Yes, there's action in rotating electrical machinery again. For decades, this was a dull and boring field.
Tesla and Steinmetz figured out the theory of AC machines in the early 20th century. This was the first industrial technology where you needed advanced math to get anything to work right. Complex numbers. Calculus. Laplace transforms. That bothered some people, such as Edison. By the 1930s it was figured out, and generations of EEs struggled through rotating machine theory in college.
Then all the cool kids went off to radio and transistors and computers. Rotating electrical machinery was a mature field. Maybe a few people at GE in Schenectady worked on it.
Then came power semiconductors, and chopper-type motor control, where power was being turned on and off at moderately high frequencies. At first this was just applied to existing motor designs. But AC motors were designed for sine wave power. Choppers didn't produce clean sine waves. Much effort was put into making variable-speed controls that produced the nice sine waves motors needed. Classical AC theory was built around sine waves, and engineers knew how to do that kind of analysis. This worked, but it made AC motors buzz at the chopper frequency, and as chopper frequencies went up, whine. When you ride on BART, that's what you're hearing from the motors. The waveform mismatch also led to unwanted heating in the windings and inefficiency.
Variable-frequency 3-phase AC motors went from exotic to normal. Today, everything from a Tesla to a drone to a Diesel-electric locomotive uses such motors. The big power semiconductors required aren't that big. Here's one for a locomotive.[1]
In recent years, motors have started to be designed for the non sinusoidal waveforms that come out of chopper power supplies. This required new theory and much simulation of magnetic fields. There's plenty of compute power available and commercial packages for that kind of analysis. Now we're seeing more advanced motor designs that match well with their control electronics.
After most of a century, rotating electrical machinery design is cool again.
This melody is unique (on London Underground) to the Jubilee line.
Although the Northern line trains have an almost identical body design, they use a more modern IGBT traction system which, although presumably more efficient, has a little less character!
Yes, the 3-phase synchronous AC locomotives driven with IGBTs seem to be quieter.[1] But the real advantage is precise wheel control. Here's the biggest steam locomotive ever built being towed out of the Pomona Fairgrounds for restoration. They're towing it through a very tight turn on temporary track to get it out.
The locomotive doing the towing is a 2006-model Electro-Motive Diesel-electric locomotive. It's towing the old steam locomotive at a very slow speed, smoothly, with no wheel slip. Nothing special about it; Union Pacific has hundreds of them. Six axles, each powered by its own motor. AC synchronous, IGBT power control. The motors are run as servomotors, all locked together. No wheel can slip relative to the others. This is a huge win when you need to get a few thousand tons moving.
This boring but useful modern locomotive, although much smaller, has more drawbar pull than the Big Boy. Multiple locomotives can be ganged together with wheels locked in sync, if you need more pulling power. Here's Union Pacific overdoing that.[2] They put together a train 3.5 miles long, with 9 locomotives spaced throughout the train, and ran it from Long Beach to Denver. This was just a test; they don't normally run trains that long.
All this is made possible by modern electronic motor controls.
Oh, that's cute. Siemens makes a locomotive that uses switching frequencies spaced one note apart and steps through them during acceleration. That has to be on purpose.
Likely due to some exponential thing with the switching frequency following the soft acceleration, as the speed as far as I know increases according to a cubic function until about half of full acceleration is reached, and from there on it goes over to quadratic until the train hits about 80 km/h, as they lack power at around that speed to keep the acceleration at the usual 0.9-1.1 m/s^2. And the harmonics are exponential, with log_2(#of_notes/12) giving you the relative frequency difference for a given number of notes spacing.
Those are relay contacts selecting which field windings are getting power. As the locomotive accelerates, the number of enegerqzed coils is reduced in order to reduce back EMF (electro motive force)
> Tesla and Steinmetz figured out the theory of AC machines in the early 20th century. This was the first industrial technology where you needed advanced math to get anything to work right. Complex numbers. Calculus. Laplace transforms. That bothered some people, such as Edison. By the 1930s it was figured out, and generations of EEs struggled through rotating machine theory in college.
It's always interesting to observe differences in history from different vantage points.
