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A proposed framework for coordinated power system stability control: reference 742
RISE - Research Institutes of Sweden, Safety and Transport, Measurement Science and Technology. (Högspänning)
Number of Authors: 162018 (English)Report (Other academic)
Abstract [en]

Power system security is defined as the ability of the power system to withstand the occurrence of

credible disturbances as defined by security criteria or standards. Stability control, which is one of the

pillars to system security and the subject of this technical brochure, aims at maintaining the security

of supply according to cost-effective criteria. It has always been a top priority in both industrial

practice and academic research to ensure the reliable operation of power systems. To this end,

extensive activities have already been undertaken by e.g. CIGRE in the field of power system stability

control and Dynamic Security Assessment (DSA).

Analysis from past blackouts and major system disturbances has pointed out some potential

deficiencies in current stability control techniques. These deficiencies are related to various aspects of

design and maintenance of control systems, being a direct result of the insufficient systematic design

and adaptability of, and coordination among, the conventional stability controls. According to a

questionnaire survey conducted by this JWG, the full benefits from a systematic framework approach

for power system stability were recognized by many of the respondents. All these key elements are

integrated in the framework proposed by this JWG and reflect the existing experience.

This TB proposes a framework consisting of the four established control types described below and

coordinating them to achieve enhanced performance. As fundamental requirement to achieve this

goal, the proposed framework associates these stability control types with their respective system

states. The first control type is named preventive control. It is activated in the normal or alert state,

and is carried out to maintain a sufficient stability margin. Once a predefined contingency occurs the

system could rapidly evolve towards an emergency state, where the second stability control type,

called event-based control, is triggered. The third stability control type, called response-based control,

is usually initiated following the violation of key variable limits in the emergency state. In cases where

the operation of all the previous controls proves insufficient, the system will degrade to a blackout

state. Restorative control, the fourth control type, is activated following a blackout or after an

emergency state and remains active over the whole restoration process.

This TB emphasises that these control types gain added value if they are adaptive and coordinated as

recommended in the proposed framework. When adaptive, they are able to adjust their control

decision set to the current operating condition and identify the contingencies. The coordination of

these adaptive controls yields a more cost-effective set of planned control decisions

This TB describes the functional structure of the proposed framework whose design shares the same

architecture of an online DSA system as well as the same configuration and hardware of existing

automatic control devices at substations.

This functional structure is comprised of four high-levels modules:

Wide area data acquisition and information processing,

Real-time monitoring, online estimation and online stability analysis,

Adaptive and coordinated decision planning of stability control, and

Automatic activation of event-based and response-based controls.

The first and second high-level modules are already well established in the industry. However, the

third module is not yet at the same maturity level. To this end, this TB recommends the following

elements in order to design and develop software with required functionalities in the proposed

framework: Quantitative stability analysis, Determining in advance the optimal stability control decision for each relevant control type,

and

Coordinating the previously determined stability control decisions across all control types.

This framework and its underlying software strongly rely on its integration with online DSA and other

tools used at the control centre. Besides, these systems are fed with field data from measurement

devices (e.g. PMUs) whose number and location should be effectively selected. Data exchange

protocols between all these elements are critical for their integration into the framework. Bad data

detection is a prerequisite for online monitoring and analysis, and absolutely critical for the smooth

functioning of the framework so that proper stability control decisions are always taken.

This TB also provides some key considerations and recommendations in the design and

implementation of the proposed framework for 1) specification designers, 2) manufacturers and 3)

system operators.

Before implementing such a framework, the grid owner (and also the specification designer) should

conduct a cost benefit analysis to compare its effectiveness with alternatives.

After the grid owner decides to implement such framework, demonstration projects and trial

operations have to be conducted with a particular focus on validation of

control decision planning. It is

highly recommended to develop laboratory or field validation tests for key devices and systems. These

tests need to be conducted before as well as after commissioning. Especially for event-based and

response-based controls, which operate infrequently, post-commissioning testing remains important.

It has to be mentioned that there are still some remaining issues. One of these is the execution of the

optimisation process that is quite complex and consists of an iterative search based on simulations.

Currently this optimisation does not guarantee a global optimum or even convergence. This issue

should be the focus of research and development by both manufacturers and academia. Another

major issue to be tackled by specification designers relates to cyber security aspects, which have only

been briefly touched upon in this TB. Thirdly, the remote modification of control settings is not yet a

widely accepted practice, and the proper design of operator’s intervention and validation mechanisms

is still lacking. To address these issues more effort is needed mainly from the system operator’s perspectives.

The proposed framework is expected to overcome most of the deficiencies of the current stability

controls. Yet, some challenges do remain and the following suggestions for future work are provided.

Firstly, the applicability of the proposed framework in a multi-TSO environment with common grid

model, mainly in the emergency state, needs further investigation. Secondly, power oscillations that

occasionally occur and might cause the triggering of incorrect control decisions, should be fully

understood and have their adverse consequences mitigated. Further development would be directed

towards the improvement of control decision planning by combining system-wide response

measurements with pre-disturbance simulation results. Thirdly, the stability characteristics of modern

power systems are changing due to the increasing level of power electronics devices. Its impact on

stability control needs to be properly determined in order to ensure the correct operation of the proposed framework.

Place, publisher, year, edition, pages
2018. , p. 147
Series
CIGRE C2/C4 Technical Broschure ; JWG C2/C4.37
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:ri:diva-36992ISBN: 978-2-85873-444-3 (print)OAI: oai:DiVA.org:ri-36992DiVA, id: diva2:1276709
Available from: 2019-01-08 Created: 2019-01-08 Last updated: 2019-01-29Bibliographically approved

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