So I’m in the process of making my own simplefoc board and I’m wondering what happens if i spinn a motor and want to break it abruptly.
I assume the DC bus voltage would rise because the motor is back feeding trough (in my case a igbt module) to the DC bus. (Correct me if I’m wrong here)
To stop the voltage from going to high (and damaging something) in the DC bus what would be my options?
This is what I think is possible:
Tvs diode
MOV
Resistor that is switched across the DC bus with separate igbt/mosfet.
Are there any other options?
My smallest rated component is 600v and operating voltage is around 320v Or maybe 500v but most likely 320v.
I think there’s another option. I have not experimented with this myself, but you could monitor the DC bus voltage and if you detect an over-voltage command a non 0 value to the D current phase for the time the over-voltage is present. This means you “dump” the energy into the D phase and pretty much convert the energy to heat.
David is (I think) referring to the D & Q components of the motor’s coordinate system when commanding with FOC.
The FOC algorithm normally tries to maximize the Q component, as this drives the motors rotation. If you instead maximized the D component during the breaking period, the energy would be “lost” (spent as heat in the motor or holding it in position).
In my setups motor heat is a problem, so I would not want to do this, but in other situations one might have reserves that make this a viable strategy.
What I am wondering is whether this alone is sufficient, or you would need additional protection anyway for the case the voltage rises too quickly?
My current thinking is to use a voltage divider to measure the DC bus voltage and then pwm a igbt with a breaking resistor, like the odrive does. Also I’m putting a MOV on the DC bus as well with the correct rating for the voltage the driver is working with.
I’m not sure there’s any other way noticing an over-voltage event. Maybe always commanding a non zero value for D every time you’re breaking might be a way to do it, maybe through experimental data one could determine the optimal way to do so.
Take a look at these resistors.
They aren’t that expensive, but will need a “valve” mosfet, in order to dissipate or burn the heat in the resistor.
Like the Odrive, yes…
When using a battery, im contemplating a way to use a boost circuit to raise the voltage to charging voltage, if the motor kv does not allow charging in normal use. Any ideas regarding how to implement a boost circuit is most welcome. On a side note, there is no doubt in my mind about the need for a boost button on my bike setup. That would, depending on motor and controller temperature allow a 10sek increase in winding current. This makes sense on a steep climb where you need that extra power. Kinda like mariocard.
F*** the law, it is our duty as citizens to investigate new methods.
Edith: Coming from a EU citizen where 250w is the limit on non speed pedelec bikes. “Cycles with pedal assistance which are equipped with an auxiliary electric motor having a maximum continuous rated power of 0.25 kW, of which the output is progressively reduced and finally cut off as the vehicle reaches a speed of 25 km/h (15.5 mph) or if the cyclist stops pedaling.” WTF!
So 250w is average power right? Well then we are in the golden zone. 750w boost for 10 sek. shouldn’t make much difference.
