7 ms·

Lucid Motors' Peter Rawlinson Talks E-Car Efficiency

33 points by pross356 7y ago

ctdonath 7y ago
What makes Lucid different? Base price of $60,000 ... and no factory to build it. Why the excitement?
- Shivetya 7y ago
  well until the big manufacturers actually start delivering multiple models there is ample time for start ups in this segment to establish themselves or their technology. the key is, are they looking to sell cars or their technology?
  - freeopinion 7y ago
    Funny. While reading, I got the strong impression Lucid wanted to sell technology rather than cars. Perhaps, they even just want to sell companies.
  - ctdonath 7y ago
    Your post makes me keenly aware of Tesla’s future: the only company really taking EVs seriously, with a massive head start.
- jsight 7y ago
  Hope! There isn't much other reason to be excited about it at this point, tbh. Almost all such efforts fail before getting to 20k units of production.
timerol 7y ago
> So he designed the Lucid around a 900-watt architecture. “It’s the only one I’m aware of,” he says. “Tesla’s round about 400 V. Porsche, they upped the ante last year to 800 V.” Is that supposed to be 900 V? Considering the car can push out 750 kW, a "900-watt architecture" doesn't mean much. I would think that the IEEE would be the one place I could trust to not mess up electrical units...
- zbrozek 7y ago
  I found the whole article to be pretty disappointing wrt/technical content, doubly so for something from IEEE.
- aidenn0 7y ago
  I originally read right over that as 900V. I think I'm so used to reading articles with energy/voltage/power mixed up I just gloss over it now.
- Kirby64 7y ago
  Has to be a typo. 900V is the only thing that makes sense in the context of the 'reducing current' since that is the 'main loss'. This whole article is kind of terrible though... they're talking about reducing losses by using SiC MOSFETs and using higher voltage architecture... except they fail to recognize that higher voltage MOSFETs inherently have higher impedance when on, and it causes a bunch of other potential issues. Also, they're comparing themselves against the Porsche Taycan... which is one of the worst performing (in kWh/efficiency value) cars out there. Why not compare against the Model 3? The Model 3 uses SiC MOSFETs (although, 400V rated ones) just like they're talking about here.
aidenn0 7y ago
Just because I was doing my own hobbyist research on power switching, and encountered the IGBT vs power MOSFET tradeoff: The current path for an IGBT looks largely like a diode; it has a fixed voltage drop (0.6V in silicon), so the losses in the "On" state are linear with current. A MOSFET, however looks largely like a resistor in the "On" state, so the losses are quadratic with current. There are also switching losses, which are a bit more complicated, but largely scale quadratically with frequency (for IGBTs there usually aren't actual formulae but just a curve from the datasheet; MOSFETs are a bit more amenable to calculation). For relatively low-frequency and high-current switching like a high-power permanent magnet motor, you will tend try to keep switching losses low relative to conduction losses; in any event IGBTs are low-frequency devices so if IGBTs are in discussion typically switching losses will be low. As anyone who has studied asymptotic performance will know, for low-frequency applications, as current goes towards infinity, IGBTs are better. At low currents, however, MOSFETs trounce IGBTs; A resistor that drops 0.6V at 1A would have 600mOhms of resistance, and a $0.10 Power MOSFET can beat that in low voltage (<120V) applications, with on resistances on the order of 1mOhm. At 100A there are similar conductive losses. As you design power MOSFETs for higher voltage handling though, the on resistance goes up. There are ways to design power MOSFETs with lower on-resistance, but they will make them much harder to switch and increase the switching losses to the point where that bit I said earlier about conduction losses dominating becomes not true. For switching 900V you will want a MOSFET rated for at least 1200V and now you are looking at 100s of mOhm of on resistance, so even at say 2A, the IGBT is looking quite good. Enter SiC. I know absolutely nothing about semiconductor design, but the way it was explained to me is that the design parameters of an SiC MOSFET are such that it can block a larger voltage than a silicon MOSFET, so that the envelope shifts "up" for working voltage at any given amount of on-resistance ant gate-charge (which relates to switching losses). Lastly, if you aren't a racecar driver, most of the time the power draw will be far below the max, so even if an IGBT beats an SiC MOSFET handily under hard acceleration (it almost certainly does), for highway cruising there is a good chance the MOSFET will win.
- gens 7y ago
  From what i remember when i cared about such things: It's the gate capacitance (and gates resistance) that leads to switching losses. Usually the biggest part of the switching losses is because the transistor is not fully "on" or "off" for the whole time, but is in between when in the process of switching. The gate capacitance is probably one of the biggest problems (more for FET, but also for bipolar), that influences the speed of the transistor (presented as frequency or as slew rate). Otherwise you could just put a bunch of MOSFET-s in parallel and get much lower resistance, thus greater efficiency (and it works, to a point). Another thing to consider is that FET-s let the current go back and a motor is an inductive load, while bipolar transistors do not. I forgot how much that matters, but it probably does plenty. Thankfully electronics is one of those fields of engineering where you can get all the information you need from a datasheet. Unlike from those damned headphone manufacturers (embarrassments to engineering, 99.9% of them). PS "..you will tend try to keep switching losses low relative to conduction losses.." I think you meant the other way around.
adrianN 7y ago
I think an important problem with cars, e- or not, is size and weight. Moving two tons of car to move 100kg of passengers and baggage is just excessive. Compare cars with bicycles where less than 100W sustained are enough to navigate city traffic about 80% as fast as in a car. There must be a better trade-off point of comfort, safety and efficiency than a modern car.
- skyfaller 7y ago
  Yeah, I think that electric bicycles are clearly superior in urban environments. Here in Philadelphia I sold my pickup truck and replaced it with a Tern GSD electric cargo bike, and it can do just about anything a car can do, including carry an adult passenger. Protection from the elements and accessibility are two legitimate concerns that might be addressed by bike-cars like the PEBL in the future: https://www.better.bike/ https://www.better.bike/ Outside of urban environments, velomobiles with aerodynamic shells have some potential, and would allow travel at highway speeds while using much less energy. Low-Tech Magazine suggests "If all 300 million Americans replace their car with an electric velomobile, they need only 25 % of the electricity produced by existing American wind turbines": https://solar.lowtechmagazine.com/2012/10/electric-velomobiles.html https://solar.lowtechmagazine.com/2012/10/electric-velomobil... - Part 2 (link in footer is broken) https://solar.lowtechmagazine.com/2012/10/electric-velomobiles-part-two.html https://solar.lowtechmagazine.com/2012/10/electric-velomobil... https://solar.lowtechmagazine.com/2010/09/the-velomobile-high-tech-bike-or-low-tech-car.html https://solar.lowtechmagazine.com/2010/09/the-velomobile-hig... The main problem with high-speed velomobiles is they're too fast for bike trails, but are too small and low to the ground to safely share highways with cars. Most pictures/videos I see of them are on rural roads with almost no traffic. In order for them to become popular, we probably would have to completely reimagine our transportation infrastructure.
  - api 7y ago
    Isn't safety an issue too? You'd be turned into pizza toppings in a highway speed accident in one of those. They do show that huge efficiency improvements are possible, but they are not there yet. I feel like there's probably a happy medium: a larger somewhat heavier car with safety features built around active immobilization and advanced materials. It wouldn't be quite as efficient as these, but it would be more efficient than a conventionally built car. I also must point out that weight and aerodynamics are more significant for efficiency than size in an absolute sense. Aerodynamics matters the most at highway speeds. You can lengthen the vehicle and add a trunk for cargo without losing too much.

