Indirect Use Capacitor Current Digital Control For Buck Converter

Digital switching power supply is a kind of switch power supply, its main characteristic is to use digital processor (FPGA, DSP and ARM, etc.) to calculation the various digital data which is collected and converted by Analog to Digital Converter(ADC) chip and then depend on these calculated data to control switch tube. Compare with analog switch power supply, digital switching power supply not only can change no hardware circuit to alter controls parameter and shift control method, but also attach various kind complicated functions which is hardly realize on analog switch power supply, such as adaptive power management, real time monitoring, remote control, etc. in the early days, digital switching power supply is unable to contend with analog power supply in the market because digital switching power supply is limited by high cost and low performance on digital processor and Analog to Digital Converter(ADC) chip, especially in the low end of the power market. In recently year, with the rapid development of digital processor makes the digital switch power supply high frequency and low cost to be possible, which is significantly increase digital switching power supply market competitiveness, at the same time, put forward higher performance requirements to digital control algorithm of switch power supply.The motivation of this research is to explore more excellent performance of digital algorithm on Digital switching power supply, based on analyze existing outstanding digital algorithm, trying to make up for the deficiency.Firstly, reviews the principle of analog circuit V^2 control BUCK converter, and introduce the typical structure of digital switching power supply, Analyzes the Digital Peak Voltage control algorithm and its improved algorithm that can overcome one cycle delay. Then research on the problems existing in the traditional V^2 controlled BUCK converter:V^2 controlled BUCK converter control correctness work correctly rely on large ESR Capacitor, but use large ESR output Capacitor will increase the output voltage ripple and reduced power converter efficiency.Secondly, through the analysis and comparison to use voltage ripple and the current ripple of two different control modes of transient performance difference, a concept which can explain why Digital Peak Voltage control has better transient performance than peak current control is put forward in this paper that use Voltage ripple as control parameter contains both the information of inductor current ripple and the load change information. Based on this concept propose a new digital control algorithm which is called "Indirect use Capacitor current digital control". This digital control algorithm are obtained by sampling capacitor voltage to calculate the specific time through the direction and size of capacitive current, and use the calculated capacitive current as control parameter to design Duty ratio algorithm. This digital control algorithm have the same fast load response speed with Digital Peak Voltage control algorithm, but independent of use large ESR Capacitor, which means it can correctly control without Highly linear output voltage. Therefore, low capacity and low output voltage can realize in BUCK converter with this digital control algorithm. Indirect capacitive current control algorithm are studied in detail on the leading edge and trailing edge, delta front and rear triangle modulation methods in this paper, in addition, studied the stable condition of the indirect use Capacitor current digital control algorithm and give the solution when control algorithm is unstable.Lastly, design the experimental platform, the correctness of the algorithm verify by simulation and experiment.