1、Best Practices Entry: Best Practice Info:a71 Committee Approval Date: 2000-04-24a71 Center Point of Contact: KSCa71 Submitted by: Wilson HarkinsSubject: AC - Variable Frequency Drive Systems Practice: During the design of new or modifications to existing systems requiring motor speed control, consid
2、er the use of alternating current (AC) variable frequency drive systems for motor control.Programs that Certify Usage: This practice has been used on Launch Complex 39A an orderly shutdown is performed.d. Commutation: Commutation is a process by which an SCR is forced out of a conducting state by re
3、verse biasing. Two types of commutation normally occur in the power circuit, natural and forced.e. Regeneration: The SCR converter is a two-quadrant device capable of accepting power from the DC bus and returning it to the line when the DC bus potential is negative. This capability makes the current
4、 source inverter one of the few inverter types that are inherently regenerative without excessive circuit complication.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-f. Low speed cogging: Each commutation in the inverter module causes the current fl
5、ow to the motor to be abruptly stopped in one phase and started in another. This action forces the motor to turn one-sixth of a rotation on a 2-pole machine, one-half on a 4-pole machine, etc. This explains why, at very low speeds, the motor appears to move in discrete steps rather than smoothly rot
6、ate. At a frequency of 1 Hertz, for example, a two-pole machine would perform one complete rotation in six distinct steps at a rate of six steps per second. This effect is reduced depending on the inertia of the connected load. The visual effect completely disappears at speeds above a few Hertz.Refe
7、rence:1. KSC Electrical Advanced Schematic Drawing 79K06382.2. KSC Electrical Advanced Schematic Drawing 79K40029.Impact of Non-Practice: Variable frequency drive systems are installed at the Shuttle launch pads at KSC. The system allows for a direct coupling between the main propulsion system liqui
8、d oxygen pump and drive motor. This eliminates the motor clutch system, a high maintenance item, and gaseous nitrogen lines used to purge the clutch system.Related Practices: N/AAdditional Info: Approval Info: a71 Approval Date: 2000-04-24a71 Approval Name: Eric Raynora71 Approval Organization: QSa71 Approval Phone Number: 202-358-4738Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
