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Self-bearing machines do not contain physical bearings but magnetic bearings. Both rotor rotary and spatial positions displacement are required in these types of machines to control the rotor position while it is levitating. Self-bearing machines often use external sensors for x (horizontal) and y (vertical) spatial position measurement, which will result in additional cost, volume, complexity, and number of parts susceptible to failure. To overcome these issues, this paper proposes a x y -position estimation self-sensing technique based on both main- and cross-inductance variation. The proposed method estimates x and y position based on inductive saliency between two sets of three-phase coils. The proposed idea is applied on a combined winding self-bearing machine which does not require additional suspension force winding. No additional search coil placement for x y -position estimation is required. Therefore, the proposed algorithm can result in a compact size self-bearing machine that does not require external sensors for x y -position measurement and suspension force winding. [ABSTRACT FROM AUTHOR]

Online detection of rotor and load faults in permanent magnet synchronous motors (PMSM) based on spectrum analysis of current or vibration is not capable of identifying the root cause of the fault, since all faults produce identical fault signatures. The sensitivity of fault detection also depends on the motor and controller design making fault detection unreliable. In addition, operation under variable frequency and load limits the effectiveness of spectrum analysis based methods. In this article, airgap flux monitoring is investigated as an alternative for providing reliable identification of rotor and load faults in PMSMs. Based on the analysis of airgap flux under partial and uniform demagnetization, dynamic eccentricity, and load unbalance, an airgap search coil voltage based method for detection and classification of the faults is proposed. The claims made in the article are verified through experimental testing on an IPMSM under emulated fault conditions along with a comparison to vibration and current spectra-based detection. It is shown that the proposed method provides reliable online identification of the faults for cases where conventional spectrum analysis based methods fail. [ABSTRACT FROM AUTHOR]

There has been active research in fault diagnosis of permanent magnet synchronous motors (PMSMs) with the recent increase in reliability-critical PMSM applications. Most of the research efforts are focused on the motor current signature analysis (MCSA), as it allows remote online detection of the rotor and load defects using the current measurement available in the drive. A critical limitation of MCSA or vibration analysis is their inability to distinguish the type of rotor or load defect. It is crucial for the maintenance engineer to identify the type of defect since the course of action for continued operation differs depending on the fault. In this letter, a simple automated test method for identifying mass unbalance using vibration measurement commonly available in motor drive systems is proposed. The effectiveness of the proposed method is verified on a PMSM under emulated PM demagnetization, dynamic eccentricity, and mass unbalance conditions. [ABSTRACT FROM AUTHOR]

High-frequency (HF) signal injection-based has been widely investigated for sensorless position/speed control of permanent magnet synchronous machines (PMSMs). In PMSMs, the HF signal must be injected in the stator windings and an asymmetric (salient) rotor is required. The extension of HF injection-based sensorless methods with wound-rotor synchronous motors is studied in this article. The fact that rotor terminals are accessible opens interesting possibilities, as avoids the dependency on rotor asymmetries. [ABSTRACT FROM AUTHOR]

Precise output torque control is often required in applications using synchronous reluctance machines. Direct measurement of torque has drawbacks due to both cost and reliability issues. To overcome these limitations, the development of torque estimation methods has received significant research attention. Most of the exiting torque estimation methods require knowledge of machine parameters, suffering, therefore, from parameter sensitivity. Load and saturation are recognized as the primary source of parameter variation. This article proposes the use of a high-frequency signal injection for the online estimation of the machine parameters required for torque estimation. The improvement in the torque estimation will be especially relevant in deep-saturation regions. The method operates without interfering with the normal operation of the machine. [ABSTRACT FROM AUTHOR]

