EPE Association: EPE 2015 - DS3h: Grids & Smart Grids

EPE 2015 - DS3h: Grids & Smart Grids
You are here: EPE Documents > 01 - EPE & EPE ECCE Conference Proceedings > EPE 2015 ECCE Europe - Conference > EPE 2015 - Topic 06: Grids and Smart Grids > EPE 2015 - DS3h: Grids & Smart Grids

   [return to parent folder]

   A Fast Reactive Power Sharing Strategy based on Feeder Current Sensing
By Yixin ZHU [View]
[Download]

Abstract: To solve the reactive power sharing issue in droop control, many improved methods have beendeveloped. However, existing methods can't provide both accurate and fast performance in reactivepower sharing, no matter wireless or communication methods. In fact, rapidity is an importantindicator for reactive power sharing control, especially when load changes frequently. In this paper, afast reactive power sharing strategy that employs feeder current sensing and feeder voltage dropcompensation is proposed for islanded microgrid. The proposed strategy introduces feeder currentsensing based on the conventional droop control method. With the instant information of feedercurrent, the mismatched feeder voltage drops that cause reactive power sharing errors in microgrid are calculated and compensated in real time. The proposed strategy can not only reach the same accuracy as communication based solutions, but also provide faster response to load change. Moreover, it is more convenient to be applied due to its wireless manner. Matlab simulation and experimental results are used to validate the feasibility of this strategy.

   A Hierarchical Control Scheme for Reactive Power and Harmonic Current Sharing in Islanded Microgrids
By Iman LORZADEH [View]
[Download]

Abstract: In this paper, a hierarchical control scheme consisting of primary and secondary levels is proposed forachieving accurate reactive power and harmonic currents sharing among interface inverters ofdistributed generators (DGs) in islanded microgrids. Firstly, fundamental and main harmoniccomponents of each inverter output current are extracted at primary level and transmitted to thesecondary controller. Then, instantaneous circulating currents at different frequencies are calculatedand applied by the secondary level to generate proper control signals for accurate reactive power andharmonic current sharing among the inverters. Consequently, these signals are sent to the primarylevel and inserted as voltage references after passing the control blocks. In contrast to the conventionalvirtual impedance schemes, where reactive power and harmonic current sharing are realized at theexpense of introducing additional voltage drop and distortion, the proposed control strategy effect onthe amplitude and waveform quality of DGs' voltage is negligible. Meanwhile, it is able to provideaccurate harmonic current sharing even if nonlinear loads are directly connected at the terminal of DGunits. Control system design is described in detail and simulation results are provided to demonstratethe effectiveness of the proposed control method.

   A seamless Transfer Algorithm Based on Active Frequency Detection with Feed-forward Control Method in Distributed Generation System
By Kiryong KIM [View]
[Download]

Abstract: This paper proposes a control strategy for grid-interactive Power Conditioning System (PCS) with feedforwardcontrol method based on active frequency detection. PCS should supply the power to criticalloads continuously regardless of grid condition. Hence, PCS detects grid condition fast and transfersbetween two operation modes smoothly. In addition, it also important to detect its operating conditionaccurately for safety. In most of cases, PCS can detect its operation mode. However, when PCS operatesin Non-Detection Zone (NDZ) condition, power gap between PCS and load is almost same, it cannotdetect its operation mode precisely. Hence, other technique is needed to escape NDZ condition. Thispaper proposes using an active frequency method to get out of NDZ condition and a feedforward controlto detect grid condition rapidly for seamless transfer. Controllers are composed of a current controllerwith a feedforward voltage controller. Each of the controllers checks power components independently,Hence, it helps restore the load voltage quickly when grid fault occurs. In NDZ condition, active frequencymethod helps PCS escape this condition. Proposed seamless transfer control strategy is verifiedby the experimental results.

