Brushless Doubly-fed Induction Machine Research Articles

Time-harmonic finite element model for brushless doubly-fed induction machine in natural operating mode

The natural mode of operation for the brushless doubly-fed induction machine is a particular instance of synchronism at a so-called natural rotor velocity when one stator winding is powered by an AC and the other by a DC voltage source. Consequently, in addition to the rotating magnetic field, there exists a magnetic field that is fixed to the stator frame of reference. Analysis in this specific mode is essential as the natural velocity arises from the choice of pole numbers, thereby determining machine efficiency. However, this presents a significant challenge when it comes to mathematical modeling using complex-valued steady-state models through either equivalent-circuit or finite element analysis. This paper presents a study on the extension of the recently-proposed steady-state complex-valued finite element model for the brushless doubly-fed induction machine to enable its application in the natural operating mode. A high correlation with the data obtained from a time-stepping model is obtained for the extended model when subjected to both low and high levels of saturation of the magnetic circuit. This extension makes the whole approach applicable in all operating conditions and modes of the brushless doubly-fed induction machine. Considering the nearly two orders of magnitude lower computational costs associated with analysis via the proposed model compared to time-stepping analysis, it is particularly useful in scenarios that involve extensive computations and require multiple cases to be considered such as design sensitivity analysis, topology optimization or a connection with machine learning techniques.

Vector Control of Brushless Doubly-Fed Induction Machines Based on Highly Efficient Nonlinear Controllers

Vector Control of Brushless Doubly-Fed Induction Machines Based on Highly Efficient Nonlinear Controllers

State-feedback control of a grid-tied cascaded brushless doubly-fed induction machine

The cascaded brushless doubly-fed induction machine (CBDFIM) is the developed version of a classic slip-ring doubly-fed induction machine (DFIM). Deprived of the main DFIM disadvantage - the slip-ring connection, the cascaded brushless doubly-fed induction machine has better durability and lower maintenance costs. Structurally it is realized by the presence of control stator and main stator working with a common rotor shaft. However, this type of electrical machine is characterized by much higher control inertia and larger dq control axis coupling, in comparison to DFIM. This fact makes problematic obtainment good dynamic performance and stability of the controlled system for classic control schemes. In the paper presented cascaded brushless doubly-fed induction machine state-feedback control schemes, based on CBDFIM full and reduced state-space model. Proposed algorithms allow control of CBDFIM generated active and reactive power components in a grid-tied operation and offer great possibilities of obtaining the desired dynamics parameters and stability of the controlled system. The main paper goal is to prove that reduced order state feedback control can be equally effective than full state feedback control in terms of obtained closed loop system dynamics and reduces influence of the couplings between the controlled variables.

Control of Cascaded/Brushless Doubly-Fed Induction Motors With Real-Time Torque Optimization

Brushless doubly-fed induction machines offer a potential alternative to regular doubly-fed induction generators for wind turbines, due to higher reliability and lower maintenance costs. As motors and generators, the brushless machines could also be part of new technological solutions for hybrid-electric propulsion, including aircraft propulsion. A main advantage is that most of the power would be transferred from generators to motors without electronic conversion. The paper proposes a new speed control algorithm that maximizes the available torque within the limits of the control winding currents and ensures anti-windup protection. The maximum torque and the control variables are obtained through simple analytical computations. The derivations of the paper are based on a complex-variable representation that simplifies the mathematical model and the control algorithm. Compact formulas specify the controller parameters as functions of the machine parameters and of the desired closed-loop behavior. The results are tested on a laboratory testbed using a cascaded doubly-fed induction motor and demonstrate fast responses reaching torque limits that are computed in real-time by the algorithm. While control is achieved through the converter interfaced with the control windings, the data shows that most of the active and reactive power is exchanged directly through the power windings. Similar results are obtained in simulations of a larger brushless doubly-fed induction motor.

