The Power – and Power Savings – of PMS Technology with Regenerative Drives

In the last decades of the 20th century, microprocessor controls replaced conventional relay controls, and AC variable-voltage drive systems were upgraded with AC VV, variable-frequeny technology. However, one of the most profound advancements in the elevator industry is the ever-increasing application of permanent magnet-synchronous (PMS) gearless traction machines.

The AC gearless PMS machine has the best of both worlds.

PMS technology will dominate future lift drive systems, covering all speed ranges currently served by AC geared and DC gearless drives. Thanks to the remarkable breakthrough in research of rare-earth materials for permanent magnets (PMs), PMS technology has progressed rapidly. Its unique and dynamic features, such as high stability, precision operation, more torque at lower speeds, accurate control of rotor position and self-locking stopping without power consumption, have enabled PMS machines to have wide applications in our industry. And, as customers continue to seek more energy-efficient solutions for their buildings, the ability for these machines to couple with regenerative-type VF drives to reduce power consumption by 50% guarantees they will continue to be the go-to technology for years to come.

The following features, which are increasingly available, make the PMS machine part of the go-to “green” elevator.

Compact Size

These drives have a reduced machine footprint, size and weight, making possible a compact machine room (same dimensions as the hoistway) with the option of a machine-room-less elevator. The machine can now be mounted on the car and counterweight rails, as the overall system weight is reduced. A smaller or nonexistent machine room means more usable space in the building and more potential revenue for building owners.

Enhanced Safety and Reliability

In a PMS drive system, the power supply to the drive control is immediately switched off in the event of a power failure, upon which the motor will come to a “self-locking” status at reduced speed. The self-locking effect created by PM bodies and looped armature circuits offers an effective non-contact, bidirectional protection to the lift car. Caliper-type disc brakes greatly enhance safety and reliability of the entire lift system.

Reduced Noise

A geared speed-reduction mechanism such as a worm gear or planetary gear is eliminated, as the motor is effectively running at slow speeds, drastically reducing noise levels to less than 50 dB(A).

Environmentally Sustainable

With No Oil Pollution As lubrication is a must for geared transmissions to reduce friction and heat, oil leakage and disposal are environmental concerns. The PMS machine is “lubrication free,” as the reduction gear has been eliminated.

In addition, these systems can be used with sealed-bearing roller guides (no lubrication to rails), polyurethane (not oil-filled) buffers, coated steel belts (instead of ropes and sealed bearings), requiring no additional lubrication to pulleys and sheaves. This creates a total system that becomes “lubrication free,” meaning no additional lubrication is required for the life of the elevator, which reduces maintenance hours and improves reliability.

No Electrical Noise Interference

The PMS motor does not generate any harmonic wave interference. As a result, it does not affect wireless communication systems such as radio, TV and mobile.

As customers continue to seek more energy-efficient solutions for their buildings, the ability for these machines to couple with regenerative-type VF drives to reduce power consumption by 50% guarantees they will continue to be the go-to technology for years to come.

Increased PF, Reduced Power Consumption

The PMS motor does not require excitation, and, as a result, the power factor (PF) gets very close to 1, increasing efficiency by approximately 15% for a small number of poles and by 40% if the motor has a large number of poles, compared to a traditional worm-gear machine. This translates into reduced power consumption.

Advantages of AC and Gearless Machine Combined

The AC gearless PMS machine has the best of both worlds. It combines the advantages of an AC motor – including no brushes and accurate motor speed control – with those of gearless machines – no gearbox, no oil pollution, less noise, less vibration, low RPM, less wear and tear, and higher traction, among others.

With additional advantages of the PMS motor, it makes the PM AC synchronous machines the right choice for modern elevator technology.

Regenerative Drives

Energy consumption in an elevator system comes from three main areas:

• Car interior, including lighting and ventilation

• Car interior, including lighting and ventilation

• Control systems, including security circuits

• PropulsionDepending on different parameters (traffic, load, speed, etc.)

Energy consumed by propulsion represents 20-50% of the total energy consumed by the whole elevator system. To focus on the energy savings of the propulsion system, the application of regenerative drives should be addressed. At Otis, we call ours the ReGen™ drive.

In a conventional elevator system, energy is consumed when a fully or heavily loaded car travels in the up direction, or a lightly loaded or empty car travels in the down direction. When energy or power is generated (full load down, light load up), in the case of a non-regenerative drive, this energy is wasted and dissipated through braking resistors, creating excess heat in the building. But, when using a regenerative drive, this energy is converted into power and fed back to the building’s grid to be reused for other utilities, such as lighting and computers, which reduces the building’s overall electricity consumption.

PM machines with regenerative drives are becoming more prevalent, not just because of the improved performance and reduced maintenance requirements, but because they truly have the ability to increase value for customers, saving space and energy.


Abhijit Dandekar is director, Supply Chain, Quality & Product Safety at Otis’ South Asia Pacific headquarters. With almost three decades at Otis, Dandekar’s experience spans across various functions, including Otis’ R&D department, Field Engineering, Training, Quality & Codes. Qualified as ISO 9000:2000 Lead Auditor, Dandekar is responsible for sustaining the ISO 9000:2000 quality management system. He is an electronics engineer with a post graduate degree in marketing management.

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