Unbalanced Voltage Source Research Articles

Stator Fault Detection and Faulty Phase Identification in Network/Inverter-fed Induction Machines using Negative Sequence Current Component

This paper proposes a non-invasive negative sequence impedance-based technique to detect stator turn-to-turn faults (STTFs) and dentify the related faulty phase at early stages based on the tracking the magnitude and angle variations of the negative sequence current component generated due to STTFs. To extract these indicators, a simplified steady-state negative sequence equivalent circuit of the induction motor is used. To neutralize the effect of various produced disturbances by the inherent non-ideal construction of the machine and also unbalanced feed voltage to the STTF diagnosis, they will be estimated and removed from the main obtained component. It is shown experimentally that the introduced technique is independent of mechanical loading level (load variations) and is applicable for network or inverter-fed motors as well. Online fault detection and faulty phase identification, as the most important goals of the protection plan, are accessible by defining an appropriate threshold for the magnitude and allowable range of angle variation of the introduced criterion, respectively. The performance of the method is evaluated by simulation as well as multiple experimental tests. The experimental results have shown that from the sensitivity point of view, even weak faults are detectable by such a technique. Also, the obtained tests showed that such technique is robust, reliable and secure in the face of unbalanced voltage sources and load level variations. In addition, the performance of this method for the inverter-fed mode showed that the related sensitivity will be increased in such a condition.

A secure and sensitive wavelet transform based technique for stator fault detection in the cases of line‐connected and inverter‐fed induction machines

Here a new sensitive fault detection criterion is proposed, based on the stationary wavelet transform (SWT) decomposition components of the stator currents, for the online detection of stator winding turn-to-turn faults at an early stage of development. The energies of the desired detail components are calculated and the normalized Euclidean distance of the energy differences between the three phases is used as a new fault detection criterion. The robustness of the proposed technique against the presence of rotor turn-to-turn faults and loading variations is demonstrated. In addition, an adaptive threshold level as a function of the voltage unbalance factor is proposed to guarantee the robustness of the diagnostic technique against unbalanced voltage sources. Experimental results demonstrate the effectiveness and sensitivity of the proposed diagnostic approach for the detection of stator faults in line-connected and inverter-fed motors.

A Combined Sliding Mode Space vector Modulation Control of the Shunt Active Power Filter Using Robust Harmonic Extraction Method

This paper presents a combined sliding mode space vector modulation control of the shunt active power filter using robust harmonic extraction method to improve the power quality such as current harmonics and reactive power compensation due to the non-linear loads and unbalanced voltage source. To verify the validity of the analysis and the feasibility of the proposed control method a set of simulation tests have been conducted using Matlab/Simulink. A comparison between the conventional instantaneous powers method (PQ) used for harmonic extracting and the new PQ based on a multivariable extraction filter demonstrates the superiority of the proposed control scheme.

Voltage sensorless based virtual flux control of three level NPC back-to-back converter dfigunder grid fault

In this paper, a harmonic elimination of grid and stator currents of doubly fed induction generator (DFIG) in case of grid fault without line voltage sensors is proposed . This can be achieved by compensating power based on virtual flux voltage sensorless technique. Direct power control with space vector modulation (DPC-SVM) is used to control both grid-side (GSC)and rotor-side converters (RSC). To achieve the control objective, compensated active and reactive powers are calculated based on virtual flux technique with balanced and harmonic free current as a control target. A theoretical analysis of active and reactive powers under unbalanced voltage source is clearly demonstrated and the effect of grid fault on the performance of DFIG is profoundly discussed. Simulation results verified the effectiveness of the modified control strategy.

Broken Rotor Bar Detection in Induction Motors Based on Air-Gap Rotational Magnetic Field Measurement

This paper presents a novel technique for the online detection of broken rotor bar(s) (BRBs) in induction motors, based on the analysis of the air-gap rotational magnetic field (RMF), being it indirectly sensed using the voltages induced in dual search coils installed in several stator regions. The induced voltages allow obtaining three differential voltages which reveal the symmetricity level of the mentioned field along the stator circumference. Under the presence of the broken bar(s), the RMF is disturbed by the rotor magneto-motive force, being these disturbances detected through the fundamental components of the differential voltages using a new time-domain analysis technique. The proposed diagnostic approach is verified by finite-element analysis and also by several experimental tests. A high sensitivity, robustness in the face of unbalanced voltage sources and motor load level variations are the main advantages of the proposed technique. Moreover, it is a secure method for BRB detection, easily implementable in low-cost digital signal processing units.

