EPE Association: EPE 2001 - Topic 10a: Renewable Energy Systems

EPE 2001 - Topic 10a: Renewable Energy Systems
You are here: EPE Documents > 01 - EPE & EPE ECCE Conference Proceedings > EPE 2001 - Conference > EPE 2001 - Topic 10: POWER ELECTRONICS IN GENERATION, TRANSMISSION AND DISTRIBUTION OF ELECTRICAL ENERGY > EPE 2001 - Topic 10a: Renewable Energy Systems

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   A Measuring Procedure To Assess The Photovoltaic Inverter Performance
By A. Abete; G. Bergamasco; L. Ferraris; F. Spertino [View]
[Download]

Abstract: The grid connected Photovoltaic (PV) systems are essentially constituted by arrays of PV modules and inverters, i.e. the Power Conditioning Units (PCUs) that ensure optimum utilisation for the PV arrays, power quality and safety for the utility. Since the PV generator supplies DC power as a function of solar irradiance and temperature, it is advisable to track the Maximum Power Point (MPP) of the current-voltage I(U) characteristic of PV array with the highest possible accuracy. This task, integrated into the PCU, is performed by a properly controlled DC/DC converter (MPPT). The inverter requirements include the highest possible efficiency for a wide range of irradiance, high power factor and low total harmonic distortion. Since a PV system must be disconnected (islanding prevention) whenever an utility switches off the distribution line, suitable protections shut down the PV system within the required time limits. The paper presents a measuring procedure to determine the PCU performance. This procedure, including new measuring methods, is carried out by a dedicated software for automatic data acquisition. The experimental tests of the procedure determine the following parameters: the MPPT efficiency (how close to maximum power the MPPT is operating); the inverter efficiency, the power factor, and the total harmonic distortion of the AC current supplied to the loads; the islanding time i.e. the time interval between the grid switching off and the automatic disconnection of the PCU. The experimental results are reported with respect to AC modules which consist of PV modules with integrated inverters. The described procedure can be useful for quality control of the inverter manufacturers and for acceptance tests of the system owners. The procedure can be also applied for on-site monitoring of any grid connected PV system.

   A novel intelligent battery charge controller for Standalone PV System
By F. Krim [View]
[Download]

Abstract: A novel, intelligent microcontroller - based battery charge controller (BCC) for stand-alone photovoltaic (PV) system is described. This BCC presents the advantage of permitting maximum power tracking for the battery charging and also real-time battery state-of-charge ( SOC) monitoring. For this purpose, a new efficient control and regulation technique combining coulometric measurement technique and open-circuit voltage (OCV) reading technique has been developed and implemented. A prototype of the BCC has been built and tested. Experimental results show acceptable results confirming higher performance and reliability of this new BCC.

   An improved modular, along the sun pumping system
By T. Martire; C. Joubert; C. Glaize; B. Rouviére [View]
[Download]

Abstract: A photovoltaic system for pumping from deep wells is presented in this paper. The power structure is made of paralleled multilevel DC/DC boost converters used as DC current transformers and coupled with a voltage source inverter. The system was simulated under Matlab / Simulink and its stability has been proven as much as in simulation than in experimentation.

   Application of a Novel Gas Expansion System
By W-R. Canders; J. Heldt; R.K. Jardan; I. Nagy; H.J. Prümper [View]
[Download]

Abstract: A system, consisting of a magnetically suspended high speed turbine-generator machine set and an AC/AC converter is applied in gas expansion stations for pressure reduction. This system, apart from producing active electric power, can also be operated to provide power factor correction and, as the primary energy source is independent from the mains, UPS service. In this paper the operation parallell to the line and operation as UPS is investigated by numerical simulation. The simulation was veryfied by measurements from an installation to be commissioned in summer 2001.

   Comparison of a step-up converter and an electronic DC transformer ...
By K.J.P. Macken; J.J.L. Driesen; R.J.M. Belmans [View]
[Download]

Abstract: One of the issues in a DC bus based power collection system for offshore wind turbines is voltage transformation. For this purpose two DC-Dc converter topologies are suggested and compared. Based on this comparison, the electronic DC transformer is selected. In addition, a design example of a modular 15 kV/60 kV 18 MW, 10kHz electronic DC transformer is given.

