EPE Association: EPE 2011 - DS3j: Topic 14: Converters for Rotating and Linear Generators

EPE 2011 - DS3j: Topic 14: Converters for Rotating and Linear Generators
You are here: EPE Documents > 01 - EPE & EPE ECCE Conference Proceedings > EPE 2011 ECCE Europe - Conference > EPE 2011 - Topic 14: Converters for rotating and linear generators > EPE 2011 - DS3j: Topic 14: Converters for Rotating and Linear Generators

   [return to parent folder]

   A Novel Position Sensorless Control Strategy of Doubly-fed Induction Generator (DFIG) for Wind Turbine
By Wenqiang YANG, Yunfeng LIU [View]
[Download]

Abstract: No abstract provided.

   A Sensorless Control Method for Maximum Power Point Tracking of Wind Turbine Generators
By Zhenyu MA [View]
[Download]

Abstract: Wind energy has been regarded as an environmentally friendly, logistically feasible and economicallyresponsible alternative energy resource. In order to produce as much power as possible in variable speedwind turbine generators, the maximum power point tracking (MPPT) becomes a hotspot of research inthis field. In this paper, a simple control method for maximum power point tracking (MPPT) in a variablespeed wind turbine by using a boost converter without mechanical sensors is proposed. A climbingalgorithm is used to achieve MPPT. Simulation and experimental results are presented to validate theproposed technique.

   Circulating current control of double converter system for wind power generation
By Toshimitsu MORIZANE, Noriyuki KIMURA [View]
[Download]

Abstract: This paper investigates advantages of new double converter system with the induction generator for wind power generation. The PFC converter and the voltage source converter are used. The voltage source converter controls the exciting voltage and frequency to generate the maximum power of the induction generator. The voltage source converter supplies the reactive power only. All real power from the induction generator is converted with the PFC converter. The rating of the voltage source converter becomes larger because of the circulating current through the double converter. It is necessary to suppress the circulating current. The investigation of the control strategy is performed by the theoretical analysis, the simulation, and experiment.

   Control of a Hybrid Excitation Synchronous Generator for a wind energy application
By Emna BEN SEDRINE, Lionel VIDO, Ilhem SLAMA-BELKHODJA, Mohamed GABSI [View]
[Download]

Abstract: The paper’s aim consists on achieving the control of a HESG for a wind turbine application. Thismachine has an auxiliary power source that offers the possibility to control the excitation flux and thusthe machine’s rotation speed. It makes it possible to achieve a variable speed wind turbine thatproperly operates according to a MPPT algorithm.

   Control of SCIG wind farm using a single VSC
By Lluis TRILLA, Oriol GOMIS, Jun LIANG, Tianjun JING, Antoni SUDRIA [View]
[Download]

Abstract: A wind farm with multiple squirrel cage induction generator (SCIG) controlled by a single voltage sourceconverter (VSC) is presented. This configuration removes the need of individual wind turbine converters.The proposed topology is specially interesting for offshore applications which may require HVDC connection. The set of generators is controlled by adjusting the variable slip to its optimum averagevalue. Power maximization is achieved using a wind farm grid with variable frequency and voltage.A VSC-HVDC transmission system is analyzed and a test system composed of twenty turbines and atransmission system is built. A power reduction technique is implemented to stabilize the system duringAC line faults. Steady state and fault ride-through performance are validated using a Real-TimeDigital-Simulator (RTDS).

   Design of Passive Converter for Wind Driven Generators
By Alex VAN DEN BOSSCHE, Plamen YANKOV, Vencislav VALCHEV [View]
[Download]

Abstract: The aim of the paper is to design and to do the fine tuning of a passive converter from apermanent magnet wind generator to a fixed DC link. It shapes a torque speed curve with only passiveelements like diodes, inductors and capacitors. The result is a power/frequency (power/speed)characteristic close to the optimal one for wind turbines. The proposed novel circuit has the advantageto be a reliable, robust, and maintenance free and cost effective solution.

