Modularity and flexible use form the basis of a new concept for medium-voltage converters from the Siemens Drive Technologies Division. In the future, it will be possible to use different topologies in a common modular system.
This opens up new areas of application for medium-voltage converters in special purpose applications, for example on ships, in offshore wind farms or in the steel industry. Use of the new “Modular Multilevel Converter” (M2C) topology is an integral part of this concept. Customers benefit from increased reliability and availability of the converters, as well as from improved network compatibility. The first solutions have already been installed.
The new concept for modular medium-voltage converters follows the trend toward increasingly high system ratings, and will in the future provide more capabilities in special purpose applications. A distinguishing feature is the ability to flexibly combine known and new converter topologies in a common modular system. An important element is the utilization of the new “Modular Multilevel Converter” (M2C) topology. Whereas a variety of different devices would usually be needed to cover the whole range of applications, with this topology identical components are connected in series. This allows the converters to be used from low to high power ratings in the medium-voltage range as needed. They continue to work reliably even if a cell fails. These multi-level converters provide a fine scalability of voltage and power, provide high line and motor compatibility (due to the excellent voltage quality) and ensure a high level of availability thanks to the uncomplicated implementation of redundancy. The steel industry (for example) benefits from enhanced reliability and availability of the converters, as well as from improved network compatibility, especially in cases where conventional solutions have limitations due to long infeed lines or weak networks.
A further benefit of the new modular concept for medium-voltage converters is their robust performance on weak networks. For example, the multi-level converter allows direct connection of multi-megawatt-class offshore wind farms to the public network without the need for complicated line filters or transformers. The new medium-voltage technology works in a significantly more energy-efficient way than the previously used low-voltage solutions. Analysis on a wind turbine with a rated power of three megawatts shows that an additional amount of approximately 24,000 kilowatt hours of electrical energy per year and wind farm can be fed into the grid, when the new, highly efficient converter is used. Extrapolated to a wind farm with 50 turbines, this means that about 400 more households can be supplied with electricity than before. Tidal power plants are likewise potential fields of application for the modular technology.
Pilot applications in marine engineering
In marine engineering too, the medium-voltage converters with the “Modular Multilevel Converter” topology open up new areas of application, for example for shaft generators which supply the on-board power system from the main diesel set. The system integrator SAM Electronics is one of the first customers to use the modular system. The converters based on the M2C topology are operating on the new mega container vessels of a German shipping company. They feed power taken from the shaft generator directly into the medium-voltage on-board network, without intermediary transformers or filters. By means of the new topology, output voltages from 2.3 to 7.2 kilovolts can be covered, and output currents from 500 to around 1000 amperes can be provided. Especially in marine applications, the converter complies with all common on-board specifications, both in terms of overload capability as well as behavior in the event of short circuit.
Offshore WIND staff, March 16, 2012; Image: siemens