EPE Association: EPE 2005 - Topic 15-4a - DS: Power conditioning, line side converters and Power Quality

EPE 2005 - Topic 15-4a - DS: Power conditioning, line side converters and Power Quality
You are here: EPE Documents > 01 - EPE & EPE ECCE Conference Proceedings > EPE 2005 - Conference > EPE 2005 - Topic 15: POWER ELECTRONICS IN TRANSMISSION AND DISTRIBUTION OF ELECTRICAL ENERGY > EPE 2005 - Topic 15-4a - DS: Power conditioning, line side converters and Power Quality

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   A COMPARISON OF BASIC PROPERTIES OF SINGLE-PHASE SERIAL AC VOLTAGE CONTROLLERS USING BIPOLAR PWM CHOPPER
By JANKOWSKI Maciej; FEDYCZAK Zbigniew [View]
[Download]

Abstract: This paper deals with two solutions for single-phase serial AC voltage controllers with bipolar PWM chopper. In these converters, either the bipolar PWM AC matrix chopper (MC) based on full-bridge topology or the bipolar PWM AC matrix-reactance chopper (MRC) based on Ćuk B2 topology and auxiliary transformer is applied. The MRC, in distinction to MC, has a magnitude of voltage transformation function greater than one. The peak detection method in the control circuit of both controller solutions is applied for fast control of the load voltage changes. The steady state theoretical analysis based on averaged models and transient state analysis based on small-signal averaged models of the presented controllers are employed. Furthermore, simulation and experimental test results are provided to confirm and verify the theoretical approach. On the basis of these investigations a comparative study of the results showing performance of both controller solutions is presented

   A STUDY OF INSULATION FAILURE IN A HIGH VOLTAGE CURRENT TRANSFORMER
By NICOLAE Dan Valentin; JIMOH Adisa; MAHLASELA Vusi [View]
[Download]

Abstract: The ageing and deterioration of insulation in high voltage (HV) plants have been a source of concerns to utilities. Breakdown of insulation leads to failures of HV equipment. The ageing and eventual failure of insulation in a high voltage current transformer (HVCT) is the subject of investigation in this paper. A lumped parameter model of HVCT is developed. This model is used to study the influence of deteriorating and failed insulation on the state variables of the HVCT. Some possible scenarios that could lead to a CT failure are investigated in this paper. For all the scenarios considered, steady and transient equations relating the state variables of the model have been developed and analyzed. The objectives of these analyses are to establish the behavioural characteristics of the state variables, establish the interactions between these variables, and investigate the possible generations of harmonics under the various scenarios of deteriorating and outright failure of insulation in the CT. The paper concludes with a discussion of the results obtained.

   Analysis of Thyristor Switch in Power Conditioning System with SMES
By PASKO Szymon; BUHRER Carsten; ZYGMANOWSKI Marcin; KELLERS Jurgen; GRZESIK BogusłAw; KRIJGSMAN Josien; MICHALAK JarosłAw; STĘPIEŃ Mariusz; BI [View]
[Download]

Abstract: Ensuring high level of power quality (PQ) is one of most important issues in supplying in industry loads. There exist some critical types of loads that should be protected from any voltage disturbance. If any voltage disturbance (like voltage sag or dip) occurs an alternative energy source is used to ensure constant voltage amplitude across protected load. In described power conditioning system (PCS), power electronic system is connected in parallel to group of protected loads. The PCS together with protected loads have to be disconnecting from the mains in the case of voltage sag or dip occurs. Disconnection is necessary, if any voltage disturbance occurs, to prevent from delivering energy to low impedance part of power system (the mains in such case) from energy storage that is contained in the PCS (in this situation – high temperature Superconducting Magnetic Energy Storage (SMES)). In described system breaking the connection between the mains and the load takes place thanks to the thyristor switch (TS). Disconnection and reconnection modes of operation of the PCS are particularly described and analysed in the paper. To obtain relatively low turn off time of thyristor switch a new method of controlling the PCS has been proposed that can assist turning off process of the TS and decreasing turn off time. The resynchronisation of the load voltage and the mains voltage of the PCS is also presented in the paper. It is used to limit the amplitude of the mains current after reconnection process. Influences of resynchronisation and reconnection processes on load voltage are also analysed. To proof correctness of designed controller the simulation and experimental results have been presented and discussed in the paper.