   Fault ride through study of doubly fed induction generator wind turbine in real time simulation environment
By Anssi MÄKINEN, Heikki TUUSA [View]
[Download]

Abstract: In this paper, the fault ride through (FRT) of the doubly fed induction generator (DFIG) wind turbine is studied. The study is done by using a simulation environment in which the network is simulated using Real-Time Digital Simulator (RTDS) and the wind turbine is simulated using dSPACE in real time. The effect of transient flux on the operation of the wind turbine during a network voltage dip is analyzed. The simulation results show that the network voltage support can be maximized if the transient flux is compensated. In addition, it is proposed that different crowbar resistances should be used during the voltage drop and the voltage recovery in order to avoid network short-term voltage stability problems.

   Flicker Mitigation in DFIG Wind Turbine Systems
By Tan Luong VAN, Thanh Hai NGUYEN, Dong-Choon LEE [View]
[Download]

Abstract: This paper presents an approach that mitigates the flicker in doubly-fed induction generator (DFIG) wind turbine systems. The reactive power is controlled to compensate for the flicker from the grid-side converter (GSC). However, it is not sufficient to eliminate the flicker fully in the case of the low grid impedance ratio and the limited capacity of converters. So, a method using an energy storage system (ESS) for the output power smoothening is combined with the reactive power control to reduce the flicker. The PSCAD/EMTDC simulation results show the effectiveness of the proposed method for a 2[MW] DFIG wind turbine system.

   GRID CONNECTION FOR WAVE POWER FARMS
By Marcos BLANCO, Marcos LAFOZ, Dionisio RAMÍREZ [View]
[Download]

Abstract: Linear generators used as direct-drive solution in wave energy conversion have the main advantage ofhigher efficiency and more simple and robust system. However there are some important drawbacksthat should be solved to increase the reliability and feasibility. This paper will study in detail theproblem of the power oscillation introduced intro the electric grid due to the zero speed point at theend of the stroke. Four different solutions are analyzed: first option is to plan the distribution of thepoint absorbers in the wave farm considering the most predominant wave period; second is to controlthe device by means of supplying some reactive PTO force in order to get a more reduced poweroscillation, maintaining a compromise with the resonance situation which is desired to get themaximum energy transference; third consists on controlling the system with a hybrid strategy thatincludes a DC-link voltage control and direct power control; and finally the fourth solution consists onthe addition of energy storage systems, independent of the generator to absorb and develop the excessand defaults of energy. Some of the solutions can be implemented together and the benefits of theresulting system increase.

   Impact of Different Control Schemes on the Life Consumption of Power Electronic Modules for Variable Speed Wind Turbines
By Mahera MUSALLAM, Mark JOHNSON, Meghdad FAZELI, Greg ASHER , Chris BAILEY [View]
[Download]

Abstract: This paper presents a real-time prognosis technique to estimate the life consumption in power modules in a variable-speed wind turbine generator. This approach is used to evaluate the expected life of power electronic modules for a range of drive control strategies in a doubly fed induction (DFIG) generator which is fitted in a variable speed wind turbine including Maximum Power Tracking (MPT), Constant Power Mode (CPM) and Constant Torque Mode (CTM). Using real-time compact thermal models which are integrated with life time models for two common wear-out mechanisms (wire bond and solder substrate ) made it useful to estimate the life consumption of power modules in use. The impact of Maximum Power Tracking, Constant Power Mode and Constant Torque Mode control schemes on the life of power module bond wires and solder layers is demonstrated. The results showed that using MPT control method can affect badly the expected life of power modules simply because it generates more thermal cycling. On the other hand, both the CPM and the CTM have less impact on the life of the power modules used in DFIG converters.

   Improvement of Fault Ride Through Capability of Wind Farm using DFIG Considering SDBR
By Kenneth OKEDU, S.M. MUYEEN, Rion TAKAHASHI, Junji TAMURA [View]
[Download]

Abstract: A new control strategy for improving fault ride-through capability of wind farms composed of fixedand variable speed wind generators has been proposed, in this study. In this new control scheme, asmall series dynamic braking resistor (SDBR) is used in the stator circuit of doubly fed inductiongenerator (DFIG) along with DC-chopper braking resistor. Simulation results show the advantages ofthe combined control strategy for the resumption of normal operation efficiently, with shortenedpossible operating time during grid fault in the multi-machine power system that connects wind farm.

