An approach to controlling an active parallel interface between a transient energy source and a dc voltage bus

摘要

This thesis investigates controlling a dc-dc converter connecting a capacitor or ultracapacitor (UC) to a dc voltage bus by regulating the series impedance of the converter. Decoupling the capacitance from the voltage bus is shown to reduce the size and/or weight of the power source. The impedance of the dc-dc converter is shaped by a high-pass filter so that it is low at high frequencies, but infinite at dc. This shaped-impedance controller allows load current to be shared between the dc source and decoupled capacitor, even when the dc source is uncontrolled, as long as the dc source has nonzero source impedance. Charge transfer to and from the capacitor is limited to a finite value proportional to a step change in bus voltage. The same control approach was applied to the converter which added decoupled bus capacitance to an electric vehicle power source, where the dc source is a battery connected directly to the output voltage bus, and to a voltage regulator module (VRM) for a desktop computer processor. Design equations and small- and large-signal models are developed in detail for the vehicle power source. A second loop was added to the controller to help regulate UC charge level. Small-signal system stability is verified across the range of expected operating points. Experimental results of a scaled-down combined source verify theoretical predictions. For the VRM, a multiphase buck converter is augmented by a second set of phases which carry only fast current transients. Large-signal models and switch dissipation analyses predict that the proposed topology eliminates the need for bulk electrolytic capacitors on the voltage bus yet has efficiency comparable to a conventional multiphase VRM.