   DC-DC conversion for off shore windfarms
By J. Morren; M. Pavlovsky; S.W.H. de Haan; J.A. Ferreira [View]
[Download]

Abstract: This paper describes the design of a high-efficient DC-DC converter, which can be used to convert voltage and current in DC networks. For example offshore windfarms. A comparison is made between two possible DC-converters: the boost step up converter and the Electronic DC-Transformer. This DC-Transformer, consists of a zero-voltage switching, phase-shift controlled, full-bridge IGBTinverter, a high-frequency transformer and a voltage rectifier. In this paper an analysis of such an Electronic DC-Transformer is made. Design results of a 1 MW Electronic DC-Transformer are presented. And also design, simulation and test results of a 3.6 kW, scaled model are presented. The DC-Transformer must be able to control voltage and current. A description of methods to control voltage and current by introducing a varying delay between the two legs of the inverter is given.

   End User Three Levels Vsi For Photovoltaic Generator
By B. Dakyo; R. Hangnilo; J. Barrai; P. Reghem [View]
[Download]

Abstract: The world wide standards, make it obvious that a high power qualitity must be secured for every interface connected to the utility grid. The study concerns results of analytical modelling and laboratory tests of special Reduced Bidirectional Neutral Point Switch inverter, used for sinusoidal current delivery from Photovoltaic generator.

   Experimental Emulation of Wind Turbines and Flywheels
By R. Cardenas; R. Peña; G. M. Asher; J. C. Clare [View]
[Download]

Abstract: This paper describes the experimantal emulation of the static and dynamic characteristics of wind turbines and flywheels in the laboratory by using electrical machines, thus enabling system studies to be undertaken without the need for real turbines or flywheels. It is shown that the emulation of the turbine or flywheel characteristics especially the system inertial characteristics, is not a straightforward problem if the mechanical dynamics are to be preserved. The paper considers certain emulation control structures that must be implemented in order to achieve good emulation under dynamic conditions. Experimental results obtained from 2.5kW prototype are discussed.

   Load Torque Estimators For Wind Turbine Simulators
By D. Luca; C. Nichita; A. D. Diop; B. Dakyo; E. Ceanga [View]
[Download]

Abstract: This paper deals with load torque estimators for a speed-controlled real time wind turbine simulator. The simulator is formed by two subsystems: a real time soft simulator and an electromechanical tracking system. The latter can be speed or torque-controlled. The speed control is an expensive solution since it implies the use of a costly torque transducer, while the torque control is rather difficult to achieve. This paper presents a speed control structure which uses first and second order load torque estimators. The advantages of using this method are discussed and experimental results obtained with the simulator are presented.

   Multi-String-converter: The Next Step in Evolution of String-converter
By M. Meinhardt; G. Cramer [View]
[Download]

Abstract: The development of a PV-converter based on the advanced Multi-String concept results in significantly reduced specific costs while still profiting from the well-known advantages of the String-converter technology developed by ISET and SMA in the mid-nineties. The paper deals with the basic considerations from a system’s point of view that resulted in the development of the Multi-String-converter. The features of the Multi-String-Converter concerning operational behaviour and PV-system design are described. Due to enhanced capacity of the operational control unit the Multi-String-converter can be used additionally for active compensation of harmonics and reactive power in order to improve the power quality. An evaluation of Multi-String-converters in comparison with String-converters or conventional Central-converter concepts is presented. The selected topology and the control strategy for the Multi-String-converter are introduced.

   Offshore Windfarms Electrical Systems Configuration - A Case Study
By P. Bauer; S.W.H. de Haan; M.E.C. Damen; J.T.G. Pierik [View]
[Download]

Abstract: A tool for Evaluation of Configuration of Offshore Windparks is suggested and models of the components studied. Several methods to collect the power can be distinguished and the designer has to evaluate the technical and economical properties of several different configurations. The transmission of the electric power to shore and concepts for the electrical system of offshore wind farms are evaluated with respect to costs due to losses, and energy yield. Both string and star cluster formation and the different types of coupling of variable and constant speed generators are considered. The interest lies primarily in identifying farm configurations with a low cost profile and high efficiency. Case study for a 500MW park for two different locations is presented.

   Optimization of a utility interface in photovoltaic power systems
By J. Gow; J A M Bleijs; R Jones [View]
[Download]

Abstract: This paper discusses techniques involved in the development and optimization of control algorithms associated with large scale photovoltaic power conversion systems. These include maximum power tracking algorithms used by a series of low-power d.c.-d.c. converter modules feeding a common d.c. link, and the control of an inverter forming the utility interface.

   Reactive power regulation in wind farms: control strategies
By J.R. Saenz; A. Tapia; G. Tapia; X. Ostolaza; I. Albizu; F. Pérez-Hidalgo; M. Irizar [View]
[Download]

Abstract: This paper presents a model for a wind farm made up with doubly fed induction machines, some simulation results and some real results of the performance of the wind farm. At the same time, a control strategy has been developed in order to maintain the electric grid parameters into optimal levels. This is possible because the doubly fed induction machine can be regulated with different power factors.

