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EPE 2007 - Subtopic 13-7 - DS: Adjustable speed generation systems
You are here: EPE Documents > 01 - EPE & EPE ECCE Conference Proceedings > EPE 2007 - Conference > EPE 2007 - Topic 13: 'Electrical energy generating systems, renewable energy systems' > EPE 2007 - Subtopic 13-7 - DS: Adjustable speed generation systems
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	A Comparative Study of Steady-State Characteristics of Permanent Magnet Synchronous Generator Systems   By KATO Shinji; INUI Yoshitaka; MICHIHIRA Masakazu	[View]   [Download]
Abstract: The steady-state characteristics of a novel wind generator system proposed by the present authors are discussed in comparison with the conventional wind generator system consisting of a permanent magnet synchronous generator, a three-phase diode bridge rectifier, and so on. The simulation and experimental results show the ripple of the DC current and developed torque in the proposed system is significantly reduced by about 70\%. Furthermore, the efficiency of the generator is improved by more than 3\%. The advantage in the proposed system is that a fractional smoothing reactor can be used to draw a DC current without ripple, and a higher DC voltage compared to the conventional system is easily produced.
	A Control Strategy for an Autonomous Induction Generator Taking the Saturation Effect into Account    By REKIOUA Djamila	[View]   [Download]
Abstract: In this paper, we present the voltage built up process and a control to regulate the DC voltage of an isolated induction generator connected to a rectifier and driven by a variable speed wind turbine. Two strategies, based on the rotor flux oriented vector control, are proposed. Both rotor flux and DC bus voltage are regulated by two control loops which operate in parallel. The model used for the induction generator is obtained by the application of the Park transform. This model takes account of the saturation effect by a variable magnetizing inductance function of the current. The inductance variation is described by a polynomial function. The proposed control strategies are validated through simulations. The obtained results are presented and discussed.
	A Fault Converter topology for Wind Energy Conversion System with Doubly Fed Induction Generator   By KARIMI Shahram; POURE Philippe; GAILLARD Arnaud; SAADATE Shahrokh; GHOLIPOUR Eskandar	[View]   [Download]
Abstract: This paper presents a novel fault tolerant converter topology for grid connected Wind Energy Conversion System (WECS) with Doubly Fed Induction Generator (DFIG). This topology allows fault detection and compensation of one of the semiconductors or drivers by using isolating and connecting devices. It is based on a unique redundant leg for both back to back converters. We present a new detection algorithm, robust to false fault detection due to semiconductor switching. Simulation results are presented for two open circuit cases on both back to back converters.
	A Novel Small-Scale Variable Speed Hydropower Emulator Using an Inverter-Controlled Induction Motor   By MAURI Marco; MARCHEGIANI Gabriele; CASTELLI DEZZA Francesco	[View]   [Download]
Abstract: The test procedure of an electrical drive control generally requires connecting the control to the power converter, the motor and the load. This is an expensive, time and power consuming procedure especially when it is necessary to test new control algorithms or architectures as often happen in renewable energy generation power plants. This paper introduces a low power emulator of a Small Hydropower generator used to develop and test the Power Quality functions of a Universal Digital Controller for Distributed Generation Systems.
	A Redundant Electrical Braking System for Wind Turbine Generators   By YANG Wenqiang; WANG Timothy; YUAN Xiaoming; TEICHMANN Ralph	[View]   [Download]
Abstract: Mechanical brake is typically used in wind turbine, which typically suffers from frequent wear-out, more trip opportunities and high maintenance cost. To addressing this issue, a redundant electrical braking system is proposed in this paper. It comprises a conventional dynamic brake connected to the converter DC link and a fully controllable resistive load connected to the generator terminals. The resistive load can be engaged by an active power semiconductor and a NC(Normally Closed) contactor. The key advantages with the proposed braking mechanism are: (1) Relief mechanical braker's loading significantly since electrical braking is the primary braking method and mechanical braking only functions as back-up; (2) The total braking torque is controllable, which allows some pre-determined braking torque along with decreasing turbine speed could be followed during braking process. The specific designed braking torque curve could minimize the drive train fatigue; (3) High reliability could be obtained based on the proposed control logics. Even under the worst case, where all electrical components fail, the resistive load on generator terminals can still be engaged through a Normal-Closed mechanical contactor. The engagement of this resistive load could prevent the turbine from free-wheeling and stop the turbine working with mechanical braker. The optimum load sharing between dynamic brake and resistive ac load is discussed. A state machine control system is presented.
