– mathematical modelling of power systems and networks, investigation of their control issues;
– modelling and optimisation research of ICT-based control systems of power systems.
Power system (PS) is one of the most complex technical and organizational systems covering generators, power networks and consumers, which operate synchronously, i.e., under the same mode and with the same current frequency in large areas. The operational modes of PS, specified by energy, powers, currents, voltages, phase angles and other parameters, are characterized by continuous change. All the modes should be kept within the pre-determined parameter limits, and this is the major responsibility of the PS operator. Control is a rather complex task even under normal operation; however, systems often get into stressed modes, sometimes emergency and post-emergency modes, the control of which is more complicated. Out-of-control operational modes may lead to loss of stability, voltage collapses, and failures of individual parts or total blackout. System and preventive automatics with protection relays and multiple digital controllers, and systems of data communication, connecting generators and network substations with dispatch control centers, help the dispatchers to control the systems and networks and protect them from emergencies. Operators prepare control measures (equipment switch-over plans, settings of automatics, dispatch control signals) based on modeling, i.e. on calculations. This is an activity requiring a great deal of scientific knowledge and methods: adequate algorithms, assessment methodologies and analysis procedures need to be developed.
Laboratory of Systems Control and Automation carries out research and offers services in the following fields:
– Smart grids solutions and development;
– Digitalization and Big data solutions and algorithms.
– mathematical modelling of power systems, analysis and assessment of their parameters;
– investigation of PS control issues and development of respective algorithms to deal with frequency regulation, active and reactive power control, static and dynamic stability, minimization of transfer losses, electric power quality, emergency prevention;
– investigation of advanced PS control methods and application of new automatic control devices and information and communication technologies (ICT), cyber security;
– analysis and assessment of PS reliability, security and risks;
– optimisation of PS operation in competitive market environment, development of competitive balancing mechanisms and ancillary service mechanisms;
– research on the integration of renewable energy sources (wind, solar, etc.) and distributed generation into PS;
– legal regulation of PS control and use-of-electricity issues;
– economic efficiency analysis related to PS control and extension, and use of electricity;
– promotion of smart grids.
Huge changes are traced in the evolution of modern PS. Cross-system electricity trade that will incorporate a variety of new market products (active power reserves, other ancillary services, forward financial transactions) is expanding geographically as well as in volume. Electricity consumers and small generators are increasingly involved into electricity trade and provision of ancillary services. Electricity is becoming more environment-friendly due to growing share of generation based on renewable sources, and probably, due to expansion of nuclear energy. Power systems will become more resistant to disturbances; reliability of power supply and energy quality will improve (near-to-regular shape of voltage sine curve, minimization of voltage flickers, etc.). Such changes are mostly induced by smart technologies, based on ICT. Their uptake is determined by new concepts as smart generation, smart grids, smart relays, smart meters and even smart house. Smartness is based on logic devices (controllers with microprocessors) and their intercommunication, including links with power network dispatchers. Smart technologies enable power network operators to more efficiently and reliably control their networks in real time and even simplify this work in certain sense (since a part of control and monitoring functions is performed by smart controllers without human intervention). On the other hand, control becomes more complex and sophisticated for operators, since more additional algorithms and software programs are embedded into controllers, their operation has to be monitored and coordinated, controllers have to be reprogrammed in order to eliminate the detected operation errors.
Structural scheme of mathematical model for calculation of power system operation modes
In 2014, the Laboratory (together with the researchers from the Laboratory of Nuclear Installation Safety) completed the project Research and Assessment Methodology of Energy Systems Reliability and its Impact on Energy Security under the national research program Energy for the Future. The program is administrated by the Research Council of Lithuania.
Power system modeling software PSS™E-33 was used to investigate operational modes of Lithuanian PS. The calculations were performed for the current 2014 scheme and the perspective 2020 scheme basing on winter and summer maximum and minimum loads. Simulation schemes were composed of Lithuanian, Latvian, Estonian PS, Kaliningrad (Russia), Belarusian, Ukrainian, Northwest and Central Russian PS, also NORDIC and Continental Europe equivalent nodes. In 2020 scheme, Baltic PS and Kaliningrad PS synchronically work with Continental Europe Network (CEN). The interlinking with Russian and Belarusian PS was simulated via DC cross-border links in Estonia, Latvia and Lithuania (e.g., in Lithuanian-Belarus case - via the single 330 kV line Alytus-Hrodna, other four cross-border lines being disconnected). Lithuanian PS comprised 1123 nodes, 812 power transmission lines and branches, 368 generators (out of which 310 are wind turbine generators). Imitating various combinations of outages in 330 kV network, post-contingency modes were simulated, and then networks were examined for overloads and stability.
