Top Ten Challenges – Energy Storage

Thinking about the top challenges we face in mechatronoics there is one that’s connected and not really obvious.  It’s energy storage.  The energy storge problem takes many forms based on the application.  Our tendency is think in terms of batteries because that’s most likely the form of energy storage that we are most familiar with.  Cell phones, laptop computers and many other portable gadgets of the Internet Age are very dependent on their energy storage systems for their size, weight and hours of service.  But of course, these are all battery applications.

So  our first reaction to energy storage as a mechatronic challenge  might be that it’s really just a chemistry problem and not mechatronic at all.  But energy storage comes in many forms and applications.  Energy storage is a requirement of almost every form of energy and control systems.  Hydraulic and Pneumatic systems require accumulators to store energy so that short term loads don’t use up enough power to make the system unable to respond to demands placed on them.  Energy rate over time is a governing principle in all these systems.

The initial linkage in my thinking was the electric car.  As someone who worked in the electric car field many years ago, it was that the battery that killed the electric car.  Carry 2200 pounds of lead acid batteries to make a car go from here to there simply didn’t make sense.

There has been a lot of debate on that subject and a LOT of incomplete information offered which clouds our understanding of the social or political problem.  But the cost and energy density of the battery pack is making sufficient progress to insure that quite a few new vehicle options will be available in 2010 and 2011.

In normal batteries energy densities of 30 Watt hours per kilogram of weight are common.  Nickel metal hydride doubled the energy density to about 80Wh/kg.  But the real improvements are coming from the lithium chemistries at 130+Wh/kg.  There are more dense chemistries around, but they are typically very high temperature or otherwise very expensive, and so not practical for widespread use.

But the energy storage problem is not limited to chemistry.  The flywheel energy storage system has been a topic of engineering development for decades.  Energy density in these systems is in the range of 100 to 130 Kilowatt hours per kilogram, a thousand times more power.

So why aren’t we working on that for cars?  It’s been done several times and never quite works out.  Chrysler had a prototype K type car with a Garrett flywheel system.  Couldn’t make it small enough to be cost effective.  And there were issues of life expectancy and failure modes due to the fact that flywheel was operating on magnetic bearings in a vacuum housing.

The national power grid has exactly the same problem at orders of magnitude more power.  If there is to be any hope of an intelligent national power grid, storage systems of this kind are needed.   Solar power only happens when it is daylight and there are no clouds.  Wind power only happens when the wind is blowing.  So if there are big fleets of electric cars charging overnight, there have to be storage systems that can manage the energy storage requirement.

So mechtronic challenge #4 – Energy storage. Large and small, high efficiency and long term.

Electric Vehicles and Electric Motors

A friend of mine finally got delivery of a Tesla Roadster.  This prompted discussion of the drive train and the fact that Tesla has had to go from two speed transmissions which were failing to a transmissionless drive train.  The ultimate mechatronic challenge, the electric car, is also a challenger in terms of the precise  application of electric motor technology.

But it has to be said that the motor and drive solution for the electric car is not where the problem has to be solved.  Any motor can be made to run an electric car.  What is critical is how you apply it.  The starting conditions require high torque at low speed and the running conditions require low torque at high speed.  So, typically, what looks like a small 5 to 15 horsepower running requirement at full speed, becomes a 150 horsepower starting requirement depending on how quickly you would like to start.  If you want to keep up with a Corvette, it uses 450 HP to start.

And this produces a lot of confusion.  Why not use at 2 speed transmission to help the situation.  Fine, but the ones that are available can’t handle the dynamic response of the electric motor.

Can electronics help this situation?  Interestingly, yes.  There is a control algorithm generally called vector control which allows you to manage the rotor torque and stator torque separately.  By varying the phase angle between the two, like advancing and retarding the timing of a mechanical distributor cap on an internal combustion engine, you get different speed torque curves out of the motor.  COOL!  Is there any downside to this?

Yes.  You need more current to produce more torque.  That doesn’t change.  So you have to be able to supply the current, and you have to be able to manage the heat.  The heat is transitory since you only need the high current during starting, but it is best to have sophisticated software running to keep track of the RMS temperature of the motor.  Lower operating temperatures mean longer life and reduced risk of demagnetizing the motor.

