Analysis and Control of the Synchronous Buck Converter with a Constant Power Load

摘要

This thesis examines the effects of loads with constant power characteristics on the operation of the synchronous buck converter. Loads with constant power characteristics occur when a regulated converter is used as a load, which is the case in power distribution architectures composed of power electronics converters rather than direct connection of sources, loads, or energy storage. ududIn this thesis, the large signal behavior and control of a system comprised of an ideal synchronous buck converter feeding an ideal constant power load are examined. A polar coordinate model of the system is derived for use in the analysis of both the constant duty cycle and controlled duty cycle behavior of the system, and the unstable nature of the single equilibrium point and the global absence of convergence to any point or limit cycle for non-equilibrium initial conditions is proven mathematically for the constant duty cycle case.ud udTo stabilize the system, geometrical boundary control and PD control are examined. The analysis and design of the boundary controller in the polar coordinate representation is presented, and the region of convergence and local stabilization of the system under boundary control are verified using numerical simulation. The analysis and design of the PD controller is then presented using both small-signal techniques and geometrical insights from boundary control, and the region of convergence and local stabilization are verified using numerical simulation. Lastly, the addition of an integral component to the PD controller to compensate for operating point changes, control signal error, and parameter uncertainty is analyzed using small-signal techniques, and performance of the system under PID control is verified using numerical simulation.ududThroughout, simulation results from a switching model of a synchronous buck converter feeding a point of load buck converter are included to verify the performance of the control strategies in a more realistic circuit.