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Modular MV converters `will open up new applications`

15 March, 2012

Siemens has developed a modular medium-voltage converter technology that, it says, will open up new applications for MV converters in areas such as shipping, offshore wind farms and the steel industry. The development will allow different topologies to be combined in a common modular system and will deliver customer benefits such as increased reliability and availability, higher efficiency, and improved network compatibility.

The new modular approach follows the trend toward increasingly higher system power ratings and will allow new and existing converter topologies to be combined flexibly.

Previously, different devices were needed to cover different applications. With the new topology, known as the “modular multilevel converter” (M2C), identical components can be connected in series, allowing the same MV converters to be used from low to high power ratings.

Even if one cell fails, the multilevel converters will continue to work reliably. They are said to provide a fine scalability of voltage and power, high line and motor compatibility (due to the good voltage quality), and a high level of availability, thanks to the uncomplicated implementation of redundancy.

For example, the steel industry will benefit from enhanced reliability and converter availability, as well as from improved network compatibility, especially in cases where conventional systems are limited by long infeed lines or weak networks.

A further claimed benefit of the modular MV concept is robust performance on weak networks. For example, the multi-level converter can be used to connect multi-megawatt offshore wind farms directly to an electricity network without needing complicated line filters or transformers.

The new MV technology is also said to be significantly more efficient than previous low-voltage systems. Analysis has shown that a 3MW wind turbine used with the new converters could feed around 24,000kWh of extra electrical energy into a grid every year. This means that a 50-turbine wind farm could supply about 400 more households with electricity than before. Similarly, tidal power plants could benefit from the modular technology.

In marine engineering too, MV converters with the M2C topology will open up new areas of application – for example for shaft generators that supply on-board power systems from a main diesel generator set.

One of the first customers to use the new technology is the German marine systems integrator, Sam Electronics, which has installed M2C converters on large container vessels for a German shipping company. The converters are feeding power from the shaft generator directly into the on-board MV network, without intermediary transformers or filters. The new topology can supply output voltages from 2.3–7.2kV and output currents from 500–1,000A.

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