   A Small Signal Model of an Inverter-Based Microgrid including DC Link Voltages
By Walid ISSA [View]
[Download]

Abstract: In this paper, a small signal model of an islanded microgrid containing any number of parallel inverters is developed. Each inverter is modelled as an ideal voltage source with an equivalent output impedance as the dynamics of the inner voltage loop controller is significantly faster than the dynamics of the power control loop and DC link voltage, which is included in the model. The model, therefore, can be used to study the dynamics of the DC link voltages during unintentional islanding in addition to analysing the dynamics of the power flow controllers. The model is validated using Matlab/Simulink simulations.

   An anti-islanding method for voltage controlled VSI
By DANIEL HEREDERO-PERIS [View]
[Download]

Abstract: Islanding detection methods have been widely applied and thought for current-controlled voltage sourceinverters, as in case of photovoltaic inverters. However, some considerations have to be taken into account when anti-islanding detection strategies are applied on voltage controlled-voltage source inverters, for example in case of using AC droop control. This paper shows different issues when anti-islanding algorithms based on the voltage and frequency displacements are used in voltage-controlled inverters. The impedance measurement of the point of common coupling is presented as a mechanism to achieve the islanding detection. An anti-islanding method for voltage-controlled voltage source inverters is proposed, and the suitable frequencies to be used are analysed. The concept of frequency detection band is defined allowing the impedance measurement to improve its behaviour towards resonant and non-resonant loads.

   Control loops design in a grid supporting mode inverter connected to a microgrid
By Roberto PERINI [View]
[Download]

Abstract: This paper deals with some design aspects of the control loops in a droop-controlled VSI connected to other inverters of greater ratings or to a strong grid, which sets the frequency. The design of a damping resistor in series with the AC filter capacitor is discussed and the impact of strong feedback between the output current and the capacitor voltage is investigated. Moreover an analysis of the derivative droop coefficients is carried out through a simplified equivalent circuit.

   Experimental Verification of an Active Microgrid with Distributed Power-Based Control
By Tommaso CALDOGNETTO [View]
[Download]

Abstract: This paper presents and analyzes experimentally an active microgrid architecture. The microgrid archi- tecture is described and the employed control scheme reviewed, showing how the devised system is able to meet energy needs, ensure good power quality, and allow seamless transitions from grid-connected to islanded operation. Also, the proposed solution is briefly contextualized with respect to approaches based on the droop control. Finally, we consider the implementation of the experimental testbed that is employed to show the operational capabilities of the microgrid.

   Harmonic Circulation Method with Single-Phase Distributed Generation Units in Three-Phase Three-Wire Power Distribution Systems
By Hidehito YOSHIDA [View]
[Download]

Abstract: In recent years, distributed generation (DG) units with a harmonic compensation function have attracted considerable attention as a solution for harmonic current suppression in low-power single-phase applications. This paper presents a harmonic circulation method for harmonic current suppression with single-phase DG units in three-phase three-wire systems. Using the proposed control strategy, all harmonic currents in three-phase grids can be removed without the installation of DG units at all harmonic sources. Furthermore, the proposed method requires less power for harmonic current suppression than the conventional method. Experimental results are presented to verify the validity of the proposed method.

   Inverter design for four-wire micro-grids
By DANIEL HEREDERO-PERIS [View]
[Download]

Abstract: This paper presents a PQ four quadrant four-wire three-phase inverter for microgrids integration. Theinverter is based in two full-bridge IGBT modules connected in a three-phase configuration plus a threephase parallelized neutral branch. This topology is galvanically isolated through a single-phase transformer bank. The converter operates as a non-ideal voltage-controlled voltage source inverter under AC droop strategy with hot-swap capability based on a dynamic virtual impedance.

   Low-frequency reduced-order modeling approach and implementation of grid emulation in hardware-in-the-loop platforms
By Virgilio VALDIVIA [View]
[Download]

Abstract: A simple and effective modelling approach of the electrical grid and implementation in Hardware inthe Loop (HIL) device is presented in this paper. A low-frequency reduced-order modelling approachhas been followed, which reduces dramatically the computational requirements and implementationcomplexity in comparison to an equivalent full grid model, and offers an intuitive way to tune the griddynamic behaviour.