   Applications of power electronics converters for control of specific parameters in high voltage transmission network
By BLAJSZCZAK Grzegorz [View]
[Download]

Abstract: The paper presents possibility of applications of high voltage power electronic converters for different ancillary services that enable proper operation of transmission network and entire power grid system. A short description of these services is provided for better explanation of the converter functions. The functions that can prevent a black-out are underlined.

   Calculation of a three phase fault in a network with a power electronic based Fault Current Limiter (FCL)
By BARTMANN Andreas; RUBENBAUER Hubert; HEROLD Gerhard [View]
[Download]

Abstract: The model of a Fault Current Limiter (FCL) based on a six-pulse thyristor rectifier with a freewheeling diode is described in this paper. The FCL is connected to a transformer’s neutral terminal. Furthermore the state space description and the calculation method are presented. A three phase fault from the beginning till its clearing demonstrates the function of the FCL with different parameters.

   Comparison of SMES and ScES Based Power Conditioning Systems
By KELLERS Jurgen; KRIJGSMAN Josien; GRZESIK Boguslaw; BUHRER Carsten; STEPIEN Mariusz; BISKUP Tomasz; PASKO Szymon; ZYGMANOWSKI Marcin; MICHALAK Jaroslaw [View]
[Download]

Abstract: The selection of the less expensive Power Conditioning System (PCS) is the aim of the work where two types of PCS are taken into consideration. The first type of PCS is based on Superconducting Magnetic Energy Storage (SMES) while the second one is based on Supercapacitor Energy Storage (ScES). The comparison is based on installed power as the criterion. An illustrative example is given in the work.

   Compensating the Line Current Harmonics with Three-Switch Current-Source PWM Rectifier
By SALO Mika [View]
[Download]

Abstract: In recent years, harmonic currents caused by power converters have been serious problem in many electric power systems. Thyristor and diode converters are widely used in industrial applications these days and they can be considered as a typical example causing that electrical pollution. In this paper the capability of 3-switch current current-source rectifier (3SW-CSR) to compensate harmonics produced by other converters is studied. The presented theory and experimental tests show that 3SW-CSR offers effective and low-cost solution to improve the quality of electrical power in applications where three-phase rectifier are needed.

   Converter control and stability of the 110-kV railway grid with the increasing use of the static frequency converters
By HAUBRICH Han; ZYNOVCHENKO Andriy; LI Feng; TREIGE Peter; XIE Jian [View]
[Download]

Abstract: Compared to generators and mechanical frequency converters, static frequency converters have no rotating mass and can’t be overloaded. In this work converter control and stability of the 110 kV railway grid with the increasing use of frequency converter are investigated by digital dynamic simulations. Results and models of the simulations are presented.

   Development of SMES using dry type superconducting coil designed to protect from momentary voltage drop
By OKUMURA Kagao; IWAKUMA Masataka; SUMIYOSHI Fumio; CHIKARAISHI Hirotaka; MITO Toshiyuki [View]
[Download]

Abstract: To protect a facility from momentary voltage drop, we are studying a short time SMES system. For this SMES, a helium free superconducting pulse coil using conduction cooling is developed.Also short time power converters and a high-speed voltage drop detector for a 1MJ class SMES are designed. To confirm the design of components, a 100kJ class demo coil and converters are constructed and tested.

   FEEDER' LOAD BALANCING
By NICOLAE Dan Valentin; JIMOH Adisa; SITI Willy [View]
[Download]

Abstract: The electrical distribution system is to ensure that an adequate supply is available to meet the estimated load of the consumers in both the near and more distant future. This must of course, be done for minimum possible cost consistent with satisfactory reliability and quality of the supply. In order to avoid excessive voltage drop and minimize technical loss, it may be economical to install apparatus to balance or partially balance the loads. It is believed that the technology to achieve an automatic load balancing lends itself readily for the implementation of different types of algorithms for automatically reconfiguring a distribution network system for optimal performance.

   Five Level Neutral-Point Clamped Inverter for a Dynamic Voltage Restorer
By DE DONCKER Rik W.; ROMAUS Christoph; MEYER Christoph [View]
[Download]

Abstract: DVRs are of utmost importance to secure sensitive loads from voltage sags. Especially, in medium-voltage grids the demand for securing larger loads has increased significantly. Installing higher power levels leads to the consideration of multi-level converters with an increased number of levels. Therefore, the 5-level NPC could be an interesting solution. The drawback of this topology is that its voltage levels are not stable for active power transmission. This paper presents a method to allow a short-time stable operation of this topology - without oversizing the DC-link capacitor - and therefore the usage of this converter for DVR applications.