Torque measurement/estimation in permanent magnet synchronous machines (PMSMs) is required in a large variety of applications. Direct torque measurement by means of torque transducers is typically limited to laboratory applications due to cost, reliability, and room concerns. Alternatively, torque can be estimated. Torque estimation methods require accurate knowledge of machine parameters. Injection of a high frequency (HF) signal in the stator via inverter has been shown to be a viable option for online machine parameters identification in PMSMs. However, this introduces concerns on the performance of the machine due to the noise, vibration, and additional losses produced by the HF signal. This article proposes a torque estimation method for PMSMs using low cost Hall-effect sensors. The method is based on the dependency of the leakage flux complex vector due to interaction between permanent magnet flux and stator coil flux and does not interfere with the drive operation of the machine. [ABSTRACT FROM AUTHOR]

This article proposes a high-frequency injection based dq-inductance estimation technique for synchronous machines. The d- and q-axis inductance is estimated using a single HFI between d and q axes, i.e., 45° injection angle. The d- and q-axis incremental inductance variation over four quadrants dq-plane operating condition is evaluated. The proposed technique can operate in real-time without a controlled position or velocity from the load side. Neither previous knowledge of machine parameters nor computationally expensive regression processes are required. The proposed technique can be used to evaluate the sensitivity of inductive saliency based self-sensing to determine preferable self-sensing operating conditions for permanent magnet synchronous machines. [ABSTRACT FROM AUTHOR]

Torque pulsations are one of the major concerns in permanent magnet synchronous machines (PMSMs). Torque pulsations can be mitigated by proper machine design and/or by control. Independently of the means being used, precise measurement of torque pulsation is highly desirable for the validation and improvement of machine designs and control strategies. This article proposes a non-invasive, wireless vibration measurement system aimed to provide precise estimates of torque pulsations. The system is mounted on the rotor shaft of the PMSM, i.e., there is no mechanical coupling, and allows on-line measurement without interfering with the normal operation of the machine. [ABSTRACT FROM AUTHOR]

Control of permanent magnet synchronous machines (PMSMs) requires absolute rotor position measurement/estimation, as well as the magnet polarity detection for the machine start-up, encoders/resolvers being normally used for this purpose. However, these sensors can account for a large portion of the overall drive cost, and require additional room and cabling, therefore penalizing the size and reliability of the drive. This article proposes a method to emulate a resolver in machines using low cost Hall-effect sensors. The proposed Hall-effect resolver system is a new type of angular position sensor for PMSMs. This allows to control machines which do not include a resolver from inverters which require a resolver signal to operate. [ABSTRACT FROM AUTHOR]

Torque measurement/estimation in surface permanent magnet synchronous machines (SPMSMs) is needed in many applications. Torque measurement systems are expensive, require extra room, add weight, can introduce resonances into the system, and their performance can be compromised due to electromagnetic interference. Alternatively, torque can be estimated, accurate knowledge of machine parameters being critical in this case. Injection of a high-frequency (HF) signal in the stator via an inverter has been shown to be a viable option for online identification of machine parameters identification required by torque estimation methods for interior PMSMs. However, the reported methods require the use of two pulsating HF currents, which introduces concerns both on the adverse effects on machine's performance (additional noise, vibration, losses, etc.) as well as to the additional computational burden, as HF current controllers are required. This article proposes a torque estimation method for SPMSMs using a single HF signal; furthermore, a HF voltage signal can be used, avoiding the use of HF current controllers, and therefore simplifying the implementation. [ABSTRACT FROM AUTHOR]

Small grid-tied wind turbines based on permanent magnet generators often use a cost-effective power converter topology consisting of a passive rectifier, a boost converter, and an H-bridge inverter. Speed or position sensors are rarely used due to cost issues. Model-based estimators relying on electrical magnitudes are used instead. However, such estimators are parameter sensitive, which limit their accuracy. Further concerns arise if these parameters change with the operating condition of the machine, mainly due to temperature. Speed sensorless control using the rectifier voltage ripple is analyzed in this paper. This technique provides good dynamic response and does not depend on machine parameters. Simulations are provided for speed and power tracking comparison with an accurate model-based speed estimation method operating at non-rated parameters. They show the speed accuracy and power tracking capability of the proposed method are similar to that provided by a speed sensor. This is translated into a 0.9% power increase when the model-based speed estimator shows 9% of error. Experimental results are carried out to test the effect of current and temperature in the estimation, showing temperature insensitivity and some distortion due to fast current transients. A speed estimation accuracy of zero mean error and 1.7% standard error is experimentally obtained in the regular operation of the wind turbine. [ABSTRACT FROM AUTHOR]

