EPE Association: EPE 2009 - Topic 14-13 - DS (not A, B): 'STATCOM, FACTS, PFC and Offshore Power Transmission'

EPE 2009 - Topic 14-13 - DS (not A, B): 'STATCOM, FACTS, PFC and Offshore Power Transmission'
You are here: EPE Documents > 01 - EPE & EPE ECCE Conference Proceedings > EPE 2009 - Conference > EPE 2009 - Topic 14: 'Electrical Energy Generating Systems, Renewable Energy Systems' > EPE 2009 - Topic 14-13 - DS (not A, B): 'STATCOM, FACTS, PFC and Offshore Power Transmission'

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   A Coordinated System of Control in an Offshore Wind Farm
By Miguel MONTILLA D JESUS [View]
[Download]

Abstract: This paper describes the coordination in control systems between the DFIG and the firing delay angle control of the rectifier that comprise the HVDC-LCC Link; as well as the Generator + Transmission topology formed by the DFIG and HVDC link to maintain voltage and frequency output of offshore wind farms constant.

   A Design Methodology for Boost Inductor Applied to PFC Converters Considering the Core Temperature Rise and the Conducted EMI Noise
By Jonatan ZIENTARSKI, JosÃ© Renes PINHEIRO, HÃ©lio LeÃ£es HEY, Rafael Concatto BELTRAME, Diogo Brum CÃ‚NDIDO [View]
[Download]

Abstract: This paper presents a design methodology to minimize the magnetic volume in a single-phase boost PFC converter operating in the continuous conduction mode (CCM) through the choice of the switching frequency and the input current ripple, taking into account the choice of magnetic material, the standard limits for conducted electromagnetic interference (EMI) noise generated, as well as ensuring single-layer winding and maximum temperature rise (losses) of the boost inductor. Some differences in the operation point that minimize the volume for the Sendust, Molypermalloy and High-Flux powder cores are discussed. The design methodology based on the models described in the paper is confirmed by experimental results obtained from a 650 W (400 V output voltage) universal line input (90-264 VRMS) PFC boost prototype, considering a switching frequency of 70 kHz and an input current ripple of 40\%.

   A MERS type Series FACTS Controller for Low Voltage Ride Through of Induction Generators in Wind Farms
By Jan Arild WIIK, Olav J. FÃ˜NSTELIEN, Ryuichi SHIMADA [View]
[Download]

Abstract: Low voltage ride through (LVRT) of squirrel cage induction generators in wind farms is challenging due to the large required reactive power after low voltage period. Reactive power compensation with shunt compensation can improve the LVRT capability, but requires a large rating. The alternative use of series compensation is studied. Series compensation is based on increasing the reactive power transfer from the grid, and can by this reduce the required rating of the compensator compared to shunt compensation. A series compensator called magnetic energy recovery switch (MERS) is found suitable due to large control range and good over-current capability. Simulations and experimental results demonstrate that MERS can improve the LVRT capability by injecting a series voltage during and/or after the low voltage period. Finally, evaluation of series compensation suggests cost reductions compared to shunt compensation; however, the influence on power system stability of increased reactive power transfer from the grid after low voltage period should be investigated in future works.

   A New Switched Inductor VAR Compensator
By Christos MAROUCHOS [View]
[Download]

Abstract: A new circuit configuration for the generation of both reactive power and harmonic current is presented. Unlike Thyristor Controlled Reactors (TCR), the voltage across an inductor is pulseâ€“width modulated in such a way to produce the required line current. In this presentation the switched inductor is producing lagging reactive power. In conjunction with a fixed parallel capacitor, good quality variable leading and lagging reactive power can be generated. The modulation of the voltage across the inductor is achieved by two semiconductor switches. A relatively high switching frequency is used shifting the line harmonics to a high order for ease of filtering. The size of the passive filters is potentially reduced bringing the cost and size of the system to more attractive levels. The switching frequency and choice of switching semiconductors can be optimized to keep efficiency high. The Switching Function technique is used throughout to analyze the circuit using Mathcad. A PSPICE model is constructed and an experimental set up is presented. PSPICE circuit and Switching Function PSPICE simulations are presented to support the theory

