Reducing motor winding stress in MV drives

Use multilevel to its full extent!

Variable speed drives are used in a wide range of applications in industry and transport, such as wind turbines, mining, marine, and naval applications. Demand for these drives has been growing for a few years, especially at the megawatt level (i.e. at the medium voltage level), due to the increasing need for efficient motor control because of rising energy prices and environmental concerns.

Thus, in such cases, this often requires a bulky and costly output sine filter in order to preserve the motor’s windings from excessive current harmonics and voltage overshoots.

  1. In most of the cases, the use of 3-level inverters (such as NPC or T-type topologies) is already a well-established solution. However, further increasing the number of levels (to 5 for example) can change the game, first by reducing the current harmonics, which leads to significant filter downsizing.
  2. Moreover, fast voltage transitions caused by the PWM waveform may cause voltage spikes that degrade the insulation of the motor winding. Sometimes, voltage transitions are slowed down by increasing the gate resistance of the switches, but the overall efficiency is affected.
  3. Here again: multilevel solutions reduce the voltage step, thus reducing the spike amplitude.
  4. At last, it also opens options such as the use of cheaper low-voltage IGBT modules.

To sum-up, increasing the number of levels of the multilevel topologies can…

  • Reduce the currents harmonics (THD),
  • Limit the voltage overshoots,
  • Lead to significant filter downsizing…

But in this case, many questions can be raised:

  • Which topology fits better to my application?
  • How many voltage levels?
  • Depending on the number of voltage levels, which power switch?
  • What about the switching frequency?

This the kind of questions we can answer using PowerForge, the platform to help engineers to design their power converters!

Our Experts:

Guillaume Fontes – CSO & Co-founder / Power Design Technologies

Guillaume has been an associate Professor at the Polytechnic National Institute of Toulouse and at the LAPLACE lab since 2006. He studied electrochemical storage of electric energy and now focuses on methods and tools for the design of power converters. He co-developed a power converter design software prototype in 2013, which is now owned by Power Design Technologies.

Guillaume received the M.Sc from INP-ENSEEIHT in 2001, graduated from the Ecole Normale Supérieure de Cachan in 2003 and received his PhD from the National Polytechnic of Toulouse in 2005.

Thierry Meynard – Co-founder & Scientific Advisor / Power Design Technologies

Thierry Meynard graduated from the Ecole Nationale Supérieure d’Electrotechnique, d’Electronique, d’Hydraulique de Toulouse in 1985, became a Doctor of the Institut National Polytechnique de Toulouse, France, in 1988 and was then an invited researcher at the Université du Québec à Trois Rivières, Canada, in 1989. He joined the CNRS (Centre National de la Recherche Scientifique) as a full-time researcher in 1990, was Head of the Static Converter Group from 1994 to 2001, and has been a part-time consultant with Cirtem from 2000 to 2016. He is now Directeur de Recherches CNRS at the LAPLACE(*) laboratory, associate director of the national program 3DPHI (3-Dimensional Power Hybrid Integration) and co-founder and part-time consultant of the start-up Power Design Technologies.

His main research interests are related to series and parallel multicell converters, magnetic components and the development of design tools for power electronics.

He is the co-inventor of several topologies of multilevel converter used by ABB, Alstom, Cirtem, General Electric, Schneider Electric: ‘Flying capacitor’, ‘Stacked MultiCell’, ‘5LANPC’, ‘AC/AC chopper’,….

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