   Harmonic Calculation Software for Industrial Applications with Adjustable Speed Drives
By STEFFAN Hansen; FREDE Blaabjerg; LUCIAN Asiminoaei [View]
[Download]

Abstract: This paper describes the evaluation of a new harmonic calculation software. By using a combination of a pre-stored database and new interpolation techniques the software can very fast provide the harmonic data on real applications. The harmonic results obtained with this software have acceptable precision even with limited input data. The evaluation concludes here that this approach is very practical compared to other advanced harmonic analysis methods. The results are supported by comparisons of calculations and measurements given in an industrial application.

   High Frequency Modeling of DC/AC Converters
By CONSOLI Alfio; TESTA Antonio; CACCIATO Mario; SCARCELLA Giuseppe; DE CARO Salvatore [View]
[Download]

Abstract: The paper proposes a new method to measure the High Frequency (HF) current components in electronic converters and defines a model able to address the converter operation on a wide frequency range (100 kHz ÷ 30 MHz). Main features of the proposed approach are that the developed model is calculated by a suitable automatic procedure that performs the measurements during the normal operations of the converter, instead of using HF circuital sub-models of the power devices, only related to the parasitic inner parameters, connection wires, and diodes, and therefore regardless the modulation technique. In this way, the HF admittance of the converter has been calculated taking to account the instantaneous switches configuration and, therefore on the basis of the switching PWM strategy. According to the proposed approach, the proposed dynamic HF model of the power converter is composed by several black boxes, each related to a single converter status or to a groups of states with the same response. Each box acts differently to a HF voltage excitation, according to the number of devices that are contemporary on and off, while the converter is modulated. By knowing the PWM modulation strategy, the sequence of the states is unambiguous and therefore the model of the converter is entirely definite. Simulations and experimental results are presented in order to evaluate the consistence of the proposed approach.

   HYBRID ENERGY STORAGE SYSTEM BASED ON COMPRESSED AIR AND SUPERCAPACITORS WITH MAXIMUM EFFICIENCY POINT TRACKING
By RUFER Alfred; LEMOFOUET Sylvain [View]
[Download]

Abstract: Beside the high-capacity storage facilities based on hydro-power technologies, electrochemical solutions are the today's candidate for storage for renewable energy sources. However, limited life-cycles and sustainability of batteries are often inhibiting factors. This paper presents a hybrid energy storage system with high life cycle, based on Compressed Air Energy Storage. The storage and discharge are done within maximum efficiency conditions. As the maximum efficiency conditions impose the level of converted power, an intermittent time-modulated operation mode is applied to the thermodynamic converter to obtain a variable converted power. A smoothly variable output power is achieved with the help of a supercapacitive auxiliary storage device used as a filter. The paper describes the concept of the system, the power-electronic interface circuits and especially the Maximum Efficiency Point Tracking algorithm and the strategy used to vary the output power. In addition, the paper describes the principles of higher efficiency storage systems where the air machine is replaced by an oil hydro-pneumatic converter, used under isothermal conditions. Practical results are reported, that have been recorded from a low-power pneumatic motor coupled to a small DC generator for the purely pneumatic system, and from a first prototype of the oil-hydraulics and pneumatic system. Some economical considerations are also made, through a comparative cost evaluation of the presented hydro-pneumatic systems and a lead acid batteries system, in the context of a stand alone photovoltaic home application.

   New assessing criteria for the contribution of nonlinear loads to the supply voltage harmonic distortion
By DELLAQUILA Antonio; ZANCHETTA Pericle; MARINELLI Maria [View]
[Download]

Abstract: This paper presents the definition of a new weighted power quality index to be used to coherently evaluate the level of harmonic distortion in electrical systems and quantify the share of responsibility between loads and mains. Simulation and experimental tests carried out under different load conditions, show the proposed performance index gives correct information about the actual contribution of a non-linear load to the voltage quality at the point of common coupling (PCC).