   Bridgeless Boost PFC with Fast Dynamic Response Algorithm
By wei WANG, guihua LIU, dianguo XU [View]
[Download]

Abstract: In order to improve dynamic performance to load variation of PFC circuit, a digital PFC algorithm with fast dynamic response is proposed in bridgeless Boost PFC. The proposed algorithm improves dynamic response by increasing voltage loop bandwidth, and uses vector rotation scheme to generate compensating harmonic signal which counteracts second order harmonic resulted from increased voltage loop bandwidth. Without adding auxiliary circuit, the fast dynamic response digital algorithm is programmed with graphical approach which corresponds to control chip. Experimental results verify that the system has fast dynamic response when the load power varies in a large-scale, the power factor reaches 0.99 and input current total harmonic distortion (THD) is lower than 10\%.

   Design Considerations for Medium-Frequency Power Transformers in Offshore Wind Farms
By Stephan MEIER, Tommy KJELLQVIST, Staffan NORRGA, Hans-Peter NEE [View]
[Download]

Abstract: In a recently proposed converter system for offshore wind farms, single-phase medium-frequency transformers replace the conventional three-phase line-frequency transformers that convert the electricity from the wind turbine generators to high voltage. Medium-frequency operation allows a reduction of the transformer size and weight, thus leading to a compact and efficient design, which minimizes the installation and maintenance costs. This paper presents design considerations for dry-type single-phase medium-frequency power transformers in offshore wind farms. Recent transformer problems in large wind turbines have shown that a thorough and careful magnetic, electric, and thermal design is required to ensure the reliability and performance of the transformers. As a result, a suitable design for a 3 MW wind turbine transformer is proposed.

   Dynamic performance analysis of a wind turbine generating system with series connected wind generators using a current source thyristor inverter
By Fujio TATSUTA, Shoji NISHIKATA [View]
[Download]

Abstract: Dynamic performances of a wind turbine generating system consisting of series connected wind generator/rectifiers and a current source thyristor inverter are discussed. A simulation model for the whole system including the wind turbines is presented to demonstrate the feasibility of the system for the case of two wind turbine/generators. It is shown that the tip speed ratios of the individual turbines with different wind velocities can be controlled almost constant with the proposed control method for a large and capricious change in the wind velocity, making an effective operation of the system possible.

   Evaluation and selection of AC transmission lay-outs for large offshore wind farms
By Markel ZUBIAGA, Gonzalo ABAD, Jon Andoni BARRENA, Sergio AURTENETXEA, Ainhoa CÃRCAR [View]
[Download]

Abstract: This paper studies different energy transmission solutions for AC offshore wind farms. This transmission of energy is based on AC submarine cables that present a strong capacitive behavior. Therefore, an analysis is necessary to determine transmission characteristics such as, the number of submarine cables, voltage or rated power. For that purpose, three different transmission configurations will be considered: unique HVAC, various HVAC and MVAC, combined with three submarine cables of different characteristics. By using a design procedure, it is shown that based on the electric characteristics provided by the manufacturer of the submarine cable, it is possible to determine the most efficient energy transmission solution, from the perspective of the submarine cable. Different variables will be taken into account, including transmission current, active power losses, the cost of the transmitted energy and the reactive power compensation required. In addition, the consequences of the selected transmission solution to other more general aspects of the wind farm such as, necessity of the offshore platform or local inter-turbine network are also discussed.

   Power Electronic Loads as providers of reactive power ancillary service to the grid: an experimental study
By Marta MOLINAS, Junji KONDOH [View]
[Download]

Abstract: Reactive power injection has been the common practice to stabilize and support the voltage in electric power systems and its provision was traditionally considered to be part of the duties of the units dispatching active power. This article proposes the provision of reactive power by electric loads which are interfaced to the grid by active rectifiers that enable them to inject reactive current to support the electric grid voltage locally. The reactive power characteristic at the point of load connection in a distribution system was analytically obtained and experimentally verified in a reduced scale laboratory model. The obtained reactive power curves are used to determine the required rating of the converter interfacing the load, for consideration of stability and operability margins, effect on power factor, impact of distributed compensation and for operation after transients. Relevance of the curves is also discussed for LVRT operation of the converters interfacing the loads. Influence of the type of line (X/R >1, X/R=1, X/R<1) is discussed as well as the sensitivity of the reactive power compensation to the resistance and reactance of the line impedance. The required rating of the converter for voltage compensation in steady state conditions is found to be high when a single load is considered, but can be significantly reduced and becomes reasonable when distributed compensation by several loads is assumed along the line. When the analytical investigation considered only ideal controllers, behavior of the system during experiments suggests that the control of the converter is a critical aspect of the stability problem especially during and after transient events and that the operability limits can be highly influenced by the controller stability. This suggests that special attention must be given to the structure and tuning of controllers for stable operation of converters that are simultaneously absorbing power and injecting reactive current for voltage compensation.

