Open-loop stability analysis of multi-loop current-injected switching regulator is performed using a small signal model containing a power stage, an error processor and a duty cycle pulse modulator. Two design constraints and the effects of various critical control circuit parameters are pinpointed and the analysis-based design guidelines are established in order to optimize the switching regulator performances. In addition, an external ramp slope is proposed to obtain the optimal performance and eliminate the 50% duty cycle instability when operated in constant frequency mode. The effects of the second stage output filter are also examined. / Master of Science

M.S.

Two new classes of soft switching pulse-width-modulated (PWM) converters, named zero-voltage-switched (ZVS) PWM converters and zero-voltage-transition (ZVT) PWM converters, are proposed. The proposed ZVS-PWM converters combine the merits of conventional PWM and ZVS-QRC techniques. They are capable of regulating the output for a wide load and input voltage range while maintaining constant-frequency operation. By employing a saturable inductor, the load range under which ZVS is maintained can be significantly extended without increasing the voltage stress of the power switch. The parasitic oscillations between the diode junction capacitance and the resonant inductor are also significantly reduced. In the new class of ZVT-PWM converters, both the power switch and the rectifier diode are operated with zero-voltage switching, and are subjected to low voltage and current stresses associated with those in their PWM counterparts. Thus switching losses are significantly reduced at a slight increase in conduction losses. In addition, the circuit optimization is simplified because of constant-frequency operation. The operation principles of the proposed converters are described by using several examples. Several breadboarded converters are implemented to verify the theoretical analysis and to demonstrate the feasibility of the proposed technologies. / Master of Science

An analysis is presented on current-mode control of a magnetic amplifier post regulator. Small-signal models for a magnetic amplifier reset method are developed for post regulators operating in continuous conduction mode. A design procedure is given and experimental verification of the model is provided. / Master of Science

There are two important issues about a spacecraft power conversion system: low ripple current flowing through both battery and bus, and bi-directional power flow to and from the battery. This thesis introduces a novel low ripple current bi-directional battery charge/discharge converter using coupled-inductor. Bi-directional switch structures and proper control scheme make it possible for the power to flow through the same converter in both directions: charging and discharging the battery. Meanwhile, the coupled-inductor is designed in such a way that all the magnetizing current (ripple current) is confined within the converter, yielding "zero-current-ripple" (ZCR) on both battery side and bus side. ZCR condition analysis, topological comparison with similar approach, and circuit design guide line are given in this thesis. Circuit operation and performance, bi-directional control strategy, and small signal characteristics of the converter are also presented along with experimental verification. / Master of Science

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