   Optimal control of Static VAr Compensators in power supply systems with electrical arc furnaces
By PRINZ Steffen; STADE Dietrich; PIETZSCH Hermann [View]
[Download]

Abstract: Electrical arc furnaces (EAF) with power ratings of, in-part, far more than 100 MVA, cause voltage fluctuations and flickers in the supplying power system. Static VAr Compensators (SVC) are typically used for reactive power correction. This paper presents a solution for how to obtain an optimum flicker reduction at a comparatively low compensator power rating by an anti-windup extension of the controller. Based on an example of dimensioning a SVC for a steel plant grid with high-power A.C. EAF savings amounting to approx. 2.1 M US$ can be realised by implementing the proposed amendments to the compensator control. The researched compensator solution represents an optimum from the technical as well as from the economic point of view.

   Power Factor Correction of Three-Phase Diode Rectifiers Using Optimum Ripple Currents Injection
By SARV Vello; SAKKOS Tiiu [View]
[Download]

Abstract: Two new schemes of low-distorting three-phase diode-bridge rectifiers with capacitive smoothing of the output voltage are proposed, analyzed, and verified. The harmonic distortion reduction technique proposed is based on optimum injection of the third-, sixth-, and ninth-harmonic ripple currents. To improve the efficiency, the third-harmonic ripple power is re-rectified using a low-power auxiliary AC-DC converter. Function of the sixth-harmonic current branch is, firstly, to compensate inductive current component of the smoothing inductors and, secondly, to induce a small active sixth-harmonic current component that enables to reduce the total harmonic distortion THD about 2\%. The ninth-harmonic current branch enables a further reduction of the THD about 1.5\%. In proposed schemes, low values of the THD hold in wide range of the load and supply-voltage variation.

   SINGLE-PHASE SERIAL AC VOLTAGE CONTROLLER BASED ON BIPOLAR MATRIX-REACTANCE CHOPPER
By FEDYCZAK Zbigniew; FRĄCKOWIAK Leszek; JANKOWSKI Maciej [View]
[Download]

Abstract: This paper deals with a new solution for a single-phase serial AC voltage controller. In this converter the bipolar PWM AC Matrix-Reactance Chopper (MRC), based on Ćuk B2 topology and auxiliary transformer, are applied. The MRC applied in this controller make possible the bipolar voltage conversion with magnitude of voltage transformation function greater than one. The peak voltage detection method in the control circuit is applied to fast control of the load voltage changes. The paper presents a detailed description of the controller. The steady state theoretical analysis based on an averaged model of the presented controller is used. Furthermore, simulation and experimental test results of 3 kVA models are provided to confirm and verify the theoretical approach.

EPE 2005 - Topic 15-4a - DS: Power conditioning, line side converters and Power Quality
You are here: EPE Documents > 01 - EPE & EPE ECCE Conference Proceedings > EPE 2005 - Conference > EPE 2005 - Topic 15: POWER ELECTRONICS IN TRANSMISSION AND DISTRIBUTION OF ELECTRICAL ENERGY > EPE 2005 - Topic 15-4a - DS: Power conditioning, line side converters and Power Quality
	[return to parent folder]

	A COMPARISON OF BASIC PROPERTIES OF SINGLE-PHASE SERIAL AC VOLTAGE CONTROLLERS USING BIPOLAR PWM CHOPPER By JANKOWSKI Maciej; FEDYCZAK Zbigniew	[View] [Download]
Abstract: This paper deals with two solutions for single-phase serial AC voltage controllers with bipolar PWM chopper. In these converters, either the bipolar PWM AC matrix chopper (MC) based on full-bridge topology or the bipolar PWM AC matrix-reactance chopper (MRC) based on Ćuk B2 topology and auxiliary transformer is applied. The MRC, in distinction to MC, has a magnitude of voltage transformation function greater than one. The peak detection method in the control circuit of both controller solutions is applied for fast control of the load voltage changes. The steady state theoretical analysis based on averaged models and transient state analysis based on small-signal averaged models of the presented controllers are employed. Furthermore, simulation and experimental test results are provided to confirm and verify the theoretical approach. On the basis of these investigations a comparative study of the results showing performance of both controller solutions is presented

	A STUDY OF INSULATION FAILURE IN A HIGH VOLTAGE CURRENT TRANSFORMER By NICOLAE Dan Valentin; JIMOH Adisa; MAHLASELA Vusi	[View] [Download]
Abstract: The ageing and deterioration of insulation in high voltage (HV) plants have been a source of concerns to utilities. Breakdown of insulation leads to failures of HV equipment. The ageing and eventual failure of insulation in a high voltage current transformer (HVCT) is the subject of investigation in this paper. A lumped parameter model of HVCT is developed. This model is used to study the influence of deteriorating and failed insulation on the state variables of the HVCT. Some possible scenarios that could lead to a CT failure are investigated in this paper. For all the scenarios considered, steady and transient equations relating the state variables of the model have been developed and analyzed. The objectives of these analyses are to establish the behavioural characteristics of the state variables, establish the interactions between these variables, and investigate the possible generations of harmonics under the various scenarios of deteriorating and outright failure of insulation in the CT. The paper concludes with a discussion of the results obtained.