   SINGLE-PHASE PWM BOOST-TYPE UNIDIRECTIONAL RECTIFIER DOUBLING THE SWITCHING FREQUENCY
By SAMIR AHMAD MUSSA, MARCELO LOBO HELDWEIN, MARCIO ORTMANN [View]
[Download]

Abstract: Decades of research have seen single-phase boost-type PWM converters be employed as front-end PFC rectiﬁers in commercial power supplies. The beneﬁts of employing this technology to comply with power quality standards while assuring high efﬁciency and low volume and weight have been observed. However, this work shows that further efforts can be driven into new topologies. In this context, a new topology is introduced, which is able to double the frequency present in the input and output passive components and, thus, working as a full-bridge converter while employing only one additional controlled switch. Furthermore, the switches are utilized during, both, negative and positive mains half-cycles. The theoretical analysis of the topology as well as its use in a PFC application are performed and experimental veriﬁcation is presented in a 1kWprototype employing a current self-control strategy.

   Transformerless STATCOM based on a five-level modular multilevel converter
By Grain Philip ADAM [View]
[Download]

Abstract: A transformless static synchronous compensator based on a modular multilevel converter is presented. Its principle of operation, dc link capacitors voltage balancing technique and control system are described in detail. To demonstrate the suitability of the proposed STATCOM and its effectiveness in medium/high voltage applications where converters with higher number of levels are required, several operating scenarios are considered, including reactive power support and flicker mitigation of offshore wind farms connected to the grid through ac submarine cable.

EPE 2009 - Topic 14-13 - DS (not A, B): 'STATCOM, FACTS, PFC and Offshore Power Transmission'
You are here: EPE Documents > 01 - EPE & EPE ECCE Conference Proceedings > EPE 2009 - Conference > EPE 2009 - Topic 14: 'Electrical Energy Generating Systems, Renewable Energy Systems' > EPE 2009 - Topic 14-13 - DS (not A, B): 'STATCOM, FACTS, PFC and Offshore Power Transmission'
	[return to parent folder]

	A Coordinated System of Control in an Offshore Wind Farm By Miguel MONTILLA D JESUS	[View] [Download]
Abstract: This paper describes the coordination in control systems between the DFIG and the firing delay angle control of the rectifier that comprise the HVDC-LCC Link; as well as the Generator + Transmission topology formed by the DFIG and HVDC link to maintain voltage and frequency output of offshore wind farms constant.

	A Design Methodology for Boost Inductor Applied to PFC Converters Considering the Core Temperature Rise and the Conducted EMI Noise By Jonatan ZIENTARSKI, JosÃ© Renes PINHEIRO, HÃ©lio LeÃ£es HEY, Rafael Concatto BELTRAME, Diogo Brum CÃ‚NDIDO	[View] [Download]
Abstract: This paper presents a design methodology to minimize the magnetic volume in a single-phase boost PFC converter operating in the continuous conduction mode (CCM) through the choice of the switching frequency and the input current ripple, taking into account the choice of magnetic material, the standard limits for conducted electromagnetic interference (EMI) noise generated, as well as ensuring single-layer winding and maximum temperature rise (losses) of the boost inductor. Some differences in the operation point that minimize the volume for the Sendust, Molypermalloy and High-Flux powder cores are discussed. The design methodology based on the models described in the paper is confirmed by experimental results obtained from a 650 W (400 V output voltage) universal line input (90-264 VRMS) PFC boost prototype, considering a switching frequency of 70 kHz and an input current ripple of 40\%.

