An interesting question got posted on the Quora question/answer site recently. It asked for opinions about what constitutes Tesla Motors’ most significant technological breakthrough. An answer that has been viewed 40,800 times so far is from data scientist John Gustafson:
My present company is involved in making high-performance capacitors of the type used in inverters. That was how I uncovered a particular bit of genius in the Tesla design that, to me, stands out.
The problem they solved is this: The battery produces DC current, of course. A lot of DC current, and at high voltage, because the motor can be driven at over 200 kilowatts. But the induction motor uses alternating current. To turn 200 kilowatts of DC into 200 kilowatts of AC is not easy, and would seem to demand a huge, heavy inverter, perhaps even bigger than the battery itself. And if any part of the battery were to fail, the car would be dead.
Their breakthrough was realizing they put the inversion task in the motor itself by breaking the rotation into many phases and assigning each phase to a different subset of the battery pack. Not only did this make everything much smaller and lighter (and cheaper), it also made it fail-safe to battery subset failures. The independent “slices” in the battery organization could fail completely and you would only lose a few percent of the motor power, that’s it. Sort of like having a gasoline engine with 30 cylinders, and one of them fails. You’d barely notice.
I’m not sure which one of Tesla’s many patents describes this innovation, but it’s a beauty.
One viewer helpfully posted a link to a patent (https://www.google.com/patents/US20120153718) but it doesn’t seem to pertain to the dividing of motor phases and pairing them with portions of the battery pack.
The utility of what Gustafson describes wasn’t exactly clear to me when I read his answer, and judging by comments from other viewers, I’m not the only one who is confused.
Anyone else out there want to comment on what might be going on here? One thing the above-mentioned patent does say is that Tesla uses bus bars instead of cables to make connections between the inverter and motor, which I suppose has advantages if you have somehow subdivided the battery into direct connections to the motor. But the motor phase/battery pack connection is still a bit mysterious.
Readers are invited to chime in on this one.
Filed Under: Capacitors, Power Electronic Tips