Design and experimental validation of a multiphase VRM controller

By combining the concepts of multiple-sliding-surface and integral-variable-structure controls, one can develop a robust controller for a multiphase 9 V VRM, which comprises four parallel DC–DC synchronous buck convertors operating at 300 kHz. The advantages of the control scheme are its simplicity in design, good dynamic response, robustness, ability to nullify the bus-voltage error and the error between the load currents of the convertor modules, and ability to reduce the impact of high-frequency dynamics due to parasitics on the closed-loop control system. Unlike a conventional variable-structure controller (VSC), which achieves superior transient performance by optimising (and hence, by varying) the switching frequency, the novel controller is able to retain the excellent dynamic performance of a conventional VSC and yet maintain a constant-frequency operation of a PWM controller under ‘steady-state’ condition. The latter is achieved by obtaining a duty-ratio signal; however, unlike a PWM controller, the new controller calculates the duty ratio based on Lyapunov's stability crietrion. Thus, the new controller also permits interleaved operation of the VRM modules.