Abstract
Fault Tolerant Control (FTC) systems are crucial in industry to ensure safe and reliable operation, especially of motor drives. This paper proposes the use of multiple controllers for a FTC system of an induction motor drive, selected based on a switching mechanism. The system switches between sensor vector control, sensorless vector control, closed-loop voltage by frequency (V/f) control and open loop V/f control. Vector control offers high performance, while V/f is a simple, low cost strategy with high speed and satisfactory performance. The faults dealt with are speed sensor failures, stator winding open circuits, shorts and minimum voltage faults. In the event of compound faults, a protection unit halts motor operation. The faults are detected using a wavelet index. For the sensorless vector control, a novel Boosted Model Reference Adaptive System (BMRAS) to estimate the motor speed is presented, which reduces tuning time. Both simulation results and experimental results with an induction motor drive show the scheme to be a fast and effective one for fault detection, while the control methods transition smoothly and ensure the effectiveness of the FTC system. The system is also shown to be flexible, reverting rapidly back to the dominant controller if the motor returns to a healthy state.
Highlights
Practical control systems are susceptible to component malfunctions which may cause significant performance degradation and even instability of the system
Fault Tolerant Control (FTC) systems are designed to allow recovery from damage and system faults. When it comes to electrical drives used in safety critical applications or industrial processes where system faults may lead to enormous costs, FTC systems are crucial [1]
An open circuit in the stator winding or a short reverts the system to closed loop voltage by frequency (V/f) control .V/F controlled drives are very reliable due to the restriction to low dynamic performance and the absence of closed loop control, while a minimum voltage fault enables open loop V/f control to maintain acceptable level of operation due to the degradation of the system performance and the difficulties of keeping good performance with the closed loop
Summary
Practical control systems are susceptible to component malfunctions which may cause significant performance degradation and even instability of the system. A very promising avenue in motor fault detection is wavelet-based. Wavelets provide both time and frequency domain information. A more extensive wavelet-based fault detection algorithm was used by Schmitt et al [11], with open winding faults, unbalanced voltage and unbalanced stator resistance taken into consideration. A fault tolerant control strategy which deals with a wide range of induction motor faults is implemented. The system has the ability to revert back to the dominant controller if the motor resumes normal operation, ensuring its availability at all times.
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