Analysis of three-phase imbalance or abnormal current sampling circuit of electric scroll compressor

The electric vehicle compressor is driven by high-voltage electricity provided by a power battery. The motor of the electric compressor is a three-phase permanent magnet synchronous motor. The internal IGBT inverter circuit converts direct current into alternating current, driving the three-phase motor to operate. The common main faults of electric vehicle compressors include scroll plate movement faults, motor module faults, and compressor motor control module faults. Now we will discuss one of the common faults of the compressor - three-phase imbalance or current sampling circuit fault of the compressor.
The three phases of the electric compressor are U, V, and W, respectively. When the phase voltage between the three phases is unbalanced, that is, if the compressor is running when a phase loss occurs, it will continue to operate but will have a large load current. The motor winding can quickly overheat, and normally the compressor will be shut down due to thermal protection. When a complete vehicle reports three-phase imbalance in the compressor, it is necessary to troubleshoot the entire compressor. Generally, compressors have a phase current sampling circuit. If this circuit is abnormal, the entire vehicle will report an analog sampling fault alarm, but some vehicle manufacturers may not have added fault information about the current sampling circuit to the vehicle diagnostic apparatus. When reading compressor faults, it is necessary to use computer software to read the historical fault information inside the compressor, Check whether a fault such as high current or three-phase imbalance is reported.
The main reason for three-phase imbalance of the compressor is that the three-phase terminal of the compressor falls off or lacks phase.
The main reason for the abnormality of the three-phase current sampling circuit of the compressor is a faulty soldering or short circuit in the three-phase current sampling circuit of the control module.
1) The three-phase wiring terminal of the compressor falls off or lacks phase
The three-phase harness terminals of the compressor motor control module in the red circle in Figure 1 are directly connected to the three-phase terminal of the compressor motor. If three-phase imbalance occurs, it is necessary to check whether the three-phase terminal and the three-phase terminal of the motor are properly connected.
2) There is faulty soldering or short circuit in the three-phase current sampling circuit of the control module
The three-phase current sampling circuit of the compressor uses an operational amplifier to collect both ends of the U, V, and W three-phase lower bridge sampling resistors. As shown in Figure 2, use both ends of the two parallel resistors of the U phase as forward U+and reverse U - to create a simple differential amplification circuit. As shown in Figure 3, the U+must be connected to the forward input terminal of the amplifier, and the U - must be connected to the reverse input terminal of the amplifier. If it is connected in the reverse direction, it may burn out after being powered on.
Figure 3 shows the circuit schematic diagram. The amplification factor is the ratio of the output voltage to the input differential mode voltage. The amplification factor can be determined by the ratio of the output resistance R03 to the input resistance R02, and the amplification factor is R03/R02.
When the compressor has reported a three-phase current sampling circuit fault, it can be detected from the control board whether the compressor sampling circuit is normal, and whether the voltage output to the AD acquisition port of the microcontroller is consistent with the calculated theoretical value. If the voltage is not within the theoretical value range, it indicates that there is a problem in the circuit around the operational amplifier, that is, there is a faulty soldering or short circuit phenomenon in electronic components.