Using UPSs to provide secondary power for emergency evacuation lifts - Standard UPS explode with regenerative energy from motors during motor braking.

Using UPSs to provide secondary power for emergency evacuation lifts

 Have you ever considered how you would evacuate people from a multistory building in case of power failure?

Do you have responsibility for people coming and going from public buildings? If you do, you need to consider how you’re going to handle evacuation in the event of an extended power failure and are not equipped with a standby generator.

It doesn’t need to be a dramatic situation just an extended power outage. Lifts by default should have the means to travel to the closest floor and open their doors so occupants can leave in the case of power failure.

That is fine for able-bodied persons who are capable of continuing evacuation using the staircase.

How Would You Evacuate People With Mobility Issues?

A simple cost-effective solution is to power lift through UPS, however, it may not be as simple as it seems.

Suppliers and installers of UPS systems intended to support lifts should be aware that some lifts have regenerative braking, which generates a potentially damaging back–EMF onto the DC Bus within the UPS.

Harnessing Energy with Regenerative Loads

The capacity of the lift motor, compactness, and high inrush are some of the features that can be easily managed for UPS’s on the market nowadays, but being able to handle regenerative loads is a completely different situation. Regenerative UPS units use the regenerative load from braking action; this load is used for creating regulated power which is connected to machines generating regenerative load.

Regenerative Uninterruptible Power Supply (UPS)

Forwarding Mode

• When the Elevator is moving upwards with the load, the motor drive is in forwarding mode (normal mode) drawing energy from Utility or UPS.
• The motor will converts the supplied electrical energy into kinetic energy.

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  Breaking Mode

• Every elevator motors operate like a generator while braking when moving downwards with load.
• During regenerative braking, the motor restores part of the kinetic energy into electrical energy.
• This electrical energy will be directed to the UPS, and use to charge the UPS BATTERY or recycle back to the utility.
• No energy is wasted.
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  REGENERATIVE LOAD OPERATION
•  The EF LIFT UPS incorporates an intelligent braking system, using IGBT controllers to electronically absorb any regenerative back feed energy from the lift. Regenerative load causes reverse current to flow to the output of the UPS system. This reverse energy causes the internal DC bus within the UPS to rise above safe levels of the UPS design and can cause damage to the DC Capacitors, Rectifier and Inverter. The PowerPro EF Lift system has a separate IGBT Controlled Regeneration Box that connects directly to the UPS DC Bus. The DC bus voltage of the UPS typically floats at ±405Vdc and can boost up to 435Vdc. The Regen Box monitoring system continuously analyses the internal rise of the DC bus voltage, when the voltage increases over 435Vdc fast switching IGBTs connect DC resistors and dissipate the energy into heat, protecting the UPS components and Inverter operation. When the DC bus voltage decreases back down to an acceptable level, the Regen Box self deactivates.
• SOURCE 1:https://www.kohler-ups.co.uk/using-upss-to-provide-secondary-power-for-emergency-evacuation-lifts/
• SOUCE2: https://www.everexceed.com/blog/ups-for-lift-application_b267