   Rotor-Controlled Generator Systems For Wind Energy Applications
By H-J. Conraths [View]
[Download]

Abstract: In the last two decades renewable energy systems have become of major interest all over the world. Besides the well established generation of electrical energy by hydropower, wind energy systems have proved to be a technical and economical alternative to the conventional thermal power stations. Different concepts of wind turbine systems are on the market, which differ not only in total power and mechanical design, but also in the way the mechanical energy of the rotating turbine is converted to electricity. The increasing power of the wind converters and their integration into wind parks demands for a higher control level, for an efficient control of the speed as well as the active and reactive power of the generator. In the present paper the asynchronous slipring generator with inverter control in the rotor circuit is presented in detail. The major characteristics of the system are discussed.

   Simulation of 12MW wind farm
By L. Jánosi; F. Blaabjerg; A. D. Hansen; J. Bech [View]
[Download]

Abstract: The installation of wind turbines in power systems has developed rapidly through the last 20 years. In this paper a complete simulation model of a 12 MW wind farm is presented using data from a new wind farm. The model describes the behavior from wind to electrical power to the grid. A model of the wind turbine with 2 MW induction generator is presented in details including the control. A set of simulations is performed and they show that it is possible to simulate a complete wind farm from wind to the grid. Simulation and measurements are performed on one wind turbine. They show a nice accordance with each other. The simulation tool can be used to simulate bigger wind farms connected to the grid.

   Wind power plant harmonics reduction with CSI
By P. Puttonen; M. Salo; H. Tuusa [View]
[Download]

Abstract: This paper presents pulse width modulated (PWM) current-source inverters (CSI) with a 6-pulse diode rectifier and a controlled PWM rectifier used in a variable speed wind power application. Due to the high modulation frequency of the CSI with PWM rectifier, the total harmonic distortion of the generator and supply current is much smaller compared to the CSI with diode rectifier, thus yielding almost sinusoidal waveforms and smaller d.c. link L filter. The paper presents some experimental results of the CSI with diode rectifier and controlled PWM rectifier and simulation results dealing with current harmonics.

EPE 2001 - Topic 10a: Renewable Energy Systems
You are here: EPE Documents > 01 - EPE & EPE ECCE Conference Proceedings > EPE 2001 - Conference > EPE 2001 - Topic 10: POWER ELECTRONICS IN GENERATION, TRANSMISSION AND DISTRIBUTION OF ELECTRICAL ENERGY > EPE 2001 - Topic 10a: Renewable Energy Systems
	[return to parent folder]

	A Measuring Procedure To Assess The Photovoltaic Inverter Performance By A. Abete; G. Bergamasco; L. Ferraris; F. Spertino	[View] [Download]
Abstract: The grid connected Photovoltaic (PV) systems are essentially constituted by arrays of PV modules and inverters, i.e. the Power Conditioning Units (PCUs) that ensure optimum utilisation for the PV arrays, power quality and safety for the utility. Since the PV generator supplies DC power as a function of solar irradiance and temperature, it is advisable to track the Maximum Power Point (MPP) of the current-voltage I(U) characteristic of PV array with the highest possible accuracy. This task, integrated into the PCU, is performed by a properly controlled DC/DC converter (MPPT). The inverter requirements include the highest possible efficiency for a wide range of irradiance, high power factor and low total harmonic distortion. Since a PV system must be disconnected (islanding prevention) whenever an utility switches off the distribution line, suitable protections shut down the PV system within the required time limits. The paper presents a measuring procedure to determine the PCU performance. This procedure, including new measuring methods, is carried out by a dedicated software for automatic data acquisition. The experimental tests of the procedure determine the following parameters: the MPPT efficiency (how close to maximum power the MPPT is operating); the inverter efficiency, the power factor, and the total harmonic distortion of the AC current supplied to the loads; the islanding time i.e. the time interval between the grid switching off and the automatic disconnection of the PCU. The experimental results are reported with respect to AC modules which consist of PV modules with integrated inverters. The described procedure can be useful for quality control of the inverter manufacturers and for acceptance tests of the system owners. The procedure can be also applied for on-site monitoring of any grid connected PV system.

