Question about Regenerative Braking Parameters

[KevinD]

Hi, I'm new here and have a question about setting regenerative braking parameters.

We have a VEC300 controller and are configuring it using the PI-800 software (V3.1.3). I assumed that the EBS Reverse Charging Voltage (V) and EBS Reverse Charging Current (A) parameters set the maximum regen voltage and current used to charge the battery. However, when I tested the actual voltage and current using a multimeter, they did not even come close to the values I set. For example, when I set EBS Reverse Charging Voltage (V) = 60 and EBS Reverse Charging Current (A) = 10, the actual voltage and current measured were ~53V and ~0.7A.

I'd like some advice on if I'm changing the correct parameters, and if so, am I setting the correct values? Thanks!

[Bikemad]

Hi Kevin andto the forum.

I'm pretty sure that you are adjusting the correct parameters that should set the maximum voltage and current allowed during regenerative braking, but I'm not sure how fast the motor would have to be turning before it is likely to reach the set voltage and current limits.

The EBS function (Electronic Braking System) basically allows the motor to be used as a non-frictional braking device to assist the mechanical brakes, and if the motor is turning fast enough it can also produce surplus energy.
This surplus energy is allowed to flow back into the battery without exceeding the preset maximum current and voltage values.

Is it possible that you have not been braking at high enough speeds to produce much regen current?

The hub motors fitted with the internal vector controllers seem to immediately produce plenty of electromagnetic dynamic braking force the instant the brake switch is operated.
However, at lower speeds (below 15mph) I noticed that the motor doesn't actually produce any noticeable current (even though the braking effect is very strong) whereas braking at higher speeds can produce a large amount of current.

I used two wattmeters connected in series to measure the maximum motor drawn current and regen current throughout the ride, one is simply wired in reverse (battery on LOAD side and motor on SOURCE side) to enable the regen current to be measured:



Maximum wattage was 892.8W under power and 567.4W generated during regen @ 21.87mph with ~31V battery voltage.
Maximum current was 29.98A under power and 17.92A produced during regen.

I tried the same test later when the battery voltage had dropped and the regen result was much higher:

Maximum wattage was 798.2W under power and 805.2W generated during regen @ 20.00mph with ~30V battery voltage.
Maximum current was 27.46A under power and 26.12A produced during regen.

It would be interesting to see some dynamometer style testbed figures showing current and voltage output from the EBS function in relation to the actual motor rpm.

Alan
 

[KevinD]

Hi Alan, thank you for your quick reply. I think you're right; we have only been testing the motor without a load, so perhaps that is why we are getting lower readings.

However, if the EBS Reverse Charging Current does control the limit of the current, we are a bit worried about accidentally setting it too high, since we found that in general the PI-800 software does not warn the user if an incorrect value is configured (say for example, if we accidentally entered FFF as an input). What would happen if the user inputs a value outside of the allowable range for a parameter? If I enter a value of 80A for the current limit were the max permissible is only 20A, would the software just ignore my input, or would it saturate it at 20A, or something else?

Also, on a related note, when the VEC300 does limit the energy going back to the battery, where does the extra amount go? Is it converted into heat in the motor/controller, stay as kinetic energy in the wheel or something else?

Thank you!

[Bikemad]

Hi Kevin,

I have only used the Pi-800 software with the internal vector controllers fitted to the GM hub motors, and these will not store values outside the acceptable range. If the range is 20-80 Amps and I try to enter a higher or lower value, an error message stating "Invalid Value" appears when I try to save the parameter settings to the controller.

Regarding the excess energy, I would have thought that the VEC300 controller would simply reduce the power being absorbed by the battery from electromagnetic dynamic braking force to prevent generating too much current/voltage in the same way that the Vectrix controller on the VX-1 Scooter does.

I find that my Vectrix produces very little regen braking force when slowing down with a freshly charged battery, and I have to also use the mechanical brakes to slow up at the first couple of junctions etc.. But when the battery voltage drops below ~140V, the braking force increases significantly, to such an extent that I no longer need to use either the front or rear disc brakes as it slows down relatively quickly just using the regen on its own.

Alan
 

[KevinD]

Hi Alan,

One last question on this thread. Perhaps the reason why we are not getting the "Invalid Value" error message is because our Pi-800 software and VEC300 controller are having issues talking to each other. When we plug in the controller and click the connect button in the software, a "Controller Version Incorrect" message appears. When we attempt to load parameters from the controller, no numbers show in the columns. Strangely enough however, when we enter numbers into the columns and attempt to save them to the controller, they do seem to have an effect (they just disappear visually from the columns when we are done saving). I have attached a picture to show what we are seeing.

Would you have any idea why we are getting this behaviour from the software? Is there another specific version we must download for the VEC300?

Thank you!

[Bikemad]

Hi Kevin,

As I don't have a VEC controller to test, I don't know whether it is a PC problem, a controller problem, a software problem or perhaps the USB cable itself.

I have attached another version of the programming software for you to try, but I don't know whether it will make any difference. 

Alan

[KevinD]

Hi Alan,

Thanks for all your help! We'll try out the version you sent and hopefully that will resolve the issue.