Thermal and magnetization state monitoring of permanent magnet synchronous machines (PMSMs) is important for reliability purposes. Use of magnet high-frequency (HF) resistance has been proposed both for thermal and magnetization state monitoring, as it directly depends on PM temperature and magnetization state. Machine d-axis HF inductance has been recently proposed for thermal state monitoring, though its use for magnetization state estimation remains to be explored yet. This article reviews the use of HF-signal-injection-based methods for thermal and magnetization state monitoring on PMSMs, including the use of the HF inductance for magnetization state monitoring. [ABSTRACT FROM AUTHOR]

Online monitoring and diagnostics of permanent magnet synchronous motors (PMSMs) is becoming important with the increasing demand in PMSM applications. Most of the research effort focuses on motor current signature analysis (MCSA) as it can provide remote, online monitoring at low cost. However, all types of defects that produce asymmetries in the PMSM rotor or load produce identical rotor rotational frequency components. This is a serious limitation when applying MCSA since it can produce false indications and degrade the sensitivity of fault detection. The requirement of complex time–frequency analysis techniques is another limitation of MCSA for applications with speed variations. In this paper, the feasibility of using analog Hall sensor signals to complement MCSA for detection and classification of rotor- and load-related defects is investigated. It is shown that Hall sensors installed in machines for initial rotor position estimation can be used with minimal hardware modifications to detect and classify signatures produced by the rotor and load for cases where MCSA fails, even during transient conditions. Experimental testing performed on an interior permanent magnet synchronous motor (IPMSM) under eccentricity, local demagnetization, and load unbalance conditions shows that the reliability and sensitivity of fault detection in PMSM systems can be improved at low added cost. [ABSTRACT FROM AUTHOR]

Rotor eccentricity and local demagnetization in permanent magnet synchronous motors (PMSMs) increase unbalanced magnetic pull and motor vibration resulting in accelerated aging of motor components. If the asymmetry in the rotor remains undetected, it can increase in severity, and increase the risk of stator–rotor contact, which causes forced outage of the motor and driven process. Detection of PMSM rotor asymmetry currently relies on offline testing and online vibration/current spectrum analysis. However, they are inconvenient or cannot provide reliable detection of rotor faults for all PMSM designs. In this paper, the feasibility of using the signals from analog Hall-effect field sensors for detecting eccentricity and local demagnetization is investigated. It is shown that Hall sensors present in machines for motion control can be used for directly measuring the variation in the flux inside the motor due to rotor magnetic asymmetry with minimal hardware modifications. Three-dimensional finite-element analysis and experimental results performed on an interior PMSM show that the proposed method can provide sensitive and reliable detection of dynamic/mixed eccentricity and local PM demagnetization. [ABSTRACT FROM AUTHOR]

Control of permanent magnet synchronous machines (PMSMs) requires rotor position measurement/estimation, as well as the magnet polarity detection for startup of the machine. The rotor position of PMSMs is typically measured using a speed/position sensor (e.g., an encoder), while the magnet polarity is commonly measured using digital hall-effect sensors. Since simplifying the system can help improve reliability and reduce the cost associated with the measurements, the use of low cost analog hall-effect sensors for the estimation of the PM position, and polarity for control of PMSMs drives is evaluated in this paper. Experimental results performed on a 7.5-kW motor confirm that analog hall-effect sensors can replace both speed/position sensors and digital hall-effect sensors while maintaining adequate performance of the drive at a lower cost. [ABSTRACT FROM PUBLISHER]

