Tesla manufactures its drive inverter for the Model S/X in-house at its Fremont factory, but the automaker is using proven off-the-shelf products — primarily TO-247 transistor packages. The company used this approach from the start when working on the Roadster. Like what it has been doing with battery cell technology, the automaker saw an opportunity to attach its product to improvements in transistor systems to gradually allow more powerful and efficient powertrains.
While the strategy served it well so far, Tesla is moving away from it with its third generation platform and consequently, with the Tesla Model 3. The company will be using new battery cells manufactured at its Gigafactory in Nevada and as it turns out, it also started from a blank sheet for its new inverter architecture. Electrek has learned new information about the system which has some interesting implications for the upcoming $35,000 all-electric sedan.
First off, it could be useful to briefly revisit Tesla’s history with inverters.
A drive inverter in an electric vehicle is used to convert DC current from the battery pack into AC current for the motor. It’s an essential part of any electric powertrain with an AC motor since its power rating limits the output to a motor and its efficiency affects energy consumption.
The company made most of its drive inverter developments working on the Roadster. Tesla CTO JB Straubel is on record saying that in Tesla’s several iterations of the all-electric sports car, the inverter is likely what changed the most.
At a power electronic convention when he was working on the Model S powertrain, Straubel said:
“We are increasing the current rating (of the inverter) that’s the most tangible thing you see from a performance point of view. Every time we can push up the current in the inverter a little bit, we are able to get a little bit higher motor torque and that translate into a little bit faster 0 to 60 time, more responsive acceleration and those sort of things.”
The engineer went on to describe how Tesla is using off-the-shelf power electronics for the system:
“The power rating increases are largely enabled by better and better power electronics – transistors or IGBTs which is what we are using. As those improve, we can continue pushing up the current rating and continue increasing performance. If we can make the inverter just half a percent more efficient, that’s half a percent less battery pack that we have to put in the car or half a percent more range that the customer gets to have so it a very strong and virtuous feedback cycle with high efficiency.”
Tesla’s RWD motor for the Model S and X is equipped with a 320kW inverter built on TO-247 insulated-gate bipolar transistor packages or IGBTs:
The method has been satisfactory for Tesla even for its latest inverter models. The latest inverter developed by the company was the unit for its dual motor which was also built on TO-247 packages.
Even though they still had to use the off-the-shelf power semiconductor packages, Tesla engineers were still able to make several improvements to the dual motor inverter compared to the one found in the RWD drivetrain, making it more compact and significantly reducing the total of unique parts. The dual motor inverter architecture, the one for the new smaller front motor, is rated at a peak power capability of over 250 kW.
The Model 3
A source very familiar with the Model 3 powertrain program confirmed that Tesla tapped the same engineers who worked on the dual motor inverter architecture to develop the Model 3’s, but this time, they were given a blank sheet to develop the system from the ground up, including the power semiconductor package.
Considering that Tesla now plans to produce as many as 500,000 cars in 2018, the volume is starting to make more sense for developing custom components for its power electronics.
According to the source, the strategy paid off and the inverter architecture for the Model 3 will have a capacity of “over 300kW”, comparable to the Model S’ RWD system even though the S is a much higher-end and bigger vehicle.
The system is also geared toward manufacturing with ~25% fewer unique parts and they managed to significantly increase both the volumetric and gravimetric current density. The Model 3 inverter is also expected to be much cheaper on a dollar per power capacity basis than even Tesla’s most recent dual motor inverter system.
What are the implications for the Model 3 performance?
When unveiling the Model 3 earlier this year, Tesla CEO Elon Musk said that the base version will be able to travel 215 miles on a single charge and accelerate from 0 to 60 mph in “under 6 seconds”. He specified that this was a minimum for the base model and that higher-end versions of the Model 3 will feature better specs, even its own Ludicrous mode.
The day before the unveiling event, we published an exclusive report based on an inside source accurately describing the Model 3 design. The same source revealed that at the time, Tesla was aiming for the higher-end dual motor AWD version of the Model 3 to achieve a 0-60 time in under 4 seconds.
Our new details on the Model 3 powertrain are in line with these expectations. A main drive unit delivering over 300 kW combined with a similar dual motor as Tesla’s current system delivering up to ~250kW could easily achieve supercar-like performance similar to the Model S.
Though we wouldn’t be surprised if Tesla makes further improvements to the Model S (and X) to further distance the vehicles from its upcoming entry model. The latest Model S P90D cars being delivered are reportedly achieving higher power outputs than previous versions of the vehicle.
The Model 3 is expected to go in production next year with deliveries starting in late 2017.
A Tesla spokesperson refused to officially comment on this report.
Our recent coverage of the Tesla Model 3:
- New Tesla Model 3 prototype pictures with rare shot of the interior [Gallery]
- Tesla Model 3 reservation holders are starting to receive their ‘token of appreciation’
- Tesla applied for a $106 million tax break on $1.26 billion expansion of Fremont Factory for the Model 3
Pictures courtesy of Tesla and Tesla Motors Club