Muhamad Mansor

Voltage sag detection - A survey

Voltage sag has been the focus of considerable research in recent years. It can cause expensive downtime. Research on voltage sag detection has also grown up and it is an essential part of the voltage sag compensator. There are many methods have been introduced to measure and detect voltage sags. Among these are RMS Value Evaluation, Peak Value Evaluation, Missing Voltage technique and Hysteresis Voltage Control technique. In this paper, a study is carried out to observe the different techniques of voltage sag detection. Since, precise and fast voltage detection is an essential behavior for a voltage sag compensator, therefore, observation on detection time of each detection methods will also be carried out.

Classification of PD patterns in XLPE cables under various soil conditions using statistical technique

Partial discharge (PD) is identified as a main factor contributing to the insulation deterioration in HV equipment including underground cable. This is the first time an attempt has been made to investigate the effect of soil thermal resistivity on PD activities in underground power cables. In this paper, a detailed experiment has been carried out on a simulated set up to study the effect of various soil conditions on the level of PD in an 11 kV, single core, 240 mm /sup 2/ XLPE cable. The PD parameters are measured with the help of Haefely Trench TE 571, PD measurement system using straight detection method. PD patterns obtained in the form of elliptical waveform are then analysed using statistical techniques. In this paper, the statistical pattern recognition technique has been successfully applied to classify the PD patterns obtained from the experiment under different soil conditions. Thus, classification of PD patterns aims at the recognition of discharges from a particular soil condition. This information is vital for estimating the harmful effect of the thermal property of soil on the level of PD and can lead to decision making like reconditioning of backfill material and adjustment in cable loading.

Assessment of wind and solar energy potentials in Malaysia

Renewable energy sources This paper presents a comparison between five different cities in term of wind and solar energy potentials. It first describes the Weibull distribution functions and then analyzes the data collected from the Malaysian Meteorological Department. It then shows the average wind speed and the operation probability of a wind turbine with a cut in speed of 2.5m/s over the five chosen cities. Power density at the wind turbines hub height is calculated with the annual operating hours of the turbine. Second, this paper compares the power output of a certain PV module in these five different cities. The implication of this study is that it gives an overall review on the wind and solar energy potentials in Malaysia and its results are significant for feasibility and optimization studies. The data obtained from the Malaysian Meteorological Department are on a daily basis from 2011 to 2012.

Voltage balancing in DC link capacitor for seven level cascaded multilevel inverter

Multilevel inverters enables implementation of high-power-medium-voltage applications using smaller rated devices resulting to cheaper and compact design. Currently, researchers are interested in developing distributed generation (DG) with multilevel topology that produces not just active power demands, but also incorporated with custom power capabilities for power quality improvement. However, multilevel inverters are susceptive to voltage unbalance at the DC link capacitor which affects the output voltages. For this reason, a voltage balancing method is presented for a seven level cascaded multilevel inverter using phase-shifted carrier PWM (PSCPWM). This method is base on modifying the switching state without any external circuit.

Three-Phase PWM-Switched Autotransformer Voltage-Sag Compensator Based on Phase Angle Analysis

Many voltage sag compensators have been introduced, including the traditional dynamic voltage restorer (DVR), which requires an energy storage device but is inadequate for compensating deep and long-duration voltage sags. The AC-AC sag compensators introduced next do not require a storage device and they are capable of compensating voltage sags. This type of compensator needs an AC-AC converter to regulate the output voltage. Presented in this paper is a three-phase PWM-switched autotransformer voltage sag compensator based on an AC-AC converter that uses a proposed detection technique and PWM voltage control as a controller. Its effectiveness and capability in instantly detecting and compensating voltage sags were verified via MATLAB/Simulink simulations and further investigated through a laboratory prototype developed with a TMS320F2812 DSP as the main controller.

New voltage sag detection based on phase angle analysis for the new topology of voltage sag compensator

This paper implements two main works. First, a new voltage-sag detection technique based on phase-angle analysis is proposed. It is simple to implement and able to detect and compensate sag the moment it occurs. Second, a new topology of voltage sag compensator is introduced. The proposed topology is able to reduce stress effect due to current flows into the switches and avoid non-stop operation during sag events. This proposed work had been verified and investigated by developing a laboratory prototype where a TMS320F2812 DSP is used as the main controller.