Soft-stall control of small wind turbines is a method to protect the generation system and/or load from excessive wind speeds and wind gusts without discontinuing power generation. Soft-stall can be activated due to an excess of the power and/or torque/current. This paper proposes a method to improve the existing soft-stall methods for over torque/current protection using a turbine torque estimator. In addition, this paper also proposes two methods to emulate the wind turbine inertia without communications between the load drive (wind turbine emulator) and the generation system controller. This will allow the evaluation of the proposed methods in working conditions. [ABSTRACT FROM AUTHOR]

Thermal monitoring is a common feature in most electric machine drives since thermal overloading is one of the most common causes of motor failures. Contact-type sensors are normally used to measure the stator temperature in electric machines. However, use of this type of sensor is not advisable in the rotor as it requires cabling to a rotating part or the use of a wireless transmission system. Consequently, measurement of the rotor temperature is not easy in practice and is not normally implemented in standard machines. An alternative to rotor temperature measurement is rotor temperature estimation. To date, only thermal models have been used for rotor temperature estimation in doubly-fed induction machines (DFIMs). This paper proposes rotor temperature estimation in DFIMs using high-frequency signal injection. The proposed method estimates the rotor temperature from the rotor high frequency resistance, which is a function of the rotor windings temperature. The method does not interfere with the normal operation of the drive and can be implemented in existing DFIM drives without requiring additional hardware. [ABSTRACT FROM AUTHOR]

This paper proposes a new soft-stalling control strategy for grid-connected small wind turbines operating in the high and very high wind speed conditions. The proposed method is driven by the rated current/torque limits of the electrical machine and/or the power converter, instead of the rated power of the connected load, which is the limiting factor in other methods. The developed strategy additionally deals with the problem of system startup preventing the generator from accelerating to an uncontrollable operating point under a high wind speed situation. This is accomplished using only voltage and current sensors, not being required direct measurements of the wind speed nor the generator speed. The proposed method is applied to a small wind turbine system consisting of a permanent magnet synchronous generator (PMSG) and a simple power converter topology. Simulation and experimental results are included to demonstrate the performance of the proposed method. The paper also shows the limitations of using the stator back electromotive force to estimate the rotor speed in PMSG connected to a rectifier, due to significant $d$-axis current at high load. [ABSTRACT FROM AUTHOR]

Permanent-magnet (PM) magnetization state estimation in PM synchronous machines (PMSMs) is of great importance for torque control and monitoring purposes. The magnetization state of a PMSM can change due to several reasons, injection of stator current ( $d$-axis or $q$-axis) and variation of magnet temperature being the primary reasons. PM magnetization state estimation is not easy once the machine is assembled. Methods based on the back electromotive force can be used, but they require that the machine is rotating. This paper analyzes the use of high-frequency signal injection for PM magnetization state estimation in PMSMs. The magnetization state of the PMs in PMSMs affects the stator-reflected PM high-frequency resistance. The stator-reflected PM high-frequency resistance can be estimated by injecting a high-frequency voltage/current using the inverter. The high-frequency signal is superposed on the fundamental excitation used to produce torque, meaning that the method can operate at any speed, including zero speed, and without interfering with the normal operation of the machine. [ABSTRACT FROM PUBLISHER]

The injection of a high-frequency signal in the stator via inverter has been shown to be a viable option to estimate the magnet temperature in permanent-magnet synchronous machines (PMSMs). The variation of the magnet resistance with temperature is reflected in the stator high-frequency resistance, which can be measured from the resulting current when a high-frequency voltage is injected. However, this method is sensitive to d- and q-axis inductance ( Ld and Lq ) variations, as well as to the machine speed. In addition, it is only suitable for surface PMSMs (SPMSMs) and inadequate for interior PMSMs (IPMSMs) . In this paper, the use of a pulsating high-frequency current injection in the d-axis of the machine for temperature estimation purposes is proposed. The proposed method will be shown to be insensitive to the speed, L_{q}, and L_{d} $ variations. Furthermore, it can be used with both SPMSMs and IPMSMs. [ABSTRACT FROM PUBLISHER]

