Custom Controller Build + Needed Feedback! :)

[glenn0010]

Hey Lads,

Before I start a bit of a background. I am an Electronics and Plant Process Control Engineering Student finalizing my degree. For my Higher national Diploma I made my own Brushless motor controller and it worked. It can be seen here: https://endless-sphere.com/forums/viewtopic.php?f=3&t=70870&start=50
Having said that it was very expensive and bulky to make because I took to much advice from my mentor. This time however I want to do it right, cheap and compact which would make it suitable for mass production.

I have already designed some circuits and need some feedback on my plan.

Supply to controller:

I plan to use the following DC/DC converter to supply the power to the contorller:
http://www.mouser.tw/pdfdocs/BD9G341-ad.pdf

I plan to use 2 of these DC/DC converters. 1 to step down battery pack voltage to 12V to drive the Mosfets and another one to step down from battery pack voltage to 5V to supply the micocontroller and hall sensors. I could use and LM7805 with the 12V DC/DC converter but I am trying to keep efficiency at a maximum.

Also would anyone be interested in buying standalone versions of this DC/DC converter as it is very versatile since it can handle 76V and supply 3A!? I could make this circuit and sell it to any one who wants one

Mosfet Drivers

I plan to use the following Mosfet Drivers:
http://www.infineon.com/dgdl/ir2104.pdf?fileId=5546d462533600a4015355c7c1c31671

The one thing I am not sure about is whether my calculations for the bootstrap capacitor size are correct. I have used this application note to make my calculations: http://www.infineon.com/dgdl/an-978.pdf?fileId=5546d462533600a40153559f7cf21200

As seen on page 6 there is an equation to calculate the boot strap capacitor.
Here are the parameters I have.

Qg = 88nC (this can be seen from the mosfets chosen below)
Frequency of operation = 32kHz in my case
ICbs (leak) = bootstrap capacitor leakage current I am ignoring this one since I will use cermaic capacitors as staed in the application note
Iqbs (max) = Maximum VBS quiescent current = 55uA found from gate driver datasheet
VCC = Logic section voltage source = 12V from DC/DC converter
Vf = Forward voltage drop across the bootstrap diode = 0.39V from the diode I chose
VLS = Voltage drop across the low-side FET or load = 0.15V Calculated this by using I squared R
VMin = Minimum voltage between VB and VS. = 11V not too sure about this parameter
Qls = level shift charge required per cycle (typically 5 nC for 500 V/600 V MGDs and 20 nC for
1200 V MGDs) = 5nC

Using the Values above,it was determined that the bootstrap capacitor needs to be 0.8uF. is this correct?
Also in the application note on page 14 it is stated that mosfet modules require more current to be driven and the gate driver may not be sufficient do you think this will be a problem for me?

Power Stage

For the power stage I want to keep things as simple as possible regarding soldering heatsinking and size. Therefore I have opted to use this Mosfet Module. The MTI85W100GC: http://ixapps.ixys.com/Datasheet/MTI85W100GC.pdf

This will make the controller to be very compact and the power stage should have low inductance correct?
I also plan to add things such as current sensing and temperature sensing but first I want to finalize my supply and mosfet drivers.
Aslo I need to calculate Snubbers etc but this will come soon.

If any one read this all I respect you haha and any feed back would be appreciated!

Regards Glenn

 

[SjwNz]

I am no good at calculations but after looking at different deigns over the years I saw a number of controllers in the 1 to 3kw power range were using 10uF for the bootstrap cap
and I used 10uF on my first controller.
That power module looks nice, but I would be worried about heat and think it might only be ok for under 1kw.
What power rating are you aiming for with your new controller.

 

[glenn0010]

I am no good at calculations but after looking at different deigns over the years I saw a number of controllers in the 1 to 3kw power range were using 10uF for the bootstrap cap
and I used 10uF on my first controller.
That power module looks nice, but I would be worried about heat and think it might only be ok for under 1kw.
What power rating are you aiming for with your new controller.

