

--- Quote from: WattsThat on October 12, 2022, 02:48:41 am ---Is there any feedback from the motor back to the inverter? Some motors use three Hall effect sensors to tell the inverter where the rotor is, needed for proper switching. If there are no sensors/feedback, it should run with a resistive load so long as the current is close to that of the compressor load.

--- End quote ---

No, the motor has only three wires, the three power phases from the inverter.
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