Sensorless position estimation in fault-tolerant permanent magnet AC motor drives with redundancy.

Safety critical applications are heavily dependent on fault-tolerant motor drives being capable of continuing to operate satisfactorily under faults. This research utilizes a fault-tolerant PMAC motor drive with redundancy involving dual drives to provide parallel redundancy where each drive has electrically, magnetically, thermally and physically independent phases to improve its fault-tolerant capabilities. PMAC motor drives can offer high power and torque densities which are essential in high performance applications, for example, more-electric airplanes. In this thesis, two sensorless algorithms are proposed to estimate the rotor position in a fault-tolerant three-phase surface-mounted sinusoidal PMAC motor drive with redundancy under normal and faulted operating conditions. The key aims are to improve the reliability by eliminating the use of a position sensor which is one of major sources of failures, as well as by offering fault-tolerant position estimation. The algorithms utilize measurements of the winding currents and phase voltages, to compute flux linkage increments without integration, hence producing the predicted position values. Estimation errors due measurements are compensated for by a modified phase-locked loop technique which forces the predicted positions to track the flux linkage increments, finally generating the rotor position estimate. The fault-tolerant three-phase sensorless position estimation method utilizes the measured data from the three phase windings in each drive, consequently obtaining a total of two position estimates. However, the fault-tolerant two-phase sensorless position estimation method uses measurements from pairs of phases and produces three position estimates for each drive. Therefore, six position estimates are available in the dual drive system. In normal operation, all of these position estimates can be averaged to achieve a final rotor angle estimate in both schemes. Under faulted operating conditions, on the other hand, a final position estimate should be achieved by averaging position estimates obtained with measurements from healthy phases since unacceptable estimation errors can be created by making use of measured values from phases with failures. In order to validate the effectiveness of the proposed fault-tolerant sensorless position estimation schemes, the algorithms were tested using both simulated data and offline measured data from an experimental fault-tolerant PMAC motor drive system. In the healthy condition, both techniques presented good performance with acceptable accuracies under low and high steady-state speeds, starting from standstill and step load changes. In addition, they had robustness against parameter variations and measurement errors, as well as the ability to recover quickly from large incorrect initial position information. Under faulted operating conditions such as sensor failures, however, the two-phase sensorless method was more reliable than the threephase sensorless method since it could operate even with a faulty phase.Thesis (Ph.D.) -- University of Adelaide, School of Electrical and Electronic Engineering, 201

Performance improvement of permanent magnet ac motors

Multi-phase motors have several advantages over the traditional three-phase motors. In this study, the additional degrees of freedom available in five-phase permanent magnet motors have been used for three purposes: 1) enhancing the torque producing capability of the motor, 2) improving the reliability of the system, and 3) better adjusting of the torque and flux linkages of the five-phase direct torque controlled system. 1) Due to the fact that space and time harmonics of the same orders will contribute positively to output torque, a five-phase permanent magnet motor with quasi-rectangular back-EMF waveform is supplied with combined fundamental and third harmonic of currents. For modeling and analysis of the motor a 0 3 3 1 1 q d q d frame of reference is defined where 1 1q d rotates at the synchronous speed and 3 3q d rotates at the three times synchronous speed. Based on the mathematical model in the 0 3 3 1 1 q d q d frame of reference, it is shown that this system while having a higher torque density with respect to a conventional permanent magnet synchronous machine, is also compatible with vector control algorithm. 2) A resilient current control of the five-phase permanent motor with both sinusoidal and trapezoidal back-EMF waveforms under asymmetrical fault condition is proposed. In this scheme, the stator MMF is kept unchanged during healthy and faulty condition. Therefore, the five-phase permanent magnet motor operates continuously and steadily without additional hardware and just by modifying the control algorithm in case of loss of up to two phases. The feature is of major importance in some specific applications where high reliability is required. 3) High torque and flux ripple are the major drawbacks of a three-phase direct torque controlled system. The number of space voltage vectors directly influences the performance of DTC system. A five-phase drive, while benefiting from other advantages of high order phase drives, has inherently 32 space voltage vectors which permits better flexibility in selecting the switching states and finer adjustment of flux and torque. A sensorless direct torque control of five-phase permanent magnet motor is implemented. Speed information is obtained based on the position of stator flux linkages and load angle. Experiments have been conducted on a 5kW five-phase surface mount permanent magnet motor and a 3kW five-phase interior permanent magnet motor by using TMS320C32 DSP. The results obtained are consistent with theoretical studies and simulation analysis, which further demonstrate the feasibility and practical significance of the five-phase permanent magnet motor drives

