Switched-mode power conversion
The thesis begins with a general introduction to switched-mode power conversion. The main application areas of the technique are outlined and a summary is presented of current research work. The following chapters then focus on one recent development in the field, the Cuk converter and integrated magnetics. First, the steady-state performance limitations of the Cuk converter are explored through a comparison with the basic switched-mode converter topologies. The circuit is seen to possess several attractive properties including input and output current waveforms which are continuous rather than pulsating. However, the switching losses are shown to be high. A regenerative snubber is presented which reduces the transistor turn-off loss whilst preserving the high-quality input and output current waveforms of the converter. The integrated magnetics technique is discussed in the following chapter. This is the technique whereby converter magnetic components are coupled to eliminate input and output ripple currents and therefore improve steady-state performance. The possible problems are highlighted of attempting to couple transformers and inductors on a single core and an alternative coupling technique is outlined which uses an auxiliary electric circuit. The introduction of magnetic coupling in the Cuk converter to eliminate input and output ripple currents and improve steady-state performance results in more complicated dynamic characteristics and a more complex control problem. The state-space averaging technique is used in chapter 4 with the aid of a control engineering design package, CLADP, to analyse the problem. The impact of component coupling on the converter dynamic characteristics is explained and possible control strategies are suggested and verified. Finally, the Cuk converter with component coupling is assessed as a large-signal waveshaper. Several inverter configurations are examined in which a switched-mode converter operating under closed-loop control is used as a waveshaper to synthesise high-quality sinusoidal output currents. The implementation of the schemes using a Cuk converter with component coupling is described.