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Abstract
A system for DC-DC power conversion based on a buck-boost converter topology is presented which makes power flow in both directions possible. The possibility of bidirectional power flow is useful for certain applications, such as uninterruptable power supplies (UPS) etc. The structure is compared with the well known unidirectional buck-boost converter. Open-loop control is treated based on simulation using duty cycle averaging. The system behaviour of the bidirectional converter is analyzed; a structure diagram is given and the transfer function of the system is derived. The validity of the duty cycle averaging is proven by comparison to a switched model. The controller for the converter is then realized as simple voltage controller, as voltage controller with an inner-loop current controller (cascade control) and with two kinds of state space control. The transfer functions of the different system parts are derived and dimensioning guide-lines for the controller sections are presented. The closed-loop behaviours of the bidirectional converter for the different control structures are analyzed based on simulation using duty cycle averaging; Bode diagrams and step responses are shown for an example. Finally, applications of the analyzed system are discussed.
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