A Flux-Based Differential Technique for Turn-to-Turn Fault Detection and Defective Region Identification in Line-Connected and Inverter-Fed Induction Motors

A new air-gap flux-based technique is proposed in this paper for turn-to-turn fault (TTF) detection and defective region identification, which is implemented in line-connected and inverter-fed induction motors. Some search coils (SCs) are used to measure the magnetic flux in various air-gap regions of the mentioned motor. The induced voltages in the SCs reveal the configuration of the rotational magnetic field (RMF) along the stator inner circumference to assess the symmetricity level of the flux distribution at each time instant. The RMF asymmetric distribution can be detected by comparing the induced voltages in various dual SCs (which under healthy conditions must sense identical magnetic flux) to detect TTFs and identify the faulty region as well. The proposed method is verified through finite element simulations and also by carrying out several experimental tests. Despite the fact that the proposed method is an invasive diagnostic technique, significant sensitivity and robustness in the face of unbalanced voltage sources and/or loading level are compelling evidence to use it for TTF detection at an incipient stage. The capability of the proposed technique to identify the faulty phase and the related region in the stator is another advantage of this invasive method, which cannot be ignored.

Neural speed estimator for line-connected induction motor embedded in a digital processor

Estimating the electrical and mechanical parameters involved in three-phase induction motors is frequently employed to avoid measuring every variable in the process. Among mechanical parameters, speed is an important variable: it is involved in control, diagnosis, condition monitoring, and can be measured or estimated by sensorless methods. These technologies offer advantages when compared with direct measurement, such as lower cost or more robust systems. This paper proposes the use of artificial neural networks to estimate rotor speed by using current sensors for balanced and unbalanced voltage sources with a wide mechanical load range in a line-connected induction motor. This paper also presents two case analyses: (i) a single current sensor; and (ii) a multiple currents sensors. Simulation and experimental results are presented to validate the proposed approach. A neural speed estimator embedded in a digital processor is also presented.

Analysis of 12-Pulse Rectifier Operation Under Balanced and Unbalanced Voltage Source with Input Impedance

This paper presents a study of modeling and simulation of a twelve-pulse circuit rectifier taking into consideration the effects of the voltage source impedance on the commutation angle for the system operating under a balanced and unbalanced three-phase supply. Three conduction modes are formed in this analysis. Based on the source inductances, the converter conduction modes will change including mode 3 overlap when the angle overlap μ extends beyond 60° and the number of conducting devices alternate between 3 & 4 devices in each state for both upper and lower bridges. These results are verified using a detail proposed analytical matlab model simulation. Also, the proposed analytical model results are compared to Simulink Powersys Toolbox model results and they are corresponded very well. The analytical method clearly shows the conduction states in all cases which could not identified using the simulink powersys toolbox model.

Analysis of a DC motor drive in the presence of unbalance

Abstract The increasing presence of harmonics in power system has caused a need for the development of analytical methods of studying harmonic current effects. This paper describes a new method for modeling a six-pulse DC motor drive. One of the main features is that this model is derived from the actual waveform, which can be more accurate than the traditional constant current source model. Computer simulation method is used to analyze the six-pulse DC motor drive system and to compute the steady state responses of the DC load current and the AC line currents. The currents can be presented as a convenient set of mathematical expressions. The harmonic contents of currents can be obtained using fast Fourier transforms (FFT). In this paper, the effect of unbalanced voltage source is also studied. In addition, a full understanding of the sensitivity of the harmonic currents to different operating conditions is introduced.

Reactive and harmonic current compensation for unbalanced three-phase systems using the synchronous detection method

This paper presents the application of the synchronous detection method for reactive and harmonic current compensation in an unbalanced three-phase power system. When the instantaneous power theory is applied, a balanced three-phase voltage source is required. However, in practical distribution systems, it is difficult to maintain balanced three-phase voltage along the feeder lines. To handle the reactive and harmonic current compensation in an unbalanced voltage source, the synchronous detection method is applied by per-phase calculation to obtain proper compensating components. Three different approaches using equal power, equal line current, and equal load resistance concepts in the synchronous detection method are discussed. Formulations and calculation algorithms are derived for each approach. By simulation, it is proved that the synchronous detection method is effective in unbalanced system compensation and gives a better performance than the instantaneous power theory. In this paper, preliminary results from simulations are obtained. Using the different approaches of the synchronous detection method, the line loss after compensation can also be minimized.

Improvement of power-factor and commutation conditions in single-phase series motors

The increasing presence of harmonics in power system has caused a need for the development of analytical methods of studying harmonic current effects. This paper describes a new method for modeling a six-pulse DC motor drive. One of the main features is that this model is derived from the actual waveform, which can be more accurate than the traditional constant current source model. Computer simulation method is used to analyze the six-pulse DC motor drive system and to compute the steady state responses of the DC load current and the AC line currents. The currents can be presented as a convenient set of mathematical expressions. The harmonic contents of currents can be obtained using fast Fourier transforms (FFT). In this paper, the effect of unbalanced voltage source is also studied. In addition, a full understanding of the sensitivity of the harmonic currents to different operating conditions is introduced.