An Interactive Energy System with Grid, Heating and Transportation Systems

Research output: Book/ReportPh.D. thesis

Abstract

The environmental consciousness and the fact of achieving greater energy independency have led many countries to apply important changes in their energy systems. The intensive renewable energy growth of the last decades represents the most notorious example at this moment. However, this is not only occurring with power generation purposes, there is an interest on extending this tendency to other strategic systems like the heating, gas and transportation. This implies that at least an important part of these systems will have to be electrified. From a power system perspective, this means that it will have to undergo a significant load increase in the future.

Due to its nature, most of this load is expected to be accommodated at the power distribution level. This implies a need for finding new alternatives to operate and control the medium and low voltage networks. Considering the technical and economic aspects of these networks, an active demand response represents a promising solution. This research work is based on the opportunity of interacting the electrical power system and the heating, gas and transportation systems to ensure a correct and efficient operation of the distribution systems.

The aim of this work is to introduce new modelling approaches, methods of analysis and control strategies to represent the active loads and the power distribution systems in the future. Unlike for large transmission systems, in distribution systems a more detailed modelling from each network element is required. The models developed in this thesis include different features (thermal, mechanical, chemical…) which are not normally considered in the traditional power system modelling. In this sense, they are intended to serve as a reference for the new researchers starting in the field. Moreover, the grid studies and the demand response strategies introduced are intended to be beneficial for distribution system operators (DSO) in the planning and development of the future distribution networks.

The following thesis covers four main areas; modelling of active loads and residential user requirements, flexibility definition and quantification, stochastic impact assessment of LV networks and control of the demand response in LV networks.

In a first stage, different residential and non-residential loads are modelled with system analysis purposes. The active loads considered can be categorized as: thermostatic loads (electric water heaters and heat pumps), loads for hydrogen generation (alkaline electrolyzers) and load for electric mobility (plug-in and vehicle-to-grid concepts). Many of these are considered domestic loads and they fulfill certain need to the household they belong. Depending on the user requirements, these may perform a different power consumption patterns. In this context, the thermal comfort or mobility needs from Danish users are statistically analyzed. The outcome is used to generate random profiles that define the different thermal and mobility requirements from the users of a network.

The flexibility expected from users holding these loads, despite of being constantly mentioned, is usually not properly defined and even rarer quantified. Therefore, it represents another significant factor to be assessed. In this work, a methodology to probabilistically quantify the potential flexibility from residential users is introduced. The approach is based on non-flexible consumer clustering and subsequent statistical analysis and the comparison with the power consumption pattern of flexible consumers. The strong relationship of certain loads flexibility and the season of the year are clearly highlighted.

Demand response, especially from residential users, is lately acquiring lots of attention due to the advantages that it introduces in regards the power system regulation. However, depending on the load penetration and location, distribution grids may be leaded to serious congestion problems. In this situation, not only the security and reliability of these networks are in danger, the flexibility offered by the active loads may also be limited. It is then decisive, to understand what is the hosting capability of this networks and their vulnerable points. In this stage of the thesis, a methodology for stochastically evaluating the impact caused by thermostatic and plug-in electric vehicle loads in low voltage grids is introduced. Even though the actual systems seem to be overdesigned, sometimes their hosting capability may be poor for the integration levels expected.

Finally, in the last stage of this research work the control of the demand response in LV networks is tackled. The hierarchical structure presented aims to control the operation of heat pumps and plug-in electric vehicles to satisfy technical and commercial aspects of LV grids. This strategy allows system operators to perform their energy commitments, taking advantage of the flexible demand, while ensuring the security and reliability of the LV network each moment of the day. A proper demand response strategy makes possible to obtain economic benefits from the balancing service provision while decongesting the LV network in critical moments.
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The environmental consciousness and the fact of achieving greater energy independency have led many countries to apply important changes in their energy systems. The intensive renewable energy growth of the last decades represents the most notorious example at this moment. However, this is not only occurring with power generation purposes, there is an interest on extending this tendency to other strategic systems like the heating, gas and transportation. This implies that at least an important part of these systems will have to be electrified. From a power system perspective, this means that it will have to undergo a significant load increase in the future.

Due to its nature, most of this load is expected to be accommodated at the power distribution level. This implies a need for finding new alternatives to operate and control the medium and low voltage networks. Considering the technical and economic aspects of these networks, an active demand response represents a promising solution. This research work is based on the opportunity of interacting the electrical power system and the heating, gas and transportation systems to ensure a correct and efficient operation of the distribution systems.

The aim of this work is to introduce new modelling approaches, methods of analysis and control strategies to represent the active loads and the power distribution systems in the future. Unlike for large transmission systems, in distribution systems a more detailed modelling from each network element is required. The models developed in this thesis include different features (thermal, mechanical, chemical…) which are not normally considered in the traditional power system modelling. In this sense, they are intended to serve as a reference for the new researchers starting in the field. Moreover, the grid studies and the demand response strategies introduced are intended to be beneficial for distribution system operators (DSO) in the planning and development of the future distribution networks.

The following thesis covers four main areas; modelling of active loads and residential user requirements, flexibility definition and quantification, stochastic impact assessment of LV networks and control of the demand response in LV networks.

In a first stage, different residential and non-residential loads are modelled with system analysis purposes. The active loads considered can be categorized as: thermostatic loads (electric water heaters and heat pumps), loads for hydrogen generation (alkaline electrolyzers) and load for electric mobility (plug-in and vehicle-to-grid concepts). Many of these are considered domestic loads and they fulfill certain need to the household they belong. Depending on the user requirements, these may perform a different power consumption patterns. In this context, the thermal comfort or mobility needs from Danish users are statistically analyzed. The outcome is used to generate random profiles that define the different thermal and mobility requirements from the users of a network.

The flexibility expected from users holding these loads, despite of being constantly mentioned, is usually not properly defined and even rarer quantified. Therefore, it represents another significant factor to be assessed. In this work, a methodology to probabilistically quantify the potential flexibility from residential users is introduced. The approach is based on non-flexible consumer clustering and subsequent statistical analysis and the comparison with the power consumption pattern of flexible consumers. The strong relationship of certain loads flexibility and the season of the year are clearly highlighted.

Demand response, especially from residential users, is lately acquiring lots of attention due to the advantages that it introduces in regards the power system regulation. However, depending on the load penetration and location, distribution grids may be leaded to serious congestion problems. In this situation, not only the security and reliability of these networks are in danger, the flexibility offered by the active loads may also be limited. It is then decisive, to understand what is the hosting capability of this networks and their vulnerable points. In this stage of the thesis, a methodology for stochastically evaluating the impact caused by thermostatic and plug-in electric vehicle loads in low voltage grids is introduced. Even though the actual systems seem to be overdesigned, sometimes their hosting capability may be poor for the integration levels expected.

Finally, in the last stage of this research work the control of the demand response in LV networks is tackled. The hierarchical structure presented aims to control the operation of heat pumps and plug-in electric vehicles to satisfy technical and commercial aspects of LV grids. This strategy allows system operators to perform their energy commitments, taking advantage of the flexible demand, while ensuring the security and reliability of the LV network each moment of the day. A proper demand response strategy makes possible to obtain economic benefits from the balancing service provision while decongesting the LV network in critical moments.
Original languageEnglish
PublisherDepartment of Energy Technology, Aalborg University
Number of pages214
ISBN (Print)978-87-92846-42-6
StatePublished - Oct 2014
Publication categoryResearch

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