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A Framework for Modeling Motor Drive Reliability

A Framework for Modeling Motor Drive Reliability. Ali M. Bazzi Power Affiliates Program 2010 May 14 th , 2010. Outline. Motivation Methodology Implementation Reliability Model Concluding Remarks. Motivation. Induction motors have been part of several traction and propulsion systems.

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A Framework for Modeling Motor Drive Reliability

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  1. A Framework for Modeling Motor Drive Reliability Ali M. Bazzi Power Affiliates Program 2010 May 14th, 2010

  2. Outline • Motivation • Methodology • Implementation • Reliability Model • Concluding Remarks

  3. Motivation • Induction motors have been part of several traction and propulsion systems. • Drives with field-oriented or vector control have been well-established and commercialized. • Safety and reliability are major drive requirements, e.g. transportation applications. University of Illinois Hybrid Car Tesla Roadster http://www.teslamotors.com

  4. Motivation Plenty of work on fault tolerant control and fault diagnosis. Literature lacks a complete methodology of reliability modeling of motor drives. The purpose of this research is to develop such a model. The first step is to assess the impact of faults on the FOC drive through injecting faults and checking the drive performance. The second step is to develop a Markov reliability model.

  5. Methodology Modeling A motor drive simulation model, including several fault models, is used along with experiments. Fault Injection:

  6. Methodology Performance Evaluation: Performance bounds are set based on typical operation. An example of highway cruising in an electric vehicle is used here. Performance bounds Performance Measure 2 Time to return within bounds Signal Upper bound Performance Measure 2 Survival Lower bound Failure! time Performance Measure 1 Fault Performance Measure 1

  7. Methodology Fault Impact Assessment: After every fault, the system speed, current, and settling time are compared to the performance bounds. Violation of the performance bounds means that the system is in failure mode. If the response is within desired bounds, the system survived the fault. Fault Coverage: The same procedure is repeated for different values of an input command, e.g. torque command, flux command, etc. If the system survives under a fault with a probability of c % and fails for (1-c) %, then c is called the coverage.

  8. Methodology Simple Example:

  9. Methodology

  10. Implementation MATLAB/Simulink is used as the simulation environment. SimPowerSystems Toolbox is used to model power electronics and the induction machine. Indirect FOC (IFOC) is used for control of speed and flux.

  11. Implementation 300V/10A inverter feeds a 1.5 hp induction machine. eZdsp2812 is used to implement IFOC. Faults could be injected through DSP control or through hard-wired faults. Simulation model was verified through injecting mild faults that would not damage the setup.

  12. Implementation Fault Fault Simulation results for speed encoder omission Experimental results for speed encoder omission

  13. Implementation Fault Fault Simulation results of system failure after an open circuit on phase “a”. Experimental results for system failure after an open circuit on phase “a”.

  14. Implementation Fault Fault Simulation results of system survival within performance bounds after speed encoder constant. Experimental results of system survival within performance bounds after speed encoder constant.

  15. Reliability Model • Two fault layers and fault coverage of the flux input were studied.

  16. Reliability Model • Based on the previous table, a Markov model was constructed. • The Markov model allows to calculate the probability of being at every state. • The sum of the probabilities results in the survivor function • R(t) is used to find the mean time to failure (MTTF)

  17. Reliability Model • Sample failure rates of components were used to find an approximate R(t) and MTTF. • All components are assumed to have exponential survivor functions, i.e. constant failure rates. • MTTF = 57.2 years. • Special case considering only speed encoder faults: • MTTF = 84.7 years.

  18. Reliability Model

  19. Concluding Remarks • A complete procedure for modeling the reliability of induction motor drives was presented. • The procedure is flexible and expandable to include more or less faults, and model other machines and drives. • With the validated simulation model, fault coverage can be studied through input sweeping. • A complete Markov reliability model was developed to find the overall reliability function and MTTF.

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