High-frequency-signal-injection-based methods have been widely investigated for sensorless position/speed control of induction machines (IMs), permanent magnet synchronous machines (PMSMs), and, more recently, doubly fed induction generators (DFIGs). When used with IMs and PMSMs, the high-frequency signal is injected in the stator windings, an asymmetric (salient) rotor being required for this case. Contrary to this, both stator and rotor terminals are accessible and sensored in DFIGs, being therefore possible to inject the high-frequency signal either in the stator or the rotor terminals. As a consequence of this, the method can be used even if the machine is nonsalient. In the implementation of the method with DFIGs, the high-frequency voltage signal is typically injected in the rotor, the high-frequency components (voltages of currents) induced in the stator being used for rotor position estimation. A drawback of this alternative is that the method is sensitive to the grid impedance in the stator side, which will be affected by the grid configuration, and is normally unknown. This paper proposes the sensorless control of a DFIG injecting the high-frequency voltage in the stator side and using a high-frequency current cancellation strategy in the rotor side. The main advantage of the proposed strategy is that the estimated position is independent of the grid characteristics. [ABSTRACT FROM AUTHOR]

This paper analyzes the use of high-frequency signal injection methods for the sensorless control of doubly fed induction generators (DFIGs). High-frequency signal injection methods have been widely investigated for the sensorless control at very low speed and position control of induction machines and permanent-magnet synchronous machines. Most of these methods inject a high-frequency voltage signal in the stator windings, which interacts with the machine asymmetries (saliencies), modulating the resulting stator high-frequency currents, from which the rotor position is estimated. The use of these methods with DFIGs is studied in this paper, with special focus on two distinguishing features compared with the case of other types of three-phase machines: 1) It is feasible to inject the high-frequency signal in the rotor since the rotor windings are accessible; and 2) as a consequence of this, it is possible to use the method with nonsalient machines. [ABSTRACT FROM PUBLISHER]

The flux-intensified interior permanent-magnet synchronous machine (IPMSM) (FI-IPMSM) lends itself to designing for good self-sensing properties. This paper begins by evaluating the self-sensing position estimation performance of a suitably designed FI-IPMSM machine using different high-frequency injection methods. This paper then uses an alternative square-wave injection method to estimate the FI-IPMSM rotor position. The experiment results show that the estimation accuracy and system robustness are improved. It is known that secondary saliencies and saliency offset caused by the saturation of the machine can degrade the estimation accuracy. This paper also includes modeling, measurement, and decoupling methods that mitigate these undesirable effects, which are also implemented using an experimental FI-IPMSM. Estimation accuracy and torque ripple caused by the injection current are examined for this FI-IPMSM. Comparisons of the methods are presented. [ABSTRACT FROM AUTHOR]

This paper presents a method for estimating the magnet temperature in surface permanent-magnet (PM) synchronous machines during six-step operation. Six-step operation allows the maximum available dc-bus voltage to be applied to a machine, which maximizes its torque and speed range. This can be of importance in electric traction applications, including railway as well as electric and hybrid electric vehicles. However, six-step operation produces current harmonics that induce additional losses in the PMs and can therefore increase their temperature. An increase of magnet temperature can result in a reduced torque capability and eventually in a risk of demagnetization if excessive values are reached, with real-time rotor magnet temperature monitoring being therefore advisable. Six-step operation provides opportunities for rotor temperature monitoring from the electrical terminal variables (voltages and currents) of the motor. To achieve this goal, the rotor high-frequency resistance is measured using the harmonic voltages and currents due to six-step operation, from which the magnet temperature can be estimated. [ABSTRACT FROM AUTHOR]