	Additional Application Fields of a Modern Wind Generator Even at No-Wind   By SCHMIDT Istvan; VESZPREMI Karoly	[View]   [Download]
Abstract: A modern variable speed wind turbine generator is connected to the lines (grid) through a both sides PWM controlled dc link voltage source inverter. The fast current control of the line currents by the line-side converter makes possible to compensate the deviation of the line currents from their fundamental component. This possibility can be used to compensate the lower order current harmonics in the line currents (injected by nonlinear loads on the lines) and to balance the negative sequence current component (caused by asymmetrical load). Besides, advanced control strategies make possible to control the reactive (and also the active) power of the lines, resulting in power factor correction. Since all the mentioned subjects of compensations require at most pulsating active power with zero mean value, the listed compensations are possible even at no-wind condition. Of course, the pulsating active power affects the pulsation of the dc link voltage, the limits of the compensations in this sense must be investigated. All the investigated additional application fields improve the power quality of lines (grid) where the wind turbine generator is connected to. The practical aim of this paper is to attract the attention of the wind turbine makers to these additional application fields. The paper presents the advanced possible line-side converter control schemes. The physical and theoretical background of the different compensations are discussed. The issues of their implementation by the presented control methods are detailed. The methods are investigated and validated by simulations of practical examples. Design criteria are given based on the considerations.
	An Encoder-free Grid Synchronization Method for a Doubly-fed Induction Generator   By LEE Kwangsoo; PARK Jinsoon; KIM Dongwook; LEE Kiwook; PARK Jungwoo	[View]   [Download]
Abstract: In order to transfer energy generated through the stator winding of a doubly-fed induction generator (DFIG) to an electric power grid, we first need to synchronize the generated voltage vector with the grid voltage vector. However, the existing synchronization methods work only when the encoder is installed at a specific position and the system parameters are correct. In order to solve these problems, a new synchronization method has been proposed and a way of applying the method to the existing doubly-fed induction generator control algorithm has been suggested also. The validity of the proposed methods were verified by using a prototype converter for a MW-class doubly-fed induction generator and experimental results showed robust synchronization characteristics against variation of encoder positions, generator parameters, and grid voltages.
	Analysis of Three Phase Grid Failure and Doubly Fed Induction Generator Ride-through using Crowbars   By JENSEN Simon; FUCHS F.W.; KNOP Andre; LOHDE Ralf	[View]   [Download]
Abstract: Doubly Fed Induction Generators (DFIG) are nowadays widely used in variable speed wind power plants. The behaviour of these machines during grid failure is an important issue, since in case of under voltage of the mains it is not allowed to simply disconnect the turbine but it is mandatory that it keeps on delivering power to the mains supply system. To protect the rotor side converter, a crowbar at the rotor has to be switched on. The performance of an active crowbar during voltage dips is investigated for several parameter sets of machine, resistor and control.
	Comparison of Active Stabilization Methods for the Doubly-Fed Induction Generator - Quadrature versus Direct Inner Control Loops   By MARQUES Gil	[View]   [Download]
Abstract: The doubly-fed induction generator DFIG, when controlled with the stator flux oriented method with impressed rotor currents, is characterized by oscillations on the flux and torque and an unstable region. This region occurs when direct rotor current is bigger than a critical value. Several techniques can be used for the damping and stabilization of this system. Some methods are based in additional inner closed loops for damping and stabilization. This paper presents a comparison of two methods for damping and stabilization of the DFIG. Both are based in additional inner current loops. The first method, in function of the stator flux amplitude, corrects the direct current reference adding a term proportional to the stator flux error. The second method, in function of an internal angle, acts on the quadrature impressed rotor current reference. The stability criteria for both methods are analysed and compared. It is shown that, in per unit values, the two methods are equivalent leading to equal damping for equal damping constants. Both can be used at the same time as a vector damping method.
