| Analysis of the power electronics literature shows that bidirectional dc-dc converters find many applications in do uninterruptible power supplies, battery chargers, electric vehicles, battery chargers/dischargers for satellites, photovoltaic applications, back-fire applications, auxiliary power supplies, and more. The input to these converters is often an unregulated line voltage with fluctuations. There are also load variations. Primarily, the feedback control converts unregulated voltages to a desired do output. The controller must have robust characteristics and should perform perfect tracking of the reference voltage (zero steady-state error). Traditional designs of feedback loops in dc-dc switch-mode systems, after linearization, are based on frequency-domain analysis. A major problem is encountered when the transfer function of the power stage has zeros in the right-half-plane. In flyback and Ćuk converters, the presence of such zeros severely restricts the closed-loop bandwidth obtained by the classical frequency-domain approach.; To overcome these problems, a recently introduced H∞ control approach was used for controlling switch-mode systems. The main difference between this control approach and the traditional one is in relation to attenuation of low-output impedance. In the H∞ control approach, the control goal can be formulated to directly include the reduction of the output impedance as much as possible over a given frequency range. The research in this dissertation focuses on design and implementation of the H∞ controller.; First an analog H∞ controller was designed, built, and tested for a bidirectional flyback and for Ćuk converters. Saber Version 5.2 and MATLAB Version 6.0 are the software used for design simulations and analyses. This controller was improved by using digital signal processing (DSP). With DSP, more improvements were obtained by incorporating a pulse width modulating (PWM) circuit.; Analysis and simulations have shown that the H∞ controller is superior to a traditional reference-to-output frequency-compensated controller primarily because it reduces output impedance. A prototype of each topology was built; data were obtained to verify the simulated results. Measurements of the H∞ controller circuit in a closed loop are in agreement with theoretical and simulated predictions. |
