EPE Association: EPE 2013 - DS1f: Power Electronics for the grid: Microgrid control

EPE 2013 - DS1f: Power Electronics for the grid: Microgrid control
You are here: EPE Documents > 01 - EPE & EPE ECCE Conference Proceedings > EPE 2013 ECCE Europe - Conference > EPE 2013 - Topic 16: Power electronics in transmission and distribution > EPE 2013 - DS1f: Power Electronics for the grid: Microgrid control

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   An Impedance-Based Method for the Detection of Over-Load and Network Faults in Inverter Interfaced Distributed Generation
By Nathaniel BOTTRELL, Timothy C. GREEN [View]
[Download]

Abstract: An impedance-based method is presented for detecting and differentiating over-load and fault conditions for an inverter-interfaced power generator. When the observed impedance falls below a threshold, current limiting occurs. The impedance-based method, unlike other current limiting strategies, is able to differentiate between an over-load and a network fault. The inverter presented in this paper exports a fixed current for detected over-loads and a higher fixed current for detected faults. An experimental system using a 10 kVA inverter was used to test three cases. The first demonstrates the response of the inverter when the impedance of the load is gradually decreased. The second demonstrates the output of the inverter when a three-phase fault is applied and the third demonstrates the output when a single-phase fault is applied. The impedance-based method is shown to be able to ride-thought the fault and return to normal operation once the fault has been cleared.

   Analysis of Stability Aspects of a Large Constant Power Load in a Local Grid
By Mohammad Fakhizan ROMLIE, Christian KLUMPNER, Mohamed RASHED, Greg ASHER, Milijana ODAVIC [View]
[Download]

Abstract: This paper investigate the problem of instability of constant power load (CPL) fed via a diode bridgerectifier connected in a local AC distribution system fed by wind farm with energy storage systeminstalled. Analysis and simulation illustrates first that the instability as a function of the various systemparameters, then control based solutions for improving the stability is proposed and verified byanalytical method and simulation in PSCAD.

   Autonomous Droop Scheme with Reduced Generation Cost
By Inam ULLAH, Poh Chiang LOH, Frede BLAABJERG [View]
[Download]

Abstract: Droop scheme has been widely applied to the control of Distributed Generators (DGs) in microgrids for proportional power sharing based on their ratings. For standalone microgrid, where centralized management system is not viable, the proportional power sharing based droop might not suit well since DGs are usually of different types unlike synchronous generators. This paper presents an autonomous droop scheme that takes into consideration the operating cost, efficiency and emission penalty of each DG since all these factors directly or indirectly contributes to the Total Generation Cost (TGC) of the overall microgrid. Comparing it with the traditional scheme, the proposed scheme has retained its simplicity, which certainly is a feature preferred by the industry. The overall performance of the proposed scheme has been verified through simulation and experiment.

   Configuration, modelling and control of a microgrid for commercial buildings application
By Francisco GONZALEZ-ESPIN, Nicolas CHANG, Virgilio VALDIVIA, Raymond FOLEY [View]
[Download]

Abstract: Distributed generation with a high penetration of renewable energies has been presented as an alternative for traditional centralized power plants. This distributed generation can be managed by means of microgrids. The microgrid concept can be extended to commercial and residential buildings, where there exist growing opportunities in energy saving and market profit for stakeholders. The aim of this paper is to present an overview of a microgrid for commercial buildings, with integrated control of thermal and electrical aspects, as well as to describe each of the electrical power sources, including a small-signal state-space representation and the control structure of each of the generators. The generators described in this paper are a small permanent magnet wind turbine, a storage unit based on a Li-Ion battery and a combined heat and power (CHP) based on a gas reciprocating engine connected to a synchronous generator.

   DC Network Characteristics and Modeling for Power Distribution
By Pasi PELTONIEMI, Pasi NUUTINEN [View]
[Download]

Abstract: The paper studies the fundamental characteristics of commonly used DC network topologies. These network topologies include unipolar and bipolar structures. Paper also addresses important issues such as DC network modeling and voltage stability. The theoretical results achieved are verified using relevant simulation and measurement results.