In Europe the story told goes like this: Some time in the early 19th century people noticed that a thing called induction exists. Then in the later 19th century a chap called Ferraris (also known for his AC energy meter) developed multi-phase AC and the general idea of an induction motor. Some bit later, a Russian guy named Dolivo Dobrowolsky, invented a two-phase induction motor. Meanwhile, some other folks started to build transformers. Not even a handful decades later and virtually everyone in Europe used AC and both synchronous and asynchronous generators and motors were used everywhere for everything in industry.
The reason for these differences is of course that in these few years key advancements were made by different people at the same time.
> In recent years, motors have started to be designed for the non sinusoidal waveforms that come out of chopper power supplies.
From what i remember, square waves are better for a motor.
Thinking about it i see no benefit of it being sine (*with many poles, that is, as a square would shake the mechanical parts too much otherwise).
Depends on the windings. Synchronous motors have had windings designed for sq. wave drive for many years now, prominently for stepper, servo and BLDC motors. These still use some filtering to reduce the insulation stresses.
A scrapyard. Both the rotor and stator are water cooled in Tesla motors. The motor shaft has two holes drilled down the length of it which is fantastically expensive to get done in units of less than tens of thousands. However there is a steady business of resold Teslas from crashes etc.
Pretty bad article. Its conclusions are broadly correct, but the way it gets there is not. There hasn't been any major change in motors- the major change has come in Variable Frequency Drives (VFDs). Older motors are hooked directly into the grid and deal poorly with changing speed and torque, and can drop drastically in efficiency. A motor can be 60% efficient at low load, and 98% efficient at its rated load.
VFDs are very complex pieces of circuitry- far more than you'd expect. Efficient drivers require a great deal of computation, and 16 or 32 bit processors are not uncommon. That also requires high-power, cheap silicon transistors which are only gradually taking over from simpler control schemes. They make a huge difference in a lot of cases.
The author is also very wrong on Synchronous Reluctance-assisted Permanent Magnet motors, but its hard to fault them on that; it's complicated even for many engineers. The purpose is not to increase the power density, it's to increase efficiency. The magnets act like a "cruise" motor. At low torque, they provide all of the rotor magnetization at a very high efficiency. At higher torque, the stator induces a stronger field into the rotor, causing it to act like a reluctance motor. That allows you to turn on extra power as demanded at the price of lower efficiency (the same as a reluctance motor).
If, instead, you just used a larger PM motor, it would be more expensive and it would also have an efficiency drop at low torque (where the motor spends most of its time operating). The magnets are highly efficient but they "set" the operating torque of the motor somewhat, so there is a loss at low power/high speed to hysteresis. A reluctance motor meanwhile never reaches the peak efficiency of a PM motor.
Anyway the article doesn't really say much convincing and feels mostly like fluff.
Just wanted to mention that Visedo also has its own line of VFDs utilizing IGBTs (insulated-gate bipolar transistors). The software is definitely a large part of the drive.
They aren't used for their cost, rather it's the fact that they are synchronous that is advantageous. It's possible to use an induction motor but it's much more complex and because of that less accurate. A reluctance motor and PM motor with the same pole count can be driven at the same speed, whereas the speed of an induction motor depends heavily on the voltage driving it, the current speed, and the torque on it. You can only solve the drive equations accurately at zero load.
Commutated DC motors could also be used but they are low efficiency.
you ought to get into the habit of looking at a spectral analysis of the sound in your home. modern power supplies and motors rely on the ever more powerful and cheap power transistors that we have these days -- they are able to switch power on and off at very high frequencies and thus reduce the size of the rest of the circuitry needed to raise or lower voltage. but this often results in extremely high pitched sound coming from parts that, for whatever reason, physically move or expand in response to current or voltage changes. in cheap electronics, this effect is not accounted for and controlled with vibration dampening materials applied to the vibrating parts, and the result is a maddening high pitched squeal. even if humans arent able to hear it, there could be devices in your house that make some kinds of pets uncomfortable. ive been meaning to buy something that will let me detect ultrasonic sound so that i can smash those devices with a hammer.
ive always wondered what it would be like if you used a dual motor system in a car, where one motor is wound and sized for very high torque and the other motor is wound and sized for very high speed. i think it would be great because, as long as they were induction based motors, you could run one and leave the other off with no interference from the one that is turned off. it would be like having a transmission without any of the energy loss or maintenance problems. you could also distribute power however you want among the two motors, and in a way have something like an infinitely variable transmission. that would be really cool.
