An analytic electromagnetic calculation method for performance evolution of doubly fed induction generators for wind turbines

An analytic electromagnetic calculation method for doubly fed induction generator(DFIG) in wind turbine system was presented. Based on the operation principles, steady state equivalent circuit and basic equations of DFIG, the modeling for electromagnetic calculation of DFIG was proposed. The electromagnetic calculation of DFIG was divided into three steps: the magnetic flux calculation, parameters derivation and performance checks. For each step, the detailed numeric calculation formulas were all derived. Combining the calculation formulas, the whole electromagnetic calculation procedure was established, which consisted of three iterative calculation loops, including magnetic saturation coefficient, electromotive force and total output power. All of the electromagnetic and performance data of DIFG can be calculated conveniently by the established calculation procedure, which can be used to evaluate the new designed machine. A 1.5 MW DFIG designed by the proposed procedure was built, for which the whole type tests including no-load test, load test and temperature rising test were carried out. The test results have shown that the DFIG satisfies technical requirements and the test data fit well with the calculation results which prove the correctness of the presented calculation method.

Effects of Wind Turbines Equipped with Doubly-fed Induction Generators on Distance Protection

Nowadays wind energy is the fastest growing renewable energy resource in the world.The problems of integrating wind farms are caused by changes of wind speed during a day.Moreover,the behaviors of wind turbines equipped with doubly-fed induction generators differ fundamentally from synchronous generators.Therefore,more considerations are needed to analyze the performances of the distance protection relays.The protection of a wind farm with distance relay is inspected.By changing the conditions of the wind farm,the characteristics of the distance relay are studied.

A Gain Scheduled Method for Speed Control of Wind Driven Doubly Fed Induction Generator

This paper proposes a gain scheduled control method for a doubly fed induction generator driven by a wind turbine. The purpose is to design a variable speed control system so as to extract the maximum power in the region below the rated wind speed. Gain scheduled control approach is applied in order to achieve high performance over a wide range of wind speed. A double loop configuration is adopted. In the inner loop, the rotor speed is used as the scheduling parameter, while a function of wind and rotor speed is used as the scheduling parameter in the outer loop. It is verified in simulations that a high tracking performance has been achieved.

A Novel Grid Synchronization Control of Doubly-fed Induction Generator

The dynamic performance of doubly-fed induction generator(DFIG) before and after connection is analyzed based on corresponding mathematical models and transfer functions in decoupled vector control.The parameter tuning methods of rotor current regulator before and after connection are given.To reach same dynamic performance the parameters should take different values and be switched before and after connection.However on one hand the closing moment of stator contactor is difficult to get as the feedback signal is usually twenty millisecond delay or so.The delay in parameter switching will affect rotor current and torque dynamics during the delayed period after connection. On the other hand parameter switching is troublesome.Hence a synchronization control strategy without parameter switching is proposed and analyzed in detail,which has linear rising exciting current to avoid current overshooting. The dynamic performance of the proposed strategy is analyzed in frequency domain and implemented on a DFIG experimental platform subsequently.The proposed synchronization strategy is validated by experimental results.

A novel transient rotor current control scheme of a doubly-fed induction generator equipped with superconducting magnetic energy storage for voltage and frequency support

A novel transient rotor current control scheme is proposed in this paper for a doubly-fed induction generator（DFIG）equipped with a superconducting magnetic energy storage（SMES） device to enhance its transient voltage and frequency support capacity during grid faults. The SMES connected to the DC-link capacitor of the DFIG is controlled to regulate the transient dc-link voltage so that the whole capacity of the grid side converter（GSC） is dedicated to injecting reactive power to the grid for the transient voltage support. However, the rotor-side converter（RSC） has different control tasks for different periods of the grid fault. Firstly, for Period I, the RSC injects the demagnetizing current to ensure the controllability of the rotor voltage. Then, since the dc stator flux degenerates rapidly in Period II, the required demagnetizing current is low in Period II and the RSC uses the spare capacity to additionally generate the reactive（priority） and active current so that the transient voltage capability is corroborated and the DFIG also positively responds to the system frequency dynamic at the earliest time. Finally, a small amount of demagnetizing current is provided after the fault clearance. Most of the RSC capacity is used to inject the active current to further support the frequency recovery of the system. Simulations are carried out on a simple power system with a wind farm. Comparisons with other commonly used control methods are performed to validate the proposed control method.