Improved Sensorless Control of Multiphase Synchronous Reluctance Machine Under Position Sensor Fault

This article presents an investigation on the self- sensing capability of a dual three-phase synchronous reluctance motor. Self-sensing capability refers to the ability of the motor to properly operate in a sensorless drive. The multiphase machine is decomposed into two different three-phase systems according to the multistator approach. Several supply scenarios are studied where the two three-phase windings are controlled at different operating points along a reference trajectory. The analysis is carried out both with finite element analysis simulations and experimental tests. In the first part of this article, the rotor is locked to derive the observer trajectories and find the regions in which the motor can operate without position sensor. A comparison between simulated and experimental results is given. Finally, a sensorless control strategy that allows exploiting the motor self-sensing capability under position sensor fault is developed and validated through experimental tests

Analysis, design and test of high efficiency electrical machines with a rotor winding

This thesis deals with the analysis, design and test of three-phase high efficiency electrical motors, with particular reference to motors with a rotor winding. At first, the background and the motivations of this work are described. The bibliography on the subjects is deeply examined and a selection of the most relevant papers can be found in the reference. In this scenario, the main objective of this thesis are illustrated. The Line-Start (LS) Synchronous Machine (SyM) design is a subject under investigation since the beginning of the last century, when solid state power converters was not available to drive SyMs. The LS SyM diffusion was limited by the intrinsic difficulties in its design and by the availability of the cheaper and more robust Induction Machine (IM). The working principle of IM and LS SyM are briefly described, as well as the state of the art of the techniques of analysis. Recently, there is a renewed interest on LS SyMs due to the new efficiency requirements and fast analysis techniques are required for the LS SyM design. A Finite-Element (FE) aided analytical model is developed to simulate the LS SyM dynamic. The aim is to develop a model that gives reliable solutions with limited computational efforts compared with other analysis techniques. With this procedure, the LS SyM rotor parameters can be quickly calibrated to fulfill the dynamic load requirements. An innovative analysis technique of LS SyM steady state condition is described. Such an analysis is carried out in the same reference frame used for classical SyMs. It is shown that the analysis can be used to optimize some machine parameters. The issues in LS SyM manufacturing are introduced, with particular reference to the die casting process. The possibility to apply the recent improvements in the SRM design to LS SyM is discussed from the manufacturing point of view. Stochastic optimization has been adopted for the design of electrical motors to reduce the torque ripple, increase the average torque and reduce the losses. The LS SyM torque ripple reduction, achieving at the same time a high average torque, is an important issue even though this topic is not treated extensively in the literature for LS SyM. For this reason, a stochastic optimization is considered in this thesis for the design of a new LS SyM lamination. The analysis is applied on a small size, 2-pole, three-phase LS SyM as this category is still not found in the motor market. The optimization is carried out considering the necessity to achieve a robust design, suitable for the industrial production, as such a LS SyM must be competitive with the workhorse of electrical motors, the IM. One of the most promising design is prototyped. Its performance are compared with the corresponding IM. To demonstrate the feasibility in adopting LS SyM in the large-scale production, an innovative LS SyM design is proposed. The main aim is to use the same lamination for motors of different number of poles so as to reduce the manufacturing cost. A tradeoff between contrasting aspects is necessary in the design step. The performance achievable by these rotor structures are quantified. An analytical model that describes the mutual interaction between coupled electrical circuits in machines with complex rotor structure is developed. Such a model is useful to analyze the parasitic torques in the torque characteristic of motors with rotor cage such as IM and LS SyM. The literature reveals that this topic has been discussed extensively for IM. As regards LS SyM, there is a lack of theoretical studies regarding harmonic phenomena due to the complex machine structure. This part of the thesis aims to fill this gap. The high and unstable cost of rare-earth PMs, together with the advances in solid-state control technology, leads designers to reconsider IM for variable speed drive (VSD) applications. To the aim of making the IM suitable for the full-speed sensorless control, a particular cage design is considered. An intentionally created saliency is introduced in the rotor so as to allow the rotor position to be estimated by means of a high frequency (HF) injected signal in the stator winding also at zero-speed. Different experimental tests are carried out on IMs with asymmetrical rotor cage to validate the analysis techniques and quantify the achievable performance. As far as the HF signal injection sensorless technique is concerned, the cross-saturation differential inductance of SyMs represents an issue. It causes a rotor position estimation error, reducing the region in which such technique is effective. The proper-ties of the cross-saturation inductance are deeply discussed. It is originally shown that the cross-saturation inductance depends from certain machine parameters. With such an analysis, a designer can consider the effect of the cross-saturation inductance in any model-based control algorithm. A rotor winding is added in Surface-mounted permanent-magnet machine (SPM) to create a HF anisotropy that is useful to detect the rotor position by means of a HF signal injection. Such a configuration is called ”ringed-pole”. In literature, this technique has been used on small-size machines. In certain configuration, the presence of the additional rotor winding causes significant rotor losses. This part of the thesis studies the rotor losses in ringed pole machines by means of FE analysis and analytical models. The aim is to investigate if the ringed-pole technique can be adopted also for large machines from the point of view of additional losses. With few exceptions, the work described in this thesis is always supported by means of experimental measurements. Dedicated experiments has been designed. Their results are compared with those achieved with analytical models or FE analysis

