Permanent Magnet Wind Generator Research Articles

A Control Method of Permanent Magnet Wind Generators in Grid Connected Wind Farm to Damp Load Frequency Oscillation

A Control Method of Permanent Magnet Wind Generators in Grid Connected Wind Farm to Damp Load Frequency Oscillation

Electromagnetic Design of Concentrated Winding in a Direct-Drive Permanent Magnet Wind Generator with Evaporative-Cooling and Inner-Cooling System

This paper describes the fundamental principle of the direct-drive permanent magnet wind generator with evaporative-cooling and inner-cooling system and raises a method to apply concentrated winding to the electromagnetic design of this motor in order to simplify its processing technic. It also includes simulation and comparison of electromotive force of fundamental wave produced by concentrated winding under different slot-opening factors. A reasonable slot-opening factor was selected in the electromagnetic design of a 2 MW direct-drive permanent magnet wind generator with evaporative-cooling and inner-cooling system and the validity of the design has been proved by simulation.

Multi-Machine Controller Design of Permanent Magnet Wind Generators using Hamiltonian Energy Method

In this paper, the nonlinear control problem of permanent magnet wind generators is investigated based on Hamiltonian energy method. A nonlinear design method is proposed for the multi-machine system, such that the closed-loop system is stable simultaneously. Moreover, in the presence of disturbances, the closed-loop is finite–gain L 2 stable under the action of the Hamiltonian controller. In order to illustrate the effectiveness of the proposed method, the simulations are performed which show that the gotten controller can improve the transient property and robustness of the system. DOI: http://dx.doi.org/10.11591/telkomnika.v11i7.2824

Inertia response from full-power converter-based permanent magnet wind generators

With a high penetration of wind turbines, the proportion of synchronous generation in the power system will be reduced at times, thus creating operating difficulties especially during frequency events. Therefore, it is anticipated that many grid operators will demand inertia response from wind turbines. In this article, different ways for emulating inertia response in full-rated power converter-based wind turbines equipped with permanent magnet synchronous generators are considered. Supplementary control signals are added to the controller of the wind turbine to extract stored energy from the rotating mass and DC-link capacitors. Simulations in MATLAB/Simulink show that the inertia response is improved by adding a term proportional to the rate of change of frequency and by extracting the stored energy in the DC-link capacitors.

Stabilization of Fixed Speed Wind Generator by using Variable Speed PM Wind Generator in Multi-Machine Power System

This paper present stabilization control of fixed speed wind generator by using variable speed permanent magnet wind generator in a wind farm connected with multi-machine power system. A novel direct-current based d-q vector control technique of back to back converter integrated with Fuzzy Logic Controller for optimal control configuration is proposed, in which both active and reactive powers delivered to a power grid system are controlled effectively. Simulation analyses have been performed using PSCAD/EMTDC. Simulation results show that the proposed control scheme is very effective to enhance the voltage stability of the wind farm during fault condition.

Hamiltonian Robust Controller Design of Permanent Magnet Wind Generators

In this paper, the dual-input nonlinear controller of permanent magnet wind generators was designed based on energy dissipation theory and Hamiltonian energy approach. Under the action of the Hamiltonian controller, the closed-loop system is asymptotically stable on case of no disturbances and finite-gain L2 stable in the presence of disturbances. The Hamiltonian energy approach provides us a physical insight and a new way to the controller design of nonlinear systems. The simulation results show the effectiveness of the proposed robust controller.

A Design Fuzzy Logic Controller for a Permanent Magnet Wind Generator to Enhance the Dynamic Stability of Wind Farms

In this paper, a design fuzzy logic controller for a variable speed permanent magnet wind generator connected to a grid system through a LC-filter is proposed. A new current control method of grid side conversion is developed by integrating the fuzzy controller, in which both active and reactive power, delivered to a power grid system, is controlled effectively. The fuzzy logic controller is designed to adjust the gain parameters of the PI controllers under any operating conditions, so that the dynamic stability is enhanced. A new simple method, based on frequency response of the bode diagram, is proposed in the design of the fuzzy logic controller. To evaluate the controller system capabilities, simulation analyses are performed on a small wind farm model system including an induction wind generator connected to an infinite bus. The simulations have been performed using PSCAD/EMTDC. Simulation results show that the proposed control scheme is more effective for enhancing the stability of wind farms during temporary and permanent network disturbances and randomly fluctuating wind speed, compared with that of a conventional PI controller.

