Smart Grid, Integration of Renewable Sources and Improvement of Power Quality

Transcription

1 st International Conference on Control Systems and Computer Science Smart Grid, Integration of Renewable Sources and Improvement of Power Quality Stefan Gheorghe George-Cristian Lazaroiu Nicolae Golovanov Radu Porumb Abstract The paper presents the impact of connecting Renewable sources to the Smart Grid with regard to improving Power Quality aspects. The impact of integrating renewable sources on Power Quality indices in the grid wes analyzed and the measures for avoiding the negative impact are included in the paper. Challenges coming from the integration of renewables variability and uncertainty and the correlation with smart grid technologies used in the power system are discussed in detail. Aspects related to the exchange of information among different systems used in the Smart Grid DMS, SCADA, DFR, OMS, MDMS, security of the grid and security of IT networks have been reached in the work. The final part of the paper contains the authors conclusions on issues addressed in it. Keywords-component: renewable energy source; smart grid; electromagnetic compatibility; power quality; distribution system operator I. INTRODUCTION This triangle: Smart Grid, Renewable with regard to improving Power Quality (PQ) is a very actual issue and it is an important direction for the near future. Smart Grid represents a trend of modernization of power networks, the connection of renewables to the system means a change of the structure between conventional sources and renewable sources and power quality improvement represents a desire of all electricity end users. The global approach of these three concepts gives more consistency to the study (Fig.1). The substantial increase of the number of electronically controlled equipment and the volatile nature of energy generated from renewable sources can cause large variations of power flow in electricity transmission and distribution networks. The complexity is given by the possibility of end users to participate in the market of energy supply as "prosumer" (producer or user), the islanding operating regime of micro Smart Grids and the propagation of important electromagnetic interferences with negative effects on the Power Quality indices of the networks. The current trend in widespread adoption of the smart grid paradigm is an incremental-step transition from current state of electrical networks and traditional customers. This approach is performed through increasing adoption of renewable resources, combined with constant assessment of the power quality boundaries and imposing limits adapted to multiple operating scenarios. Another trend is the ongoing transition from traditional PQ measurement devices and systems towards multi-vendor compliant systems, using common interface and plug-andplay capabilities, being able to comply with virtually any kind of grid topology, and tailored to suit the need for control and information exchange between various energy vectors and players. A strong implementation of renewable energy sources can have a positive impact (smart grid technologies offer opportunities to improve reliability as experiences by the customers) and a negative impact on Power Quality (harmonics perturbations, voltage fluctuations) [1]. Developing Smart Grid networks will allow the increase of system flexibility with a specific approach to the problems of PQ, taking into consideration both the changing of the generation and use system s structure, but also the possibility of special procedures of operation (islanding of micro-grids, functioning as virtual plants and so on). SMART GRID POWER QUALITY RENEWABLE Figure 1. The association of three concepts: Smart Grid, Renewable sources and Power Quality conditions /17 $ IEEE DOI /CSCS

2 TABLE I. SYSTEMS USED ON THE PLATFORM SCADA Protection System Outage Management System - OMS Digital Fault Recorder - DFR Distribution Management System - DMS Meter Data Management System - MDMS Power Quality Monitoring System - PQMS Process Management Systems Analyse systems As a common aspect of the triangle: Smart Grid, Renewable Sources of energy and Power Quality, we can discuss about the exchange of information among different systems as follow: DMS (Distribution Management System), OMS (Outage Management System), MDMS (Meter Data Management Systems), DFR (Digital Fault Recorder), Power Quality Management System (PQMS), SCADA system and Protection System. The paper presents a common IT platform that will integrate the main systems from above. Monitoring the PQ indices and taking measures to maintain them at the admissible quality standards is up to the network s operators (DSOs), both for classic power grids and also for the smart ones (Smart Grid). Addressing these issues, we can split them into two main types of systems: Process Management Systems (SCADA and Protection System) and Analysis Systems (OMS, DFR, DMS, MDMS, PQMS) Table I. Work Management Outage Management System (OTS) SCADA Protection system Real Time Data GIS ERP Call Center MDMS CIS PQMS Fault Information Real Time DMS Figure 2. The architecture of the platform including existing systems (blue light) and new systems (red light) All analyzing systems send the information to Power Quality Management System (PQMS). The process systems respect special conditions related to security of information [2]. The Outage Management System (OMS) (Fig.2) gives the capability to efficiently identify and resolve outages and to report valuable historical information. This system operates as a central point of information about interruptions and also helps the DSO to inform the customers of the outage stage and restoration status. The OMS operates in correlation with other systems as follow: Geographic Information System (GIS) and DSO s Customer Information System (CIS). For DSO, this system is focused on the reporting the historical information, which has to be sent to PQMS. The main function of the Digital fault Recorder (DFR) is to create a transient oscillography record of the current and voltages. The events are recorded for a period of time which covers the time before, during and after the fault. The transient recording rate could be programmed by the user up to 24 khz. In the power system analysis, this system is very useful The Distribution Management System (DMS) allows the DSO to plan, to increase system efficiency and to optimize power flows. DMS can be interfaced with other systems, such as: Geographic Information Systems (GIS), Outage Management Systems (OMS), and Customer Information Systems (CIS). The implementation of the platform including the analysis system is in progress at one DSO from Romania. The concept One system for all PQ data is a part of implementation by TSO and DSOs for increasing the efficiency of the management, using the information coming from the many systems. In the nodes of Power System in which the renewable sources of energy will be connected, PQ devices have to be installed. These devices have to be included in PQMS of TSO and DSOs. II. SMART GRID AND INTEGRATION OF RENEWABLE SOURCES The most important technical challenges related to the connection of renewable sources to Smart Grid and some action to mitigate their impact are accounted below: Management of variability and uncertainty production of renewable sources. The participation of this production to the balancing power in the system is a big challenge [3]. The solar sources are more variable than wind (changes faster), but these sources are less uncertain than wind. As a potential action for hedging these impact is to increase the capability of the system and generation operators to predict the production. Getting better forecasts through the use of more complex mathematical models helps generation operators reach this target. 642

3 Management of balancing supply and demand, as long as renewable source production could be lower or higher than estimated before. The solution is for the system operator to create, the reserve power on a few levels. These reserves can be created in hydro capacity, having a short answer time to start from 0 to one demand level. The Smart Grid solutions to manage balancing in power in the system contain: Smart devices for connection and other advanced power controls. The power electronic devices provide control functions to the system operators and they can reduce the need for significant grid transmission and distribution upgrades. Finally, cost is the drive for this decision. The integration of the storage system. These system smooth the variations in renewable sources production (short-term). The first storage solution for wind farms was implemented in Romania at the end of Information about this project is presented below: - The wind farm has 26 MW (13 turbines of 2 MW). - A storage battery having 1.26 MW/1.368 MWh has been installed. - The connected solution to 110/33 kv substation uses a transformer 33/0.36 kv, 1250 MVA. - The storage consists of 30 batteries, divided by three per inverter. The control of all of the 10 inverters is integrated in the SCADA and protection system of the substation. Using the Real time management system, the control of power system will be better. It allows the DSO to make better decisions related to the power networks.. Improvement of forecasting advanced forecast models, using multi-criterial functions in the algorithm of the model. Demand response of the devices. Currently, smart meters have specific functions and can be integrated in smart applications. Smart meter and smart loads of customers can help the system operator to better manage the excess of renewable production. Related to the stability of the system, integration of renewable sources in smart grid has to consider the measurement for avoiding the islanding regime. It is identified by tight control of the power flows and voltages, using Phasor Measurement Units (s). The management of renewable sources connected to the grid integrates technical, regulatory and managerial aspects of national power system processes. Regulatory issues, which are very important for investors, for operators and for regulatory body are included in the framework for the connection process, commissioning, operation, and monitoring of the power quality indices in accordance with the standards [3]. Smart grid technologies can allow fine-grained information from the components