ECE Senior Design Reliability Analysis ReportForScalable Regulated Three Phase Power RectifierOctober 18, 2004 Rev. 1.0I.IntroductionII.System Failure Rate CalculationsA. Reliability Analysis OverviewIII.Conclusion of Failure Mode and Effect Critical AnalysisECE Senior Design Reliability Analysis Report For Scalable Regulated Three Phase Power Rectifier October 18, 2004 Rev. 1.0 Sponsors: Dr. Herb Hess (University of Idaho) Dr. Richard Wall (University of Idaho) Instructor: Dr. Jim Frenzel (University of Idaho) Prepared By, Tao Nguyen Tyler Budzianowski [email protected] [email protected] Reliability Analysis Report of the Three Phase Rectifier Senior Design Project (October 2004) Abstract - This technical paper is intended to provide the reader with the necessary information to fully understand the reliability analysis that was performed on the Three Phase Rectifier Senior Design Project. It is based on content and format requirements that were specified by the instructor. I. Introduction The reliability characteristics of a designed system are important to incorporate into a successful end product. By analyzing the behavior of integrated components and individual subsystems, the performance and lifecycle characteristics of an entire system design can be determined. This information can be used to identify any potential design problems or flaws as early as possible in the design process and to allocate effort and resources into the research and prevention of any identified problem. By dividing an entire system into smaller subsystems and individual components, the reliability of the entire system can be comprised of the total of each individual section. This divide and conquer technique is useful in focusing on only subsystems or components that most need attention following a reliability analysis. Using software and FMECA standards and techniques, an accurate and beneficial reliability analysis can be performed. II. System Failure Rate Calculations A. Reliability Analysis Overview The overall failure rate of the system was calculated using the Relex Analytical Tools (demo version) from the Relex Software Corporation. This software program has the ability to calculate the overall failure rate and Mean Time Between Failure (MTBF) values based upon the actual components utilized within the system design. Because each individual component and the subsystems comprised of these components has its own individual performance and reliability characteristics, the overall failure rate and MTBF can be comprised of the sum of each individual component failure rate and MTBF. The demo version used for these calculations unfortunately did not contain all of our specific components utilized in the design (such as the PIC16C74B microcontroller) within its component library. Similar components to the actual components were selected as an estimating alternative. Our particular design has been divided into three main subsystems and are as follows: zero-crossing detector, microcontroller, and the three phase rectifying circuit. The zero-crossing detector is comprised mainly of a comparator circuit utilizing an LM393 integrated circuit, resistors, capacitors, and a supply voltage source. The microcontroller system includes a PIC16C74B processor, 9 volt DC voltage source, and demonstration board. Finally, the rectifier circuit requires 6 silicon-controlled rectifiers (SCRs), a snubbing circuit comprised of resistors and capacitors for each SCR, MOVs, and an SCR gate firing circuit system. The following table (please see Table 1) illustrates the results of the Relex failure rate and MTBF calculations. Table 1. Reliability scores for the Hardware System Part Failure Rate MTBF (hours) Zero Crossing 0.045784 21842000 Rectifier Circuit 0.312870 3196217.33 Microcontroller 0.015281 65440800 B. Failure Modes and FMECA Analysis 1) Potential Failure Modes All potential failures modes that may be associated with the system design throughout its lifecycle are presented in the following table. They are based on each individual subsystem and the components used to implement each subsystem (please see Table 2). Table 2. List of potential failure modes 1. Firing gate circuit failure 2. SCR failures 3. Software failure 4. Zero crossing detector 5. Snubber and protection circuit failure 6. Physical damage 7. Improper set up or use 8. Over voltage 9. Microcontroller malfunction 10. Mechanical Problem 11. Three phase input line noise 12. Temperature increase/decrease 13. Uneven load/output current3 2) Failure Mode Severity Rating The severity of each failure mode has been determined based upon the FMECA Failure Effect Rating Scale and is based on a range of ‘1’ to ‘10’. The scale spans the categories of ‘Not Noticeable’ to ‘Moderate’ to ‘Hazardous’, respectfully. These ratings are determined by the severity of the effect on the system/customer, the potential for property damage, and the potential injury hazard. 3) Probability of Occurrence Rating The probability of the occurrence of each outlined failure mode has been determined based on the FMECA Probability of Occurrence Rating Scale and illustrates how likely a determined failure mode may or may not occur. Spanning from ‘Extremely Remote’ to ‘Occasional’ to ‘Extremely High’, this is also based on a scale from ‘1’ to ‘10’, respectfully. 4) Probability of Failure Detection Rating This rating is based on the FMECA Probability of Failure Detection Rating Scale and is used to determine how likely it may or may not be to detect a potential failure mode before actual failure or malfunction actually occurs. It ranges from ‘Almost Certain’ to ‘Moderate’ to ‘Almost None’. Also based on ‘1’ to ’10’, the scale defines more detectable failure modes to have a higher number than less detectable failure modes. 5) Risk Priority Number The Risk Priority Number (RPN) was determined from the product of the previously determined failure mode severity, probability of occurrence, and probability of detection ratings: [(severity) X (prob. of occurrence) X (prob. of detection)]. This calculated value ultimately determines the overall priority of system risks and influences what and how