Diagnosis Method for Fault of Inverter Power Switch Tube
The variable frequency speed control system is composed of two parts: a frequency converter and an electric motor. However, the probability of faults occurring in the frequency converter part is higher, and an important factor leading to the high failure rate of the frequency converter is the frequent occurrence of switch tube faults. There are four main methods for fault diagnosis of switch tubes: expert system method, voltage detection method, intelligent algorithm, and current detection method.
(1) Expert system method refers to the listing of possible faults based on experience in fault diagnosis and combined with specific situations, continuously enriching and summarizing them, and ultimately forming a systematic knowledge base. So when the fault occurs again, diagnosis can be made by querying this knowledge base, but the drawback of this diagnostic method is that it cannot establish the knowledge base completely and completely.
(2) Voltage detection method is used to diagnose faults by examining the deviation between the phase voltage, line voltage, or neutral point voltage of the motor during a frequency converter fault and normal conditions.
(3) Intelligent algorithms refer to general optimization algorithms. In variable frequency speed control systems, intelligent algorithms mainly include artificial neural networks, wavelet analysis, and fuzzy control.
(4) Current detection method is mainly used to normalize the current by grasping the current value, in order to control the switch tube well.
After a switch tube failure, there are two methods for recovery: one is to use redundant control; Another type is fault-tolerant control. Redundant control is used in systems with high reliability. It is to use redundant switches during operation when there is a malfunction in the switch tube. Fault tolerant control is the connection between each phase bridge arm and the motor through a relay. During normal operation, the relay for the neutral phase of the motor is disconnected and this phase is not activated. When a switch tube of a certain section malfunctions during operation, the relay of that phase opens, which can minimize the losses caused by sudden failures.