   Multiagent based distributed control for operation cost minimization of droop controlled AC microgrid using incremental cost consensus
By Chendan LI [View]
[Download]

Abstract: Microgrid, as a promising technology to integrate renewable energy resources in the distribution system, is gaining increasing research interests recently. Although many previous works have been done based on the droop control in a microgrid, they mainly focus on achieving proportional power sharing based on the power rating. With various types of distributed generator (DG) units in the system, factors that closely related to the operation cost, such as fuel cost and efficiencies of the generator should be taken into account in order to improve the efficiency of the whole system. In this paper, a multiagent based distributed method is proposed to minimize operation cost of the AC microgrid. Each DG is acting as an agent which regulates the power individually using proposed frequency scheduling method. Optimal power command is obtained through carefully designed consensus algorithm with only light communication between neighboring agents. Case studies verified that the proposed control strategy can effectively reduce the operation cost.

   Performance of a new fast switching DC-Breaker for meshed HVDC-Grids
By Yeqi WANG [View]
[Download]

Abstract: For the future demand of electrical energy, both a reliable and an environmental friendly solution is of high importance. The integration of many widely dispersed regenerative energy sources imposes a great challenge for the existing HVAC grids. A meshed, multiterminal HVDC-SuperGrid is considered to be the best and most efficient solution. This concept would be realized as an overlay grid alongside existing AC-grids, which enables large and controllable energy exchanges over long distances. Extremely high reliability and availability of this HVDC-Grid will become a key point in future, obviously. Fast acting, robust DC-Breakers will be necessary for this purpose, too.This paper presents a new thyristor based DC-Breaker of high switching speed and robustness. The generic requirements for HVDC-Breakers are discussed alongside with known proposed concepts. Afterwards, the characteristics and the dimensioning of the new DC-Breaker is presented and investigated in detail. Measuring results from a test setup show the capabilities and advantages of the new topology.

   Phase locked loop effect on Non Detection Zone of Unintentional Islanding
By Riccardo SGARBOSSA [View]
[Download]

Abstract: The number of small power distributed generators connected to the low voltage distribution networks has increased the possibility of unintentional islanding operations. In this paper, the influence of the Synchronous Reference Frame - Phase Locked Loop (SRF-PLL) for single-phase and three-phase inverter, combined with the wider frequency and voltage protection ranges stated by the Standards, has been considered as causes of increasing possibility of unintentional islanding events. The paper is focused on the enlargement of the protection system Non Detection Zone, due to the single phase PLL on a current- controlled Inverter, as typically used in PhotoVoltaic (PV) or Renewable Energy Source (RES) applications.

   Power Quality Optimization for Droop-based Voltage Source Inverters in Microgrids
By Wenfeng CUI [View]
[Download]

Abstract: Recently, microgrids are receiving an increasing interest with the development of the distributed generation (DG). The droop control is often adopted in voltage source inverters (VSI) to realize the power control and sharing in microgrids. However, voltage and frequency derivations are inevitable due to the employment of the droop control, which degrades the output power quality of the VSIs. This paper focuses on improving the output current quality of the DG units by optimizing the conventional current droop control without additional sensors or devices. The virtual impedance in the control scheme is optimized to improve the low frequency distortion induced by the non-ideal feature of the devices and the dead-time effect. Furthermore, good dynamic performance of the output current is achieved by adding the current forward control into the system control. Therefore, better output quality can be with the presented control method in microgrids.

   Secondary Droop for Frequency and Voltage Restoration in Microgrids
By Inam Ullah NUTKANI [View]
[Download]

Abstract: Droop based autonomous control offers several advantages such as communication independence, plug-n-play capability and enhanced reliability of the system. Despite these advantages, frequency and voltage of droop controlled microgrid varies with the load change which is one of the major drawback of the droop control. Presently, the frequency and voltage restoration in microgrid is achieved through secondary control using low bandwidth communication links. This paper presents secondary-droop based frequency and voltage restoration method which is fully autonomous and independent of communication links. With the proposed method, the microgrid frequency and voltage can be restored back to nominal value without affecting the power sharing performance of the generation sources. The proposed scheme performance has been validated in simulation for several cases of active and reactive power load conditions.

