# Is Throttle signal a Voltage command or Current command



## praveen (Feb 17, 2015)

Hi 
I am building EV motor controller. Need help regarding the control algorithm of the motor.

*Setup Details: *For the sake of simplicity lets consider
1) Brushed DC motor.
2) 100Volt battery Voltage
3) 100V, 1000Watt Continuous power(Rated 10Amp continuous current motor)
4) NO Speed sensor
5) Current(Torque) sensor on the Controller available.

*Doubts:*
1) Should the Throttle signal be considered as
a) Voltage command (From 0- 100V) ..??
b) Current Command (From 0 - 10Amp)...??

2) If Throttle signal is Voltage command.
a) How is the Surge/Peak current controlled. (Mainly required to overcome inertial torque during STOP to START and even during climbing uphill.)

3) If Torque Command(Current control)
a) Is Full throttle to be programmed as 10Amp Command Current..??
If so, during STOP to START the Throttle needs to be almost completely ripped to get the Max Torque from the motor (10Amp) to overcome the high inertial torque.

Is my above analysis correct..?


Please shed some inputs regarding the best possible control algorithm to safe guard both the motor and Controller and have a better riding comfort.

Thank in advance.....


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## Sonikaccord (Dec 17, 2012)

It would be voltage controlling through the use of PWM. 

Full throttle would be 100% duty cycle so everything in between would be 0-99%

The nature of the DC motor is that it draws lots of current(torque) when the rotor is locked (at a standstill) so the PWM regulates the percentage of voltage that the motor sees. As the motor begins to rotate the back-emf will counter the pack voltage and also reduce the current until pack voltage=back-emf, in theory of course. There are other losses to consider.


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## Duncan (Dec 8, 2008)

Hi Praveen
The normal system is that the throttle controls motor current

In my car the throttle is a 0-5Kohm potentiometer that provides "Current demand"
0 ohms = 0 Amps
1Kohms = 200 Amps
2Kohms = 400 Amps
3Kohms = 600 Amps
4Kohms = 800 Amps
5Kohms = 1000 Amps

This provides a "demand" my controller will change the Pulse width until the current sensor in the controller matches that "demand"

As the motor rpm rises more voltage will be required for a given current 
the controller will increase the pulse width to maintain current

From a drivers point of view I have a throttle that directly controls torque


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## dougingraham (Jul 26, 2011)

As Duncan indicated an EV motor controller is a torque control. And since current almost directly tracks torque controlling current makes this easy.

The good motor controllers will regulate motor current (torque) but also regulate the following as part of the control loop.

1) Battery voltage (low).
2) Battery current.
3) Motor RPM.
4) Semiconductor switch temperature.
5) Rate of motor current change (slew).

Additionally you should consider inputs for:

1) Sensing brake pedal operation for safety shutdown.
2) Reverse for current limit because in lots of vehicles the reverse gears are weak and you don't ever need to go fast backwards.
3) Valet mode (or as Jack Rickard calls it Daughter mode) to set additional restrictions on output.

Good luck with your project!


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## praveen (Feb 17, 2015)

Hi all thanks for the quick reply.
Duncan thanks for providing the specifics of ur system.

Duncan considering your system 
At max throttle the current is limited to 1000Amps.
1) Is 1000Amps max continuous current that ur motor can handle without any damage...??? Or something like 1000amps for 10secs or 15secs.

2) For my system as motor continuous rated current is 10amp, should my full throttle correspond to 10amp or something like 20amp for 15secs etc..???


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## Duncan (Dec 8, 2008)

Hi Praveen

My motor has a one hour rating of 10Kw at 48v - about 200amps

General thoughts are it should be good for about 180v and 1000amps for 15 seconds


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