Issue 2/2006


03/02/06

Gearless, No Slip, No brake resistor?

If a braking resistor component is not there, it cannot produce losses, adds no cost and cannot break down. The more simple a machine is designed, concentrating on the essential functions, the more reliable and efficient it will be. Gearless Drives have conceptual advantages and thus are become more and more popular for many applications including for lift drives. Beside the compact size their specific shape perfectly suits installations without a machine room.
Category: Issue 2/2006
Posted by: Editor
As with the amount of users, the variety of machine manufacturers is steadily growing. But which one should be used? As well as the technically convincing concept of the components, high quality production and of course competitive pricing, it is important to consider the life cycle cost.
 
Which motor to use with which inverter?
 
A package solution - from a single supplier source has its advantages:
 
• The buying process is simplified in terms of order processing, accounting and storage.
• Warranty issues are optimized: If the “plug and play” solution does not
work as expected, the system supplier assumes responsible for this inter-face. Troubleshooting and support is handled by a single supplier.
 
On the other hand there are certainly some aspects relating to the use of other combinations:
 
• The lift company has good experiences with their current inverter supplier.
• The price/performance ratio of the product is satisfactory, the service teams are well trained on the product and the spare parts availability is well established.
 
Yaskawa generally supports both components in every combination with products available on the market. Ultimately it is up to the customer to decide which aspects are the most important for its company structure and requirements.
 
Yaskawa does not only produce motors, but is also one of the world’s largest manufacturers of motion control products. Consequently Yaskawa also offers inverters. For lift applications currently two technologies have been provided:
 
• Lift inverter Varispeed L7
• 3 level control inverter Varispeed G7
 
 
Lift inverter Varispeed L7
 
The Varispeed L7 is a specialized inverter for lift-applications. The parameter settings and possibilities provided are customized for lift applications. The start-up is very easy thanks to the specialized parameter set and the powerful Autotun-ing function. Not only can Autotuning be executed with an unloaded and rotating motor, but also, as very often requested by lift builders, with the load and consequently without rotating the motor shaft.
 
When operating for example a Yaskawa PM160 gearless motor with the Varispeed L7 the system will be able to operate with a relatively simple pulse generator not requiring absolute position information. The Varispeed L7 is capable of finding the exact rotor displacement angle after the power supply has been shut off or has failed. When power returns a voltage is applied to the motor at standstill and by detecting the resulting asymmetrical currents caused by Lq and Ld , the actual rotor position is detected. This feature combined with an easily accessed pulse generator, minimizes service tasks as the replacement of the PG becomes easy.
 
 
The Varispeed G7 is not a specific lift inverter, but its big advantage is the 3 level control technology. This technology was first implemented in a 400 V class series model by Yaskawa in 2001. The power circuit layout switches only half of the DC bus voltage at once which brings the ouput voltage waveform closer to a sine wave. As a result of this the isolation of the motor windings is far less stressed. Although originally designed for industrial applications the Varispeed G7 is also used for lift installation upgrades where the originally installed motor is not replaced.
 
 
 
 
But what will the future bring? What development stages lie ahead?
 
Concerning the inverter - side, it is likely that regenerative operation will be considered with more emphasis; why should the regenerative energy be wasted in a braking resistor?
Radio interference and harmonics in the power supply are another conceptual problem, especially in island installations such as on ships.
 
The answer to this is a direct inverter; the matrix converter:
 
With out a DC circuit there is no need for electrolytic capacitors that are one of the critical life limiting components of clas-sically designed inverters.
In the Matrix converter the voltages of the 3 input phases are directly switched to the motor via a switching matrix (thus the name) consisting of 18 IGBTs switched by a sinusoidal PWM pattern. Thanks to this configuration the matrix converter’s output voltage is sinusoidal as well as the input current. This reduces power supply harmonics from typically 80 % down to approximately 8 %.
 
Particular interesting for lift applications is the matrix converter’s ability to directly feed back the regenerative energy into the power supply network. This means no requirement for braking resistors and choppers and a tremendous increase in the system’s efficiency; thus energy is saved.
 
On the motor side, next to the efficiency, optimized power density is an important consideration. Today, the shape of the machines is very important for the lift industry. The variety of patents for even non-realized technical concepts and those available in the market, is limiting flexibility more than innovative lift builders would like. This challenge has also to be taken by independent lift companies. Component suppliers can contribute by introducing not only very small, but also extremely flat / thin motors which open up new design possibilities.
 
Yaskawa has vast experience in developing and producing such motors. Being the market-leader Japan, world wide 27,000 lifts are running with permanent magnet synchronous machines produced by Yaskawa. In the field of lift applications Yaskawa supplies over 30.000 inverters a year.
 
Yoshikatsu Minami, the president of the European association has ambitious plans for Yaskawa Electric Europe GmbH. Yaskawa is broadening its activities in Europe: not only is the actual production of inverters located in Europe, but also software changes and key account support is handled by the European Headquarters in Schwalbach, near Frankfurt. In the near future more advanced development tasks will also be handled in Europe.
 
 
The range of permanent magnet lift motors will steadily widen. On the inverter side, the next product generation is under preparation. In spring 2006 the first matrix converters will be delivered to customers. Although price is in the upper area because of the special features for specific applications - e.g. for heavily utilized escalators - they are already a considerable solution today.
 
 
Yaskawa Electric Europe GmbH, D-65824 Schwalbach
 
2/2006

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