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Regenerative Braking Explanation with Ultracapacitors PDF Print E-mail
Written by Leslie Hodge   
Friday, 26 September 2008
Regenerative braking strategies are moving beyond automobiles and into the more broad category of regenerative. What goes up must come down! Is now as applicable as What speeds up must slow down! Regenerative Braking Elevator

Many industries can significantly reduce their carbon footprint by designing ultracapacitors into their machinery. The goals is regeneration of lost energy. Similar to regeneration of lost energy during braking, other machinery loses energy.

As an example, construction and cargo cranes can recapture lost energy to be utilized as an assist to bring the crane back up. Another example is an elevator. Elevators come in many sizes. From freight and passenger elevators to mining and aircraft elevators. The amount of energy that is lost during the decent is immense and designing a bank of ultracapacitor to instantly catch this energy is not difficult. Braking is aided by a motor that acts as a generator, converting kinetic energy to electrical energy.  If the electrical energy is passed through brake resistors, the energy gets dissipated as Joule heat; if it is captured by energy storage device such as ultracapacitors, there will be less heat dissipation + regeneration.

Or, you may want to use the energy in as a backup emergency system in the event of a power failure. For example, how many times have we experienced a ‘stuck’ elevator. We have heard of people spending hours and even days in these situations. With ultracapacitors, you can have enough energy storage to get the elevator to the designated floor with the doors open.

Many industries can significantly reduce their carbon footprint by designing ultracapacitors into their machinery.  If you have an application that could benefit from regeneration of lost energy or emergency power backup and would like to know a deeper understanding of how a it could be designed into your application, all you have to do is ask an expert....

Leslie

Me trapped in an elevator...

Readers have left 5 comments.
 No.1  Untitled
The use in cargo elevators is an interesting application. I have not thought of that.
Jimmy (Unregistered) • 2008-09-26 13:34:44
 No.2  Untitled
Only anybody in it is not interested in Russia.
Guest (Unregistered) • 2008-10-13 22:24:48
 No.3  Untitled
I just want to know purely about capacitor and their uses
Ahmed (Unregistered) • 2008-11-06 00:37:23
 No.4  Retired Elevator Design Engineer
First, any elevator (as opposed to a “hoist”) is counterbalanced so that the only dead weight to be moved, as a maximum, is approximately 55% of the rated loading of the elevator. The mass of the car, and the transfer mass of the elevator ropes and trailing cables is normally counterbalanced so that no energy is expended in ‘lifting’ this weight.
Second, the presence of the counterbalance means that a descending elevator is as likely to constitute a ‘hauling’ load as it is to be an ‘overhauling’ load.
Third, virtually all modern elevator systems are already fully regenerative, whether they employ a.c. or d.c. motors. In Europe, as opposed to the United States, a.c. motors are the norm, either synchronous or asynchronous. On smaller elevators, regenerative braking may not be provided simply because the additional cost of the equipment to provide regenerative braking outweighs the cost savings in energy to be obtained (see below).
Fourth, the control system for an elevator must control, very tightly, not only the speed, but also the acceleration and jerk (rate of change of acceleration) of the elevator in order to ensure passenger comfort and safety. Consequently, the control of the regeneration is not simple, since the elevator control must, where necessary, transfer from energy input (during acceleration) to controlled regeneration IN FLIGHT without perceptible disturbance to the speed and acceleration profile of the elevator. In this respect, elevators are almost unique amongst industrial speed control systems.
Fifth, the inclusion of any energy storage element, such as a capacitor, in the main power control loop has serious implications for passenger safety and requires even more additional equipment in order to comply with the requirements of national and international safety standards, with consequent additional cost (see ASME/ANSI A17.1 or EN81-1/EN81-2). The same comment applies to power factor correction capacitors.
Sixth, it is well established that it is rare for the elevators to account for more than 5% of a building energy consumption. The elevator system as a whole will account, typically, for less than three percent (3%) of the overall building energy consumption. There are almost always other areas of energy saving in any building which will be far more rewarding and far less hazardous than will the elevator system in respect of environmental effects or cost saving.
Guest (Unregistered) • 2009-01-15 03:04:47
 No.5  Not so fast!
All these things are true, but then they are equally true in practically all aspects, in the automotive application. And every percent must count.

Unless I am mistaken, lift (elevator) technology still operates on an intermediate "DC rail" since variable speed control is required, which immediately puts it on a par with the automotive application - or indeed just about any transport technology. In the "old days", the DC was produced by a rotary converter which was certainly a point of lost efficiency and regeneration into the power grid quite impractical as this would require a synchronous converter or other substantial complexity. Batteries would have been an alternative, but not cost-effective.

Nowadays of course, this has been replaced by solid-state power conversion with substantially increased efficiency and the motors also use solid-state commutation and regeneration. Nevertheless, there is still a DC intermediate rail where the ultracapacitor and its power converter could attach with the utmost ease (i.e., inexpensively) with convenient offsets. Since the system is always a net consumer, there is no need for regeneration into the AC mains (less complexity there), but the "buffer" substantially reduces the peak load on the mains.

Safety is not a concern, just design, design, design! An inexpensive resistive "dump" can be present as a "fail safe". Rating of the ultracapacitors, unlike the matter of power factor correction, is nowhere near as critical since they are "isolated" by their power converter (required by all ultracapacitor designs due to their continuously varying voltage) which can disconnect them instantly should they fail. And since we are using continuously variable power conversion anyway, various modes of "limp home" function are already in place.

The fact that lifts are counterweighted is irrelevant, other than that it reduces the overall power rating required of the system. The inertia of the lift (and its contents, plus the counterweight) is still of major significance except to the extent of pneumatic piston losses, but these must always be minimised as a matter of efficiency.
Guest (Unregistered) • 2009-02-22 04:26:03
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