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SUMMARYOngoing changes in energy systems offer the opportunity to reconsider the design of our current energy infrastructures. As many new grid participants like combined heat and power plants involve other forms of energy in addition to electricity, the consideration of multi-energy networks represents a useful planning approach. This approach consists in an integrated analysis of combined infrastructures for conversion, transmission and storage of electricity, heat and chemical energy carriers. The integrated operation of systems with different energy carriers offers a new degree of freedom to system planners: energy can be generated, stored, and transmitted in various forms before being distributed to consumers in the adequate form. Different possible solutions for the design of multi-energy systems will exhibit differences in costs and risks. In order to adequately assess these two quantities, mean-variance portfolio theory is applied. Portfolio theory has been used in several cases of electricity generation planning. This paper shows the required modeling adaptations for the analysis of portfolios with multiple energy outputs and illustrates the application of portfolio theory in the context of multi-energy infrastructures. The presented method can be used for the integrated planning of energy systems including the generation, the transmission and the possibility of additional conversion of multiple energy carriers.

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The understanding of harmonics propagation in power systems recently gained interest. In HV networks, the current trend of undergrounding is modifying the network resonance frequencies. In LV distribution systems, the increasing deployment of decentralized generation induces new harmonic pollution, which could interfere with power line communications (PLC). In this analysis, the most important elements of power systems (overhead lines, underground cables, power transformers, linear loads and inverters) are modelled in frequency and integrated into Frequency scan and Resonance Mode Analysis methods. Two network types are analysed to point out the specificities of each network level: the first one is an EHV/HV network (380 kV, 220 kV, 125 kV and 50 kV) and the second one is a part of a MV/LV distribution system (20 kV and 400 V). With this method the network behaviour in a large frequency bandwidth (up to 5 kHz for transport grids and up to 200 kHz for the distribution system) can be predicted. Recent network impedance measurements contribute to the validation of this method by showing the same trends and resonance frequencies close to the ones visible in the simulation results.

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