This paper proposes a new rotor design for flux-intensifying interior permanent magnet synchronous machine (FI-IPM SM) that is more suitable for self-sensing control at zero/very low speed based on saliency-tracking methods and retains acceptable power conversion capability as compared to a traditional flux-weakening IPM SM (FW-IPM SM). Design steps for the rotor structure of the new machine are laid out and discussed to emphasize key design challenges. The proposed FI-IPM SM and a conventional FW-IPM SM with similar torque-speed capability are made to evaluate performances in power conversion as well as self-sensing capability at very low speed. Finite-element analysis (FEA) is used to evaluate each machine's performance. The proposed FI-IPM SM shows less variation in the saliency when the machine is loaded, leading to a possibility of better self-sensing performance at very low speed as compared to the traditional FW-IPM SM. Experimental results on the efficiency and self-sensing performance of these two machines are presented to verify the design methodology. [ABSTRACT FROM AUTHOR]

This paper analyzes two types of effects caused by the fundamental current in saliency-tracking-based techniques for sensorless control of three-pole active magnetic bearings, i.e., saturation and insufficient spectral separation of the fundamental current command during transients. Injection of a high-frequency signal superimposed to the fundamental excitation providing active control allows the measurement of changes in the air gap, from which an estimation of the rotor position can be obtained. Interference of the fundamental current, which is needed to operate the magnetic bearing, with the high-frequency current can occur through two mechanisms: 1) saturation; and 2) high-frequency harmonics caused by fast transients of the fundamental current. Both phenomena can interfere with the sensorless control resulting in a decrease in its performance. The effects caused by the fundamental current on the negative-sequence high-frequency current, used as a position estimation signal, are studied, and a decoupling mechanism is proposed. An analysis of high-frequency leakage flux is presented. and a simple analytical model is developed for describing the aforementioned phenomena. Finite-element analysis of the magnetic bearing under fundamental excitation, as well as experimental verification, is used to validate the analytical findings. [ABSTRACT FROM PUBLISHER]

High-frequency carrier signal excitation has been widely investigated for the position sensorless control of permanent-magnet synchronous machines (PMSMs) near and at zero speed. Selection of the injected signal characteristics (shape, frequency, magnitude, etc.) is a tradeoff between performance criteria of the sensorless control (stability, accuracy, robustness, bandwidth, etc.) and minimization of its adverse effects (additional losses, noise, vibration, etc.). The increased losses due to the injected signal can be of importance in PMSMs since they can produce a significant increase of the temperature in the rotor magnets. This can adversely impact the normal operation of the machine and can eventually result in the irreversible demagnetization of the magnets. This paper analyzes the impact that excitation using high-frequency signals for sensorless control of PMSMs has on the machine's temperature. The machine design, as well as the type of injected high-frequency signal, will be shown to strongly influence the machine's thermal behavior. Analytical models will be developed to explain this behavior, with experimental results being used to verify the analysis. [ABSTRACT FROM AUTHOR]

This paper analyzes the effects of fractional pitch and distributed winding stators on the self-sensing performance of permanent-magnet machines. Three rotor configurations (i.e., a flux-weakened interior permanent-magnet synchronous machine (IPMSM) and two flux-intensified IPMSMs) and two stator designs (i.e., distributed and concentrated windings) are presented to analyze the cross saturation, secondary saliencies, saturation-induced saliencies, and saliency ratio, depending on the possible rotor and stator configurations. Finite-element modeling has been used to obtain a detailed understanding of the self-sensing performance of these machines. [ABSTRACT FROM PUBLISHER]

This paper proposes a method to estimate the magnet temperature in surface permanent-magnet machines using high-frequency carrier signal injection. The injection of a high-frequency signal, superimposed on the fundamental excitation, allows the estimation of the stator high-frequency impedance, which is a function of both the stator and rotor impedances. The temperature of the magnets is shown to have a significant weight on the overall stator high-frequency impedance, from which it can be estimated. The high-frequency carrier signal is injected intermittently in order to minimize potential adverse effects on the normal operation of the machine. This paper first explains the physics behind the magnet temperature dependence. Then, the principles of the method, as well as its practical implementation, are discussed. Experimental verification of the method is provided. [ABSTRACT FROM AUTHOR]