FEATURE DRIVES, CONTROLS & MOTORS
MATRIX CONVERTERS GET OFF TO A FLYING START ON MUNICH’S
ESCALATOR NETWORK M
unich has Germany’s largest escalator network, which transports over half a billion people through the subway system every
year. The network operator, Münchner Verkehrsgesellschaft (MVG), a subsidiary of Stadtwerke Munchen (SWM), deploys trains and buses in subway and tram stations, as well as the 770 escalators (compared to around 450 currently operating on the London Underground). Safety and reliability are, of course, essential, and the need to
maintain so many escalators means any technical change has significant implications. But, with the service life of an escalator around 30 years, multiple generations and models from different manufacturers are in use across the network. With every system unique, MVG is used to innovating, with one
example being the manufacturer-independent escalator control system which the company developed itself. This enables each escalator to be maintained by in-house personnel, enabling faults to be rectified faster and costs for spare parts and conversions minimised. MVG uses inverter drives on its upward escalators as they enable
variable start-up and stopping, so are more comfortable for the users while also protecting the mechanisms. The company, however, needed a solution for the downward escalators. While many systems work with conventional braking resistors, the resulting waste heat has to be dissipated safely, not least for fire safety reasons. The motor windings can also serve as ‘braking resistors’, converting energy into heat, but only to a limited extent and not continually. It would also be possible
to supplement an inverter drive with an additional regenerative unit, but this is not feasible due to limited space in the escalator control cabinets. To meet requirements, the company selected a technology that is still rarely used in low voltage applications – a matrix converter, which combines the
inverter and regenerative unit in a single device. In the spring of 2016 MVG tested the capability of the few market-ready options available using their own simulator. Among the specific escalator requirements was a flying start function to ensure synchronised start-up after automatic deactivation, and that all electrical components would be able to operate year round at outside temperatures. Yaskawa’s U1000 met the demands. This is a highly efficient, regenerative direct inverter for powering induction and permanent magnet machines, with or without speed sensors. Today, the range covers a wide power range from 2.2 to 500kW and, thanks to its innovative design, is capable of direct regeneration and doesn’t
require any DC bus capacitors. No space is needed for an additional regenerative unit and, like all Yaskawa 1000 Series drives, the U1000 is designed for ten years of maintenance-free, continuous operation.
TAKING A LOOK AT THE BENEFITS Not only can the regenerative energy be fed back into the system to meet other needs in the building such as lighting, but in this application the U1000 removed the need for regenerative resistors, greatly simplifying the cooling or ventilation of the system. Another advantage of the Yaskawa system was the upkeep of the grid quality during regeneration. The line currents during operation of the U1000 are nearly sinusoidal in both motor and regenerative mode, and harmonics are reduced to a minimum. While this reduces losses in network components, such as transformers, cables and lines, it improves the efficiency of the whole system. This also reduces potential interference with other system components which, in turn, helps to prevent failures and subsequently removes the need for complicated procedures and the unavoidable downtimes associated with identifying the cause. The U1000 already features an integrated EMC filter, removing the need for
external components such as DC reactors or LC filters, and has a built-in SIL3 STO input to allow for high machine safety requirements. Yaskawa also offers options for all common fieldbuses, making connection to EtherCAT, Powerlink, Profinet, Profibus, Ethernet IP and other systems extremely straightforward.
MONITORING IN REAL-TIME Following testing of the latest U1000 matrix converters at new subway station locations where space is even more limited, the converters have been duct mounted on the side wall of control cabinets, meaning the cooling module is on the outside. The device is connected to the MVG control system so that current operation status can be monitored in real-time, providing reliable test data at all times.
Yaskawa 28 DECEMBER/JANUARY 2021 | DESIGN SOLUTIONS
www.yaskawa.eu.com
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