Brushless Doubly Fed Induction Generator Research Articles

A Comprehensive Study on Model Simplification and Parameter Estimation of Brushless Doubly Fed Standalone Generation System

Brushless doubly-fed induction generator (BDFIG) has great potential in stand-alone generation applications. Currently, lots of control strategies have been proposed based on the BDFIG d-q model with different machine parameters ignored for simplification, but the simplification influences on model accuracy have not been discussed systematically, and the application ranges are not clear. Therefore, aiming at controller design, this paper provides a comprehensive study on model simplification and parameter estimation of brushless doubly-fed stand- alone generation. Based on the intuitive DFIG-like BDFIG model and the typical electrical quantity relations widely used in stand-alone controller design, steady-state and dynamic parameter sensitivities of BDFIG are analyzed with operation condition fully considered. Based on the analysis, the universal BDFIG simplified d-q model aiming at stand-alone control is evaluated sufficiently, and the application range is clarified. The simplification of control analysis is illustrated, and a highly-targeted and simple parameter estimation method is proposed for simplified modeling and control. Finally, simulations and experiments verify the analysis accuracy of the simplified DFIG-like BDFIG model and the feasibility of the proposed parameter estimation method.

Stability Analysis and Enhanced Virtual Synchronous Control for Brushless Doubly-fed Induction Generator Based Wind Turbines

Stability Analysis and Enhanced Virtual Synchronous Control for Brushless Doubly-fed Induction Generator Based Wind Turbines

Sliding mode control of brushless doubly-fed machine used in wind energy conversion system

This paper presents the applications of the sliding mode control to a brushless doubly fed induction generator (BDFG) used in wind-energy conversion systems. The controller is designed based on the sliding mode control combined with a the stator power winding flux oriented vector principle, the independent control of active and reactive powers has been developed and the performance of proposed the block diagram of the variable speed constant-frequency (VSCF) wind energy generation system is validated in the Matlab/Simulink environment and the computer simulation results obtained confirm the effectiveness of this control strategy.

Control of a wind energy conversion system based on brushless doubly fed induction generator

This paper discusses the control a new topology of a brushless doubly-fed induction generator (BDFIG) using back-to-back PWM converters. The goal of BDFIG control is to achieve a similar dynamic performance to the doubly fed induction generator (DFIG), The control strategy for flexible power flow control is developed. Currently the BDFIG has been the subject of current investigation and it shows to be a valid alternative for wind energy systems.

Analysis on the Characteristic of the Instantaneous Inrush Current of Brushless Doubly Fed Induction Generator

Compared with traditional doubly-fed induction generator (DFIG), the brushless doubly-fed induction generator (BDFIG) eliminates the slip rings and brush gear, which benefits high reliability and low maintenance costs. Thus BDFIG promises broad application prospects in power generation. With the rapid growth capacity of the power generation system, the inrush transient current becomes an important factor that cannot be ignored. The paper analyzes the characteristic of the inrush current of BDFIG under synchronization error. First, the character of the inrush current is analyzed under the s-domain, which can be understood more clearly; Second, in order to analyze character of the inrush current under time-domain, the specific expression of inrush current is obtained with amplitude error and phase error. Third, the influence of amplitude error or phase error is also investigated based on the obtained expressions. Finally, the analysis is verified by both the simulation and experimental results. The work could facilitate future research on suppressed the inrush current of BDFIG, thereby increasing the security and stability of the system

Improved Efficiency Optimization Control for Brushless Doubly Fed Induction Generator–DC System by Regulating Stator Frequency

Taking into account the relatively low efficiency of brushless doubly fed induction generator (BDFIG) at present, the efficiency optimization is important to promote the industrial application of BDFIGs. The power winding (PW) frequency of the BDFIG–dc system is with the additional freedom of control, which provides an important condition for efficiency optimization. In this article, based on the loss analysis of the power converter and the improved steady-state equivalent circuit of BDFIG considering iron loss, the loss model of BDFIG–dc system is derived. Furthermore, the system loss model is established with the PW frequency of BDFIG as the main state variable. From the proposed loss model, the maximum efficiency of BDFIG–dc system can be achieved by optimizing the PW frequency. The comprehensive simulation and experimental results demonstrate that proposed efficiency optimization control strategy can increase the efficiency of both the standalone and grid-connected BDFIG–dc systems by 0.2–7.8% under different operation conditions.

An MRAS Speed Observer Based on dq-axis Power Winding Flux for Sensorless Control of Standalone BDFIGs

This paper addresses a new mechanical rotor speed observer for sensorless control of standalone Brushless Doubly-Fed Induction Generators (BDFIGs) based on the dq axis power winding flux Model Reference Adaptive System (MRAS) observer. The observer is integrated in the control method for control the terminal frequency and voltage magnitude under various work conditions. The efficiency of the proposed observer and control strategy is proved by overall simulation results and confirmed by experiments. As illustrated without using physical rotor speed sensors, the sensorless control strategy integrating the proposed speed observer can keep effectively the frequency and amplitude of power winding voltage fixed at various rotor speeds and under various conditions of machine parameter and load changes.

