SSD2014 Invited keynote: Research challenges in Microgrid technolgies
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microgrid could be defined as a part of the grid with elements like distributed energy sources, power electronics converters, energy storage devices and controllable local loads that could operate autonomously islanded but also interacting with the main power network in a controlled, coordinated way. Following the introduction of distributed control of these elements, cooperative control and hierarchical control schemes for coordination of the power electronics converters in order to control the power flow and to enhance the power quality will be elaborated. The focus will be on the analysis, modelling, and control design of power electronics based microgrids as well as power electronics control and communications. Further, the interconnection of microgrid clusters will be emphasized as an important step towards utilization of the Smartgrid concept.
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SSD2014 Invited keynote: Research challenges in Microgrid technolgies
- 1. RESEARCH CHALLENGES IN MICROGRID TECHNOLOGIES PostDoc - DFF Juan C. Vasquez juq@et.aau.dk Professor Josep M. Guerrero joz@et.aau.dk
- 2. Microgrid Definition and Operation Microgrid Research Programme in AAU Microgrid Research activities and laboratories International Conference on Power Electrical Systems - SSD 2014 2
- 3. Hybrid AC/DC Microgrids What is a Microgrid? Household appliances and electronics PCC DC Coupled Subsystem Main Utility Grid International Conference on Power Electrical Systems - SSD 2014 3
- 4. Modes of Operation: ISLANDED Household appliances and electronics PCC DC Coupled Subsystem Main Utility Grid International Conference on Power Electrical Systems - SSD 2014 4
- 5. Modes of Operation: GRID CONNECTED Household appliances and electronics DC Coupled Subsystem PCC Main Utility Grid International Conference on Power Electrical Systems - SSD 2014 5
- 6. Tertiary Control Power Import/export from/to the grid. Secondary Control Primary Control f/V Restoration (Island) Synchronization (Island to grid Connected mode) Modeling + Inner loops + droop Control (P/Q Sharing). International Conference on Power Electrical Systems - SSD 2014 6
- 7. Problem: Harmonics in Microgrids Possible solutions: - One DG unit could give more harmonics than another. (harmonic current sharing) - Voltage Harmonic Reduction (Control strategies for HC) Problem: Unbalances in Microgrids Possible solutions: - By means of sec. control, PCC voltage unbalances can be compensated by control signals to the primary level. - Voltage Unbalance Compensation (Control strategies) Test and verification that the proposed solutions follow the European power quality standards IEC 61727 and IEC 61000-3-6. International Conference on Power Electrical Systems - SSD 2014 7
- 8. Communication model provided by IEC 61850 & IEC 61400-25 to describe the physical devices in the network model. • Study meter-bus technology solutions to integrate smart meters and data concentrators according to EN13757. •Develop different levels of communications architectures for residential AMI following IEC61968-9 (interface standard for meter reading and control). •Integrate smart meters and data concentrators in different levels of wireless and meshed network architectures, according to EN13757-5 (standard for radio mesh meter-bus) and EN13757-4 (wireless meter-bus). Timbus et Al. Management of DER Using Standarized Communications and modern Technologies International Conference on Power Electrical Systems - SSD 2014 8
- 9. Household appliances and electronics PCC DC Coupled Subsystem Main Utility Grid Source Protection Network Protection Bidirectional Protection International Conference on Power Electrical Systems - SSD 2014 9
- 10. Microgrid Definition and Operation Microgrid Research Activities Microgrid Research Programme and laboratories International Conference on Power Electrical Systems - SSD 2014 10
- 11. COORDINATED CONTROL FOR POWER QUALITY IN GRID CONNECTED - ISLANDED MICROGRIDS AC Low voltage coordinated control: MicroGrid AC Microgrids: Bus frequency signaling DC Microgrids: Bus voltage signaling International Conference on Power Electrical Systems - SSD 2014 11
