Showing papers in "IEEE Transactions on Industry Applications in 2006"
TL;DR: In this article, the authors proposed two constant boost control methods for the Z-source inverter, which can obtain maximum voltage gain at any given modulation index without producing any low-frequency ripple that is related to the output frequency and minimize the voltage stress at the same time.
Abstract: This paper proposes two constant boost-control methods for the Z-source inverter, which can obtain maximum voltage gain at any given modulation index without producing any low-frequency ripple that is related to the output frequency and minimize the voltage stress at the same time. Thus, the Z-network requirement will be independent of the output frequency and determined only by the switching frequency. The relationship of voltage gain to modulation index is analyzed in detail and verified by simulation and experiments.
685 citations
TL;DR: In this article, the authors presented some design considerations for synchronous machines characterized by a fractional number of slots per pole per phase, which is a smooth torque, due to the elimination of periodicity between slots and poles.
Abstract: This paper presents some design considerations for synchronous machines characterized by a fractional number of slots per pole per phase. The main advantage of this configuration is a smooth torque, which is due to the elimination of periodicity between slots and poles. A second advantage is a higher fault-tolerant capability, making the machine able to work even in faulty conditions. However, the fractional-slot configuration presents a high content of MMF harmonics that may cause an unbalanced saturation and thus an unbearable torque ripple. A method to design fractional-slot machines is illustrated in this paper, including double-layer and single-layer windings. The analytical computation is extended to determine the harmonics of MMF distribution. Their effect is highlighted in isotropic as well as anisotropic machines. Finally, some considerations are reported to avoid unsuitable configurations
402 citations
TL;DR: In this paper, the authors proposed a method for the diagnosis of rotor bar failures in induction machines, based on the analysis of the stator current during the startup using the discrete wavelet transform (DWT).
Abstract: In this paper, the authors propose a method for the diagnosis of rotor bar failures in induction machines, based on the analysis of the stator current during the startup using the discrete wavelet transform (DWT). Unlike other approaches, the study of the high-order wavelet signals resulting from the decomposition is the core of the proposed method. After an introduction of the physical and mathematical bases of the method, a description of the proposed approach is given; for this purpose, a numerical model of induction machine is used in such a way that the effects of a bar breakage can clearly be shown, avoiding the influence of other phenomena not related with the fault. Afterward, the new diagnosis method is validated using a set of commercial induction motors. Several experiments are developed under different machine conditions (healthy machine and machine with different levels of failure) and operating conditions (no load, full load, pulsating load, and fluctuating voltage). In each case, the results are compared with those obtained using the classical approach, based on the analysis of the steady-state current using the Fourier transform. Finally, the results are discussed, and some considerations about the influence of the DWT parameters (type of mother wavelet, order of the mother wavelet, sampling rate, or number of levels of the decomposition) over the diagnosis are done
303 citations
TL;DR: In this article, a simple control method to achieve active sharing of input voltage and load current among modular converters that are connected in series at the input and in parallel at the output is proposed.
Abstract: This paper proposes a simple control method to achieve active sharing of input voltage and load current among modular converters that are connected in series at the input and in parallel at the output. The input-series connection enables a fully modular power-system architecture, where low voltage and low power modules can be connected in any combination at the input and/or at the output, to realize any given specifications. Further, the input-series connection enables the use of low-voltage MOSFETs that are optimized for very low RDSON , thus, resulting in lower conduction losses. In the proposed scheme, the duty ratio to all the converter modules connected in input-series and output-parallel (ISOP) configuration is made common. This scheme does not require a dedicated input-voltage or load-current-share controller. It relies on the inherent self-correcting characteristic of the ISOP connection when the duty ratio of all the converters is the same. The proposed scheme is analyzed using the average model of a forward converter. The stability and performance of the scheme are verified through numerical simulation, both in frequency domain and in time domain. The proposed control method is also validated on an experimental prototype ISOP system comprising of two forward converters
291 citations
TL;DR: In this paper, a model of core losses, in which the hysteresis coefficients are variable with the frequency and induction (flux density) and the eddy-current and excess loss coefficients were variable only with the induction, is proposed.