Fabrication and Mathematical Modeling of the Brushless Doubly Fed Induction Generator-Based Wind Electric Conversion System

Electricity generation with minimal environmental pollution is required for the world’s sustainable future, and wind electric generation is one of them. Brushless doubly fed induction generator (BDFIG), which derives from cascade induction machine technology, has grown in popularity as a wind electric generator due to advantages over doubly fed induction generator (DFIG) and permanent magnet synchronous generator (PMSG) such as the absence of slip rings and brushes and high-cost permanent magnets. Wind energy research is critical for any country’s economic development and long-term sustainability. As a result, an experimental setup in a laboratory is required to replicate the behaviour of a wind turbine in the steady state. This study discusses the emulation of wind turbine characteristics in the laboratory using a prototype of a separately excited DC motor mechanically coupled to a brushless doubly fed induction generator (BDFIG). The wind turbine emulator-brushless doubly fed induction machine (WTE-BDFIM) prototype was tested in the laboratory under high power and low wind speed conditions. As a result, the simulation of the same hardware configuration in MATLAB was performed to investigate the overall performance of the BDFIM-based WECS. To determine the equivalent circuit parameters of the BDFIM, which are required for simulation, tests were performed on a prototype of 3.5 kW, 2/6 pole, 400 V, star/delta-star, and BDFIM in two modes, namely, the simple induction mode and the cascade induction mode. Based on the BDFIM parameters, a MATLAB Simulink model of a BDFIG-based wind electric conversion system (WECS) is created and its performance is investigated. Results of both hardware and simulation show that BDFIG can be used as the wind electric generator over a wider speed range compared to that of DFIG, an important feature that is required to get maximum power extraction from the wind turbine.

Performance Investigation of Wind Turbine Induction Generators connected with a Single-Area Power System

Wind turbine power is a vital source of renewable energy and accounts for major plants in generating electricity in various countries. The aim of this paper is to develop the physical model of three types of wind-turbine induction generators and to investigate their impacts on the frequency in a single-area power system. The generator types are as follows: (i) squirrel cage induction generator (SCIG); (ii) doublyfed induction generator (DFIG) and (iii) brushless doubly-fed induction generator (BDFIG). The analysis scenario is demonstrating the effect of variable wind speeds on the grid frequency under load variations. The simulation results show that BDFIG achieves better performance in comparison with DFIG and SCIG in terms of maintaining the grid frequency.

Performances of Vector Control of Brushless Doubly-Fed Induction Generator Incorporate in Wind Energy Conversion System with TSR MPPT

Currently, variable speed wind systems based on the Brushless Doubly-Fed Induction Machine (BDFIM) are the most used in Wind Energy Conversion System (WECS). The main features of BDFIM are high reliability due to its brushless operating, lower capital and operational costs. This work presents a field-oriented control scheme for a BDFIG acting as a variable-speed generator. The presented vector control is determined on the power-winding stator-flux frame and can be employed to control both the speed and the reactive power. In addition, use of wind speed sensors by an anemometer, and maximize wind energy extraction Tip Speed Ratio (TSR) Maximum Power Point Tracker (MPPT) is proposed. Several simulation results under different operating conditions are provided to prove the effectiveness of the presented scheme. The obtained results show the efficiency and validity of the proposed control strategy.

Voltage regulation-based sensorless position observer with high-frequency signal injection topology for BDFIGs in ship power microgrid systems

The aim of this paper is to propose a new rotor position observer based on the approach of high-frequency signal (HFS) injection for sensorless direct voltage control (DVC) strategy of the stand-alone brushless doubly-fed induction generators (BDFIGs). The proposed new observer is relied on the injection of HFS into the control winding (CW) side, (CW-HFS), while the resulted induced signal detected from the power winding (PW) side will observe the information of rotor position. The suggested new sensorless control method neither need any saliencies in the rotor side nor require any flux computation process, which can ensure the simplicity and efficacy of the proposed method. Comprehensive experimental results are obtained with a prototype wound-rotor BDFIG. The corresponding results ensure the capability and efficacy of the suggested sensorless DVC strategy based on the proposed rotor position observer using the CW-HFS injection approach with a good transient behavior under different operating conditions for the stand-alone BDFIG systems.