   Thermal Stress Comparison in Modular Power Converter Topologies for Smart Transformers in the Electrical Distribution System
By Markus ANDRESEN [View]
[Download]

Abstract: A Smart Transformer (ST) can cover an important managing role in the future electrical distribution grid. For the moment, the reliability and cost are not competitive with traditional transformers and create a barrier for its application. This work conduct detail designs and analysis for a promising modular ST solution, which is composed of Modular Multi-level converter, Quad Active Bridge DC-DC converters, and two-level voltage source converters. The focus is put on the loading conditions and thermal stress of power semiconductor devices in order to discover critical parts of the whole system when performing various mission profiles in the realistic distribution grid. It is concluded that the thermal stress for all stages is low during normal operation and especially the isolation stage is stressed least.

   Virtual Electrical Test Bench for More Electrical Aircraft Architecture Verification and Energy Management Development
By Jean BESTER [View]
[Download]

Abstract: The shift towards More Electrical Aircraft is bringing with it many new technologies and a redesign of the existing aircraft electrical network, both of which require thorough testing before their implementation. This led to the creation of the Copper Bird® test bench which recreates the aircraft electrical system and is used for equipment evaluation and validation. This paper details the development of an accompanying virtual electrical test bench; modelling and real-time simulation of the operation of an aircraft electrical system for conducting verification activities over different aircraft electrical architectures and developing energy management strategies. In this paper particular attention is given to the PEM fuel cell model which has been characterized and validated using a scaled version of the electrical test bench. The model shows good accuracy, giving an average error of less than ±350mV and a max error of only ±3\%. Fuzzy logic-based energy management was then developed for a fuel cell and battery-based auxiliary power unit with the fuel cell supplying average load power (whilst acting as a current source) and the battery handling load transients and overload situations. The energy management attains its goals of operating the fuel cell at its average power, in order to extend its lifetime, whilst maintaining the battery state of charge between 50\% and 90\%, also in order to extend its lifetime as well as maintaining its ability to absorb excess generated power.

EPE 2015 - DS3h: Grids & Smart Grids
You are here: EPE Documents > 01 - EPE & EPE ECCE Conference Proceedings > EPE 2015 ECCE Europe - Conference > EPE 2015 - Topic 06: Grids and Smart Grids > EPE 2015 - DS3h: Grids & Smart Grids
	[return to parent folder]

	A Fast Reactive Power Sharing Strategy based on Feeder Current Sensing By Yixin ZHU	[View] [Download]
Abstract: To solve the reactive power sharing issue in droop control, many improved methods have beendeveloped. However, existing methods can't provide both accurate and fast performance in reactivepower sharing, no matter wireless or communication methods. In fact, rapidity is an importantindicator for reactive power sharing control, especially when load changes frequently. In this paper, afast reactive power sharing strategy that employs feeder current sensing and feeder voltage dropcompensation is proposed for islanded microgrid. The proposed strategy introduces feeder currentsensing based on the conventional droop control method. With the instant information of feedercurrent, the mismatched feeder voltage drops that cause reactive power sharing errors in microgrid are calculated and compensated in real time. The proposed strategy can not only reach the same accuracy as communication based solutions, but also provide faster response to load change. Moreover, it is more convenient to be applied due to its wireless manner. Matlab simulation and experimental results are used to validate the feasibility of this strategy.

	A Hierarchical Control Scheme for Reactive Power and Harmonic Current Sharing in Islanded Microgrids By Iman LORZADEH	[View] [Download]
Abstract: In this paper, a hierarchical control scheme consisting of primary and secondary levels is proposed forachieving accurate reactive power and harmonic currents sharing among interface inverters ofdistributed generators (DGs) in islanded microgrids. Firstly, fundamental and main harmoniccomponents of each inverter output current are extracted at primary level and transmitted to thesecondary controller. Then, instantaneous circulating currents at different frequencies are calculatedand applied by the secondary level to generate proper control signals for accurate reactive power andharmonic current sharing among the inverters. Consequently, these signals are sent to the primarylevel and inserted as voltage references after passing the control blocks. In contrast to the conventionalvirtual impedance schemes, where reactive power and harmonic current sharing are realized at theexpense of introducing additional voltage drop and distortion, the proposed control strategy effect onthe amplitude and waveform quality of DGs' voltage is negligible. Meanwhile, it is able to provideaccurate harmonic current sharing even if nonlinear loads are directly connected at the terminal of DGunits. Control system design is described in detail and simulation results are provided to demonstratethe effectiveness of the proposed control method.

