This is how to make a lift an energy-intelligent lift

Lifts consume energy, lifts supply energy. Intelligent ultracapacitor technology makes notable lift operation energy savings possible.

The electric motor also acts as a generator during upwards and downwards trips of electric lifts irrespective of the load. Due to the general efficiency of the overall system, the energy generated is always less than that consumed. ISO 25745 – Part 2 describes how to conduct energy calculations in relation to the use of the lift.

There are three alternatives for destroying or using the energy generated:
1. Most frequently, it is destroyed (as heat) in a brake resistor.
2. However, the energy generated can also be fed back into the grid. This is achieved by exchanging the normal, unidirectional drive for a bi-directional (regenerative) one. However, the energy cannot be stored, but must be simultaneously consumed elsewhere.
3. The third solution, proposed here, stores the braking energy in supercapacitors where it can be retrieved by the system. This bidirectional energy storage process is carried out in DC, thus avoiding additional filtering.

What are supercapacitors?

Supercapacitors employ an energy storage technology that boasts a long service life, a million charging and discharging cycles, high power density and especial reliability. The kinetic energy recover system (KERS) is the ideal application platform for supercapacitors, since they are in addition distinguished by fast charging and discharging. They are based on "curved graphene", a raw material made of carbon patented by Skeleton Technologies.

How does Kers Work?

Every VVVF (variable voltage variable frequency) drive converts the 50 Hz AC grid power into direct current (approx. 560 VDC). This DC voltage is then converted back to AC voltage, which is variable in voltage and frequency. Supercapacitors are low voltage storage elements that convert voltages of 600V with an intermediate element to lower values. To use this energy, the element has to be bidirectional and is termed a DC/DC converter. Basically, the KERS from Epic Power is a piece of power electronics that converts energy in the supercapacitors into direct current and this in turn into low voltage.

The converter has to be configured as follows to make this process practicable for use:

Efficient. During the energy exchange, all of the losses in the process are duplicated. Electrical efficiency of more than 98 percent is required, since otherwise the ROI plummets.

Effortless connection. The plug-and-play functionality automatically recognises when the motor is acting as a generator. The supercapacitors store the energy before it reaches the brake resistor and return it before the drive draws it from the grid. Once the supercapacitors are fully charged, the excess energy passes to the brake resistor. When the energy has been consumed, it is drawn from the grid.

Compact. For ease of operation, the module includes supercapacitors and power electronics in an easy all-in-one system.

Compatible. Irrespective of VVVF or lift manufacturer, no adjustments have to be made.

Flexible. Not all lifts are the same in terms of energy consumption, energy generated and energy requirements. For this reason, the base system is designed to transfer power in kW and store energy in kJ. Parallel operation is also possible at any time in order to double the power or energy. Parallelisation in DC is simple and only requires a direct connection without additional wiring. KERS is the result of the combination of Skeleton’s supercapacitor cells and the intelligent power electronics of Epic Power.

Authors
Dr Pilar Molina Gaudó, Ph.D. Professor for Electrical Engineering, CEO of Epic Power.
Ants Vill, Vice President Product von Skeleton Technologies

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