   Indirect Vector Control of an Induction Generator
By Jose Luis DOMÍNGUEZ-GARCÍA, Oriol GOMIS-BELLMUNT, Antoni SUDRIA-ANDREU, Lluis TRILLA-ROMERO [View]
[Download]

Abstract: The paper deals with variable speed squirrel cage induction generator. The whole system is composedby a squirrel cage induction generator and a full power converter connected between generator and grid.The stator-side converter is controlled by means of an indirect vector control, which allows the systemworks without sensors requirement. The stator-side converter controls the torque of the generator andthe grid-side converter regulate the bus voltage and controls the output of the reactive power. Also, it isincluded a torque regulation in order to make the system capable of ride through a low voltage, withoutany extra device. The proposal is tested by means of simulations of a variable wind speed and a voltagesag.

   Investigation of Variable DC Link Voltage Operation of a Permanent Magnet SynchronousGenerator (PMSG) based Wind Turbine with Fully Rated Converters at Steady S
By Upendra DAYARATNE, Sarath TENNAKOON, Jeremy KNIGHT, Noel SHAMMAS [View]
[Download]

Abstract: The variable speed wind turbine with a multi-pole Permanent Magnet Synchronous Generator (PMSG)and Fully Rated Converter (FRC) is a popular choice for modern megawatt scale wind turbines. Twoback to back 2-level pulse width modulated (PWM) voltage source converters are typically used for theFRCs. The two converters are interconnected through the dc link capacitors. The power converters arebased on multi-chip IGBT modules. One way of increasing the inherent reliability of the FRC is toreduce the operating electrical and thermal stresses on these IGBT modules. A higher dc link voltageleads to high IGBT stresses. Higher dc link voltage is also a major contributor to cosmic ray inducedfailures. In the existing FRCs in wind turbine systems, the dc link voltage is maintained at a fixed valuewhile the modulation indices of the two converters are varied. The investigation presented in this paperand authors’ previous work shows that this fixed dc link voltage is significantly higher than the minimumdc link voltage required at the majority of the operating conditions in the maximum power point trackingrange. In the case study based on a multi-megawatt wind turbine, for generator speeds up to about 85\%of the rated speed, the dc link voltage can be lowered to match the ac system voltage by setting themodulation index of the network bridge converter to the maximum value while the modulation index ofthe generator bridge is varied to match the generator voltage. Above this speed, the generator bridgeconverter dominates at certain network conditions where its modulation index needs to be at maximumwhile network bridge modulation index is varied to match the network voltage. Simulation results showsuccessful operation of the system with minimum dc link voltages at steady state. A study on cosmicray induced failure rate calculations shows higher reliability may be achieved when the FRC is operatedwith a variable dc link voltage optimised to minimum values.

   Operating characteristics of a 1 kW three-phase to single-phase matrix converter with hybrid control scheme of power compensation and modulation applied to gas
By Yushi MIURA, Tomofumi AMANO, Toshifumi ISE [View]
[Download]

Abstract: Operating characteristics of a three-phase to single-phase matrix converter applied to a gas enginecogeneration system is investigated in this paper. Application of the matrix converter can enhanceefficiency of a synchronous generator and converter because it improves total power factor of thegenerator and reduce losses in the converter. This matrix converter has no dc link but a small capacitorto compensate single-phase power pulsation, however the capacitor size is still required to be smaller.To reduce its size further, a novel power control scheme has been proposed. According to this controlscheme, instantaneous three-phase power is modulated and power pulsation is partially absorbed byrotor inertia of the generator and gas engine. Primary results of experiment of small output poweroperation have been reported. In this paper, results of experiment of rated output power of 1 kW aredescribed and efficiency measurement of the matrix converter is newly conducted.

