EPE Association: EPE 2013 - DS1g: HVDC Transmission

EPE 2013 - DS1g: HVDC Transmission
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 - DS1g: HVDC Transmission

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   A competitive medium frequency AC distribution grid for offshore wind farms using HVDC
By Sidney GIERSCHNER, Hans-Guenter ECKEL, Mark-Matthias BAKRAN [View]
[Download]

Abstract: HVDC transmission becomes more important for wind farms located over hundred kilometres from theshore. For offshore wind farms decoupled by HVDC transmission, frequency is a degree of freedom.State of the art for offshore wind farms is a 50Hz AC distribution grid.In this paper the effects of a higher line frequency on the main parts of an offshore wind farm are investigated.The main advantages and drawbacks are revealed and compared to a wind farm topology usinga DC distribution grid. A loss calculation for a whole wind farm was done to highlight the opportunitiesand restrictions.

   A Generalized Power Control Approach in ABC Frame for Modular Multilevel Converters based on Lagrange Multipliers
By Gilbert BERGNA, Alejandro GARCES, Erik BERNE, Marta MOLINAS, Jean-Claude VANNIER, Philippe EGROT [View]
[Download]

Abstract: This work presents a generalized and versatile control approach for Modular Multilevel Converters using Lagrange Multipliers in the ABC frame. The methodology is capable of analytically obtaining desired operative conditions by calculating the differential current references previously established by the constraints in the optimization formulation, whilst obtaining the result with minimum I) differential current oscillations, or II) capacitive phase energy oscillations. Furthermore, the energy distribution inside the MMC; i.e., the capacitive phase average energy sum and difference, is being regulated by means of the constraint definitions.

   A new HVDC-DC converter with inherent fault clearing capability
By Andre SCHOEN, Mark-Matthias BAKRAN [View]
[Download]

Abstract: For the upcoming need to transfer bulk power over long onshore distances, HVDC power transmission is the preferred choice. However, components like HVDC-DC converters and a protection concept for DC line faults present challenges, that still have to be solved. As up today, the sections of a segmented DC transmission corridor would still be linked via an AC connection, leading to high transformation losses, and high investment costs. With the newly presented HVDC-DC auto transformer it is possible to directly link two DC lines with different voltage levels. In this paper the ability of this HVDC-DC converter to interrupt DC faults is investigated and compared to the state of the art topology of linking two DC lines via an AC connection.

   A Sub-module Capacitor Voltage Balancing Scheme for the Alternate Arm Converter (AAC)
By Ewan FARR, Jon CLARE, Alan WATSON, Ralph FELDMAN, Pat WHEELER [View]
[Download]

Abstract: A per-phase sub-module capacitor voltage balancing scheme for the Alternate Arm Converter (AAC) is proposed. Leg balancing regulates the sum of sub-module capacitor voltages in a leg to its set-point. Armbalancing regulates each sub-module capacitor voltage to the nominal sub-module capacitor voltage.Additional converter control requirements and the modulation scheme are also discussed. The controland modulation scheme has been verified by simulation. The leg balancing control loop was designed tobe critically damped to primarily limit oscillations in the output variable caused by changes in AC-sidepower demands; the simulation results indicated this specification was met.

   Analysis of Communication Based Distributed Control of MMC for HVDC
By Shaojun HUANG, Remus TEODORESCU, Laszlo MATHE [View]
[Download]

Abstract: Modular Multilevel Converter (MMC) has gained a lot of interest in industry in the recent years due toits modular design and easy adaption for applications that require different power and voltage level.However, the control and operation of a real MMC consisting of large number of sub modules for highpower and high voltage application is a very challenging task. For the reason that distributed controlarchitecture could maintain the modularity of the MMC, this control architecture will be investigatedand a distributed control system dedicated for MMC will be proposed in this paper. The suitablecommunication technologies, modulation and control techniques for the proposed distributed controlsystem are discussed and compared. Based on the frequency domain modeling and analysis of thedistributed control system, the controllers of the different control loops are designed by analyticalmethods and Matlab tools. Finally, sensitiveness of the distributed control system to modulation effect(phase-shifted PWM), communication delay, individual carrier frequency and sampling frequency isstudied through simulations that are made in Matlab Simulink and PLECS.