Digital current sensing in modular multilevel converter for HVDC applications

For long-distance transmission, HVDC (High-Voltage, Direct-Current) is proven to be less expensive and have lower electrical losses as compared to HVAC (High-Voltage, Alternating-Current). Now a days, the advancement of power electronic switches such as IGBT’s and MOSFET enables the use of converters for HVDC applications. Among the well-known converters used for HVDC are Voltage Source Converter (VSC) Line Commutated Converter (LCC) and Modular Multilevel Converter (MMC). The MMC is still new and a promising technology for HVDC application. The MMC has many advantages such as controlling high amount of active/reactive power and possess lower losses as compared to other converters. To control the active/reactive power in a MMC, control scheme such as free-running hysteresis uses the reference voltage and the inductor current to produce the required switching pulses. This study proposed a technique in which a voltage sensor is use to measure the inductor current. Conventionally, the inductor current is sensed either with a resistor or Current Transformer (CT). This method is associated with some disadvantages; requires additional circuitry which introduces some power loss and requires higher bandwidth in order to sense accurately. This study instead, measures the current indirectly by using the information of the phase inductor voltage. As the voltage sensor is placed in parallel to the inductor, this measuring technique is immune to I2R loss. The proposed technique will be investigated using MATLAB simulation to determine its current sensing capability in a MMC for HVDC applications. To design an improved current-less sensing method using a digital RC network. To extract the inductor current values from the phase inductor voltage an RC filter is required and placed in parallel across the inductor. In this way, all the high frequency harmonics will be filtered out and only the low frequency inductor current can be seen across the capacitor. The selection of RC values, however is dependent on the inductor value and inductor DC-Resistance (RDCR ). The main concern with this technique is that selection of DCR RC values sometimes can be unavailable for hardware implementation. To further improve the implementation of RC network and eliminate the problems of selecting suitable RC values for hardware implementation. This paper proposed the used of digital filter based on the RC network concept. Instead of using the actual components for filtering the high frequency harmonics, this technique uses only the DSP for filtering to remove the high frequency harmonics. The proposed technique is able to convert the high frequency voltage VL1 measured from the phase inductor L1 into the phase inductor current iL1without any delay or difficulty. By 1 L1 comparing the signals of proposed method to the series sensing method and the conventional RC filter method the waveforms of both signals are almost identical. However, the proposed method eliminates the need for RC components as compared to the conventional RC filter method. This technique improves the efficiency of the system in terms of improve signal noise ratio and eliminates the need for passive component on the system.

Fast charger for Li-ion batteries based on battery temperature

A fuzzy controlled fast charger for Lithium Ion (Li-ion) batteries based on battery temperature is investigated and simulated by using MATLAB/Simulink. The main objective of this study is to control temperature rise during fast charging. A fuzzy control system is applied to a DC-DC converter that functions as a battery charger. During the charging process, battery temperature and battery state-of-charge (SOC) were used as controller input variables and charging current as output variable. The battery is charged at 3C charging rate from 0% to 80% SOC. The simulation result is compared with the Constant-Current Constant-Voltage (CC-CV) charging algorithm and analysed. According to the simulation result, the proposed charger is capable of charging li-ion battery with reduced rate of temperature rise.

Current control loop of 3-phase grid-connected inverter

This paper presents a comparative study of current control loop in 3-phase inverter which is used to control the active and reactive output power. Generally, current control loop, power control loop and phase lock-loop are the conventional parameters that can be found in an inverter system controlled by the conventional linear control type, for instance proportional (P), integral (I) and derivative (D). If the grid remains stable throughout the day, PID control can be use. However variation of magnitude, frequency, voltage dips, transient, and other related power quality issues occur in a 3-phase grid often affects the control loop. This paper aims to provide an overall review on the available current control techniques used in grid connected system.

Efficiency improvement of the maximum power point tracking for PV systems using support vector machine technique

The aim of this paper is to improve efficiency of maximum power point tracking (MPPT) for PV systems. The Support Vector Machine (SVM) was proposed to achieve the MPPT controller. The theoretical, the perturbation and observation (P&O), and incremental conductance (IC) algorithms were used to compare with proposed SVM algorithm. MATLAB models for PV module, theoretical, SVM, P&O, and IC algorithms are implemented. The improved MPPT uses the SVM method to predict the optimum voltage of the PV system in order to extract the maximum power point (MPP). The SVM technique used two inputs which are solar radiation and ambient temperature of the modeled PV module. The results show that the proposed SVM technique has less Root Mean Square Error (RMSE) and higher efficiency than P&O and IC methods.