   Power Cycling Test Bench for IGBT Power Modules used in Wind Applications
By Dennis WAGENITZ, André WESTERHOLZ, Eike ERDMANN, Andreas HAMBRECHT, Sibylle DIECKERHOFF [View]
[Download]

Abstract: A power cycling test bench is realized for the lifetime analysis of IGBT power modules and for the development of a reliability management system predicting the deterioration of the devices. The focus is on converters for doubly-fed induction generators used in wind turbines. In these applications, due to the low frequent power losses under steady state conditions and due to changing wind conditions, the thermomechanical stress on IGBT power modules is high. The presented test bench offers accelerated ageing of the power semiconductor devices under real load conditions with the phase legs operating from a 1070VDC dc-link allowing sinusoidal load currents up to 800A amplitude at frequencies from 0.1Hz to 13Hz.

   Reduction of Voltage Violations at Remote Location by Intelligent Active and Reactive Power Control of a DFIG Based Wind Turbine
By Jean Patric DA COSTA, Francisco GAFARO, Peter ZACHARIAS [View]
[Download]

Abstract: This paper presents a Doubly Fed Induction Generator (DFIG) with an intelligent active and reactive power control to support the operation in weak networks. The impact of a 850 kW DFIG based Wind Turbine on the voltage profile of a sample distribution feeder is analyzed. Then, the DFIG power capability is designed to support the grid voltage with reactive power compensation. The grid-side converter works in this case as a shunt Static Synchronous Compensator (STATCOM) even if the WT has not mechanical power available. Three different operation modes are used to reduce the DFIG active and reactive power pulsations due to possible unbalanced voltage problems at point of connection. Simulation results are given to illustrate the performance of grid connected DFIG with proposed intelligent active and reactive power control.

   Steady State Lifetime Estimation of Power Semiconductors in Rotor Side Converter of a 2 MW DFIG Wind Turbine via Power Cycling Capability Analysis
By Felix FUCHS, Axel MERTENS [View]
[Download]

Abstract: In this paper the lifetime of the power semiconductors in the rotor side converter of a wind turbine with Doubly Fed Induction Generator (DFIG) concerning their power cycle capability is examined. Based on the offshore wind velocity data of one year (FINO station), the corresponding temperature cycles of the power semiconductors in the converter are simulated for a 2 MW DFIG. The simulation is based on a partial load control strategy and an adequate selection of the power module. With three different cycles-to-failure statistics, the lifetime consumption of one year is estimated.

   Thermal Stress Analysis of IGBT Modules in VSCs for PMSG in Large Offshore Wind Energy Conversion Systems
By Riccardo PITTINI, Salvatore D'ARCO, Magnar HERNES, Astrid PETTERTEIG [View]
[Download]

Abstract: Components for offshore wind farms are required to be highly reliable due to harshenvironmental conditions and poor accessibility for maintenance. Direct-Drive Permanent MagnetSynchronous Generator (PMSG) connected with back to back converters represents an attractivesolution for large offshore Wind Energy Conversion Systems (WECSs). Large direct driven WindTurbine Generators (WTGs) operate at lower speed compared to conventional geared WTs withoperating frequencies that can be as low as 6-13 Hz (e.g. Enercon). The low operating frequenciesintroduce a continuous power cycling of the semiconductor devices and can lead to a reduced lifetimeof the generator side converter. Accurate thermal models integrated with circuital simulations canassist in predicting these stresses and in analyzing countermeasures.This paper describes a method for thermal analysis of power converters based on a customdeveloped module in PSCAD/ETMDC that implements a thermal model running in parallel to theelectrical simulations. The custom module calculates the power dissipation and the temperature of thedevices based on their physical characteristics and on their operating conditions derived from theelectrical simulation. The method is applied for the analysis of a Voltage Source Converter (VSC)connected to the PMSG in a Direct Drive WECS. The simulations prove that the worst operatingcondition for the generator side converter in the sample system examined is represented by the turbinegenerating at its rated power. The temperature swings over the power semiconductors at lower powerand lower generator frequency induce a minor stress. However, the worst operating condition may notcorrespond to the rated power in other cases especially for Direct Drive PMSG-WTs with a relativelylow number of poles.