- 12. CENTRALIZED AND DECENTRALIZED SECONDARY CONTROL FOR ISLANDED MICROGRIDS Amplitude droop Frequency droop * * mP E* E E * nQ E Pmax P Connection/disconnection load or generation Frequency and voltage deviation Frequency Restoration Voltage Amplitude Restoration E f Secondary response f MG Qmax Q Secondary response E Primary response PDGk Primary response P Pmax Qmax Q QDGk Qmax International Conference on Power Electrical Systems - SSD 2014 12
- 13. Communication link Secondary Control Communications Remote sensing Local Control Local Control Local Control … Microgrid International Conference on Power Electrical Systems - SSD 2014 13
- 14. TERTIARY CONTROL AND ENERGY MANAGEMENT SYSTEM IN MICROGRIDS International Conference on Power Electrical Systems - SSD 2014 14
- 15. TERTIARY CONTROL AND DC System Optimization ---- Local Generation Control ENERGY MANAGEMENT Objective SYSTEM IN MICROGRIDS • System Overall Efficiency DC/DC CONVERTER Load DC INPUT DC/DC CONVERTER Constraints • Capacity • DC Bus Voltage • System Dynamics Load Rdroop DC COMMON BUS Vr DC COMMON BUS Problem Formulation Typical Efficiency Curve International Conference on Power Electrical Systems - SSD 2014 15
- 16. <=2. 5 PQ TERTIARY CONTROL AND ENERGY MANAGEMENT SYSTEM IN MICROGRIDS PQ PQ PQ PQ International Conference on Power Electrical Systems - SSD 2014 16
- 17. DISTRIBUTED ACTIVE SYNCHRONIZATION FOR MICROGRID UNDER UNBALANCE AND HARMONIC DISTORTIONS Current/Voltage Source Shut down Gridconnected mode STS = ON Intentional/ Unintentional islanding Sync ISLANDED STS = OFF Voltage Source MODE Stop Black start International Conference on Power Electrical Systems - SSD 2014 17 17
- 18. • • • • Remote telecom applications Coupled renewable systems DC powered homes Fast HEV charging stations Configuration Basic control Basic control International Conference on Power Electrical Systems - SSD 2014 18 18
- 19. Danish International Conference on Power Electrical Systems - SSD 2014 19 19
- 20. 380Vdc Powered Home Phase 1. Phase 2. Phase 3 International Conference on Power Electrical Systems - SSD 2014 20 20
- 21. 1. Vdc consumer electronics 380Vdc Powered Home 2. 12/24 Vdc wall sockets 3. 12 Vdc LED lighting 4. 24 Vdc home entertainment system 5. 12 Vdc coffee maker 6. 12 Vdc refrigerator 7. 24 Vdc vacuum cleaner 8. 48 Vdc washing machine 9. 48 Vdc air conditioner 10. 12 Vdc hair dryer 11. 48 Vdc whisper wind turbine 12. PVs connected in 380vdc bus bar 13. 380vdc charger 14. 380vdc busway distribution system 21
- 22. 5 Workstations - FC emulators Battery emulators Flywheels Supercaps Dedicated DC/DC converters Constant power loads Real-time monitoring, Control and supervision 1 Setup for Demonstration of DC-home with Real DC appliances. International Conference on Power Electrical Systems - SSD 2014 22 22
- 23. Microgrid Definition and Operation Microgrid Research Activities Microgrid Research Programme and laboratories International Conference on Power Electrical Systems - SSD 2014 23
- 24. MICROGRID RESEARCH PROGRAMME Modeling Control & Operation MicroGrid Research Programme Areas AC MicroGrids DC MicroGrids Energy Storage Protection Power Quality Standard-based ICT Networked Control EMS & Optimization Multi-Agents International Conference on Power Electrical Systems - SSD 2014 24
- 25. MICROGRID RESEARCH T AALBORG MICROGRID RESEARCH TEAM @ EAM Tomislav Dragicevic Josep M. Guerrero Juan C. Vasquez Ernane Coelho MGs modelling Javier Roldan LVRT & PQ DC MGs Fabio Andrade MGs stability Min Chen Power Electronics Yang Han Dan Wu Primary Control Qobad Shafiee Secondary Control Lexuan Meng Tertiary Control Yajuan Guan Ancillary services for MGs Nelson Diaz Energy storage for MicroGrids Chi Zhang LVDC distribution MGs PQ & MV MGs Chendan Li MGs Agents Valerio Mariani Nonlinear Control Hengwei Lin Management and Protection for Microgrids Xin Zhao AC/DC Hybrid MG Bo Sun EV Charging Stations International Conference on Power Electrical Systems - SSD 2014 25
- 26. INTELLIGENT MICROGRID LAB - iMGLAB ET Location DEPARTMENT OF ENERGY TECHNOLOGY – ET-AAU International Conference on Power Electrical Systems - SSD 2014 26
