Watt Control Via Duty Cycle Control?

General topics and discussions about the VESC and its development.
devin
Posts: 255
Joined: 08 May 2017, 01:55
Location: San Francisco, California, US

Re: Watt Control Via Duty Cycle Control?

Postby devin » 19 Sep 2017, 12:41

pf26 wrote:Watt control from the battery is already implemented, since you can configure a limitting max battery current, and the battery voltage should be very stable.
If you give enough throttle, the duty cycle and motor current will be determined by the max battery current, ie watt-control.
It might be interesting to have the throttle control the battery max current parameter instead of duty cycle or motor current. It should be quite easy to create a custom app doing this.


@pf26 lipos are usually somewhere between 4.2v and 3.2v per cell while discharging...

using 12S that's a range of 50.4V to 38.4V during a single pack discharge...

if a person simply selects a 10a battery amp limit.... at start of discharge thats 504w, but at the end of discharge that is only 384w... that is an unacceptable 23.81% decrease in wattage, power & vehicle performance from start of discharge to end of discharge. wattage control is not currently implemented but solves the problem by providing constant watts -- regardless of voltage sag -- by effectively increasing the battery amp limit when the voltage sags enabling constant watts "availability" at all physically possible rpms (including very close to 0rpm, and including when the voltage sags).

pf26
Posts: 305
Joined: 28 Mar 2016, 14:37
Location: FR Valence

Re: Watt Control Via Duty Cycle Control?

Postby pf26 » 19 Sep 2017, 15:50

I guess you won't stay long at 4.2 Volts, and not at 3.2 Volts either. I may even be cool to warn the user by decreasing the available power when the battery goes low. Anyway, if this is unacceptable for you.. With an open source code, and so much CPU ressources, nearly everything is possible.

rew
Posts: 943
Joined: 25 Mar 2016, 12:29
Location: Delft, Netherlands.

Re: Watt Control Via Duty Cycle Control?

Postby rew » 21 Sep 2017, 03:27

Yes some loss of power is a very intuitive signal to the user that the battery is nearing its end.

devin
Posts: 255
Joined: 08 May 2017, 01:55
Location: San Francisco, California, US

Re: Watt Control Via Duty Cycle Control?

Postby devin » 21 Sep 2017, 15:32

pf26 wrote:I guess you won't stay long at 4.2 Volts, and not at 3.2 Volts either. I may even be cool to warn the user by decreasing the available power when the battery goes low. Anyway, if this is unacceptable for you.. With an open source code, and so much CPU ressources, nearly everything is possible.


rew wrote:Yes some loss of power is a very intuitive signal to the user that the battery is nearing its end.


@pf26 @rew... a decrease % in desired wattage when the battery reaches a certain state could be programmed if desired. another solution is voltage display on the vehicle.

devin wrote:A= XX.XXXA = Battery Amps
B= XX.XXXA = Motor Amps
C= 54.795% Duty Cycle
D= 22.22222V = Present Back Emf V
E= XX.XXXV = Effective PWM Voltage
F= 0.083ohm = Winding Resistance
G= 46.5V = Pack Voltage
H= 1000w = Desired Wattage

I= XX.XXXkv = Motor KV
J= XX.XXXrpm = Present RPM

C=(50(sqrt(D^2+4*F*H)+D))/G


^ @rew roughly how many times per second could a vesc run this equation in theory?

rew
Posts: 943
Joined: 25 Mar 2016, 12:29
Location: Delft, Netherlands.

Re: Watt Control Via Duty Cycle Control?

Postby rew » 21 Sep 2017, 21:39

20k should be enough.


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