Chaos control of voltage mode controlled buck-boost converter

Abstract

Due to the limitation to the development level of modern science and technology, DC-DC (where DC stands for direct current) converters operating in chaotic state cannot be used to achieve some desired goals yet and the chaotic phenomena occurring in DC-DC converters are almost restrained. For DC-DC converter operating in continuous conduction mode (CCM), its characteristic has been widely studied, but DC-DC converter needs to operate in discontinuous conduction mode (DCM) at light load. Because if it always works in CCM, the inductor current will be less than zero when the load is light, which will increase conduction loss and reduce conversion efficiency. Moreover, DCM operation is frequently encountered, since power converters are usually required to operate with loads removed. For buck-boost converter, the obvious oscillation will appear when it works under the condition of varying operating point, so it is difficult to control. Considering the reasons above, the voltage mode controlled buck-boost converter operating in DCM is chosen to be studied to verify the validity of the two control methods presented in this paper. Under a certain condition, chaos and bifurcation will occur in the voltage mode controlled buck-boost converter operating in DCM. Having discussed its chaotic phenomenon, in this paper we present two ways to control the system to operate stably in one-cycle state. The first way is the self-controlling delayed feedback control method. The basic idea of this method is to use the difference between the delayed output signal and the output signal to form a feedback signal, and return it to the control circuit in a form of negative feedback to control the output signal. The simulation results show that the self-controlling delayed feedback control method can make the system which has already entered into chaos operate stably in one-cycle state. Besides, its dynamic response speed is fast and it does not change the system frequency. However, this method fails to work when the disturbance is too large. Therefore, the self-controlling delayed feedback control method is more suitable for small disturbance condition. The second way is the improved sliding mode control method. The basic idea of the sliding mode control is to design a switching function to determine a switching surface which represents a desired system dynamics, then, design a variable structure control law to drive any state to reach the switching surface, therefore, the sliding mode takes place and the system follows the desired dynamics. The simulation results show that the improved sliding mode control method can force the system which has already entered into chaos to operate stably in one-cycle state even when the system encounters large disturbance. In addition, although it is more complicated to design, it has great dynamic response characteristics and excellent robustness. Because the methods presented in this paper do not rely on the buck-boost converter itself, both methods can be used to control other DC-DC converters. When the disturbance is small, the self-controlling delayed feedback control method should be considered first, for it is easier to achieve. When the system encounters large disturbances the sliding mode control method has the priority, because this method is valid while the self-controlling delayed feedback control method may fails under such a condition.