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| Inverter drive module overvolt fault |
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| capt bullshot:
See the attached sketch for the basic idea of using a "standard mains step down transformer" to add / subtract its secondary voltage from mains. Load current shall be lower than the ampere rating of the secondary. Previous posters thought about the PFC stage: I have to agree, this is plausible. There are components that look just like a PFC stage, and said "plate voltage" might have something to do with the PFC stage. Disabling the PFC stage could work - e.g. by removing the transistor. In general the inverter is able to run without a PFC stage, it is required for compliance, not for function. Depending on how it is done, the inverter might throw other errors if one disables the PFC. Once you've started investigating, scoping the waveforms at the DC link capacitors and at the switching node of the PFC might give some insights. |
| Eamon:
I've spent a fair bit of time trying to reverse engineer the schematic and have what is attached so far. I have a little more around the gate drivers for the two PFC MOSFETs but not sure its too important here; it's essentially a ucc27524 with some resistors and an unidentified SOT-23 transistor. The three 150k resistors in series head off on a trace that jumps back and forth through vias and ends up in a sea of smd passives and a few SOT-23 diodes near the MPC. I can't identify the pin arrangement on the diodes as the only marking on D5 is "HA7" which is not much use for searching, but the "idle" state voltage at the end of the 3 series resistors is 2.08v The three 200k resistors that come out after the first choke also head off to a bunch of smd parts and becomes hard to follow but given that I think this is the only path the MPC could potentially measure an AC signal, I'll try to follow it further. If there is a problem with the PFC circuit, what is the most likely culprit? No progress finding a compressor substitute so I'll probably just have to put the module back into the heat pump and put the scope on it in place. Are there particular points in the circuit I should focus on? |
| capt bullshot:
The R3 ... R5 string might be the startup supply for the PFC controller IC, or the other auxiliary SMPS. Doesn't look like a typical AC sense circuit at a first glance. The R54 ... R99 string most probably is an input signal to the PFC controller, as these need the actual half bridge rectified voltage for their control loop. If you have a stable DC voltage at E1 ... E3 that is higher then the peak value of the input AC voltage, the PFC should be considered OK. I'd recon the controller turning on/off the PFC stage depending on the compressor motor stage (PFC off while motor is off to save energy). So the voltage across these capacitors might actually rise when the motor starts. The UCC27524 is a simple gate driver, not a PFC controller. My guess the PFC is done by the MCU in software, as the inverter control loop and modulator is done there too. You could measure the voltage across the electrolytics (with a multimeter) to see if it matches one of the reported voltages, or if this voltage rises unexpectedly high (whatever a "normal" voltage would be, one can rely on guesses only - I'd consider 350V for a PFC DC-Link "normal"). |
| capt bullshot:
Another thought: TI publishes quite a few reference designs using their chips. You might want to search for motor control reference designs using the TMS320F28027 (or similar) maybe even including a PFC stage. There are designers out there, that use these reference designs as a guide or copy parts of the schematic. This might ease the reverse engineering and help understanding the circuit. |
| florentbr:
The AC input voltage in question could be measured at R94 even though it's rectified. 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. 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. 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. The PFC from your schematic seems to match this one: https://www.digikey.be/de/articles/hvac-dual-ac-motor-control-with-active-pfc-implementation-using-piccolo-mcus |
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