I've always wondered what it would be like if you used a dual motor system in a car, where one motor is wound and sized for very high torque and the other motor is wound and sized for very high speed.
Traction motors for locomotives and transit vehicles used to be built with multiple windings and switching. The windings were switched from series to parallel as speed increased. Locomotives once had manual "transition controllers" for this.[1] Here's the more automatic mechanism from a PCC streetcar of the late 1940s.[2] The operator just has an accelerator pedal, and all that control gear takes care of the complexity of operating the motors.
I've always wondered what it would be like if you used a dual motor system in a car, where one motor is wound and sized for very high torque and the other motor is wound and sized for very high speed.
The dual motor versions (D) of Tesla electric vehicles (models S and X at least) use this principle. As far as I know, they have induction motors. However, I am not sure to which extent one of the motors is used primarily for high torque and the other for high speed.
Yup, the front motor is the cruising motor and the rear one is the accelerating one(since weight distribution means that the rear wheels get a bit more traction).
They shut the rear motor down at highway speeds giving the Dual Motor cars slightly better range.
Dual motor, non-P: 2 small motors in front/rear with front motor geared for cruising, rear for accel.
Dual motor, Performance: 1 small motor in front geared for cruising, one large motor in the rear.
There's really no reason to have a front motor only. It's done in ICE cars to save cost/complexity since the engine is up front. With how the center of gravity shifts during accel you want the drive wheels to be on the rear since they have better traction.
Same reason in reverse you have large disk brakes on the front wheels and drum in the rear.
Not really, unless you're in a panic brake situation(where I want friction brakes anyway) Tesla only brakes to 60kW which is more than plenty for normal driving.
You also want friction braking for cases where you've got 100% charge or the battery is cold and you can't dump energy into the pack.
Maybe you want the rear wheels driving under acceleration if accelerating in a straight line is the only metric your optimising for.
I'll argue front wheel drive is better / safer for most driving situations most people find themselves in, especially in slippery conditions, on wet or dirt roads.
I'd argue that independent all wheel drive is better / safer for most people ;).
That said the traction control on Tesla is responsive to < 1ms. Lots of throttle inputs that would cause traction to break free on a traditional ICE due to momentum in the drivetrain doesn't on our Tesla. Heck I can floor it in the rain and it doesn't step out at all.
The first time I sat in a Prius, I heard an annoying high-pitched noise like this. I don't hear them in current models, but it's possible that this is just because I'm 15 years older now and my high-frequency hearing is not as good.
That phenomenon is known as cogging[1]. Improved motor controls (Direct Torque Control) and motor designs (trapezoidal magnetization) have indeed eliminated it from all but the cheapest designs. Induction motors like those in the Tesla model S and X (but not the upcoming 3) don't have any cogging at all.
>modern power supplies and motors rely on the ever more powerful and cheap power transistors that we have these days -- they are able to switch power on and off at very high frequencies and thus reduce the size of the rest of the circuitry needed to raise or lower voltage. but this often results in extremely high pitched sound coming from parts that, for whatever reason, physically move or expand in response to current or voltage changes. in cheap electronics, this effect is not accounted for and controlled with vibration dampening materials applied to the vibrating parts, and the result is a maddening high pitched squeal.
Battery-powered motors almost always operate in the range of 80 to several hundred kHz, which is basically unavoidable. Those make up a minority of motors in your home. Wall-plugged motors use AC, in which case they have no high-frequency harmonics, or they are DC in which case the ultrasonic noise comes from the brushes scraping and arcing on the commutator. This is the source of noise in vacuums and the one you're most likely to hear but it's basically static at a very high frequency. Supposedly this is one of the reasons pets hate vacuums, because it's a loud noise of a rarely-heard pitch. Vacuums will be much louder than almost any other motor in your house.
The difference between cheap an expensive power supplies is often down to the use of fully integrated PSUs. The expensive ones operate in the MHz, which lets them use very small capacitors that are built into the chip. Cheaper supplies operate at closer to audible frequency, but they aren't actually louder despite using larger components. The efficiency is relatively close to a more expensive supply so the amount of energy loss is also similar.
