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modelling bidirectional dc-dc converters for hybrid vehicles

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Nickys13

New Member
Hello everyone, I would be very grateful if I could have some advice regarding my project.

My task is to connect the HV battery of a plug in series hybrid vehicle to the motor using the appropriate converter. I will need to boost the voltage from approximately 280V to 700V. This connection needs to be bidirectional because the motor is operating as a generator during regenerative braking and needs to charge the battery back. However the generator's output is Ac so I will need an Ac/dc inverter as well.

the last part is to connect another generator driven by the Internal Combustion Engine to charge the battery but also with the ability to drive the motor directly.. This will need another ac/dc inverter.

For the first part I was thinking of an isolated bidirectional dc-dc converter followed by a buck boost. I would like to ask if you know any literature that give a similar solution to this problem, preferably sources that provide all the relevant equations.
Also I would be pleased if I could find some relevant simulations of the above converters in Simulink.

I can provide the vehicle's schematic which shows all the relevant connections and also the simulink files of the motor and the generators upon request, if you need it to offer any advice.

Thanks a lot in advance!
 

MikeMl

Well-Known Member
Most Helpful Member
Let me guess. This is GM's strategy to come out of bankruptcy :D :D :D
 

Nickys13

New Member
I am a 4th Year student, unfortunately I am not much of an expert. I will have to come up with a few ideas - solutions to the problem and try to simulate them in simulink by connecting the already designed motor and generator.

The motor is a Permanent Magnet Synchronous Motor which is a Brushless DC motor that uses a synchronous mode of operation. I am not required to know about it in detail, it just needs to be supplied by constant voltage of 700V as previously mentioned. This is a bit higher than usual but not surprising- common value is around 600V.

Someone mentioned to me that it is too much of a step -up in voltage. How about making this in 2 steps if this poses a problem?

As for the isolated converter, it is not a requirement I had just come accross a few papers suggesting this. Do you have any simulations in simulink of bidirectional converters, buck-boost or ac/dc inverters?



Thanks
 

tcmtech

Banned
Most Helpful Member
Using a motor that does not match the batteries or the engine driven generation system is a stupid idea! It requires several extra unneeded steps and reduces overall system efficiency considerably. Plus adds unneeded weight and cost to the vehicle. :(

Tell who ever has this design their retarded and dont know anything about system design or efficiency principals.;)

Definitely GM technology! :eek: :(

I am a 4th Year student, unfortunately I am not much of an expert.
There is a lot of that going around these days! Crappy college eduction system gets the blame for that! :mad:
I think GM training spin offs are being implemented at colleges. :(:D


Check out the golf cart electrical systems they have all the right stuff in the right sizes, perfectly matched too!

The 36 volt battery runs through a 36 volt control system to a 36 volt motor.
During regenerative braking the 36 volt motor back feeds through the 36 volt controller to the 36 volt batteries. Just add a small internal combustion engine with a 36 volt high amp charging system and your set to go the distance! And very efficiently too! :)
 

Nickys13

New Member
I don''t know why you are mentioning the GM all the time. This is a project done by a few universities!!

You can''t compare the golf car with the commercial car. The commercial car needs much more speed and torque, it has more passengers and more weight. The motor therefore needs to be operating in much higher voltage and for some reasons the students have designed the motor to be operating at 700V. I have read in a few papers that it is common practice for these motors to be operating at 600+ Volts.

On the other hand you can't have a battery matching the motor at 600Volts. This is too much and unnecessary weight for the car because each kg of battery cell unit only produces a certain amount of voltage . Therefore it needs to be boosted up.
 

tcmtech

Banned
Most Helpful Member
Of course I cant compare a golf cart to a commercial EV. Golf carts have great range power and system simplicity and they work! :D

Just saying scale up the golf cart design.
making a 600 -700 volt battery is not hard. Use smaller AH cells but far more of them and you still get the same battery capacity but at much higher voltage.

How much power does a full sized EV of the design you are working on take? Battery volts, amp hours, motor amps at 600 - 700 volts.

I had a full sized electric car for many years. It was built back in the early 1980's and it could easily go 75 MPH on near 30 year old design technology.;)
It also had a realistic driving range of 30 - 40 miles at highway speeds (55 MPH) too. It had by todays standards a low efficiency controller and no regenerative braking.

With a better control system it would have been able to regenerative brake and if the Lead acid Golf cart batteries (16 6 volt 220Ah) were changed out for modern high energy batteries that have known energy density's better than 10x the golf cart batteries when comparing volume to usable power ratios.
I know dam well it could be driven at todays high way speeds for 250 -300 miles between charges.

I sold it to my mom last year and she absolutely loves it! Operating cost is about 1 tenth that of her regular car on a cost per mile comparison.:)

EV technology is not new is just overpriced because of lack of proper research and design ideas. Simple works and it always will!

I just used the golf carts as an example of EV technology that has proven itself practical, reliable, and reasonably priced. All I was saying was take that technology and multiply the voltage capacities by 10 or so and the amp capacity by ten or so.
With power electronics thats a no brainier for any one that works with it.

I have seen and worked around modern VFD unit and huge industrial stepper motor drive systems that are the size of a home computer case and easily control 200 hp electric motors and already have regenerative feed back capacity.

They typically have 600 volt internal Bus voltages too! ;)
 
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