	Induction generator model in phase coordinates for fault ride-through capability studies of wind turbines   By HANSEN Anca Daniela; BLAABJERG Frede; FAJARDO L.A.; MEDINA-RIOS J.Aurelio; IOV Florin	[View]   [Download]
Abstract: A phase coordinates induction generator model with time varying electrical parameters as influenced by magnetic saturation and rotor deep bar effects, is presented in this paper. The model exhibits a per-phase formulation, uses standard data sheet for characterization of the electrical parameters, is developed in C-code and interfaced with Matlab/Simulink through an S-Function. Saturation uses a direct non-linear magnetizing inductance versus input voltage function. Deep-bar effect is evaluated using voltage reliant correction factors to make both rotor resistance and leakage inductance dependent on the rotor speed. The investigation compares the behaviour of three models in the presence of external faults, namely the "classical" DQ model, a phase coordinates model with constant parameters and the proposed phase coordinates model with time varying rotor and magnetic electrical parameters. Case studies are conducted in a representative sized system and results show aptness of the proposed model over other two models. This approach is also constructive to support grid code requirements
	Inverter Excited Induction Machine for High Performance Wind Power Generation System   By HAMADA Tomoyuki; KIMURA Noriyuki; MORIZANE Toshimitsu; TANIGUCHI Katsunori	[View]   [Download]
Abstract: This paper investigates new system configuration of induction generator for wind power generation. Proposed system realizes the variable speed generation with small capacity of inverter by using PFC converter with a diode rectifier and a boost chopper as the active power converter. The inverter supplies the reactive power only for the induction generator. The reduction of the capacity of the inverter leads to the lower system cost. It is also advantageous that the dc side of the rectifier is connected to the dc transmission line and the dc battery charger to reduce the total cost by omitting the inverter to connect to the utility system. Simulation results show that the capacity of the inverter is reduced to almost 1/5 of full rating. It is also shown that the duty factor of the boost chopper of the PFC converter can control the active power of the PFC converter and the inverter simultaneously.
	Load Sharing of the Parallel Operating Adjustable Speed Generation Systems without Control Signal Interconnection   By AL-KHAYAT Nazar; MOSKWA Marcin; KOCZARA Wlod	[View]   [Download]
Abstract: This paper presents a novel method for parallel operation of adjustable speed power-electronic generation systems. The proposed method is based on the well known droop scheme and therefore does not require any additional interconnections between units operating in parallel. Modifications and extensions to the conventional droop scheme are introduced to resolve problems specific for the parallel operation of adjustable speed generation systems. These include novel methods for connecting and disconnecting units to and from parallel system as well as method for sustaining required load sharing between units during sudden load changes. The results from the real laboratory system are presented to justify the proposed methods.
	Modeling and Simulation of Variable Speed Wind Generator System Using Boost Converter of Permanent Magnet Synchronous Generator   By OHYAMA Kazuhiro	[View]   [Download]
Abstract: This paper proposes the variable-speed wind generator system using the boost converter. The proposed system has three speed control modes for the wind velocity. The control mode of low wind velocity regulates the armature current of the generator with the boost converter to control the windmill speed. The control mode of middle wind velocity regulates the DC link voltage with vector controlled inverter to control the windmill speed. The control mode of high wind velocity regulates the pitch angle of the wind turbine with the pitch angle control system to control the windmill speed. The hybrid of three speed control scheme extends the variable-speed range. The proposed system simplifies the maintenance, improves the reliability, and reduces the cost in compare with variable-speed wind generation system using PWM converter.
	Optimal Direct-Drive Permanent Magnet Wind Generator Systems for Different Rated Wind Speeds   By LI Hui; CHEN Zhe	[View]   [Download]
Abstract: The objective of this paper is to investigate possible ranges of rated wind speeds and rated power levels to have the better performance of the annual energy output per cost (AEOPC) for an individual direct-drive wind energy conversion system. Based on a given rated wind speed, the turbine blade sizing and rotor speed can be determined by using the maximal wind energy capture characteristics, the calculation of annual energy output (AEO) of wind turbines are also described. Based on a given wind turbine, a three-phase radial-flux PM synchronous generator (PMSG) with a back-to-back power converter is optimized for the minimal generator system cost. The analytical design models and optimization are developed and demonstrated by a rated power 500kW PMSG. The optimal results of direct-drive PM wind generator systems with various combinations of different rated wind speeds and different rated power levels of wind turbines are obtained and compared, including the AEO and AEOPC at the high, medium and low wind speed sites, respectively. By comparison with the AEOPC of the optimized PM generators, the appropriate design ranges with the more cost-effective performance are analyzed and discussed for the direct-drive PM wind generator systems.