33 points by pross356 7y ago

ctdonath 7y ago

What makes Lucid different? Base price of $60,000 ... and no factory to build it. Why the excitement?

Shivetya 7y ago
well until the big manufacturers actually start delivering multiple models there is ample time for start ups in this segment to establish themselves or their technology. the key is, are they looking to sell cars or their technology?
- freeopinion 7y ago
  Funny. While reading, I got the strong impression Lucid wanted to sell technology rather than cars. Perhaps, they even just want to sell companies.
- ctdonath 7y ago
  Your post makes me keenly aware of Tesla’s future: the only company really taking EVs seriously, with a massive head start.
jsight 7y ago
Hope! There isn't much other reason to be excited about it at this point, tbh. Almost all such efforts fail before getting to 20k units of production.

timerol 7y ago

> So he designed the Lucid around a 900-watt architecture. “It’s the only one I’m aware of,” he says. “Tesla’s round about 400 V. Porsche, they upped the ante last year to 800 V.” Is that supposed to be 900 V? Considering the car can push out 750 kW, a "900-watt architecture" doesn't mean much. I would think that the IEEE would be the one place I could trust to not mess up electrical units...

zbrozek 7y ago
I found the whole article to be pretty disappointing wrt/technical content, doubly so for something from IEEE.
aidenn0 7y ago
I originally read right over that as 900V. I think I'm so used to reading articles with energy/voltage/power mixed up I just gloss over it now.
Kirby64 7y ago
Has to be a typo. 900V is the only thing that makes sense in the context of the 'reducing current' since that is the 'main loss'. This whole article is kind of terrible though... they're talking about reducing losses by using SiC MOSFETs and using higher voltage architecture... except they fail to recognize that higher voltage MOSFETs inherently have higher impedance when on, and it causes a bunch of other potential issues. Also, they're comparing themselves against the Porsche Taycan... which is one of the worst performing (in kWh/efficiency value) cars out there. Why not compare against the Model 3? The Model 3 uses SiC MOSFETs (although, 400V rated ones) just like they're talking about here.