Sensorless operation of permanent magnet brushless dc motor based on infinite impulse response digital filter.

Disertasi ini membentangkan operasi baru tanpa penderia bagi motor arus terus magnet kekal tanpa berus (BLDC) berasaskan pada penapisan digit gelombang daya gerak elektrik balik dengan menggunakan dsPIC30F6010 mikropengawal. Dari segi motor pacuan, teknik pemodulatan lebar denyut (PWM) biasanya digunakan untuk mengubah voltan yang dikenakan pada pangkalan motor supaya dapat mengendalikan kelajuan motornya. This dissertation presents a new sensorless operation for permanent magnet brushless DC motor based on digital filtering of back-EMF waveform using dsPIC30F6010 microcontroller. In motor drives, PWM technique is normally used to vary the voltage imposed on the motor terminals, and therefore controlling the speed of the motor

Optimum Remedial Operation of Permanent Magnet Synchronous Motor

In critical systems, the reliability of the drive is very important. The faults are unwanted. The faults may be lead to loss of the human life and capital. This paper is addressed this problem and suggested two models to solve it. The first model doesn’t contain any special tools to improve the torque ripple and THD. The second model contains 2PI current controllers to improvement the performance at fault and remedial operation. One is for the torque and the other is for the flux. The first PI controller is feeding from the torque error between the reference and estimated torques to get new q-axis current component representing modifier current arises from uncertain things inside the machine and drive system such as temperature and parameters variations. This current will add to reference q-axis current to get robust new q-axis current to satisfy the drive requirement and solve the torque problem (ripple torque). With robust current, the total harmonic distortion is a decrease but doesn’t reach the best value so the other PI controller is used to adjust the THD. In this PI controller, the d-axis flux is compared to rotor permanent magnet flux to solve this problem arises from non-sinusoidal of the magnetic flux. The output of the PI controller is introduced to the reference d-axis current. The new d-axis current will reach the best value of THD. The simulation of the second controller is compared to the simulation of first controller to show if the second controller strong or weak. Matlab simulink is used to simulate the drive system.DOI:http://dx.doi.org/10.11591/ijece.v2i5.72

Fault analysis and remedial strategies on a fault-tolerant motor drive with redundancy

Copyright © 2007 IEEEFault-tolerant motor drives are required in a range of safety-critical applications. Using a special motor design and an appropriate inverter topology, brushless permanent magnet AC motor drives can have an effective fault-tolerant capability. Although a single motor fault-tolerant drive system may be sufficient in many critical applications, a higher degree of fault tolerance requires redundancy in the motor system as considered in this paper. This is achieved by using a dual motor module on a common shaft. The simulation model of the entire drive system and the analysis of the various faults are presented in this paper. The effects of fault(s) on the phase current and output torque are provided. Three remedial operating modes are proposed and their features are compared. In addition, an experimental setup was introduced, which is based on dual electrically and magnetically isolated brushless AC motor modules, H-bridge inverters for individual phases and dsPICDEM MCU motor controller. © 2007 IEEE