   Calculation of Power Losses for MMC-based VSC HVDC Stations
By Colin DAVIDSON, Phil JONES [View]
[Download]

Abstract: VSC technology is now well established in HVDC and is, in many respects, complementary to the older Line Commutated Converter (LCC) technology. Many advantages have been claimed for VSC technology in HVDC, including the smaller site footprint. On the other hand, VSC HVDC stations have higher power losses than LCC stations. Although the relative advantages and disadvantages are well known within the industry, there have been very few attempts to quantify these factors on an objective basis. In part, this is because of the lack of applicable standards for determining the power losses of a VSC station. No equivalent of IEC 61803 is today available for VSC-HVDC, but now a draft IEC standard (IEC 62751) is in preparation, which will permit objective comparisons to be made between power losses of LCC and VSC stations.

   Continuous Modeling of Open-Loop Control Based Negative Sequence Current Control of Modular Multilevel Converters for HVDC Transmission
By Noman AHMED, Lennart ANGQUIST, Hans-Peter NEE [View]
[Download]

Abstract: Negative sequence currents are obtained during ac-side asymmetrical faults of converters in high- voltage direct current (HVDC) transmission systems. Consequently, second order harmonics in the dc-side voltage and current, unbalanced ac-side currents, and power oscillations can be observed. This paper presents a negative sequence current control (NSCC) scheme that eliminates second order harmonic ripples in the voltage and current of the dc-side during unbalanced grid conditions. Controllers for this purpose are investigated using a continuous model of the modular multilevel converter (M2C). The proposed scheme utilizes an open-loop controller for lower level control of the M2C. The continuous model used also has the capability to model blocking and deblocking events which may be used during protective actions. Simulation results reveal that the proposed NSCC scheme is effective in suppressing dc-side voltage and current ripples. Moreover, it keeps the ac-side phase currents balanced during asymmetrical fault conditions.

   DC transformer for DC/DC connection in HVDC network
By Miguel JIMENEZ CARRIZOSA, Abdelkrim BENCHAIB, Pedro ALOU, Gilney DAMM [View]
[Download]

Abstract: This paper presents the modeling and control of a multilevel DC/DC bidirectional converter suitablefor medium voltage and power applications, with a special interest in wind-power applications. Theproposed multilevel topology has a modular structure constituted by base DC/DC converter cells. Themultilevel converter is consequently based on Dual Active Bridge (DAB). The overall control of theDC/DC converter is achieved by using a nonlinear control based in Lyapunov theory.

   Estimation of sub-module capacitor voltages in Modular Multilevel Converters
By Salvatore D'ARCO, Jon Are SUUL [View]
[Download]

Abstract: This paper presents a method for estimating the voltages at the individual sub-module capacitors ofModular Multilevel Converters (MMCs). The estimation method is designed according to a predictor-corrector scheme with a model-based prediction stage utilizing the arm current measurements and theinternal modulation signals of the control system. The corrector stage is based on measurement of thetotal output voltage from each arm of the MMC. Thus, only two voltage measurements for each phaseof the MMC must be continuously processed by the control system instead of individual voltagemeasurements for each sub-module. This can significantly reduce the communication requirements forthe MMC control system and by that simplify the implementation. The principles of the proposedestimation method are described in detail in the paper, and the operation is demonstrated by simulationresults. Estimation accuracy and settling time of the proposed method have been investigated withrespect to the number of sub-modules in each arm of the MMC. Quantization effects due to limitedresolution of the arm voltage sensors and the influence of parameter deviations have also beenconsidered. The presented results illustrate the response of the proposed algorithm and indicate itspotential for limiting the communication requirements and increasing system reliability by reducingthe control system dependency on individual sub-module capacitor voltage measurements.

   Future HVDC-Grids employing Modular Multilevel Converters and Hybrid DC-Breakers
By Yeqi WANG, Rainer MARQUARDT [View]
[Download]

Abstract: The necessary shift from fossil fuels to regenerative sources imposes a great challenge forfuture power transmission. A large, meshed HVDC-Grid is proposed by several experts as thebest and most efficient solution. For meshed DC-Grids, however, new and essentialrequirements – especially regarding availability and reliability – have to be researched verythoroughly. Fast and reliable handling of DC-faults must be ensured without disturbing theenergy flow in the whole grid. The following paper deals with the key components (ModularMultilevel Converters and DC-Breakers) in large meshed HVDC-Grids. A comparisonbetween suitable submodule topologies with DC-fault handling abilities is presentedalongside with a new topology for a hybrid DC-Breaker.