	A novel intelligent battery charge controller for Standalone PV System By F. Krim	[View] [Download]
Abstract: A novel, intelligent microcontroller - based battery charge controller (BCC) for stand-alone photovoltaic (PV) system is described. This BCC presents the advantage of permitting maximum power tracking for the battery charging and also real-time battery state-of-charge ( SOC) monitoring. For this purpose, a new efficient control and regulation technique combining coulometric measurement technique and open-circuit voltage (OCV) reading technique has been developed and implemented. A prototype of the BCC has been built and tested. Experimental results show acceptable results confirming higher performance and reliability of this new BCC.

	An improved modular, along the sun pumping system By T. Martire; C. Joubert; C. Glaize; B. Rouviére	[View] [Download]
Abstract: A photovoltaic system for pumping from deep wells is presented in this paper. The power structure is made of paralleled multilevel DC/DC boost converters used as DC current transformers and coupled with a voltage source inverter. The system was simulated under Matlab / Simulink and its stability has been proven as much as in simulation than in experimentation.

	Application of a Novel Gas Expansion System By W-R. Canders; J. Heldt; R.K. Jardan; I. Nagy; H.J. Prümper	[View] [Download]
Abstract: A system, consisting of a magnetically suspended high speed turbine-generator machine set and an AC/AC converter is applied in gas expansion stations for pressure reduction. This system, apart from producing active electric power, can also be operated to provide power factor correction and, as the primary energy source is independent from the mains, UPS service. In this paper the operation parallell to the line and operation as UPS is investigated by numerical simulation. The simulation was veryfied by measurements from an installation to be commissioned in summer 2001.

	Comparison of a step-up converter and an electronic DC transformer ... By K.J.P. Macken; J.J.L. Driesen; R.J.M. Belmans	[View] [Download]
Abstract: One of the issues in a DC bus based power collection system for offshore wind turbines is voltage transformation. For this purpose two DC-Dc converter topologies are suggested and compared. Based on this comparison, the electronic DC transformer is selected. In addition, a design example of a modular 15 kV/60 kV 18 MW, 10kHz electronic DC transformer is given.

	DC-DC conversion for off shore windfarms By J. Morren; M. Pavlovsky; S.W.H. de Haan; J.A. Ferreira	[View] [Download]
Abstract: This paper describes the design of a high-efficient DC-DC converter, which can be used to convert voltage and current in DC networks. For example offshore windfarms. A comparison is made between two possible DC-converters: the boost step up converter and the Electronic DC-Transformer. This DC-Transformer, consists of a zero-voltage switching, phase-shift controlled, full-bridge IGBTinverter, a high-frequency transformer and a voltage rectifier. In this paper an analysis of such an Electronic DC-Transformer is made. Design results of a 1 MW Electronic DC-Transformer are presented. And also design, simulation and test results of a 3.6 kW, scaled model are presented. The DC-Transformer must be able to control voltage and current. A description of methods to control voltage and current by introducing a varying delay between the two legs of the inverter is given.

	End User Three Levels Vsi For Photovoltaic Generator By B. Dakyo; R. Hangnilo; J. Barrai; P. Reghem	[View] [Download]
Abstract: The world wide standards, make it obvious that a high power qualitity must be secured for every interface connected to the utility grid. The study concerns results of analytical modelling and laboratory tests of special Reduced Bidirectional Neutral Point Switch inverter, used for sinusoidal current delivery from Photovoltaic generator.

	Experimental Emulation of Wind Turbines and Flywheels By R. Cardenas; R. Peña; G. M. Asher; J. C. Clare	[View] [Download]
Abstract: This paper describes the experimantal emulation of the static and dynamic characteristics of wind turbines and flywheels in the laboratory by using electrical machines, thus enabling system studies to be undertaken without the need for real turbines or flywheels. It is shown that the emulation of the turbine or flywheel characteristics especially the system inertial characteristics, is not a straightforward problem if the mechanical dynamics are to be preserved. The paper considers certain emulation control structures that must be implemented in order to achieve good emulation under dynamic conditions. Experimental results obtained from 2.5kW prototype are discussed.

	Load Torque Estimators For Wind Turbine Simulators By D. Luca; C. Nichita; A. D. Diop; B. Dakyo; E. Ceanga	[View] [Download]
Abstract: This paper deals with load torque estimators for a speed-controlled real time wind turbine simulator. The simulator is formed by two subsystems: a real time soft simulator and an electromechanical tracking system. The latter can be speed or torque-controlled. The speed control is an expensive solution since it implies the use of a costly torque transducer, while the torque control is rather difficult to achieve. This paper presents a speed control structure which uses first and second order load torque estimators. The advantages of using this method are discussed and experimental results obtained with the simulator are presented.