of TSO and DSOs, which determine a high sensibility and selectivity of the protection system, and as a consequence, safe operation and stability of the power system [4]. III. RENEWABLE SOURCES AND POWER QUALITY The connection of the renewable sources to the grid can degrade the PQ indices (power electronic devices inverters -generate harmonic regime), this having a negative impact on the operation of other devices. The clear regulations can avoid these situations of exceeding the admissible limits of the standards. In regards to the connections of renewable sources, Regulatory body has performed a review of the national technical regulations on flicker, harmonic and unbalanced regimes, resulting in performance standards and an upgrade methodology, and has also optimized the technical norms for connection of new power sources, such as wind and photovoltaic power plants, for power quality requirements. In the process of connection to the network, new renewable sources need to comply with the power quality limits. Compliance must be proved through power quality parameters in the PCCs, and the calculations are made based on technical documents and certificates of voltage fluctuations (flicker) emission measurement considering the minimum short-circuit power of the connection node levels [5]. On the other site, a larger limits of variation of reactive power per wind farm and solar farm, means a better control of the voltage levels in the grid. This advantage determines a positive impact consisting in an improvement of the PQ indices. Generally speaking, a power quality indicator means a characteristic of a qualitative evaluation of the property of product/services, which have been analyzed under the respecting of the requirements related to performing, operation or consumption. DSOs have the responsibility to respect the PQ standards and they have implemented PQMSs for monitoring PQ indices in PCC of the connection of renewable sources to the grid [6]. Next generation of PQMS will use more Virtual instruments for measurements, analysis and monitoring PQ [2]. These instruments will simulate the propagation of the disturbances in the power network. This approach will be focused on the nonsinusoidal, unbalanced and flicker regimes. Requirements of the connection of renewable sources to the distribution grid are very strongly related to PQ issues. IV. POWER QUALITY AND SMART GRID Power Quality ensuring to users connected to smart grids (Smart Grid) requires an ample presence of the new control technologies of quantities in the electrical network. 643

4 U 1 I 1 R 1 ; X 1 2 I 3 U 3 1 U 2 3 ψ 1=0 ψ 2 ψ 3 I 3 ψ 2 ψ 3 I 1 U 2 U 3 U 1 R 1 I 1 jx 3 I 3 a) R 3 I 3 jx 1 I 1 b) U 2 = U 1 R1 I1 jx1 I1 ; U 3 = U 2 + R3 I 3 + jx 3 I 3 Figure 3 The control of the voltage angle in the nodes in Smart network, reported to reference node (a) and the phasor diagram of the network (b) Monitoring the indicators of power quality and taking measures to maintain them at the prescribed quality standards is up to the network s operators (DSOS), both for classic power grids (classical power network) and also for the smart ones (Smart Grid). Fig.3 presents a general overview for determinating voltage drops in distribution networks, having two sources of power, using the synchronization of measurement devices by GSM. The control of the voltage level in the network s nodes, the control of the power flow in the system and the control of the reactive power sources ensure needed information about predefined voltage levels and the adoption of the needed measures for ensuring voltage quality in the network s nodes. The operation of the Smart microgrid is checked by Energy Management System (EMS), using devices (Fig.3) [4]. The control of events that appear in the grid allows the improvement of the performance in operation of the distribution system. This control is possible in the Smart Grid, using smart devices which record all events generated by different perturbations. Most events are recorded by the SCADA system and can be analyzed post event. This function is operational in all modernized substations of DSOs. The implementation of PQMS in TSO and DSOs represents a very good solution for monitoring Power Quality indices online in different nodes of the power system, which represent Points of Common Coupling (PCC) [4]. The PQMS uses dedicated devices (PQ Analyzers), having high accuracy, being installed in PCC. Taking into account the extension of other smart systems in many substations (for example smart meters), the use of the Figure 4. Evolution of voltages in case of fault in a 20kV network devices having PQ functionalities and the integration of PQ functions from these devices in PQMS are more efficient (economically). Even if the accuracy of these devices is lower, from economic point of view, to use this solution is more efficient. The solution has already been used by DSOs. In Fig. 4 a temporary fault (few cycles) in a 20kV network B phase to earth has been recorded. This recording allows to identify the causes of the fault, that means an important benefit of the using of this tool PQMS. The management of transmission and distribution system, using the SCADA system, gives