Team 4: Direct Current Micro-grid (DC Micro-grid)

Direct Current Micro-grid (DC Micro-grid)

Team involved
Name of the project manager :
Liouane Noureddine - Professor
Name of teacher-researchers involved Grade
Hédi YAHIA Assistant Master
Adel JEMNI Assistant Master

Name of doctoral students to be mobilized within the framework of the project:




Walid ABID


Tayssir BEN SAID


Several components deserve their development to achieve the realization of this project which contains the different research themes of this group involved in this project.

  • Renewable energies, wind and photovoltaic,
  • DC / DC and DC / AC converters,
  • Special machines, MRV and polyphase induction,
  • Deterministic and stochastic multi-objective optimization, soft computing, metaheuristics,.


Microgrid demonstrations and deployments are growing around the world. Although the objectives are specific to each location, these micro-grids have demonstrated their ability to provide greater reliability and better energy quality than traditional power supply systems and better use of energy. In addition, manufacturers, electrical system designers and researchers demonstrate and deploy DC power distribution systems for applications where end-use loads are in continuous mode, e.g. computers, lighting. semiconductor (LED) and building networks. These early DC applications can provide higher efficiency, increased flexibility, lower capital costs compared to their AC counterparts. Additionally, where generation is renewable on-site, electric vehicles and storage systems are present, DC microgrids can provide additional benefits. The early successes of these efforts raise a question: Can a combination of micro-grid concepts and DC distribution systems provide additional benefits over what has been achieved individually?


With the growing demand for improved reliability and energy efficiency in all commercial buildings, there is a tremendous opportunity to capitalize on the benefits of the DC micro-grid. Sustainability initiatives and energy targets encourage the use of renewable energy sources, such as solar photovoltaic systems, wind turbines and other alternative sources. These DC power sources can be integrated for direct use by a micro-grid system, eliminating DC-AC-DC conversion losses.

The objective of this project is to realize a prototype of a direct current micro-grid allowing the integration of decentralized productions of renewable energies, wind and photovoltaic in order to examine and provide the advantages and disadvantages of the potential applications of DC micro-grids against their AC counterparts and provide recommendations for future research and potential deployment. The performance of DC micro-grids will be estimated and compared to their AC counterparts. This comparison will focus on the following indices:

  1. security and protection
  2. reliability
  3. capital cost
  4. energetic efficiency
  5. exploitation cost
  6. engineering costs
  7. environmental impact
  8. energy quality
  9. resilience.

Summary :

The distributed generation takes advantage of the advantages of direct current (DC) over alternating current (AC). In the presence of renewable energy systems that are more efficient today, the opportunities for electricity savings for customers have increased. DC is also suitable for storage in batteries, for later use if the regular power supply is interrupted.

Many electricity users looking to cut costs or 'go green' are concerned with producing and using electricity on their side of the meter, not selling AC power to the local grid. . There may not be much surplus to sell, and the price the local utility is allowed to offer may not be attractive. The real goal is to reduce dependence on the grid. DC systems powered by photovoltaic cells, for example, can achieve this goal with greater efficiency, through local generation and the use of energy on a customer-owned “micro-grid”.

A micro-grid is an independent system that supplies electricity to a defined physical entity, such as a store, office building, or factory. He can accept energy of all kinds. The owner can still be connected to the local distribution grid and will always need this AC power source. However, when needed, the micro-grid will efficiently generate and store DC power, which is needed for most electronic devices. If the DC power supply is to exceed the demand, the excess can be converted to AC power and sold back to the grid.

As presented at the beginning, several themes are necessary for the smooth running of this project:

Operational controllers will be designed to support the integration of wind and solar power into micro-grids. A precise and adequate model of renewable energy production, wind and solar for the forecast will be proposed to estimate in real time the quantity of reserves for daily scheduling. The combination of wind and solar resources on the same location leads to reduced local storage requirements. The combination of various, but complementary storage technologies can in turn form multi-level energy storage, where a supra-capacitor or flywheel provides control of the energy reserve to compensate for fluctuations in fast power and to smooth the transient regimes encountered by a battery with greater energy capacity. A micro-grid or hybrid energy system provides an efficient structure for the local interconnection of distributed renewable energy production, for loads, and for storage.

The DC micro-grid system is offered as an electrical grid allowing the introduction of a large amount of renewable energy by using photovoltaic and wind production units distributed under the following three conditions which are briefly recalled to ensure the smooth running of the DC micro-grid:

- Increase the introduction of distributed photovoltaic and wind units.

- Reduce energy dissipation and installation costs resulting from AC / DC conversion by integrating the junction between the commercial network and DC bus which connects the PV units and accumulators.

- Supply energy to loads via regular distribution lines even during blackout of commercial networks.

To meet these conditions, DC-DC and AC-DC converters will be designed and produced. These converters always follow the maximum operating point of the power sources (PV and / or wind power: MPPT) which varies according to the intensity of solar radiation and wind respectively. The storage batteries are also linked to the DC bus. The DC distribution system reduces installation costs and associated energy dissipation.

Compared to conventional machines integrated in wind power applications, the variable reluctance generator shows a simplified construction associated with the absence of a permanent or conductive magnet in the rotor, thus resulting in reduced manufacturing costs. In addition ; both the machine and the associated power converter are robust. The rotor has low inertia allows the machine to react quickly to fluctuations in the load.

This project analyzes the generator mode of the switched reluctance machine in the direct coupling to the turbine shaft without gearbox.

The solution for the conversion of low-medium voltage wind power at variable speed is today based on the polyphase machine. Compared to conventional three-phase machines, polyphase induction machines have better fault tolerance, lower pulsation torque and lower power per phase for a given power. Polyphase generators have been much less studied and this constitutes a real topical research topic for the conversion of wind energy. The modularity of three-phase windings in many three-phase winding machines can take advantage of the well-established three-phase technology, allowing the use of ready-made three-phase converter products.

To achieve the smooth running of all these engineering topics, a mastery of modeling and optimization tools is of capital importance. These tools allow the computation of robust optimal solutions, i.e. optimal solutions which are insensitive to variations of random parameters, when appropriate deterministic substitution problems are needed. Based on the probability distribution of the random data and using theoretical decision concepts, optimization problems under stochastic uncertainty are converted into appropriate deterministic substitution problems.

Several deterministic and stochastic approximation methods are proposed: Taylor expansion methods, response surface and regression methods, probability inequalities, multiple linearization of survival / failure domains, discretization methods, convex approximation / deterministic directions of descent / efficient points, stochastic approximation and gradient differentiation procedures and formulas for probabilities.

All the actions that will lead to the design and testing of the various components of the DC micro-grid take place in parallel with the aim of facilitating monitoring. Monthly presentations make it possible to follow the progress, the scientific production and the difficulties encountered.