Wednesday, 16 April 2014

High-Efficiency Single-Phase Transformerless PV H6 Inverter With Hybrid Modulation Method


The main contribution of this paper is the derivation rules summarized from existing high-performance inverters with H6-type configuration, which makes novel topologies possible. In addition, a novel high-efficiency single-phase transformerless photovoltaic inverter with hybrid modulation method is also proposed and evaluated as an example. Without input split capacitors, common-mode voltage and leakage current issues in a nonisolated system with H6-type configuration are eliminated, and the feature of a three-level output voltage in the inverter bridge’s middle point helps inductors and power quality optimization. The detailed operation principles with hybrid modulation strategy combined with unipolar and bipolar pulsewidth modulation schemes are presented. Experimental results of a 2200VA prototype verify the proposed topology with hybrid modulation method.

Tuesday, 15 April 2014

An Adjustable-Speed PFC Bridgeless Buck–Boost Converter-Fed BLDC Motor Drive


This paper presents a power factor corrected (PFC) bridgeless (BL) buck–boost converter-fed brushless direct current (BLDC) motor drive as a cost-effective solution for low-power applications. An approach of speed control of the BLDC motor by controlling the dc link voltage of the voltage source inverter (VSI) is used with a single voltage sensor. This facilitates the operation of VSI at fundamental frequency switching by using the electronic commutation of the BLDC motor which offers reduced switching losses. A BL configuration of the buck–boost converter is proposed which offers the elimination of the diode bridge rectifier, thus reducing the conduction losses associated with it. A PFC BL buck–boost converter is designed to operate in discontinuous inductor current mode (DICM) to provide an inherent PFC at ac mains. The performance of the proposed drive is evaluated over a wide range of speed control and varying supply voltages (universal ac mains at 90–265 V) with improved power quality at ac mains. The obtained power quality indices are within the acceptable limits of international power quality standards such as the IEC 61000-3-2. The performance of the proposed drive is simulated in MATLAB/Simulink environment, and the obtained results are validated experimentally on a developed prototype of the drive.

A Novel Variable-Speed Wind Energy System Using Induction Generator and Six-Switch ACIAC Converter


Nowadays using of the wind energy has a growing trend in the world due to their numerous advantages. The wind energy is free, inexhaustible and it produces no waste or greenhouse gases. Furthermore, it is a good method of supplying energy to remote areas. In this paper, a new variable-speed wind energy conversion systems (WECSs) with a squirrel cage induction generator (SCIG) and a new six-switch AC/AC converter as power electronic interface between SCIG and network is proposed. Characteristics of six-switch AC/AC converter are used for maximum power tracking control under different wind speed and delivering power to the grid, simultaneously. This configuration uses only six active switches and six diodes and has the lowest number of active switches among three-phase to three-phase AC/AC converters proposed hitherto in the literature. This converter offers sinusoidal input and output, unity power factor and more importantly, low manufacturing cost. Two simulations are performed for proposed configurations and results are presented. The results verify effectiveness of the proposed interface configuration.


Distributed FACTS—A New Concept for Realizing Grid Power Flow Control


Flexible ac Transmission Systems (FACTS) devices are used to control power flow in the transmission grid to relieve congestion and limit loop flows. High cost and reliability concerns have limited the widespread deployment of FACTS solutions. This paper introduces the concept of Distributed FACTS (D-FACTS) as an alternative approach to realizing cost-effective power flow control. By way of example, a distributed series impedance (DSI) and a distributed static series compensator (DSSC) are shown that can be clipped on to an existing power line and can, dynamically and statically, change the impedance of the line so as to control power flow. Details of implementation and system impact are presented in the paper, along with experimental results.

Thursday, 20 March 2014

Transient Stability Analysis of the IEEE 9-Bus Electric Power System


It is widely accepted that transient stability is an important aspect in designing and upgrading electric power system. This paper covers the modelling and the transient stability analysis of the IEEE 9 bus test system using ETAP. In this, for various faults on the test system  fast fault clearing  and load  shed are analysed to bring back the system to the stability. Frequency is a reliable indicator if deficiency condition in the power system exists or not. Change in power demand or in production causes a fluctuation of the speed of the turbine-generator condition exists on the power system, resulting in fluctuation of the frequency of the power system. So rate of change of frequency is used as indicator of the transient stability of the system and to calculate the amount of load to be shed by adaptive load shedding and measures taken to maintain stability and frequency of the system. 



The paper describes direct vector control with stator flux orientation for controlling the speed a PWM inverter induction motor drive system without speed sensor. Modeling and simulation results of the drive system are presented with some practical results. The proposed control method assures good dynamic response of the system.

Direct Torque Control of Permanent Magnet Synchronous Motors – An Overview


In high-performance servo applications a rapid and accurate torque control is desired, preferably without the use of a motion-state sensor. The use of permanent magnet synchronous motors (PMSMs) combined with the direct torque control (DTC) scheme offers many opportunities to achieve this goal. Recently several authors have proposed possible implementations of direct torque control for permanent magnet synchronous motors. In this paper an overview is given. The basic principles of DTC for PMSMs are explained. Topologies and algorithms described in the literature for interior PMSMs as well as surface mounted PMSMs are discussed. Estimations of stator flux linkage and initial rotor position are needed in these control schemes. Techniques to achieve these estimations are discussed in this paper as well. The main goal of the paper is to give an outline of what is already achieved and to determine points of interest for further research.