MIL-HDBK-1003/3
APPENDIX D (Continued)
(4)
High voltage spikes to motor windings.
(5)
Load dependent; poor for multimotor
applications.
(6)
Poor input power factor due to SCR converter
section.
D-1.04.3 VSI Design. The VSI drive is very similar to a CSI
drive in that it also uses an SCR converter section to regulate
DC bus voltage. Its inverter section produces a six-step output,
but is not a current regulator like the CSI drive. This drive is
considered a voltage regulator and uses transistors, SCR's, or
gate turn off thyristors (GTO's) to generate an adjustable
frequency output to the motor.
a)
VSI's have the following advantages:
(1)
Basic simplicity in design.
(2)
Applicable to multimotor operations.
(3)
Operation not load dependent.
b) As with other types of drives, there are
disadvantages:
(1)
Large power harmonic generation back into the
power source.
(2)
Poor input power factor due to SCR converter
section.
(3)
Cogging below 6 Hz due to square wave output.
(4)
Non-regenerative operation.
D-1.04-4
Flux Vector PWM Drives
a) PWM drive technology is still considered new and is
continuously being refined with new power switching devices and
smart 32-bit microprocessors. AC drives have always been limited
to normal torque applications while high torque, low rpm
applications have been the domain of DC drives. This has changed
recently with the introduction of a new breed of PWM drive, the
flux vector drive.
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