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Some fields of application demand absolutely everything of medium-voltage converters. They are expected to offer maximum availability while being motor or network-friendly. The most reliable option in these situations is the modular multilevel converter, or M2C for short. The technology patented by Siemens is based on a modular system that makes the converter extremely flexible, scalable, reliable to use and extremely easy to maintain.
Up to 99% availability is achievable: a totally new level of efficiency!
Modular multilevel converters and the theory behind them
An M2C medium-voltage converter consists of several low-voltage cells. Switched in series, they generate an output voltage at medium-voltage level. Within the converter, each cell can be controlled individually, and each has a local energy storage unit that contributes a proportion of the link voltage. This means the output voltage can be modulated so finely that it almost forms a sine curve. That’s what is innovative about the M2C technology, first patented by Siemens in 2002, which has gone on to capture more and more of the market ever since. A more detailed look will reveal even more advantages.
The M2C topology is DC bus-capable. This means that additional topologies can be combined with M2C at both the network and the motor end. This gives you huge freedom to configure the converter – whether for single or multi-axis drives. For a rectifier, for example, you can choose between different pulse counts, depending on how “clean” you need the input voltage to be.
At the same time, this freedom can be transferred to the system design as a whole. Technically, a converter based on M2C does not necessarily need a transformer, and if one is used (to adapt the voltage), it does not have to be located in the immediate vicinity of the converter. You can plan more flexibly as a result, and so, more than ever before, you can get the most out of the space available for installation.
A critical factor in day-to-day operations is what happens in an outage. This is where the cell-based principle kicks in. If a cell fails, a bypass is automatically activated within the converter – in other words, the critical point is short-circuited within an extremely short time (< 1 ms). This brief voltage failure is not perceptible from the outside, either during or after the outage. The module will cease to function only if several cells in a given branch should fail.
The advantage of the cell-based principle is also evident when it comes to maintenance. In a redundant configuration, cells do not have to be replaced immediately. Operators can wait until the next scheduled downtime, when the part can be swapped very quickly. As a rule it should take no more than 15 minutes. These conditions ensure that you can always enjoy maximum system availability.
The more scalable the converter, the better chance you have to achieve the ideal layout for the system as a whole. By itself, that’s enough to save costs and improve the overall quality of your system. The cell-based design used in M2C technology creates the best conditions to achieve this. The converter is easy to adapt – in terms of voltage, redundancy and the necessary power output. As a result, M2C can meet your requirements perfectly, even if what you need from the converter should change over time.
Just how scalable the topology is has already been demonstrated in other areas of application, like high-voltage DC transmission (HVDC applications). These involve switching up to 200 cells in series in a single M2C branch. Output voltages of up to 400 kV can be achieved as a result.
From theory to practice
The technological innovations contained in a modular multilevel converter provide many additional advantages in application, even compared to other medium-voltage converters.
Overview of M2C solutions
Two of our medium-voltage converters are currently available with M2C technology. Both have been proven in practice for a number of years now.
SINAMICS medium-voltage converters based on M2C are already in use in many locations, and are winners in every respect. Companies from all over the world have taken a vital step forward by adopting this innovation from Siemens. We have listed a few of these success stories here.
SINAMICS SM120 CM for the test bench for deep-sea submersible pumps
Customized converter developed in record time
Start of a long-term strategic partnership between Aker and Siemens
SIHARBOR (with the SINAMICS SM120 CM converter) gives ships in port an onshore power supply
No need to use the ship’s own diesel generators
Less carbon dioxide, nitrogen oxides and particulates – less air and noise pollution
Order your no-obligation copy now
This includes e.g. the electrotechnical basics of the technology and specific examples for the cabinet installation. On the basis of simulation examples and vivid graphics, a deep insight is given into the operating principle and its benefits. The M2C white paper is written for all technical interested persons.