	Output Maximization of Wind Generation System Using Sensorless Controlled IPMSG    By KAWABE Izumi; MORIMOTO Shigeo; SANADA Masayuki	[View]   [Download]
Abstract: This paper proposes an output maximization control for a wind generation system with a variable speed interior permanent magnet synchronous generator (IPMSG). The generator torque is controlled according to the generator speed by employing maximum power point tracking control. The IPMSG current vector is controlled so as to minimize the generator losses and maximize the output power while considering the converter capacity. Moreover, the converter control method is switched from sinusoidal pulse width modulator (PWM) control to square-wave operation in the high-speed region in order to increase output power. The proposed output maximization control is achieved without the use of mechanical sensors such as wind speed sensor and position sensor. The performance of the proposed generation system is examined by simulation and experiment.
	Parallel-connected converters for optimizing efficiency, reliability and grid harmonics in a wind turbine   By ANDRESEN Björn; BIRK Jens	[View]   [Download]
Abstract: The converter system for the Gamesa G10x 4.5 MW wind turbine consisting of 6 parallel-connected converters and some of the converter system control algorithms are presented. The benefits of this solution compared with a solution with only one converter are higher reliability, higher efficiency and possibility of extremely low grid harmonics.
	Performance Characteristics of a Practical Scale Wind Turbine Generating System using a Shaft Generator System   By TATSUTA Fujio	[View]   [Download]
Abstract: In this paper, the performances of a new and practical scale wind turbine generating system are discussed. The system was constructed on the basis of a shaft generator system widely used in large ships. This system has many features such as high reliability and output power of high quality. It is shown that electric power with constant frequency and voltage with low distortion can be obtained with this novel system. Furthermore the analytical model for computer simulation is proposed. Good agreement between simulated and experimental results is obtained, confirming the validity of the model.
	Simple Fault-Ride Through Capability Analysis for Wind Power Plants under Different Grid Code Requirements   By HOFMANN Wilfried; RABELO Balduino	[View]   [Download]
Abstract: The various grid codes regulating the connection of wind energy conversion systems (WECS) to the transmission network present different requirements between each other, making the evaluation of fault ride-through capability of wind turbines a time consuming repetitive task. This work presents a simplified analysis based on energy conservation principle, on system empirical data and on the power companies voltage drop profile. The method enables a preliminary evaluation of the plant stability under different grid codes and points out possible design modifications that will enable compliance with the requirements.
	Sliding mode control of a doubly-fed induction generator   By PATIN Nicolas; NAASSANI Ammar; MONMASSON Eric; LOUIS Jean-Paul	[View]   [Download]
Abstract: This paper deals with the sliding mode control of a doubly-fed induction generator. The controller synthesis, based on a dynamical equivalent circuit representation of the machine, is presented. Then, its robustness against parametric variations of the system is evaluated and compared to the results obtained with a linear control scheme. The controller is finally validated by experimental results.
	Static Synchronous Series Compensation applied to Small Wind Energy Conversion System   By SINGER Amr; HOFMANN Wilfried	[View]   [Download]
Abstract: Permanent magnet salient pole synchronous connected dc network produces less power than the rated power even at rated excitation. Static synchronous series compensation (SSSC) provides a solution to this problem. Since SSSC compensates the reactance voltage drop of the generator. This paper presents simulation and experimental results when applying static synchronous series compensation to permanent magnet salient pole synchronous generator (PSG) in order to increase the output power and stabilise the output voltage.
	Test bench for grid code simulations for multi-MW wind turbines   By BOCQUEL Aurelie; SANITER Christoph; JANNING Jörg	[View]   [Download]
Abstract: The hardware configuration and control methodology for a test bench for power grid simulations for multi-MW wind energy applications are described. The variable voltage is generated using two (four in the final stage) medium voltage, three-phase, three-level voltage source converters with press-pack IGBTs and a specially designed step-up transformer. This system differs fundamentally from known grid simulation test benches that almost always use switched inductances. Simulation results using MATLAB/Simulink and measurements as well as constraints to the system are discussed.