Lumped-parameter-based thermal analysis of a doubly radial forced-air-cooled direct-driven permanent magnet wind generator

A lumped-parameter-based thermal analysis of a direct-driven permanent magnet wind generator with double radial forced-air cooling is presented. In the proposed thermal model, the thermal conduction and convection as well as the heating of the cooling fluid are modeled in terms of thermal resistances. The electromagnetic losses of the generator are calculated by a two-dimensional, non-linear, time-stepping finite element method. The developed thermal calculation model can be applied both to static and transient problems. The performance of the proposed thermal model is compared with the results calculated by using computational fluid dynamics. The presented modeling strategy is implemented into an analytical calculation tool, which is used in the design process of a 3.35MW high-torque low-speed direct-driven permanent magnet synchronous generator. Experimental results for a 3.35MW permanent magnet generator are presented.

3-D Finite Element Method Analysis of Additional Load Losses in the End Region of Permanent-Magnet Generators

Machine design typically concentrates on the main magnetic and electric circuits while various additional losses are evaluated only by simple empirical equations. The objective of this paper is to examine the importance of the additional losses in the stator end region and in the housing of a 3.1 MW permanent-magnet wind generator. Stator stack clamping ring and finger plate losses are investigated using a 3-D finite element method. 2-D FEM analysis of the stator supporting housing losses is also performed. Two common mechanical component materials are analyzed in the 3-D studies; construction steel and stainless steel. The results show that failure to consider stator end areas and stator supporting constructions at the design stage can result in unwanted additional losses and affect machine efficiency. Indirect verification of the results is provided by efficiency measurements of different versions of the real 3.1 MW machine.

A Transformer-Less High-Power Converter for Large Permanent Magnet Wind Generator Systems

The power conversion systems for large wind turbines are facing a great challenge as today's wind turbine power outputs approach 5 MW and above. The conventional low voltage power conversion system will suffer from a high transmission current, which significantly increases losses and cost of the cables as well as voltage drop. This paper proposes a modular, medium voltage, high-power converter topology for the large permanent magnet wind generator system, eliminating the grid-side step-up transformer, which is desirable for both onshore and offshore wind turbines. The converter modules are cascaded to achieve medium voltage output. Each converter module is fed by a pair of generator coils with 90 phase shift to get the stable dc-link power. The power factor correction (PFC) circuit enables the generator to achieve unity power factor operation and the generator armature inductance is used as ac-side PFC boost inductance. At the grid-side, H-bridge inverters are connected in series to generate multilevel medium voltage output and the voltage-oriented vector control scheme is adopted to regulate the converter active and reactive power transferred to the grid. Simulation results with a 2-MW wind turbine system and experimental results with a down-scaled 3-kW system validate the proposed topology and control methods. The proposed system can successfully deliver power from the wind generator to the grid.

Torque and Voltage Quality in Design Optimization of Low-Cost Non-Overlap Single Layer Winding Permanent Magnet Wind Generator

The main focus of this paper is cost-effective techniques to reduce the cogging torque in permanent magnet (PM) wind generators. However, there are also certain limits with which other machine design aspects need to comply. These aspects include ease of manufacturing, mass, load torque ripple, and voltage quality. In this paper, a low-cost single layer PM wind generator with an irregular, parallel slotted stator is analyzed. The sensitivity of average torque and cogging torque to machine dimension variations is investigated, as well as the effects imposed upon the load torque ripple and the voltage quality. Methods are proposed whereby regions of low cogging torque can be identified more quickly in the design optimization. Furthermore, an interesting observation is made regarding the effects imposed upon the cogging torque by varying the yoke heights. Finite element calculated results are validated by practical measurements on a 15-kW PM wind generator.

