Mohd Hatta Jopri

Power quality signals detection using S-transform

Power quality has become very important issue over the last decade. Poor quality can cause equipment failure, data and economical. An automated monitoring system is needed to ensure signal quality, reduces diagnostic time and rectifies failures. In this paper, S-transform is used to analyze the power quality signals such as swell, sag, interruption, harmonic, interharmonic and transient based on IEEE Std. 1159-2009 to detect, localize and classify the disturbance. The S-transform is used to represent the signals in time-frequency representation (TFR).). To get an accurate TFR, the parameters are estimated to identify the signal characteristics. The signal characteristics are the root means square voltage (Vrms), total harmonic distortion (THD), total non harmonic distortion (TnHD) and total waveform distortion (TWD). To verify the performance of S-transform several sets of data with different time duration are analyzed to determine the accuracy of S-transform. The lowest value of mean absolute percentage error (MAPE) gives the highest accuracy to provide the best performance of TFD.

Current control of BLDC drives for EV application

This paper presents a current blocking strategy of brushless DC (BLDC) motor drive to prolong the capacity voltage of batteries per charge in electric vehicle applications. The BLDC motor employs a simple torque hysteresis control (THC) that can offer a robust control and quick torque dynamic performance. At first, a mathematical modeling of BLDC motor and principle of torque hysteresis control will be described, so that the benefit offered by the proposed current blocking strategy can be highlighted. It can be shown that the current control method naturally provides current limitation, in which the current error (or ripple) is restricted within the pre-defined band-gap furthermore provide current protection. The benefit of proposed current blocking strategy will be highlighted such that it can prevent the current drained from the batteries when the torque demand is released to set to 0 Nm. The control scheme is validated and verified by the simulation and experimental results.

A new vector draft method for harmonic source detection at point of common coupling

In modern power networks, the issue of power quality (PQ) is becoming very important because of the increasing of load which sensitive to current disturbances. This is mainly due to the increasing use of non-linear power electronic devices draws non-sinusoidal current and creating a current distortion. As a result there is increasing need for PQ to be monitored to establish the type, sources and locations of PQ disturbances, allowing remedial measures to be taken. Consequently, harmonic is one of the most concerned power quality disturbances. The detection of harmonic source is necessary for power quality strategy development. This paper introduces a new single-point measurement method to estimate the harmonic source by using phase spectrogram (PS) and frequency spectrogram (FS) based on a vector draft method. A measurement at the point of common coupling (PCC) with harmonic distortion is done by simulation via PSCAD. Then PSCADs data are analyzed by using spectrogram in MATLAB. To be precise, voltage and current waveforms are normalized with fundamental magnitude respectively. Next, the normalized voltage and current are plotted on the vector draft to estimate the perpendicular point between the vectors. The center point of the normalized voltage is the boundary between downstream and upstream. The harmonic source can be detected base on the perpendicular points location that fall on the particular region. The comparison between actual and power direction result have been conducted. Finally, the proposed method is similar with the actual result and more truthful than power direction method.

Improved performance of DTC of five-phase induction machines

The paper describes about optimal voltage vector selection for high-performance of Direct Torque Control (DTC) of five-phase induction machine. The decoupled control of stator flux and electromagnetic torque based on hysteresis controllers as employed in conventional DTC is applied to retain the simplicity and to provide quick instantaneous control. A look-up table that selects the most optimal voltage vectors according to the speed operations, i.e. low-speed, middle-speed and high-speed is proposed to improve DTC performances such as excellent torque dynamic control, minimization of torque ripple, high-efficiency (due to lower switching frequency) and extension of constant torque region. All the improvements are validated through simulation results.

Minimization of torque ripple utilizing by 3-L CHMI in DTC

A topology of multilevel inverter was to analysised and performed by using the 3-Level Cascaded-H Brigde-Multilevel Inverter (3L-CHMI) in DTC conventional hysteresis-based controller. This topology is similar with the conventional inverter, but it has more strategy for switching states. In this work, hysteresis comparator were used for flux and torque, with 12 sectors stator flux angle and will provide more selection of voltage vector. The basic concept of DTC system for torque and flux control consists of estimator of flux and torque and voltage vector. In conventional DTC, it has a several major issues which are largest torque ripple and unconstant switching frequency at low speed condition operation. So, the main purpose of this research is focusing more on how to reduce the output torque ripple at low speed operation condition. A simulation program had been developed to validate the results by using Matlab/Simulink.

