Study On Synergetic Control And Pulse Width Modulation Of Switching Power Supply

A central purpose of this dissertation is to apply synergetic approach to control theory (SACT) for switching converters and study on pulse width modulation technology. The first one emphasizes on theoretical analysis and the last one studies on practical application. The fundermental theory and application of synergetic control and the design of synergetic controller are studied intensely in order to improve the robustness of controlled converters and search for control schemes which implemented easily. In addition, improvements on circuit design and modulation strategy are provided to eliminate shimmer to digital display in the present LED constant current drivers. The main contributions of this thesis are listed below:(1) Convergence speed and manifold existence are analyzed and the sufficient conditions of robustness against external perturbation and system parameter variation are obtained,which provide theoretical basis of synergetic control. The design of synergetic controller for the Boost converter with constant power load is discussed. The stability criterions of the closed-loop system under small signal and large signal are given. Simulative results with Simulink indicate that the synergetic controller is asymptotically stabilized at the objective working point and has robustness against the sudden change of load and load power, which verify the theoretical analysis.(2) The general form of a discrete synergetic controller is briefly presented. Its convergence speed and the existence and hitting conditions of its manifold are discussed based on the similarity of sliding-mode control and synergetic control and variable structure theory. The robustness of the closed-loop system driven by the synergetic controller is detailed and certain conditions are obtained. The Buck converter is taken as an example and the design of synergetic controller is discussed. Simulative results with Simulink indicate that the discrete-time synergetic controller is asympototically stabilized at the objective working point and has robustness against the sudden change of load and input source.(3) Continuous and discrete synergetic control are improved through macro-variable definitions and control parameter settings and verified with Simulink. In order to verify superiority of the synergetic control, synergetic controls in continuous and discrete form are both compared with proportional–integral–derivative (PID) in case of load and circuit parameters variations.(4) An LED drive circuit with constant output current and no load feedback and a method to distribute pulses of a pulse width modulated signal over a time period are proposed. The present LED drive circuit usually uses two-level modulation strategy and generates a low frequency rectangle wave with harmonics on LED load, which will generate shimmer to digital display devices. The low frequency rectangle wave is difficult to be filtered in practical applications. This LED drive circuit in this thesis sets the current sampling on the switch tube so that direct current on LED is obtained, which makes it possible to eliminate shimmer through circuit design. In view of filtering, by distributing pulses of a pulse width modulated signal over a time period to drive the switch tube and filtering on LED through capacitors, a direct current with very small amplitude harmonics can be obtained to eliminate shimmer.