- Maren Istad
- Research Scientist
- 901 15 557
- Energy Systems
- SINTEF Energi AS
Interaction DSO/TSO (WP3)
The objectives of WP3 are to develop concepts and solutions for utilizing flexible resources (DER = Distributed Energy Resources = Energy storage, distributed generation from renewable sources and demand response) indifferent market products and ancillary services, for increased observability between the distribution and transmission systems and business models regarding utilisation of customer flexibility.
The expected impact from these objectives is improved interaction DSO-TSO to benefit the total power system, especially by enabling DER flexibility to all voltage levels.
- Ancillary services – needs and requirements
- Increased observability between distribution and transmission system levels
- Business models for utilization of customer flexibility in the interaction DSO/TSO
- Improved plans for defence and restoration
In WP3 we are developing concepts and solutions for utilizing flexible resources in diff erent market products and ancillary services, for increased observability between the distribution and transmission systems and business models regarding utilisation of customer flexibility.
Utilizing flexible resources in ancillary services
Coordination between TSOs and DSOs is essential to ensure that flexibility resources in distribution networks remain available for system balancing purposes without inducing unmanageable local congestions, which could affect the local grid. An optimal mix of flexibility resources can be obtained through a holistic approach considering technical, market and environmental aspects.
To get an overview related to how flexibility can be utilised, we have developed use cases focusing on voltage control, congestion management and balancing.
Use case for voltage control
In this Use Case, reactive power is controlled for the benefit of both TSO and DSO. TSOs are responsible for keeping regional voltage levels to the standard limits while DSOs are responsible for keeping the voltages within limits both at customer premises as well as at the coupling point to the transmission network.
With the ever-increasing integration of power electronic devices, such as inverters, and due to the large variation of the generation of distributed generations, voltage level problems are becoming increasingly common. Hence, there is greater interest to deploy the controllable and distributed flexibility resources to solve voltage problems. In addition, there is greater interest to offer flexibility potential in DSO premises to voltage regulation in TSO areas and vice-versa.
With this use case we aim to utilize reactive power provision capabilities of RES and DERs as well as emerging technologies in the distribution grids to increase the hosting capacity and to improve voltage profiles both in transmission and distribution grids. This involves coordination between two real-time Optimal Power Flows (OPFs) running at the TSO and DSO control centres.
Use case for congestion management
There are growing concerns about congestions in the distribution networks in the next decades, including electrification of transport and space heating as well growth of DERs such as photovoltaics. Problems with congestions can result in voltage problems and overloads. Even if voltage problems occur in the distribution grid, they can also affect higher voltage levels. To avoid this, the problems should be solved locally.
In this Use Case we present a method to mitigate congestions in the distribution network by using flexible active power resources, procured via a specific two-step market arrangement. The use case includes different phases related to congestion management: Forecasting phase, market phase, monitoring and activation phase, and measurement and settlement phase.
Use case for balancing
To maintain the stability of the power system, the instantaneous generation and consumption have to be in balance at all times. But the increasing amount of non-dispatchable forms of generation in the power system makes it more challenging to balance it. Today, TSO is responsible for balancing the grid. But in the future, we expected that balancing services will be necessary in the distribution grid too.
This implies that flexible resources located in the distribution grid should be utilized in different ancillary services. By both DSO and TSO. Several ancillary services with the aim of keeping the power system in balance, have different requirements related to the response, from seconds up to 15 minutes.
We have therefore developed a Use Case describing how flexible resources can be included in system balancing, focusing on utilizing flexible resources as tertiary reserves is developed. Depending on the grid level where the balancing market is implemented, the buyer of flexibility services could be the TSO or DSO. Today the capacity and balancing markets are implemented on the transmission level and the TSO buys the flexibility. If the DSO in the future is responsible for balancing services in the distribution grid, the DSO can buy flexibility too.
Pilot project on flexibility markets
WP3 has also been involved in a pilot project on NODE’s marketplace for flexibility trading. You can read more on the pilot project website.
In WP3 we are developing concepts and solutions for utilizing flexible resources (Distributed Energy Resources) in different market products and ancillary services, for increased observability between the distribution and transmission systems and business models regarding utilisation of customer flexibility (Distributed Energy Resources).
