Positive Sequence Voltage Components Research Articles

The significance of the mode of voltage imbalance on the operation and energy losses of a 3-phase induction motor

Induction motors are key to the operation of industries due to their ruggedness, but their performance is often impaired by power supply quality issues. This has triggered research on how voltage imbalance affects the operation and performance of such motors. This study considers the effect of the manner of variation of the positive sequence voltage component on the output power, losses and sensitivity of induction motor parameters. It applies three scenarios of positive sequence variation with respect to the negative sequence component. The results show that the performance of the motor, i.e., motor losses, output power, and the sensitivity of the motor’s torque, power, and efficiency to sequence currents is dependent on the level of imbalance, and also, on the nature of the positive sequence voltage variation. Hence, the same level of voltage imbalance can trigger different operational scenarios and losses depending on how the imbalance occurs.

Performance analysis of a multilevel inverter based shunt active filter with RT‐EMD control technique under ideal and non‐ideal supply voltage conditions

In this study, a real-time empirical mode decomposition (RT-EMD) based control technique is adopted for effective mitigation of system harmonics under ideal and non-ideal supply voltage conditions. The proposed control algorithm takes the active component of load current samples and the positive sequence voltage component for generating the desired reference. The fundamental component of load current is found by employing RT-EMD, which decomposes the distorted non-linear sample into a finite number of fine-scale signals termed as intrinsic mode function (IMF). Each IMF is extracted adopting continuous calculation of upper and lower envelopes using a series pipeline structure which decreases the computational complexity. The proposed control algorithm takes the positive sequence voltage component for generating the desired reference so that the system can operate in non-sinusoidal grid voltage conditions. The proposed control algorithm adopts carrier-based modulation scheme for switching of the inverter module. The effectiveness of the proposed control approach is investigated in MATLAB-Simulink environment with balanced and unbalanced loading condition and its experimental validation is carried out by a hardware prototype model using a Spartan 6 FPGA controller.

PMU Assisted Integrated Impedance Angle-Based Microgrid Protection Scheme

Development of protection scheme for microgrid is a challenging issue due to the inclusion of distributed generations (DGs). The research work for developing the primary protection scheme for microgrid is progressing continuously. This paper proposes an integrated impedance angle (IIA) based protection scheme using wide-area positive sequence components of voltages and currents. The proposed scheme uses data retrieved from the phasor measurement units (PMUs) of IEEE C37.118.1 complied standards. Furthermore, the IIA for the line is computed considering both ends PMU information, which is the key indicator for identifying the faults in the microgrid. The proposed protection scheme is extensively tested considering the different operating conditions of microgrid, variation in DG penetration and variation in fault parameters such as fault resistance, fault types, and fault location. Furthermore, cross validation on no-fault situations including section cutoff, disconnection of high penetration DG, grid-islanding resynchronization, motor starting, capacitor switching, and load encroachment are carried out. The proposed scheme is also tested for the insensitivity towards the external faults. The test results on both 15-bus and 34-bus systems clearly indicate that the proposed IIA-based wide-area scheme can be a potential protection measure for microgrid under varied operating circumstances.

Effects of sequence voltage components on torque and efficiency of a three-phase induction motor

For quantifying voltage unbalance, some standards adopt the index provided by the ratio between the negative and positive sequence component magnitudes. In these documents, the use of an indicator that includes the zero sequence component is not obligatory. This article presents the results from evaluations of the effects of the zero, negative and positive sequence voltage components on the torque and efficiency of a three-phase induction motor. These evaluations are performed through laboratory experiments and the application of incremental sensitivity analysis. The results of this investigation allow for, among other things, identifying the consequences of the absence of the zero sequence component in unbalance quantification.

Design of DSTATCOM Controller for Compensating Unbalances

In a three phase power system, the voltages at the generation side are in sinusoidal and equal in magnitude with 120? phase difference between the phases. However, at the load side voltages may become unbalanced due to unequal voltage magnitudes at the fundamental frequency, phase angle deviations or unequal distribution of single phase loads. The voltage unbalance is a major power quality issue, because a small unbalance in the phase voltages can cause a larger unbalance in the phase currents. A completely balanced three-phase three wire system contains only positive sequence components of voltage, current and impedance, whereas unbalanced system contains both positive and negative sequence components of voltages and currents. The negative sequence component of current in the unbalanced system increases the temperature and losses in the equipments. Hence, it is necessary to mitigate this problem by supplying the negative sequence current to the load at the load side and keep the source side balanced. This paper proposes the shunt connected, current injecting Distribution Static Synchronous Compensator (DSTATCOM) with appropriate controller to mitigate the unbalanced load current. The symmetrical components based Hysteresis Current Controller (HCC) is designed for DSTATCOM to diminish the unbalances in a three-phase three-wire system. The performance of the controller is studied by simulating the entire system in the MATLAB/Simulink environment. The DSTATCOM with HCC is found to be better than other controllers because it is suitable for compensating both balanced and unbalanced loads.

