Quick question - can linear induction motors be used to generate electricity?

[Howard]

Say you use one to propel a vehicle down a track (check out the SERAPHIM motor, it's cool stuff), can you use it to brake the vehicle by converting the kinetic energy of the vehicle into electricity?

I know that with most other types of electric motors, you can do it.

 

[Rhin0]

or you could use regenerative braking technology that has already been around for a while. The kinetic energy is turned into potential energy and then when you start again it uses that trapped energy to get you going, saving gas or power. Since the inital acceleration is the energy hog this really helps.

Think they store the energy hydraulically if im not mistaken.

 

[Howard]

Originally posted by: Rhin0
or you could use regenerative braking technology that has already been around for a while. The kinetic energy is turned into potential energy and then when you start again it uses that trapped energy to get you going, saving gas or power. Since the inital acceleration is the energy hog this really helps.

Think they store the energy hydraulically if im not mistaken.

Is there a way to convert kinetic energy into electricity using a LIM, though?

 

[Mark R]

Don't see why not.

Just like a squirrel cage induction motor, a LIM should operate as a generator if the energising AC is of a lower frequency than corresponds to the (angular) velocity of the motor.

Electronically controlled bi-directional inverter drives are, of course, recommended to provide optimal drive/braking irrespective of motor type.

 

[Howard]

Originally posted by: Mark R
Don't see why not.

Just like a squirrel cage induction motor, a LIM should operate as a generator if the energising AC is of a lower frequency than corresponds to the (angular) velocity of the motor.

Electronically controlled bi-directional inverter drives are, of course, recommended to provide optimal drive/braking irrespective of motor type.

Thanks. I was wondering how suitable SERAPHIM motors were for car suspensions - kind of like the BOSE suspension, but I was thinking about it before they ran the press for that.

 

[jagec]

Originally posted by: Rhin0
or you could use regenerative braking technology that has already been around for a while. The kinetic energy is turned into potential energy and then when you start again it uses that trapped energy to get you going, saving gas or power. Since the inital acceleration is the energy hog this really helps.

Think they store the energy hydraulically if im not mistaken.

Regenerative braking almost always = using electric motor to generate electricity.

From what I understand about LIMs, you could use it to generate electricity, but it would be in an awfully funny waveform (AC with a frequency proportional to the speed, right?), and would take a bit of signal processing to be able to store it in a capacitor or something.

 

[Howard]

Originally posted by: jagec

Originally posted by: Rhin0
or you could use regenerative braking technology that has already been around for a while. The kinetic energy is turned into potential energy and then when you start again it uses that trapped energy to get you going, saving gas or power. Since the inital acceleration is the energy hog this really helps.

Think they store the energy hydraulically if im not mistaken.

Regenerative braking almost always = using electric motor to generate electricity.

From what I understand about LIMs, you could use it to generate electricity, but it would be in an awfully funny waveform (AC with a frequency proportional to the speed, right?), and would take a bit of signal processing to be able to store it in a capacitor or something.

Ford introduced a truck that used a tank into which oil was pumped at high pressure. The pump was powered from the driveshaft, I believe, and was engaged during braking. This slowed the car down and stored energy in the tank, which could then be released during acceleration or whatnot.

 

[Evadman]

Originally posted by: Howard
Ford introduced a truck that used a tank into which oil was pumped at high pressure. The pump was powered from the driveshaft, I believe, and was engaged during braking. This slowed the car down and stored energy in the tank, which could then be released during acceleration or whatnot.

Yep, I wanted to get it retrofitted to my Truck, but it was way to expensive. (6x what I paid for my truck)

As for your original question, You can, and I can think of one place that does it off the top of my head. It is an amusment park ride actually, Top Fuel Dragster @ Cedar Point. LIM's start accelerate and decelerate the coaster.

 

[TheDude05]

Actually Top Thrill Dragster does NOT use LIM motors. It uses a form of hydraulics and a launch cable like that used on aircraft carriers. However there is another ride at the same park called Wicked Twister that uses LIMs. Theres lot of roller coasters out there that use LIMs but its starting to get replaced by hydraulic launches. Its faster in terms of mph, can accelerate faster, and the main reason, much much cheaper. (coasters are my other hobby)

 

[KMurphy]

Most motors do not make good generators. That's because the most common type of motor is the squirrel cage induction motor. It can be used as a generator, although a very poor performing one. You have to rely on residual magnetism in the rotor to generate electricity (no external field excitation), you have to run it faster than its synchronous speed and there is no voltage regulation. This makes it very unfeasible to store back into a battery, batteries require a steady and stable DC voltage to charge properly.

Synchronous motors perform well as generators, but these are usually very large machines (serveral 1000's HP). They are prime movers, not suitable for commuter transporation.

I don't have any experience with LIM's though, I suggest you post your querry to the eng-tips forums at eng-tips.com. (Homework questions are not allowed there)

DC motors are also suitable for regeneration, but again you need to control the field excitation. These type of motors are typically used for motive power because of easy speed control. In the industrial world, VFD's are replacing DC drives as the choice for process speed control. DC motors are expensive and require a lot of maintenance for brush changes.

Some smaller DC motors use permanent rare earth magnets for field excitation; these were limited to fractional to integral horsepower sizes. Today, PMDC motors up to a few hundred HP are available and are very expensive.

The big problem with electricity in general is that it is difficult to store once generated. Electricity is also difficult to control; though we've come a long way at present. Batteries still remain the premier storage media for electricity and the technology has been around since electricity was discovered.

If you really want to come up with a breakthrough, find a way to massively store electricity long term. Until then, the most efficient method is to carry onboard fules and perform energy conversion via the use of fuel cells, internal combustion engines, gas turbines, steam turbines; etc.