	A seamless Transfer Algorithm Based on Active Frequency Detection with Feed-forward Control Method in Distributed Generation System By Kiryong KIM	[View] [Download]
Abstract: This paper proposes a control strategy for grid-interactive Power Conditioning System (PCS) with feedforwardcontrol method based on active frequency detection. PCS should supply the power to criticalloads continuously regardless of grid condition. Hence, PCS detects grid condition fast and transfersbetween two operation modes smoothly. In addition, it also important to detect its operating conditionaccurately for safety. In most of cases, PCS can detect its operation mode. However, when PCS operatesin Non-Detection Zone (NDZ) condition, power gap between PCS and load is almost same, it cannotdetect its operation mode precisely. Hence, other technique is needed to escape NDZ condition. Thispaper proposes using an active frequency method to get out of NDZ condition and a feedforward controlto detect grid condition rapidly for seamless transfer. Controllers are composed of a current controllerwith a feedforward voltage controller. Each of the controllers checks power components independently,Hence, it helps restore the load voltage quickly when grid fault occurs. In NDZ condition, active frequencymethod helps PCS escape this condition. Proposed seamless transfer control strategy is verifiedby the experimental results.

	A Small Signal Model of an Inverter-Based Microgrid including DC Link Voltages By Walid ISSA	[View] [Download]
Abstract: In this paper, a small signal model of an islanded microgrid containing any number of parallel inverters is developed. Each inverter is modelled as an ideal voltage source with an equivalent output impedance as the dynamics of the inner voltage loop controller is significantly faster than the dynamics of the power control loop and DC link voltage, which is included in the model. The model, therefore, can be used to study the dynamics of the DC link voltages during unintentional islanding in addition to analysing the dynamics of the power flow controllers. The model is validated using Matlab/Simulink simulations.

	An anti-islanding method for voltage controlled VSI By DANIEL HEREDERO-PERIS	[View] [Download]
Abstract: Islanding detection methods have been widely applied and thought for current-controlled voltage sourceinverters, as in case of photovoltaic inverters. However, some considerations have to be taken into account when anti-islanding detection strategies are applied on voltage controlled-voltage source inverters, for example in case of using AC droop control. This paper shows different issues when anti-islanding algorithms based on the voltage and frequency displacements are used in voltage-controlled inverters. The impedance measurement of the point of common coupling is presented as a mechanism to achieve the islanding detection. An anti-islanding method for voltage-controlled voltage source inverters is proposed, and the suitable frequencies to be used are analysed. The concept of frequency detection band is defined allowing the impedance measurement to improve its behaviour towards resonant and non-resonant loads.

	Control loops design in a grid supporting mode inverter connected to a microgrid By Roberto PERINI	[View] [Download]
Abstract: This paper deals with some design aspects of the control loops in a droop-controlled VSI connected to other inverters of greater ratings or to a strong grid, which sets the frequency. The design of a damping resistor in series with the AC filter capacitor is discussed and the impact of strong feedback between the output current and the capacitor voltage is investigated. Moreover an analysis of the derivative droop coefficients is carried out through a simplified equivalent circuit.

	Experimental Verification of an Active Microgrid with Distributed Power-Based Control By Tommaso CALDOGNETTO	[View] [Download]
Abstract: This paper presents and analyzes experimentally an active microgrid architecture. The microgrid archi- tecture is described and the employed control scheme reviewed, showing how the devised system is able to meet energy needs, ensure good power quality, and allow seamless transitions from grid-connected to islanded operation. Also, the proposed solution is briefly contextualized with respect to approaches based on the droop control. Finally, we consider the implementation of the experimental testbed that is employed to show the operational capabilities of the microgrid.