Improved MRAS Rotor Position Observer Based on Control Winding Power Factor for Stand-Alone Brushless Doubly-Fed Induction Generators

The main contribution of this study is to propose a new rotor position observer with the approach of model reference adaptive system (MRAS) associated with the quantity of control winding (CW) power factor of the brushless doubly-fed induction generator (BDFIG) for sensorless voltage control target in stand-alone systems. The proposed observer relies on the field-orientation scheme of power winding (PW) side. The proposed sensorless methodology does not need any computation process with integration for obtaining the flux components. In addition, the new methodology can reduce the voltage sensors required for detecting the actual CW voltage quantities to be used in the calculations process of the proposed MRAS procedure by directly realizing the CW reference stationary voltages from the input path of SVPWM. This would ensure the simplicity of the suggested procedure for detecting the rotational position of the generator. The stability confirmation of the presented estimation method is analyzed and realized with the aid of technique of hyperstability concept and aided with the criteria of Popov's analysis. Moreover, the verification of robustness for the proposed observer is studied via uncertainty issues of machine parameters. Comprehensive simulation and experimental results are carried out to verify this method,

Enhanced control and operation for brushless doubly-fed induction generator based wind turbine system under grid voltage unbalance

This paper presents an enhanced control and operation for brushless doubly-fed induction generator (BDFIG) based wind turbine system under grid voltage unbalance by considering the controls of machine side converter(MSC) and grid side converter(GSC) together. The MSC is controlled to eliminate torque oscillations and realize decoupling control of power winding(PW) average active and reactive power while the GSC is controlled to eliminate oscillations in the total output active power. A single current closed-loop controller composed of a positive sequence current controller in the positive synchronous reference frame and a negative sequence current controller in the negative synchronous reference frame is designed for both MSC and GSC. To achieve decoupling control and improve system dynamic response, in current loops, all the disturbances and cross-coupling terms are derived and used for feedforward control. A fast sequence decomposition algorithm is employed to reduce the considerable time delays of using notch filers. In order to validate the effectiveness of proposed control, simulations for a 2WM BDFIG based wind generation system were carried out, the results demonstrated that the proposed control can effectively eliminate oscillations of BDFIG torque and total output active power, and has good dynamic and stable performance.

Full-Order Terminal Sliding-Mode Control of Brushless Doubly Fed Induction Generator for Ship Microgrids

This paper proposes a full-order terminal sliding-mode (FOTSM) control scheme for brushless doubly fed induction generator (BDFIG)-based islanded microgrids. To deal with mismatched uncertainties in the BDFIG system, virtual control technique-based full-order sliding-mode control is applied to stabilize the amplitude and frequency of terminal voltage. In the current loops, two full-order terminal sliding-mode controllers are designed to make sure that the current tracking errors can reach their equilibrium points in finite time. It is demonstrated by the comprehensive simulations that the proposed method can significantly improve the tracking accuracy, the rapidness, and the robustness to the uncertainties of the BDFIG control system and can enhance the output voltage quality. Furthermore, an experimental study of the proposed control method for BDFIG-based islanded microgrids would be another important future work.

Dynamic Low Voltage Ride through Detection and Mitigation in Brushless Doubly Fed Induction Generators

Brushless doubly-fed induction generators have higher reliability, making them an attractive choice for not only offshore applications but also for remote locations. These machines are composed of two back-to-back voltage source converters: the grid side converter and the rotor side converter. The rotor side converter is typically used for reactive current control of the power winding using the control winding current. A low voltage ride through (LVRT) fault is detected using a hysterisis comparison of the power winding voltage. This approach leads to two problems, firstly, the use of only voltage to detect faults results in erroneous or slow response, and secondly, sub-optimal control of voltage drop because of static reference values for reactive current compensation. This paper solves these problems by using an analytical model of the voltage drop caused by a short circuit. Moreover, using a fuzzy logic controller, the proposed technique employs the voltage frequency in addition to the power winding voltage magnitude to detect LVRT conditions. The analytical model helps in reducing the power winding voltage drop while the fuzzy logic controller leads to better and faster detection of faults, leading to an overall faster response of the system. Simulations in Matlab/Simulink show that the proposed technique can reduce the voltage drop by up to 0.12 p.u. and result in significantly lower transients in the power winding voltage as compared to existing techniques.

Dynamic Modeling and Control of BDFRG under Unbalanced Grid Conditions

The Brushless Doubly-Fed Reluctance Generator (BDFRG) is a potential alternative to the Doubly Fed Induction Generator (DFIG) in wind power applications owing to its reasonable cost, competitive performance, and high reliability. In comparison with the Brushless Doubly-Fed Induction Generator (BDFIG), the BDFRG is more efficient and easier to control owing to the cage-less rotor. One of the most preferable advantages of BDFRG over DFIG is the inherently better performance under unbalanced grid conditions. The study conducted in this paper showed that conventional vector control of the BDFRG results in excessive oscillations of the primary active/reactive power, electromagnetic torque, and primary/secondary currents in this case. In order to address such limitations, this paper presented a new control strategy for the unbalanced operation of BDFRG-based wind generation systems. A modified vector control scheme was proposed with the capability to control the positive and the negative sequences of the secondary currents independently, thus greatly reducing the adverse implications of the unbalanced supply. The controller performance has been validated by simulations using a 1.5 MW BDFRG dynamical model built upon the positive and negative sequence equations. The main benefits of the new control strategy are quantified in comparison with conventional PI current control design.