Hi Thanks for the reply!

I'll make sure to order.some 10uF caps as well in case my calculations are off. Thanks for the info.

As with regards to the power module I plan on mounting a heat sink on top of it with some thermal paste and that should allow ne to drive large amounts of power through it.

The motor I currently have is 48V 1kW. Having said that I want my controller to be 5kW+ approaching 10kW. However for that passive heating will most likely not be enough and I might have to add some fans.

Any thoughts regarding the DC/DC converter? Do you think the ES community would be interested in buying the DC/DC converter to drop down battery pack voltages down to 12v/5V for use of accessories like lights etc?

Really Appreciate your response Thanks a lot!

 

[Drunkskunk]

Can't really comment without knowing your goals for output. But I can say most ebikes would have a problem with that MOSFET module. There are good reasons why most controllers use the TO220 package MOSFET. The design is very good for shedding heat, and with each FET isolated, they aren't getting heat soak from another FET. With the T0220, You have a large flat metal surface designed to pull heat rapidly away from the junction, keeping the FET cool and happy.

I really don't think it matters how big of a heatsink you use with the power module, I don't think you will be able to transfer enough heat fast enough from the module to the heatsink to keep the FETs from frying.

 

[glenn0010]

Can't really comment without knowing your goals for output. But I can say most ebikes would have a problem with that MOSFET module. There are good reasons why most controllers use the TO220 package MOSFET. The design is very good for shedding heat, and with each FET isolated, they aren't getting heat soak from another FET. With the T0220, You have a large flat metal surface designed to pull heat rapidly away from the junction, keeping the FET cool and happy.

I really don't think it matters how big of a heatsink you use with the power module, I don't think you will be able to transfer enough heat fast enough from the module to the heatsink to keep the FETs from frying.

Hey Thanks a lot for your input.

To be honest I did think the same thing because the surface area in contact with the heat sink is relatively small.What I liked a out the module is it's simplicity for soldering etc. Could you recommend some books/website which have tips to design the power stage with the T0220 Fets?

The first Controller I designed, I used T0220 Fets. I ended up using copper bus bars to to transfer the current. My main problem with the T0220 is the tracks on the PCBs. When using 1oz or 2oz boards, I really doubt the Tracks will be able to handle large amounts of current. Any tips towards this? I was thinking of perhaps soldering copper wires on top of the tracks?

Also could you recommend and point me towards and good compact designs of the power stage using T0220?
I am planning to run the controller at around 5kW or more if possible.
Finally if multiple Fets are used in parallel to switch the same phase, they can still be driven over one gate driver correct?

Sorry for all the questions but I want a good clean design

Thanks a lot for your Help!

 

[glenn0010]

Hi Guys,

So I have been working on the Power Stage.

Could anyone give any suggestions on how to best connect the traces between the transistors. I am expecting to pass around 20A through the traces. I am going to use a 1oz PCB should I just pass traces and add copper wires on top of them or are there better ways there?

Take a look at the Image attached.

 

[SjwNz]

Just solder on some extra wire to the tracks, I added 2 layers of 0.3mm think copper sheet on my controller but was running around 80amps.
Maybe have a look for a PCB track current calculator to get an idea of track width.
Do you have a circuit diagram.

 

[glenn0010]

Just solder on some extra wire to the tracks, I added 2 layers of 0.3mm think copper sheet on my controller but was running around 80amps.
Maybe have a look for a PCB track current calculator to get an idea of track width.
Do you have a circuit diagram.

Hi thanks for your reply.

Here is my schematic and PCB layout so far. Could you take a look at them and offer any potential improvements in the layout?

 

[glenn0010]

Hi guys,

I have completed the design of my power stage and mosfet driver stage. I am posting the schematics, the gerber files and a 3D rendering of the Board. Before I go ahead and order the PCB can anyone take a look at the board and see if any improvements can be made?

Thanks, Glenn





View attachment Gate Driver Board - Gerber Files.ZIP