- 27. Every setup is able to emulate a multi-converter lowvoltage Microgrid, local and energy management control programmed in dSPACE real-time control platforms. International Conference on Power Electrical Systems - SSD 2014 27 27
- 28. International Conference on Power Electrical Systems - SSD 2014 28 28
- 29. www.microgrids.et.aau.dk Microgrid research and activities International Conference on Power Electrical Systems - SSD 2014 29 29
- 30. juq@et.aau.dk joz@et.aau.dk International Conference on Power Electrical Systems - SSD 2014 30 30
Hinweis der Redaktion
- Thanks you chairman, ok, Good morning to everyone, in this talk I will like to mention different control aspects, future trends and current research activities regarding AC and DC Microgrid technologies.
- Microgrid definition and operation
- The concept of MicroGrids, according to CIGRE C6.22 definition, are electricity LV distribution systems which contain distributed energy resources, (such as distributed generators, storage devices, or controllable loads) that can be operated in a controlled and coordinated way through power electronics interfaces and a defined communication topology. These last ones can be set as VSC where it is possible to fix voltage and frequency (islanded purposes) or CSC to inject only active power like pv installations.According to the standard already approved IEEE1547.4 Guide for Design, Operation, and Integration of Distributed Resource Island Systems with Electric Power Systems. Customer facility micro-grids and electric utility distribution circuit micro-grids are two instances of planned DR islands. DR islands, sometimes referred to as micro-grids, are "islanded" power generation and distribution areas that can operate autonomously from the larger grid infrastructure. MicroGrid encompasses several layers which are held together by means of a compact compound of power electronics interfaced renewable energy technologies, distributed generation (DG) and distributed storage systems [6].These units are typically coordinated by the centralized supervision system which uses telecommunications, and information technologiesMicrogrid concept is related with the micro generation in the origin, called Distributed generation. It consists on generating electrical power near to the consuption area and reducing the transmission losses.
- One of the main strengh of Microgrid is its autonomous/stand alone or islanded capability especially when a fault in the main grid is detected or due to a intentional planed scenario (e.g DSO sometimes can decide to desconect the mg from the utility main grid due to an economical criterion). The micro sources that feed the system are responsible for nominal voltage and frequency stability when power is shared by the generation units. Power qualityshould be ensured here.
- Once the ibs detects main grid is fault free, the microgrid voltage amplitude, phase and frequency and the grid voltage amplitude and phase must be synchronize before power restoration back to grid connected mode to continue exchanging active and reactive power from/to the grid.
- Conceptually, A microgrid can operate within 3 control hierarchical levels:The Primary control enables power sharing among converters and defines system stability based on the proper design of the V/I inner control loops, Virtual impedance loop (which fix the output impedance of the inverter by substracting a portion of the output current),P/Q power loops by means of Droop control. Secondary control (which can be done in a centralized or distributed manner), is responsible to send reference control signals to the primary level by using low bandwidth communication in order to restore the Microgrid voltage and frequency. In this sense, synchronization process can be done especially when we want to switch from island to grid connected mode. Also, this control can deals with power quality issues such as harmonics and unbalances. Finally the tertiary control acts on set-points within the primary and secondary control, energy flows are optimized and Microgrid optimal operation is achieve while taking into consideration both safety and economics.f/V Restoration (Island) : Set-points assignation from MGCC to the DGs .
