Conference Paper

Real-time rotor bar current measurements using Bluetooth technology for a brushless doubly fed machine (BDFM)

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Abstract

The brushless doubly fed machine (BDFM) shows economic promise as a variable speed drive or generator. The optimization of the machine and model-based control strategies both rely on machine models, and the experimental verification of these models. To date, dynamic measurements of rotor quantities have not been possible. The authors present a system of measuring rotor bar currents in real time using a Rogowski coil to detect the current and recently developed Bluetooth wireless technology to transmit the data from the moving rotor to a computer. Experimental data collected from the system are included.

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... Abdi-Jalebi et al. developed an instrumentation technique to measure rotor bar currents in real time using a Rogowski coil to detect the current and recently developed Bluetooth wireless technology to transmit the data from the moving rotor to a computer [41][42][43][44]. The system will be described in detail in this dissertation. ...
... However, there has not been any work on the measurements of rotor currents in real time in the BDFM. It is believed that the only significant contribution in this area is due to the authors [41,42]. The design of the rotor is critical to good performance and direct measurements of rotor currents would help to build confidence in rotor performance as machine sizes increase. ...
... A system has been developed to measure rotor bar currents directly with Rogowski coils, using the Bluetooth wireless technology to transmit the signal from the moving rotor back to a computer for logging and analysis [41,42,61]. Bluetooth is one of a range of recently introduced digital wireless protocols developed for the transmission of digital data [62]. ...
Thesis
Full-text available
The Brushless Doubly-Fed Machine (BDFM) shows promise as a variable speed drive and generator. The BDFM is particularly attractive for use as a generator in wind turbines as the machine's brushless operation reduces maintenance requirements. However, a deeper understanding of the machine is needed before full size generators can be designed. This dissertation contributes towards this goal through machine analysis, modelling and instrumentation. A system of measuring rotor bar currents in real-time is developed using a Rogowski probe to transduce the signal and Bluetooth wireless technology to transmit data from a moving rotor back to a computer for logging and analysis. The design of the rotor is critical to good performance and direct measurements of rotor currents would help to build confidence in rotor performance as machine sizes increase. As well as verifying theoretical predictions, measurements of rotor currents are employed to acquire parameter values for machine models. A coupled-circuit model is developed for a general class of BDFMs. A simple analytical method to calculate the parameter values is presented. An equivalent circuit model is derived from the coupled-circuit model by performing suitable transformations. The order of the rotor states is reduced to allow parameter values to be computed for a simple equivalent circuit representation of the machine. Both coupled-circuit and equivalent circuit models are verified by experimental tests on a prototype BDFM. An experimental method of parameter estimation is developed for the equivalent circuit model, based on the curve-fitting approach. Three widely adopted optimisation algorithms are implemented as the solution methods to the nonlinear problem. The proposed algorithms are compared with respect to their performance, computational cost and simplicity. Rotor current measurements are employed to estimate the parameter values for the full equivalent circuit. A method of obtaining the rotor current in the equivalent circuit from the measured bar currents is presented. The effects of iron saturation in the BDFM modelling are investigated. A method of calculating the parameter values for the coupled-circuit model, taking tooth saturation into account, is presented. The model is able to calculate the flux density in the machine air gap and stator and rotor teeth. These flux densities are also measured using the flux search coils. The issue of the specific magnetic loading for the BDFM is discussed and its calculation from the fundamental components of the air gap flux density is presented. The equivalent circuit parameter values are derived from the coupled-circuit model and from experimental tests under saturation. It is shown that the predictions of the equivalent circuit model are within acceptable accuracy if its parameter values are obtained at the same operating specific magnetic loading.
... The authors have constructed a frame size 180 machine which has been used to study control and measurement aspects of the BDFM [13][14][15]. The authors have more recently reported on the performance of alternative rotor configurations [16]. ...
... In the cascade mode the speed varies with load, but (1) and (5) still apply. Table 1 gives the physical data for the prototype machine used throughout this and the work described in [13][14][15][16]. The machine is shown in Fig. 2 on the experimental test rig. ...
... However, in a BDFM the referred series rotor inductance is likely to be larger than the series stator inductance so differences in inductance values between the two circuits will be small. Direct measurements of rotor bar currents, for example using techniques described in [13], enable all parameters in Fig. 10 to be determined, but the relationship of these currents to those in the equivalent circuit must be known. ...
... In [2], [3] the current measuring method of the cage bars using the Rogowski coil in the Brushless Doubly Fed Machine (BDFM) had been presented. The measurement of the cage bars current of the cage induction motor is described in [7]- [8]. ...
... In the development of diagnostic and evaluation methods, based on rotor cage bar currents measurement, the problem is the difficulty in transmitting the measured signals from the rotor to the recording devices. The best solution to this problem seems to be the wireless data transmission method [2], [3]. ...
Conference Paper
The article presents a method of currents measurement in the rotor bars of a prototype induction motor with the use of Rogowski coils. Measuring coils are placed on each of the 30 cage bars of the rotor. Signals proportional to the derivative of rotor bars currents are led outside the machine to special slip rings and then from the band of brushes adjacent to the slip rings transmitted to the integrating amplifiers and recorded with help of measuring card and dedicated software. Studies were carried out during the machine normal operation state at different loads. The currents of squirrel cage bars, recorded for different cage damages, were processed and analyzed. The results of current measurements of cage bars with help of Rogowski coils were checked numerically. The possibility of using the measurements results to improve diagnostic algorithms for detecting induction motor cage damage have been presented.
