On The Relationships Among Different Voltage Unbalance Definitions

Growing penetrations of distributed energy resources (DERs) increase the power injection variability in distribution systems, which can result in power quality issues such as voltage unbalance. To measure unbalance, organizations such as IEC, NEMA and IEEE define phase unbalance in their power quality standards. However, the definitions in these different standards are not consistent, and voltages that are considered acceptable by one standard may violate good practices defined by another standard. To address this issue, this paper provides analytical comparisons of the most common voltage unbalance definitions, which are supplemented with numerical simulations. The analytical relationships suggest that it is possible to approximately bound the symmetrical-component-based voltage unbalance factor (which depends on the magnitude and relative phase angle) by limiting the line-to-line voltage unbalance, whereas applying line-to-ground voltage unbalance definitions neglects all information about phase angle offsets.

Analysis of Synoptic Disturbance in Maritim Continent Using Spherical Harmonics Transformation Method

This study aims to modify the idea of ​​WK99-analyzing the existence of signature in wave-number and frequency spectrum when the analyzed Outgoing Longwave Radiation (OLR) data is associated with a unique phenomenon in Maritime Continent (MC), Borneo vortex (BV). Although BV is often related to easterly equatorial wave disturbances, there was no specific study to examine its behavior in the spectral domain. The purpose of this study is to develop a method to diagnose certain signatures of BV through spectrum analysis of OLR data when BV occurs. In contrast to previous studies, to present the unique phenomenon in MC as a target for diagnostics, spectrum analysis is performed by Spherical Harmonics (SH). The results of the OLR data spectrum comparison when BV occurs with the OLR data spectrum when BV does not occur that in the anti-symmetrical component when BV occurs, the tropical depression-mixed Rossby gravity (TD-MRG) wave spectrum is stronger, especially in zonal wave-numbers 5 to 10 and frequencies 0.12 to 0.2. Similar to the anti-symmetrical component, the TD-MRG spectrum of the symmetrical component is also stronger at zonal wave-numbers 5 to 10 and frequencies 0.12 to 0.2. Moreover, the westward-propagating inertio-gravity (WIG) wave spectrum in the symmetrical component is also stronger at the time of BV than when there is no BV, especially at zonal wave-numbers 7 to 13 and frequencies 0.38 to 0.5. It can be concluded that when BV occurs, equatorial waves that propagate to the west, especially the types of TD-MRG and WIG waves are stronger than when BV did not occur. The results of durational grouped spectrum analysis of OLR data when BV occurs indicate that the longer the duration of BV occurs, the stronger the spectrum of TD-MRG and WIG wave types gets.

Optimization of Voltage Unbalance Compensation by Smart Inverter

This paper presents a compensation method for unbalanced voltage through active and reactive power control by utilizing a smart inverter that improves the voltage unbalance index and detects an unbalanced state of voltage magnitude and phase, and thus enhances power quality by minimizing the voltage imbalance. First of all, this paper presents an analysis of a mathematical approach, which demonstrates that the conventional voltage unbalanced factor (VUF) using the symmetrical component cannot correctly detect the imbalanced state from index equations; and by only minimizing the VUF value, it cannot establish a balanced condition for an unbalanced state of the voltage profile. This paper further discusses that intermittent photovoltaic (PV) output power and diversified load demand lead to an unexpected voltage imbalance. Therefore, considering the complexity of unbalanced voltage conditions, a specific load and an PV profile were extracted from big data and applied to the distribution system model. The effectiveness of the proposed scheme was verified by comparing VUF indices and controlling the active and reactive power of a smart inverter through a numerical simulation.

Instantaneous Symmetrical Component Theory (ISCT) Controller for Mitigation of Harmonics in Micro-grid System

Now a days, the usage of non-linear loads are increased rapidly which increased the power quality (PQ) problems in electric power system like voltage sag and swell, harmonics, etc., in the mentioned problems, one of the major significant PQ problem is the harmonics. This paper proposes the power quality improvement by using Shunt Active Power Filter (SAPF) in AC Electric supply System feeding 3-phase balanced non-linear load. For reduction of harmonics in the system, the Instantaneous Symmetrical Component Theory (ISCT) based controller along with the other controllers named PI controller and Hysteresis current controller are which helps in the micro-grid system. In this, hysteresis current control compares the difference of compensating current, load current with filter current of DSTATCOM. In the proposed method, DSTATCOM has shown good performance in the system to eliminate harmonic component. The system performance is simulated in the MATLAB environment and it is evaluated by calculating the source current Total Harmonic Distortion(THD).

Power Quality Improvement using D-STATCOM with Instantaneous Symmetrical Component Theory

A technique is introduced to improve the voltage sag under sudden changes in load. The proposed technique is implemented by D-STATCOM (Distribution static compensator) and it is controlled by ISCT (Instantaneous Symmetrical Component Theory). Due to sudden changes in load, the voltage dip occurs at the time of switching of loads. At this time, the control technique generates reference currents and hysteresis block compares these currents with the reference currents and generates the pulses to D-STATCOM. Implementation of system along with compensation is carried out in MATLAB/SIMULINK