Fluctuations of wind power generation in case of short-circuiting of Lithuanian system
Under the contract with SC LITGRID, the project Analysis of asynchronous operation (swings) in cross-border sections was carried out and completed in 2014. The following tasks were investigated and solved:
• drafting of Methodology for choosing the measures for automatic elimination of asynchronous mode (swings) and the respective settings;
• scenarios of emergence of asynchronous modes and identification of triggering events;
• examination of operability of existing out-of-step automatics on Lithuanian-Latvian cross-border section, with the view to the year 2017;
• feasibility of installing the out-of-step automatics on all lines of Lithuanian-Latvian cross-border section;
• examination of operability of existing out-of-step automatics on Lithuanian-Belarusian cross-border section, with the view to the year 2017;
• feasibility of installing the out-of-step automatics on all lines of Lithuanian-Belarusian cross-border section;
• necessity of installing the out-of-step automatics on Lithuanian-Kaliningrad cross-system section, with regard to the existing automatics in Kaliningrad CHP.
Laboratory staff on the visit to SC LITGRID
In 2014, under the topic Possibilities of Lithuanian power system synchronous operation with ENTSO-E taking into account perspective development of generation sources (in the framework of national long-term institutional program), the Laboratory carried out the research on the adequate load-frequency control methods for Lithuanian PS, with the view to the perspective of synchronous operation with ENTSO-E.
Transitional processes of Lithuanian and Belarusian PS, when they are linked by one interconnection
One of the critical aspects in negotiation with ENTSO-E on the conditions of synchronous connection of Lithuanian PS (Baltic PS) to Continental Europe Network is the evidence of ability of Baltic PS to work independently, i.e. in “island mode” (Baltic PS must not disturb the operation of neighboring PS).
To comply with such requirement and to minimize probable frequency deviations and their durations, it is necessary to develop algorithms that effectively control the active power reserves. As one of the most promising alternatives, a fuzzy logic is proposed to be included into the algorithms for secondary load-frequency control. In scientific publications, quite a few algorithms applying fuzzy logics are presented; however those are not sufficiently capable to take into account the size and characteristics of the smaller systems.
The research was focused on the most heavy operational mode when Lithuanian PS works within the isolated Baltic PS under summer minimum loads. In order to examine the effectiveness of fuzzy regulator for secondary load-frequency control, the critical disturbances were imitated caused by an abrupt change in generation/consumption loads.
The simulations showed that under normal operation of isolated Baltic PS the fuzzy regulator eliminates frequency deviations significantly better than traditional one. This was also confirmed for the cases when wind power plants operate, no matter what is the wind speed correlation (high, low) between these power plants. As for large disturbances, the fuzzy regulator also demonstrated better results reducing the transient processes by several times and successfully coping with small frequency deviations. Nevertheless, in critical case, the stability of the system can be lost. The research results will be employed in joint work Economic and sustainability analysis of development of energy sector that is implemented by the Laboratory staff together with the Laboratory of Energy Systems Research and the Laboratory for Renewable Energy and Energy Efficiency.
Root mean square errors (RMSE) histograms of wind speed forecast for 6–48 hours
Researchers of the Laboratory together with the Laboratory for Renewable Energy and Energy Efficiency carried out the state-funded project Research of intensity of application of low power wind power plants and solar energy systems and their development possibilities in Lithuania. In this study, the forecasting model of wind generated power was developed employing artificial neuron networks (ANN).
Scheme of artificial neuron
The study Technical expertise of unplanned power supply interruption for the Druskininkai city was performed together with the researchers of the power system department of Kaunas University of Technology. On April 8, 2014, failures occurred at Druskininkai transformer substation, which caused a series of outages and cut off the power supply to consumers of the Druskininkai city for more than 2.5 hours. The study identified the reason of failures and presented recommendations on how to prevent the similar power supply interruptions in the future or, if occurred, reduce their scope and durations.
Active role of the Laboratory in activity of Lithuanian Smart Technologies Association (SMARTTA) did not go unnoticed. Working on an international scale, SMARTTA became a partner of consortium of the project Planning of Energy Efficient Cities (code name PLEEC) under the 7th European Framework Program. The major part of tasks designated to SMARTTA was performed by the Laboratory. The objective of the project is to increase energy efficiency of a smart city at the planning stage. The drawback of the current planning is that many development strategies are designed for individual aspects of city economy, infrastructure and social life. The strategies are presented by various interested parties that are interested in their individual aspect only. Such method of planning hinders strategic planning of energy efficiency of the city. It is hoped to overcome this drawback by forming an integrated planning approach, the key point of which is a smart city. Such planning shall be based on principles of sustainable development and innovativity.
Vision of energy efficiency cities
The problem solution will be enabled by better coordination of individual strategies and building upon the experience from the best practice examples. The major outcome of the project will be a new energy-efficient city-planning model. The specialists of the Laboratory carried out a technological assessment of the best practice projects submitted by PLEEC partners (public lighting and other activity sectors of the city) and prepared baseline reports on technology progress.
In 2014, the results of research were presented in the proceedings of one international conference, also in an article in the journal listed in Thomson-Reuters database Web of Science Core.