Abstract: A model of core losses, in which the hysteresis coefficients are variable with the frequency and induction (flux density) and the eddy-current and excess loss coefficients are variable only with the induction, is proposed. A procedure for identifying the model coefficients from multifrequency Epstein tests is described, and examples are provided for three typical grades of non-grain-oriented laminated steel suitable for electric motor manufacturing. Over a wide range of frequencies between 20-400 Hz and inductions from 0.05 to 2 T, the new model yielded much lower errors for the specific core losses than conventional models. The applicability of the model for electric machine analysis is also discussed, and examples from an interior permanent-magnet and an induction motor are included.
239 citations
TL;DR: Permanent-magnet-assisted synchronous reluctance motors are well suited to zero-speed sensorless control because of their inherently salient behavior but the cross-saturation effect can lead to large errors on the position estimate, which is based on the differential anisotropy.
Abstract: Permanent-magnet-assisted synchronous reluctance motors are well suited to zero-speed sensorless control because of their inherently salient behavior. However, the cross-saturation effect can lead to large errors on the position estimate, which is based on the differential anisotropy. These errors are quantified in this paper as a function of the working point. The errors that are calculated are then found to be in good accordance with the purposely obtained experimental measurements
226 citations
TL;DR: In this article, the authors investigated the iron loss of interior permanent magnet motors driven by PWM inverters from both results of the experiments and the finite-element analysis, and clarified that the largest component at low speed condition under maximum torque control, whereas the loss caused by the harmonic magnetomotive forces of the permanent magnet remarkably increase at high-speed condition under flux-weakening control.
Abstract: In this paper, the authors investigate the iron loss of interior permanent magnet motors driven by pulsewidth modulation (PWM) inverters from both results of the experiments and the finite-element analysis. In the analysis, the iron loss of the motor is decomposed into several components due to their origins, for instance, the fundamental field, carrier of the PWM inverter, slot ripples, and harmonic magnetomotive forces of the permanent magnet in order to clarify the main loss factors. The Fourier transformation and the finite-element method considering the carrier harmonics are applied to this calculation. The calculated iron loss is compared with the measurement at each driving condition. The measured and the calculated results agree well. It is clarified that the iron loss caused by the carrier of the PWM inverter is the largest component at low-speed condition under the maximum torque control, whereas the loss caused by the harmonic magnetomotive forces of the permanent magnet remarkably increase at high-speed condition under the flux-weakening control
226 citations
TL;DR: In this article, the authors examined the detection of mechanical faults in induction motors by an original use of stator current time-frequency analysis, which leads generally to periodic load torque oscillations.
Abstract: This paper examines the detection of mechanical faults in induction motors by an original use of stator current time-frequency analysis. Mechanical faults lead generally to periodic load torque oscillations. The influence of the torque oscillations on the induction motor stator current is studied using an analytical approach. The mechanical fault results in a sinusoidal phase modulation of the stator current, which is equivalent to a time-varying frequency. Based on these assumptions, several signal processing methods suitable for stator current signature analysis are discussed: classical spectral analysis, instantaneous frequency estimation, and the Wigner distribution. Experimental and simulation results validate the theoretical approach in steady-state operating conditions
203 citations
TL;DR: In this paper, an up-to-date literature survey on efficiency-estimation methods of in-service motors, particularly with considerations of the motor-condition-monitoring requirements, is presented.
Abstract: Condition monitoring of electric motors avoids severe economical losses resulting from unexpected motor failures and greatly improves the system reliability and maintainability. Efficiency estimation, which shares many common requirements with condition monitoring in terms of data collections, is expected to be implemented in an integrated product. This brings more considerations into the selection of the efficiency-estimation methods. This paper presents the results of an up-to-date literature survey on efficiency-estimation methods of in-service motors, particularly with considerations of the motor-condition-monitoring requirements. More than 20 of the most commonly used methods are briefly described and classified into nine categories according to their physical properties. Six categories of these methods are more related to in-service testing and are compared in a table summarizing the required tests and measurements, intrusion level, and average accuracy. Estimation of the rotor speed and the stator resistance, the two stumbling blocks of various efficiency-estimation methods, is also carefully studied; commonly used methods are summarized. Based on the survey results, four efficiency-estimation methods are suggested as candidates for nonintrusive in-service motor-efficiency estimation and condition-monitoring applications. Another contribution of this paper is that a general approach for developing nonintrusive motor-efficiency-estimation methods is proposed, incorporating rotor speed, stator resistance, and no-load loss estimations
183 citations
TL;DR: In this paper, an electromechanical converter with two mechanical ports and one electrical port (consisting of two concentric machines and two inverters) is considered, and the working principle of this converter is explained.
