From: gunnarhs on diyelectriccar forum
Hi, as stated from members before , the dyno tests starts at 70V /4000 RPM with very low load. At this point efficiency is very low (30-40%)
When more load is applied (holding voltage, and rpm "constant" ) amperage, torque and efficiency increases, efficiency up to 80%.
The highest efficiency should be near base-speed of motor (which is??) and under full load. For a PM-AC this should normally be about 90%.
So I assume that either
1) The motor is not fully loaded
2) The base speed is not 4000 RPM
And now to the FOC - algorithm which holds the voltage/rpm "constant" under different load. Assuming magnets are in the rotor you apply three AC phases to the stator which are typically 120 degree shifted.
When adding the three components (either in rotor or stator frame) you get 2 currents Id and Iq (and two corresponding magnetic fields induced by this currents) which are 90 degree shifted.
One magnetic component is parallel to the magnetic rotor field (induced by Id), the other to the stator coil field (induced by Iq). Together they produce the torque required for the rotation of the load in addition to the magnetic field of the PM present:
T = k1*Iq X (k2*Id + Bpm),
k1 and k2 are constants based on stator inductance,Bpm is the PM-field
For PM-machine the present PM-field in the rotor is usually strong so you try to keep the current Id as little as possible to simplify control.
That leaves Iq as the torque determining component (Id -> 0):
T = k1*Iq X Bpm, with Bpm the constant field from the PM.
As load increases, Iq is increased, this works up to base speed.
Over base-speed Id must be set negative to produce a field opposing Bpm.
From Riwe on diyelectriccar forum
During testing we took some logs as well. Both Iq and Id was monitored and we saw that the highest motor rpm without applied Id is approx. 1650 rpm. This is using a 48V controller.
The picture on the bottom shows the motor running at approx. 2400rpm. Id applied is at the moment -138 A. We can also see that Id is not present until approx. 1650rpm.
As I was told the base speed is dependent on the voltage of the controller. If I would use a 72 Volt controller the base speed would be higher because the controller can handle a higher voltage from the motor before applying Id.
Id in motenergy motors are “normally” (I’ve seen this value in 3 different configurations from Sevcon) set to -200A and we hit that value during our tests. If we increased the Id we got a higher RPM.
I would think that even if I dont run the motor at 72volt the efficiency would be higher and as Major said motenergy claim up to 92% between 24-72V.
I guess there is something wrong with either my config or the way we measure.
To be continued...
Thank you all!
Rikard