By the end of our work we expect to have improved the interaction between DSOs and TSOs to benefit the total power system, especially by enabling DER flexibility to all voltage levels.
Use cases for application of flexible resources in future ancillary services
We investigate needs, gaps and opportunities related to utilizing flexible resources in different market and ancillary services on transmission level, including services delivered on the interface DSO/ TSO. Utilization of flexible resources should be made possible in a coordinated way between DSOs and TSOs regarding e.g. purpose and consequence. In fact, there might be flexible resources planned to be used in ancillary services on the transmission level, that also can be utilized on the distribution level. For example when regulation of distributed generation (DG) in the distribution grid is necessary due to bottlenecks. This interface will be further elaborated.
"Ancillary services" (AS) are services necessary for the operation of a transmission or distribution system, and they can be clustered into frequency ancillary services (balancing of the system) and non-frequency ancillary services (voltage control and black-start capability). Potential future ancillary services were evaluated based on CINELDI mini scenarios. They are basis for development of use cases describing how different flexibility resources can be utilized in different ancillary services. The main focus was on ancillary services for frequency control (e.g. fast frequency reserves), voltage control (e.g. primary, secondary and tertiary voltage control) and services such as for example black start capability. The main focus is on the ancillary services voltage regulation, management of bottlenecks in the distribution or transmission grid, including in balancing market.
The use cases that are under development will give a broader overview of how different flexible resources can be utilised in different ancillary services. Combining this with CINELDI mini scenarios will give input to the direction of the research within WP3, and knowledge related to when utilizing flexibility can be a new solution.
Algorithms for observability in TSO/DSO interface
Dynamic state estimation of power networks has absorbed increasing attention since the distributed generation and Phasor Measurement Units (PMUs) and other types of fast sensors have been increasingly used in modern power systems. The application of the simultaneous input and state estimation algorithm to the problem has been studied. The proposed algorithm performs dynamic state estimation in a power grid using the partially known network concept in which the unmodeled disturbance signals can be estimated through smoothing. Even though the classic Kalman filtering methods have achieved satisfactory results for state estimation of a power grid, they require strong assumptions such as all parts of the system, including disturbance models, which must be known, and it is problematic primarily for the distribution part of power grids. Thus, a power network has been modeled as a system with known and unknown parts. The derivation of the state estimation is based on the model of the known part of the system such that the unknown connected signals are captured using the simultaneous input and state estimation (SISE). The physical nature of power grids admits the application of this estimation approach more widely than is suggested by the disturbance reconstruction condition.
The focus has been narrowed to linearized power systems, and the term “known” has been used to describe a subsystem whose dynamic model is available. In a power grid such as that depicted in the figure above, a virtual circuit cut can be performed to divide the grid into two parts, the left side is known, and the right side is unknown. The interacting power signals between the known and unknown parts are treated as disturbances flowing into the known part of the system.
During this work, the fast dynamic states and transients of a power network are captured using dynamic procedures, the number of measurements needed for state estimation was reduced significantly, and all available measurements are used at the same time. The unknown parts of a power grid are estimated very accurately without having any information or data from there.
The work was published in both a paper presented at the IEEE Conference on Control Technology and Applications (Aug 2019) and in the Journal Automatica (2019).
Market architecture for TSO-DSO interaction in the context of European regulation
The growing need for ancillary services due to the variability and uncertainty of distributed generation based on renewable energy sources requires implementation of coordinated market schemes allowing procurement of flexible resources from the distribution grid for ancillary services in both distribution and transmission networks.
Five coordination schemes for TSO-DSO interaction, necessary for procurement and activation of ancillary services were developed and comparatively evaluated. Each of the coordination schemes (CSs) present a different way of organizing the coordination between transmission and distribution system operators (TSOs and DSOs), when distributed resources (production, storage or demand) are used for ancillary services. Each coordination scheme is characterized by a specific set of roles and responsibilities, taken up by system operators and a detailed market design.
The different coordination schemes all have specific benefits and attention points related to operation of the TSO and DSO grids, other market participants involved and the market operation in general. The feasibility of the implementation of each coordination scheme is very dependent upon the regulatory framework.