Abstract: First, an electromechanical converter with two mechanical ports and one electrical port (consisting of two concentric machines and two inverters) is considered. This converter works as a continuously variable transmission between the mechanical ports and may, e.g., replace the clutch, gearbox, generator, and starter motor in a motor vehicle. The working principle of this converter is explained. Next, a new converter, the electric variable transmission (EVT), is presented. This converter has similar properties, but is smaller and lighter. The EVT may be seen as built up from two concentric induction machines with a combined relatively thin yoke. Thus, we obtain one electromagnetic device instead of two magnetically separated devices. The working principle of the EVT is explained, and its losses are discussed
176 citations
TL;DR: In this article, a series voltage injection type flywheel energy storage system (FESS) is used to mitigate voltage sags and maximize the survivability of the ship during battle conditions.
Abstract: The U.S. Navy is looking for methods to maximize the survivability of combat ships during battle conditions. A shipboard power distribution system is a stiff isolated power system that is vulnerable to voltage sags, which arise due to faults or pulsed loads, which can cause interruptions of critical loads. A series voltage injection type flywheel energy storage system (FESS) is used to mitigate voltage sags and maximize the survivability of the ship. The basic circuit consists of an energy storage system, power electronic interface, and a series injection transformer. In this case, the energy storage system consists of a flywheel coupled to an induction machine. The stored energy is used for sag correction for the critical load. Indirect field-oriented control (IDFOC) with space-vector pulsewidth modulation (SVPWM) is used to control the induction machine. Sinusoidal PWM is used for controlling the power system side converter. This paper presents the modeling, simulation, and analysis of a FESS with a power converter interface using PSCAD/EMTDC.
TL;DR: In this article, the authors present a technique for the diagnosis of broken rotor bars in an induction motor using the Bartlett periodogram and different global fault indexes on the instantaneous power spectrum and on the line current spectrum for the fault detection are evaluated.
Abstract: Induction motors play a very important part in the safe and efficient running of any industrial plant. Early detection of abnormalities in the motor would help to avoid costly breakdowns. Accordingly, this work presents a technique for the diagnosis of broken rotor bars in induction motor. Stator voltage and current in an induction motor were measured and employed for computation of the input power of one stator phase. Waveforms of the instantaneous power and line current were subsequently analyzed using the Bartlett periodogram. Different global fault indexes on the instantaneous power spectrum and on the line current spectrum for the fault detection are evaluated. Several rotor cage faults of increasing severity were studied with various load effects. Experimental results prove the efficiency of the employed method.
TL;DR: In this paper, the authors introduce new materials, components, and system concepts (such as wide bandgap materials, silicon-carbide-based power semiconductor devices, power electronics building blocks (PEBBs), and integrated power systems) and explore new design methods to simplify marine electrical system development.
Abstract: Tomorrow's marine electrical systems will be profoundly different from today's systems. Power electronics is making major impacts on virtually every marine system including propulsion, power distribution, auxiliaries, sonar, and radar. Newly emerging materials, components, and system concepts (such as wide band-gap materials, silicon-carbide-based power semiconductor devices, power electronics building blocks (PEBBs), and integrated power systems) are, and will continue, enabling future marine systems as different from today's systems as steam ships were to sailing ships. However, these enabling technologies and concepts are not well known and have been difficult to understand. This paper will introduce these new concepts and technologies, identify potential impacts, and explore new design methods to simplify marine electrical system development.
