Enhancing digital control for DC/DC converters

The continuing trend in switched-mode power supplies clearly leads to the delivery of more output power with an ever increasing number of voltages more efficiently at less cost. Increasing power management requirements, i.e. communication functionalities, contribute significantly to the need for digitally controlled power supplies. While most of these designs still use simple PID compensators, the introduction of more advanced compensation techniques will improve the system performance considerably. However, one reason for the slow adoption of digital power converters is the lack of proper design tools for advanced digital controllers. This issue is addressed in this thesis where an automated design procedure based on Generalized Predictive Control (GPC) has been developed. Reallife design criteria are used to optimize compensators for application-specific requirements without the need for extensive control expertise. Another issue in today’s digital power systems is the choice of system architecture. Two different concepts are widely used. For high output power demands and fast transient response, multi-phase converters are used which modulate a number of parallel power converters (phases). In this thesis, a new modulator concept is proposed which enables the use of efficiency-improving techniques without increasing the design complexity. The proposed modulator features an internal duty cycle redistribution without complex management overhead. With this modulator, phase shedding can be accommodated together with improved transient behaviour. An alternative concept commonly used today is an intermediate bus architecture with multiple separate point-of-load converters; each controlled by its individual digital core. Digital communication signals between the converters are required to implement advanced control features, such as phase shedding or current sharing. In this thesis, new techniques are proposed which enable the use of these advanced control features without the need for digital communication signals. Firstly, a new algorithm for phase alignment and frequency synchronization between the individual converters is detailed which uses the perturbance generated by the individual power supplies on the input voltage. Secondly, a novel current distribution principle based on smart power converters is presented. It enables the distribution of the output current over the individual power converters to optimize overall efficiency. Each converter optimizes its output current based on predefined optimal currents without requiring information about the total output current.