	Multi-String-converter: The Next Step in Evolution of String-converter By M. Meinhardt; G. Cramer	[View] [Download]
Abstract: The development of a PV-converter based on the advanced Multi-String concept results in significantly reduced specific costs while still profiting from the well-known advantages of the String-converter technology developed by ISET and SMA in the mid-nineties. The paper deals with the basic considerations from a system’s point of view that resulted in the development of the Multi-String-converter. The features of the Multi-String-Converter concerning operational behaviour and PV-system design are described. Due to enhanced capacity of the operational control unit the Multi-String-converter can be used additionally for active compensation of harmonics and reactive power in order to improve the power quality. An evaluation of Multi-String-converters in comparison with String-converters or conventional Central-converter concepts is presented. The selected topology and the control strategy for the Multi-String-converter are introduced.

	Offshore Windfarms Electrical Systems Configuration - A Case Study By P. Bauer; S.W.H. de Haan; M.E.C. Damen; J.T.G. Pierik	[View] [Download]
Abstract: A tool for Evaluation of Configuration of Offshore Windparks is suggested and models of the components studied. Several methods to collect the power can be distinguished and the designer has to evaluate the technical and economical properties of several different configurations. The transmission of the electric power to shore and concepts for the electrical system of offshore wind farms are evaluated with respect to costs due to losses, and energy yield. Both string and star cluster formation and the different types of coupling of variable and constant speed generators are considered. The interest lies primarily in identifying farm configurations with a low cost profile and high efficiency. Case study for a 500MW park for two different locations is presented.

	Optimization of a utility interface in photovoltaic power systems By J. Gow; J A M Bleijs; R Jones	[View] [Download]
Abstract: This paper discusses techniques involved in the development and optimization of control algorithms associated with large scale photovoltaic power conversion systems. These include maximum power tracking algorithms used by a series of low-power d.c.-d.c. converter modules feeding a common d.c. link, and the control of an inverter forming the utility interface.

	Reactive power regulation in wind farms: control strategies By J.R. Saenz; A. Tapia; G. Tapia; X. Ostolaza; I. Albizu; F. Pérez-Hidalgo; M. Irizar	[View] [Download]
Abstract: This paper presents a model for a wind farm made up with doubly fed induction machines, some simulation results and some real results of the performance of the wind farm. At the same time, a control strategy has been developed in order to maintain the electric grid parameters into optimal levels. This is possible because the doubly fed induction machine can be regulated with different power factors.

	Rotor-Controlled Generator Systems For Wind Energy Applications By H-J. Conraths	[View] [Download]
Abstract: In the last two decades renewable energy systems have become of major interest all over the world. Besides the well established generation of electrical energy by hydropower, wind energy systems have proved to be a technical and economical alternative to the conventional thermal power stations. Different concepts of wind turbine systems are on the market, which differ not only in total power and mechanical design, but also in the way the mechanical energy of the rotating turbine is converted to electricity. The increasing power of the wind converters and their integration into wind parks demands for a higher control level, for an efficient control of the speed as well as the active and reactive power of the generator. In the present paper the asynchronous slipring generator with inverter control in the rotor circuit is presented in detail. The major characteristics of the system are discussed.

	Simulation of 12MW wind farm By L. Jánosi; F. Blaabjerg; A. D. Hansen; J. Bech	[View] [Download]
Abstract: The installation of wind turbines in power systems has developed rapidly through the last 20 years. In this paper a complete simulation model of a 12 MW wind farm is presented using data from a new wind farm. The model describes the behavior from wind to electrical power to the grid. A model of the wind turbine with 2 MW induction generator is presented in details including the control. A set of simulations is performed and they show that it is possible to simulate a complete wind farm from wind to the grid. Simulation and measurements are performed on one wind turbine. They show a nice accordance with each other. The simulation tool can be used to simulate bigger wind farms connected to the grid.

	Wind power plant harmonics reduction with CSI By P. Puttonen; M. Salo; H. Tuusa	[View] [Download]
Abstract: This paper presents pulse width modulated (PWM) current-source inverters (CSI) with a 6-pulse diode rectifier and a controlled PWM rectifier used in a variable speed wind power application. Due to the high modulation frequency of the CSI with PWM rectifier, the total harmonic distortion of the generator and supply current is much smaller compared to the CSI with diode rectifier, thus yielding almost sinusoidal waveforms and smaller d.c. link L filter. The paper presents some experimental results of the CSI with diode rectifier and controlled PWM rectifier and simulation results dealing with current harmonics.