TL;DR: In this article, the design of a fault-tolerant electric motor for an aircraft main engine fuel pump was discussed and the methods used to calculate rotor eddy current losses were examined.
Abstract: This paper discusses the design of a fault-tolerant electric motor for an aircraft main engine fuel pump. The motor in question is a four-phase fault-tolerant motor with separated windings and a six-pole permanent magnet rotor. Methods of reducing machine losses in both the rotor and stator are introduced and discussed. The methods used to calculate rotor eddy current losses are examined. Full three-dimensional finite-element (FE) time stepping, two-dimensional (2-D) FE time stepping, and 2-D FE harmonic methods are discussed, and the differences between them and the results they produce were investigated. Conclusions are drawn about the accuracy of the results produced and how the methods in question will help the machine designer
TL;DR: In this paper, two novel methods using windowed Fourier ridges and Wigner-Ville-based distributions are proposed for the detection of rotor faults in brushless dc motors operating under continuous nonstationarity.
Abstract: There are several applications where the motor is operating in continuous nonstationary operating conditions. Actuators and servo motors in the aerospace and transportation industries are examples of this kind of operation. Detection of faults in such applications is, however, challenging because of the need for complex signal processing techniques. Two novel methods using windowed Fourier ridges and Wigner-Ville-based distributions are proposed for the detection of rotor faults in brushless dc motors operating under continuous nonstationarity. Experimental results are presented to validate the concepts and illustrate the ability of the proposed algorithms to track and identify rotor faults. The proposed algorithms are also implemented on a digital signal processor to study their usefulness for commercial implementation
TL;DR: In this paper, an algorithm to calculate the current references on line, considering the inherent nonlinear nature of the saturation effect in an interior permanent magnet synchronous machine for the minimum-copper-loss control under the current and voltage limit of the drive system is presented.
Abstract: This paper presents an algorithm to calculate the current references on line, considering the inherent nonlinear nature of the saturation effect in an interior permanent-magnet synchronous machine for the minimum-copper-loss control under the current and voltage limit of the drive system. This paper basically approaches this issue as a nonlinearly constrained optimization problem where the torque command imposes the nonlinear equality constraint and the voltage limit imposes the nonlinear inequality constraint. Depending on the operating region, it solves the corresponding set of nonlinear equations in real time derived from the Lagrange multiplier method. Newton's method among various techniques is adopted to implement the numerical solution. This scheme gives accurate results not only in motoring but also in generating operation of the machine, since the voltage drop of the stator resistance is taken into account, which is hardly applicable to a two-dimensional lookup table where the inputs are the torque command and the maximum flux amplitude, and the output is each axis current reference in the rotor reference frame. The simulation and experimental results show the feasibility and performance of the proposed technique
TL;DR: In this article, a sensorless control method based on novel extended electromotive force (EEMF) models considering magnetic saturation is proposed for synchronous reluctance motors (SynRMs).
Abstract: A sensorless control method based on novel extended electromotive force (EEMF) models considering magnetic saturation is proposed for synchronous reluctance motors (SynRMs). Since motor parameters, particularly inductances, vary largely in SynRMs, a precise sensorless control is necessary for fully considering such variations. In this paper, the EEMF model, taking into consideration magnetic saturation, is derived and is applied to a position estimation method. The two EEMF models caused by a difference in the d-axis direction are shown, and the appropriate EEMF model that can suppress a position estimation error caused by the deviation of inductance parameters is proposed. Moreover, an online parameter identification method for sensorless control in middle- or high-speed ranges is proposed. The necessity for the use of the model, taking into consideration magnetic saturation, is verified by experiments. The proposed sensorless control system is shown useful by experiments
TL;DR: In this article, the authors proposed a high-efficiency bidirectional integrated zerovoltage transition (iZVT) pulsewidth-modulation (PWM) converter for dc-bus and battery-bank interface.