The characteristics of the different coordination schemes are:
- Centralized AS market model - The TSO operates a market for both resources connected at transmission and distribution level, without extensive involvement of the DSO.
- Local AS market model - The DSO organizes a local market for resources connected to the DSO-grid and, after solving local grid constraints, aggregates and offers the remaining bids to the TSO.
- Shared balancing Responsibility Model - Balancing responsibilities are exercised separately by TSO and DSO, each on its own network. The DSO organizes a local market while respecting an exchange power schedule agreed with the TSO, while the TSO has no access to the resources connected to the distribution grid.
- Common TSO-DSO AS Market Model: The TSO and the DSO have a common objective to decrease the cost of the resources they need, and this common objective could be realized by the joint operation of a common market (centralized variant), or the dynamic integration of a local market, operated by the DSO, and a central market, operated by the TSO (decentralized variant).
- Integrated Flexibility Market Model: The market is open for both regulated (TSOs, DSOs) and non-regulated market parties, which requires the introduction of an independent market operator to guarantee neutrality.
The implementation of a coordination scheme is influenced by the national organization of TSOs and DSOs, e.g. the number of system operators (both TSOs and DSOs) and the way they currently interact. Although TSO-DSO coordination could be organized on a country level, it is important to integrate national TSO-DSO coordination set-ups within the process of EU harmonization and integration.
The work is performed in cooperation with H2020 project SmartNet.
Operation – today and in the future (2030/2040)
In the beginning of 2018, a survey was sent out to the DSOs in CINELDI, with the objective to map the status of interaction DSO/TSO and the use of flexible resources in the operation today, and input related to what is expected in the future (2030/2040). To be able to discuss the transition towards this long-term period, the assumed starting point has been a survey mapping today’s status and future expectations about the DSO/ TSO interactions, and focusing especially on how and how much flexible resources are and will potentially be utilised in the power system operation and also on what kind of information it is necessary to monitor. According to the survey, the use of flexible resources today is mainly related to disconnection of unprioritized demand units that have an agreement for disconnection through a reduced grid tariff. Typically, these loads can be disconnected for an unlimited period (disconnected in periods with temporary problems with limited grid capacity), and the customers have alternative energy carriers to use when the electric load is disconnected. Based on experience, this agreement for disconnection is seldom in use. In the future, the DSOs expect that there will be an increasing focus on flexible resources, and not only to be used in periods with limited grid capacity in the power system. Due to technology development combined with reduced costs for different technologies (for example PV panels, electric batteries and communication and control technologies), flexible resources are evaluated as a new source to be included in cost efficient operation of the power system. In other words, it is expected that a wider variety of flexible resources will be available in 2030/2040, and that these will also be used in normal operation of the grid. The evaluation of future use of flexible resources was combined with the suggestion from EU FP7 project ELECTRA IRP, for a future (2030+) decentralized control architecture (Web-of-Cells) for balance (including frequency) and voltage control, as opposed to the current centralized control approach typical of Transmission System Operators (TSOs).
European legislation related to the DSO-TSO cooperation
Important topics for DSO-TSO cooperation in the European legislation has been studied, in cooperation with the SmartNet project. The study is structured around the following topics of interest: Market layer, Bidding layer and Physical layer. These topics of interest were evaluated based on more than 40 different documents as position papers, strategies, roadmaps and legislation/regulation (EU Directives, Network guidelines).
Evaluation of use case (repository) and relevant mini-scenarios
Existing use cases have been evaluated, with the purpose to get an overview of use cases from other projects, covering topics relevant for WP3. 213 use cases gathered from EPRI, ELECTRA IRP and DISCERN were evaluated. Both EPRI and DISCERN refer to use case repositories, which gathers use case and sort them by topic. 86 use cases were evaluated as relevant for WP3. The use cases were sorted according to the following categories, and the number of relevant use cases within each category are presented in brackets:
1. Utilising flexible resources (DER) (21 use cases)
2. Demand response (28 use cases)
3. Flexibility bids to the market (6 use cases)
4. System services that support frequency regulation (5 use cases)
5. System services that support voltage regulation (9 use cases)
6. Congestion management (3 use cases)
7. Other system services (14 use cases)
At the end of the year work for evaluating the mini scenarios from WP6, related to the focus within WP3 was started and will be continued in 2019. This work will be basis for development of the future use cases: use of flexible resources for balancing, handling bottlenecks and voltage regulation.