	Analysis of Thyristor Switch in Power Conditioning System with SMES By PASKO Szymon; BUHRER Carsten; ZYGMANOWSKI Marcin; KELLERS Jurgen; GRZESIK BogusłAw; KRIJGSMAN Josien; MICHALAK JarosłAw; STĘPIEŃ Mariusz; BI	[View] [Download]
Abstract: Ensuring high level of power quality (PQ) is one of most important issues in supplying in industry loads. There exist some critical types of loads that should be protected from any voltage disturbance. If any voltage disturbance (like voltage sag or dip) occurs an alternative energy source is used to ensure constant voltage amplitude across protected load. In described power conditioning system (PCS), power electronic system is connected in parallel to group of protected loads. The PCS together with protected loads have to be disconnecting from the mains in the case of voltage sag or dip occurs. Disconnection is necessary, if any voltage disturbance occurs, to prevent from delivering energy to low impedance part of power system (the mains in such case) from energy storage that is contained in the PCS (in this situation – high temperature Superconducting Magnetic Energy Storage (SMES)). In described system breaking the connection between the mains and the load takes place thanks to the thyristor switch (TS). Disconnection and reconnection modes of operation of the PCS are particularly described and analysed in the paper. To obtain relatively low turn off time of thyristor switch a new method of controlling the PCS has been proposed that can assist turning off process of the TS and decreasing turn off time. The resynchronisation of the load voltage and the mains voltage of the PCS is also presented in the paper. It is used to limit the amplitude of the mains current after reconnection process. Influences of resynchronisation and reconnection processes on load voltage are also analysed. To proof correctness of designed controller the simulation and experimental results have been presented and discussed in the paper.

	Applications of power electronics converters for control of specific parameters in high voltage transmission network By BLAJSZCZAK Grzegorz	[View] [Download]
Abstract: The paper presents possibility of applications of high voltage power electronic converters for different ancillary services that enable proper operation of transmission network and entire power grid system. A short description of these services is provided for better explanation of the converter functions. The functions that can prevent a black-out are underlined.

	Calculation of a three phase fault in a network with a power electronic based Fault Current Limiter (FCL) By BARTMANN Andreas; RUBENBAUER Hubert; HEROLD Gerhard	[View] [Download]
Abstract: The model of a Fault Current Limiter (FCL) based on a six-pulse thyristor rectifier with a freewheeling diode is described in this paper. The FCL is connected to a transformer’s neutral terminal. Furthermore the state space description and the calculation method are presented. A three phase fault from the beginning till its clearing demonstrates the function of the FCL with different parameters.

	Comparison of SMES and ScES Based Power Conditioning Systems By KELLERS Jurgen; KRIJGSMAN Josien; GRZESIK Boguslaw; BUHRER Carsten; STEPIEN Mariusz; BISKUP Tomasz; PASKO Szymon; ZYGMANOWSKI Marcin; MICHALAK Jaroslaw	[View] [Download]
Abstract: The selection of the less expensive Power Conditioning System (PCS) is the aim of the work where two types of PCS are taken into consideration. The first type of PCS is based on Superconducting Magnetic Energy Storage (SMES) while the second one is based on Supercapacitor Energy Storage (ScES). The comparison is based on installed power as the criterion. An illustrative example is given in the work.

	Compensating the Line Current Harmonics with Three-Switch Current-Source PWM Rectifier By SALO Mika	[View] [Download]
Abstract: In recent years, harmonic currents caused by power converters have been serious problem in many electric power systems. Thyristor and diode converters are widely used in industrial applications these days and they can be considered as a typical example causing that electrical pollution. In this paper the capability of 3-switch current current-source rectifier (3SW-CSR) to compensate harmonics produced by other converters is studied. The presented theory and experimental tests show that 3SW-CSR offers effective and low-cost solution to improve the quality of electrical power in applications where three-phase rectifier are needed.