   Generalized ABC Frame Differential Current Control ensuring constant DC Power for Modular Multilevel Converters under Unbalanced Operation
By Gilbert BERGNA, Jon Are SUUL, Erik BERNE, Marta MOLINAS, Jean-Claude VANNIER, Philippe EGROT [View]
[Download]

Abstract: This work presents a generalized and versatile approach for controlling Modular Multilevel Converters (MMC), with three or more phases, by means of Lagrange Multipliers in the ABC frame. The resulting control method is suitable for operation of HVDC converters under both balanced and unbalanced AC grid voltages, since it is designed for eliminating oscillations in the DC power flow independently of the AC grid voltage conditions. This is achieved by the analytical resolution of a mathematical optimization problem using Lagrange multipliers in order to calculate the differential current references for the converter directly in the ABC frame. The resulting equation for current reference calculation is generalized by a weighting factor introduced in the objective function for the optimization problem, and this allows to select between the following two operating conditions or any intermediate point between them: I) minimum differential current oscillations, or II) minimum capacitive phase energy oscillations. Furthermore, the constraints defined in the optimization regulate the average energy distribution inside the MMC; i.e., the capacitive phase average energy sum and difference whilst ensuring non-oscillatory power output on the DC terminals of the MMC.

   Modular Multilevel Converter in HVDC systems under fault conditions
By Mario MARCHESONI, Paolo BORDIGNON, Gianluca PARODI, Luis VACCARO [View]
[Download]

Abstract: A detailed analysis of the behaviour of a Modular Multilevel Converter (MMC) in a HVDC system, in case of both DC and AC faults, is provided. Results related to a two-terminal HVDC system are presented.

   Multiterminal-HVDC scaled platform for off shore wind transmission systems emulation
By Agusti EGEA-ALVAREZ, Adria JUNYENT-FERRE, Gabriel GROSS, Samuel GALCERAN-ARELLANO, Oriol GOMIS-BELLMUNT [View]
[Download]

Abstract: This paper presents a Multiterminal VSC-HVDC (Voltage Sources Converter, High Voltage Direct Current) emulation platform. Design details of the scaled platform are discussed. A DC grid droop-based voltage control method designed following Lyapunov control theory has been adopted. In addition, operational points of the Multiterminal HVDC grid are described. The emulation platform have been tested under wind power change and power converter disconnection scenarios. The emulation results has been verified by means of simulations.

   Optimized Control of Multi-Terminal DC Power Systmes Using Particle Swarm Optimization
By Kumars ROUZBEHI, Arash MIRANIAN, Alvaro LUNA, Pedro RODRIGUEZ [View]
[Download]

Abstract: This paper addresses the important issue of Multi-Terminal DC (MTDC) grid control strategy basedon the particle swarm optimization (PSO) technique. The MTDC grid is controlled by the concept ofvector control, in which the AC currents and voltages are transformed into the rotating directquadrature(d-q) reference quantities which are subsequently used for decoupled control of the activeand reactive powers as well as the DC and AC voltages. The paper employs an efficient PSOalgorithm for optimal tuning of the controllers’ parameters in an MTDC grid. In addition, voltagedroop control scheme is utilized to ensure the balance of active power within the MTDC grid.Simulation results that has obtained through detailed modeling of a four-terminal DC grid,demonstrate the efficiency of the proposed approach. Comparison to controllers optimized by geneticalgorithm (GA) also confirmed the favorable performance of the proposed PSO-tuned controllers.

   Resonant Test Circuit for High-Power Cascaded Converter Submodules
By Tomas MODEER, Staffan NORRGA, Hans-Peter NEE [View]
[Download]

Abstract: This paper presents a test circuit and methodology suitable for testing high-power half-bridge submodulessuch as would be used in cascaded converters for high-voltage dc converters. The circuit utilizes aseries resonant tank and two half-bridge submodules with voltage and impedance cancellation in orderto minimize hardware requirements.

   Voltage and Power Control in Multi-Terminal HVDC Grids without Communication
By Johannes VOSS, Florian MURA, Rik W. DE DONCKER, Hanno STAGGE [View]
[Download]

Abstract: The change to a sustainable energy supply advances further development in grid interconnection, especially for offshore wind farms. This enables future wind farms to be interconnected by high voltage dctransmission grids. In this paper, a case study for dc grid with integrated offshore wind farms is studiedand a system control is developed.

