Quote:
Originally Posted by Al Skierkiewicz
Joe,
Your response triggered something else I had forgotten. The Jaguars have a much higher switching frequency than the Victors (15kHz vs 15o Hz for the Victors). As such the inductance of the motors play into the rise times of the pulses supplied to the motor. This effect is particularly nasty at low throttle values but the effect is a more linear response of throttle command to motor speed than in the Victors. Due to the effects of the inductance, small motor pulses cannot reach full battery voltage during the pulse width.
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I've seen this a number of times in my automotive experience. We get a door working at 100 or 400Hz PWM frequency, then in the middle of a program, someone decides that that hum has just got to go... ...so we switch the PWM frequency to 8kHz or 10kHz or in one case 20kHz, but the system inevitably has some flaky behavior. The culprit is usually the effect you discuss.
Essentially, changing to the higher PWM frequency screws up all the motor calibrations for low duty cycles. A 10% duty cycle at 100Hz is a 10msec pulse which is FOREVER for these small PM motors so they get up to "full speed" in less a single pulse. Not true for a 10% duty cycle at 10kHz (= a .01msec pulse).
On the ups side, velocity control at low loads usually improves (for the same reasons only in reverse).
It's all good...
Joe J.