Literature review on the control of brushless doubly-fed induction machine

In recent years, dual-fed brushless asynchronous generators (BDFIG) have attracted considerable attention in variable-speed drive applications due to their simple and robust structure, good operating characteristics, and low maintenance requirements. The purpose of controlling dual-fed brushless induction generators is to achieve better performance. However, various control techniques applied to this machine have shown their limits in case of sudden fluctuations in rotor speed, relatively long response time, poor stability and high performance sensitivity to parameter fluctuations. Given its difficulty, research has focused on the most advanced technology in the world: artificial intelligence (AI). The main objective of this article is to list all the control techniques that have been applied to the BDFIG. It appears from our study that genetic algorithms as well as the multilayer perceptron have not yet been applied for the control of BDFIG.

High-Efficient Nonlinear Control for Brushless Doubly-Fed Induction Machines

The brushless doubly-fed induction machine (BDFIM) is suitable for applications that need adjustable speed within limited ranges. It is a promising machine if its control strategies, such as the maximum torque per total copper losses (MTPCL) control, are well designed. A BDFIM has two stator windings, a power winding (not controllable) and a control winding (CW) (controllable through a partially rated back-to-back converter). Unlike singly-fed electrical machines, which are fully controllable and the MTPCL can be easily implemented to them, implementing the MTPCL control in a BDFIM is challenging. In this paper, the model-based MTPCL control strategy in the presence of a nonlinear controller in the BDFIM drive is developed. To realize this strategy, we first determine an expression in terms of the angle of the CW's current as a controllable variable. The optimal angle of the CW's current, which guarantees the realization of the MTPCL strategy, is then mathematically obtained using the numerical minimization approach. Next, the proposed passivity-based nonlinear controller regulates both the MTPCL criterion and the electromagnetic torque directly as the output variables. The proposed strategy is validated by a TMS320F2833 microcontroller synchronized with a personal computer for a 3 kW prototype D132s-BDFIM.

Time‐harmonic field‐circuit model for brushless doubly fed induction machine

AbstractA computationally efficient time‐harmonic finite element model for the steady‐state analysis of a brushless doubly fed induction machine (BDFIM) is proposed. In the model, the electromagnetic couplings of the BDFIM are described by means of the sum of two complex magnetic vector potentials that represent the two fundamental harmonic time components of the magnetic flux density distribution in the rotor frame of reference. As in an ordinary induction motor, the non‐linearity of the magnetisation characteristic is accounted for using an effective magnetic permeability. For the BDFIM, this is derived by considering the features of modulated magnetic flux density waveform. The accuracy of the approach has been validated by comparing the characteristics of a D270 machine operating in the double‐feed mode with ones obtained from the experimentally verified time‐stepping model at various operating conditions. High accuracy of the results coming from the proposed model is demonstrated even under deep saturation conditions within the magnetic circuit.

Novel Equivalent Circuit Model Applicable to All Operation Modes for Brushless Doubly Fed Induction Machines

The equivalent circuit is an indispensable tool for analyzing the steady-state characteristics of the brushless doubly fed induction machine (BDFIM). However, the most commonly used equivalent circuits are not available to analyze some special operation modes, such as the natural synchronous mode with one set of winding powered by dc current. In order to overcome the limitation, in this article, a novel equivalent circuit is proposed. At first, the electromagnetic relations within BDFIMs are described by a new approach in which the cause of working magnetic fields is refined. Then, the equivalent circuit is built by the rigorous derivation of electromagnetic relations. And a few features of BDFIMs in some typical operation modes including the natural synchronous mode are introduced in details. Finally, the validity of the equivalent circuit is made by comparison of model and experimental results based on a wound-rotor BDFIM prototype. The proposed model with clear physical concept can cover all operation modes. And both power relationship and torque components reflected in the proposed model is more detailed and clearer than those reflected in the traditional one.

Novel fully sensorless synergetic control of brushless doubly fed induction machine integrated in wind energy conversion system driven by fuzzy-based HCS MPPT algorithm

This paper proposes a novel fully sensorless synergetic algorithm that adopts concerns from both power, torque, and speed of brushless doubly fed induction machine (BDFIM) for application in wind energy conversion system (WECS). A sensorless fuzzy-based hills climb search algorithm (HCS-MPPT) is introduced to the control system along with a comparison study with the conventional tip speed ratio algorithm (TSR-MPPT). For studying the feasibility of the suggested control, a robust control of the BDFIM based on synergetic control theory is build up for the first time ever on this machine type with different scenarios where the active and reactive power, the torque, and speed of the machine are controlled. In the second step, the aim is maximizing the wind’s energy extraction by replacing the wind speed sensors with a fuzzy-based HCS-MPPT approach. Lastly, to increase the robustness of the suggested scheme control, an extended Kalman filter EKF is employed for the estimation of rotor speed in presence of considerable noise values in order to make it closer to reality as possible. Computational simulation results confirm that the proposed method, consistently outperforms other techniques and proves effectiveness under several conditions.

