Do the drive systems constructors think about safety in their futire products for elevators, and what are the future trends in the technology of AC drives for elevators.

-- Zied M'nasri (zied_m_nasri@ch.schindler.com), November 17, 2003

Answers

Yes. Reliability of the main drive is a primary design issue related to elevator safety. The minimum protection of adjuster personnel from accidental electrocution or fire is dictated by insulation type, clearances, material choices and physical shielding means specified by national codes (UL/CSA/ASME/CE/VDE etc.) Reliability is more about designing the equipment to meet the requirements of real life elevator operation with enough margin to ensure continued operation through 'unexpected' events (like lightning impulses or ground faults). Some manufacturers perform better in this regard than others by doing more than the minimum. However, the design and implementation of safety related operating sequences of the elevator lift controls is often decided by car controller and/or control panel manufacturers. The drives themselves merely follow what the 'relay logic' tells it to do. Again, some elevator control manufacturers make better choices than others.

Regarding the future - AC drives are becoming smaller, more technologically advanced and able to handle larger hp/kW. Modern vector control will always work better than VVVF. Closed loop drives with encoder feedback will always work better than those without. Mid - high hp (kW) size elevator drives require regeneration to be practical. [Resistor braking is just too wasteful.] This does save on operating energy costs but also makes the drives physically larger and cost more. An active rectifier front-end can also clean up those nasty utility line harmonics. Matrix power converters may eventually replace the AC-DC-AC types of today, but the IGBT manufacturers need to build the right bi-directional AC switch parts. The change-over from induction to PM motors does not really affect the cost of the drives that much, only the complexity of the internal computer code to make it operate.

-- Don Vollrath (dvollrath@magnetek.com), November 17, 2003.