- Harmonics: Microgrids needs to supply nonlinear currents (Ancillary Services)Unbalances: PCC voltage data and the control signal are transmitted to/from secondary level through low bandwidth communication links.In the case of having voltage harmonic distortion it is possible to attenuate them by means of proportional +resonant controllers rotating at the harmonic frequency in order to enhance power quality.Virtual impedance loop can be adjusted to share properly the load current but without increasing the voltage THD. Also, a soft-start virtual impedance can be implemented for hot-swap operation, this is useful when several units are connected (plug´n play) in order to reduce the large current disturbances.
- Nowadays in MicroGrid research, more robust communication architectures and topologies should be developed in order to implement for example a supervisory centralized control. As you can see in the picture, different levels of network control architectures are using IEC61850 and EN13757 standards for smart-meters and data concentrators, Intended to the control, management, and advanced metering infrastructure (AMI).
- Architecture of the MicroGrid with four different zones of protection where all the breakers in a given bus is involved in bus protection. decision trees ,preventive control . The method can correctly predict and prevent the voltage collapse, and minimize the amount of load shedding. In the intelligent MicroGrid test bed, different circuit breakers and relays will be integrated in different critical places. As well, several static switches will be placed, one at the PCC in order to disconnect the microgrid from the main grid thus operating in island mode, and the other to reconfigure the microgrid from radial to loop.
- When MicroGrids operates in islanded mode with ESS and multiple RESs, usually a coordinated control behavior is required for the system. This is because ESSs have limitations in terms of state-of-charge (SoC) that have to be respected to avoid damages and failuresFirstly a primary local control which is different for the Distributed Generation units and the ESS is proposed. The ESS adopts Frequency Bus Signaling control which is based on changing slightly the bus frequency in the microgrid when the SOC state-of-charge is near to the limit. this way, when the DG detecting that the frequency is increasing, will reduce the injected power by using a virtual inertia control loop going back to power regulation mode. When the SoC of ESS is approaching to the maximum allowed, the power of ESS is limited; at the same time the RESs operate in off-MPPT or regulation mode automatically.Consequently, in an islanded microgrid there is a need of coordination between DGs and ESS units.Similar with the high SoC scenario, to avoid the ESS result in over discharging, ESS can automatically decrease the bus frequency to enable the loads shedding procedure
- As a control main loop, inverters are programmed to act as generators by includingvirtual inertias by means of the droop method. It specifically adjusts the frequency or amplitude output voltage as a function of the desired active and reactive power. Thus, active and reactive power can be shared equally among the inverters. For reliability and to ensure local stability, voltage regulation is needed.
- Here you can see 2 different secondary control architectures. The Centralized approach consists in measuring the mg voltage and frequency and by means of a microgrid central controller since the reference signals to each distributed generation unit.The advantage of this architecture is that the communication system is not too busy, and those reference signals are sent in only one direction (from the remote sensing platform to the MGCC and from the MGCC to each DG unit). The drawback is that the MGCC is not highly reliable since a failure of this controller is enough to stop the secondary control action.In the second case the distributed secondary control approach, The initial idea is to implement primary and secondary controllers together as a local controller. The advantage of this concept is that the communication among units is improved, robustness under communication impairments but at expenses of having high communication traffic.
- As I explained at the beggining of this talk, the terciary control level deals with energy management and efficient power flow of one microgrid of even several of them. As it can be seen, we can conceive several levels. the unit level regards distributed resources local controllers and loads , in a second tier the microgrid level in which we can ensure the optimal operation in every microgrid, and which considers market price, electric power request and offer, local generation/consumption/storage status, costs, political economical aspects etc. and finally a distribution level who deals with the decisions imposed by market operator or distribution netwrok operators.