Reactive Current Allocation and Control Strategies Improvement of Low Voltage Ride Though for Doubly Fed Induction Wind Turbine Generation System

为满足风电机组低电压穿越（low voltage ride through,LVRT）的测试要求及其电气模型一致性评估需要,提出考虑向电网注入无功电流的双馈风电机组LVRT的控制策略。在阐述风电机组LVRT测试要求及控制原理的基础上,推导双馈发电机（doubly fed induction generator,DFIG）定子侧及网侧变流器输出无功电流极限表达式,研究电网电压跌落深度和发电机总输出有功功率对其无功电流极限值的影响规律,进而提出DFIG在LVRT期间的无功电流分配算法和改进的有功、无功功率控制策略。最后,以某实际2 MW双馈风电机组为例,分别对风速为5和12 m/s、电网电压对称跌落至20%和50%工况下的LVRT运行性能进行仿真比较和样机测试。与传统LVRT控制方法的对比表明,所提改进控制策略能更好地满足风电机组LVRT的测试要求。样机测试结果进一步证明了改进控制策略和仿真模型的有效性。

Performance Description of Brushless Doubly-Fed Induction Machine in Its Asynchronous and Variable Speed Synchronous Modes

Brushless Doubly-Fed Machine has attracted considerable attention in recent years due to its advantages. It has the robustness of the squirrel cage induction machine, and the speed and power factor controllability of the synchronous machine as well as the absence of brushes and slip rings, and using a fractionally rated frequency converter. Hence, there are considerable benefits over the conventional machines, when the machine is applied to applications such as a wind turbine generator or high power adjustable speed drive. However, these benefits are obtained in slightly more complex structure, higher cost and larger dimensions in comparison to the conventional induction machine. This paper presents fundamental aspects of the three modes of operation of brushless doubly fed machine, i.e. simple induction mode, cascade induction mode, and synchronous mode. The investigation is performed by analyzing the spatial harmonic contents of the rotor magnetic flux density. The direct cross couplings between stator and rotor fields as well as, indirect cross coupling between stator fields by the special rotor of this machine is described. Furthermore, loss analysis of the machine in various modes is presented and the torque-speed curves for asynchronous modes are obtained. A 2-D magnetodynamic finite element model based on the D-180 4/8 pole prototype machine is extracted and simulated to verify the results.

Robust direct power control based on the Lyapunov theory of a grid-connected brushless doubly fed induction generator

This paper deals with robust direct power control of a grid-connected bmshless doubly-fed induction generator（BDFIG）. Using a nonlinear feedback lineariza- tion strategy, an attempt is made to improve the desired performances by controlling the generated stator active and reactive power in a linear and decoupled manner. There- fore, to achieve this objective, the Lyapunov approach is used associated with a sliding mode control to guarantee the global asymptotical stability. Thus, an optimal operation of the BDFIG in sub-synchronous operation is obtained as well as the stator power flows with the possibility of keeping stator power factor at a unity. The proposed method is tested with the Matlab/Simulink software. Simulation results illustrate the performances and the feasibility of the designed control.

Phase–amplitude model for doubly fed induction generators

The doubly fed induction generator(DFIG) is major type of wind turbine generator used in grid-connected wind farms. Practical models of DFIG have been built to study the influence of wind power generation on power system dynamics. However, most existing practical models of the DFIG are based on rectangular coordinates,in which frequency variation is neglected. In this paper, a phase-amplitude(P-A) model is proposed for a DFIG based on phase and amplitude of the internal voltage. The model structure is much like that of the synchronous generator, and the rotor voltage can manipulate both the amplitude and the phase of the internal voltage.Comparisons have been made between the new P-A model of the DFIG and the synchronous generator model,as well as the asynchronous motor model.The contributions of the new P-A model of the DFIG are discussed and it is demonstrated that the proposed model has better ability in describing power system dynamic phenomena such as voltage dynamics and structural dynamics. Simulation results and a field test validate these contributions.

Robust control based on the Lyapunov theory of a grid-connected doubly fed induction generator

This paper discusses the robust control of a grid-connected doubly-fed induction generator （DFIG） controlled by vector control using a nonlinear feedback linearization strategy in order to ameliorate the performances of the control and to govern the developed stator active and reactive power in a linear and decoupled manner, in which an optimal operation of the DFIG in subsynchronous operation is given, as well as the control stator power flow with the possibility of keeping stator power factor at a unity. The use of the state-all-flux induction machine model gives place to a simpler control model. So, to achieve this objective, the Lyapunov approach is used associated with a sliding mode control to guarantee the global asymptotical stability and the robustness of the parametric variations.

Robust nonlinear controller design of wind turbine with doubly fed induction generator by using Hamiltonian energy approach

Based on Hamiltonian energy theory, this paper proposes a robust nonlinear controller for the wind turbine with doubly fed induction generator （DFIG）, such that the closed-loop system can achieve its stability. Furthermore, in the presence of disturbances, the closed-loop system is finite-gain L2 stable by the Hamiltonian controller. The Hamiltonian energy approach provides us a physical insight and gives a new way to the controller design. The simulation results illustrate that the proposed method is effective and has its advantage.