	A MERS type Series FACTS Controller for Low Voltage Ride Through of Induction Generators in Wind Farms By Jan Arild WIIK, Olav J. FÃ˜NSTELIEN, Ryuichi SHIMADA	[View] [Download]
Abstract: Low voltage ride through (LVRT) of squirrel cage induction generators in wind farms is challenging due to the large required reactive power after low voltage period. Reactive power compensation with shunt compensation can improve the LVRT capability, but requires a large rating. The alternative use of series compensation is studied. Series compensation is based on increasing the reactive power transfer from the grid, and can by this reduce the required rating of the compensator compared to shunt compensation. A series compensator called magnetic energy recovery switch (MERS) is found suitable due to large control range and good over-current capability. Simulations and experimental results demonstrate that MERS can improve the LVRT capability by injecting a series voltage during and/or after the low voltage period. Finally, evaluation of series compensation suggests cost reductions compared to shunt compensation; however, the influence on power system stability of increased reactive power transfer from the grid after low voltage period should be investigated in future works.

	A New Switched Inductor VAR Compensator By Christos MAROUCHOS	[View] [Download]
Abstract: A new circuit configuration for the generation of both reactive power and harmonic current is presented. Unlike Thyristor Controlled Reactors (TCR), the voltage across an inductor is pulseâ€“width modulated in such a way to produce the required line current. In this presentation the switched inductor is producing lagging reactive power. In conjunction with a fixed parallel capacitor, good quality variable leading and lagging reactive power can be generated. The modulation of the voltage across the inductor is achieved by two semiconductor switches. A relatively high switching frequency is used shifting the line harmonics to a high order for ease of filtering. The size of the passive filters is potentially reduced bringing the cost and size of the system to more attractive levels. The switching frequency and choice of switching semiconductors can be optimized to keep efficiency high. The Switching Function technique is used throughout to analyze the circuit using Mathcad. A PSPICE model is constructed and an experimental set up is presented. PSPICE circuit and Switching Function PSPICE simulations are presented to support the theory

	Bridgeless Boost PFC with Fast Dynamic Response Algorithm By wei WANG, guihua LIU, dianguo XU	[View] [Download]
Abstract: In order to improve dynamic performance to load variation of PFC circuit, a digital PFC algorithm with fast dynamic response is proposed in bridgeless Boost PFC. The proposed algorithm improves dynamic response by increasing voltage loop bandwidth, and uses vector rotation scheme to generate compensating harmonic signal which counteracts second order harmonic resulted from increased voltage loop bandwidth. Without adding auxiliary circuit, the fast dynamic response digital algorithm is programmed with graphical approach which corresponds to control chip. Experimental results verify that the system has fast dynamic response when the load power varies in a large-scale, the power factor reaches 0.99 and input current total harmonic distortion (THD) is lower than 10\%.

	Design Considerations for Medium-Frequency Power Transformers in Offshore Wind Farms By Stephan MEIER, Tommy KJELLQVIST, Staffan NORRGA, Hans-Peter NEE	[View] [Download]
Abstract: In a recently proposed converter system for offshore wind farms, single-phase medium-frequency transformers replace the conventional three-phase line-frequency transformers that convert the electricity from the wind turbine generators to high voltage. Medium-frequency operation allows a reduction of the transformer size and weight, thus leading to a compact and efficient design, which minimizes the installation and maintenance costs. This paper presents design considerations for dry-type single-phase medium-frequency power transformers in offshore wind farms. Recent transformer problems in large wind turbines have shown that a thorough and careful magnetic, electric, and thermal design is required to ensure the reliability and performance of the transformers. As a result, a suitable design for a 3 MW wind turbine transformer is proposed.

	Dynamic performance analysis of a wind turbine generating system with series connected wind generators using a current source thyristor inverter By Fujio TATSUTA, Shoji NISHIKATA	[View] [Download]
Abstract: Dynamic performances of a wind turbine generating system consisting of series connected wind generator/rectifiers and a current source thyristor inverter are discussed. A simulation model for the whole system including the wind turbines is presented to demonstrate the feasibility of the system for the case of two wind turbine/generators. It is shown that the tip speed ratios of the individual turbines with different wind velocities can be controlled almost constant with the proposed control method for a large and capricious change in the wind velocity, making an effective operation of the system possible.