Performance Analysis of Nested-loop Secondary Linear Doubly-fed Machine Considering End Effects

Nested-loop secondary linear doubly-fed machine (NLS-LDFM) is a novel linear machine evolved from rotary brushless doubly-fed induction machine, which has a good application prospect in linear metro. In order to analyze the performance of NLS-LDFM, the mechanism and action rules of end effects are investigated in this paper. Firstly, the mechanism of static and dynamic end effects is analyzed in aspect of direct coupling, winding asymmetry and transient secondary current. Furthermore, based on the winding theory for short primary linear machines, the machine parameters are established qualitatively considering pulsating magnetic field of NLS-LDFM. Finally, the NLS-LDFM performance analysis is supplemented by the finite element algorithm (FEA) simulation and experiments under different operating conditions.

Modeling and Vector Control of a Cage+Nested-Loop Rotor Brushless Doubly Fed Induction Motor

The brushless doubly fed induction machine (BDFIM) is being considered as a possible solution for low-speed wind energy generator applications. It has been proposed as an alternative to the doubly fed induction machine (DFIM) due to its robust rotor structure as well as low operational maintenance requirements. However, due to its complicated control philosophy, higher overall machine size due to the extra set of control windings in the stator, and slightly lower efficiency, it is yet to be adopted in commercial applications. In this paper, a simplified vector control scheme for the control winding of a cage+nested-loop (cage+NL) rotor BDFIM is proposed. Experimental results are compared with simulations to validate the effectiveness of the proposed control scheme.

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.

Design and analysis of a dual-stator brushless doubly-fed induction machine with a staggered dual-cage rotor

Design and analysis of a dual-stator brushless doubly-fed induction machine with a staggered dual-cage rotor

A Review of the Advancements in the Design of Brushless Doubly Fed Machines

Research interest on brushless doubly fed induction machines (BDFMs) is increasing, as they offer higher reliability compared to doubly fed induction generators (DFIGs) in wind turbines. At the moment, BDFMs do not have a definitive structure nor design process, as literature is rife with different approaches to designing BDFMs. In this paper, a comprehensive review of the design of BDFMs from available literature is conducted. The evolution of cascade induction machine systems to contemporary BDFMs is first illustrated. Pioneering research work in the evolution which have influences on modern BDFM designs are highlighted. Relevant research on different aspects of present day BDFM design are then discussed. BDFM design and optimization methodologies applied in available literature are also explored.

A Cascade PI-SMC Method for Matrix Converter-Fed BDFIM Drives

This article proposes a cascade proportional-integral second-order sliding mode control (PI-SMC) method for matrix converter-fed brushless doubly fed induction machine (BDFIM). The PI-SMC method consists of a PI speed controller with an inner-loop second-order sliding mode control (SMC). The PI controller provides a reference to the inner-loop second-order SMC with constraints according to the system requirements in terms of maximum current and speed. As the discontinuous sign function in the traditional SMC is replaced by the continuous supertwisting function, the chattering problem is eliminated for inner-loop second-order SMC. Moreover, the inner-loop second-order SMC has robustness and interference immunity against nonlinear disturbances of the BDFIM. Simulation and experimental results demonstrate the excellent robust tracking performance of the proposed PI-SMC method.

