Advanced Motor Drives Studies

This report presents an evaluation of advanced motor drive systems as a replacement for the hydrazine fueled APU units. The replacement technology must meet several requirements which are particular to the space applications and the Orbiter in general. Some of these requirements are high efficiency, small size, high power density. In the first part of the study several motors are compared, based on their characteristics and in light of the Orbiter requirements. The best candidate, the brushless DC is chosen because of its particularly good performance with regards to efficiency. Several power electronics drive technologies including the conventional three-phase hard switched and several soft-switched inverters are then presented. In the last part of the study, a soft-switched inverter is analyzed and compared to its conventional hard-switched counterpart. Optimal efficiency is a basic requirement for space applications and the soft-switched technology represents an unavoidable trend for the future

Soft switching techniques for multilevel inverters

Tese (doutorado) - Universidade Federal de Santa Catarina, Centro Tecnológico. Programa de Pós-Graduação em Engenharia Elétrica

A NEW REDUCED SWITCH ZVS-PWM THREE-PHASE INVERTER

Dc-ac inverters convert a dc input voltage into a desired ac output voltage and are widely used in many industrial applications, including utility grid interfaces, motor drives, and wind energy systems. Because of their widespread use, there has been considerable interest to try to make them more efficient to conserve energy. One way of doing so is to reduce the losses that are generated by the switching of the inverter devices as they help convert the dc input voltage into an ac output. As a result, there has been considerable research into implementing inverters with so-called soft-switching - zero-voltage and zero-current switching techniques that make either the voltage across a switch or the current through it zero at the time of a switching transition (from on to off or off to on). Since the power dissipated in a switch is related to the amount of overlap of voltage and current during a switching transition, making either the switch voltage or switch current zero at this time can result in a significant reduction in switching losses. A new, reduced switch, zero-voltage switching (ZVS), three-phase dc-ac inverter is proposed in this thesis. The proposed inverter does not have the drawbacks that other previously proposed ZVS-PWM inverters have such as cost, increased conduction losses, the appearance of distortion in the output waveforms, and the lack of bidirectional operation capability. In the thesis, an extensive literature review of previously proposed soft-switched inverters is performed. The new inverter is then presented and its operation is explained in detail. The steady-state operation of the new inverter is analyzed and the results of the analysis are used to determine the converter\u27s steady-state characteristics. Based on these characteristics, a procedure for the design of the inverter is developed and then demonstrated with an example. Finally, the feasibility of the proposed converter and the validity of the analysis are confirmed with simulation results obtained from PSIM, a widely used, commercially available software simulation package for power electronic

Design and Implementation of a Soft Switched Inverter Based 400 Hz Power Supply

In this dissertation, the suitability of Resonant DC Link Inverter (RDCLI) for a 400 Hz Power Supply usually applicable for Aircrafts/ Ships etc. is investigated. Aircrafts and such equipment usually operate at 400 Hz (8 times the standard frequency) primarily for the purpose of reducing the sizes of the connected loads. Since usually available generators are designed for 50 Hz, power converters and controls come into force for designing a 400 Hz supply. Basically we have two options (Hard switched and Soft-Switched) while adopting AC-DC-AC conversion. Soft-switched inverters will score over this specific application for constructing a 400 Hz waveform usual PWM frequency required would be at least 4 kHz. For medium power applications (100 kVA) operating at 4 kHz could be a difficult task for a hard-switched inverter. However, Soft-Switching Inverter in the form of RDCLI is a better option as it would provide a huge current regulator bandwidth. Furthermore, switching losses would be virtually zero that would facilitate improving the efficiency of the power supply

Resonant DC link converters and their use in rail traction applications

Conventional 'hard switching' converters suffer from significant switching loss due to thesimultaneous imposition of high values of current and voltage on the devices during commutation.Resonant converters offer a solution to this problem. A review of resonant circuit topologies ispresented, which includes a summary of the interference problems which may occur when usingpower converters in the rail traction environment. Particular attention is given to the ResonantDC Link Inverter (RDCLI) which shows a great deal of pronuse using currently availabledevices.The frequency domain simulation of RDCLIs is discussed as a means of rapidly evaluatingcircuit behaviour, especially in relation to modulation strategies. A novel modulation strategy isproposed for Resonant DC Link Inverters, based on a procedure known as Simulated Annealingwhich allows complex harmonic manipulations such as han-nonic minimisation, to be performed.This is despite the fact that RDCLIs are constrained to use Discrete Pulse Modulation wherebyswitch commutations are restricted to specific moments in time. The modulation algorithms wereverified by use of a low-power test rig and the results obtained are compared against theoreticalvalues. Details of the hardware implementation are also included.A single-phase pulse-converter input stage is described which may be incorporated into theResonant DC Link Inverter topology. This input stage also benefits from soft-sVVItching andallows four-quadrant operation at any desired power factor. A modulation scheme based onSiMulated Annealing is proposed for the pulse-converter, to achieve hannomc control whilst alsosynchronising with the supply wavefon-n. Practical results are presented and compared with thoseobtained by simulation and calculation.Finally the design of Resonant DC Link Converters is discussed and reconunendations made forthe choice of resonant components based on the minimisation of overall losses. Comparisons aremade between hard-switching and soft-switching converters in terms of loss and harmonicperformance, in an attempt to quantify the benefits which may be obtained by the application ofsoft-switching

Modulation and Control Techniques for Performance Improvement of Micro Grid Tie Inverters

The concept of microgrids is a new building block of smart grid that acts as a single controllable entity which allows reliable interconnection of distributed energy resources and loads and provides alternative way of their integration into power system. Due to its specifics, microgrids require different control strategies and dynamics of regulation as compared to ones used in conventional utility grids. All types of power converters used in microgrid share commonalities which potentially affect high frequency modes of microgrid in same manner. There are numerous unique design requirements imposed on microgrid tie inverters, which are dictated by the nature of the microgrid system and bring major challenges that are reviewed and further analyzed in this work. This work introduces, performs a detailed study on, and implements nonconventional control and modulation techniques leading to performance improvement of microgrid tie inverters in respect to aforementioned challenges