to the operator the possibility to know the events from the network, especially information related to the quality of supply can be obtained [2], [7]. The Smart meters used for energy measurement give information related to voltage quality, as well. The obtained data from SCADA system and smart meters can be used for an informative level, being a base for the request to perform a more detailed study, using specialized devices in the PQ analysis (PQ Analyzers).. Collecting the PQ data from the SCADA Systems and from the modern meters can be used as informative information and usually can be a base for the request to perform a special study using the specialized PQ analyzers. Power Quality could be considered as an Electromagnetic Compatibility standard which has to be respected by the components of Smart Grid: renewable and distributed generation sources, connected to the grid and end users (customers) as final beneficiary of all of these facilities [8]. V. CONCLUSIONS The integration of Renewable sources into Smart Grid and respecting of the PQ conditions of the standards represent two important targets of DSOs. The technical and regulatory challenges offer experts the opportunity to research and study how these three concepts operate together in a global approach [9]. Based on the characteristics of inverters, the range of reactive power in the grid where renewables are connected is high, using an easy and modern solution for adjusting by the dispatcher. That means a good condition of better control of the voltages in Smart Grid and the PQ indices 644

5 related to voltage levels will be kept in the admissible limits. This is a good opportunity which can be used by TSO for ancillary services. The level of short-circuit power in the nodes of the grid influences the investment and operational costs of the grid. Based on the increasing of the renewable source of energy, many conventional sources are in reserve, that means a decreasing of short-circuit power in smart grid. That means a reduction of the investment and operational costs. On the other side, this reduction of short-circuit power means increasing of the weight of perturbed load. Re-sizing of the technical characteristics of the attenuation of the disturbances in the systems have to be taken into account. An own monitoring of the harmonics in the PCCs where renewable are connected could be solved by the inverter control, that means keeping the PQ indices into the admissible limits of the standards. The research study for propagation of the disturbances in the power grid is necessary. It has to give more attention to the propagation of the harmonic pollution and flicker from MV network to HV level of the network. These studies will take into consideration and interharmonics which are present much more nowadays. The installation of many renewables, especially solar sources, connected to Medium Voltage (MV) network, determines the achievement of the study related to the propagation of disturbances to High Voltage (HV) network. In the same time, the requirements related to the avoiding of islanded regime, have to be respected. The last, but not the least conclusion can be formulated as follows: The Smart Grid represents the future of the power system; the renewable sources of energy will replace a part of the conventional sources of energy and we should not forget the increasing immunity of the devices, because sometimes is cheaper to adopt this action than decreasing the level of emissivity, under PQ conditions. ABBREVIATIONS AND ACRONYMS DSO Distribution System Operator HV High Voltage LV Low Voltage MV Medium Voltage PCC Point of Common Coupling SCADA Supervisory Control And Data Acquisition TSO - Transmission System Operator REFERENCES [1] M.H.J. Bollen, J. Zhong, F. Zavoda, J. Meyer, A. McEachern, F.Corcoles Lopez, Power Quality and Smart Grids, ICREPQ 2010, Granada, Spain. [2] S. Gheorghe, N. Golovanov, C. Stanescu, G. Gheorghe, Results of Power Quality Monitoring in Romanian Transmission and Distribution System Operators, ICATE 2016 Conference, Craiova, Romania, 2016; [3] N. Golovanov, H. Albert, S. Gheorghe, N. Mogoreanu, and G.C. Lazaroiu, Renewable sources in Power System, Ed. AGIR, 2015, Bucharest. [4] H. Albert, S. Gheorghe, N. Golovanov, L. Elefterescu, R. Porumb, Power Quality. Contributions, Results, and Perspectives, Ed. AGIR, Bucharest, 2013; [5] ANRE, Romania, 2014, Technical regulation regarding limitation of voltage including the effect of flicker in power transmission and distribution networks, NTE 012/14/00, Laws Monitor no. 884/ , [6] S. Gheorghe, N. Golovanov, H. Albert, C. Stanescu, The Management of Power Quality, Energy Efficiency and The Performance of The Companies, ICHQP, Bucharest, 2014, #165; [7] S. Gheorghe, C. Stanescu, Performance of Services Achieved by Transmission and Distribution System Operators in Romanian Power Grid, DAS 2016 Conference, Suceava, Romania, 2016; [8] S.P. Verma, P. Kumar, N.ul Islam, Smart Grid, Its Power Quality and Electromagnetic Compatibility, MIT International Journal of Electrical and Instrumentation Engineering, Vol. 2, No. 1, Jan. 2012, pp. (55-64). [9] CIGRE/CIRED WG C4.07 Report, POWER QUALITY INDICES AND OBJECTIVES, Paris,