Abstract: This paper proposes a high-efficiency bidirectional integrated zero-voltage transition (iZVT) pulsewidth-modulation (PWM) converter for dc-bus and battery-bank interface. The proposed converter can operate as battery charger when the utility is within its acceptable voltage range and can supply energy to critical loads when the utility fails. The converter practically eliminates both low- and high-frequency current ripple on the batteries, thus maximizing battery life without penalizing the volume of the converter. Moreover, soft switching of all switches is achieved using the proposed integrated auxiliary commutation circuit (iACC). Just one iACC is used to provide soft-switching conditions for the three converters that compose the system: the preregulator (boost), the battery charger (bidirectional converter operating as a buck), and the backup converter (bidirectional converter operating as a boost). This auxiliary circuit has few components and low reactive energy, increasing the system's overall efficiency. Experimental results based on a 580-W prototype are presented to validate the analysis and the proposed design procedure and to demonstrate the performance of the proposed approach
TL;DR: In this article, a simple analytical technique is proposed to synthesize the cogging-torque waveform of a permanent-magnet brushless machine from cogging torque, which is associated with a single stator slot.
Abstract: A simple analytical technique is proposed to synthesize the cogging-torque waveform of a permanent-magnet brushless machine from the cogging torque, which is associated with a single stator slot. An analytical expression is derived, which reveals the relationship between the two. It is then applied to two motors, which have a fractional number of slots per pole. It is shown that the resultant cogging-torque waveform can be synthesized to a high accuracy, as confirmed by both finite-element analysis and measurements. It is also shown that not all the cogging-torque harmonics that exist in the cogging-torque waveform due to a single slot will be present in the resultant cogging torque, and that the most significant components can be identified analytically.
TL;DR: In this paper, a fault-signature model and a faultdetection scheme for using machine vibration to detect inner-race defects were developed, where the authors examined machine-vibration spectra for peaks with phase-coupled sidebands occurring at a spacing predicted by the model.
Abstract: This paper develops a fault-signature model and a fault-detection scheme for using machine vibration to detect inner-race defects. To motivate this research, it is explained and illustrated with experimental results why fault signatures from nonouter-race defects (e.g., inner-race defects) can be less salient than those from outer-race defects. Then, a signal model is presented for the production and propagation of an inner-race fault signature; this model is then used to design an inner-race fault-detection scheme. This scheme examines machine-vibration spectra for peaks with phase-coupled sidebands occurring at a spacing predicted by the model. The proficiency of this fault-detection scheme at detecting inner-race bearing faults is then experimentally verified with results from 12 bearings representing varying degrees of fault severity.
TL;DR: In this article, the use of Taguchi methods in optimizing a switched reluctance motor (SRM) for applications requiring fast actuation is presented. But the performance of the motor designs generated by the Taguchi DOE is not evaluated.
Abstract: This paper presents the use of Taguchi methods in optimizing a switched reluctance motor (SRM) for applications requiring fast actuation. In these applications, the SRM is designed to provide a high electromagnetic torque-to-inertia ratio required for high rates of mechanical acceleration. This is accomplished using two simultaneous robust optimizations of an SRM, namely: 1) an optimization of the motor torque and 2) an optimization of the torque per inertia (mechanical acceleration). The Taguchi two-step optimization method and the zero-point-proportional dynamic response were used successfully in the double optimization. Two orthogonal arrays were used to lead the design of experiments (DOE). Finite-element analysis was used to compute the performance of the motor designs generated by the Taguchi DOE.
TL;DR: A technique is proposed to reduce current errors which arise due to inaccuracies in the system parameters and the non-ideal behaviour of the inverter during steady-state operation, while a current-regulated delta modulator is employed to achieve a fast dynamic response during transient operation.
Abstract: The performance of the conventional predictive current control (PCC) when applied to a permanent-magnet brushless ac (PM BLAC) drive is analyzed. A technique is proposed to reduce the current errors that arise due to the inaccuracies in the system parameters and the nonideal behavior of the inverter during a steady-state operation. In addition, a current-regulated delta modulator is employed to achieve a fast dynamic response during a transient operation. The performance of the proposed PCC, which is simple to implement on a low-cost fixed-point DSP, is demonstrated experimentally
TL;DR: Different control principles, indirect vector control and deadbeat current control, are developed for a voltage source pulsewidth-modulation (PWM) converter and the three-phase variable-speed squirrel-cage IG to regulate dc link and generator voltages with the newly designed phase-locked loop circuit.