aidenn0 7y ago

Just because I was doing my own hobbyist research on power switching, and encountered the IGBT vs power MOSFET tradeoff: The current path for an IGBT looks largely like a diode; it has a fixed voltage drop (0.6V in silicon), so the losses in the "On" state are linear with current. A MOSFET, however looks largely like a resistor in the "On" state, so the losses are quadratic with current. There are also switching losses, which are a bit more complicated, but largely scale quadratically with frequency (for IGBTs there usually aren't actual formulae but just a curve from the datasheet; MOSFETs are a bit more amenable to calculation). For relatively low-frequency and high-current switching like a high-power permanent magnet motor, you will tend try to keep switching losses low relative to conduction losses; in any event IGBTs are low-frequency devices so if IGBTs are in discussion typically switching losses will be low. As anyone who has studied asymptotic performance will know, for low-frequency applications, as current goes towards infinity, IGBTs are better. At low currents, however, MOSFETs trounce IGBTs; A resistor that drops 0.6V at 1A would have 600mOhms of resistance, and a $0.10 Power MOSFET can beat that in low voltage (<120V) applications, with on resistances on the order of 1mOhm. At 100A there are similar conductive losses. As you design power MOSFETs for higher voltage handling though, the on resistance goes up. There are ways to design power MOSFETs with lower on-resistance, but they will make them much harder to switch and increase the switching losses to the point where that bit I said earlier about conduction losses dominating becomes not true. For switching 900V you will want a MOSFET rated for at least 1200V and now you are looking at 100s of mOhm of on resistance, so even at say 2A, the IGBT is looking quite good. Enter SiC. I know absolutely nothing about semiconductor design, but the way it was explained to me is that the design parameters of an SiC MOSFET are such that it can block a larger voltage than a silicon MOSFET, so that the envelope shifts "up" for working voltage at any given amount of on-resistance ant gate-charge (which relates to switching losses). Lastly, if you aren't a racecar driver, most of the time the power draw will be far below the max, so even if an IGBT beats an SiC MOSFET handily under hard acceleration (it almost certainly does), for highway cruising there is a good chance the MOSFET will win.

gens 7y ago
From what i remember when i cared about such things: It's the gate capacitance (and gates resistance) that leads to switching losses. Usually the biggest part of the switching losses is because the transistor is not fully "on" or "off" for the whole time, but is in between when in the process of switching. The gate capacitance is probably one of the biggest problems (more for FET, but also for bipolar), that influences the speed of the transistor (presented as frequency or as slew rate). Otherwise you could just put a bunch of MOSFET-s in parallel and get much lower resistance, thus greater efficiency (and it works, to a point). Another thing to consider is that FET-s let the current go back and a motor is an inductive load, while bipolar transistors do not. I forgot how much that matters, but it probably does plenty. Thankfully electronics is one of those fields of engineering where you can get all the information you need from a datasheet. Unlike from those damned headphone manufacturers (embarrassments to engineering, 99.9% of them). PS "..you will tend try to keep switching losses low relative to conduction losses.." I think you meant the other way around.

adrianN 7y ago

I think an important problem with cars, e- or not, is size and weight. Moving two tons of car to move 100kg of passengers and baggage is just excessive. Compare cars with bicycles where less than 100W sustained are enough to navigate city traffic about 80% as fast as in a car. There must be a better trade-off point of comfort, safety and efficiency than a modern car.

skyfaller 7y ago
Yeah, I think that electric bicycles are clearly superior in urban environments. Here in Philadelphia I sold my pickup truck and replaced it with a Tern GSD electric cargo bike, and it can do just about anything a car can do, including carry an adult passenger. Protection from the elements and accessibility are two legitimate concerns that might be addressed by bike-cars like the PEBL in the future: https://www.better.bike/ https://www.better.bike/ Outside of urban environments, velomobiles with aerodynamic shells have some potential, and would allow travel at highway speeds while using much less energy. Low-Tech Magazine suggests "If all 300 million Americans replace their car with an electric velomobile, they need only 25 % of the electricity produced by existing American wind turbines": https://solar.lowtechmagazine.com/2012/10/electric-velomobiles.html https://solar.lowtechmagazine.com/2012/10/electric-velomobil... - Part 2 (link in footer is broken) https://solar.lowtechmagazine.com/2012/10/electric-velomobiles-part-two.html https://solar.lowtechmagazine.com/2012/10/electric-velomobil... https://solar.lowtechmagazine.com/2010/09/the-velomobile-high-tech-bike-or-low-tech-car.html https://solar.lowtechmagazine.com/2010/09/the-velomobile-hig... The main problem with high-speed velomobiles is they're too fast for bike trails, but are too small and low to the ground to safely share highways with cars. Most pictures/videos I see of them are on rural roads with almost no traffic. In order for them to become popular, we probably would have to completely reimagine our transportation infrastructure.
- api 7y ago
  Isn't safety an issue too? You'd be turned into pizza toppings in a highway speed accident in one of those. They do show that huge efficiency improvements are possible, but they are not there yet. I feel like there's probably a happy medium: a larger somewhat heavier car with safety features built around active immobilization and advanced materials. It wouldn't be quite as efficient as these, but it would be more efficient than a conventionally built car. I also must point out that weight and aerodynamics are more significant for efficiency than size in an absolute sense. Aerodynamics matters the most at highway speeds. You can lengthen the vehicle and add a trunk for cargo without losing too much.