Abstract
A new discrete-time state feedback controller is presented, which allows high-bandwidth voltage control of a buck converter for any load condition, whether it operates in discontinuous conduction mode (DCM), continuous conduction mode (CCM), or at the boundary of these regions. This makes the buck converter applicable for a wide range of applications. For the control design process, two large-signal models, which represent the buck converter's discrete time dynamics in CCM and DCM, are developed. A simple proportional-integral regulator is used for the voltage control of the converter. The operation mode is detected and the voltage controller is connected in cascade to a current controller in CCM or to a nonlinear state feedback decoupling structure in DCM. In this paper, the modeling and design of the proposed control topology are introduced and its performance is demonstrated in simulation and experiment.
Highlights
F OR today’s industrial and commercial voltage supplies, buck converters are a popular choice
The regions in which such a controller can be operated robust and safely can be identified according to [12] or [13], where it is demonstrated that this simple control structure does not guarantee stable and well-behaved dynamics over a wide operation range. To overcome these problems, [14]–[16] suggest alternative control structures, which take into account the load dependent dynamics and improve the stability of the converter. These approaches are not suitable for a general design approach, as they do not take into account the change of the system dynamics that occurs when changing between conduction mode (CCM) and discontinuous conduction mode (DCM) operation
The inductor current in CCM can be controlled with a proportional state feedback controller, whose state feedback gain Ra can be determined as a function of the desired current loop bandwidth according to 1 − e−ωbTs
Summary
F OR today’s industrial and commercial voltage supplies, buck converters are a popular choice. To overcome these problems, [14]–[16] suggest alternative control structures, which take into account the load dependent dynamics and improve the stability of the converter These approaches are not suitable for a general design approach, as they do not take into account the change of the system dynamics that occurs when changing between CCM and DCM operation. In [17], a controller for a synchronous buck converter is proposed, based on the large-signal converter model, which enables operation in CCM and smooth transition to DCM. Based on two large-signal models describing the buck converter dynamics in CCM and DCM, a cascaded control structure with a single PI voltage controller is developed.
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