Erkennung defekter Rotorstäbe an umrichter- und netzgespeisten Asynchronmaschinen durch die Vienna Monitoring Method

The introduced paper deals with faulty rotor bars in the squirrel cage of an induction machine including the detection by means of the Vienna Monitoring Method. Electrical asymmetries in the rotor cage lead to thermal stress of the rotor and to additional modulations of shaft torque. Furthermore additional harmonic components in the currents (and voltages) occur. The fault related torque modulations can be seized by means of models and are reliably detectable by the Vienna Monitoring Method. This robust monitoring technique is therefore suitable for grid supplied machines and for inverter drives.     

Robust Rotor Fault Detection by Means of the Vienna Monitoring Method and a Parameter Tracking Technique

The Vienna Monitoring Method (VMM) is a model-based rotor fault detection method that utilizes the voltage and current models for the computation of a fault indicator. So far, the VMM was investigated with fixed rotor parameters only. In this paper, the parameters of the current model are provided by a parameter tracking technique. For this advanced rotor fault detection method, measurement results are presented for steady-state and varying load torque operations.      

On-line rotor cage monitoring of inverter-fed induction machines bymeans of an improved method

This paper suggests a fault-detection technique to monitor defects such as cracked rotor bars in induction machines. It has been introduced as the Vienna monitoring method. Rotor bar faults cause an asymmetric magnetic flux pattern in the air gap. Thus, the current phasor (or voltage phasor at current-controlled machines), flux phasor and air-gap torque differ from those of an ideal symmetric machine. The Vienna monitoring method compares the outputs of a reference model, which represents an ideal machine, to a measurement model. Observing the deviations of these two models makes it possible to detect and even locate rotor faults. It can be applied to inverter-fed machines as no frequency analysis is used. The method is verified by online experimental results from a DSP-controlled IGBT inverter drive. The findings match the outcomes of a detailed machine simulation. Air-gap flux density evaluation by a measurement coil system proves both the excellent sensitivity and fault location ability of the proposed scheme     

Implementation of a DSP based real-time estimator of inductionmotors rotor time constant

Implementation of ac drives insensitive to parameter variations is an important need in the field of high performance drives. For drives controlled by the indirect rotor flux oriented control method (IRFOC), the rotor time constant (τ_r = L_r/R_r) exerts a dominant role in the loss of dynamic performance and its variation results in an undesirable coupling between flux and torque of the machine. This paper presents a new scheme for on-line estimation of rotor time constant using dq representation of the model in the stationary reference frame and measurements of accessible motor variables only (voltages, currents and speed). The estimator is tested by simulation in the MATLAB/SIMULINK environment and validated experimentally on a 1/4 hp squirrel cage motor and a 1/4 hp wound rotor motor with implementation on a TMS320C31 digital signal processor     

A fully digitized field-oriented controlled induction motor driveusing only current sensors

A field-oriented control method based on a predictive observer with digital current regulation of an induction motor, without speed and voltage sensors, is proposed. Measuring only stator currents and estimating motor speed and rotor fluxes by a predictive state observer with variable pole selection the stator currents are controlled to be exactly equal to the reference currents at every sampling instant. The resulting speed and rotor fluxes are estimated with low sensitivity to parameter variation, and the torque ripples are reduced. The proposed method consists of four parts: identification of the rotor speed, derivation of a digital control law, construction of a state observer that predicts the rotor flux and the stator currents, and derivation of field-oriented control. A theoretical analysis of the method, computer simulations, and experimental results are described     

Sensorless control of induction Machines at zero and low frequency using zero sequence currents

This paper considers both flux and rotor position estimations for sensorless control of delta-connected cage induction machines (IMs) at low and zero frequency operation. The variation of leakage inductance due to either saturation or rotor slotting is tracked by measuring the derivative of the zero sequence current in response to the application of appropriate voltage test vectors. The method requires only a single extra sensor. It requires access to machine phase windings and is appropriate for integrated-type induction motor drives. Both a closed-slot and an open-slot machine is used to demonstrate rotor flux and rotor position tracking, respectively. Experimental results are presented showing sensorless torque control and sensorless speed and position control at low and zero frequencies.     