EPE 2011 - DS3j: Topic 14: Converters for Rotating and Linear Generators
You are here: EPE Documents > 01 - EPE & EPE ECCE Conference Proceedings > EPE 2011 ECCE Europe - Conference > EPE 2011 - Topic 14: Converters for rotating and linear generators > EPE 2011 - DS3j: Topic 14: Converters for Rotating and Linear Generators
	[return to parent folder]

	A Novel Position Sensorless Control Strategy of Doubly-fed Induction Generator (DFIG) for Wind Turbine By Wenqiang YANG, Yunfeng LIU	[View] [Download]
Abstract: No abstract provided.

	A Sensorless Control Method for Maximum Power Point Tracking of Wind Turbine Generators By Zhenyu MA	[View] [Download]
Abstract: Wind energy has been regarded as an environmentally friendly, logistically feasible and economicallyresponsible alternative energy resource. In order to produce as much power as possible in variable speedwind turbine generators, the maximum power point tracking (MPPT) becomes a hotspot of research inthis field. In this paper, a simple control method for maximum power point tracking (MPPT) in a variablespeed wind turbine by using a boost converter without mechanical sensors is proposed. A climbingalgorithm is used to achieve MPPT. Simulation and experimental results are presented to validate theproposed technique.

	Circulating current control of double converter system for wind power generation By Toshimitsu MORIZANE, Noriyuki KIMURA	[View] [Download]
Abstract: This paper investigates advantages of new double converter system with the induction generator for wind power generation. The PFC converter and the voltage source converter are used. The voltage source converter controls the exciting voltage and frequency to generate the maximum power of the induction generator. The voltage source converter supplies the reactive power only. All real power from the induction generator is converted with the PFC converter. The rating of the voltage source converter becomes larger because of the circulating current through the double converter. It is necessary to suppress the circulating current. The investigation of the control strategy is performed by the theoretical analysis, the simulation, and experiment.

	Control of a Hybrid Excitation Synchronous Generator for a wind energy application By Emna BEN SEDRINE, Lionel VIDO, Ilhem SLAMA-BELKHODJA, Mohamed GABSI	[View] [Download]
Abstract: The paper’s aim consists on achieving the control of a HESG for a wind turbine application. Thismachine has an auxiliary power source that offers the possibility to control the excitation flux and thusthe machine’s rotation speed. It makes it possible to achieve a variable speed wind turbine thatproperly operates according to a MPPT algorithm.

	Control of SCIG wind farm using a single VSC By Lluis TRILLA, Oriol GOMIS, Jun LIANG, Tianjun JING, Antoni SUDRIA	[View] [Download]
Abstract: A wind farm with multiple squirrel cage induction generator (SCIG) controlled by a single voltage sourceconverter (VSC) is presented. This configuration removes the need of individual wind turbine converters.The proposed topology is specially interesting for offshore applications which may require HVDC connection. The set of generators is controlled by adjusting the variable slip to its optimum averagevalue. Power maximization is achieved using a wind farm grid with variable frequency and voltage.A VSC-HVDC transmission system is analyzed and a test system composed of twenty turbines and atransmission system is built. A power reduction technique is implemented to stabilize the system duringAC line faults. Steady state and fault ride-through performance are validated using a Real-TimeDigital-Simulator (RTDS).

	Design of Passive Converter for Wind Driven Generators By Alex VAN DEN BOSSCHE, Plamen YANKOV, Vencislav VALCHEV	[View] [Download]
Abstract: The aim of the paper is to design and to do the fine tuning of a passive converter from apermanent magnet wind generator to a fixed DC link. It shapes a torque speed curve with only passiveelements like diodes, inductors and capacitors. The result is a power/frequency (power/speed)characteristic close to the optimal one for wind turbines. The proposed novel circuit has the advantageto be a reliable, robust, and maintenance free and cost effective solution.