Technical and practical approaches to define new DSO-TSO interaction schemes
A literature study with the objective to study and report the technical and practical approaches used in the literature to define new DSO-TSO interaction schemes has been performed. Most of the reviewed research activities focused on devising DSO-TSO joint optimal flexibility dispatching techniques. There is limited research regarding markets' influence and data privacy issues with regards to DSO-TSO interactions. The reviewed literature also indicates that there are significant numbers of demo activities testing the merits of increased data exchange between TSO and DSO. Based on the literature study, summary of the contemporary DSO-TSO interactions and the recommended future practices are presented.
2017 has been a year for start-up of the activities within WP3. The main activities are therefore related to a first workshop with the partners in CINELDI, a concept study of ancillary services and interaction DSO/TSO and recruitment of PhD students.
Workshop with partners – arranged in cooperation with WP4 and WP5 (2017-09-07)
A partner workshop was arranged in the beginning of September in cooperation with WP4 "Microgrids" and WP5 "Flexible resources in the distribution grid". The workshop was divided in two parts, where an introduction to each WP and input from selected partners were given in the first part, and group discussions related to the topics within the relevant WPs were performed in the second part of the workshop.
The results from the group discussions will give important information for the research to be done within WP3. Two groups were established discussing how flexible resources are in use today, how they can be used in near future (2020-2030) and after CINELDI (2030-2040), both for the market and in system services.
To a limited degree some flexible resources (mainly for large industry or electrical boilers) are in use in balancing services today – as tertiary reserve with response within 15 minutes, activated by a phone call from the TSO.
In the near future, there will be an increased focus on other flexible resources, but customer involvement is a challenge. The interaction DSO/TSO has to be defined, to make it possible to activate flexible resources without generating any problems for other stakeholders. This a topic that WP3 will study.
Concept study of ancillary services and interaction DSO/TSO
A concept study was started in 2017, evaluating today's ancillary services and interaction DSO/TSO. This work will be the basis for the evaluation of the ancillary services in the future intelligent and flexible power system (2030-2040). Topics to be evaluated are state of the art in Norway and other relevant countries (based on today's power system) for the interaction DSO/TSO. Present functionalities are in use to secure a stable operation of the power system, both on transmission and distribution level, and an evaluation of which problem(s) the different ancillary services should solve such as when are different services needed? When is there a problem to solve? And what should be the physical parameters to trigger the need for activating a service? (voltage, frequency and other). This study will be completed in 2018. Important experiences from the Horizon 2020 project "SmartNet" will be important input to this work, as this project also is included as in-kind to CINELDI.
A survey for mapping the status of today's interaction between DSOs and TSO in Norway has been developed. The focus in the survey will be on the use of flexible resources in today's power system and what kind of information the DSOs are selected related to interaction DSO/TSO. The survey will be sent out to the DSOs in CINELDI in the beginning of 2018.
Two PhDs were recruited to WP3 in 2017, focusing on the following topics:
Distributed and hierarchical dynamic state estimation for smart distribution grids
The PhD will study accurate monitoring of the power system, while handling (or avoiding) the 'data deluge'. At substation level, detailed dynamical models will be utilized, with full utilization of sensor data. Information transmitted to higher voltage levels of the power system will be filtered to focus on information and system services of relevance to those higher levels. Methodology will need to be developed for sensor selection and placement for observability at the lower level, and for filtering and data fusion under consideration of the particular dynamic phenomena to be observed at higher levels.
Techno-economic optimization for analysing consumer flexibility and related market structures
The main objective of the PhD project is to develop models, concepts and solutions for utilization of customer flexibility in the energy system. This includes realization of balancing services and flexibility services as an alternative to grid reinforcement, minimizing grid asset investments and maintenance costs. The project will study market structures for trading flexibility, the different players, business models and decision support for the analysis of markets, contracts, tariffs and cooperation
The PhD students started up with their coursework in 2017, that will be continued in 2018. Additional, the PhD students in cooperation with their supervisors will start on the academic work related to each PhD topic.