Design and implementation of the extended Kalman filter for thespeed and rotor position estimation of brushless DC motor

A method for speed and rotor position estimation of a brushless DC motor (BLDCM) is presented in this paper. An extended Kalman filter (EKF) is employed to estimate the motor state variables by only using measurements of the stator fine voltages and currents. When applying the EKF, it was necessary to solve some specific problems related to the voltage and current waveforms of the BLDCM. During the estimation procedure, the voltage- and current-measuring signals are not filtered, which is otherwise usually done when applying similar methods. The voltage average value during the sampling interval is obtained by combining measurements and calculations, owing to the application of the predictive current controller which is based on the mathematical model of motor. Two variants of the estimation algorithm are considered: (1) speed and rotor position are estimated with constant motor parameters and (2) the stator resistance is estimated simultaneously with motor state variables. In order to verify the estimation results, the laboratory setup has been constructed using a motor with ratings of 1.5 kW, 2000 r/min, fed by an insulated gate bipolar transistor inverter. The speed and current controls, as well as the estimation algorithm, have been implemented by a digital signal processor (TMS320C50). The experimental results show that is possible to estimate the speed and rotor position of the BLDCM with sufficient accuracy in both steady-state and dynamic operation. Introducing the estimation of the stator resistance, the speed estimation accuracy is increased, particularly at low speeds. At the end of the paper, the characteristics of the sensorless drive are analyzed. A sensorless speed control system has been achieved with maximum steady-state error between reference and actual motor speed of ±1% at speeds above 5% of the rated value     

A speed estimator for high performance sensorless control ofinduction motors in the field weakening region

The paper proposes a modified version of the model reference adaptive system (MRAS) based speed estimator, whose outputs of the reference and the adjustable model are rotor flux space vectors. The estimator is modified in such a way that the variation in the instantaneous level of the main flux saturation during operation in the field weakening is recognized and properly compensated at all times. The speed estimation scheme is equally applicable to both vector controlled and direct torque controlled induction machines, since it operates in the stationary reference frame and requires measurement of only stator voltages and currents. Verification of the proposed scheme is provided by simulation and by experimentation on an indirect feedforward rotor flux oriented induction machine for speed references of up to twice the base speed     

Diagnose von Dämpferstabbrüchen in Synchronmaschinen

This paper attempts to complete the existing diagnosis systems of synchronous machines. In order to avoid break downs caused by broken damper bars, a method to diagnose such failures is presented. The main idea of the method is the separation of voltages of the field winding induced according to their polarity. So, the difference of the pole voltages can be determined. This voltage difference is triggered off by the magnetic field disturbance caused by the missing damper bar. The main field in a symmetrical built machine disappears in the difference voltage. The broken damper bar location is fixed to the rotor and also to the field winding. Moreover, the voltage difference depends on the position of the missing damper bar as well as on the distribution of the field winding. In the case of a distributed winding, the damper bars under the edges of each pole can be detected exactly. The theoretical ideas are presented and checked by measurements in a model machine.     

Direct power control of grid-connected wound rotor inductionmachine without rotor position sensors

A method is presented for fast response control of the torque and flux of a grid connected wound rotor induction machine fed by back to back connected voltage source inverters on the rotor side. It is based on the measurement of active and reactive power on the grid side where voltages and currents are alternating at fixed frequency. The active and reactive powers are made to track references using hysteresis controllers. The method eliminates the need for rotor position sensing and gives excellent dynamic performance, as shown by simulation and experimental results from a variable speed constant frequency induction generator system. It is also capable of starting on the fly. It is thus an attractive sensorless control method for drive as well as generator applications     

Implementation and experimental investigation of sensorless speed control with initial rotor position estimation for interior permanent magnet synchronous motor drive

In this paper, a new approach to sensorless speed control and initial rotor position estimation for interior permanent magnet synchronous motor (IPMSM) drive is presented. In rotating condition, speed and rotor position estimation of IPMSM drive are obtained through an extended Kalman filter (EKF) algorithm simply by measurement of the stator line voltages and currents. The main difficulty in developing an EKF for IPMSM is the complexity of the dynamic model expressed in the stationary coordinate system. This model is more complex than that of the surface PMSM, because of the asymmetry of the magnetic circuit. The starting procedure is a problem under sensorless drives, because no information is available before starting. The initial rotor position is estimated by a suitable sequence of voltage pulses intermittently applied to the stator windings at standstill and the measurement of the peak current values of the current leads to the rotor position. Magnetic saturation effect on the saliency is used to distinguish the north magnetic pole from the south. To illustrate our work, we present experimental results for an IPMSM obtained on a floating point digital signal processor (DSP) TMS320C31/40 MHz based control system.     

Influence of the motor load inertia and torque in the fault diagnosis of rotors in induction machines

During the last decades, non-invasive techniques have been proposed to carry out the fault diagnosis in electric machines. When these techniques are employed in the fault detection of the induction machine's rotors, they exhibit a strong dependence on factors such as the motor load inertia or the opposed torque. In order to develop automatic diagnostic systems or the diagnosis assistance over the rotor state, such as expert systems or knowledge based systems, it is necessary to have available further information to weigh up the influence of these factors. This work presents a study done, based on induction motor's mathematical models, about the incidence of the motor inertia and the opposed torque in some non-invasive fault detection technique employed more frequently. The model takes into account in an independent way each of the rotor bars and then allows to represent different faulty situations. These techniques with non-invasive features do not require sensors directly over the motor and thus allow a diagnosis even on-line when the machine is running. Particularly the study of the following techniques was approached: power spectral analysis, torque spectral analysis, stator current spectral analysis and Park's current vector behaviour. Therefore the diagnostic may be based in the measurement of motor's external variables such as applied voltages and stator currents.     