Dynamic Torque Analysis of a Wind Turbine Drive Train Including a Direct-Driven Permanent-Magnet Generator

Mechanical interactions between a wind turbine and a direct-driven permanent-magnet synchronous generator (PMSG) are studied, and a model to analyze the system behavior is suggested. The proposed model can be applied to analyze the mechanical vibrations of direct-driven wind turbine installations both in steady state and in dynamic cases. The cogging torque and torque ripple of the PMSG are used as excitation sources in the mechanical model. Four different permanent-magnet rotor constructions are analyzed. It is shown that the maximum allowable value of the cogging torque of the direct-driven permanent-magnet wind generator in this case is 1.5%-2% of the rated torque even when the corresponding resonance frequency does not occur in the operational speed range of the wind turbine. Furthermore, it was noticed that the resonance caused by the excitation torque should occur at the lowest possible speed.

Control and Interfacing of a Grid-Connected Small-Scale Wind Turbine Generator

An ac/dc/ac power converter is an important device used to extract power from variable speed permanent magnet wind generators and feed it into the grid. This paper describes how these converters incorporate maximum power point tracking based on its power feed to the grid at different wind speeds. Using the permanent magnet generator voltage, grid current, and grid voltage samples, the proposed system achieves an enhanced dynamic behavior. This feature effectively prevents the grid from “boost” charging the dc side of the H-bridge inverter at the start of operation. Since small wind turbines normally do not have expensive pitch control mechanisms, a thyristor-based “dump-load circuit” is employed to protect the turbine from high wind speed operation when disconnected from the grid. The thyristor controller also protects the inverter from high dc voltage input from the wind generator at high wind speed. Preliminary results are included using a laboratory 2-kW prototype converter.

Steady-state performance analysis and modelling of directly driven interior permanent magnet wind generators

This study presents a systematic approach for modelling, analysing and evaluating steady-state performances of directly driven interior permanent magnet generators (IPMG) for wind energy conversion systems. The proposed approach for modelling and analysing the performance of PMGs is based on relating the harmonic components present in the stator currents to the harmonic components present in the terminal voltages. Three laboratory IPMG of 1, 5 and 50 kW are tested at different shaft speeds for supplying a resistive load, a rectifier and a resistive load and rectifier inverter with a resistive load. Experimental performances of the tested IPMGs demonstrate direct relationships between terminal voltage harmonic components and harmonic components present in stator currents. Also, investigated experimental performances show significant impacts of stator currents harmonic components on the IPMG efficiency.

Design Aspects of Double-Sided Rotor Radial Flux Air-Cored Permanent-Magnet Wind Generator

The electromagnetic and mechanical design aspects of optimally designed double rotor radial flux permanent-magnet wind generators with nonoverlap air-cored (ironless) stator windings are analyzed in this paper. An accurate analytical design optimization method is proposed. The analytical model is confirmed by finite-element analysis. It is shown, among other things, that the electromagnetic design, and not the mechanical design, determines the rotor yoke dimensions and, thus largely, the mass and cost of the generator.

Stability Augmentation of Wind Farm using Variable Speed Permanent Magnet Synchronous Generator

This paper presents a new control strategy of variable speed permanent magnet wind generator for stability augmentation of wind farm including fixed speed wind turbine with Induction Generator (IG). A new control scheme is developed for two levels back-to-back converters of Permanent Magnet Synchronous Generator (PMSG), by which both active and reactive powers delivered to the grid can be controlled easily. To avoid the converter damage, the DC link protection controller is also proposed in order to protect the dc link circuit during fault condition. To evaluate the control capability of the proposed controllers, simulations are performed on two model systems composed of wind farms connected to an infinite bus. From transient and steady state analyses by using PSCAD/EMTDC, it is concluded that the proposed control scheme is very effective to improve the stability of wind farm for severe network disturbance and randomly fluctuating wind speed.

