A state-space approach to modeling and ripple reduction in AC-DC converters

This work develops a systematic state-space approach to modeling and control design for AC-DC converters. Several types of AC-DC converters are considered. The control objective is to minimize the output voltage ripple via simple feedback while keeping the size of the elements, such as inductors and capacitors, small.;The first AC-DC converter considered in this work is a transformer cascaded by a full-wave diode bridge and a boost converter where the switching is realized by one MOSFET and one diode. The complex nonlinear and uncertain behavior of the transformer and the diode bridge is handled by modeling the output voltage of the bridge rectifier as a periodic disturbance whose harmonics have given frequencies but uncertain phases and magnitude. This type of disturbances are described as the output of an external autonomous linear system, called an exogenous system, with uncertain initial conditions. The exogenous system is integrated with the boost converter as a whole system in state-space description. The whole system is a nonlinear system whose differential equations have bilinear terms, which are handled by a nonlinear differential inclusion. Via a recently developed Lyapanov framework, the problem of ripple reduction is converted into a numerically efficient optimization problem which involves linear matrix inequalities (LMIs). The resulting feedback law is a simple linear state feedback. The effectiveness of the theoretical approach and design method are validated by experimental results, both in Simulink simulation and in an experimental circuit.;The first AC-DC converter works very well for output voltage within a certain range, but has significant ripples for output voltage above or below a certain value. This is due to the intrinsic limitation of boost converters with only one MOSFET. To extend the range of output voltage with satisfactory ripple size, this work considers two other types of AC-DC converters, where the boost converter is replaced by a synchronous boost converter with two MOSFETs or a buck-boost converter. Experimental results confirmed the performance improvement by these converters.