Multiphase Two-loop Control in Digital Controlled Buck Converter with Fast Load Transient

With the development of the processes in datacentre servers, the power supply requirements become more and more strict, and the over-regulation issue of VRM needs to be solved in load step transient. In this paper, a multiphase control called multiphase two-loop control is proposed. It applies the unique outer voltage loop and per phase inner current loop structure, to reconstruct the Buck power stage, solving the issue of large resonance peak value at the light load conditions and keeping the system a low Q value under various load conditions. In this way, it improves transient stability and eliminates over-regulation. The equivalent model of the multiphase two-loop control structure is proposed and a scanning algorithm is proposed for the modelling of the control parameters. Besides, the multiphase two-loop structure achieves the automatic current sharing without extra compensation. Finally, the 4-phase two-loop control is tested on the multiphase Buck system, the transient performance is tested with a 150A load step with the slew rate of 550A/μs. The undershoot and overshoot are 45mV and 96mV respectively and perform good transient response without over-regulation.