   Decentralized Converter Controller for Multiterminal HVDC Grids
By Georgios STAMATIOU, Massimo BONGIORNO [View]
[Download]

Abstract: Multiterminal High Voltage Direct Current (MTDC) grids based on Voltage Source Converters (VSC) are considered ideal for the future integration of large scale and highly distributed renewable power generation, as well as interconnection of remote power systems. The control of such grids is challenging as it is necessary to provide accurate power flow control and multiple voltage controlling stations. Existing control techniques either fail to fulfill those requirements or achieve them at a cost of maintaining a communication channel between the local station controllers and a master central control level. This paper suggests a decentralized controller for MTDC grids that ensures accurate power flow control, provides voltage control capabilities to all stations and requires no need for communication between the stations. The validity of the controller was tested in a five-terminal MTDC model proving its functionality.

   Design And Control Of A Three-Phase Four-Leg Inverter For Solid-State Transformer Applications
By Aniel SHRI, Mark GERBER, Jelena POPOVIC, J.A. FERREIRA [View]
[Download]

Abstract: This paper proposes the use of a three-phase four-leg (3P4L) converter in combination with an LCL filter for the inverter stage of a solid state transformer (SST). This configuration gives full control over the line-to-line, as well as the line-to-neutral voltage and currents, while providing exceptional harmonics mitigation. A procedure to calculate the passive components for the LCL filter is presented, as well as a method to reduce resonance caused by the filter. Furthermore, two feedback control schemes are derived and are enhanced with a feed-forward control scheme.

   Design Principles of Low Voltage Distributed Generation Units with Increased Fault Ride Through Capability
By Ioannis PERPINIAS, Nikolaos PAPANIKOLAOU, Emmanuel TATAKIS [View]
[Download]

Abstract: The high integration of distributed generation units (DG) in Low Voltage Distribution Networks (LVDNs) has raised many designing issues regarding their behavior in case of network disturbances. This paper presents the design principles and the power converters’ appropriate behavior that DG units must incorporate in order to meet the requirements of Fault Ride Through Capability. Also, simulation results and insightful discussion of them are included.

   Development of a laboratory platform for testing new solutions to integrate renewable energy sources in power systems
By Eduardo PRIETO-ARAUJO, Marc CHEAH-MANE, Roberto VILLAFAFILA-ROBLES, Oriol GOMIS-BELLMUNT, Adria JUNYENT-FERRE [View]
[Download]

Abstract: The article deals with the design and implementation of a reduced scale laboratory platform consisting ofa number of programmable emulators. By connecting these devices into the same grid, different microgridconfigurations can be emulated, allowing to perform many experiments related to its management,control and protection. Here, the proposed platform layout is described and its performance is shownthrough experimental results.

   Implementing the Virtual Output Impedance Concept in a Three Phase System Utilising Cascaded PI Controllers in the dq Rotating Reference Frame for Microgrid In
By Tim MOORE, Christopher TOWNSEND, Christopher ROWE, Terrence SUMMERS, Robert BETZ [View]
[Download]

Abstract: This paper extends research on single phase microgrids [1] to implement a Virtual Output Impedance (VOI)in a three phase system utilising cascaded PI voltage and current control in the Rotating Reference Frame (RRF). The paper proposes two methods for the selection of VOI values; a selection surface and a summation approach. SABER simulations and dSPACE hardware results are provided for a two inverter microgrid to validate the control scheme and selection techniques.

   Power Flow Control in Single-Phase and Three-Phase Grid-Connected Inverters using LMI, State-Feedback Linearization and D-stability
By Leonardo SAMPAIO, Carlos CANESIN, Moacyr DE BRITO, Guilherme MELO [View]
[Download]

Abstract: This paper proposes a methodology for the active and reactive power flow controls, applied at single-phase and three-phase inverters operating in grid-connected mode at low voltage. The converter's control technique is based on Linear Matrix Inequalities (LMI) together with D-stability criteria and state-feedback linearization. The power flow control uses the power transfer curves (similarly to droop control) P-ω e Q-V, applied to a multi-loop control system. The multi-loop control uses the technique of state-feedback linearization in order to minimize the non linearities of system, improving the controller's performance and mitigating potential system's disturbs. Moreover, the purpose of the methodology is to obtain the best controllers with the lowest gains placing the poles in the left-half s-plane region specified during the design stage, resulting in fast responses with reduced oscillations. Finally, a 1000VA single-phase and one 3000VA three-phase prototypes were implemented in order to demonstrate the feasibility of the proposed control.

