Author Topic: Inside the Tesla Roadster power inverter for 200kW motor  (Read 1977 times)

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Offline tom66

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Inside the Tesla Roadster power inverter for 200kW motor
« on: February 26, 2014, 10:53:15 PM »
Engineering pr0nography with thanks to "Marco2228" of Tesla Motors Club -- here's what's inside the power pack for a 300hp/200kW performance electric sportscar. He's the first to attempt a repair of such a unit after damage occurred (I doubt anyone would be tearing down a working one...!)

I'm quite surprised that they used discrete IGBTs rather than dedicated hybrid modules, but it looks to be a cost decision.

Charging input / contactors (240V @ 70A)
http://www.teslamotorsclub.com/attachment.php?attachmentid=44149&d=1393359626

Two phases ("Megapole logic") of inverter drive - identical to each other
http://www.teslamotorsclub.com/attachment.php?attachmentid=44154&d=1393359673

High performance DSP for traction control, safety interlocks, ADC/DAC and motor drive plus fan controller (far right)
http://www.teslamotorsclub.com/attachment.php?attachmentid=44151&d=1393359647

One IGBT "module" (a "Megapole") - 110kW IGBT block, 350VDC @ 650A peak (~310Arms)
http://www.teslamotorsclub.com/attachment.php?attachmentid=44150&d=1393359635

Thread:
http://www.teslamotorsclub.com/showthread.php/20709-34-Salvage-auction/page11

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« Last Edit: February 26, 2014, 10:56:02 PM by tom66 »

Offline Psi

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Re: Inside the Tesla Roadster power inverter for 200kW motor
« Reply #1 on: February 26, 2014, 11:03:37 PM »
Aw doesn't seem to mention what IGBT part they're using.

That's pretty awesome though,  28 IGBT's per phase.
Some serious power switching there.
« Last Edit: February 26, 2014, 11:09:43 PM by Psi »
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Online Dago

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Re: Inside the Tesla Roadster power inverter for 200kW motor
« Reply #2 on: February 26, 2014, 11:07:50 PM »
Very interesting find!

28 TO-247 IGBTs per phase is indeed an interesting design choice. Considering the thing can put out 200kW at least for some time it's very compact.
Come and check my projects at http://www.dgkelectronics.com ! I also tweet as https://twitter.com/DGKelectronics

Offline dr.diesel

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Re: Inside the Tesla Roadster power inverter for 200kW motor
« Reply #3 on: February 26, 2014, 11:12:59 PM »
That is pretty awesome.  Corp666 was right, pretty soon Summit Racing will be selling Souped-Up boards with 96 IGBT's/phase. 

Wonder when the local track's Supercharger will be installed? 

Offline NiHaoMike

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Re: Inside the Tesla Roadster power inverter for 200kW motor
« Reply #4 on: February 27, 2014, 03:28:55 AM »
I was expecting a large FPGA or two to handle the low level modulation and control. (There might be, just not pictured.) Hard to tell for sure, but it might also be a multi level inverter with all those transistors and capacitors per phase.

Meanwhile, Toyota directly mounts IGBTs dies into modules and uses custom ASICs, but they're also dealing with much higher volumes.
Electrical engineering would be a lot more fun if I looked like Tiffany Yep. As if it's not fun enough already...

In power electronics, transistors should ideally be either fully on or fully off, because a half-on transistor just makes a really poor imitation of Tiffany Yep...

Offline free_electron

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Re: Inside the Tesla Roadster power inverter for 200kW motor
« Reply #5 on: February 27, 2014, 03:59:41 AM »
Model S uses Ixys IGBT's. there is a reason for not using modules : individual monitoring and control. These guys are not stupid ...
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Online T3sl4co1l

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Re: Inside the Tesla Roadster power inverter for 200kW motor
« Reply #6 on: February 27, 2014, 06:09:31 AM »
I'm going to do that myself one of these days, that is, make an array with the transistors on the backside so the heatsink is clamped by screws through the board.

Discrete transistors are so damn cheap, it almost doesn't make sense to use modules.  The main difference is convenience and serviceability, I think.  For sure, if you're doing something at high frequencies, there is no module in existence that can go fast -- think the highest I've seen is a Microsemi/APT MOSFET half-bridge only rated for 200kHz resonant (compare to a fast IGBT bridge that wheezes out around 50kHz, or discrete MOSFETs that'll do MHz these days).  It appears they made no effort whatsoever to reduce lead inductance, which is shameful.

Hmm, also curious what isolation they use.  All those heatsink pads are at different potentials (B+ and AC, respectively).  Wonder if it's hardcoat anodized...

Tim
« Last Edit: February 27, 2014, 06:12:04 AM by T3sl4co1l »

Offline NiHaoMike

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Re: Inside the Tesla Roadster power inverter for 200kW motor
« Reply #7 on: February 27, 2014, 06:51:03 AM »
Discrete transistors are so damn cheap, it almost doesn't make sense to use modules.  The main difference is convenience and serviceability, I think.  For sure, if you're doing something at high frequencies, there is no module in existence that can go fast -- think the highest I've seen is a Microsemi/APT MOSFET half-bridge only rated for 200kHz resonant (compare to a fast IGBT bridge that wheezes out around 50kHz, or discrete MOSFETs that'll do MHz these days).  It appears they made no effort whatsoever to reduce lead inductance, which is shameful.
I'm surprised just how many modern digital audio amplifiers are using through hole modules when surface mount discrete MOSFETs and chips are superior at high switching frequencies. Of course, they deal with small amounts of power as far as power electronics go.
Electrical engineering would be a lot more fun if I looked like Tiffany Yep. As if it's not fun enough already...

