Common faults of motor resolvers in new energy vehicles

1. Principle The resolver is a position sensor commonly used in motor control. The function of the resolver is to accurately measure the position, speed and rotation direction of the motor rotor, transmit these signals to the electronic control, and control the motor by the software control algorithm.

It can control the frequency and sequence of three-phase alternating current, thereby changing the speed and direction (forward and reverse) of the drive motor. When the permanent magnet synchronous motor is working, the rotating magnetic field generated by the stator coil rotates synchronously with the rotor, and the rotating magnetic field poles and the rotor poles maintain a certain angle, and the resolver monitors the position and speed of the rotor.

The principle of resolver: by inputting a high-frequency sinusoidal signal into the rotor coil, which is what we often call the excitation signal (the power supply of the resolver), we can then receive the high-frequency induction signal fed back from the induction resolver rotor in the coil. After processing, we can get the corresponding sine and cosine information, and after software analysis, we can get the absolute position of the stator.

2. Calibration

There are many popular terms for resolver calibration in daily work, such as zero angle calibration, motor angle calibration, etc. Although the terms are different, the content and function are the same, that is, to know the angle deviation between the zero position of the resolver and the zero position of the motor.

3. Common faults

If there is a problem with the resolver, there will inevitably be problems with the rotational speed.

1. When the vehicle is static (the actual motor speed is zero), the instrument falsely reports that the motor has speed; 2. When the high voltage is normal, the motor has no output speed when the gear is engaged and the accelerator is pressed;

3. Cause three-phase hardware overcurrent fault;

4. Cause IGBT failure;

5. Cause the motor speed to shake;

6. Cause the motor to stall;

7. Vibration, abnormal noise

A new fault occurred due to incorrect connection sequence of the resolver wiring harness: a motor passed the controller software and hardware version detection, but when it entered the NVH working condition, it made abnormal noises, had an abnormal characteristic curve, and had a negative speed. Finally, it was discovered that the resolver wiring harness was designed incorrectly.

1) Measured by electrical detection

There are generally 6 resolver lines connected from the motor controller to the motor, namely: ref± (excitation signal), sin± (sine signal) and cos± (cosine signal). Each set of signals has its own corresponding resistance value. You can determine whether the resolver is faulty by measuring the three sets of resolver resistance values ​​at the motor control plug-in end or the motor end.

2) Characteristic curve Motor speed is a companion signal of motor torque, just like a gear. If you want the gear to rotate, you need an external force.

Normal motor speed changes smoothly and linearly.

Abnormal: Due to the resolver fault, the motor speed curve displayed looks like it has burrs. During the driving of the vehicle, the jitter of the motor speed will cause the driving jitter of the whole vehicle.

The resolver wiring harness has one end connected to the low-voltage plug-in of the motor controller and the other end connected to the resolver low-voltage plug-in of the motor. We have the following diagnostic methods:

1) Unplug the low-voltage plug-in on the motor controller end and the resolver low-voltage plug-in on the motor end, and use a multimeter to measure the on/off of the excitation (ref±), sine (sin±), and cosine (cos±);

2) If the measured resolver resistance is normal, but it is not possible to determine whether the wiring harness and plug-in are poorly connected, you can install the low-voltage plug-ins at both ends, grab the wiring harness and shake it vigorously. If the instrument speed fluctuates abnormally, you still need to carefully check the wiring harness and low-voltage plug-in;

3) If the measured resolver resistance is normal (from the motor controller low-voltage plug-in end and the motor end), and the wiring harness and plug-in are confirmed to be normal, the motor controller needs to be replaced.