February 2010 Modern VVVF Drives
SPECIAL NOTICE: Please check each course for verification of approval before purchasing. This test is based on the article, Electrically Assisted Braking Using DC Hoist Motors published in the February 2011 issue and counts as two contact hour (0.2 CEU) of elevator-industry continuing-education credit. Most courses are approved by NAEC for CET/CAT and NAESAI for QEI and in the following states: Alabama, Arkansas, Florida, Georgia, Illinois, Indiana, Kentucky, Maryland, Mississippi, Missouri, Montana, Oklahoma, Pennsylvania, Vermont, Virginia, Washington, West Virginia, Wisconsin. Learning Objectives - After reading this article, you should have learned:
- Elevator AC and DC motors, when applied to several different types of drive/control designs, have the capability of regenerating electrical energy
- The regeneration of electrical energy can provide a braking torque from both an AC and a DC motor to decelerate the mechanical load on the motor shaft
- For DC control, the typical designs of the loop circuit and the effects on emergency stopping when the loop circuit is kept closed and it is opened during the stop
- The difference between regenerative and dynamic braking as applied to both AC and DC motors/drives/control systems
- The control methods by which elevator AC motors can provide a braking torque
- During typical elevator emergency stops (e-stops), both the elevator machine brake and the regenerative or dynamic braking contribute to the total braking effort on the system
- The sequence of events during a typical e-stop
- That there are many elevator system parameters in play at the time of thee-stop, and that they influence the deceleration rate of the stop
- There can be mechanical and electrical design conflicts for emergency stop braking systems when considering balancing ride quality issues during the stop with the effectiveness of making the stop
- Looking forward, there are many design challenges to develop the optimum elevator braking systems that provide acceptable performance during an e-stop under all elevator operating conditions
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