High Performance Low Cost Digitally Controlled Power Conversion Technology

Digital control of switch-mode power supplies and converters has within the last decade evolved from being an academic subject to an emerging market in the power electronics industry. This development has been pushed mainly by the computer industry that is looking towards digital power management in order to reduce the power consumption of servers and datacenters.

The work presented in this thesis includes digital control methods for switch-mode converters implemented in microcontrollers, digital signal controllers and field programmable gate arrays. Microcontrollers are cheap devices that can be used for real-time control of switch-mode converters. Software design in the assembly language of the microcontroller is important because of the limited resources of the microcontroller.

Microcontrollers are best suited for power electronics applications with low bandwidth requirements because the execution time of the software algorithm that realises the digital control law will constitute a considerable delay in the control loop. Digital signal controllers are powerful devices capable of performing arithmetic functions much faster than a microcontroller can.

Digital signal controllers are well suited for digital control schemes involving multiple control loops such as digital control of a switch-mode power supply with several converter stages. Customised digital control solutions implemented in application specific integrated circuits are the best solution for high bandwidth digital control of non-isolated DC-DC converters.

A customised digital control solution for a voltage mode control scheme should include a digital pulse width modulator which can generate a pulse width modulated signal with high switching frequency and high resolution, a digital compensator with a short execution time and an analogue to digital converter with a short sampling time.

A digital self-oscillating modulator is proposed in the present thesis. The modulator is a free-running modulator which operates without an external carrier signal. Customised digital control solutions offers the best performance for non-isolated DC-DC converters. The best digital control solution presented in this thesis, which was implemented with the digital self-oscillating modulator, performs comparable to common analogue control IC solutions.

It is however possible to achieve an even better performance with an analogue control circuit built with separate analogue components.