	Fault ride through study of doubly fed induction generator wind turbine in real time simulation environment By Anssi MÄKINEN, Heikki TUUSA	[View] [Download]
Abstract: In this paper, the fault ride through (FRT) of the doubly fed induction generator (DFIG) wind turbine is studied. The study is done by using a simulation environment in which the network is simulated using Real-Time Digital Simulator (RTDS) and the wind turbine is simulated using dSPACE in real time. The effect of transient flux on the operation of the wind turbine during a network voltage dip is analyzed. The simulation results show that the network voltage support can be maximized if the transient flux is compensated. In addition, it is proposed that different crowbar resistances should be used during the voltage drop and the voltage recovery in order to avoid network short-term voltage stability problems.

	Flicker Mitigation in DFIG Wind Turbine Systems By Tan Luong VAN, Thanh Hai NGUYEN, Dong-Choon LEE	[View] [Download]
Abstract: This paper presents an approach that mitigates the flicker in doubly-fed induction generator (DFIG) wind turbine systems. The reactive power is controlled to compensate for the flicker from the grid-side converter (GSC). However, it is not sufficient to eliminate the flicker fully in the case of the low grid impedance ratio and the limited capacity of converters. So, a method using an energy storage system (ESS) for the output power smoothening is combined with the reactive power control to reduce the flicker. The PSCAD/EMTDC simulation results show the effectiveness of the proposed method for a 2[MW] DFIG wind turbine system.

	GRID CONNECTION FOR WAVE POWER FARMS By Marcos BLANCO, Marcos LAFOZ, Dionisio RAMÍREZ	[View] [Download]
Abstract: Linear generators used as direct-drive solution in wave energy conversion have the main advantage ofhigher efficiency and more simple and robust system. However there are some important drawbacksthat should be solved to increase the reliability and feasibility. This paper will study in detail theproblem of the power oscillation introduced intro the electric grid due to the zero speed point at theend of the stroke. Four different solutions are analyzed: first option is to plan the distribution of thepoint absorbers in the wave farm considering the most predominant wave period; second is to controlthe device by means of supplying some reactive PTO force in order to get a more reduced poweroscillation, maintaining a compromise with the resonance situation which is desired to get themaximum energy transference; third consists on controlling the system with a hybrid strategy thatincludes a DC-link voltage control and direct power control; and finally the fourth solution consists onthe addition of energy storage systems, independent of the generator to absorb and develop the excessand defaults of energy. Some of the solutions can be implemented together and the benefits of theresulting system increase.

	Impact of Different Control Schemes on the Life Consumption of Power Electronic Modules for Variable Speed Wind Turbines By Mahera MUSALLAM, Mark JOHNSON, Meghdad FAZELI, Greg ASHER , Chris BAILEY	[View] [Download]
Abstract: This paper presents a real-time prognosis technique to estimate the life consumption in power modules in a variable-speed wind turbine generator. This approach is used to evaluate the expected life of power electronic modules for a range of drive control strategies in a doubly fed induction (DFIG) generator which is fitted in a variable speed wind turbine including Maximum Power Tracking (MPT), Constant Power Mode (CPM) and Constant Torque Mode (CTM). Using real-time compact thermal models which are integrated with life time models for two common wear-out mechanisms (wire bond and solder substrate ) made it useful to estimate the life consumption of power modules in use. The impact of Maximum Power Tracking, Constant Power Mode and Constant Torque Mode control schemes on the life of power module bond wires and solder layers is demonstrated. The results showed that using MPT control method can affect badly the expected life of power modules simply because it generates more thermal cycling. On the other hand, both the CPM and the CTM have less impact on the life of the power modules used in DFIG converters.

	Improvement of Fault Ride Through Capability of Wind Farm using DFIG Considering SDBR By Kenneth OKEDU, S.M. MUYEEN, Rion TAKAHASHI, Junji TAMURA	[View] [Download]
Abstract: A new control strategy for improving fault ride-through capability of wind farms composed of fixedand variable speed wind generators has been proposed, in this study. In this new control scheme, asmall series dynamic braking resistor (SDBR) is used in the stator circuit of doubly fed inductiongenerator (DFIG) along with DC-chopper braking resistor. Simulation results show the advantages ofthe combined control strategy for the resumption of normal operation efficiently, with shortenedpossible operating time during grid fault in the multi-machine power system that connects wind farm.

