Analysis of problems such as startup failure or internal overcurrent failure of the scroll compressor for air conditioning of new energy electric vehicles

The common main faults of the scroll compressor for the air conditioning of new energy electric vehicles include scroll plate movement faults, motor module faults, and compressor motor control module faults. Now let's discuss one of the common faults of compressors - compressor startup failure or internal overcurrent fault. The compressor stops immediately after starting for a few seconds, and this situation is repeated several times continuously, which will generally be judged as a compressor startup failure by the entire vehicle system. During the startup phase, a shutdown due to a fault (excluding overvoltage and undervoltage alarms) is defined as a startup failure. Excessive current can also trigger shutdown protection. The similarities between the compressor startup failure fault and the internal overcurrent fault of the compressor are: the effective value of the phase current ≥ the overcurrent alarm threshold.
The main reason for compressor startup failure or overcurrent is excessive compressor phase current. If the torque required for starting the compressor increases, the compressor phase current will also increase accordingly. There are seven main reasons for excessive compressor phase current in automotive air conditioning systems:
1) The electronic fan is not running;
2) The expansion valve is blocked;
3) Other parts of the system are blocked;
4) Incorrect refrigerant injection amount;
5) Air enters the system;
6) The internal structure of the compressor is stuck;
7) The opening of the electromagnetic expansion valve is incorrect;
Therefore, based on the above information, when faced with a compressor startup failure or internal overcurrent fault reported by the entire vehicle, the following judgment needs to be made based on the on-site situation:
① If the compressor fails to start and an internal overcurrent fault is reported, vacuum the system and refill the refrigerant. The refrigerant oil of the compressor is also replenished. After a period of shutdown, the compressor can be started normally, and the high and low pressure pipeline pressures of the compressor system are normal. This indicates that it is a problem with the system itself and has nothing to do with the compressor motor control module.
② If the compressor fails to start and is shut down for a period of time, the refrigerant is refilled, the compressor refrigerant oil is also replenished, and the other systems operate normally. The high and low pressure pipeline pressures of the compressor system are normal, but the compressor still cannot start normally. It indicates that the compressor itself is abnormal and can be disassembled for inspection.
③ After disassembly, if it is found that the external profile of the scroll plate inside the compressor is broken or the bearing is damaged, it indicates that the compressor structure is abnormal. Otherwise, it indicates that the compressor motor control module is abnormal, leading to compressor startup failure.
④ After performing the above steps, analyze the compressor motor control module and plug the faulty motor control module into the new compressor motor for power-on operation. If the operation is successful, it is necessary to check the condition of the original faulty motor to see if there are any phenomena such as poor bonding between the compressor motor control module and the motor, abnormal stator, etc. If the operation fails and keeps restarting, it indicates that the compressor motor control module is abnormal.
Root cause analysis of abnormal motor control module:
Generally, electric compressor software is equipped with an overcurrent protection mechanism. The three-phase analog phase current value is collected through a hardware operational amplifier. The operational amplifier circuit is shown in Figure 2. Then, the microcontroller calculates the value and triggers the overcurrent protection. This type of compressor is software overcurrent protection, lacking hardware overcurrent protection. There may also be a delay in the time period from the occurrence of overcurrent to the software triggering of overcurrent protection, so the IGBT of the compressor motor control module hardware may not be able to withstand large current shocks and be damaged at this stage. The internal damage of the IGBT is only a superficial phenomenon. The root cause is that the load of the air conditioning and refrigeration system is too large, resulting in a large torque required for the compressor to operate, and driving such a large load also requires a large phase current. Prolonged overcurrent leads to damage to the internal chips of the IGBT. Although this IGBT has not been broken down, internal damage has occurred, so it cannot meet the conditions required for compressor startup.