EPE 2013 - DS1g: HVDC Transmission
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 - DS1g: HVDC Transmission
	[return to parent folder]

	A competitive medium frequency AC distribution grid for offshore wind farms using HVDC By Sidney GIERSCHNER, Hans-Guenter ECKEL, Mark-Matthias BAKRAN	[View] [Download]
Abstract: HVDC transmission becomes more important for wind farms located over hundred kilometres from theshore. For offshore wind farms decoupled by HVDC transmission, frequency is a degree of freedom.State of the art for offshore wind farms is a 50Hz AC distribution grid.In this paper the effects of a higher line frequency on the main parts of an offshore wind farm are investigated.The main advantages and drawbacks are revealed and compared to a wind farm topology usinga DC distribution grid. A loss calculation for a whole wind farm was done to highlight the opportunitiesand restrictions.

	A Generalized Power Control Approach in ABC Frame for Modular Multilevel Converters based on Lagrange Multipliers By Gilbert BERGNA, Alejandro GARCES, Erik BERNE, Marta MOLINAS, Jean-Claude VANNIER, Philippe EGROT	[View] [Download]
Abstract: This work presents a generalized and versatile control approach for Modular Multilevel Converters using Lagrange Multipliers in the ABC frame. The methodology is capable of analytically obtaining desired operative conditions by calculating the differential current references previously established by the constraints in the optimization formulation, whilst obtaining the result with minimum I) differential current oscillations, or II) capacitive phase energy oscillations. Furthermore, the energy distribution inside the MMC; i.e., the capacitive phase average energy sum and difference, is being regulated by means of the constraint definitions.

	A new HVDC-DC converter with inherent fault clearing capability By Andre SCHOEN, Mark-Matthias BAKRAN	[View] [Download]
Abstract: For the upcoming need to transfer bulk power over long onshore distances, HVDC power transmission is the preferred choice. However, components like HVDC-DC converters and a protection concept for DC line faults present challenges, that still have to be solved. As up today, the sections of a segmented DC transmission corridor would still be linked via an AC connection, leading to high transformation losses, and high investment costs. With the newly presented HVDC-DC auto transformer it is possible to directly link two DC lines with different voltage levels. In this paper the ability of this HVDC-DC converter to interrupt DC faults is investigated and compared to the state of the art topology of linking two DC lines via an AC connection.

	A Sub-module Capacitor Voltage Balancing Scheme for the Alternate Arm Converter (AAC) By Ewan FARR, Jon CLARE, Alan WATSON, Ralph FELDMAN, Pat WHEELER	[View] [Download]
Abstract: A per-phase sub-module capacitor voltage balancing scheme for the Alternate Arm Converter (AAC) is proposed. Leg balancing regulates the sum of sub-module capacitor voltages in a leg to its set-point. Armbalancing regulates each sub-module capacitor voltage to the nominal sub-module capacitor voltage.Additional converter control requirements and the modulation scheme are also discussed. The controland modulation scheme has been verified by simulation. The leg balancing control loop was designed tobe critically damped to primarily limit oscillations in the output variable caused by changes in AC-sidepower demands; the simulation results indicated this specification was met.

	Analysis of Communication Based Distributed Control of MMC for HVDC By Shaojun HUANG, Remus TEODORESCU, Laszlo MATHE	[View] [Download]
Abstract: Modular Multilevel Converter (MMC) has gained a lot of interest in industry in the recent years due toits modular design and easy adaption for applications that require different power and voltage level.However, the control and operation of a real MMC consisting of large number of sub modules for highpower and high voltage application is a very challenging task. For the reason that distributed controlarchitecture could maintain the modularity of the MMC, this control architecture will be investigatedand a distributed control system dedicated for MMC will be proposed in this paper. The suitablecommunication technologies, modulation and control techniques for the proposed distributed controlsystem are discussed and compared. Based on the frequency domain modeling and analysis of thedistributed control system, the controllers of the different control loops are designed by analyticalmethods and Matlab tools. Finally, sensitiveness of the distributed control system to modulation effect(phase-shifted PWM), communication delay, individual carrier frequency and sampling frequency isstudied through simulations that are made in Matlab Simulink and PLECS.

