The research outlined in this thesis is involved with some aspects of power electronics. In particular, within the area of machine drives, a new type of inverter is investigated. This inverter, referred to as the delta inverter, is principally intended for incorporation into an ac drive system. The inverter appears to offer some advantage in circuit design over conventional inverters and this is discussed in the context of the inverters overall performance and characteristics. Chapter 1 presents a review of machine drives, both ac and dc systems, and, in accepting the relative merits of the ac squirrel cage induction machine, outlines the penalties generally paid in conventional ac inverter complexity. The delta inverter configuration, which appears to offer a reduction in circuit complexity, is then introduced. Chapter 2 investigates the general behaviour of the delta inverter, specifically with passive loads, and outlines a suitable control strategy for the inverter. Chapter 3 deals with the subject of harmonic improvement of inverter waveforms. Two methods which appear particularly attractive, selective harmonic reduction (SHR) and sinusoidal pulse-width modulation (PWM), are presented. Using the strategy suggested in Chapter 2, the implementation of methods of sinusoidal pulse-width modulation applicable to the delta inverter are derived in this chapter and a theoretical comparison is made with the conventional bridge inverter. Chapter 4 presents both experimental and computed results for a delta inverter ac drive system using the previously derived switching techniques. The results are compared with the bridge inverter performance and with a mains quality sinusoidal supply. This chapter concludes with some discussion of the delta inverter ac drive system and some general points are made. Chapter 5 summarises the main conclusions that have been established, in the course of the present research, concerning the delta inverter system and its feasibility as an alternative ac drive circuit.
|Date of Award||1984|