Abstract: This paper describes simple control structures for the vector-controlled stand-alone induction generator (IG) used to operate under variable speeds. Different control principles, indirect vector control and deadbeat current control, are developed for a voltage source pulsewidth-modulation (PWM) converter and the three-phase variable-speed squirrel-cage IG to regulate dc link and generator voltages with the newly designed phase-locked loop circuit. The required reactive power for the variable-speed IG is supplied by means of the PWM converter and a capacitor bank to buildup the voltage of the IG without the need for a battery, to reduce the rating of the PWM converter with the need for only three sensors, and to eliminate the harmonics generated by the PWM converter. These proposed schemes can be used efficiently for variable-speed wind energy conversion systems. The measurements of the IG systems at various speeds and loads are given and show that these systems are capable of good ac and dc voltage regulations
TL;DR: In this paper, the authors proposed a new compensation algorithm for the current measurement errors in the motor control drive by using the integrator output signal of the d-axis proportional plus integral (PI) current regulator.
Abstract: The errors generated from the current-measurement path are inevitable, and they can be divided into two categories: offset errors and scaling errors. Current data including these errors cause the periodic rotor speed ripples, which are one and two times the fundamental stator current frequency. Since these undesirable ripples can harm the motor drive system, a compensation algorithm must be included in the motor control drive. In this paper, a new compensation algorithm is proposed. The principal feature of the proposed algorithm is the use of the integrator output signal of the d-axis proportional plus integral (PI) current regulator. This output signal is nearly zero or constant because the d-axis current command is zero or constant, so that the maximum torque or unity power factor can be acquired in the ac drive system. If the stator currents include offset and scaling errors, the integrator output signal of the d-axis PI current regulator ripples in the rotor speed of the same frequency. The proposed compensating algorithm for the current-measurement errors can be easily implemented by subtracting the dc offset value or rescaling the input measurement gain of the stator currents. Therefore, the proposed algorithm has several advantages: it is robust with regard to the variation of the motor parameters; it is applicable to steady and transient states; it is easy to implement; and it requires less computation time. The MATLAB simulation and the experimental results verify the usefulness of the proposed current compensating algorithm
TL;DR: In this paper, an Artificial Neural Network based short-term load forecaster (ANNSTLF) engine has been utilized in a real utility system and performance analysis over the past year shows that a majority of forecast error was detected in a consistent period with a large temperature forecast error.
Abstract: A significant portion of electric utility operating expense comes from the energy production. In order to minimize the cost, unit commitment (UC) scheduling is an important tool to properly assign generation units to accommodate the forecasted system demand. The short-term load forecast is a prerequisite for UC planning. The projected load up to 7 days ahead is important for the reconfiguration of generation units. Hour-ahead forecast is used for optimally dispatching online resources to supply the next hour load. This paper addresses the systematic design of Artificial Neural Network based short-term load forecaster (ANNSTLF). The developed ANNSTLF engine has been utilized in a real utility system. The performance analysis over the past year shows that a majority of forecast error was detected in a consistent period with a large temperature forecast error. The enhancement of Multi-Stage ANNSTLF is proposed to improve the forecasting performance. The comparison of forecasting accuracy due to this enhancement is analyzed.
TL;DR: An ac brushless drive in which Hall-effect sensors are used as rotor position sensors is presented in this article, where three different methods to obtain a high-resolution position estimation from the low-resolution sensors are described and compared through simulation and experimental testing.
Abstract: An ac brushless drive in which Hall-effect sensors are used as rotor position sensors is presented in this paper. Three different methods to obtain a high-resolution position estimation from the low-resolution sensors are described and compared through simulation and experimental testing. The proposed control algorithm's most innovative feature is its adaptability to the entire speed range, including startup, when using any of the three estimation algorithms. The control algorithm has been implemented and tested in order to drive a slotless axial-flux permanent-magnet (PM) machine for domestic appliance applications.
TL;DR: In this article, the thermal behavior of two induction motors (22 and 4 kW, four poles) and two synchronous reluctance motors (SynRMs) transverse-laminated are investigated and compared.