	Calculation of Power Losses for MMC-based VSC HVDC Stations By Colin DAVIDSON, Phil JONES	[View] [Download]
Abstract: VSC technology is now well established in HVDC and is, in many respects, complementary to the older Line Commutated Converter (LCC) technology. Many advantages have been claimed for VSC technology in HVDC, including the smaller site footprint. On the other hand, VSC HVDC stations have higher power losses than LCC stations. Although the relative advantages and disadvantages are well known within the industry, there have been very few attempts to quantify these factors on an objective basis. In part, this is because of the lack of applicable standards for determining the power losses of a VSC station. No equivalent of IEC 61803 is today available for VSC-HVDC, but now a draft IEC standard (IEC 62751) is in preparation, which will permit objective comparisons to be made between power losses of LCC and VSC stations.

	Continuous Modeling of Open-Loop Control Based Negative Sequence Current Control of Modular Multilevel Converters for HVDC Transmission By Noman AHMED, Lennart ANGQUIST, Hans-Peter NEE	[View] [Download]
Abstract: Negative sequence currents are obtained during ac-side asymmetrical faults of converters in high- voltage direct current (HVDC) transmission systems. Consequently, second order harmonics in the dc-side voltage and current, unbalanced ac-side currents, and power oscillations can be observed. This paper presents a negative sequence current control (NSCC) scheme that eliminates second order harmonic ripples in the voltage and current of the dc-side during unbalanced grid conditions. Controllers for this purpose are investigated using a continuous model of the modular multilevel converter (M2C). The proposed scheme utilizes an open-loop controller for lower level control of the M2C. The continuous model used also has the capability to model blocking and deblocking events which may be used during protective actions. Simulation results reveal that the proposed NSCC scheme is effective in suppressing dc-side voltage and current ripples. Moreover, it keeps the ac-side phase currents balanced during asymmetrical fault conditions.

	DC transformer for DC/DC connection in HVDC network By Miguel JIMENEZ CARRIZOSA, Abdelkrim BENCHAIB, Pedro ALOU, Gilney DAMM	[View] [Download]
Abstract: This paper presents the modeling and control of a multilevel DC/DC bidirectional converter suitablefor medium voltage and power applications, with a special interest in wind-power applications. Theproposed multilevel topology has a modular structure constituted by base DC/DC converter cells. Themultilevel converter is consequently based on Dual Active Bridge (DAB). The overall control of theDC/DC converter is achieved by using a nonlinear control based in Lyapunov theory.

	Estimation of sub-module capacitor voltages in Modular Multilevel Converters By Salvatore D'ARCO, Jon Are SUUL	[View] [Download]
Abstract: This paper presents a method for estimating the voltages at the individual sub-module capacitors ofModular Multilevel Converters (MMCs). The estimation method is designed according to a predictor-corrector scheme with a model-based prediction stage utilizing the arm current measurements and theinternal modulation signals of the control system. The corrector stage is based on measurement of thetotal output voltage from each arm of the MMC. Thus, only two voltage measurements for each phaseof the MMC must be continuously processed by the control system instead of individual voltagemeasurements for each sub-module. This can significantly reduce the communication requirements forthe MMC control system and by that simplify the implementation. The principles of the proposedestimation method are described in detail in the paper, and the operation is demonstrated by simulationresults. Estimation accuracy and settling time of the proposed method have been investigated withrespect to the number of sub-modules in each arm of the MMC. Quantization effects due to limitedresolution of the arm voltage sensors and the influence of parameter deviations have also beenconsidered. The presented results illustrate the response of the proposed algorithm and indicate itspotential for limiting the communication requirements and increasing system reliability by reducingthe control system dependency on individual sub-module capacitor voltage measurements.

	Future HVDC-Grids employing Modular Multilevel Converters and Hybrid DC-Breakers By Yeqi WANG, Rainer MARQUARDT	[View] [Download]
Abstract: The necessary shift from fossil fuels to regenerative sources imposes a great challenge forfuture power transmission. A large, meshed HVDC-Grid is proposed by several experts as thebest and most efficient solution. For meshed DC-Grids, however, new and essentialrequirements – especially regarding availability and reliability – have to be researched verythoroughly. Fast and reliable handling of DC-faults must be ensured without disturbing theenergy flow in the whole grid. The following paper deals with the key components (ModularMultilevel Converters and DC-Breakers) in large meshed HVDC-Grids. A comparisonbetween suitable submodule topologies with DC-fault handling abilities is presentedalongside with a new topology for a hybrid DC-Breaker.