	Indirect Vector Control of an Induction Generator By Jose Luis DOMÍNGUEZ-GARCÍA, Oriol GOMIS-BELLMUNT, Antoni SUDRIA-ANDREU, Lluis TRILLA-ROMERO	[View] [Download]
Abstract: The paper deals with variable speed squirrel cage induction generator. The whole system is composedby a squirrel cage induction generator and a full power converter connected between generator and grid.The stator-side converter is controlled by means of an indirect vector control, which allows the systemworks without sensors requirement. The stator-side converter controls the torque of the generator andthe grid-side converter regulate the bus voltage and controls the output of the reactive power. Also, it isincluded a torque regulation in order to make the system capable of ride through a low voltage, withoutany extra device. The proposal is tested by means of simulations of a variable wind speed and a voltagesag.

	Investigation of Variable DC Link Voltage Operation of a Permanent Magnet SynchronousGenerator (PMSG) based Wind Turbine with Fully Rated Converters at Steady S By Upendra DAYARATNE, Sarath TENNAKOON, Jeremy KNIGHT, Noel SHAMMAS	[View] [Download]
Abstract: The variable speed wind turbine with a multi-pole Permanent Magnet Synchronous Generator (PMSG)and Fully Rated Converter (FRC) is a popular choice for modern megawatt scale wind turbines. Twoback to back 2-level pulse width modulated (PWM) voltage source converters are typically used for theFRCs. The two converters are interconnected through the dc link capacitors. The power converters arebased on multi-chip IGBT modules. One way of increasing the inherent reliability of the FRC is toreduce the operating electrical and thermal stresses on these IGBT modules. A higher dc link voltageleads to high IGBT stresses. Higher dc link voltage is also a major contributor to cosmic ray inducedfailures. In the existing FRCs in wind turbine systems, the dc link voltage is maintained at a fixed valuewhile the modulation indices of the two converters are varied. The investigation presented in this paperand authors’ previous work shows that this fixed dc link voltage is significantly higher than the minimumdc link voltage required at the majority of the operating conditions in the maximum power point trackingrange. In the case study based on a multi-megawatt wind turbine, for generator speeds up to about 85\%of the rated speed, the dc link voltage can be lowered to match the ac system voltage by setting themodulation index of the network bridge converter to the maximum value while the modulation index ofthe generator bridge is varied to match the generator voltage. Above this speed, the generator bridgeconverter dominates at certain network conditions where its modulation index needs to be at maximumwhile network bridge modulation index is varied to match the network voltage. Simulation results showsuccessful operation of the system with minimum dc link voltages at steady state. A study on cosmicray induced failure rate calculations shows higher reliability may be achieved when the FRC is operatedwith a variable dc link voltage optimised to minimum values.

	Operating characteristics of a 1 kW three-phase to single-phase matrix converter with hybrid control scheme of power compensation and modulation applied to gas By Yushi MIURA, Tomofumi AMANO, Toshifumi ISE	[View] [Download]
Abstract: Operating characteristics of a three-phase to single-phase matrix converter applied to a gas enginecogeneration system is investigated in this paper. Application of the matrix converter can enhanceefficiency of a synchronous generator and converter because it improves total power factor of thegenerator and reduce losses in the converter. This matrix converter has no dc link but a small capacitorto compensate single-phase power pulsation, however the capacitor size is still required to be smaller.To reduce its size further, a novel power control scheme has been proposed. According to this controlscheme, instantaneous three-phase power is modulated and power pulsation is partially absorbed byrotor inertia of the generator and gas engine. Primary results of experiment of small output poweroperation have been reported. In this paper, results of experiment of rated output power of 1 kW aredescribed and efficiency measurement of the matrix converter is newly conducted.

