Electrical Engineering of "coupling" the range-extender to the BEV

[terry.kane]

Use this topic to post questions and answers about how best to couple the genset to the BEV, from an electrical standpoint.  How do we prevent the motor from trying to draw more current out of the generator than it is capable to provide?  Todd Dore mentioned stalling his gas genset when he tried to direct-couple it to "Electric Blue".

We've toiled over this one in the meetings, wishing we had an electrical engineer in our midst to help us through the apparent challenges of coupling the battery/controller on the vehicle to the incoming supplemental power coming from the range extender (genset).

It looks like Manzanita Micro may already have this figured out, with their PFC Series chargers.  The description mentions that the units include a "throttling" feature which allows one to limit the current the charger will draw out of the source.

http://www.manzanitamicro.com/chargers3.htm

Sounds like the only problem with MM is they can't deliver when you order.  And the fact that the PFC-50 is $3,600!

[miodrag.zubic]

Well, in general terms, in order to maintain/control/limit the amount of current drawn from the genset there has to be either
1. throttle control that adjusts the rpm of the genset to acheive the desired current flow into batteries, or (and/or)
2. An electronic device capable of controlling its input current (charger in case the genset has an AC motor, DC-DC converter if its a DC genset)

It sounds like you already have an AC genset and a charger in mind. That sounds like a good way to do it. Only, I guess finding a charger that is not as expensive as MM (or a more affordable one that can be altered to limit its input current) is the challenge.

Have you chosen the genset?

[terry.kane]

Hi Miodrag,

We'd love to have you join in on the discussion and participate in the planning & implementation!  I think our envisioned mode of operation will dictate that the genset never run until its full output can be utilized.  That means we will tune the genset to run at its optimum economy while producing output capable of most or all of the current demand of the EV while cruising along. 

So in the long-range mode of operation, the vehicle could run as a true series hybrid with indefinite range.  That's a worst-case scenario from an environmental standpoint but it's our design goal.

This also means that the genset will never run unless the battery is discharged to a level where it can begin to take the full genset output as a charging current.  For example: you have 40 miles range on your battery alone and you have a 50 round-trip mile commute, with no opportunity charging at the turn.  You would drive to work and start the genset at, say, the 15 mile mark.  This way, no matter if you are cruising (consuming the full genset output) or stop-and-go (alternately charging or feeding the motor), none of the genset's output would be wasted.  When you arrive at mile 25, the genset can continue running until the full charge is attained, then it will shut down automatically.  On the return trip, the genset stays off and you plug in at home to recharge for tomorrow.

The reason for the long-winded example is that we don't envision throttling the output of the genset.  Instead, we want to limit the draw of the motor on the genset to its actual output.  If the genset can produce 20kW, then any demand by the motor/drive above 20kW would have to come from the battery pack (like during hard acceleration).  Conversely, we would want the "coupling means" to be able to feed excess current not demanded by the motor into the batteries (like during a stop, deceleration, low speed driving).

The reason for all of this management of constant output of the genset is to make maximum/optimum use of every drop of (fossil) fuel.  This can be best accomplished by tuning the ICE to the perfect RPM for efficiency/minimum emissions and then running it as little as possible in the various modes of operation.

Bottom line: we need your help in figuring out how to limit the motor's draw on the genset to its optimum output level!

[nathan.stowe]

Hi guys,

When optimizing the electronics for the generator, please keep in mind that unless the generator is running a wide open throttle, the ICE is probably not working at an optimum efficiency.  So hopefully the generator can be sized appropriately.

It would be relatively easy to map out the efficiency of the generator set.  I did a project in college where which involved a generator where we made simple measuring devices to measure the efficiency base on power output and fuel flow rates. The fuel flow rate can be measured by by putting all the fuel in a remote tank and recording its weight at timed intervals.  The power output can be measured by a heating element and measuring the voltage with a simple P=I^2R relationship.

If you need a hand with this project, let me know.

Nathan.