	Harmonic Circulation Method with Single-Phase Distributed Generation Units in Three-Phase Three-Wire Power Distribution Systems By Hidehito YOSHIDA	[View] [Download]
Abstract: In recent years, distributed generation (DG) units with a harmonic compensation function have attracted considerable attention as a solution for harmonic current suppression in low-power single-phase applications. This paper presents a harmonic circulation method for harmonic current suppression with single-phase DG units in three-phase three-wire systems. Using the proposed control strategy, all harmonic currents in three-phase grids can be removed without the installation of DG units at all harmonic sources. Furthermore, the proposed method requires less power for harmonic current suppression than the conventional method. Experimental results are presented to verify the validity of the proposed method.

	Inverter design for four-wire micro-grids By DANIEL HEREDERO-PERIS	[View] [Download]
Abstract: This paper presents a PQ four quadrant four-wire three-phase inverter for microgrids integration. Theinverter is based in two full-bridge IGBT modules connected in a three-phase configuration plus a threephase parallelized neutral branch. This topology is galvanically isolated through a single-phase transformer bank. The converter operates as a non-ideal voltage-controlled voltage source inverter under AC droop strategy with hot-swap capability based on a dynamic virtual impedance.

	Low-frequency reduced-order modeling approach and implementation of grid emulation in hardware-in-the-loop platforms By Virgilio VALDIVIA	[View] [Download]
Abstract: A simple and effective modelling approach of the electrical grid and implementation in Hardware inthe Loop (HIL) device is presented in this paper. A low-frequency reduced-order modelling approachhas been followed, which reduces dramatically the computational requirements and implementationcomplexity in comparison to an equivalent full grid model, and offers an intuitive way to tune the griddynamic behaviour.

	Multiagent based distributed control for operation cost minimization of droop controlled AC microgrid using incremental cost consensus By Chendan LI	[View] [Download]
Abstract: Microgrid, as a promising technology to integrate renewable energy resources in the distribution system, is gaining increasing research interests recently. Although many previous works have been done based on the droop control in a microgrid, they mainly focus on achieving proportional power sharing based on the power rating. With various types of distributed generator (DG) units in the system, factors that closely related to the operation cost, such as fuel cost and efficiencies of the generator should be taken into account in order to improve the efficiency of the whole system. In this paper, a multiagent based distributed method is proposed to minimize operation cost of the AC microgrid. Each DG is acting as an agent which regulates the power individually using proposed frequency scheduling method. Optimal power command is obtained through carefully designed consensus algorithm with only light communication between neighboring agents. Case studies verified that the proposed control strategy can effectively reduce the operation cost.

	Performance of a new fast switching DC-Breaker for meshed HVDC-Grids By Yeqi WANG	[View] [Download]
Abstract: For the future demand of electrical energy, both a reliable and an environmental friendly solution is of high importance. The integration of many widely dispersed regenerative energy sources imposes a great challenge for the existing HVAC grids. A meshed, multiterminal HVDC-SuperGrid is considered to be the best and most efficient solution. This concept would be realized as an overlay grid alongside existing AC-grids, which enables large and controllable energy exchanges over long distances. Extremely high reliability and availability of this HVDC-Grid will become a key point in future, obviously. Fast acting, robust DC-Breakers will be necessary for this purpose, too.This paper presents a new thyristor based DC-Breaker of high switching speed and robustness. The generic requirements for HVDC-Breakers are discussed alongside with known proposed concepts. Afterwards, the characteristics and the dimensioning of the new DC-Breaker is presented and investigated in detail. Measuring results from a test setup show the capabilities and advantages of the new topology.