>ive been meaning to buy something that will let me detect ultrasonic sound so that i can smash those devices with a hammer.
It's actually very easy to make one! Cheap (<50 cents) electret microphones can hear up to 100 kHz and are pretty common in DIY bat detecting microphones[1]. Note that you can't use normal ultrasonic sensors like those used in rangefinders (about 1 cm wide, black plastic cylinders). Those are heavily tuned to resonate at 40 kHz and can't pick up sound outside that range at all.
>ive always wondered what it would be like if you used a dual motor system in a car, where one motor is wound and sized for very high torque and the other motor is wound and sized for very high speed.
That's exactly why 4wd Tesla models have a longer EPA rated range, or at least speculated to be why, anyway. The EPA range test is done at a set speed and Tesla optimized on that by having one motor for lower speed and one for higher speed. It's also useful for vectoring torque to the front/back for braking/acceleration. You can't use it like a variable transmission though, since there's very limited benefit to splitting the power up.
The benefit in practice is pretty unclear since you won't be driving the exact speed it's optimized for and the difference in efficiency is only a few percent anyway.
Expense of motors (not to mention batteries to support them) is still a problem with electrifying smaller equipment. I was looking at repowering one of my old 12hp Gravely walk-behind tractors -- to find an equivalent torque / HP EV motor to replace the Kohler 301 in it would have been upwards of $2-3k. And that's not including sourcing batteries, supporting electronics, etc. A little diesel engine would be about $600.
I hope to see the day when projects like this could be cost effective.
Where you likely want to search for affordable electric motors is 'electric golf cart motors'. When I was looking at refurbishing a golf cart in the early 2000's I was a bit surprised to see high performance brushless dc motors being used.
motors are dead cheap- maybe 6x more than the cost of their weight in steel for non-PM motors. The problem is availability. Chinese factories don't sell in low volumes.
The terminology around motors is... inconsistent. Induction motors are a specific kind of brushless motor with windings on both the stator and rotor, so named because it induces a current inside the rotor windings.
Reluctance motors don't use permanent magnets or rotor windings and don't have rotor currents. Universal motors (which until very recently were absolutely ubiquitous in appliances) are commutated rather than inductively coupled and also don't have motors. There are a half-dozen other types but they're mostly novelties or variations on a theme.
What is there to improve in motors ? They are already 95% efficient, and some BLDC motors even 99% efficient. The most efficient machinery created by man. What really needs improvement are battery storage, to be more dense and lightweight.
I worked for a BLDC company in their research division for a few years and there are many things that can still be improved. At the time we were working on reducing the size of motors without sacrificing torque or efficiency. This was particularly the case for industry motors where we developing a motor half the size of an older industry standard AC motor, but with the same power and 94% efficiency.
Size is where the majority of advancements for BLDC motors will come.
Reading from other comments: the 95% efficiency in "traditional" motors is only reached in ideal, fixed conditions (in terms of speed and torque). New advanced control systems increase efficiency at different speeds/torque.
Accurate! For many applications it was considered irrelevant and motors were just wound for a fixed speed. Outside this range the efficiency can drop drastically, below 50% for some motors (hence why shunt-wound motors were once used).
They are essentially an offshoot from the decision made nearly 20 years ago: Lappeenranta University of Technology decided to focus on energy tech, and added environmental tech as a second leg a few years later. Visedo is one of the results.
I also remember, while their offices were still in the tech incubator warehouse, trying out their prototype electric "car". Lightweight, all sheet metal, uncomfortable to sit in and steer - but went from stand-still to ~50km/h in no time at all. Looks like they've managed to scale up and refine their technology quite a bit since then.
Is anyone researching motors that use elerctric charge instead of magnetism? Couldnt those be cheaper to build and possibly more efficient and powerful?
> Is anyone researching motors that use elerctric charge instead of magnetism? Couldnt those be cheaper to build and possibly more efficient and powerful?
In general the magnetic permeability of materials is 1-3 orders of magnitude higher than the electrical permittivity. Materials with high permeability are also 2-3 orders of magnitude cheaper than materials with high permittivity. It makes much more sense to make magnetic motors because of those two facts.