   Selective Compensation of Reactive, Unbalance, and Distortion Power in Smart Grids by Synergistic Control of Distributed Switching Power Interfaces
By Alessandro COSTABEBER, Paolo TENTI [View]
[Download]

Abstract: Smart grids feature distributed energy resources interfaced to the grid by means of switching power converters. Synergistic control of these units can considerably increase the distribution efficiency and power quality by limiting the unbalance, reactive, and harmonic currents flowing through distribution lines. This can be achieved by a distributed control and communication architecture which implements suitable control strategies. This paper deals with a control approach, based on conservative power commands, which allows selective elimination of the main causes affecting the power quality, i.e., load asymmetry, harmonics, and useless reactive power flow. As a result, distribution efficiency improves, voltage asymmetry and distortion diminishes, and the distribution infrastructure is better exploited, thus allowing an increase of the hosting capacity of the grid.

   Sustainable DC-Microgrid Control System for Electric-Vehicle Charging Stations
By Behtzua ELIZONDO NORIEGA, Rodrigo TEIXEIRA PINTO, Pavol BAUER [View]
[Download]

Abstract: As renewable energies and electric-vehicles increase in popularity, their interaction with existinggrids becomes inevitable. This paper proposes a power management system to distributeacquainted power in a dc-microgrid supplying energy to a fleet of electric vehicles (EVs) used astaxis. A dynamic dc-microgrid model is used to validate the algorithm, including the dc-dcconverters that interact with the grid and a PI controller to regulate the dc voltage. The proposedalgorithm and voltage control are validated with several test cases.

   Voltage Stability Assessment in Semi-Autonomous DC-Grids with Multiple Power Modules
By Jorge DUARTE, Kirill RYKOV, Ulrich BOEKE, Matthias WENDT, Roland WEISS [View]
[Download]

Abstract: Basic concepts with respect to stable operation of semi-autonomous low-voltage DC-grids are discussed.Design considerations on the output impedances of power electronic converters are analysed in order to avoid resonance issues within a DC-grid. With calculated or measured converter output impedances,potential resonance problems due to background harmonics between aggregated power modules and theDC-grid can be forecasted. Simulation results are included for verification of the proposed ideas.

EPE 2013 - DS1f: Power Electronics for the grid: Microgrid control
You are here: EPE Documents > 01 - EPE & EPE ECCE Conference Proceedings > EPE 2013 ECCE Europe - Conference > EPE 2013 - Topic 16: Power electronics in transmission and distribution > EPE 2013 - DS1f: Power Electronics for the grid: Microgrid control
	[return to parent folder]

	An Impedance-Based Method for the Detection of Over-Load and Network Faults in Inverter Interfaced Distributed Generation By Nathaniel BOTTRELL, Timothy C. GREEN	[View] [Download]
Abstract: An impedance-based method is presented for detecting and differentiating over-load and fault conditions for an inverter-interfaced power generator. When the observed impedance falls below a threshold, current limiting occurs. The impedance-based method, unlike other current limiting strategies, is able to differentiate between an over-load and a network fault. The inverter presented in this paper exports a fixed current for detected over-loads and a higher fixed current for detected faults. An experimental system using a 10 kVA inverter was used to test three cases. The first demonstrates the response of the inverter when the impedance of the load is gradually decreased. The second demonstrates the output of the inverter when a three-phase fault is applied and the third demonstrates the output when a single-phase fault is applied. The impedance-based method is shown to be able to ride-thought the fault and return to normal operation once the fault has been cleared.

	Analysis of Stability Aspects of a Large Constant Power Load in a Local Grid By Mohammad Fakhizan ROMLIE, Christian KLUMPNER, Mohamed RASHED, Greg ASHER, Milijana ODAVIC	[View] [Download]
Abstract: This paper investigate the problem of instability of constant power load (CPL) fed via a diode bridgerectifier connected in a local AC distribution system fed by wind farm with energy storage systeminstalled. Analysis and simulation illustrates first that the instability as a function of the various systemparameters, then control based solutions for improving the stability is proposed and verified byanalytical method and simulation in PSCAD.