	Converter control and stability of the 110-kV railway grid with the increasing use of the static frequency converters By HAUBRICH Han; ZYNOVCHENKO Andriy; LI Feng; TREIGE Peter; XIE Jian	[View] [Download]
Abstract: Compared to generators and mechanical frequency converters, static frequency converters have no rotating mass and can’t be overloaded. In this work converter control and stability of the 110 kV railway grid with the increasing use of frequency converter are investigated by digital dynamic simulations. Results and models of the simulations are presented.

	Development of SMES using dry type superconducting coil designed to protect from momentary voltage drop By OKUMURA Kagao; IWAKUMA Masataka; SUMIYOSHI Fumio; CHIKARAISHI Hirotaka; MITO Toshiyuki	[View] [Download]
Abstract: To protect a facility from momentary voltage drop, we are studying a short time SMES system. For this SMES, a helium free superconducting pulse coil using conduction cooling is developed.Also short time power converters and a high-speed voltage drop detector for a 1MJ class SMES are designed. To confirm the design of components, a 100kJ class demo coil and converters are constructed and tested.

	FEEDER' LOAD BALANCING By NICOLAE Dan Valentin; JIMOH Adisa; SITI Willy	[View] [Download]
Abstract: The electrical distribution system is to ensure that an adequate supply is available to meet the estimated load of the consumers in both the near and more distant future. This must of course, be done for minimum possible cost consistent with satisfactory reliability and quality of the supply. In order to avoid excessive voltage drop and minimize technical loss, it may be economical to install apparatus to balance or partially balance the loads. It is believed that the technology to achieve an automatic load balancing lends itself readily for the implementation of different types of algorithms for automatically reconfiguring a distribution network system for optimal performance.

	Five Level Neutral-Point Clamped Inverter for a Dynamic Voltage Restorer By DE DONCKER Rik W.; ROMAUS Christoph; MEYER Christoph	[View] [Download]
Abstract: DVRs are of utmost importance to secure sensitive loads from voltage sags. Especially, in medium-voltage grids the demand for securing larger loads has increased significantly. Installing higher power levels leads to the consideration of multi-level converters with an increased number of levels. Therefore, the 5-level NPC could be an interesting solution. The drawback of this topology is that its voltage levels are not stable for active power transmission. This paper presents a method to allow a short-time stable operation of this topology - without oversizing the DC-link capacitor - and therefore the usage of this converter for DVR applications.

	Harmonic Calculation Software for Industrial Applications with Adjustable Speed Drives By STEFFAN Hansen; FREDE Blaabjerg; LUCIAN Asiminoaei	[View] [Download]
Abstract: This paper describes the evaluation of a new harmonic calculation software. By using a combination of a pre-stored database and new interpolation techniques the software can very fast provide the harmonic data on real applications. The harmonic results obtained with this software have acceptable precision even with limited input data. The evaluation concludes here that this approach is very practical compared to other advanced harmonic analysis methods. The results are supported by comparisons of calculations and measurements given in an industrial application.

	High Frequency Modeling of DC/AC Converters By CONSOLI Alfio; TESTA Antonio; CACCIATO Mario; SCARCELLA Giuseppe; DE CARO Salvatore	[View] [Download]
Abstract: The paper proposes a new method to measure the High Frequency (HF) current components in electronic converters and defines a model able to address the converter operation on a wide frequency range (100 kHz ÷ 30 MHz). Main features of the proposed approach are that the developed model is calculated by a suitable automatic procedure that performs the measurements during the normal operations of the converter, instead of using HF circuital sub-models of the power devices, only related to the parasitic inner parameters, connection wires, and diodes, and therefore regardless the modulation technique. In this way, the HF admittance of the converter has been calculated taking to account the instantaneous switches configuration and, therefore on the basis of the switching PWM strategy. According to the proposed approach, the proposed dynamic HF model of the power converter is composed by several black boxes, each related to a single converter status or to a groups of states with the same response. Each box acts differently to a HF voltage excitation, according to the number of devices that are contemporary on and off, while the converter is modulated. By knowing the PWM modulation strategy, the sequence of the states is unambiguous and therefore the model of the converter is entirely definite. Simulations and experimental results are presented in order to evaluate the consistence of the proposed approach.

