Experimental results of 47-level switch-ladder multilevel inverter.

This paper provides experimental results for a 2.5-kW 47-level prototype of the switch-ladder multilevel inverter including the following: input and output voltage and current waveforms under resistive and inductive loads, efficiency, total harmonic distortion, voltage stresses across the switches, behavior of the system under fault condition, and no-load power dissipation. The most important advantage of this inverter is that only four switches conduct in each interval in low frequency. This matter, beside the elimination of switching losses, has made this inverter an efficient choice with 97% peak efficiency. The ability to continue working with open-circuit modules is another advantage of the inverter. Furthermore, some important factors behind the unreliability and inefficiency of inverters have been improved, including the following: low duty cycle of conducting switches, staircase voltage stresses across switches with low-voltage steppes, line switching frequency results in low temperature of switches, possibility of removing low-pass filters, and independence to capacitors. The inverter is proposed to be an advantageous choice in low-voltage stand-alone photovoltaic applications

Assessment of different voltage sags on performance of induction motors operated with shunt FACTS

Shunt FACTS devices are prevalent in industrial application of induction motors. These equipments are effective to compensate disturbances and increase motor speeding up. Whereas voltage sags is one of the most conventional power quality contexts in power systems, the performances of the induction motor under symmetrical and unsymmetrical voltage sags are investigated in this paper. The results prove that STATCOM is more effectual than SVC for reduction of transients and refinement the voltage profile. Between different types of unsymmetrical voltage sags, one type has maximum effect on variation range of voltage overshoot and voltage undershoot and two types have lowest influence on variation range of voltage overshoot and voltage undershoot

Transient response study on transformer windings under impulse voltage stresses

The study reported in this paper was aimed to investigate transient response of power transformer when lightning current pass through its winding. Analysis of distribution voltage at the winding taps was done, both by experimental and numerical simulation, by applying IEC-71 standard current surge (8/20 µs impulse current and 1.2/50 µs impulse voltage). Transformer’s constants as: R, L, C were derived from the transformer construction, which consists of 9 winding layers at HV-side. The wave-shapes of the voltage across the winding sections were recorded. The response of the windings was then compared with results of a simulation using EMTDC/PSCAD. The simulation based on an RLC network model resulted in wave-shapes that are in good agreement to those of the experiment. Both results of the simulation and experiment show that the distribution of the impulse voltage across the windings is non linear, especially during the period of fraction of microseconds. Furthermore, results of the investigation show that a simple capacitance network model is sufficient for study of the impulse voltage distribution across transformer windings

Bypassing the short-circuit faults in the switch-ladder multi-level inverter

A new hardware strategy is proposed to increase the reliability of the Switch-Ladder multi-level inverter against short-circuit (S.C.) faults in the H-Bridge and main switches Blocks. The strategy includes passive and active bypassing. Passive bypassing approach hires fuses in series-connection with the ladder`s steps. Instead, in the active method, relays are replaced the fuses and receive commands from a controller that monitors the short-circuit failures continuously. When a switch fails in short circuit behaviour, the ladder contains the failed switch is converted to open-circuit (O.C.). Owning to the ability of Switch-Ladder multi-level inverter to tolerate open-circuit faults due to its configuration and switching strategy, reliability is increased against short-circuit failures through inverting the short-circuit to open-circuit. At last the experimental result validates the claims

Voltage notch analysis of a taps-based multilevel inverter in the event of one switch failure

There are many advantages of the cascaded multilevel inverter such as low voltage stress for each switching device and higher power quality. One of the drawbacks for this type of inverter is the series switching of the cells it used in its operation. In order to properly operate, all switches must be operational; failure of only one of the switches will result in the failure of the inverter operation. This can be clearly seen in the case of cascaded H-bridge multilevel inverter and other topologies derived from it. In this paper a series cascaded cells taps-based multilevel inverter topology with a minimum number of switching devices and driver circuits needed is discussed. The voltage taps-based topology also needs to turn on only three switching devices at any operation time for any output voltage level configurations. The failure of one of the switches on this topology does not cause total malfunction of the inverter, instead it only causes voltage notches to form on the resulting sine wave output. The notch effect is verified by the experimental results of a prototype single phase 41-level inverter

A single DC source 41-level 115V, 400Hz cascaded multilevel inverter

Cascaded multilevel inverters are popular in fields such as oil and gas, power supply installations, and power quality devices. While there are many advantages of the cascaded multilevel inverter, its main disadvantage is the need for large numbers of multiple dc sources. In order to reduce total harmonics distortion (THD) of the output voltage waveform, the amount of output voltage level must be increased, hence the higher number of dc sources. This essentially complicated the inverter design, as most converter transform only one voltage source to another. In this paper a cascaded multilevel inverter topology with a single dc source is discussed. The topology is based on capacitors instead of cells as the multiple voltage sources. The cascaded multilevel inverter topology validity and functionality is verified by the Matlab Simulink simulation of a 100W and 1kW aircraft single phase 41-level inverter

Simulation of a 41-level inverter built by cascading two symmetric cascaded multilevel inverter

The main disadvantage for cascaded multilevel inverter is the high number of switching device it needs in an installation. To reduce total harmonics distortion (THD) of the output waveform, the number of output voltage level has to be increased, hence the higher number of switching devices. This consequently increases the installation cost, inverter size and voltage losses at the load terminals. In this paper a new cascaded multilevel inverter concept is proposed with a small number of switching devices and dc sources needed. The 41-level inverter consist of several high voltage and low voltage dc sources. The switching strategy of the inverter is the low voltage dc sources are switched in several times in a half cycle of the output. The 41-level cascaded multilevel inverter operation is then demonstrated by the Matlab simulation

Energy crisis 2050?: global scenario and way forward for Malaysia

To meet the energy demand of all households worldwide, energy supplies must double by 2050. While fossil fuels will continue to account for the largest proportion of primary energy requirements through the next four decades, we cannot only double world energy supplies and improve access but also effectively manage greenhouse gas emissions. Our core fossil fuel sources - oil, coal and gas - are finite natural resources, and it is being depleted at a rapid rate. The main driver to address this dual challenge will be higher energy prices. Higher prices will propel the developed world towards greater renewable and Nuclear Energy (NE) and attract higher level of energy efficiency. Many developed countries have an ambitious vision that to be powered by 100% Renewable Energy (RE) sources by the middle of this century. In many senses NE is clean. But there is always an argument whether NE is an alternative to fossil fuels and a way to fight global warming. There is much public fear about NE, fuelled by accidents such as Chernobyl, Three Mile Island and very recently Fukushima Daiichi. It is, however, an issue which is becoming more important as we approach a time when fossil fuel resources may run out, making it necessary to find quick and secured alternative sources. Technology enhancement in nuclear reactor and efficient use of nuclear fuel can lessen the risk of NE.The world needs to seriously consider what will be required for transition to a sustainable energy future, and to find solutions to the dilemmas – meet energy demand and mitigate global warming simultaneously. Answering these challenges - the solutions to the energy needs of current and future generations - is one of the most important, challenging and urgent political tasks ahea