Showing 4 results for Neutral
H. Radmanesh, M. Rostami,
Volume 7, Issue 4 (12-2011)
Abstract
this work studies the effect of neutral earth resistance on the controlling ferroresonance oscillation in the power transformer including MOV surge arrester. A simple case of ferroresonance circuit in a three phase transformer is used to show this phenomenon and the three-phase transformer core structures including nonlinear core losses are discussed. The effect of MOV surge arrester and neutral earth resistance on the onset of chaotic ferroresonance and controlling chaotic transient in a power transformer including nonlinear core losses has been studied. It is expected that these resistances generally cause into ferroresonance control. Simulation has been done on a power transformer rated 50 MVA, 635.1 kV with one open phase. The magnetization characteristic of the transformer is modelled by a single-value two-term polynomial with q=7, 11. The core losses are modelled by third order in terms of voltage. The simulation results reveal that connecting the MOV arrester and neutral resistance to the transformer, exhibits a great impact on ferroresonance over voltages.
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E. Babaei, T. Ahmadzadeh,
Volume 13, Issue 4 (12-2017)
Abstract
First of all, in this paper, the topology and operation of the three-phase three-level Z-source inverter based on neutral-point-clamped (Z-NPC) are studied. Moreover, different combinations of permissible switching states and control signals are explained for this inverter. In this paper, the topology of the three-phase three-level Z-NPC inverter is extended for an n-level state. Also, a combination of allowed switching states with relevant mathematical equations is presented for the proposed n-level Z-NPC inverter. In comparison with multilevel voltage-source inverters (only voltage-boost capability), the proposed multilevel Z-NPC inverter is a single-stage converter and it has a buck-boost capability of voltage. On the other hand, the control of two-stage converters compared to single-stage converters can be more difficult because of existing more active and passive components. In this paper, two new PWM control methods are also proposed for various multilevel Z-NPC inverters. One advantage of the proposed PWM control methods in comparison with conventional PWM control methods is maintaining the charge balance of the dc-link capacitors in neutral point. The correct performance of the proposed multilevel Z-NPC topology and PWM control methods are verified by the obtained results of analysis and simulations performed in the PSCAD software.
N. Bensaker, H. Kherfane, B. Bensaker,
Volume 16, Issue 2 (6-2020)
Abstract
In this study, delay-dependent robust stability problem is investigated for uncertain neutral systems with discrete and distributed delays. By constructing an augmented Lyapunov-Krasovskii functional involving triple integral terms and taking into account the relationships between the different delays, new less conservative stability and robust stability criteria are established first using the delay bi-decomposition approach then generalized with the delay N-decomposition technique. Some integral inequalities are employed to deal with the cross terms and few free weighing matrices are introduced to reduce the conservatism. The proposed criteria are expressed in terms of linear matrix inequalities. The effectiveness of the proposed stability conditions is illustrated by a numerical example.
S. M. Ahmed, K. S. Ahmed, Y. M. Shuaib,
Volume 19, Issue 1 (3-2023)
Abstract
This article discusses the operating principle and simulation of closed loop control of a three phase induction motor (IM) powered by five level diode clamped multilevel inverter (DCMLI) using direct torque control (DTC) technique. The main purpose of this article is to regulate the torque and speed of an IM and to decrease total harmonic distortion (THD). In this article, a five-level inverter's direct modulation approach with the dc link voltage self-balancing is presented. To reduce capacitor voltage variation, the redundancies of various switch topologies for the creation of intermediate voltages are also used. The use of LC filter results in lower output voltage and current distortion. A multicarrier PWM control technique is used for DCMLI to provide high quality sinusoidal output voltage with decreased harmonics. This can be obtained by employing Sinusoidal Pulse Width Modulation (SPWM) method for speed and torque control. This demonstrates that the recommended method of controlling the motor's speed and torque is effective. The simulation result reveals that DTC for the five-level inverter fed IM drive gives a rapid dynamic response, lower voltage and current THDs, and much less flux and torque distortion. The simulation is carried out in MATLAB Simulink (R2014).