So, yes, you can run an electric car with a garden variety AC motor, and with good electronics, you can make it run fairly efficiently.  With higher efficiency motors, the benefit is increased driving range from a given power source.  High efficiency motors are frequently smaller and lighter weigh, but a weight savings in the motor of 50 or even 100 pounds is not that big a factor in the driving range when the curb weight of the vehicle is 3000 pounds.

Basically, its F=ma.  If you can reduce the mass of the vehicle, you reduce the battery payload required to power the car.  Aluminum space frames, like on the Prowler, have been studied by the car industry and can reduce curb weight by 400 pounds and reduce cost by 10% at the same time.  We need to bring all the mechatronic leverage to the situation that we can, if we are going to make electric cars that make sense.  Before its too late for Detroit.

Super Size my Motor?

There is an interesting problem with applying electric motors that is a constant source of difficulty, the nature of peak power versus continuous power.  The problem is that few systems operate at a statistical average power demand.  Frequently, this causes equipment designers to oversize the motor for the application.  At the same time, however, this can put the motor in a very low efficiency operating range.

So what’s the right solution?  Right sizing.  Yes, just like Goldilocks and the Three Bears, not too big, not too small, but just right.

There are some great DOE publications on motor sixing that can be very helpful on the AC motor side, so make sure to give those a look.  But the implications of how to deal with varying loads are complex, each requirement having its own unique conditions that need to be considered.  Is an underpowered application actually safer?  Sometimes, yes.  I recently noticed that a particular orbital sander had been designed so that if the unit became momentarily overloaded, it stalled.  Perfectly safe.  In fact, this design is to be preferred because it prevents accidentally damaging a work piece by burying the sander in the wood and removing too much material.  Who’d have thought of it?  Certainly not Tool Time Tim.  More Power!

In fact, most of us view more as better.  More power means more production.  Or does it.  In an increasingly energy conscious community, more power means more cost.  And that’s really what its all about.  The value of the motor is not just in the purchase price, but also in the operating cost.  Especially if the motor is expected to run for 8 years, 24/7.  (That’s what the life expectancy of large AC motors is)

There’s another trick to the power requirement problem.  How much time is spent at full load and how much time is spent at average power, or, what is the duty cycle?  If the system is starting and stopping frequently it puts different constraints on the motor.  If the system is typically starting only once an hour, then we can consider the thermal duty cycle of the motor.  The momentary peak power requirement is insignificant and the vendor can usually tell from their modeling and testing of their products how much impact the peak current will have on the motor’s average temperature.

After all, its Thermodynamics 101 in the final analysis.  Every energy transformation produces heat as a byproduct.  How much heat a given system can tolerate is the key to its operating life.  In electric motors, the key values are the insulation system’s temperature rating, usually in the range of 150 to 180 C and in the case of steppers, brushless dc and permanent magnet dc motors, the magnet’s ability to resist high temperature and high coercive magnetic fields that can be generated in the motor.  Both sets of limits are generally well considered by suppliers when electrically controller motors are shipped as motor/drive combinations.  This can get a little tricky when pairing motors from one vendor with controls from another vendor.

Top 10 Mechatronic Challenges

I recently wrote on the mechatronic challenge of wind power.  Converting wind into mechanical power that can be harnessed for man’s use has been going on since the 9th Century according to Persian historians.  Certainly wind powered grinding of grains has been around in Europe for several centuries and, lest we forget, wind power pumping of water in the United States.  So there is some irony to the cultural “buzz” about wind power at home and abroad, as if the technology were entirely new.  There’s a lot of history, we’re just updating the technology to produce energy in the age of electricity.

Water has been used for power generation as well.  Following a similar path, we learned during the early part of the industrial revolution how to locate manufacturing plants near waterways so we could convert water flow into mechanical power using the water wheel.  This is, in fact the root of all modern motion control.  All the belts and pulleys, cams, gear reduction systems follow from the work done in mechanical engineering from this period of time.  All of the electronic analogs of the mechanical behaviors found in mechanical systems are the functions which we refer to in mechatronics today.

Wind power and water power gave way in the 1800’s to steam power as the improved steam engine of Watt became the standard of energy efficiency, or should I say “cost effectiveness”.  Because the absolute value of technology is in its cost effectiveness.

Still, wind energy poses a huge technology challenge, as witnessed by the number of vairations that exist and new versions that are emerging.  And hopefully improvements will continue to come from the creativity and  imagination of engineers and inventors all over the world.

But what are the other big mechatronic challenges that come to mind?