Improvement of torque characteristics of permanent magnet wind generator by FEM and optimization

This paper focuses on the improvement of the torque characteristics of the outer rotor direct drive permanent magnet wind generator that is a radial flux machine with output power of low speed and high torque, 3(kW) 90(rpm) by FEM and optimization. The optimization technique is used to find out a design solution through the comparison of cogging torques according to the shape variation such as the open slot width and the pole arc ratio. In this technique the problem is to mini mize the objective function. The automatic process that includes the automatic ACAD file drawing and mesh generation with reg ard to the shape variation is also used. The revised generator is obtained from a preliminary model. The cogging torque characteristics of the revised model and the preliminary model and the dynamic characteristics are analyzed. From the simulation result s, it is shown that the cogging torque characteristic of the revised model is better than that of the preliminary one. The prototype was manufactured and the simulation result such as induced voltage is agrees with that of the experimental one.

Particular Electromagnetic Field Computation for Permanent Magnet Generator Wind Turbine Analysis

Precise permanent magnet generator modeling requires a complex electromagnetic field analysis in order to account for rotor eccentricity and end-zone leakage field. The paper presents a particular technique that enables considering such phenomena through convenient 2-D and 3-D finite element models and incorporate electromotive force distributions including space harmonics in real time control systems. The proposed methodology has been validated by measurements on a permanent magnet wind generator prototype.

DC-link Voltage Control of a Full Power Converter for Wind Generator Operating in Weak-Grid Systems

When the wind power accounts for a large portion of the grid power, it may need to help the grid voltage and frequency regulation. This paper investigates a permanent-magnet wind generator with a full power voltage-source converter in weak-grid mode, where the DC-link voltage needs to be controlled from the generator side instead of the grid side. The energy relationship of the wind generator, DC-link energy storage, and load is established. An intrinsic right-half-plane zero, together with the wind power characteristics, the mechanical system inertia, and the DC-link energy storage, is identified as the physical limitations for the control. With the understanding of the system energy relationship and limitations, a hybrid adaptive control algorithm is proposed that searches for the optimal generator acceleration to achieve the maximum wind generator power change rate to match the load power variation. The proposed control scheme is verified through simulation of a 1.5-MW wind system as well as through the experiment of a scaled 1-kW, DSP-/field-programmable-gate-array-controlled, permanent-magnet-generator-based test bed. The results show that it is feasible to regulate DC link by the generator-side converter through the generator speed control. Some important applications issues are also investigated, including the DC-link energy storage requirement, wind speed change impact, and control transition between the weak-grid and strong-grid modes.

LVRT of Grid Interfaced Variable Speed Driven PMSG for WECS during Fault

- 392 - Abstract— Wind energy conversion systems have become a focal point in the research of renewable energy sources. This is in no small part due to the rapid advances in the size of wind generators as well as the development of power electronics and their applicability in wind energy extraction. The voltage of the direct driven permanent magnet wind generators (PMSG) is variable due to the intermittent nature of the wind energy. Fluctuating voltage and power is of major concern in the converter based grid connected wind generation systems. An inverter is essential for the interfacing of the wind source with the AC network. This paper discusses the interconnection issues of permanent magnet wind generators to local grid as per prevailing grid standards during healthy and fault conditions. The fault ride-through topology for PMSG has been demonstrated using MATLAB Simulink based simulation. Wind energy is a reliable, natural and renewable electrical power supply. The high installed capacity of today 's wind turbines and decreasing plant costs have shown that wind power can be competitive with conventional, more heavily polluting, fuels in the long term. Wind power growth with a 20% annual rate has experienced the fastest growth among all renewable energy sources science five years ago. It is predicted that by 2020 up to 12% of the world's electricity will have been supplied by wind power. Figure-1 shows the global cumulative installed capacity and global annual installed capacity. In terms of wind power generation technology, as a result of numerous technical benefits (higher energy yield, reducing power fluctuations and improving var supply) the modern MW-size wind turbines always use variable speed operation which is achieved by electrical converters .These converters are typically associated with individual generators and they contribute significantly to the costs of wind turbines. Between variable speed wind turbine generators doubly fed induction generators (DFIGs) and permanent magnet synchronous generators (PMSGs) with primary converters are emerging as the preferred technologies.