	Phase locked loop effect on Non Detection Zone of Unintentional Islanding By Riccardo SGARBOSSA	[View] [Download]
Abstract: The number of small power distributed generators connected to the low voltage distribution networks has increased the possibility of unintentional islanding operations. In this paper, the influence of the Synchronous Reference Frame - Phase Locked Loop (SRF-PLL) for single-phase and three-phase inverter, combined with the wider frequency and voltage protection ranges stated by the Standards, has been considered as causes of increasing possibility of unintentional islanding events. The paper is focused on the enlargement of the protection system Non Detection Zone, due to the single phase PLL on a current- controlled Inverter, as typically used in PhotoVoltaic (PV) or Renewable Energy Source (RES) applications.

	Power Quality Optimization for Droop-based Voltage Source Inverters in Microgrids By Wenfeng CUI	[View] [Download]
Abstract: Recently, microgrids are receiving an increasing interest with the development of the distributed generation (DG). The droop control is often adopted in voltage source inverters (VSI) to realize the power control and sharing in microgrids. However, voltage and frequency derivations are inevitable due to the employment of the droop control, which degrades the output power quality of the VSIs. This paper focuses on improving the output current quality of the DG units by optimizing the conventional current droop control without additional sensors or devices. The virtual impedance in the control scheme is optimized to improve the low frequency distortion induced by the non-ideal feature of the devices and the dead-time effect. Furthermore, good dynamic performance of the output current is achieved by adding the current forward control into the system control. Therefore, better output quality can be with the presented control method in microgrids.

	Secondary Droop for Frequency and Voltage Restoration in Microgrids By Inam Ullah NUTKANI	[View] [Download]
Abstract: Droop based autonomous control offers several advantages such as communication independence, plug-n-play capability and enhanced reliability of the system. Despite these advantages, frequency and voltage of droop controlled microgrid varies with the load change which is one of the major drawback of the droop control. Presently, the frequency and voltage restoration in microgrid is achieved through secondary control using low bandwidth communication links. This paper presents secondary-droop based frequency and voltage restoration method which is fully autonomous and independent of communication links. With the proposed method, the microgrid frequency and voltage can be restored back to nominal value without affecting the power sharing performance of the generation sources. The proposed scheme performance has been validated in simulation for several cases of active and reactive power load conditions.

	Thermal Stress Comparison in Modular Power Converter Topologies for Smart Transformers in the Electrical Distribution System By Markus ANDRESEN	[View] [Download]
Abstract: A Smart Transformer (ST) can cover an important managing role in the future electrical distribution grid. For the moment, the reliability and cost are not competitive with traditional transformers and create a barrier for its application. This work conduct detail designs and analysis for a promising modular ST solution, which is composed of Modular Multi-level converter, Quad Active Bridge DC-DC converters, and two-level voltage source converters. The focus is put on the loading conditions and thermal stress of power semiconductor devices in order to discover critical parts of the whole system when performing various mission profiles in the realistic distribution grid. It is concluded that the thermal stress for all stages is low during normal operation and especially the isolation stage is stressed least.

	Virtual Electrical Test Bench for More Electrical Aircraft Architecture Verification and Energy Management Development By Jean BESTER	[View] [Download]
Abstract: The shift towards More Electrical Aircraft is bringing with it many new technologies and a redesign of the existing aircraft electrical network, both of which require thorough testing before their implementation. This led to the creation of the Copper Bird® test bench which recreates the aircraft electrical system and is used for equipment evaluation and validation. This paper details the development of an accompanying virtual electrical test bench; modelling and real-time simulation of the operation of an aircraft electrical system for conducting verification activities over different aircraft electrical architectures and developing energy management strategies. In this paper particular attention is given to the PEM fuel cell model which has been characterized and validated using a scaled version of the electrical test bench. The model shows good accuracy, giving an average error of less than ±350mV and a max error of only ±3\%. Fuzzy logic-based energy management was then developed for a fuel cell and battery-based auxiliary power unit with the fuel cell supplying average load power (whilst acting as a current source) and the battery handling load transients and overload situations. The energy management attains its goals of operating the fuel cell at its average power, in order to extend its lifetime, whilst maintaining the battery state of charge between 50\% and 90\%, also in order to extend its lifetime as well as maintaining its ability to absorb excess generated power.