Transportation certainly ranks in the top 10.  We have seen hydraulic, pneumatic and electric vehicle solutions touted for a variety of uses, personal transport, delivery vehicles etc.  Ballard Energy and General Motors have both been building hybrid and pure electric buses for city transportation systems for several years with some success.  Interestingly, the electric bus is easier to engineer, which seems unreasonable, but the bus has more interior space to put things like batteries and a methanol converter for generating hydrogen for fuel cells.

But there is a great lesson in what appears to be an almost chaotic string of choices in the transportation arena.  One solution will not work for all requirements.  There are many people for whom a 40 mile per day drive cycle is perfect.  The NEV, Neighborhhod Electric Vehicle, is a golf cart type solution that is rated for street usage, and because of its relatively simple performance requirements, is relatively easy to achieve and lowe cost.  As we categorize cars with greater range, the problems get more difficult, and because of the storage limitations of batteries, have only been achievable as hybrids.  But with some hybrid designs reaching 50 and 60 mpg (estimated), these vehicles may be great solutions for other users.  Although, we must consider their cost effectiveness.  If they cannot be introduced at prices well below $50,000 the absolute value of the technology is not very good.

So forget the 15 second soundbyte that will solve the world’s problems.  It doesn’t presently exist.

I would like to hear from any readers about their picks for the Top Ten Mechatronic Challenge.

Link Shaft for Belt Drive Linear Modules

Belt driven linear actuators continue to increase in popularity as designers look to mechatronic systems to move products more quickly, cleanly and efficiently. Larger and faster gantries are being built for an increasing variety of applications in diverse new fields. Pick and place devices, inspection systems, and general material handling continue to take advantage of the speeds and lengths of travel these components offer.
Read more

Mechanics vs. Electronics

I have offered the opinion that mechatronics is a field whose solutions are mechanically bounded.  The limits to performance are initially constrained by the mechanical design of the system.  This is no small matter.

In many companies the mechanical design and electrical design are separate activities.  I know many companies whose mechanical and electrical departments are at war with each other after years of struggles and crises generated by the separation of the disciplines. Read more

Robotic Kits for “Do-It-Yourself” Packaging System Design

Modular programming and articulating arm kits let you design your own robotic-based packaging system.

By Tom Jensen
Engineering Manager
ELAU Inc., a Company of Schneider Electric

For many years two factors gave robot designers and manufacturers a lock on developing equipment for the packaging market: patents and the specialized kinematic knowledge required to program robotic motion. While the robotic arms were under patent, the controls held the unique motion algorithms needed to handle the complex path planning, blending, and resolution of multiple trajectories to the same point. Thus, robot articulating arms and specific controls were exclusive to robot developers.
Read more

Wabco Extends ZF Contract

WABCO Holdings Inc. (NYSE: WBC) has extended its long-term agreement to supply ZF with transmission automation systems for their AS Tronic and AS Tronic lite automatic transmissions. According to Wabco, the contract will be worth several hundred million dollars in cumulative sales into the next decade.

Wabco’s transmission automation systems enable a manual transmission to be operated automatically, using mechatronics that combine mechanical systems with electronics and computational algorithms for greater efficiency and reliability, the company said.

According to ZF, the AS Tronic is fully integrated transmission that offers reduced maintenance, reliability, cost-effectiveness and environmental compatibility.

Designing a Low-cost Electric Range Control Using a Triac

Applying mechatronics’ principles to traditional mechanical components can result in a more
sophisticated and cost-effective control

By Reston Condit,
Microchip Technology Inc.

Most countertop cooking appliances like electric ranges, skillets, and fryers have an adjustable mechanical thermostat to vary the heat output of the range. This solution is inexpensive, but there are several drawbacks to mechanical thermostats:
•  Mechanical thermostats have to be calibrated at the factory.
•  They have poor simmer performance (control is not precise at low temperatures).
•  The accuracy of these devices is poor.
•  Mechanical components wear out over time.
Read more

Ensure Gear Reducers Contribute to System Efficiency

More than $30 billion is spent on electricity dedicated to electric driven systems, of which, nearly 70% goes to motor systems. There are ways to reduce this cost in your motion based mechatronics system.
By Alex Howe, Application Engineer
US WITTENSTEIN Group

Motor-driven equipment in manufacturing currently accounts for more than 2.3 quads, or 2.3 quadrillion BTUs (roughly 674 billion kilowatt hours) of energy use, which equals nearly 23% of all electricity sold in the United States. Read more

Next Page »