Ehsan Najafi

Design and Implementation of a New Multilevel Inverter Topology

Multilevel inverters have been widely accepted for high-power high-voltage applications. Their performance is highly superior to that of conventional two-level inverters due to reduced harmonic distortion, lower electromagnetic interference, and higher dc link voltages. However, it has some disadvantages such as increased number of components, complex pulsewidth modulation control method, and voltage-balancing problem. In this paper, a new topology with a reversing-voltage component is proposed to improve the multilevel performance by compensating the disadvantages mentioned. This topology requires fewer components compared to existing inverters (particularly in higher levels) and requires fewer carrier signals and gate drives. Therefore, the overall cost and complexity are greatly reduced particularly for higher output voltage levels. Finally, a prototype of the seven-level proposed topology is built and tested to show the performance of the inverter by experimental results.

A new topology -Reversing Voltage (RV) - for multi level inverters

Multi level inverters have been widely accepted for high power high voltage applications. Their performance is highly superior to conventional two level inverters in reduced harmonic distortion, lower EMI (electro magnetic interference) and higher DC link voltages. However it has some disadvantages as increased number of components, complicated PWM control method, and voltage balancing problem at neutral point. In this paper a new topology called reversing voltage (RV) is proposed to improve the multi level performance by compensating the disadvantages already mentioned. This topology requires less components compared to available inverters (especially in higher levels) and requires less carrier signals and does not need balancing of the voltages. The topology and the control method based on PD (phase disposition) SPWM are shown and the required components are also compared to other topologies to show the superiority of the topology. Finally, output voltage and currents are demonstrated by simulation.

A D-STATCOM based on Goertzel algorithm for sag detection and a novel current mode controller

STATCOM has been widely proposed for power quality and network stability improvement. It is easily connected in parallel to the electric network and has many advantages for electrical grids. It can improve network stability; power factor, power transfer rating and can avoid some disturbances such as sags and swells. Most of STATCOM controllers are based on voltage controllers that are based on balance d-q transform. However, they are not thorough solutions for network disturbances since in most cases single-phase disturbances occur in electrical networks that cannot be avoided by the conventional controllers.

A new controlling method based on peak current mode (PCM) for PFC

A new method for controlling power factor corrector (PFC) is proposed based on the peak current method (PCM). Peak current method (PCM) is a well known method for controlling a PFC. However; it has some disadvantages as using analogue method of adding a ramp wave to the measured current. The proposed method utilizes a new digital approach instead of the traditional analogue control. In this paper, the new digital method is described and then it is analyzed with the circuit simulating software-Orcad 9.1. Simulation results illustrate the efficiency of the method.

Design and Implementation of a Dynamic Evolution Controller for Single-phase Inverters with Large Load Changes

Abstract—A new controller is developed for a single-phase inverter based on the dynamic evolution control method. The non-linear model equations and algorithm of the approach is derived and presented. The simulation is conducted based on the proposed method by MATLAB/Simulink to test the performance of the controller for large load variations. The system was also tested experimentally to show the feasibility of the proposed method applied to a single-phase inverter. Results show that the proposed approach is suitable for applications with large load variations. Practical results show that the controller can successfully handle a 40 times load change in less than 2 ms. It also has good output in the harmonic spectrum compared with the IEEE 519 harmonic standard during no-load and full-load conditions.

Design and application of a novel current mode controller on a multilevel STATCOM

Static Compensator (STATCOM) has been widely proposed for power quality and network stability improvement. It is easily connected in parallel to the electric network and has many advantages for electrical grids. It can improve network stability; power factor, power transfer rating. It can also avoid disturbances such as voltage sag (dip) and swell which is the main concern of this paper This paper uses a single phase multilevel inverter for STATCOM. It also implements a new current mode controller to control a STATCOM. In order to detect voltage sag, the STATCOM utilizes Goertzel algorithm which is more efficient and practical compared to available methods. Finally, simulations show the results of STATCOM operation for sag mitigation. The results show that the proposed controller can effectively mitigate voltage sag during disturbances.

An improved sag detection approach based on modified Goertzel algorithm

ABSTRACT Power quality is one of the key features in developing electric networks. It has been noticed because of its impact on economy and reliability of electrical networks. There are several power quality phenomena which are categorised in recent standards and literatures. Among them, voltage sag is more common and destructive for electric networks and consumers. This article presents a new detection method to monitor voltage sag in different electric network conditions. Goertzel algorithm is shown to be effective and simple for sag measurement compared to available sag detection methods. In order to increase the detection speed and response time, the Goertzel algorithm is modified. This modification will add to the speed of sag detection. The feasibility of the proposed method is justified through a measurement set-up developed using the dSPACE R1104 Digital Signal Processor Platform. The experimental results prove that sag measurement speed is improved by twice using the proposed modified Goertzel algorithm in comparison with the original method and some established methods. The results also verify that the sag detection of the proposed method is not affected by harmonic distortion of the voltage waveform.

An overview of control techniques and technical challenge for inverters in micro grid

Abstract Expanded penetration of distributed generation (DG) into power system has made major difficulties from the perspectives of control and solid operation of the systems. Microgrids (a conglomeration of DG units, burdens, and storage components) with appropriate control system can be a good solution for expelling or encouraging these difficulties. The presentation of inverter-based microgrid in a distributed network has encouraged the use of sustainable power source assets, DGs, and storage resources; besides, it has enhanced power quality and lessened losses, thus enhancing the efficiency and the reliability of the system. The theory of “Plug and Play” or distributed micro-source is the key to microgrids. Phase locked loop is the important unit, which synchronized the grid voltage into inverter voltage. The most important conditions are to hold the inverter voltage synchronization with the grid voltage before and after the inverter being connected to the grid. Therefore, this chapter deals with the different synchronization methods and inverter controls based on microgrid.