... Methods based on stator current frequency spectrum analysis are well elaborated verified in practice for induction machines in wide range of power. However as presented in [1][2][3][4][5], electrical and magnetic types of faults, although they have different origins, both result in appearing of negative sequence component of the magnetic field and its multiples. ...
... Unfortunately, rotor measurements cannot be wired out to a data acquisition system without great difficulty, thus any signal must be transmitted wirelessly. A battery powered system to measure rotor currents and transmit the data using Bluetooth has been reported [1,2]. In that approach the batteries required regular recharging and the system had to be partially dismounted from the rotor to be charged, which limits the practicality of the instrumentation system and the tests than can be carried out. ...
Article
Full-text available
It is desirable to measure rotor quantities such as currents and temperatures in an electrical machine for design verification and condition monitoring purposes. A Bluetooth module which sends data from the rotor was previously reported in literature, but this module was battery powered, and therefore the duration of the tests was limited. This study presents a solution to this problem by developing a rotor-mounted power supply system which can harvest energy from the magnetic field inside the machine, by fixing an external loop to the rotor and making use of the induced voltage in the loop. A full-bridge rectifier, boost converter and battery charging module were developed to supply sufficient power to a bespoke Bluetooth transmission system and associated sensor circuitry.
... Additionally, the extraction of EEC parameters from a brushless DFIM is not easy and obtaining a simple method to do so proves to be challenging. Most research studies apply a method based on fitting to measured torque-speed curves as proposed by [34], but other methods relying on wireless transmission of rotor current measurements via bluetooth [48,49], or using a range of different supply frequencies [50], have also been proposed. To provide more accurate models to determine 10 Page 10 of 22 ...
Article
The brushless Doubly-Fed Induction Machine (DFIM) provides an interesting alternative to the commonly applied conventional DFIM in modern multi-MW wind turbines. This paper presents a literature survey on the brushless DFIM. The evolution of the cascaded induction machine into the modern brushless DFIM is discussed, as well as several theories explaining this machines complex operating principles. Nowadays, brushless DFIM research is mainly focussed on the development of a commercially competitive brushless DFIM based drive for multi-MW wind turbine applications. An overview of the latest developments in the fields of brushless DFIM modeling, design, and control is provided. Based on this, a qualitative comparison is presented of the brushless DFIM and other well-established generator systems for wind turbines and the challenges for future research are explored.
... The parameters for such an equivalent circuit can then be obtained from the Torque-Speed curve measured in cascade operation. An additional aid to the process of parameter extraction is that the authors have perfected the means to measure the current flowing in the rotor winding, see [5]. It is proposed that the next step in this work will be to find that equivalent circuit and predict the performance from the parameters obtained. ...
Article
Full-text available
The paper presents experimental results to assess the performance of a variety of rotors used in a Brushless Doubly Fed Machine (BDFM). In the experiments the torque-speed characteristics were measured on a BDFM fitted with four rotors with five different windings. The measurements were made of the machine excited with just one stator supply with the second stator supply first open circuit, and then short- circuited. The results give valuable insight into how different rotors, including a novel design of BDFM rotor, will perform in a BDFM configured as a variable speed generator. The results highlight important differences between the rotors related to their winding construction.
... The authors have developed a system of measuring rotor bar currents directly with Rogowski coils, using the Bluetooth wireless technology to transmit the signal from the moving rotor back to a computer for logging and analysis [7], [8]. Bluetooth is one of a range of recently introduced protocols developed for the transmission of digital data. ...
Conference Paper
Full-text available
The brushless doubly-fed machine (BDFM) shows commercial promise as a variable speed drive or generator. However, for this promise to be realised, the design of the machine must be improved. Accurate machine modelling is therefore required for design optimisation. The measurement of rotor bar currents is of considerable benefit in the process of developing an accurate machine model. The authors present a system of measuring rotor bar currents in real time using a Rogowski coil to transduce the signal and recently available Bluetooth technology to transmit the data from the moving rotor to a standard PC. A coupled-circuit model has been developed for the BDFM to predict its dynamic and stead-state performance. The model has been verified using the proposed measurement system. The experiments were carried out on a frame size 180 BDFM with a nested-loop rotor design
... However, if rotor quantities can be measured, then they can be determined. Abdi Jalebi et al. have shown how this is possible using wireless transmission of current measurements by Bluetooth [12]. The ability to separate parameters has the advantage of being able to compare stator leakage reactances with manufacturers' estimates. ...
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The Brushless Doubly-Fed Machine (BDFM) is attractive for use in wind turbines, especially offshore, as it offers high reliability by virtue of the absence of brushgear. Critical issues in the use of the BDFM in this role at a system level include the appropriate mode of operation, the sizing of associated converter and the control of the machine. At a machine level, the design of the machine and the determination of its ratings are important. Both system and machine issues are reviewed in the light of recent advances in the study of the BDFM, and preliminary comparisons are made with the well-established doubly fed wound rotor induction generator.
Chapter
This chapter presents a detailed description of the presented power generation system based the brushless doubly-fed induction generator (BDFIG). The adopted system description and the main considerations of the BDFIG-construction are also illustrated. In addition, detailed abc-axis and dq0-axis dynamic models are also presented. This model can be used to investigate the dynamic behaviour of the BDFIG. Moreover, the detailed steady-state models and the power flow considerations are fully described. Furthermore, the configuration and operating characteristics of the BDFIG drive system are completely studied and analysed.KeywordsBrushless doubly-fed induction generator (BDFIG)Dynamic modelSteady-state modelOperating characteristicsDirect voltage control
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