Analysis and Implementation of Digital Control Architectures for DC-DC Switching Converters

Power electronics for consumer applications represents a typical example of engineering tradeoff between costs, performances, system complexity, efficiency and robustness. In this context, control of Switched Mode Power Supplies (SMPS) has been traditionally achieved through analog means with dedicated integrated circuits (ICs). However, as power systems are becoming increasingly complex and often composed of smaller interacting units, the classical concept of control has gradually evolved into the more general problem of power management. Beside the basic control function, a number of additional features are often required such as communication capabilities between diffrerent power converters, smart power management for efficiency maximization in critical applications like portable equipments, a certain degree of programmability of the compensation characteristics, or even intelligent solutions for automatic tuning of the compensator to the specific power processor. Though at the time of writing analog control ICs for power converters are still dominating the market, in these last years digital control solutions have been receiving increasing attention from both the scientific and industrial communities. Digital control in power electronics is potentially able to meet the aforementioned requirements of modern power supply systems and electronic equipments due to the versatility and programmability inherent in the digital approach. On the other hand, a digital controller finds its major weakness in the achievable closed-loop dynamic performances. Analog-to-digital conversion times, computational delays and sampling-related delays strongly limit the small-signal closed-loop bandwidth of a digitally controlled SMPS; quantization effects bring other severe constraints not known to analog solutions. Maily focusing on low-voltage, high-current applications, two topics related to digital control of DC-DC converters are discussed in this work. The multiple sampling technique is a non-conventional control approach which allows for analog-like performances to be achieved in terms of small-signal control bandwidth. The multiple sampling approach is analysed theoretically and experimentally validated, confirming its effectiveness in pushing the dynamic performances of a digitally controlled power supply. Secondly, a robust, low-complexity autotuning technique for proportional-Integral-Derivative (PID) digital compensators is proposed, investigated in detail and experimentally validated.