Simulation And Hardware Development Of PM Brushless Dc Motor Drives

This thesis presents simulation and hardware implementation of a 3-phase PM brushless DC (BLDC) motor drive using 120-degree, six-step current commutation control technique. The microcontroller used is PIC16F877 which functions to perform current commutation sequence, rotating direction control, speed control and reading Hall sensor signals. This microcontroller is a common and low-cost 40-pin MCU. The sensored type of controlling technique has been chosen in order to make this design suitable for both low speed and high speed applications plus control simplicity

Detection and classification of turn fault and high resistance connection fault in permanent magnet machines based on zero sequence voltage

Health monitoring and fault detection are becoming more and more important in electrical machine systems due to the increasing demand for reliability. Winding turn fault is a common fault in permanent magnet machines which can cause severe damages and requires prompt detection and mitigation. High resistance connection (HRC) fault which result in phase asymmetry may also occur but does not require immediate shutdown. Thus, apart from the fault detection, the classification between the two faults is also required. In this paper, a new technique for detecting and classifying turn fault and HRC fault by utilizing both the high and low frequency components of the zero sequence voltage is proposed. The dependence on the operating conditions is minimized with the proposed fault indicators. The effectiveness of fault detection and classification has been verified by extensive experimental tests on a triple redundant fault tolerant permanent magnet assisted synchronous reluctance machine (PMA SynRM). The robustness of the turn fault detection in transient states and under no load conditions has also been demonstrated

Switched Flux Permanent Magnet Brushless Machines for Electric Vehicles

This thesis investigates different topologies of switched flux permanent magnet (SFPM) machines and variable flux (VF) methods for high speed applications. Although several novel topologies of SFPM machines have been proposed and investigated recently, their torque-speed capability has not been studied systematically. Therefore, the torque-speed capability as well as the open circuit and electromagnetic performance of conventional SFPM machines with three different stator/rotor pole combinations, i.e. 12/10, 12/13 and 12/14, and three novel SFPM machine topologies, i.e. multi-tooth, E-core and C-core are analysed and investigated by the finite element (FE) method and experiments. Moreover, in order to improve the flux-weakening capability of these machines a variable flux method using flux adjusters (FAs) is employed and the corresponding electromagnetic performance of the machines are investigated, analysed and compared. Both FE and measured results show when the FAs are used the torque-speed capability of the three conventional machines can be improved significantly, while no improvement is shown in the three novel topologies primarily due to the large winding inductances. The technique of using flux adjusters has been improved by reducing the number of FAs. Thus, a new mechanical variable-flux machine topology, which uses only half of FAs outside the stator at alternative stator poles, is proposed, developed and analysed. Open circuit results, electromagnetic performance and torque- and power-speed curves of the 12/10, 12/13 and 12/14 stator/rotor pole SFPM machines with alternative FAs are predicted and compared by 2D and 3D-FE, and experimentally validated. Furthermore, a novel SFPM machine topology with radial and circumferential PMs is proposed, investigated and optimized. This topology reduces the stator flux leakage and offers high magnetic utilization. Moreover, this topology can also be developed as a mechanical variable flux machine. Finally, three SFPM machines with variable flux techniques, i.e. mechanically movable flux adjusters (MMFA), mechanically rotatable permanent magnet set (MRMS) and hybrid excitation with backside DC coils (HEBC) are analysed. Their open circuit results and electromagnetic performance with emphasis on torque-speed characteristic are investigated and compared. Additionally, the required power to switch between flux weakening and strengthening states, flux weakening capability and permanent magnet demagnetization withstand capability are predicted, analysed and compared. The influence of end-effect on the torque-speed capability in the conventional, multi-tooth, E-core and C-core SFPM machines is investigated. Measurements and 3D-FE are performed to obtain the torque-speed curve in order to validate the findings of the research. The 3D-FE predicted results match well with the measured results, while the 2D-FE predicted results are lower due to the high end-effect in the SFPM machines