Improving Transient Behavior of a Brushless Doubly Fed Induction Generator through Reactive Current Control of Grid-Side Converter

Brushless doubly-fed induction generators have higher reliability, making them an attractive choice for not only offshore applications but also for remote locations. These generators are composed of two back-to-back voltage source converters, a grid side converter and a rotor side converter. Existing techniques use the rotor side converter for reactive current control; however, it is more suitable for stabilizing steady state behavior. In order to stabilize the voltage fluctuations at the point of common coupling (PCC) due to sudden inductive load introduction, the grid side converter may be a better choice due to faster response and higher control bandwidth. Therefore, this paper proposes a control scheme for the grid side converter to suppress the PCC voltage fluctuations when a large inductive load is suddenly connected. The proposed technique is based on an analytical model of the transient behavior of the voltage drop at the PCC. The analysis shows that reactive current control using the grid side converter introduces a double fundamental frequency component to the PCC voltage. To block this harmonic, we designed a notch filter. The simulation results in Matlab/Simulink show that the proposed technique can not only significantly reduce the voltage drop but also results in an 82% reduction in voltage distortion at the PCC.

Dual-Mode Control for Brushless Doubly Fed Induction Generation System Based on Control-Winding-Current Orientation

Brushless doubly-fed induction generator (BDFIG) has huge potential due to its high reliability and low maintenance costs. In order to meet the requirements of the modern grid code, the BDFIG system should have dual-mode (i.e., operating in both stand-alone and grid-connected modes) capability. Rather than using two separated systems for two modes, this article proposes a unified control architecture for dual-mode operation. Such a unified architecture is based on the stand-alone control-winding (CW) current orientation, and the grid-connected functions are realized by adding three plug-in functional units: 1) the phase-lock function is realized by adding an increment adjustment controller into the CW-angle control; 2) the inrush current during mode switching is suppressed by adding a high-pass feedforward controller into the inner-loop controller; 3) the active power and reactive power are regulated by adding an amplitude-angle controller of CW current. With the proposed unified architecture, the high-performance dual-mode operation is achieved without breaking the original CW-current orientation system, facilitating the overall system design a lot. The detailed analysis and designs are given in this article, and the experiments based on a BDFIG prototype are given to verify the feasibility.

Modeling and Coordinated Control Design for Brushless Doubly-Fed Induction Generator-Based Wind Turbine to Withstand Grid Voltage Unbalance

Grid codes require wind turbines to have capability to withstand a certain grid voltage unbalance without tripping. However, existing controls for brushless doubly-fed induction generator (BDFIG) based wind turbine under grid unbalance have many problems such as difficulty in realizing decoupling control, involvement with flux or current estimations, and complex control structure. Moreover, the existing studies only focused on the control of machine side converter (MSC), but the coordinated control between MSC and grid side converter (GSC) and the control objectives of overall BDFIG wind turbine system have not yet been addressed so far. To overcome these problems and improve the control capability, this paper proposes a coordinated control strategy by considering MSC and GSC together. First, the enhanced control objectives for overall BDFIG wind turbine system are determined. Second, the simple single current closed-loop controllers without involving with any flux or current estimations are designed for MSC and GSC, respectively. Meanwhile, in current loops, all the disturbances and cross-coupling terms on <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dq</i> axes are derived and used for feedforward control so as to achieve decoupling control and improve system dynamic response. Further, a fast sequence decomposition approach is employed to enhance the control characteristics of the whole system. Finally, the effectiveness of proposed control is validated through case studies for a 2 MW BDFIG based wind generation system. The results demonstrate that the proposed control can effectively achieve the control objectives of overall wind turbine system under grid voltage unbalance and provide excellent dynamic and stable performance.

Control &amp; Design for FOPID Based Line-Side Converter of the Brushless Doubly-Fed Induction Generator

This paper deals with the operation of doubly fed induction generator (DFIG) with an integrated active filter capabilities using grid-side converter (GSC). The main contribution of this work lies in the control of GSC for supplying harmonics in addition to its slip power transfer. The rotor-side converter (RSC) is used for attaining maximum power extraction and to supply required reactive power to DFIG. This wind energy conversion system (WECS) works as a static compensator (STATCOM) for supplying harmonics even when the wind turbine is in shutdown condition. Control algorithms of both GSC and RSC are presented in detail. The proposed DFIG-based WECS is simulated using MATLAB/Simulink.