Multiple target implementation for a doubly fed induction generator based on direct power control under unbalanced and distorted grid voltage

This paper presents a multiple target implementation technique for a doubly fed induction generator(DFIG) under unbalanced and distorted grid voltage based on direct power control(DPC).Based on the mathematical model of DFIG under unbalanced and distorted voltage,the proportional and integral(PI) regulator is adopted to regulate the DFIG average active and reactive powers,while the vector PI(VPI) resonant regulator is used to achieve three alternative control targets:(1) balanced and sinusoidal stator current;(2) smooth instantaneous stator active and reactive powers;(3) smooth electromagnetic torque and instantaneous stator reactive power.The major advantage of the proposed control strategy over the conventional method is that neither negative and harmonic sequence decomposition of grid voltage nor complicated control reference calculation is required.The insensitivity of the proposed control strategy to DFIG parameter deviation is analyzed.Finally,the DFIG experimental system is developed to validate the availability of the proposed DPC strategy under unbalanced and distorted grid voltage.

Doubly-fed induction generator drive based WECS using fuzzy logic controller

The purpose of this paper is to improve the control performance of the variable speed, constant frequency doubly-fed induction generator in the wind turbine generation system by using fuzzy logic controllers. The control of the rotor-side converter is realized by stator flux oriented control, whereas the control of the grid-side converter is performed by a control strategy based on grid voltage orientation to maintain the DC-link voltage stability. An intelligent fuzzy inference system is proposed as an alternative of the conventional proportional and integral （PI） controller to overcome any disturbance, such as fast wind speed variation, short grid voltage fault, parameter variations and so on. Five fuzzy logic controllers are used in the rotor side converter （RSC） for maximum power point tracking （MPPT） algorithm, active and reactive power control loops, and another two fuzzy logic controllers for direct and quadratic rotor currents components control loops. The performances have been tested on 1.5 MW doubly-fed induction generator （DFIG） in a Matlab/Simulink software environment.

Application of fuzzy logic control algorithm as stator power controller of a grid-connected doubly-fed induction generator

This paper discusses the power outputs control of a grid-connected doubly-fed induction generator （DFIG） for a wind power generation systems. The DFIG structure control has a six diode rectifier and a PWM IGBT converter in order to control the power outputs of the DFIG driven by wind turbine. So, to supply commercially the electrical power to the grid without any problems related to power quality, the active and reactive powers （Ps, Qs） at the stator side of the DFIG are strictly controlled at a required level, which, in this paper, is realized with an optimized fuzzy logic controller based on the grid flux oriented control, which gives an optimal operation of the DFIG in sub-synchronous region, and the control of the stator power flow with the possibility of keeping stator power factor at a unity.

WIND POWER IMPACT ON TRANSIENT FAULT BEHAVIOR IN ELECTRICAL POWER GRID USING DOUBLY FED INDUCTION GENERATOR

The amount of electrical energy produced by wind mills is constantly increasing.Nowadays detailed analyzes considering the impact of wind energy integration on the transmission system are required.The goal of this study is to investigate the dynamic response of a wind turbine with doubly fed induction generator connected to the power system during grid disturbance.The current and future wind power situation is modeled as two cases and a transient fault is simulated.In order to analyze the impact of wind energy integration in electrical power grid,a power system model has been developed,integrated with wind turbine using doubly fed induction generator and transient analysis are performed.Here,an attempt has been made to compare the impact,in terms of voltages,currents,total harmonic distortion,etc.,of adding wind turbines into electrical power grid.

Analysis on Effect of Parameters of Different Wind Generator on Power Grid Transient Stability

To analyze the factors which affecting transient stability of power system, the dynamic model of doubly-fed induction generator and direct-drive PM synchronous generator has been built using PSCAD. Impact of different wind farm integration on grid typically in China has been presented. The influence of the variations of transient reactance, negative sequence reactance and rotary inertia on critical clearing time of power system transient stability is analyzed by time-domain simulation. Mixture operation of DFIG and PMSG to optimize the stability of system has been analyzed firstly. The digital simulation results show that doubly-fed induction wind turbines is a better choice to meet the requirement of system instability due to large wind farm integration in comparison with direct-drive PM synchronous wind turbines. With a rather large rotary inertia, the proper ratio of direct-drive PM synchronous wind turbines used in wind farm could be comprehensive planning by optimized the stability of system. Analysis of this paper should be provided as academic reference for improving design of wind farm system.