	Autonomous Droop Scheme with Reduced Generation Cost By Inam ULLAH, Poh Chiang LOH, Frede BLAABJERG	[View] [Download]
Abstract: Droop scheme has been widely applied to the control of Distributed Generators (DGs) in microgrids for proportional power sharing based on their ratings. For standalone microgrid, where centralized management system is not viable, the proportional power sharing based droop might not suit well since DGs are usually of different types unlike synchronous generators. This paper presents an autonomous droop scheme that takes into consideration the operating cost, efficiency and emission penalty of each DG since all these factors directly or indirectly contributes to the Total Generation Cost (TGC) of the overall microgrid. Comparing it with the traditional scheme, the proposed scheme has retained its simplicity, which certainly is a feature preferred by the industry. The overall performance of the proposed scheme has been verified through simulation and experiment.

	Configuration, modelling and control of a microgrid for commercial buildings application By Francisco GONZALEZ-ESPIN, Nicolas CHANG, Virgilio VALDIVIA, Raymond FOLEY	[View] [Download]
Abstract: Distributed generation with a high penetration of renewable energies has been presented as an alternative for traditional centralized power plants. This distributed generation can be managed by means of microgrids. The microgrid concept can be extended to commercial and residential buildings, where there exist growing opportunities in energy saving and market profit for stakeholders. The aim of this paper is to present an overview of a microgrid for commercial buildings, with integrated control of thermal and electrical aspects, as well as to describe each of the electrical power sources, including a small-signal state-space representation and the control structure of each of the generators. The generators described in this paper are a small permanent magnet wind turbine, a storage unit based on a Li-Ion battery and a combined heat and power (CHP) based on a gas reciprocating engine connected to a synchronous generator.

	DC Network Characteristics and Modeling for Power Distribution By Pasi PELTONIEMI, Pasi NUUTINEN	[View] [Download]
Abstract: The paper studies the fundamental characteristics of commonly used DC network topologies. These network topologies include unipolar and bipolar structures. Paper also addresses important issues such as DC network modeling and voltage stability. The theoretical results achieved are verified using relevant simulation and measurement results.

	Decentralized Converter Controller for Multiterminal HVDC Grids By Georgios STAMATIOU, Massimo BONGIORNO	[View] [Download]
Abstract: Multiterminal High Voltage Direct Current (MTDC) grids based on Voltage Source Converters (VSC) are considered ideal for the future integration of large scale and highly distributed renewable power generation, as well as interconnection of remote power systems. The control of such grids is challenging as it is necessary to provide accurate power flow control and multiple voltage controlling stations. Existing control techniques either fail to fulfill those requirements or achieve them at a cost of maintaining a communication channel between the local station controllers and a master central control level. This paper suggests a decentralized controller for MTDC grids that ensures accurate power flow control, provides voltage control capabilities to all stations and requires no need for communication between the stations. The validity of the controller was tested in a five-terminal MTDC model proving its functionality.

	Design And Control Of A Three-Phase Four-Leg Inverter For Solid-State Transformer Applications By Aniel SHRI, Mark GERBER, Jelena POPOVIC, J.A. FERREIRA	[View] [Download]
Abstract: This paper proposes the use of a three-phase four-leg (3P4L) converter in combination with an LCL filter for the inverter stage of a solid state transformer (SST). This configuration gives full control over the line-to-line, as well as the line-to-neutral voltage and currents, while providing exceptional harmonics mitigation. A procedure to calculate the passive components for the LCL filter is presented, as well as a method to reduce resonance caused by the filter. Furthermore, two feedback control schemes are derived and are enhanced with a feed-forward control scheme.

	Design Principles of Low Voltage Distributed Generation Units with Increased Fault Ride Through Capability By Ioannis PERPINIAS, Nikolaos PAPANIKOLAOU, Emmanuel TATAKIS	[View] [Download]
Abstract: The high integration of distributed generation units (DG) in Low Voltage Distribution Networks (LVDNs) has raised many designing issues regarding their behavior in case of network disturbances. This paper presents the design principles and the power converters’ appropriate behavior that DG units must incorporate in order to meet the requirements of Fault Ride Through Capability. Also, simulation results and insightful discussion of them are included.

