Mohd. Hafiz Habibuddin

A comprehensive overview of different protection schemes in micro-grids

Abstract In recent years, there has been an increasing interest in applying micro-grid systems not only to improve reliability but also to enhance power quality. One of the major challenges associated with the implementation of micro-grids is to design an appropriate protection scheme which has the ability to protect micro-grids in both grid-connected and islanded mode. In order to overcome this challenge, different approaches have recently appeared in the literatures. This paper aims to provide an introspective review of the available protection schemes used for addressing micro-grid protection issues in both grid-connected and islanded mode. In addition to description of existing protection schemes to date and categorizing them into specific clusters, a comparative analysis is done in which the merits and demerits of each methodology are evaluated.

An improved synchronous reference frame current control strategy for a photovoltaic grid-connected inverter under unbalanced and nonlinear load conditions

In recent years, renewable energy sources have been considered the most encouraging resources for grid and off-grid power generation. This paper presents an improved current control strategy for a three-phase photovoltaic grid-connected inverter (GCI) under unbalanced and nonlinear load conditions. It is challenging to suppress the harmonic content in the output current below a pre-set value in the GCI. It is also difficult to compensate for unbalanced loads even when the grid is under disruption due to total harmonic distortion (THD) and unbalanced loads. The primary advantage and objective of this method is to effectively compensate for the harmonic current content of the grid current and microgrid without the use of any compensation devices, such as active and passive filters. This method leads to a very low THD in both the GCI currents and the current exchanged with the grid. The control approach is designed to control the active and reactive power and harmonic current compensation, and it also corrects the system unbalance. The proposed control method features the synchronous reference frame (SRF) method. Simulation results are presented to demonstrate the effective performance of the proposed method.

Fault location and classification of combined transmission system: Economical and accurate statistic programming framework

An effective statistical feature extraction approach of data sampling of fault in the combined transmission system is presented in this paper. The proposed algorithm leads to high accuracy at minimum cost to predict fault location and fault type classification. This algorithm requires impedance measurement data from one end of the transmission line. Modal decomposition is used to extract positive sequence impedance. Then, the fault signal is decomposed by using discrete wavelet transform. Statistical sampling is used to extract appropriate fault features as benchmark of decomposed signal to train classifier. Support Vector Machine (SVM) is used to illustrate the performance of statistical sampling performance. The overall time of sampling is not exceeding 1¼ cycles, taking into account the interval time. The proposed method takes two steps of sampling. The first step takes ¾ cycle of during-fault and the second step takes ¼ cycle of post fault impedance. The interval time between the two steps is assumed to be ¼ cycle. Extensive studies using MATLAB software show accurate fault location estimation and fault type classification of the proposed method. The classifier result is presented and compared with well-established travelling wave methods and the performance of the algorithms are analyzed and discussed.

An advanced current control compensation scheme to improve the microgrid power quality without using dedicated compensation devices

For grid-connected inverters (GCI), switching harmonics can be effectively attenuated through some methods. This paper present an advanced current control method for GCI of distributed generators (DGs), which responsible for the DG to controlling the power injection to the grid and the cancellation of the harmonics in Microgrid (MG) and between MG and Power Common Coupling (PCC). The current harmonics in the grid and MG are compensated without using dedicated compensation devices, such as active power filters (APFs), by the proposed current controller which is contain an advanced synchronous reference frame (ASRF) controllers. The merged control methods are proposed for the interface inverter to perform the comprehensive activity of compensating for the harmonics, such as a correction of the system imbalance and the removal of the harmonics. The simulation results are presented to demonstrate the effective performance of the proposed method.

Performance of PI Controller Based Dynamic Voltage Restorer for Power Quality Improvement

Voltage sag and harmonics are the most frequent power quality problems faced by industrial and commercial customers today. Situation has been aggravated by modern sensitive industrial equipments which introduce system harmonics due to their inherent V-I characteristics. In this paper, proportional integral (PI) control technique based dynamic voltage restorer (DVR) is implemented in power distribution system to suppress voltage sag and harmonics under linear, non-linear and induction motor load conditions. Real-time power distribution system and DVR test models are built in Matlab/Simulink software. Simulation results exhibit excellent PI control approach with effective performance yielding excellent voltage regulation.

Control of compensation devices by synchronous reference frame and fourier control methods to improve the power quality in a microgrid

The present study used passive filters (PF) and designed Active Power Filters (APFs) with two control methods: synchronous reference frame control and Fourier methods. Studies in the domain of microgrids include distributed generation sources and non-linear loads. Distributed Generation Sources (DGs) include Micro-Turbine (MT) and Fuel Cell (FC), which act as a source of harmonic currents with non-linear loads. To achieve this goal, passive filters are applied to cancel the main harmonics and to provide reactive power, whereas SAPFs are applied to adjust system imbalances and remove the remaining harmonics in the system. The results show that the method can reduce the harmonic disturbances of the system from 24.27% to less than 5%. In addition, this study analyzes how the various control methods operate on active filters. The proposed method has been validated experimentally, and the results are in agreement with the simulation results.

A control scheme to improve the power quality with the absence of dedicated compensation devices in microgrid

In this paper, a new method is proposed to control the interface Inverter of distributed generators (DGs) in a microgrid. The objective of this method is to effectively compensate for the harmonic currents at the Point of Common Coupling (PCC) and the MG with the Absence of dedicated compensation devices, such as Active Power Filters (APFs). The proposed control method is composed of the Adjustable Synchronous Reference Frame (ASRF) and the Synchronous Reference Frame (SRF) methods. The ASRF and SRF are proposed to control the power injection and harmonic current compensation, respectively. The merged control methods are proposed for the interface inverter to perform the comprehensive activity of compensating for the harmonics, such as a correction of the system imbalance and the removal of the harmonics. The operation principle of the proposed control method is analyzed in detail, and its effectiveness is validated through simulation results.

Improved control of shunt active power filter using harmony search algorithm

This paper proposes to optimize the control parameters of DC-link voltage shunt active power filter (SAPF) by Harmony Search Algorithm (HSA) and Total Harmonic Distortion (THD) reduction in the system. The aim is motivated by the need to minimize the burden on the DC-link capacitor voltage to enhance performance of a shunt active power filter. In particular the attention has been focused on the Hybrid Compensation (HC), including an active filter and Passive Filter (PF) distributed in Micro-Grid (MG) system. Each passive filter has been designed to eliminate main harmonics; connected to nonlinear load and Dispersed Generation Sources (DGSs) and gain reactive power while it is the duty of active filter with instantaneous power theory (pq), to correct unbalanced system as well as eliminate harmonic left. Simulation results are presented to validate the proposed scheme.