Combustion Engine/BLDC generator

Support for creating custom user applications on the VESC.
polo
Posts: 8
Joined: 24 Feb 2016, 09:53
Location: Lyon, France

Combustion Engine/BLDC generator

Postby polo » 24 Feb 2016, 12:00

Hi everyone,

Thank you for this wonderfull platfrom and great hardware, I am really looking forward to test it.

I have in mind a little of track application for it :
I plan of using a BLDC motor as a generator for a combustion engine :
Image
The point would be to be able to start the combustion engine through the BLDC and then to use the BLDC as an alternator. The contexte is to use is as a lightweight electrical generator (about 1 kW) for RC applications.

I understand the VESC has a regenerative brake feature enabled and my question is :
Would the VESC work as a alternator controler for the BLDC and how will it handle voltage variation (is it possible to set the DC voltage output ?) ?
The goal would be to have a fixed DC Voltage output from the VESC (seen from the battery).

Is this possible with the VESC as it is today or I am missing something here ?

Thank you for your answers :)

itman496
Posts: 15
Joined: 28 Jan 2016, 09:41
Location: NJ, USA

Re: Combustion Engine/BLDC generator

Postby itman496 » 24 Feb 2016, 18:32

You know I was thinking about this very thing the other day. Im glad someone else was. You'd have a perfect rectifier that would also be controllable. No diode drops, and constant voltage. Very interesting.. I saw a dyno project that used the variable braking, so.. I don't know why it WOULDN'T work..

polo
Posts: 8
Joined: 24 Feb 2016, 09:53
Location: Lyon, France

Re: Combustion Engine/BLDC generator

Postby polo » 25 Feb 2016, 10:16

Hi, thank you for your reply.

Yes, I'm glad you think the same about this project. But my concern would be : how to set the DC voltage output from the VESC ?
Is it something I can modulate or will it be set by the DLBC RPM ?

izil
Posts: 1
Joined: 28 Feb 2016, 16:33
Location: France

Re: Combustion Engine/BLDC generator

Postby izil » 28 Feb 2016, 17:17

Hi polo,

I'm planning to use the same setup for the same application, but at 4kW with two motors and two VESCs.
I don't know exactly the regen capabilities of the VESC, but I know how it works on hybrid and electric race cars (it's my job).

-The battery is the reference voltage of the circuit
-You control the regen current only
-To work at "fixed" voltage, you need to use a closed loop regen current regulation based on the battery SOC (state of charge)

I hope my answer is clear :D

benjamin
Site Admin
Posts: 280
Joined: 15 Dec 2015, 08:38
Location: Sweden
Contact:

Re: Combustion Engine/BLDC generator

Postby benjamin » 29 Feb 2016, 09:52

Using the VESC to control a motor as a starter and generator for a combustion engine should work perfectly, and I happen to be building a setup with this exact application at home :-)
I will post some details and my custom application soon.

polo
Posts: 8
Joined: 24 Feb 2016, 09:53
Location: Lyon, France

Re: Combustion Engine/BLDC generator

Postby polo » 01 Mar 2016, 09:05

Hi benjamin,
That is great, I'm really looking forward to see it !

And thank you izil for your answer. I plan to use it with small lipo battery in parallel so I won't have any SOC information except the battery pack voltage.
But do you have an exemple of what a "closed loop regen current regulation" would look like ?

My basic idea would have to have a fixed voltage around 4,2V-4V per cells to keep the battery charged without overcharging it over a long period of use.
Would I need a DC/DC converter then to set the voltage level then ?

Storken
Posts: 4
Joined: 30 Apr 2016, 19:45
Location: Norway, Tr.heim

Re: Combustion Engine/BLDC generator

Postby Storken » 09 May 2016, 09:58

Any progress, gents?

sagaris
Posts: 6
Joined: 14 Sep 2016, 15:33
Location: Kyiv

Re: Combustion Engine/BLDC generator

Postby sagaris » 27 Sep 2016, 20:02

While awaiting for my VESC 4.12 and meaning to use it for ICE generator I have few questions.

BLDC have virtually linear Voltage/RPM ratio. When in generation quadrant BLDC will generate voltage with the same dynamic range as ICE does. So if my RPMs on ICE shaft varies between 2000 and 7000 (RPMmax=3.5*RPMmin) then BEMF voltage will be of that range Vmax=3.5*Vmin. If thinking of MOSFETs working as rectifier diodes than BEMF will only open diodes when output voltage will be higher than battery one. So battery will charge only when RPMs will be higher than in direct mode with battery voltage. But battery charge has smaller dynamic range (Vbatt_max=1.25*Vbat_min).

If it's so than we have two consequences:
1. BLDC will not charge battery at low RPMs;
2. ESC can't regulate output voltage and high RPMs can lead to overcharge battery with higher voltage.

Did I miss something or think wrong? I also find an Microchip presentation on this moment but haven't study it well yet. http://ww1.microchip.com/downloads/en/D ... Motors.pdf

arvidb
Posts: 201
Joined: 26 Dec 2015, 14:38
Location: Sweden, Stockholm

Re: Combustion Engine/BLDC generator

Postby arvidb » 28 Sep 2016, 10:28

The battery will charge as soon as you start regenerative braking, even if BEMF is lower than the battery voltage. The VESC acts as a DC/DC converter which adapts the output voltage to the battery voltage. Pin = Pout so that BEMF * Imotor = Vbat * Ibat - or put differently, Ibat = (BEMF * Imotor)/Vbat.

You should probably run your ICE (Internal Combustion Engine) at the rpm and torque where it is most efficient, and select a battery which can absorb the resulting power. You need to find a way to detect when it's time to stop charging the battery so that the ICE can be turned off before the battery gets overcharged.

You could probably write an app for the VESC which uses the measurement of regenerated power already done by the VESC to control the ICE, for example via a RC-servo control signal, so that the power is constant. This same app could also turn the ICE off when the battery voltage gets too high.

sagaris
Posts: 6
Joined: 14 Sep 2016, 15:33
Location: Kyiv

Re: Combustion Engine/BLDC generator

Postby sagaris » 28 Sep 2016, 10:41

arvidb wrote:The battery will charge as soon as you start regenerative braking, even if BEMF is lower than the battery voltage. The VESC acts as a DC/DC converter which adapts the output voltage to the battery voltage. Pin = Pout so that BEMF * Imotor = Vbat * Ibat - or put differently, Ibat = (BEMF * Imotor)/Vbat.

Up to what battery voltage it is adapted? To Input Max Voltage, actual battery voltage, other? Will VESC decrease output voltage on high RPMs? Or output voltage is regulated up and down via backward current control?
arvidb wrote:You should probably run your ICE (Internal Combustion Engine) at the rpm and torque where it is most efficient, and select a battery which can absorb the resulting power. You need to find a way to detect when it's time to stop charging the battery so that the ICE can be turned off before the battery gets overcharged.

You could probably write an app for the VESC which uses the measurement of regenerated power already done by the VESC to control the ICE, for example via a RC-servo control signal, so that the power is constant. This same app could also turn the ICE off when the battery voltage gets too high.

I may set the task unclear. I talk about ICE driven UAV. It's not truly hybrid vehicle. ICE is used for propulsion and BLDC generator is used for onboard equipment powering and battery charging. Since ICE is a UAV propulsion autopilot controls ICE RPMs regarding speed and altitude. During the flight RPMs can very between highest at takeoff and climb and lowest when idle or descending. Also we can't turn off ICE at all.

As far as I understand I have to choose BLDC's KV with maximum BEMF not exceeding battery voltage and manually control reverse current regarding battery voltage.


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