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On Efficient Transmission Balancing Operation: Capturing the Normal State Frequency and Active Power Dynamics
KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems. (IRES)ORCID iD: 0000-0002-8308-5884
2018 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

In an electric power system, there will always be an electric balance. Nevertheless, System Operators (SOs) often uses the term imbalance. Here, the term imbalance refers to the difference between trades and real-time measurements. This thesis defines the term imbalance and develops a framework helping SOs in finding better decisions controlling these imbalances. 

Imbalances are controlled by many decisions made at various stages before real-time. A decision can be to increase the flexibility in production and consumption. However, this is not the only decision affecting real-time balancing operation. Other decisions are grid code requirements, such as ramp rates of HVDC and generation; balancing market structure, such as imbalance fees and trading period lengths; and the strategies used in the system-operational dispatch.

The purpose of this thesis is to create a new possibility for SO to find decisions improving the balancing operation. 

In order to find and compare decisions, the thesis develops a framework that evaluates many different decisions made at various stages before real-time. The framework consists of the following. First, it develops an intra-hour model using multi-bidding zone data from a historical time-period; able to capture the normal state frequency and active power dynamics. The model creates high-resolution data from low-resolution measurements using several data-processing methods. The uncertainty from the historical time-period is re-created using many sub-models with different input data, time-scales and activation times of reserves. Secondly, the framework validates the model and identifies system parameters based on simulated frequencies and frequency measurements in the normal state operation. Finally; new decisions' are modelled, tested, and evaluated on their impact on selected targets supporting corporate missions of the SOs.

The goal of the framework is that it should be able to find better decisions for balancing operation but also that it should be applicable for real and large power systems. To verify this, the framework is tested on a synchronous area containing 11 bidding zones in northern Europe. Results show that the framework can be validated and trusted.

Three new decisions, made at various stages before real time, have been modelled, tested and evaluated. The modelled decisions were (i) lower ramp rates for generation, (ii) increased capacities for automatic reserves, and (iii) a new strategy for the system-operational dispatch. One implication of applying the balancing evaluation framework on data from July 2015 is that all tested decisions improve several selected targets supporting the corporate missions of the SOs. 

The conclusion is that the balancing framework is useful as a simulation tool in helping SOs in finding more efficient decisions for transmission system balancing operation.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2018.
Series
TRITA-EE, ISSN 1653-5146 ; 2017:161
Keyword [en]
Active Power Dynamics, Frequency Control, Normal State, Power System Balancing, Transmission System Operator
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering Control Engineering Energy Systems
Research subject
Electrical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-221221ISBN: 978-91-7729-595-2 (print)OAI: oai:DiVA.org:kth-221221DiVA, id: diva2:1174612
Presentation
2018-02-07, L1, Drottning Kristinas väg 30, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20180116

Available from: 2018-01-16 Created: 2018-01-16 Last updated: 2018-01-16Bibliographically approved
List of papers
1. Evaluation of different strategies for frequency quality control
Open this publication in new window or tab >>Evaluation of different strategies for frequency quality control
2016 (English)In: 2016 - Biennial International Conference on Power and Energy Systems: Towards Sustainable Energy, PESTSE 2016, IEEE conference proceedings, 2016Conference paper, Published paper (Refereed)
Abstract [en]

Rapid worldwide increase of Variable Generation (VG) brings new challenges for System Operators (SOs) when maintaining power balance and frequency control. SOs can apply different strategies to reach frequency quality goals. However, there is no general framework to compare these strategies in terms of cost. This is important when comparing it with the costs of implementation and costs of market limitations. A contribution is a general setup to evaluate various strategies. To apply this setup, methods to proceb available low-resolution data to high-resolution data are needed. Another contribution is a setup of these data procebing methods. The procebing methods are verified by comparing simulated and measured electric frequencies. Using the verified setup as a reference the proposed evaluation method can be applied. An optimal strategy is one improving frequency quality at lowest pobible cost. The proposed setup is tested using a Nordic Synchronous power system case study. The case study is a strategy change of the Ramping Rate (RR) of Transmibion between Asynchronous Areas (TBAA).

Place, publisher, year, edition, pages
IEEE conference proceedings, 2016
Keyword
frequency control, frequency quality, HVDC Ramping Rate, primary frequency control, Variable Generation (VG), Wind power production, Costs, Electric frequency control, Systems engineering, Wind power, Ramping rate, Variable generations, Quality control
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-197135 (URN)10.1109/PESTSE.2016.7516530 (DOI)000390837800127 ()2-s2.0-84983412634 (Scopus ID)9781467366595 (ISBN)
Conference
2nd Biennial International Conference on Power and Energy Systems, PESTSE 2016, 21 January 2016 through 23 January 2016
Note

QC 20161213

Available from: 2016-12-13 Created: 2016-11-30 Last updated: 2018-01-16Bibliographically approved
2. Balancing Strategies Evaluation Framework Using Available Multi-Area Data
Open this publication in new window or tab >>Balancing Strategies Evaluation Framework Using Available Multi-Area Data
2017 (English)In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679Article in journal (Refereed) Published
Abstract [en]

