More ups than downs using matrix converters on one of Europe’s largest network of escalators 14 January 2021

Operating Germany’s largest escalator network in Munich, which transports over half a billion people through the Bavarian capital’s subway system every year, means the scale of any technical innovations can be immense. Technicians in charge of the system have gradually deployed Yaskawa’s U1000 matrix converters for its escalators.

The network operator Münchner Verkehrsgesellschaft (MVG) deploys trains and buses in subway and tram stations. It operates 770 escalators, compared to around 450 currently operating on the entire London Underground.

Supported by a team of technicians, Mario Princip, head of MVG, has to ensure that the system operates around the clock without interruption. He comments: “A high level of reliability is extremely important and it’s also strategically significant. It’s not just a question of addressing the passenger’s needs for comfort and convenience, it’s also an important operational matter because without the escalators the passengers cannot enter and exit the stations at the required speeds.”

The escalator engineers are meticulous in assessing any new optimisation opportunities. The reality is it’s an ongoing process of modernisation in an environment that is highly resistant to standardisation. The service life of an escalator is around 30 years. At any one time, multiple generations and models from different manufacturers are in use across the network, while the individual spatial conditions are equally diverse.

Daniel Mayer, who is responsible for escalator electro-technology, says: “In a nutshell, every system is unique”. MVG tackles this challenge by drawing on its own powers of innovation, with one example being the manufacturer-independent escalator control system which it developed itself. This means each escalator can be maintained by in-house personnel, faults can be rectified faster and costs for spare parts and conversions are minimised.

MVG has been using inverter drives since before the development of the new control system. The benefits of which quickly became apparent over conventional drives in every-day operation on upward escalators. The inverter control enables variable start-up and stopping, which means not only more comfort for the users, but also protects the mechanisms.

However, as impressive these benefits were, MVG had been searching for a suitable solution for 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 escalator control cabinets.

Eventually a solution was found in the technology that is still rarely used in low-voltage applications: a matrix converter that 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 its own simulator. Among the specific escalator requirements was a ‘flying start’ function to ensure synchronised start-up after automatic deactivation. In addition, all electrical components have to operate year-round at outside temperatures.

Yaskawa’s U1000 was one of the units tested and was chosen by MVG. First introduced in 2014, the U1000 matrix converter is a regenerative direct inverter for powering induction and permanent magnet machines, with or without speed sensors. Today, the range goes from 2.2 to 500kW. Thanks to its design, it 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 10 years of continuous operation.

The regenerative energy that can be fed back into the system to meet other needs in the building such as lighting can be a significant benefit. However, this was not the main reason that prompted MVG to select the U1000 for their escalator application. More importantly, 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. Not only does this reduce losses in network components, such as transformers, cables and lines, but also it improves the efficiency of the whole system. Furthermore, this significantly 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. Nevertheless, the space requirements are still up to 50% with conventional integrated solutions with sinusoidal input and regeneration. It also features a built-in SIL3 STO input to allow for high machine safety requirements. Yaskawa also offers options for all common fieldbuses including EtherCAT, Powerlink, Profinet, Profibus, Ethernet IP.

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.

Based on initial results from these new applications, Mario Princip concludes: “We’ve addressed the main issues at these even more demanding sites and the Yaskawa U1000 is operating just as we’d hoped”.

Operations Engineer

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