Digital Current Following Control Of Buck DC-DC Converters

In order to reduce the response time and improve the control precision of current following control of Buck DC-DC converter, the existing current following control strategy has been discussed further, the problem existing in the process of load mutation is analyzed.The original control strategy is not distinguished about steady state and transient load mutation process, which leads to the problems that switch turns off too soon or turns on too late in the dynamic process, so the output voltage of the recovery process is not ideal.A new control strategy is raised in the paper, the new control strategy is divided into steady state control and load mutation process control. The detailed theoretical analysis on the process of load mutation is given and the mathematical model of the mutation process is established. The each particular point time in dynamic working process can be calculated, and recovery time and the overshoot output voltage can be estimated. The control for steady state is not changed, but the control strategies while mutation load is changed. To judge the load current is uprush or sudden drop by software. If the load current is uprush, then the switch conduction time is extended. The inductance current is raised continue to the value, which combine average inductor current value after the jump with H value has been set. The specific value H is calculated based on the hardware parameters and the size of the current surges. If the load current fell, then extend the switch off time until the output voltage fall to the desired output, and at the same inductor current is less than the hysteresis current limit, switch is open again. In a word, in the dynamic process the switch on and off no longer just depends on average inductor current and the hysteresis width, this different from the steady-state control strategy. At the same time, Papers also has made the analysis and the control strategy while converter working in light load of discontinuous conduction mode, this facilitates the start of switch power supply in the case of light load.The hardware circuit parameters and control software have been designed and simulated in the Simulink environment. The corresponding simulation waveforms are obtained. Based on the ARM-STM32F407VGT6, a circuit is maded and debuged and tested. The experimentalresults show that the new strategy about the steady state control and dynamic control are feasible. As time as to ensure steady voltage precision of the work on steady state, the dynamic characteristics of the converter is improved obviously, and the converter load regulation is improved, the transition time is reduced. And the problem in starting of the light load is solved.