Comparison performance of 3-Level and 5-Level Cascaded H-Bridge multilevel inverter of DTC of Induction Machine

Development of electrical vehicle (EV) and hybrid electrical vehicle (HEV) gives many opportunities and challenges in power electronic drive, especially in the development of traction motor drive that requires advanced power electronic inverter. Multilevel inverter was first proposed by Nabae in early 1980. The general structure of the multilevel inverter is to synthesis a sinusoidal voltage out of several levels of dc voltages. This paper shows comparison between the 3-Level Cascaded H-Bridge Multilevel Inverter and 5 -Level Cascaded H-Bridge Multilevel Inverter. It is found that by using 5-level Cascaded H-Bridge Multilevel Inverter (CHMI) can reduce torque and flux ripples compare to 3-Level CHMI and hence can improve DTC performances.

Short-circuit switches fault analysis of voltage source inverter using spectrogram

The identification of faults in voltage source inverter is highly required to ensure the reliability of the inverter. Early detection of the faults can greatly assist in maintenance of the system by avoiding possibly harmful damage borne out. This paper presents the analysis of short-circuit switches fault of voltage source inverter (VSI) using time frequency distribution (TFD). The TFD which is spectrogram represents current signal of the VSI in time-frequency representation (TFR) that provides temporal and spectral information of the signal. From the TFR, parameters of the signal are estimated such as average current, root mean square (RMS), total harmonic distortion (THD), total waveform distortion (TWD) and total non-harmonic distortion (TnHD). The results shows that the analysis using spectrogram gives information of the current signal of the VSI to identify short-circuit switches and can be implemented for faults detection system.

Optimal torque control performance of DTC of 5-phase induction machine

In this paper, optimal voltage vector selection for high-performance of Direct Torque Control (DTC) of five-phase induction machine is presented. The de-coupled control of stator flux and electromagnetic torque based on hysteresis controllers as employed in conventional DTC is applied to retain the simplicity and to provide quick instantaneous control. A single complete look-up table that selects the most optimal voltage vectors according to the motor operating condition is proposed. This improves DTC performances such as excellent torque dynamic control, minimization of torque ripple, high-efficiency (due to lower switching frequency) and extension of constant torque region. All the improvements are validated through simulation results.

Performance Evaluation of Real Power Quality Disturbances Analysis using S-transform

Power quality is main issue because of the impact to electricity suppliers, equipments, manufacturers and user.To solve the power quality problem, an analysis of power quality disturbances is required to identify and rectify any failures on power system. Most of researchers apply fourier transform in power quality analysis, however the ability of fourier transform is limited to spectral information extraction that can be applied on stationary disturbances. Thus, time-frequency analysis is introduced for analyzing the power quality distubances because of the limitation of fourier transform. This paper presents the analysis of real power quality disturbances using S-transform. This time-frequency distribution (TFD) is presented to analyze power quality disturbances in time-frequency representation (TFR). From the TFR, parameters of the disturbances such as instantaneous of root mean square (RMS), fundamental RMS, total harmonic distortion (THD), total nonharmonic distortion (TnHD) and total waveform distortion (TWD) of the disturbances are estimated. The experimental of three phase voltage inverter and starting motor are conducted in laboratory to record the real power quality disturbances. The disturbances are recorded via data logger system which is mplemented using LabVIEW while the analysis is done using Matlab in offline condition. The results show that S-transform gives good performance in identifying, detecting and analyzing the real power quality disturbances, effectively.

Power Quality Signals Classification System Using Time-Frequency Distribution

Power quality signals are an important issue to electricity consumers. The signals will affect manufacturing process, malfunction of equipment and economic losses. Thus, an automated monitoring system is required to identify and classify the signals for diagnosis purposes. This paper presents the development of power quality signals classification system using time-frequency analysis technique which is spectrogram. From the time-frequency representation (TFR), parameters of the signal are estimated to identify the characteristics of the signals. The signal parameters are instantaneous of RMS voltage, RMS fundamental voltage, total waveform distortion, total harmonic distortion and total non harmonic distortion. In this paper, major power quality signals are focused based on IEEE Std. 1159-2009 such as swell, sag, interruption, harmonic, interharmonic, and transient. An automated signal classification system using spectrogram is developed to identify, classify as well as provide the information of the signal.