Modeling Of Digitally Pulse-width Modulated DC/DC Converter

For many years, analog controllers have dominated the control of power electronics systems. Digital controls have continued to improve in cost and usability in the past several years. This has made digital controls more appealing to replace analog control in some devices. The benefits of adding digital control in power electronics are not based solely on adding performance to the individually controlled components, but in system monitoring capabilities.Digitally controlled power supply is one of them. Compared with analog control, potential advantages of digital controller implementation include much improved flexibility, reduced design time, programmability, elimination of discrete tuning components, improved system reliability, easier system integration, and possibility to include various performance enhancements such as power management. However, there are still remaining some significant challenges for the spread of the digital control techniques. How to establish the models for describing the characteristics of digital units is the point of this paper.This paper analyzes all of units making up of the control loop, especially the digital signal process units:sampling and conversion circuit, digital compensator and digital pulse width modulator. Sampling and conversion circuit, deciding the output accuracy, samples the output of the system and converts it into digital signal with filtering and a small signal model is obtained. About digital compensator, which comes from typeâ…¢compensator widely used in analog control, deals with the signal converted by ADC and calculates the control signal required. The calculation time should be highlighted as it would introduce an additional phase lag. Digital pulse width modulator can generate a duty cycle signal according to control signal from digital compensator. Going digital gives it two main effects:limit cycle oscillation and modulation effect. The models considering these effects are different since the difference in modulation modes. This paper also discusses the transfer function of main stage and uses a united model to describe all of basic topologies.At the last section, the open loop transfer function is obtained according to the analysis before. For compensating the phase lag caused by the delay effect, a modified divider network is presented and a design example is used to verify these models.