Internship – Auxiliary supply of power converters for medium voltage direct current grids (MVDC)
SuperGrid Institute
Villeurbanne, Auvergne-Rhone-Alpes, France
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SuperGrid Institute brings together 180 employees, of 28 different nationalities who work together within a dynamic environment in the city of Lyon.

As an independent research and innovation center, we are dedicated to developing technologies for the future power transmission system, the supergrid , including HVDC & MVDC technologies.

As a multi-disciplinary research center with advanced simulation capabilities & multiple test platforms, including numerous associated laboratories, SuperGrid Institute uses its comprehensive expertise to provide a wide range of services and solutions to support our customers in developing power systems, equipment and components.

We specialize in system architecture and work on ensuring network security and stability while allowing for the integration of intermittent renewable energy sources.

Find out more by visiting our website : www.supergrid-institute.com

General Context

Historically, the electrical energy was almost exclusively produced, transmitted and distributed with three-phase alternating current (AC), through a vast meshed grid, reinforced in specific places by high voltage direct current (HVDC) links.

More recently, the growing integration of renewable energy sources and the need to supply complex loads (data centers, electric vehicle charging stations, ) created a need for direct current (DC) at lower power and voltage levels, in the range called medium voltage (1500V-75kV).

This need increased the demand in power converters, which are required to perform the different transformation steps that the distribution scheme requires (AC / AC, DC / AC, AC / DC and DC / DC).

In general, these static converters use semiconducting devices (diodes, MOSFETs, IGBTs, thyristors) as controlled switches and passive elements (coils, capacitors, transformers), assembled in a need-dependent way : type of conversion, voltage, power, need for insulation and / or bi-directionality, and so on.

To operate normally, these components require additional elements : control and supervision unit, voltage and current sensors, driver interfaces for the semiconducting switches, cooling system, All these elements have to be powered : it is, thus, necessary to provide an autonomous, isolated and regulated output, with a low voltage (e.

g. 24Vdc) and a moderate power (generally

When one of the converter terminals is connected to an AC power grid, the conventional way to go relies on an auxiliary transformer : connected to the grid at its primary-side, its secondary-side voltage is then rectified and regulated the latter task being straightforward.

The transformer allows to significantly drop the voltage through a galvanic insulation, and satisfies all the aforementioned requirements.

An example of such an architecture is shown in Figure 1.

Figure 1 : Architecture of a medium voltage variable frequency drive

However, when the transmission is done in direct current, the AC grid is generally not available, and it is impossible to use this solution Even if the need for an auxiliary power source remains.

To illustrate this situation, the same variable frequency drive supplied directly in DC is shown in Figure 2.

Figure 2 : Architecture of a DC-supplied medium voltage variable frequency drive

How to perform the same function, shown in red in Figure 2? This is basically the topic of this internship. DC / DC converter or simple resistive divider?

Modifications in the system architecture? There is a wide range of solutions to imagine, as long as they fulfill the need while being industrially feasible.

Objectives / Missions

  • Exploration of the state-of-the-art (scientific publications, patents )
  • Comparative analysis of the existing solutions
  • Sizing and simulation of the most promising options
  • Bonus : propose a new solution!
  • Candidate Profile

    The candidate shall be rigorous and autonomous, and shall be able to have a general overview of his own work. Desired profile : master student in electrical engineering or equivalent.

    Firm elementary knowledge in power electronics is desired, a good synthesis ability is mandatory.

    If you want to explore an innovative and industrially useful topic, to reinforce your knowledge in the field of power electronics and power grids, and to work in an open and motivating environment, this internship is made for you!

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