	Power Cycling Test Bench for IGBT Power Modules used in Wind Applications By Dennis WAGENITZ, André WESTERHOLZ, Eike ERDMANN, Andreas HAMBRECHT, Sibylle DIECKERHOFF	[View] [Download]
Abstract: A power cycling test bench is realized for the lifetime analysis of IGBT power modules and for the development of a reliability management system predicting the deterioration of the devices. The focus is on converters for doubly-fed induction generators used in wind turbines. In these applications, due to the low frequent power losses under steady state conditions and due to changing wind conditions, the thermomechanical stress on IGBT power modules is high. The presented test bench offers accelerated ageing of the power semiconductor devices under real load conditions with the phase legs operating from a 1070VDC dc-link allowing sinusoidal load currents up to 800A amplitude at frequencies from 0.1Hz to 13Hz.

	Reduction of Voltage Violations at Remote Location by Intelligent Active and Reactive Power Control of a DFIG Based Wind Turbine By Jean Patric DA COSTA, Francisco GAFARO, Peter ZACHARIAS	[View] [Download]
Abstract: This paper presents a Doubly Fed Induction Generator (DFIG) with an intelligent active and reactive power control to support the operation in weak networks. The impact of a 850 kW DFIG based Wind Turbine on the voltage profile of a sample distribution feeder is analyzed. Then, the DFIG power capability is designed to support the grid voltage with reactive power compensation. The grid-side converter works in this case as a shunt Static Synchronous Compensator (STATCOM) even if the WT has not mechanical power available. Three different operation modes are used to reduce the DFIG active and reactive power pulsations due to possible unbalanced voltage problems at point of connection. Simulation results are given to illustrate the performance of grid connected DFIG with proposed intelligent active and reactive power control.

	Steady State Lifetime Estimation of Power Semiconductors in Rotor Side Converter of a 2 MW DFIG Wind Turbine via Power Cycling Capability Analysis By Felix FUCHS, Axel MERTENS	[View] [Download]
Abstract: In this paper the lifetime of the power semiconductors in the rotor side converter of a wind turbine with Doubly Fed Induction Generator (DFIG) concerning their power cycle capability is examined. Based on the offshore wind velocity data of one year (FINO station), the corresponding temperature cycles of the power semiconductors in the converter are simulated for a 2 MW DFIG. The simulation is based on a partial load control strategy and an adequate selection of the power module. With three different cycles-to-failure statistics, the lifetime consumption of one year is estimated.

	Thermal Stress Analysis of IGBT Modules in VSCs for PMSG in Large Offshore Wind Energy Conversion Systems By Riccardo PITTINI, Salvatore D'ARCO, Magnar HERNES, Astrid PETTERTEIG	[View] [Download]
Abstract: Components for offshore wind farms are required to be highly reliable due to harshenvironmental conditions and poor accessibility for maintenance. Direct-Drive Permanent MagnetSynchronous Generator (PMSG) connected with back to back converters represents an attractivesolution for large offshore Wind Energy Conversion Systems (WECSs). Large direct driven WindTurbine Generators (WTGs) operate at lower speed compared to conventional geared WTs withoperating frequencies that can be as low as 6-13 Hz (e.g. Enercon). The low operating frequenciesintroduce a continuous power cycling of the semiconductor devices and can lead to a reduced lifetimeof the generator side converter. Accurate thermal models integrated with circuital simulations canassist in predicting these stresses and in analyzing countermeasures.This paper describes a method for thermal analysis of power converters based on a customdeveloped module in PSCAD/ETMDC that implements a thermal model running in parallel to theelectrical simulations. The custom module calculates the power dissipation and the temperature of thedevices based on their physical characteristics and on their operating conditions derived from theelectrical simulation. The method is applied for the analysis of a Voltage Source Converter (VSC)connected to the PMSG in a Direct Drive WECS. The simulations prove that the worst operatingcondition for the generator side converter in the sample system examined is represented by the turbinegenerating at its rated power. The temperature swings over the power semiconductors at lower powerand lower generator frequency induce a minor stress. However, the worst operating condition may notcorrespond to the rated power in other cases especially for Direct Drive PMSG-WTs with a relativelylow number of poles.