Abstract: In this paper, the thermal behavior of two induction motors (22 and 4 kW, four poles) and two synchronous reluctance motors [(SynRMs) transverse-laminated] are investigated and compared Both motor types use the same stator but have different rotors Using a lumped-parameter simulation program, a thermal analysis has been also carried out, and the obtained results have been compared with the experimental ones A direct comparison of the thermal behavior of the two motor types has thus been made for constant load and constant average copper temperature conditions Inasmuch as the SynRM has negligible rotor losses compared with the induction motor, it is capable of a larger rated torque, from 10% to more than 20%, depending on the relative size of end connections and motor length
TL;DR: In this article, a fault indicator based on the rotating magnetic-field pendulousoscillation concept in faulty squirrel-cage induction motors is proposed to detect broken-bar and interturn faults.
Abstract: A fault indicator, the so-called swing angle, for broken-bar and interturn faults is investigated in this paper. This fault indicator is based on the rotating magnetic-field pendulous-oscillation concept in faulty squirrel-cage induction motors. Using the "swing-angle indicator," it will be demonstrated here that an interturn fault can be detected even in the presence of machine manufacturing imperfections. Meanwhile, a broken-bar fault can be detected under both direct-line and PWM excitations, even under the more difficult condition of partial-load levels. These two conditions of partial load and motor manufacturing imperfections, which are considered as difficult situations for fault detection, are investigated through experimentally obtained test results for a set of 2- and 5-hp induction motors.
TL;DR: In this article, the authors proposed a digital hysteresis-modulation technique based on switching-time prediction, which is suited for high-performance current (or sliding-mode) control where the digital hardware has enough computational power to allow multiple samples within a switching period.
Abstract: This paper proposes a digital hysteresis-modulation technique based on switching-time prediction. Sampling controlled variables several times within a switching period, it ensures a dynamic performance comparable to that obtainable with analog hysteresis modulation. Compared to conventional digital hysteresis modulation, it avoids frequency jitter since it predicts switching transitions. Compared to hysteresis modulation based on the detection of the zero crossing of current errors, it avoids external analog circuits. Compared to pulsewidth-modulation (PWM) techniques, it ensures faster dynamic response. These advantages are obtained at the expense of increased signal-processing requirements and of control complexity. Switching-frequency stabilization and synchronization with an external clock can be obtained extending the techniques proposed for analog hysteresis modulations. The proposed predictive algorithm does not require knowledge of load parameters and only a rough estimation of the inductor value, which can be easily self-adjusted. The proposed solution is suited for high-performance current (or sliding-mode) control where the digital hardware has enough computational power to allow multiple samples within a switching period. The proposed modulation technique has been applied to a sliding-mode control of a single-phase uninterruptible power supply (UPS). Experimental results confirm the effectiveness of the proposed approach.
TL;DR: In this paper, the authors used the third harmonic component in the line voltage and the speed ripple consequent to the reverse-rotating field as a reliable estimator of stator faults.
Abstract: Stator fault is one of the most commonly occurring faults in ac machines. Recent estimates suggest that 30%-40% of all reported induction machine faults are stator fault related. Going by the number of occurrences, the position of stator faults is only second to bearing-related faults. Third harmonic line currents, which are caused by the interaction of a reverse-rotating field and saturation-related permeance variation, the third harmonic component in the line voltage, and the speed ripple consequent to the reverse-rotating field, have been reported to increase under stator fault conditions. Since the reverse-rotating field is produced by voltage unbalance as well as stator faults, the measurement of third harmonic in the line current may not be a reliable estimator of stator faults, particularly at an incipient stage. The third and the other triplen-related harmonics are however found to be a very decisive indicator of the fault if measured in the machine terminal voltages just after switch-off. The fault-detection technique is independent of machine parameters and supply unbalances. Simulation and experimental results with very few shorted turns show that not only the presence of stator fault but also the phase in which the fault has occurred can be detected reliably. However, because of the nature of detection, it should strictly be called an offline method that can only validate existing online schemes, unless used for motors operating continuously in transient modes or form-wound machines