	Development of a laboratory platform for testing new solutions to integrate renewable energy sources in power systems By Eduardo PRIETO-ARAUJO, Marc CHEAH-MANE, Roberto VILLAFAFILA-ROBLES, Oriol GOMIS-BELLMUNT, Adria JUNYENT-FERRE	[View] [Download]
Abstract: The article deals with the design and implementation of a reduced scale laboratory platform consisting ofa number of programmable emulators. By connecting these devices into the same grid, different microgridconfigurations can be emulated, allowing to perform many experiments related to its management,control and protection. Here, the proposed platform layout is described and its performance is shownthrough experimental results.

	Implementing the Virtual Output Impedance Concept in a Three Phase System Utilising Cascaded PI Controllers in the dq Rotating Reference Frame for Microgrid In By Tim MOORE, Christopher TOWNSEND, Christopher ROWE, Terrence SUMMERS, Robert BETZ	[View] [Download]
Abstract: This paper extends research on single phase microgrids [1] to implement a Virtual Output Impedance (VOI)in a three phase system utilising cascaded PI voltage and current control in the Rotating Reference Frame (RRF). The paper proposes two methods for the selection of VOI values; a selection surface and a summation approach. SABER simulations and dSPACE hardware results are provided for a two inverter microgrid to validate the control scheme and selection techniques.

	Power Flow Control in Single-Phase and Three-Phase Grid-Connected Inverters using LMI, State-Feedback Linearization and D-stability By Leonardo SAMPAIO, Carlos CANESIN, Moacyr DE BRITO, Guilherme MELO	[View] [Download]
Abstract: This paper proposes a methodology for the active and reactive power flow controls, applied at single-phase and three-phase inverters operating in grid-connected mode at low voltage. The converter's control technique is based on Linear Matrix Inequalities (LMI) together with D-stability criteria and state-feedback linearization. The power flow control uses the power transfer curves (similarly to droop control) P-ω e Q-V, applied to a multi-loop control system. The multi-loop control uses the technique of state-feedback linearization in order to minimize the non linearities of system, improving the controller's performance and mitigating potential system's disturbs. Moreover, the purpose of the methodology is to obtain the best controllers with the lowest gains placing the poles in the left-half s-plane region specified during the design stage, resulting in fast responses with reduced oscillations. Finally, a 1000VA single-phase and one 3000VA three-phase prototypes were implemented in order to demonstrate the feasibility of the proposed control.

	Selective Compensation of Reactive, Unbalance, and Distortion Power in Smart Grids by Synergistic Control of Distributed Switching Power Interfaces By Alessandro COSTABEBER, Paolo TENTI	[View] [Download]
Abstract: Smart grids feature distributed energy resources interfaced to the grid by means of switching power converters. Synergistic control of these units can considerably increase the distribution efficiency and power quality by limiting the unbalance, reactive, and harmonic currents flowing through distribution lines. This can be achieved by a distributed control and communication architecture which implements suitable control strategies. This paper deals with a control approach, based on conservative power commands, which allows selective elimination of the main causes affecting the power quality, i.e., load asymmetry, harmonics, and useless reactive power flow. As a result, distribution efficiency improves, voltage asymmetry and distortion diminishes, and the distribution infrastructure is better exploited, thus allowing an increase of the hosting capacity of the grid.

	Sustainable DC-Microgrid Control System for Electric-Vehicle Charging Stations By Behtzua ELIZONDO NORIEGA, Rodrigo TEIXEIRA PINTO, Pavol BAUER	[View] [Download]
Abstract: As renewable energies and electric-vehicles increase in popularity, their interaction with existinggrids becomes inevitable. This paper proposes a power management system to distributeacquainted power in a dc-microgrid supplying energy to a fleet of electric vehicles (EVs) used astaxis. A dynamic dc-microgrid model is used to validate the algorithm, including the dc-dcconverters that interact with the grid and a PI controller to regulate the dc voltage. The proposedalgorithm and voltage control are validated with several test cases.

	Voltage Stability Assessment in Semi-Autonomous DC-Grids with Multiple Power Modules By Jorge DUARTE, Kirill RYKOV, Ulrich BOEKE, Matthias WENDT, Roland WEISS	[View] [Download]
Abstract: Basic concepts with respect to stable operation of semi-autonomous low-voltage DC-grids are discussed.Design considerations on the output impedances of power electronic converters are analysed in order to avoid resonance issues within a DC-grid. With calculated or measured converter output impedances,potential resonance problems due to background harmonics between aggregated power modules and theDC-grid can be forecasted. Simulation results are included for verification of the proposed ideas.