	Generalized ABC Frame Differential Current Control ensuring constant DC Power for Modular Multilevel Converters under Unbalanced Operation By Gilbert BERGNA, Jon Are SUUL, Erik BERNE, Marta MOLINAS, Jean-Claude VANNIER, Philippe EGROT	[View] [Download]
Abstract: This work presents a generalized and versatile approach for controlling Modular Multilevel Converters (MMC), with three or more phases, by means of Lagrange Multipliers in the ABC frame. The resulting control method is suitable for operation of HVDC converters under both balanced and unbalanced AC grid voltages, since it is designed for eliminating oscillations in the DC power flow independently of the AC grid voltage conditions. This is achieved by the analytical resolution of a mathematical optimization problem using Lagrange multipliers in order to calculate the differential current references for the converter directly in the ABC frame. The resulting equation for current reference calculation is generalized by a weighting factor introduced in the objective function for the optimization problem, and this allows to select between the following two operating conditions or any intermediate point between them: I) minimum differential current oscillations, or II) minimum capacitive phase energy oscillations. Furthermore, the constraints defined in the optimization regulate the average energy distribution inside the MMC; i.e., the capacitive phase average energy sum and difference whilst ensuring non-oscillatory power output on the DC terminals of the MMC.

	Modular Multilevel Converter in HVDC systems under fault conditions By Mario MARCHESONI, Paolo BORDIGNON, Gianluca PARODI, Luis VACCARO	[View] [Download]
Abstract: A detailed analysis of the behaviour of a Modular Multilevel Converter (MMC) in a HVDC system, in case of both DC and AC faults, is provided. Results related to a two-terminal HVDC system are presented.

	Multiterminal-HVDC scaled platform for off shore wind transmission systems emulation By Agusti EGEA-ALVAREZ, Adria JUNYENT-FERRE, Gabriel GROSS, Samuel GALCERAN-ARELLANO, Oriol GOMIS-BELLMUNT	[View] [Download]
Abstract: This paper presents a Multiterminal VSC-HVDC (Voltage Sources Converter, High Voltage Direct Current) emulation platform. Design details of the scaled platform are discussed. A DC grid droop-based voltage control method designed following Lyapunov control theory has been adopted. In addition, operational points of the Multiterminal HVDC grid are described. The emulation platform have been tested under wind power change and power converter disconnection scenarios. The emulation results has been verified by means of simulations.

	Optimized Control of Multi-Terminal DC Power Systmes Using Particle Swarm Optimization By Kumars ROUZBEHI, Arash MIRANIAN, Alvaro LUNA, Pedro RODRIGUEZ	[View] [Download]
Abstract: This paper addresses the important issue of Multi-Terminal DC (MTDC) grid control strategy basedon the particle swarm optimization (PSO) technique. The MTDC grid is controlled by the concept ofvector control, in which the AC currents and voltages are transformed into the rotating directquadrature(d-q) reference quantities which are subsequently used for decoupled control of the activeand reactive powers as well as the DC and AC voltages. The paper employs an efficient PSOalgorithm for optimal tuning of the controllers’ parameters in an MTDC grid. In addition, voltagedroop control scheme is utilized to ensure the balance of active power within the MTDC grid.Simulation results that has obtained through detailed modeling of a four-terminal DC grid,demonstrate the efficiency of the proposed approach. Comparison to controllers optimized by geneticalgorithm (GA) also confirmed the favorable performance of the proposed PSO-tuned controllers.

	Resonant Test Circuit for High-Power Cascaded Converter Submodules By Tomas MODEER, Staffan NORRGA, Hans-Peter NEE	[View] [Download]
Abstract: This paper presents a test circuit and methodology suitable for testing high-power half-bridge submodulessuch as would be used in cascaded converters for high-voltage dc converters. The circuit utilizes aseries resonant tank and two half-bridge submodules with voltage and impedance cancellation in orderto minimize hardware requirements.

	Voltage and Power Control in Multi-Terminal HVDC Grids without Communication By Johannes VOSS, Florian MURA, Rik W. DE DONCKER, Hanno STAGGE	[View] [Download]
Abstract: The change to a sustainable energy supply advances further development in grid interconnection, especially for offshore wind farms. This enables future wind farms to be interconnected by high voltage dctransmission grids. In this paper, a case study for dc grid with integrated offshore wind farms is studiedand a system control is developed.