	Evaluation and selection of AC transmission lay-outs for large offshore wind farms By Markel ZUBIAGA, Gonzalo ABAD, Jon Andoni BARRENA, Sergio AURTENETXEA, Ainhoa CÃRCAR	[View] [Download]
Abstract: This paper studies different energy transmission solutions for AC offshore wind farms. This transmission of energy is based on AC submarine cables that present a strong capacitive behavior. Therefore, an analysis is necessary to determine transmission characteristics such as, the number of submarine cables, voltage or rated power. For that purpose, three different transmission configurations will be considered: unique HVAC, various HVAC and MVAC, combined with three submarine cables of different characteristics. By using a design procedure, it is shown that based on the electric characteristics provided by the manufacturer of the submarine cable, it is possible to determine the most efficient energy transmission solution, from the perspective of the submarine cable. Different variables will be taken into account, including transmission current, active power losses, the cost of the transmitted energy and the reactive power compensation required. In addition, the consequences of the selected transmission solution to other more general aspects of the wind farm such as, necessity of the offshore platform or local inter-turbine network are also discussed.

	Power Electronic Loads as providers of reactive power ancillary service to the grid: an experimental study By Marta MOLINAS, Junji KONDOH	[View] [Download]
Abstract: Reactive power injection has been the common practice to stabilize and support the voltage in electric power systems and its provision was traditionally considered to be part of the duties of the units dispatching active power. This article proposes the provision of reactive power by electric loads which are interfaced to the grid by active rectifiers that enable them to inject reactive current to support the electric grid voltage locally. The reactive power characteristic at the point of load connection in a distribution system was analytically obtained and experimentally verified in a reduced scale laboratory model. The obtained reactive power curves are used to determine the required rating of the converter interfacing the load, for consideration of stability and operability margins, effect on power factor, impact of distributed compensation and for operation after transients. Relevance of the curves is also discussed for LVRT operation of the converters interfacing the loads. Influence of the type of line (X/R >1, X/R=1, X/R<1) is discussed as well as the sensitivity of the reactive power compensation to the resistance and reactance of the line impedance. The required rating of the converter for voltage compensation in steady state conditions is found to be high when a single load is considered, but can be significantly reduced and becomes reasonable when distributed compensation by several loads is assumed along the line. When the analytical investigation considered only ideal controllers, behavior of the system during experiments suggests that the control of the converter is a critical aspect of the stability problem especially during and after transient events and that the operability limits can be highly influenced by the controller stability. This suggests that special attention must be given to the structure and tuning of controllers for stable operation of converters that are simultaneously absorbing power and injecting reactive current for voltage compensation.

	SINGLE-PHASE PWM BOOST-TYPE UNIDIRECTIONAL RECTIFIER DOUBLING THE SWITCHING FREQUENCY By SAMIR AHMAD MUSSA, MARCELO LOBO HELDWEIN, MARCIO ORTMANN	[View] [Download]
Abstract: Decades of research have seen single-phase boost-type PWM converters be employed as front-end PFC rectiﬁers in commercial power supplies. The beneﬁts of employing this technology to comply with power quality standards while assuring high efﬁciency and low volume and weight have been observed. However, this work shows that further efforts can be driven into new topologies. In this context, a new topology is introduced, which is able to double the frequency present in the input and output passive components and, thus, working as a full-bridge converter while employing only one additional controlled switch. Furthermore, the switches are utilized during, both, negative and positive mains half-cycles. The theoretical analysis of the topology as well as its use in a PFC application are performed and experimental veriﬁcation is presented in a 1kWprototype employing a current self-control strategy.

	Transformerless STATCOM based on a five-level modular multilevel converter By Grain Philip ADAM	[View] [Download]
Abstract: A transformless static synchronous compensator based on a modular multilevel converter is presented. Its principle of operation, dc link capacitors voltage balancing technique and control system are described in detail. To demonstrate the suitability of the proposed STATCOM and its effectiveness in medium/high voltage applications where converters with higher number of levels are required, several operating scenarios are considered, including reactive power support and flicker mitigation of offshore wind farms connected to the grid through ac submarine cable.