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WP6-Brochure-E4 brochure - ELA European Lift Association.

WP6-Brochure-E4 brochure - ELA European Lift Association.

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If the linear motor is mounted on the car itself, then the counterweight can be eliminated, and<br />

the system becomes ropeless. This allows for designs that use horizontal switching between<br />

adjacent hoistways and for multiple cars to travel independently along the same shaft which<br />

leads to almost unlimited control options.<br />

The main limitation to the use of Linear Motors for lift propulsion are the production costs<br />

associated with the large motor length, but they are expected to decrease as the technology<br />

matures.<br />

Linear Motor technology is not expected to reach its full potential in the next few years, but<br />

the technology is clearly worthy of serious consideration for future designs.<br />

This technology has also been used to operate lift doors, reducing moving parts and<br />

maintenance issues significantly. Door problems account for around 40% of all service calls [6].<br />

3.3 Advanced Drives and Regeneration<br />

The choice of the drive has historically been motivated by factors such as travel speed,<br />

levelling accuracy and comfort. Before the introduction of solid‐state control techniques, the<br />

most common option was the Ward Leonard set which provided the best ride quality.<br />

However, there are large energy losses in the motor and generator arrangement, which<br />

converts electrical energy into mechanical energy and finally back to electrical energy again.<br />

The advent of power semiconductors and subsequent evolution of AC motor control<br />

techniques has led to its wide spread use with equivalent ride quality and even some<br />

advantages such as lower maintenance, faster response, energy savings, lower peak demand<br />

and better power factor.<br />

The most common types of motor drives in use today are:<br />

• DC motor with Ward Leonard set<br />

• DC motor with solid state controller<br />

• Two‐speed AC motor<br />

• AC induction motor with Variable Voltage controller<br />

• AC induction motor with Variable Voltage Variable Frequency controller<br />

• AC Permanent Magnet Synchronous Motor with Variable Voltage Variable Frequency<br />

controller<br />

A detailed description of these drive systems can be found in [4].<br />

In DC systems, solid state controllers have been the most common option since the early 90’s,<br />

substituting the Ward Leonard set with great efficiency improvements and more accurate<br />

speed and levelling control. The energy costs when using solid state controllers can be reduced<br />

by as much as 60% when compared with equivalent Ward Leonard drives [4].<br />

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