- One specific application is when we consider for example a DC system optimization especially when dealing with the efficiency of DC/DC converters. Here, we have several DC/dc converters connected to a DC common bus. The final objective here is to improve system overall efficiency and we add as contraints the capacity, the DC bus voltage and of course the system dinamics.The efficiency of the converters decrease rapidly when the converter is operating on low loads compared to its nominal power. Moreover, during low loads the switching losses of the transistors are in dominating role over the conductivity losses. As the efficiency of each converter changes with output power, virtual resistances (VRs) are set as decision variables for adjusting power sharing proportion among converters.Converter efficiency is related with its operation point which finally influences the system losses. Operation points for converters can be optimized so as to achieve higher system efficiency.
- Another interesting application for tertiaty control in microgrids is the unbalance compensation optimization.The general idea of this optimization approach is to ensure that the power quality in each local bus (which can accept more unbalances but have certain limits) and the sensitive bus while considering the compensation capability of each DG under different load conditions and with lowest power loss as possible.
- As I mentioned before, microgrids can operate in both grid connected mode and islanded modes. It is important to determine when to maintain connected firstly according to power quality standards but also when to disconnect our microgrid from the main grid when it requires.Moreover, it is possible to have a distributed active synchronization strategy to smoothly reconnect microgrid to the main grid. This approach can be implemented in the secondary control level of the microgrid hierarchical control by controlling fundamental positive and negative sequence components, as well as low order harmonic components of the microgrid to track the main grideven under unbalance and distorted conditions.
- Now is the turn for DC Microgrids.This figure represents an autonomous full DC MG formed around a dc common bus to which distributed sources and loads are directly connected. As in AC MGs, all the aforementioned hierarchical control strategies can be performed in several applications such as remote telecom stations, datacenters, dc powered homes, EVs charging stations etc. As it can be seen, the hierarchical control design of DC systems is significantly simpler since there are no reactive and harmonic power flows or issues related with synchronization.
- Addionally in this talk I would like to mention about a recent granted project called future residential LDC power distribution architectures. This project will be done in cooperation with international ranked research institutions such asVirginia Tech in USAINESTEC in portugalRitsumeikan university in JapanAnd the Danish companies kk electronic, neogrid and kamstrup (a smart electricity meter supplier) .
- So basically the aim is to study several LV 380v-48v-24v DC multi-bus architectures intended for residential households in terms of costeffectiveness, reliability, power quality enhacement and global system efficiency (in deed recent studies indicate up to 30% in comparison with tradicional LVAC).This project is divided in 3 phases, modeling of the architecture, coordination and control of the power electronics interfaces and finally the grid integration and interactivity by means of an AC/DC converter.
- So basically the aim is to study several LV 380v-48v-24v DC multi-bus architectures intended for residential households in terms of costeffectiveness, reliability, power quality enhacement and global system efficiency (in deed recent studies indicate up to 30% in comparison with tradicional LVAC).This project is divided in 3 phases, modeling of the architecture, coordination and control of the power electronics interfaces and finally the grid integration and interactivity by means of an AC/DC converter.
- We are building a new lab called DC living lab. It will consist of FC and battery emulators, dedicated dc/dc converters, Opal RT and a especial setup for demostration intended for DC homes with real DC appliances (laptops, smart phones, LED lights, home entertainment systems and white goods)Furthermore, the applicants are linked with the recognized open standardization body for DC architecture, Emerge Alliance.
- Finally and to conclude this talk I would like to show you more details about our research programme and MG laboratories
- The core research areas of our MG research programme is mainly focused on control, energy management and operation of AC and DC Microgrids regarding the aforementioned aspects .
- This is our MG research multicultural team...And this is how our team is organized:We have Professor Josep Guerrero as the microgrid research programme leader, Prof. Coelho as 2-years visiting professor, 3 postdocs and 10 phd students.
- This is the location of the department of energy techonology in Aalborg university and a photo of our Microgrid laboratory.
- Every microgrid is controlled by a real-time and monitoring platform called dspace.
- Every year we are running several phd/industrial courses on AC, DC PQ, EMS and is missing the communication in microgrids, and od course you are very welcome to attend them.
- This is our microgrid webpage. We try to keep it as updated as we can, and you can take a look to our projects, publications and lab facilities overview.
- And I think that´s it so, thank you very much for your attention.