We have recently put our electric formula SAE race car on the dyno. It has the following equipment
82 x 31Ah Dow-Kokam LiPo cells (300V nominal)
MES-DEA TIM600 controller
EVE M2-AC30-L motor (30kW nominal, 60kW peak)
There has been some interesting problems with our motor and controller in the past (see here http://www.diyelectriccar.com/forums/sh ... 52606.html or here viewtopic.php?t=2377&start=1) but we think we have gotten past the problems by running some series inductors on the phase leads.
So anyway, had the car on the dyno a few days ago for the first time; but with our rated settings, we were only producing less than 20kw which was less than exciting. We then slowly increased the current with interesting results;
From this we can depict that changing the voltage had no effect on the power output, but increasing the current did. However we were running the motor at its max current, and even over rating it without getting anywhere near the max power we were hoping for.
But the most interesting finding, which you may have already noticed, is the last two power and torque values... The occurred by increasing the maximum allowable motor speed from 5000RPM (nominal speed 175Hz 4-Pole) to 6000RPM.
It seems in field weakening area the motor power and torque shoots up beyond belief and the car almost jumps off the dyno!!
This shouldn’t be happening, so why is it? During field weakening you should be at your max voltage, and then to increase RPM, all you can do is increase the frequency which effectively decreases the v/f ratio. This tells me there is a v/f problem, that’s causing the motor to run incredibly inefficient before field weakening. However it would suggest the voltage is too high, yet we are already running it well below the manufacturers stated v/f setting (205V nominal 288V peak 105A 175Hz). But why didn’t changing the voltage in previous tests affect the power produced? The motor is drawing maximum current up until this massive surge, where it just takes off. Another interesting point is the manufacturers motor specifications say its peak power should be just after 3,000RPM, yet we are seeing it over 5,000RPM!
Another thought is that the motor could be running at the rated voltage at nominal speed, and then using the max voltage (which was set to 150% of Vnom) to enable the motor to spin faster without field weakening. This could have increased the v/f ratio at the nominal speed to a more efficient ratio. But again, why didn’t changing the voltage previously have any effect on the power?
This definitely is very confusing and unusual. Any help would be greatly appreciated!