	HYBRID ENERGY STORAGE SYSTEM BASED ON COMPRESSED AIR AND SUPERCAPACITORS WITH MAXIMUM EFFICIENCY POINT TRACKING By RUFER Alfred; LEMOFOUET Sylvain	[View] [Download]
Abstract: Beside the high-capacity storage facilities based on hydro-power technologies, electrochemical solutions are the today's candidate for storage for renewable energy sources. However, limited life-cycles and sustainability of batteries are often inhibiting factors. This paper presents a hybrid energy storage system with high life cycle, based on Compressed Air Energy Storage. The storage and discharge are done within maximum efficiency conditions. As the maximum efficiency conditions impose the level of converted power, an intermittent time-modulated operation mode is applied to the thermodynamic converter to obtain a variable converted power. A smoothly variable output power is achieved with the help of a supercapacitive auxiliary storage device used as a filter. The paper describes the concept of the system, the power-electronic interface circuits and especially the Maximum Efficiency Point Tracking algorithm and the strategy used to vary the output power. In addition, the paper describes the principles of higher efficiency storage systems where the air machine is replaced by an oil hydro-pneumatic converter, used under isothermal conditions. Practical results are reported, that have been recorded from a low-power pneumatic motor coupled to a small DC generator for the purely pneumatic system, and from a first prototype of the oil-hydraulics and pneumatic system. Some economical considerations are also made, through a comparative cost evaluation of the presented hydro-pneumatic systems and a lead acid batteries system, in the context of a stand alone photovoltaic home application.

	New assessing criteria for the contribution of nonlinear loads to the supply voltage harmonic distortion By DELLAQUILA Antonio; ZANCHETTA Pericle; MARINELLI Maria	[View] [Download]
Abstract: This paper presents the definition of a new weighted power quality index to be used to coherently evaluate the level of harmonic distortion in electrical systems and quantify the share of responsibility between loads and mains. Simulation and experimental tests carried out under different load conditions, show the proposed performance index gives correct information about the actual contribution of a non-linear load to the voltage quality at the point of common coupling (PCC).

	Optimal control of Static VAr Compensators in power supply systems with electrical arc furnaces By PRINZ Steffen; STADE Dietrich; PIETZSCH Hermann	[View] [Download]
Abstract: Electrical arc furnaces (EAF) with power ratings of, in-part, far more than 100 MVA, cause voltage fluctuations and flickers in the supplying power system. Static VAr Compensators (SVC) are typically used for reactive power correction. This paper presents a solution for how to obtain an optimum flicker reduction at a comparatively low compensator power rating by an anti-windup extension of the controller. Based on an example of dimensioning a SVC for a steel plant grid with high-power A.C. EAF savings amounting to approx. 2.1 M US$ can be realised by implementing the proposed amendments to the compensator control. The researched compensator solution represents an optimum from the technical as well as from the economic point of view.

	Power Factor Correction of Three-Phase Diode Rectifiers Using Optimum Ripple Currents Injection By SARV Vello; SAKKOS Tiiu	[View] [Download]
Abstract: Two new schemes of low-distorting three-phase diode-bridge rectifiers with capacitive smoothing of the output voltage are proposed, analyzed, and verified. The harmonic distortion reduction technique proposed is based on optimum injection of the third-, sixth-, and ninth-harmonic ripple currents. To improve the efficiency, the third-harmonic ripple power is re-rectified using a low-power auxiliary AC-DC converter. Function of the sixth-harmonic current branch is, firstly, to compensate inductive current component of the smoothing inductors and, secondly, to induce a small active sixth-harmonic current component that enables to reduce the total harmonic distortion THD about 2\%. The ninth-harmonic current branch enables a further reduction of the THD about 1.5\%. In proposed schemes, low values of the THD hold in wide range of the load and supply-voltage variation.

	SINGLE-PHASE SERIAL AC VOLTAGE CONTROLLER BASED ON BIPOLAR MATRIX-REACTANCE CHOPPER By FEDYCZAK Zbigniew; FRĄCKOWIAK Leszek; JANKOWSKI Maciej	[View] [Download]
Abstract: This paper deals with a new solution for a single-phase serial AC voltage controller. In this converter the bipolar PWM AC Matrix-Reactance Chopper (MRC), based on Ćuk B2 topology and auxiliary transformer, are applied. The MRC applied in this controller make possible the bipolar voltage conversion with magnitude of voltage transformation function greater than one. The peak voltage detection method in the control circuit is applied to fast control of the load voltage changes. The paper presents a detailed description of the controller. The steady state theoretical analysis based on an averaged model of the presented controller is used. Furthermore, simulation and experimental test results of 3 kVA models are provided to confirm and verify the theoretical approach.