(1) Classification of failure modes of the motor drive system According to the cause, nature, mechanism, degree, speed of occurrence, time of occurrence and consequences of failure, the failures can be classified differently. The common failure modes of electric sightseeing vehicles can be divided into: damaged, degraded, loose, misaligned, leak-proof, functional failure modes and other failure modes. This is an analysis of the failure of components or components in the system that cause the failure of the motor drive system and affect the normal operation of the vehicle.
(2) Analysis of failure mechanism of motor drive system For the motor controller, the following failure modes are selected for mechanism analysis.
1 Overpressure generally occurs in the vehicle charging conditions. Excessive voltage not only affects device insulation, but also causes device damage. The overvoltage of the electric vehicle motor system is mainly concentrated on the DC bus voltage. Overvoltage can cause damage to the busbar capacitor, power device (IGBT) or busbar insulation. The main reasons are as follows.
a. The pre-charging circuit is not cut off. After the pre-charging is completed, the main contactor is not combined due to the fault. At this time, in response to the vehicle charging command, the pre-charging resistor is divided, resulting in the voltage across the busbar being too high.
b. The voltage detection part inside the malfunction controller is faulty, and the detected voltage signal is too large, resulting in protection.
2 Undervoltage generally occurs in the electric condition of the whole vehicle. Low voltage not only affects system performance, but also damages the device. When the system outputs the same power, the voltage is too low, which will inevitably lead to an increase in current. Excessive current may exceed the operating range of the device and cause damage to the device. For the motor, long-term undervoltage operation, low efficiency, large heat, long time will cause the motor winding insulation to reduce, resulting in short circuit or open circuit of the motor winding. The main reasons are as follows.
a. High-voltage battery voltage is too low High-voltage battery system may leak or the vehicle system is in electric operation for a long time, lacking charging conditions.
b. The pre-charging circuit is not cut off. After the normal pre-charging is completed, the pre-charging circuit is not cut off. The main contactor is not engaged due to the fault, and the pre-charging resistor is divided in response to the vehicle electric command, resulting in the voltage across the busbar being too low.
c. The voltage detection part inside the malfunction controller is faulty, and the detected voltage signal is too small, resulting in protection.
3 The overcurrent motor can rotate, but the running current far exceeds the rated value, which is different from the overload. The basic reflection of overcurrent is that the current exceeds the rated value, but the magnitude of the excess is large, forming a large inrush current. In automotive motor systems, overcurrent typically occurs at the DC bus end or at the three-phase AC output. The main reasons are as follows.
a. The DC busbar and the busbar insulation damage the insulation and damage, causing the busbar to be short-circuited.
b. The three-phase winding of the three-phase unbalanced motor of the stator winding is short-circuited, causing the line current to be too large.
c. The current detection part inside the malfunction controller is faulty, and the detected current signal is too large, resulting in protection.
4 The overload motor can rotate, but the running current exceeds the rated value, which is called overload. The basic reflection of overload is that although the current exceeds the rated value, the magnitude of the excess is not large, and generally no large inrush current is formed. The output current exceeds the inverse time characteristic overload current rating, the protection function operates, and the capacity of the inverter is too small. The main reasons are as follows.
a. The main characteristic of mechanical overload is that the motor is hot, and the three-phase running current is too large. The controller PI parameter causes the dynamic response time to be too short or the mechanical structure of the motor to be stuck.
b. The three-phase voltage of the stator winding is unbalanced. The three-phase unbalance causes the operating current of a certain phase to be too large, resulting in overload protection, which is characterized by uneven heating.
c. The current detection part inside the malfunction controller is faulty, and the detected current signal is too large, resulting in protection.
5 Over-temperature is too high, which will not only affect the insulation of the motor body, but also affect the power output of the motor controller. This is because the core of the motor controller is the inverter circuit composed of switching devices. The temperature directly affects the working range of the power device. The power device operation is affected by the junction temperature of the device (typically 150 °C). When the external temperature rises and the junction temperature is given, the switching loss must be reduced. This will cause the motor controller to fail. Full power output and reduced system performance. The main reasons are as follows.
a. It is overloaded for a long time.
b. The three-phase unbalance of the stator winding of the motor.
c. Malfunction.
6 Logic voltage fault The electric motor motor logic voltage is provided by the vehicle battery. The battery voltage fluctuation range is large. A requirement is imposed on the selection of the low voltage device of the motor controller, which must meet the voltage fluctuation range of the vehicle battery. If the logic voltage is too low, some devices will not work or the logic potential in the circuit will be disordered. If the voltage is too high, it will cause damage to the device. The main reason: the vehicle battery has a short circuit point; malfunction.
7CAN communication failure The command execution and system status feedback of the electric vehicle motor system are transmitted via CAN communication. The normality of communication is directly related to whether the system can work normally. The main reason: CAN line disconnection; electromagnetic interference.
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