Modified symmetrical component method for characterization of unbalanced voltage sags

This paper suggests a modification in symmetrical component (SC) method, used for characterization and classification of voltage sags, by incorporating an angle, ɸ, in it. The ɸ is considered as an angle between drop in positive-sequence voltage components, associated with single line-to-ground and line-to-line faults. The modified formula is tested on two data sets of real power systems and compared with the SC method. The results suggest that this modification offers advantages of giving accurate comprehensive information on the nature of (i) voltage sag, (ii) associated fault, and (iii) faulted buses, simultaneously. This study aims to establish a precise characterization method for voltage sags due to faults in low-voltage resistance-grounded distribution systems (LVRGDS), as their more frequent occurrence and vulnerability of economic impacts to industrial customers than the shallow voltage sags due to faults in high-voltage solidly grounded transmission systems (HVSGTS). For this, the variations in φ, for different fault locations in LVRGDS and HVSGTS, are evaluated, resulting in large values of φ in LVRGDS. These larger values of φ establish better characterization capability, for voltage sags in distribution systems, with the proposed method than the SC method. Also, the capability of φ to identify the behavior of un-faulted phase voltages has been revealed. Copyright © 2015 John Wiley & Sons, Ltd.

Strategies for the Connection of Distributed Power Generation Units to Distorted Networks

Connection of distributed power generators (DPGs) to a utility grid requires the synchronization between the DPG and the grid voltages with the goal of controlling the power flow and limiting the currents at instant that the switch or breaker closes. Synchronization methods typically match the positive sequence voltage component of the two systems being connected, the connection being realized when the error is smaller than a preset threshold. While synchronization using the positive sequence voltage provides adequate results in the case of undistorted grid voltages, it can be inadequate if the grid is polluted, e.g., in case of weak grids. Instantaneous voltage mismatches between the DPG and the grid, e.g., due to the harmonic content or unbalances in the grid and/or DPG voltages $\ldots$ , at the instant that the breaker closes, can cause overcurrents and result in unwanted protection tripping or equipment damage, even if the corresponding positive sequence voltages perfectly match. This paper analyzes the synchronization and connection of DPGs to highly distorted grids with the goal of limiting the overcurrent due to voltage mismatch. Once the connection is realized, a transition to the conventional positive sequence voltage based synchronization occurs, as this is adequate to control the power flow in steady state.

Precise Assessment of Performance of Induction Motor under Supply Imbalance Through Impedance Unbalance Factor

This paper presents precise assessment of steady-state performance of induction motor (IM) operating under voltage unbalance. The variation of two voltage unbalance factors viz. complex voltage unbalance factor (CVUF) and impedance unbalance factor (IUF) with positive sequence voltage component, reveals that degree and manner of unbalance in supply voltage is exactly reflected in CVUF and IUF, respectively. On this basis, it is shown that for the precise assessment of IM performance, knowledge of both, manner (IUF) and degree (CVUF) of unbalance is important. Further, effect of angle of unbalance, on the performance of the IM and voltage pattern is analyzed. Results depict high sensitivity of derating factor and peak copper losses to this angle. Thus, it should be included along with unbalance factors for the precise and complete performance assessment of IM.

A New Phase Detection Method by Using Kalman Filter

This paper proposes a phase detection method for harmonics and unbalanced voltage conditions. The proposed method uses harmonics and unbalanced voltage compensation circuit in addition to basic PLL (Phase Locked Loop) circuit. In the harmonic compensation circuit, the harmonic voltage component are eliminated from the input voltages using specific harmonic detection method. Besides, frequency information of power system used in the specific harmonic detection method is estimated by an extended complex Kalman filter. In the unbalanced voltage compensation circuit, the input voltage is normalized after the calculated positive sequence component. By means of the proposed method, excellent phase detection performance can be achieved under harmonics and unbalanced voltage conditions. Moreover, detection of positive sequence voltage component becomes possible under voltage drop conditions due to faults in power systems. The effectiveness of the proposed method is verified by simulation results.

Analysis of Three-phase Induction Motor Performance under Different Voltage Unbalance Conditions Using Simulation and Experimental Results

The performance of a three-phase squirrel cage induction motor fed by an unbalanced voltage supply has been investigated in this article. Matlab/Simulink software is used for simulation of the motor using simple (conventional) and exact models under different unbalanced voltage conditions. Simulation results are verified by performing experimental tests on a 1.5-kW standard three-phase induction motor. With the aid of simulation and experimental results, variations of stator current, motor efficiency, power factor, and rotor ripple have been investigated under various steady-state unbalanced voltage conditions. It is shown that, in addition to the voltage unbalance factor, the magnitude of positive and negative sequence components of the unbalanced supply voltage have an important role on motor performance. For instance, motor power factor decreases with the increase of positive sequence voltage component, even if the voltage unbalance factor is constant. Also, the motor efficiency decreases with the increase of the voltage unbalance factor, even if the positive sequence component of the supplied voltage is constant. It is shown that the stator current unbalance factor and motor losses will increase (decreasing efficiency) with the increase of the voltage unbalance factor under constant load conditions. Moreover, the voltage unbalance factor has a negative impact on the electromagnetic torque peak due to the decrease in the positive sequence voltage component. Using different voltage unbalance factors, the motor derating factor is also calculated, where four different limits are considered. The results imply conservative limits set by standards for motor operation under unbalanced voltage conditions. A comparison between the experimental and exact model simulation results confirmed a maximum discrepancy of 4% between the results, indicating the validity of the employed exact model for motor analysis in unbalanced voltage conditions.