Comparison of Simple Control Strategies of Space-Vector Modulated Indirect Matrix Converter Under Distorted Supply Voltage

This paper concerns the effect of symmetric supply voltage harmonics in a space-vector modulated three-phase indirect matrix converter (IMC). The IMC is modulated using indirect space-vector modulation. The effect of symmetric supply harmonics on load voltages and currents is analyzed using space-vector presentation. The measurement and simulation results with distorted supply voltages are compared to the results with pure sinusoidal supply voltage. Four simple control methods of IMC are tested in simulations and measurements: 1) open-loop control without measurements (Method I); 2) calculation of modulation index using measured supply voltages (Method II); 3) closed-loop control of output currents (Method III); and 4) combination of Methods II and III, i.e., closed-loop output current control with supply voltage measurement (Method IV). All the methods are easy to implement and do not require complicated computing. It is noted that Methods II and IV, where modulation index is calculated using measured supply voltage magnitudes, can produce more sinusoidal load currents than Methods I and III, which suppose ideal supply conditions     

Digital Simulation of an Inverter-Fed Self-Controlled Synchronous Motor

This paper describes a digital simulation method for the self-controlled synchronous motor (SCSM) in time domain. A generalized machine model in direct three-phase quantities is used to represent the machine and the fourth-order numerical integration technique of Runge, Kutta, and Gill in [17] is used to solve the machine equations. Performance of the synchronous machine with nonsinusoidal voltages and currents is simulated under both steady-state and transient conditions. The effects of the damper windings and saliency on the torque, and voltage and current waveforms are studied using this digital simulation technique when the machine is operated from a voltage source inverter (VSI) and a current source inverter (CSI).     

Comparative investigation of diagnostic media for induction motors:a case of rotor cage faults

Results of a comparative experimental investigation of various media for noninvasive diagnosis of rotor faults in induction motors are presented. Stator voltages and currents in an induction motor were measured, recorded, and employed for computation of the partial and total input powers and of the estimated torque. Waveforms of the current, partial powers p_AB and p_CB, total power, and estimated torque were subsequently analyzed using the fast Fourier transform. Several rotor cage faults of increasing severity were studied with various load levels. The partial input power p_CB was observed to exhibit the highest sensitivity to rotor faults. This medium is also the most reliable, as it includes a multiplicity of fault-induced spectral components     

Feldorientierte Regelung der Permanentmagnet-Synchronmaschine auf Basis des Drehzahlistwertes mit Winkelfehlerkorrektur

This paper describes a concept for the control of a permanent magnet synchronous machine. Calculating the rotor position by integration of the measured speed signal instead of using a position sensor is the significant feature of the concept. Due to dynamic and static deviations of the speed signal an accumulation of a position-error is unavoidable. A method is presented of how to recognize and correct such errors using the measured machine currents. The usability of the concept is shown by simulation-results and measurements from a laboratory test with a 7 kW machine.     

Simple Derivative-Free Nonlinear State Observer for Sensorless AC Drives

In this paper, a new Kalman filtering technique, unscented Kalman filter (UKF), is utilized both experimentally and theoretically as a state estimation tool in field-oriented control (FOC) of sensorless ac drives. Using the advantages of this recent derivative-free nonlinear estimation tool, rotor speed and$dq$-axis fluxes of an induction motor are estimated only with the sensed stator currents and voltages information. In order to compare the estimation performances of the extended Kalman filter (EKF) and UKF explicitly, both observers are designed for the same motor model and run with the same covariance matrices under the same conditions. In the simulation results, it is shown that UKF, whose several intrinsic properties suggest its use over EKF in highly nonlinear systems, has more satisfactory rotor speed and flux estimates, which are the most critical states for FOC. These simulation results are supported with experimental results.     

DC I-V characteristics of field emitter triodes

A simple model that is applicable to Spindt-type emitter triodes is presented. Experimentally, it has been observed that the gate current at zero collector voltage follows the same Fowler-Nordheim law as the collector current at high collector voltage, and that for low emission current densities, the sum of gate and collector currents is constant for any collector voltage and is given by the Fowler-Nordheim current I_FN. Based on these observations, a simple model has been developed to calculate the I-V characteristics of a triode. By measuring the Fowler-Nordheim emission, emission area and field enhancement can be obtained assuming a value for the barrier height. Incorporating the gate current, the collector current can be calculated from I_c=I_FN-I_g as a function of collector voltage. The model's accuracy is best at low current density. At higher emission currents, deviations occur at low collector voltages because the constancy of gate and collector currents is violated