The penetration of variable RES, the deregulation of electricity markets, and the expansion of HVDC- transmission capacities all increase the variability, uncertainty, and imbalances for System Operators (SOs) to handle. Meanwhile, frequency quality has deteriorated and occurrence of balancing problems has increased. Therefore, there is an increased need for SOs to improve their balancing strategies. In this paper we present a new balancing evaluation framework. The main idea of the framework is to be applicable for real and large power systems and provide support for SOs when comparing already used balancing strategies with new ones using historical available data. This is important as only comparatively low-resolution data measurements, such as hourly-mean-values for production, consumption, and HVDC-transmission are stored in many power systems. The framework consists of model building, system parameter identification, testing different strategies and targets supporting the corporate missions of the SOs. In a case study, the framework is tested for a real power system where the model set-up mimics measured frequency accurately. The case study illustrates how the framework can be used to evaluate the impact of different balancing strategies on a series of selected targets which support the cooperate missions of ENTSO-E.

Place, publisher, year, edition, pages
Institute of Electrical and Electronics Engineers (IEEE), 2017
Keyword
Balancing strategies, imbalance, multi-area, power system control, power system modeling, sustainable development, renewable energy sources, variability, uncertainty
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-221217 (URN)10.1109/TPWRS.2017.2736604 (DOI)000425530300012 ()2-s2.0-85028959814 (Scopus ID)
Note

QC 20180116

Available from: 2018-01-16 Created: 2018-01-16 Last updated: 2018-03-14Bibliographically approved
3. Designing new proactive control-room strategies to decrease the need for automatic reserves
Open this publication in new window or tab >>Designing new proactive control-room strategies to decrease the need for automatic reserves
Show others...
2017 (English)Conference paper, Published paper (Refereed)
Abstract [en]

Maintaining automatic reserve capacities is essential for a sustainable and reliable power system. Today, many power systems experience more frequent frequency deviations coming from increased power variations. This implies an increased utilization of automatic reserves. To decrease frequency deviations, one can increase the automatic reserve capacities. However, the solution tends to be costly and ineffective. Therefore, it is urgent to develop better solutions to cease this trend. Here we have designed new proactive control-room strategies to decrease the need for automatic reserves. We design strategies for a process called Re-Scheduling of Generation and for the Tertiary Frequency Control process. The new control-room strategies are tested using an intra-hour model comparing already used strategies against new ones. It is shown that the historical used strategies are well executed. Nevertheless, results show that the proactive TFC-strategy using a forecasted frequency as control parameter would improve system security significantly.

Keyword
Control-Room Strategies, ENTSO-E, Intra-hour Simulation, Tertiary Frequency Control.
National Category
Control Engineering
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-221218 (URN)000428016500088 ()978-1-5386-1953-7 (ISBN)
Conference
2017 IEEE PES Innovative Smart Grid Technologies Conference Europe (ISGT-Europe)
Note

QC 20180116

Available from: 2018-01-16 Created: 2018-01-16 Last updated: 2018-05-24Bibliographically approved
4. Estimation of Power system frequency response based on measured & simulated frequencies
Open this publication in new window or tab >>Estimation of Power system frequency response based on measured & simulated frequencies
2016 (English)In: IEEE Power and Energy Society General Meeting, IEEE, 2016Conference paper, Published paper (Refereed)
Abstract [en]

Electrical Power systems are going through a transition of increasing penetration of Renewable Energy Sources (RES) and growing transmission capacity between Asynchronous Areas (TBAA). Maintaining a reliable power balance is essential but most new RES and TBAA are not delivering Primary Frequency Controlled Reserves (PFCR) and not enhancing power systems Frequency Response Characteristics β. The issue addressed within this paper is to estimate β in this context. Accurate estimation is important for power system modelling or Automatic Secondary Reserve (ASR) design. We propose a method to estimate Frequency Response Characteristics based on measured and simulated frequencies. In this paper, we propose an iterative optimization method to obtain high resolution data from low resolution measurement. Based on the high resolution data, β is estimated with a σ approach. Then, we use linear regression to estimate the normal Frequency Containment Reserves (FCR). The proposed methods are tested in a Nordic Synchronous Power System case. Results show that our methods can give accurate estimations of frequency response characteristics and FCR.

Place, publisher, year, edition, pages
IEEE, 2016
Keyword
Frequency Bias Factor, Frequency Controlled Reserves, Frequency Response Characteristic, Nordic Power System, Electric power system control, Electric power systems, Electric power transmission, Frequency response, Iterative methods, Renewable energy resources, Electrical power system, Frequency bias, Power system frequencies, Renewable energy source, Transmission capacities, Frequency estimation
National Category
Signal Processing
Identifiers
urn:nbn:se:kth:diva-202144 (URN)10.1109/PESGM.2016.7741498 (DOI)000399937901140 ()2-s2.0-85001764892 (Scopus ID)9781509041688 (ISBN)
Conference
2016 IEEE Power and Energy Society General Meeting, PESGM 2016, 17 July 2016 through 21 July 2016
Note

QC 20170313

Available from: 2017-03-13 Created: 2017-03-13 Last updated: 2018-01-16Bibliographically approved

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