However charge-based motors have existed since the mid 1700s[1]. They're exclusively novelties, but they are exceptional novelties indeed. You can even use a kite to power them from atmospheric electricity[2]! That's the same voltage difference that eventually creates lightning, but without a storm the electricity is quite weak and the motor quite inefficient. The voltage is high enough to be unpleasant though.
Existing motors are already very efficient when they're at maximum. The thing is that with an electric field motor you'd need to have a changing electric field which means you have a magnetic field anyways, which could result in less efficiency.
I'm surprised to read in an age of LEDs lightning is supposed to use more electricity than computers. I'm not even sure that on average the motor uses that much more energy than all the other appliances in an electrical car.
Even LED lights have a typical efficiency of only 10-20%. Low pressure sodium lamps (many yellow street lights) can reach 30% efficiency. But in general, lighting is far from being a solved problem even if you assume everyone is using state-of-the art lighting solutions.
Yes, but that doesn't explain why all the computing we are doing should spend less electricity than light. I bet I can run all the light in my apartment for 24 hours and don't use as much energy as when I'm playing a AAA 3D computer game for an hour.
If you play your AAA game on a PS4, that's about 120W [1].
Assuming you have three 60W-equivalent light bulbs on in your appartment, using halogen lamps your lights use as much power as the PS4. If you still use incandescent lamps, that's 180W, about as much as much as the PS4 and a 55" LED TV. With 7W LED bulbs you need 5 hours of lighting to match the PS4, or 8 hours to match PS4+TV.
Of course you might have a computer that uses significantly more power. But the best current-get Intel i7 still has a TDP of only 112W (165W for i9). Add to that a GeForce GTX 1080 TI with a TDP of 250W. Even during gameplay both will on average use less power than their TDP. Without going with dual-GPU configurations you can't build a reasonable current-gen computer that matches the 500Wh that our three 7W LED use over 24h. And I suspect you actually have more than three light bulbs.
1hp is ~700W. In an electric car, the big competitors with the engine are AC and heating (since you can't get that one as a side effect of the ICE's thermal waste). The rest is minor at best, leds are sub-watt.
I know its kind of a ofshot question- but is there research in non-chemical batterys? As in storing energy mechanically in nano-structures? Goggle did not reveal much there.
Batteries are chemical by definition. The closest thing to storing energy in nanostructures would be nonchemical supercapacitors, which use nanostructures or nanofabrication to achieve high surface areas. As a side effect of electrical attraction they store some energy mechanically too.
In general storing mechanical energy at the nanoscale is not efficient. As you get smaller mechanical properties become less relevant due to the increase in relative surface area (aka square-cube law). That makes electrical and chemical properties much more powerful.
Tesla and Steinmetz figured out the theory of AC machines in the early 20th century. This was the first industrial technology where you needed advanced math to get anything to work right. Complex numbers. Calculus. Laplace transforms. That bothered some people, such as Edison. By the 1930s it was figured out, and generations of EEs struggled through rotating machine theory in college.
Then all the cool kids went off to radio and transistors and computers. Rotating electrical machinery was a mature field. Maybe a few people at GE in Schenectady worked on it.
Then came power semiconductors, and chopper-type motor control, where power was being turned on and off at moderately high frequencies. At first this was just applied to existing motor designs. But AC motors were designed for sine wave power. Choppers didn't produce clean sine waves. Much effort was put into making variable-speed controls that produced the nice sine waves motors needed. Classical AC theory was built around sine waves, and engineers knew how to do that kind of analysis. This worked, but it made AC motors buzz at the chopper frequency, and as chopper frequencies went up, whine. When you ride on BART, that's what you're hearing from the motors. The waveform mismatch also led to unwanted heating in the windings and inefficiency.
Variable-frequency 3-phase AC motors went from exotic to normal. Today, everything from a Tesla to a drone to a Diesel-electric locomotive uses such motors. The big power semiconductors required aren't that big. Here's one for a locomotive.[1]
In recent years, motors have started to be designed for the non sinusoidal waveforms that come out of chopper power supplies. This required new theory and much simulation of magnetic fields. There's plenty of compute power available and commercial packages for that kind of analysis. Now we're seeing more advanced motor designs that match well with their control electronics.
After most of a century, rotating electrical machinery design is cool again.
[1] http://www.ametrade.com/eng/electronics/products/IGBT_IGCT.s...