In power electronics, transistors should ideally be either fully on or fully off, because a half-on transistor just makes a really poor imitation of Tiffany Yep...

Offline free_electron

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Re: Inside the Tesla Roadster power inverter for 200kW motor
« Reply #8 on: February 27, 2014, 09:11:04 AM »
Hmm, also curious what isolation they use.  All those heatsink pads are at different potentials (B+ and AC, respectively).  Wonder if it's hardcoat anodized...

Tim
if the transistor is built on fully depleted silicon no insulator is required. That thermal slug has no electric connection
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Offline Psi

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Re: Inside the Tesla Roadster power inverter for 200kW motor
« Reply #9 on: February 27, 2014, 09:30:16 AM »
Building my own electric car and making the speed control unit is something i would find quite fun.

Probably wouldn't do regen braking to keep things simple but testing out different control systems would be interesting.

Not sure about the safety aspect though, I wouldn't want some code error to cause fullspeed lockup while driving with other cars nearby.
In NZ all electrics cars are required to have a control for the driver that mechanically disconnects the batteries so E-stop would always be possible in an emergency.

Multi kW speed controller design is probably a lot more complex than i think it is but it still sounds like fun.
DC pwm and a brushed motor would be the easiest
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Offline tom66

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Re: Inside the Tesla Roadster power inverter for 200kW motor
« Reply #10 on: February 27, 2014, 10:00:51 AM »
For safety interlock, the simplest system would be two identical processors cross-checking each other, with each having an independent accelerator input from the pedal. The gate drive signals each generate could be AND-ed  for the final drive signals, and an XOR-circuit could be generating an interrupt indicating a processor exception which would immediately result in the battery contactors opening if the disagreement time exceeds some pre-set limit. In addition, applying the physical brake hard-down should command the inverter to stop delivering power.

In the Roadster PEM it looks like the Xilinx FPGA/CPLD near the phase connector might be doing some cross checking. It's also possible the checks are done outside the PEM, maybe in the vehicle management module, and that the PEM is fairly "dumb" - just taking a torque input command and producing an output. But the TI DSP seems like a bit much if it's just doing that. There's definitely some traction control management going on there as there's some tech docs talking about how the original "analog PEM" (presumably full of op-amps with no DSP...)  without traction control being terrible at handling.
« Last Edit: February 27, 2014, 10:04:43 AM by tom66 »

Online T3sl4co1l

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Re: Inside the Tesla Roadster power inverter for 200kW motor
« Reply #11 on: February 27, 2014, 10:01:46 AM »
if the transistor is built on fully depleted silicon no insulator is required. That thermal slug has no electric connection

I don't think a device like that has ever existed...?  It certainly wouldn't work with a minority carrier device.

All modern switching MOSFETs and IGBTs are either some variant of VDMOS (the die backside is doped for the drain/collector connection, built around a lightly doped wafer, which becomes the drift region) or superjunction (the drift region is alternating N/P columns).  In either case, the backside is always a terminal, and in TO-247 packages, almost always physically connected to the center pin (cut and formed from a single piece of tin plated copper).

There are isolated tab devices, usually using DBC (an aluminum nitride type ceramic insulator with copper plates direct-bonded to both sides). I suppose they could've used these, but I doubt the cost would be justified.  (They probably did use hardface anodize... it's cheap, and easy to apply to a lightweight aluminum heatsink, which probably needs anodizing anyway for corrosion protection.)

Tim

Online Dago

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Re: Inside the Tesla Roadster power inverter for 200kW motor
« Reply #12 on: February 27, 2014, 06:47:49 PM »
if the transistor is built on fully depleted silicon no insulator is required. That thermal slug has no electric connection

I don't think a device like that has ever existed...?  It certainly wouldn't work with a minority carrier device.

All modern switching MOSFETs and IGBTs are either some variant of VDMOS (the die backside is doped for the drain/collector connection, built around a lightly doped wafer, which becomes the drift region) or superjunction (the drift region is alternating N/P columns).  In either case, the backside is always a terminal, and in TO-247 packages, almost always physically connected to the center pin (cut and formed from a single piece of tin plated copper).

There are isolated tab devices, usually using DBC (an aluminum nitride type ceramic insulator with copper plates direct-bonded to both sides). I suppose they could've used these, but I doubt the cost would be justified.  (They probably did use hardface anodize... it's cheap, and easy to apply to a lightweight aluminum heatsink, which probably needs anodizing anyway for corrosion protection.)

Tim

There are loads of devices with insulated tabs. First one I found with 10s of searching: https://www.fairchildsemi.com/ds/HG/HGTG30N60B3.pdf
Come and check my projects at http://www.dgkelectronics.com ! I also tweet as https://twitter.com/DGKelectronics

Offline tom66

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Re: Inside the Tesla Roadster power inverter for 200kW motor
« Reply #13 on: February 28, 2014, 02:12:08 AM »
Would the isolated tab not make it harder to keep the IGBT cool?

Offline SeanB

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Re: Inside the Tesla Roadster power inverter for 200kW motor
« Reply #14 on: February 28, 2014, 05:57:53 AM »
Does not look like it does, seeing as max thermal resistance is 0.6 C/W. Even copper is around that figure, so the internal isolation must be pretty good.


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