Design Method of Differential Cascading for Dual-Stator Brushless Doubly-Fed Induction Wind Generator With Staggered Dual Cage Rotor

This article proposes a new differential-cascading-based dual-stator brushless doubly-fed induction machine with a staggered dual cage rotor. Conventional differential mode of the brushless doubly-fed machine with cage rotor suffers from the low number of rotor bars because of the low equivalent synchronous pole pairs of |p1-p2|, and thus, severe rotor flux leakage, low capacity of magnetic field conversion of the rotor and low efficiency. To overcome the obstacle of the excessive harmonics of the rotor, a design method based on the differential cascading is proposed which enables the cage rotor with a high number of conductor bars even in the case of low pole pairs of |p1-p2|, hence the greatly reduced rotor leakage inductance and enhanced performance of the machine. The rotating magneto-motive force theory is applied to derive the interconnection rule of the staggered dual cage rotor, and meanwhile, the corresponding examples are illustrated. The performance comparisons between the differential cascading and the sum cascading based on the proposed machine are carried out. The results show that the proposed machine based on the differential cascading obtains higher power densities comparing to the sum cascading at the region of sub-natural synchronous speed, while its drawback is the increment of the loss due to the high rotor frequency, gaining lower efficiencies at the region of super-natural synchronous speed.

Analytical analysis and performance characterization of brushless doubly fed induction machines based on general air-gap field modulation theory

Air-gap magnetic field modulation has been widely observed in electric machines. In this study, we present an analytical analysis and performance characterization of brushless doubly fed induction machines (BDFIMs) fed by two independent converters from the perspective of air-gap field modulation. The spiral-loop winding is studied in detail as an example to show the generalized workflow that can also be used to analyze other short-circuited rotor winding types, such as nested-loop and multiphase double-layer windings. Magnetic field conversion factors are introduced to characterize the modulation behavior of special rotor windings and facilitate their comparison in terms of cross-coupling capability, average torque, and harmonic content of the air-gap flux density waveforms. The stator magnetomotive force (MMF), rotor MMF, and resultant air-gap MMF are considered, based on which the closed-form inductance formulas are derived, and the torque equation is obtained along with the optimal current angle for maximum torque operation by using the virtual work principle. The design equations are then developed for the initial sizing and geometry scaling of the BDFIMs. Transient finite element analysis and experimental measurements are performed to validate the analysis.

Spiral vector modeling of brushless doubly-fed induction machines with short-circuited rotor windings

A unified spiral vector model is presented that can be used to assist the finite element method-based performance analysis of brushless doubly-fed induction machines with various short-circuited rotor windings. Specifically, magnet-free brushless doubly-fed induction machines working in doubly-fed or singly-fed synchronous mode are investigated. A dynamic model in spiral vector notation is developed, based on which the torque-angle and power-angle characteristics are derived. It is shown that the investigated brushless machines are equivalent to a traditional non-salient-pole synchronous machine with brushes. By introducing a conversion factor, they can also be analyzed with methods similar to the conventional phasor theory. A comparison is made between the brushless doubly-fed induction machine and non-salient-pole wound-field synchronous machine with brushes, revealing that the performance of the brushless machine degrades faster when the laminated core is saturated. A scaled-down prototype is tested to validate the effectiveness of the theoretical analysis.

Advances in Fault Diagnostics and Post‐Fault Operation of Electrical Drives

Advances in Fault Diagnostics and Post‐Fault Operation of Electrical Drives

Eccentricity fault detection in brushless doubly fed induction machines

A new fault diagnosis method for detecting the rotor eccentricity faults including static, dynamic and mixed eccentricity is proposed for brushless doubly-fed induction machines (BDFIMs). BDFIMs are attractive alternatives for the conventional doubly-fed induction generator (DFIG) for offshore wind power generation; therefore, paying attention to their fault detection is essential. Existing fault detection methods for conventional induction machines cannot be directly applied to the BDFIM due to its special rotor structure and stator winding configurations as well as complex magnetic field patterns. This article proposes a novel fault detection method based on motor current signal analysis to determine stator current harmonics, induced by the nested-loop rotor slot harmonics (NRSHs), as fault indices. The analysis is performed under healthy conditions and with different types of rotor eccentricity. Finally, a sensitivity analysis is carried out to confirm the practicability of the proposed technique with various fault intensities and load conditions. Analytical winding function approach, finite element analysis and experimental tests on a prototype D180 BDFIM are used in this study to validate the proposed fault detection technique.